Georgia Tech Vertical Flight Society

Drone Competition

$500 prize to the winning team

The Team Registration Deadline is March 15

Teams must register by emailing gt.ahs.calendar@gmail.com by March 15
Teams that have not registered by this date may not participate, although team members may be added until the competition date .

Team Requirements
Teams may consist of as many currently enrolled Georgia Tech students as desired, but the prize will remain the same regardless of team size.

Drone Requirements
Any out-of-the-box or custom-built drones allowed as long as it is equal to or smaller than 350mm
(13¾”) measured diagonally from rotor shaft to rotor shaft.  First person view, manual or autonomous flight are all permitted

The Competition is April 17

Each team will pick up and deposit as many payloads as they can during the 4 allotted minutes. The payloads will be golf balls covered in the soft side (loop side) of Velcro and will be distributed throughout the arena. Apply your creativity to design the collecting and release mechanism! Teams will compete individually on the course, and the team that collects the largest number of payloads in the time provided will be declared the winning team:

QUESTIONS?

Please submit questions by March 10 to gt.ahs.calendar@gmail.com
Answers will be posted on the Georgia Tech Vertical Flight Society website: https://ahs.gatech.edu

2020 Vertical Flight Foundation (VFF) Scholarship?

The Atlanta Chapter of the Vertical Flight Society (formerly the American Helicopter Society) is hosting an information session to explain the process and give tips to prospective applicants. Students from the AE School have done very well in this annual opportunity, probably because the local chapter does so much to help out applicants.

This is open to all students, regardless of academic major.

Women of Aeronautics & Astronautics (WoAA)  and

Students for the Exploration & Deveopment of Space (SEDS)

invite you to a

Career Information Session

with recruiters from

Blue Origin

Bring your resumes and bring your ambition. Dress is casual but the subject is serious: career opportunities and internship opportunities at Blue Origin

Questions?

Contact Megan Kim at m33kim@gatech.edu

American Institute for Aeronautics & Astronautics (AIAA)

is proud to sponsor a

Career Info Session with Relativity

Come chat with several Ralativity engineers about internships and career opportunities..

Find out more about reume submission at: Tinyurl.com/AIAA-Relativity

Urban Air Mobility: An Opportunity for Georgia

a one-day workshop that will explore the possibility of Atlanta and all of Georgia participating in the economic opportunity of Urban Air Mobility (UAM)

RSVP now

A premise of our discussion will be that the aircraft and technologies that enable UAM offer potential not only for urban operations but also for rural areas; hence our focus will be on urban and regional air mobility. For example, rapid commuting by air may enable increased wages for rural residents and also encourage rural growth and development, as people and businesses disaggregate from urban cores to outlying areas. Attendees will include business, government, and academic stakeholders from Atlanta and neighboring rural communities in Georgia, as well as representatives from NASA and companies participating in the nascent UAM industry.

About Urban Air Mobility...

The world is now entering a new era of mobility. From electric scooters to self-driving cars, we will soon have even more choices for how to travel within cities. The same technologies that are enabling new forms of ground transportation are also enabling new types of aircraft. A new industry is emerging to address a market now being called “urban air mobility (UAM)” in which passengers and cargo are transported by short-ranged electric vertical takeoff and landing (eVTOL) aircraft at an affordable price point. As cities become more congested, UAM offers the potential for significant time savings compared to driving by overflying traffic. As one of many mobility options, UAM also will enable new levels of flexibility in multi-modal trips involving cars and transit.  A recent market study by Booz Allen Hamilton found that if experts can overcome infrastructure and air traffic management constraints, the potential U.S. market for UAM exceeds $500 billion, carrying 16 million passengers daily, and served by 850,000 aircraft.  In comparison, the U.S. airline market is approximately $200 billion. 

Unlike past forms of aviation, UAM will be deeply interwoven into the fabric of cities and regions. Aircraft must be low noise to avoid annoyance, vertiports must be located in a way consistent with land use regulations, and issues such as equity of access must be addressed.  As a consumer and producer of data, UAM will be a part of the landscape of future smart cities.

Workshop Organizers: Georgia Institute of Technology, Georgia Centers for Innovation, Georgia Chamber of Commerce, Metro Atlanta Chamber

Aerospace, Astronauts & Leadership

is proud to present

“Why Do We Look Up at the Heavens?”

a talk by

Br. Guy Consolmagno

Director of the Vatican Observatory, Rome

About this talk
Why did we go to the Moon? Why does the Vatican support an astronomical observatory? These questions mask a deeper question: why do individuals choose to spend their lives in pursuit of pure knowledge? The motivation behind our choices, both as individuals and as a society, controls the sorts of science that gets done. It determines the kinds of answers that are found to be satisfying. And ultimately, it affects the way in which we think of ourselves.

About the speaker
Guy Consolmagno, SJ is a brother in the Roman Catholic Society of Jesus (the Jesuits), working since 1993 as an astronomer and meteorite specialist at the Specola Vaticana (Vatican Observatory), located in the Papal summer gardens outside Rome. Since 2014 he has been president of the Vatican Observatory Foundation, which supports the work of the Observatory and especially its 1.8 meter Vatican Advanced Technology Telescope (VATT) in Arizona. In September of 2015 he was named Director of the Vatican Observatory by Pope Francis.

Consolmagno's research explores connections between meteorites, asteroids, and the evolution of small solar system bodies. Along with more than 200 scientific publications, he is the author of a number of popular books, including: Turn Left at Orion (with Dan Davis), and most recently, Would You Baptize an Extraterrestrial? (with Fr. Paul Mueller, S.J.). He also has hosted science programs for BBC Radio 4, has been interviewed in numerous documentary films, and writes a monthly science column for the British Catholic magazine, The Tablet.

A native of Detroit, MI, Consolmagno earned two degrees from MIT and a doctorate in planetary sciences from the University of Arizona, was a postdoctoral research fellow at Harvard and MIT, served in the US Peace Corps (Kenya), and taught university physics at Lafayette College before entering the Jesuits in 1989. He has served as chair of the American Astronomical Society’s Division for Planetary Sciences (AAS/DPS) and on the planetary surfaces nomenclature committee of the International Astronomical Union (IAU). Asteroid “4597 Consolmagno” was named in recognition of his work. In 2014 he won the Carl Sagan Med al for public outreach by the AAS/DPS.

invites you to hear

Visualizing Space Flight

a talk by

Jacob Payne
AE Undergraduate & SEDS member

"FlaRe Approach for Premixed and Partially-Premixed Combustion"

Monday, January 22, 2018 @ 11:00 a.m
Montgomery Knight Rm 317

About the talk:
Premixed and partially premixed combustion is ubiquitous in practical combustion systems such as stationary and aero gas turbines.  However, the modelling of these combustion modes in turbulent flows is challenging.  Flamelet approach which views the turbulent flame as collection of flamelets helps to build a practically useful modelling approach but one must pay attention to the physical consistencies among various physical processes involved and their modelling. This important requirement is commonly overlooked in past studies leading one to conclude that the flamelet approach is inadequate and sophisticated approaches may be required.  The FlaRe approach (Flamelets Revised for physical consistencies) devotes attention to these details while keeping the modelling framework simple enough (low computational cost) for practical applications with complex geometries.  This talk will discuss this approach highlighting how the physical & mathematical consistencies are maintained among the sub-models along with few examples for its application. 

About the speaker:
N. Swaminathan is Professor of Mechanical Engineering at Cambridge University and has held and also currently holding many distinguished visiting professorship across the globe.  His research aims to shed lights on fundamental aspects and practical modelling of various facets of turbulence and combustion using mainly numerical approach leading to simple mathematical models for industry use. He has worked in industry (GE R&D Centre & Tata Consulting Services) and acted as a consultant to Pratt & Whitney, Rolls-Royce Marine Engines, Bergen Engines, Siemens, MHI and Ricardo Plc.   His research is supported by EPSRC, industries such as Rolls-Royce, Siemens and Mitshubishi, several overseas (outside UK) research organisations, and European Commission. He is on the editorial board of few journals in the area of energy, combustion and fluids, member of the advisory board of GCOE in TokyoTech (2008-2013) and, member of the advisory board and an international co-operative member for ACEEES (Academy for Co-creative Education of Environment and Energy Science) programme in TokyoTech (2013-2017).  He and his co-authors were awarded the prestigious Sugden Prize (by Combustion Institute British Section) for their paper on combustion noise in 2011.  He has published nearly 200 papers in the areas of turbulence and combustion, and co-edited a book with Professor Bray on Turbulent Premixed Flames published by CUP in 2011.

Students for the
Exploration  &
Development of
Space (SEDS)

is holding an organizational meeting on

Tuesday, January 23 @ 7 p.m. in Clough 323

SEDS is dedicated to building a community of students who are committed to the future of space exploration from every possible angle, from engineering to entrepreneurship --- and beyond!

If that describes your interest, join us at this organizational meeting, Jan. 23.

Information Session

to field interested students to work on either the

Ranging And Nannosatellite Guidance Experiment (RANGE)

or the

Tethering And Ranging mission of the Georgia Institute of Technology (TARGIT)

satellite projects that are under development with aerospace engineering professor

Dr. Brian Gunter

What you should know

• All majors and class ranks are welcome, especially those interested in electronics, optics/lasers, and programming;
• Bring your resume to this session;
• Students should plan to devote at least 8 hrs/week or 2 credit-hours, to the lab;
• Only U.S. persons (US citizens or permanent residents) may participate;
• For more information, contact Prof. Gunter at brian.gunter@ae.gatech.edu or visit bgunter.gatech.edu

About TARGIT & RANGE

A limited number of student research positions are available for two upcoming small-satellite missions. 

• The Ranging And Nanosatellite Guidance Experiment (RANGE) is a two-satellite formation that will complete assembly in Spring 2018 and will launch and commence operations in Summer 2018.
• The Tethering And Ranging mission of the Georgia Institute of Technology (TARGIT) is a NASA-sponsored CubeSat project that will deploy and conduct 3D lidar imaging on an inflatable target while in orbit, with an expected launch date in 2019.

“Breakthrough Energy Ventures (BEV)”

featuring

David Danielson

former assistant secretary of the U.S. Department of Energy’s Office of Energy Efficiency & Renewable Energy (EERE)

Bill Gates recently established a venture capital fund to foster transformational low carbon technologies. In addition to clean energy, the fund has interest in a variety of "Gigaton" technologies and approaches for reducing climate change effects (e.g., land use, agriculture, eliminating beef).

David Danielson, former assistant secretary of the U.S. Department of Energy’s Office of Energy Efficiency & Renewable Energy (EERE), has been named the managing director for science at Breakthrough Energy Ventures (BEV). Georgia Tech’s Strategic Energy Institute (SEI) will host a one-hour forum on Friday, December 15 at 12:30pm, featuring David Danielson, who will provide an overview of BEV and speak about its vision to invest in next generation technologies that provide reliable, affordable, zero-carbon energy, food, and products to the world. This group forum will be open to the Georgia Tech campus and local innovation organizations.

Seating is still available, and if you have interest in attending, please RSVP to

SEI@gatech.edu

Cheong Chan

(Advisor: Prof. Mitchell L.R. Walker)

“Experimental Investigation Fast Plasma Production for the VAIPER Antenna”

Tuesday December 5, 2017 @ 9:30 a.m.
Montgomery Knight Building, Room 317

Abstract:
Very low frequency (VLF) transmission with a range from 3 to 30 kHz is used for communications and navigation due to its ability to penetrate deeply into conductors like salt water (large skin depth) and its ability to diffract around obstacles like mountains. These features are enabled by its long wavelengths (10 to 100 km). However, traditional antennas that radiate efficiently at these long wavelengths require physical lengths of 3 to 50 km. Due to physical limitations of antenna construction, VLF radiation is usually generated with electrically short antennas (100s of meters) that thermally dissipate a significant fraction of the input power. This inefficiency is due to the signal reflecting at the end of the electrically-short antenna and interfering with the subsequent part of the signal.

This work, Very-short Antennas via Ionized Plasmas for Efficient Radiation (VAIPER), proposes a technique to combine a fast-switching plasma and a special signal modulation scheme to circumvent the limitation of traditional antennas. The idea is to use the plasma as a conducting medium for the antenna. By selectively turning on and off the plasma, we can suppress the reflected signal from an electrically short antenna. In theory, this method will greatly improve the transmission efficiency of VLF antenna of a given length. The upper frequency limit of this technique is the speed at which the plasma can be modulated. The challenge is to find a method to produce a plasma compatible with the VAIPER scheme that is also scalable to larger sizes.

For this Master’s thesis, I conducted a preliminary experimental study of fast plasma ignition times and characterization under varying conditions. This project is a collaboration between the Prof Mitchell Walker’s High Power Electric Propulsion Lab (HPEPL) in Aerospace Engineering and Prof Morris Cohen’s group in Electrical and Computer Engineering at the Georgia Institute of Technology.

Committee:
Prof. Mitchell L. R. Walker, School of Aerospace Engineering
Prof. Wenting Sun, School of Aerospace Engineering
Prof Morris Cohen, School of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign

Monday, November 20 @ 10 a.m.
Montgomery Knight, Room 317

Abstract:
Robust and reliable GPS-based navigation is critical and challenging for a variety of applications, such as airplanes, unmanned aerial vehicles (UAVs), and autonomous driving cars. GPS may suffer from signal blockage due to building and terrain masking and multipath issues. Moreover, GPS signals are vulnerable against attacks, such as jamming or spoofing. These attacks either disable GPS positioning, or more deliberately mislead with wrong positioning.

We first present our recent work on robust GPS-based navigation. We will focus on two projects: 1) multi-receiver direct position estimation, flight tested on a Beech C-12 aircraft; 2) tight GPS/LiDAR/IMU sensor fusion on the raw signal level, validated using a quadcopter designed and built by our lab. We have demonstrated improved navigation accuracy, reliability and resilience to attacks.

Grace X. Gao is an assistant professor in the Aerospace Engineering Department at University of Illinois at Urbana-Champaign. She obtained her Ph.D. degree from the GPS Laboratory at Stanford University in 2008. Before joining Illinois at Urbana-Champaign as an assistant professor in 2012, Prof. Gao was a research associate at Stanford University.

Prof. Gao has won a number of awards, including the Institute of Navigation (ION) Early Achievement Award and RTCA William E. Jackson Award. She was named one of 50 GNSS Leaders to Watch by the GPS World Magazine. She has won Best Paper/Presentation of the Session Awards 12 times at ION conferences. She received Dean's Award for Excellence in Research from College of Engineering, University of Illinois at Urbana-Champaign in 2017.

For her teaching, Prof. Gao has been on the List of Teachers Ranked as Excellent by Their Students at University of Illinois multiple times. She won the College of Engineering Everitt Award for Teaching Excellence at University of Illinois at Urbana-Champaign. She was chosen as American Institute of Aeronautics and Astronautics (AIAA) Illinois Chapter’s Teacher of the Year in 2016. She also received the Engineering Council Award for Excellence in Advising from University of Illinois at Urbana-Champaign in 2017.

Takuma Nakamura

(Advisor:  Professor Eric N. Johnson)

“Multiple-Hypothesis Vision-Based Landing Autonomy”

Wednesday, November 15, 2017 @ 1:45 p.m.
College of Computing (CoC) Room 053

Abstract: 
Unmanned Aerial Vehicles (UAVs) need humans in the mission loop for many tasks, and landing is one of the tasks that typically involve a human pilot. This is because of the complexity of a maneuver itself and flight-critical factors such as recognition of a landing zone, collision avoidance, assessment of landing sites, and decision to abort the maneuver. Another critical aspect to be considered is a reliance of UAVs on GPS systems. A GPS system is not a reliable solution for landing in some scenarios (e.g. delivering a package in an urban city, and a surveillance UAV repatriating a home ship with the jammed signals), and a landing solely based on a GPS extremely decreases the UAV operation envelope. Vision is promising to achieve fully autonomous landing because it’s a rich-sensing, light, and affordable device that functions without any external resource.

Although vision is a powerful tool for autonomous landing, the use of vision for state estimation requires extensive consideration. First of all, vision-based landing faces a problem of occlusion. The target detected at a high altitude would be lost at certain altitudes while a vehicle descends; however, a small visual target cannot be recognized at high altitude. Second, the errors of the measurements are highly nonlinear and non-Gaussian due to the discrete pixel space, conversion from the pixel to physical units, the complex camera model, and complexity of detection algorithms. The vision sensor produces the unfixed number of the measurement with each image, and the measurements may include false positives. Plus, the estimation system is excessively tasked in a realistic condition. The landing site would be moving, tilted, or close to an obstacle. The available landing location may not be limited to one. In addition to assessing these statuses, understanding the confidence of the estimations is also the tasks of the vision, and the decisions to initiate, continue, and abort the mission are made based on the estimated states and confidence. The system that handles those issues and consistently produces the navigation solution while a vehicle lands eliminates one of the limitations of the autonomous UAV operation.

This proposal presents initial work in the development of a state estimation system for UAV landing. Two types of the vision algorithms are developed to allow the system to observe a landing site at various altitudes. One uses a nested visual fiducial architecture, and the other uses a sliding window approach with a partial target. The first algorithm assumes the case where an arbitrary visual marker can be utilized. The second algorithm has a greater flexibility and can be used for any known target. The extended Kalman particle filter (PF-EKF) fuses these visual measurements with other on-board sensors such as an inertial measurement unit (IMU), a GPS, a magnetometer, and a barometer to estimate the states of a vehicle and a landing location in a paradigm known as simultaneous localization and mapping (SLAM). The PF-EKF not only deal well with a highly nonlinear and non-Gaussian distribution of the measurement errors of vision but also hypothesizes and evaluates different scenarios such as multiple targets being in the line of sight. The preliminary results of a numerical simulation and an image-in-the-loop simulation are provided.

The focus of this work is to improve accuracy and consistency of the assessment of the vehicle and the landing location while a UAV is attempting a landing. Additional validation of the proposed system with real flight test data is planned. Also, the suggested algorithm to detect an occluded target will be tested with other detection frameworks.

Committee Members:
Professor Eric N. Johnson, School of Aerospace Engineering (Advisor)
Professor Eric Feron, School of Aerospace Engineering
Professor James Hays, School of Computer Science
Professor Patricio Antonio Vela, School of Electrical Engineering

Yongeun Yoon

(Advisor:  Professor Eric N. Johnson)

“High Gain Control for Linear Systems with Unknown Higher Order Dynamics”

9:00 AM, Tuesday, November 21, 2017
Montgomery Knight Building Room 325

Abstract: 
High gain is desirable for many control systems that need to achieve both stability and a specific degree of performance. However, because higher-order dynamics (HOD) in the control systems in real world cause the undesirable limit cycle oscillation (LCO) or divergence, the applicable magnitude of gain is practically limited. This thesis proposes a new method of attaining maximum possible gain through the analysis and manipulation of LCO.

The existence of HODs within the control systems makes it difficult to analyze the system in the framework of the linear systems theory, which is not appropriate for the analysis of LCO either. Indeed, the HODs can be modeled as corresponding nonlinear analytic functions, enabling the LCO phenomena to be analyzed by the nonlinear systems theory specialized in the time periodic systems. This theory provides insights on the period and stability of the LCO inherent in the linear systems with HODs. Then we design linear compensators to adjust the LCO frequency that results in the reduction of the LCO amplitude to an acceptable level. As a result, we do not have to reduce the gain even in the presence of the LCO. If we do need to remove the LCO, we adjust the gain to an upper limit that does not cause the LCO. A hovering multi-rotor with complex motor/thrust dynamics is a good example to demonstrate the proposed idea. When the nonlinear flight dynamics of a multi-rotor is linearized near the hovering equilibrium, the system is equivalent to a low-order linear system with multiple HODs. A simple flight test can demonstrate the effectiveness of the linear compensator that modifies the LCO frequency and the critical gain that prevents from the generation of LCO.

Committee Members:
Professor   Eric N. Johnson, School of Aerospace Engineering (Advisor)
Professor   Eric M. Feron, School of Aerospace Engineering
Professor   J. V. R. Prasad, School of Aerospace Engineering
Professor   Magnus B. Egerstedt, School of Electrical and Computer Engineering
Professor   Federico Bonetto, School of Mathematics

A talk by

Dr. Paul Bogdan

Assistant Professor
Ming Hsieh Department of Electrical Engineering
University of Southern California

About the Talk
Cyber-physical systems (CPS) constitute a new generation of networked embedded systems that interweave computation, communication, and control to facilitate our interaction with the physical world. Consequently, the modeling, analysis and optimization of CPS architectures cannot be done in isolation. In this talk, we will draw inspiration from complex biological systems to define new theoretical foundations and master the spatio-temporal complexity introduced by interactive sensing, computation, communication, and control.

From microbial communities and human physiology to social and biological/neural networks, complex interdependent systems display multi-scale spatio-temporal patterns that are frequently classified as non-linear, non-Gaussian, and/or fractal structures. Drawing on observed causality of biological systems, we describe a new mathematical strategy for constructing compact yet accurate models that can capture the non-linear, non-Gaussian, and/or fractal structure through a minimum number of parameters while preserving a high degree of modeling fidelity and prediction accuracy. The benefits of this mathematical modeling are tested in the context of a CPS approach to brain-machine interface for decoding human intention and describing muscle dynamics through a set of fractional order differential equations.

Aiming at understanding and harnessing the complexity of biological systems, we develop a statistical physics inspired framework for analyzing complex collective systems. More precisely, we describe the dynamics of a collective group of agents moving and interacting in a three-dimensional space through a free-energy landscape. Based on the energy landscape, we quantify missing information, emergence, self-organization, and complexity for a collective motion. Lastly, we exploit this energy model to describe and analyze the drug-drug interaction networks. Using a complex network science approach, we uncover functional drug categories along with the intricate relationships between them. Out of the 1141 drugs from the DrugBank 4.1 database, 85% of our analytical predictions are confirmed against current state of knowledge. This analysis can be used to decode unaccounted interactions and missing pharmacological properties that can lead to drug repositioning. Motivated by the intricate geometry of complex networks, I will conclude by summarizing our work on quantifying the multi-fractal properties of brain networks and fractality implications on solving the community detection problem.

About the speaker
Paul Bogdan is an assistant professor in the Ming Hsieh Department of Electrical Engineering at University of Southern California. He received his Ph.D. degree in Electrical & Computer Engineering at Carnegie Mellon University. His work has been recognized with a number of honors and distinctions, including the 2017 Defense Advanced Research Projects Agency (DARPA) Young Faculty Award, 2017 Okawa Foundation Award, 2015 National Science Foundation CAREER Award, 2012 A.G. Jordan Award from the Electrical and Computer Engineering Department, Carnegie Mellon University for outstanding Ph.D. thesis and service, the 2012 Best Paper Award from the Networks-on-Chip Symposium (NOCS), the 2012 D.O. Pederson Best Paper Award from IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, the 2012 Best Paper Award from the International Conference on Hardware/Software Codesign and System Synthesis (CODES+ISSS), the 2013 Best Paper Award from the 18th Asia and South Pacific Design Automation Conference, and the 2009 Roberto Rocca Ph.D. Fellowship. His research interests include the theoretical foundations of cyber-physical systems, control of complex time varying interdependent networks, modeling and analysis of biological systems and swarms, new control algorithms for dynamical systems exhibiting multi-fractal characteristics, modeling biological/molecular communication, development of fractal mean field games to model and analyze biological, social and technological system-of-systems, performance analysis and design methodologies for manycore systems.

Shiang-Ting Yeh

(Advisor: Professor Vigor Yang)

“Data-Driven Feature Extraction and System Identification of Rocket Injector Dynamics”

Thursday, November 16^th, 2:00-3:00 pm
Montgomery Knight, Room 317

Abstract:
For high-performance power generation and propulsion systems, such as those of airbreathing and rocket engines, physical experiments are expensive due to the harsh requirements of operating conditions. In addition, it is difficult to gain insight into the underlying mechanisms of the physiochemical processes involved because of the typical reliance upon optical diagnostics for experimental measurements. High-fidelity simulations can be employed to capture more salient features of the flow and combustion dynamics in engines. These computations, however, are often too expensive and time-consuming for design and development purposes.

To enable usage of modeling/simulation in the design workflow, the present study proposes a data-driven framework for modeling and analysis to facilitate decision making for combustor designs. Its core is a surrogate model employing a machine-learning technique called kriging, which is combined with data-driven basis functions to extract and model the underlying coherent structures from high-fidelity simulation results. This emulation framework encompasses key design parameter sensitivity analysis, physics-guided classification of design parameter sets, and flow evolution modeling for efficient design survey. A sensitivity analysis using Sobol’ indices and a decision tree are incorporated into the framework to better inform the model. This information improves the surrogate model training process, which employs basis functions as regression functions over the design space for the kriging model. The novelty of the proposed approach is the construction of the model through Common Proper Orthogonal Decomposition, allowing for data-reduction and extraction of common coherent structures. The accuracy of prediction of mean flow features for new swirl injector designs is assessed and the dynamic flowfield is captured in the form of power spectrum densities. This data-driven framework also demonstrates the uncertainty quantification of predictions, providing a metric for model fit. The significantly reduced computation time required for evaluating new design points enables efficient survey of the design space.

To further utilize simulation results, a data analytic methodology to characterize the complex nature of turbulent combustion is used to analyze the system dynamics. Comprehensive combustion stability analysis has long been sought after, as a good understanding of the coupling process would reduce the amount of testing and level of capital required for engine development. A vital component is the quantification of the distributed combustion response. The proposed methodology leverages high-fidelity large eddy simulation (LES) in combination with machine-learning techniques to quantify the spatial combustion response. This response is intended to serve as an acoustic source term in the generalized wave equation, which can be used to analyze the stability of complex propulsion systems. Treating the extracted coherent structures as time series signals, the combustion response can be deduced through autoregressive model selection, accounting for data sparsity, multicollinearity, and noise.  The results show that acoustic-vortical dynamics is the dominant mechanism determining flame stabilization. This data-driven methodology quantifies the gain and phase relationship between flowfield variables and unsteady heat release. The methodology not only accounts for the distributed combustion response through incorporation of proper orthogonal decomposition (POD) analysis, but also uses the data to identify relevant time scales, replacing the need for forcing and focusing on intrinsic dynamics.

Committee:
Dr. Vigor Yang
Dr. Joseph Oefelein
Dr. Lakshmi Sankar
Dr. C.F. Jeff Wu (ISyE)

University of Illinois at Urbana-Champaign

Thursday, November 16 @ 3:30 p.m.
Guggenheim 442

Abstract:
While basic orbit determination is a well understood problem, determining a full solution to the pose estimation and surface feature map of a target resident space object poses a greater challenge. Most orbit determination approaches suppose the use of active radar, frequently from the ground, but when the system making the determination is itself a spacecraft in a nearby orbit, traditional approaches are insufficient. This problem is further complicated when the chase spacecraft performing the determination is only equipped with a passive, monocular sensor such as a camera, rather than active radar or binocular vision. Initially a Rao-Blackwellized Particle Filter was implemented, however this classic approach was not able to converge within the desired timeframe and system observability. A new algorithm was developed which achieves the desired solution by using nonlinear programming applied to bundle adjustments over time, while absorbing core concepts from the simultaneous location and mapping field. An extended Kalman filter is used at long distance to determine the location of the target’s center-of-mass during approach phases while at long ranges. This algorithm is ultimately capable of on-board pose and orbit determination of its target, and has applications for automated spacecraft servicing, and proximity operations at near Earth asteroids.

Achyut Panchal

(Advisor: Prof. Suresh Menon)

“Modeling & Simulation of Dense-to-Dilute Multiphase Reacting Flows”

Thursday, 9 November, 2017 @ 2:30 p.m.
Montgomery Knight Building, Room 317

Abstract:
Predicting performance of liquid fueled combustors using large-eddy simulations (LES) require accurate modeling of the spray characteristics of the fuel injector, but most existing models are often limited to the dilute regime where droplets are treated as Lagrangian point particles within a Eulerian gas phase model far from the actual injector. The near-field of the injector for these methods is often modeled using empirical breakup models (still within the EL method) that require tuning to match the experimental data, or by using decoupled interface resolved primary breakup simulations of the liquid jet from the injector which are too numerical intensive for their use in the far-field. A fully coupled approach should take advantage of both these near and far field techniques, but is currently not possible as the intermediate regimes where the finite volume fraction and finite size particle effects play an important role have not been fully addressed, and are one of the primary focus of this effort. For LES, point particles are much smaller than the grid resolution, and so, subgrid modeling is also required for their coupling with the unresolved gas phase.

In this study, the relatively unexplored moderately dense regime and its transition to dilute regime is investigated using a mathematically consistent procedure that combines a Eulerian-Eulerian (EE) dense model with a dense-to-dilute Eulerian-Lagrangian (EL) and a finite-size particle method.  Hybrid EE-EL dispersed phase method that transitions from pure EE regime in the dense phase to EL in the dilute regime is developed allowing for a finite fraction of the cell volume to be occupied by the droplets. In addition, a finite-size particle method is proposed to allow the droplets to be larger than the grid without resolving the interfacial boundary layers. Coupling of this method with the hybrid EE-EL approach is also considered using representative configurations. This hybrid method is especially needed in the near injector region where the grid is refined to resolve the gas flow but can be so small as to violate the point-particle assumption. Subgrid dispersion and vaporization modeling for unresolved gas-spray coupling in LES is combined with the EE-EL hybrid method to establish a method that can capture many of the near-injector physical processes. Verification and validation (V & V) are conducted using canonical problems involving dispersion and vaporization of single/multiple droplets in laminar/turbulent environment followed by more complex flows such as reacting spray jets.

Committee Members:
Prof. Suresh Menon (Advisor)
Prof. Joseph Oefelein
Prof. Timothy Lieuwen

“Leading the Charge on Renewable and Cleaner Energy”

a panel discussion that will include regional, national, and global perspectives

Panelists will include

• Shannon O. Pierce
  VP, External Affairs, Southern Operations, Southern Company Gas
• Stan Wise
  Chairman, Public Service Commission
• Nicole Holmes
  SVP, Sales and Contracts GE Hitachi Nuclear Energy
• Courtney Stoner
  Executive, Automation & Operations Leader for Services GE Power

RSVP by Nov. 6

The American Association of Blacks in Energy (AABE)  and the Women's Energy Network (WEN) are coming together for another powerful event to promote renewable and cleaner energy featuring the Strategic Energy Institute at GA Tech. Lunch will be served to those who RSVP by Nov. 6

Principio Tudisco

(Advisor: Prof. Suresh Menon)

“A Numerical Study of Super-Critical Reacting Flows with Vapor-Liquid Equilibrium (VLE)”

November 13, 2017 @ 4 p.m.
Montgomery Knight Building, Room 317

Abstract:
Increase of the operating pressure in combustion systems can achieve better combustion efficiency and propulsive performances. This characteristic is shared among different types of applications, ranging from diesel engines to gas turbines to liquid rocket engines (LRE). Particularly, in LRE, propellants are stored in their liquid state at high pressures but at temperatures lower than their critical values resulting in thermodynamic conditions that range from the “super-critical” regime (injection/mixing), to the “ideal gas” regime (complete combustion/nozzle expansion). Strong differences have been observed between jets at sub- and super-critical pressures, indicating that deviations in thermo-physical properties from their ideal state are extremely important and need to be accurately modeled. However, while thermodynamic models for single species are well established, correct representation of multi-component mixtures is still not well understood. This becomes an important requirement for high-fidelity simulations that aim to predict LRE conditions since early phase of propellants injection and mixing in the combustion chamber is critical for performance assessment.

In this work, the challenges associated with the thermodynamic modeling of multi-component mixtures at super-critical conditions are addressed in the context of high-fidelity simulations. It is shown that the single-fluid approach that uses a single equation of state (EoS) to model the thermodynamic properties may fail in multi-component fluids because an additional phase information is missing. This information is included by using the Vapor-Liquid Equilibrium (VLE) concept and it is shown that consistency with thermodynamic properties is obtained for a range of multi-component mixtures. The ability of VLE combined with real-gas EoS to handle mixed regimes will be assessed using large-eddy simulations (LES) of canonical reacting shear layers as well as LRE type high-pressure reacting configurations (e.g., shear coaxial injectors).

Committee Members:
Prof. Suresh Menon (Advisor)
Prof. Vigor Yang (AE)
Prof. Jerry Seitzman (AE)
Prof. Joseph Oefelein (AE)
Prof. William Sirignano (Dept. of Mech. and Aerospace Eng., UCI)

Abhishek Mishra

(Advisor: Dr. J.V.R. Prasad)

“Modelling of Multistage Axial-Centrifugal Compressor Configuration using Stream Tube Approach”

Wednesday, November 15, 2017 @ 3 p.m.
Montgomery Knight 325

Abstract:
Quasi-1D flow models based upon mean-line analysis are quite popular for design and performance evaluation of multistage axial and centrifugal compressors. However, they are not so readily used for analyzing the dynamic behavior of the compressor. In this work, an unsteady 1D axial-centrifugal compressor model has been proposed, where the stage elements i.e. rotors and stators are modelled as diffusing stream tube components. The analysis being independent of any stage aerodynamic force and work terms, accurately predicts the performance of a four-stage axial industrial compressor by the incorporation of various loss mechanisms compounding to total stagnation pressure losses within stage elements. The flow communicates dynamically between two connected stream tubes through a boundary element called Compact Interface Element (CIE) which has been implemented by making use of the characteristic-based approach. CIE achieves reference frame transformation between the successive elements and also incorporates losses due to sudden flow turning occurring in a compact zone. These inlet turning and mixing loss models constitute an important feature of this work and have been implemented by the inclusion of a single model parameter. This parameter called mixing loss factor, is then tuned for nominal shaft speed and is subsequently used to predict the compressor performance for different speeds ranging from 50% to 105%. The surge line has also been accurately predicted by the suitable choice of critical incidence angle for stage elements.

Another aspect of compressor operation is the observance of aerodynamic instabilities as the compressor is throttled to stall. Several simulations performed through the numerical solution of unsteady flow equations indicate the existence of modal perturbations prior to the stall. However, at very high compressor speeds such modal perturbations are generally not present and the compressor plunges into surge through the mechanism of spike or abrupt stall. For large plenum attached at the compressor end, the stability criterion at high speed coincides with the peak of characteristic curve.

Committee Members:
Dr. J.V.R. Prasad (Advisor)
Dr. Yedidia Neumeier
Dr. Lakshmi Sankar (AE)
Dr. Jechiel Jagoda (AE)
Dr. Rakesh Srivastava (Honeywell)

Dr. Chantal Cappelletti

Assistant Professor, Laboratory of Aerospace Science and Innovation
University de Brasilia

"Nanosatellite Mission for Cancer Research"

Monday, November 6 @ 11 a.m.
Montgomery Knight Room 317

Abstract:
The presence of microgravity conditions and ionizing radiation makes space a unique environment for biomedical research. Different studies have shown a strong correlation between exposure to space environment and increased risks for human health. This is the case, for example, of cancer and osteoporosis.  The human exploration of space is of course affected by such factors.

On the other hand, the exposure to space environment can have important effects on organisms already affected by diseases like cancers. Nevertheless, these mechanisms are not well known nor completely understood nowadays. Space environment could promote, hinder or have no effect on these cells but in any case, each result obtained by biomedical experiments in space would be of fundamental importance to increase the knowledge about the proliferation mechanisms of cancers.

Traditionally, biomedicine studies in space are performed on board large platforms such as the International Space Station. Nowadays, the advancements in technology allow to use smaller and cheaper solutions such as nanosatellite.

This seminar will present a nanosatellite mission for investigating Glioblastoma cancer cells in space. The design of the spacecraft, of all its subsystems and of the overall mission will be described. The resulting configuration will be optimized in terms of the scientific goals of the mission, taking advantage from the results of two precursor missions performed in 2011 on board the last two flights of the Space Shuttle.

Chantal Cappelletti received a BSc (2005) in Aerospace Engineering from Sapienza Università di Roma, a MSc (2008) in Astronautical Engineering and a PhD (2012) in Aerospace Engineering from the Scuola di Ingegneria Aerospaziale della Sapienza Università di Roma. She is currently an Assistant Professor at University of Brasilia, where she is associated with the Laboratory of Aerospace Science and Innovation (LAICA). She is the cofounder of the Italian company GAUSS Srl. She has led 6 satellite projects in Italy (UNISAT program and others) and in Brazil (SERPENS, TuPOD). She was PI of 2 missions concerning cancer cells behaviour in space. She was an ASI delegate at Inter-Agency Space Debris Coordination Committee (IADC). Her main research interests are related with Small Satellites, Biomedical Research in space, Space Debris, Astrodynamics and Attitude Control. She is member of the International Academy of Astronautics.

Dan Fries

(Advisor: Dr. Suresh Menon)

“Experimental Multi-Scale Analysis of Supersonic Jets in Crossflow: Mixing and Combustion”

Friday, November 10, 2017 @ 2 p.m.
Montgomery Knight, Room 317

Abstract:
To achieve novel insights into passive and chemically active turbulent mixing under conditions relevant to the development of hypersonic propulsion systems, a multi-scale (nested) diagnostic setup is proposed. A jet in supersonic crossflow is selected as the experimental setup due to it providing a complex flowfield with phenomena of current fundamental research interest. Its near field is identified as the most interesting region to characterize the interaction between small and large scales. The momentum flux ratio and molecular weight are initially varied in a single jet configuration to understand the influence of gases heavier than air/nitrogen. Subsequently, spanwise distributed jet arrays reveal the influence of jet-jet interaction on turbulent mixing in a compressible flowfield. A laser ignition system provides highly localized regions of hot plasma to initiate chemical reactions at selected locations.

Multi-scale diagnostics reveal the effects of differential filtering on mixing, the identification of characteristic scales, coherent structures, dissipation and turbulent viscosity. Turbulent kinetic energy transport from the small to the large scales against the classical view of the Kolmogorov cascade is investigated experimentally. The effect of heat release on turbulent mixing processes and the interaction between chemical reactions and compressibility features (shock and expansion waves) is assessed. Additionally, the ignition and flameholding characteristics are analyzed. In the non-reacting cases, primarily PIV and a diagnostic suitable to asses qualitative mixing (acetone PLIF or nano-particle based planar laser scattering) are used, while in the reacting cases OH-PLIF and PIV are used. Schlieren imaging is used in initial assessments and to reveal density variations and heat release in the flowfield.

Committee:
Dr. Suresh Menon (advisor)
Dr. Devesh Ranjan
Dr. Jerry M. Seitzman

Dr. Riccardo Bevilacqua

Associate Professor, Mechanical and Aerospace Engineering Department
University of Florida

“Let Me Drag You into My World: The Beauties of Spacecraft in Atmospheric Resistance”

Wednesday, November 1 @ 3 p.m.
Montgomery Knight Room 317

Abstract:

Imagine a world where every ground vehicle depleting its fuel or malfunctioning is abandoned on the road. In the space domain, this type of scenario has been unfolding since the Sputnik, particularly in Earth orbits ranging from upper LEO to GEO (low Earth to geostationary/geosynchronous orbits).

I will start the talk presenting one of the research thrusts of the Advanced Autonomous Multiple Spacecraft (ADAMUS) laboratory: propellant-less control of spacecraft formation flying via atmospheric differential drag (DD) forces. The exploitation of residual drag forces in LEO for control purposes has been one of the focuses of the ADAMUS group for several years. This has led to innovative control strategies, ways to forecast the behavior of the LEO atmosphere, new ideas for space environment modeling, and novel spacecraft designs.

After presenting the technical details of DD, I will switch gears and tackle the problem of space debris. In fact, the tools and skillsets developed during these years attracted the attention of NASA, and I will illustrate how ADAMUS and NASA are now shaping the future of propellant-less fine control of spacecraft removal from LEO and above.

I will conclude describing plans for the future, including the desire to create new standards for satellite designers and operators, for a responsible use of space.

Dr. Riccardo Bevilacqua is an Associate Professor of the Mechanical and Aerospace Engineering Department, at the University of Florida. He previously served as Assistant Professor at the Rensselaer Polytechnic Institute. He holds a M.Sc. in Aerospace Engineering (2002), and a Ph.D. in Applied Mathematics (2007), both from the University of Rome, "Sapienza", Italy. Dr. Bevilacqua is the recipient of two Young Investigator Awards, from the Air Force Office of Scientific Research (2012) and the Office of Naval Research (2013), of the 2014 Dave Ward Memorial Lecture Award from the Aerospace Controls and Guidance Systems Committee, and of two Air Force Summer Fellowships (2012 and 2015). His research interests focus on spacecraft formation flight and space robotics and he has authored and co-authored more than 80 journal and conference publications on the topic. Dr. Bevilacqua is a corresponding member of the IAA and an associate fellow of the AIAA.

is proud to present

Prof. Joseph Oefelein

who will give a talk entitled

“Multiphysics Simulation of Propulsion and Power Systems:  Challenges & Opportunities”

About the lecture

Simulation and analysis of flow and combustion processes in propulsion and power systems presents many new and interesting challenges. A multitude of strongly coupled fluid dynamic, thermodynamic, transport, chemical, multiphase, and heat transfer processes are intrinsically coupled and must be considered simultaneously in complex domains associated with devices such as gas-turbine and rocket engines. The problem is compounded by the broad range of time and length scales over which interactions occur due to turbulence and differences in chemical reaction rates. The nonlinear nature of the system significantly limits the number of simplifying assumptions that can be made. Conversely, some form of modeling is always required and significant sets of assumptions must be made to derive multiscale closures that are both accurate and affordable. This combination of challenges significantly complicates the process of scientific discovery and design. It also presents many new opportunities that intersect with the use and growing potential of high-performance massively-parallel computing and the related development of codes that effectively scale on state-of-the-art computer architectures. This presentation will outline the challenges and how they translate to new research opportunities for development of advanced simulation capabilities required for development of next generation propulsion and power systems.

Zhangxian Yuan

(Advisor: Prof. George A. Kardomateas)

“Geometric Nonlinearity Effects on the Behavior Sandwich Structures”

Tuesday, October 31 @ 10 a.m.
Weber Space Science and Technology Building, Room 200

Abstract:
The Extended High-order Sandwich Panel Theory (EHSAPT) accounts for the axial rigidity, the transverse compressibility and the shear effect of the core. Thus, it is suitable for sandwich composites made of a wide range of core materials, including soft cores and stiff cores. However, its analytical solution is only available to particular cases, i.e., sandwich panels with simply supported edges and subjected to sine distributed transverse loads. To obtain its solutions under general boundary conditions and loadings, a special finite element is first proposed to implement the EHSAPT with the finite element method. The proposed method extends the application of the EHSAPT and can easily handle arbitrary combinations of boundary conditions and loadings.

Small deformation and infinitesimal strain were considered in the EHSAPT. In this dissertation, the EHSAPT is further developed to include geometric nonlinearities. Both faces and core are considered undergoing large deformation and moderate rotation. The weak form nonlinear governing equations of static behavior are derived from the principle of minimum total potential energy, and the equations of motion for dynamic response are derived from the Hamilton's principle. The geometric nonlinearity effects on both static behavior and dynamic response of sandwich structures are investigated.

In the literature, there are various simplifying assumptions adopted in the kinematic relations of the faces and the core when considering the geometric nonlinearities in sandwich structures. It is common that only one nonlinear term appeared in faces' kinematic relations is included and the core nonlinearities are neglected. A critical assessment of these assumptions, as well as the effects of including the other nonlinear terms in the faces and the core is made. It shows that the geometric nonlinearities of the core have significant effects on the behavior of sandwich structures.

The stability behavior is very important to sandwich structures. The compressive strength of the thin faces and the overall behavior of sandwich structure can be realized only if it is stabilized against buckling. As a compound structure, a sandwich structure has more complicated stability behavior than an ordinary beam. The compressibility of the core significantly affects the stability response and contributes to the local instability phenomenon. Therefore, despite the global buckling (Euler buckling), very common in ordinary beams and plates, the wrinkling, characterized as short wave buckling, may also occur in sandwich structures.

The stability investigation of sandwich structures is carried out based on the derived weak form nonlinear governing equations. The buckling analysis, which determines buckling mode shapes and critical buckling loads at a convenient manner, and the nonlinear post-buckling analysis, which evaluates the post-buckling response of sandwich structures, are both presented. Both wrinkling and global buckling are observed. It is shown that although the axial rigidity of the core usually is hundreds times smaller than that of the faces, which is often negligible in the static analysis, it has significant influence on the stability response.

Committee Members:
Prof. George A. Kardomateas, AE, Georgia Tech
Prof. Dewey H. Hodges, AE, Georgia Tech
Prof. Massimo Ruzzene, AE, Georgia Tech
Prof. Julian J. Rimoli, AE, Georgia Tech
Prof. Yeoshua Frostig, Technion - Israel Institute of Technology

Yong Jea Kim

(Advisor: Prof. Ben T. Zinn)

“Simulation of Full-Scale Combustion Instabilities in Small-Scale Rigs using Actively Controlled Boundary Conditions”

November 6, Monday @ 3 p.m.
Montgomery Knight Building, Room 325

Abstract:

            The onset of combustion instabilities (CIs) has hindered the development and performance of combustion systems employed in industrial, power generation and propulsion systems for many decades.   To Investigate CIs, actual “full-scale” engine tests are not practical because of the exorbitant cost of such tests, the large space required to house the full-sized engine, and the inability to equip full-scale engines with diagnostic systems that could measure, e.g., the temporal and spatial dependence of the mean and acoustic pressures, velocities, temperatures, compositions, and reaction rates.  Because of these difficulties, most studies of CIs to date were performed in “small-scale” setups that were geometrically similar to but smaller than the full-scale engines combustors.  While testing with these small-scale setups reduced the cost of testing and produced important results, the acoustic modes excited in the small-scale setups had considerably higher frequencies that did not simulate the lower frequency oscillations that are excited in the unstable full-scale engines. 

                The above discussion indicates that in order to study the driving of CIs in full-scale engines in small-scale rigs, the latter must simulate the acoustic environments, the combustion processes, and the interactions between these processes in the unstable full-scale engine.  This study developed a real time active acoustic boundary control approach to simulate the acoustic environment of the full-scale engine in the small-scale rig.  The proposed approach, for the study of the driving mechanism of longitudinal CIs, is described in the left figure below.  It describes the proposed approach for experimentally studying the processes taking place in region (I)~(II) of an unstable full-scale engine in a small-scale rig.  To attain this goal, the active control system (ACS) needs to generate an acoustic impedance at location (II) of the small-scale rig that equals to the acoustic impedance at the corresponding location in the full-scale unstable engine.  If this is accomplished, the acoustic oscillations in the region between locations (I) and (II) in the small-scale rig and the full-scale engine would be identical.

              This study has developed a real time ACS, which enables the small-scale tube rig to simulate the longitudinal acoustic oscillations in the full-scale tubes (or engine), with the one-dimensional cold flow setup.  In this setup, the speaker at the left end of the small-scale tube rig generated acoustic oscillations that simulate the driving by the combustion process, and the speaker at the right end was actively controlled to simulate the acoustic field of the full-scale system.  It was demonstrated that the developed, actively controlled, small-scale, rig can simulate travelling and standing waves oscillations that are encountered in longer full-scale tubes (or engines).  By modifying the ACS setup, the length of the “missing part” (see the left figure above), the simulations of the acoustic oscillations in various lengths’ full-scale tubes (or engines) were demonstrated in the same small-scale rig. 

                This study also developed a theoretical model that determines in real time the acoustic boundary condition (BC) that must be generated by the ACS at the boundaries of a small-scale rig that simulates transverse (tangential) CI in an annular combustor similar to those used in gas turbines and jet engines.  In this case, the small-scale rig consists of a small section of the annular combustor and the “missing part” of the full-scale engine consists of what has been “left over” after the small-scale sector-rig has been removed from the annular combustor (see the right figure above).  To determine the BCs that needed to be established at the boundaries of the actively controlled, small-scale rig, the developed model accounts for the effects of the combustion processes and flows through the reactants supply and exhaust nozzles in the “missing part” of the engine, and for the presence of a tangential mean flow in the annular combustor.  The developed model was numerically validated and used to investigate the effects of the exhaust nozzle, combustion process, and tangential mean flow component upon the characteristics of tangential CIs in an annular combustor. 

Committee Members 
Prof. Ben T. Zinn (advisor)
Prof. Jechiel Jagoda
Prof. Krishan K. Ahuja
Prof. Tim Lieuwen
Prof. Ari Glezer

The Daniel Guggenheim School of Aerospace Engineering is hosting a reception in honor of

100 Years of Aviation at Georgia Tech

Engineered Biosystems Building (EBB)
Children's Healthcare of Atlanta (CHOA) Seminar Room
950 Atlantic Drive NW

"The Georgia Tech School of Aerospace Engineering Contributions to and from the Military Services Since 1917"

a talk by

Dr. Daniel P. Schrage

Professor and Director, VLRCOE and IPLE Lab
School of Aerospace Engineering, Georgia Tech
Colonel, USAR, retired

Abstract:
The Georgia Tech School of Aerospace Engineering has roots in the Georgia Tech Military School of Aviation which was briefly established in 1917. Georgia Tech graduates, both from ROTC and regular graduations have made substantial contributions to the military services ever since. In addition, the Military Services have funded numerous education and research grants and programs to the School of AE which have helped make it the top graduate and undergraduate public aerospace school in the USA. This presentation will highlight these contributions from Georgia Tech School of AE graduates to the Military Services, as well as major programs that the Military Services have established and funded at Georgia Tech.

The original founders and the first Class of 1917 are illustrated in the figure below.

Please RSVP for this reception at dcl@gatech.edu

Ioannis Exarchos

(Advisor: Prof. Panagiotis Tsiotras)

“Stochastic Optimal Control – An Fbsde Sampling Approach”

Wednesday, November 08, 2017 @ 10 a.m.
Montgomery Knight Building, Room 317

Abstract:
Stochastic optimal control lies within the foundation of mathematical control theory ever since its inception. Its usefulness has been proven in a plethora of engineering applications, such as autonomous systems, robotics, neuroscience, and financial engineering, among others. Specifically, in robotics and autonomous systems, stochastic control has become one of the most successful approaches for planning and learning, as demonstrated by its effectiveness in many applications, such as control of ground and aerial vehicles, articulated mechanisms and manipulators, and humanoid robots.  In computational neuroscience and human motor control, stochastic optimal control theory is the primary framework used in the process of modeling the underlying computational principles of the neural control of movement. Furthermore, in financial engineering, stochastic optimal control provides the main computational and analytical framework, with widespread application in portfolio management and stock market trading.

By and large, prior work on stochastic control theory and algorithms imposes restrictive conditions such as differentiability of the dynamics and cost functions, and furthermore requires certain assumptions involving the control authority and stochasticity to be met. Thus, it may only address special classes of systems. The goal of this research is to establish a framework that goes beyond these limitations. In particular, we propose a learning stochastic control framework which capitalizes on the innate relationship between certain nonlinear PDEs and Forward and Backward SDEs (FBSDEs) demonstrated by a nonlinear version of the Feynman-Kac lemma. By means of this lemma, we are able to obtain a probabilistic representation of the solution to the nonlinear Hamilton-Jacobi-Bellman equation, expressed in form of a system of decoupled FBSDEs. This system of FBSDEs can then be simulated by employing linear regression techniques. The overall approach will allow us to learn the value function in stochastic optimal control problems with highly nonlinear dynamics.  In addition, the proposed approach exhibits the following characteristics:

• It performs stochastic control and trajectory optimization without linearization of the dynamics and quadratic approximations of the cost functions.

• Yields nonlinear feedback control policies that offer higher performance than their traditional trajectory optimization counterparts.

• Is based on sampling, scalable, and therefore directly applicable to high dimensional systems.

• Expands the class of systems currently addressed by traditional stochastic optimal control methods.

The framework we develop within this thesis addresses several classes of stochastic optimal control, such as L² , L¹ , risk sensitive control, as well as differential games. Both fixed final time and first exit settings are considered.

Committee Members:
Prof. Panagiotis Tsiotras (Advisor)
Prof. Evangelos Theodorou (AE)
Prof. Wassim Haddad (AE)
Prof. Hao-min Zhou (MATH)
Prof. Ionel Popescu (MATH)

“Reconfigurable Vertical Lift”

"Some Recent Advances in Optimal Motion Planning for Autonomous Systems "

a talk by

Dr. Panagiotis Tsiotras

Matthew Sirignano

(Advisor: Prof. Tim Lieuwen)

 “Experimental Investigation of Nitrogen Oxide Production and Mitigation in a Reacting Jet in Vitiated Crossflow”

Monday, November 6th, 10:30 – 11:15 a.m.
Student Center Room 343

Abstract:
Nitrogen oxides (NOx) are an undesirable byproduct of hydro-carbon combustion in air. In lean, premixed combustion, NOx levels are exponential functions of temperature and linear functions of residence time. Historically, lean premixed technologies have enabled local flame temperatures below the value where substantial NOx production occurs; consequently, most combustor technology development to date has focused on fuel/air mixing and other operational challenges of premixed combustion (e.g., blowoff, flashback, etc). However, improved cooling technologies and high temperature materials have enabled steadily increasing combustor exit temperatures (>1800K), to the extent that this strategy is no longer capable of low NOx levels. Axial staging of combustion has been identified as a means to combat these issues while maintaining range of operability of combustors.

This paradigm shift motivates research into the canonical problem of a reacting jet-in-crossflow (RJICF). The NOx emissions of RJICF are influenced by the degree of premixing of the fuel jets before injection and jet/crossflow mixing before combustion. In turn, jet/crossflow mixing is controlled by the hydrodynamic stability of the jet, as well as degree of flame lifting. Previous work in this field has focused primarily on the flame behavior of RJICF and has established temperature rise across the jet (ΔT) as the primary driver of NOx production, but little work has been done to establish the sensitivities of NOx production of jets at equal ΔT.

Preliminary work with rich premixed jets of low momentum flux ratio (J < 5) has been conducted. Results have established a NOx emissions benefit due to axial staging above a combustor firing temperature threshold. At constant ΔT, reduced NOx production was associated with reacting jets of lower momentum flux ratio and higher jet equivalence ratio. Significant lifting of the flame was observed for jet equivalence ratios above 3.5 with a correlated impact on NOx emissions. This relationship is, however, confounded due to the sensitivities of lift-off distance to jet parameters that are shown to directly impact the NOx production of the reacting jet.

The proposed work seeks to investigate the NOx emissions and flame stabilization characteristics of premixed methane/air jets injected into a high temperature vitiated crossflow of lean natural gas/air combustion products. The work is designed to increase the understanding of NO production sensitivity to governing RJICF parameters over a wide parameter space, to include jets with: rich and lean equivalence ratios, low J (J < 10) and high J (J > 10), and even enhanced mixing due to wall effects. In addition, the proposed work will attempt to independently control degree of flame lifting in order to generate more precise understanding of its causes and NOx impact with regards to a RJICF. This will include emissions sensitivity studies as well as detailed high speed diagnostics of the flow/flame interaction of the lifted flame. Finally, utilizing this increased understanding, a model for a characteristic equivalence ratio of combustion based on jet and crossflow parameters as well as lift-off distance will be formulated to improve prediction and mitigation of RJICF NOx production.

Emmanuel Boidot

(Advisor: Prof. Eric Feron)

“Ambush Games in Discrete and Continuous Environments”

Monday, November 6, 2017 @ 3p.m.
Technology Square Research Building (TSRB) 509

Abstract:
We consider an autonomous navigation problem, whereby a traveler aims at traversing an environment in which an adversary sets an ambush. A two-players zero- sum game is introduced, describing the initial strategy of the traveler and the ambusher based on a description of the environment and the traveler initial location and desired goal. The process is single-step in the sense that agents do not reevaluate their strategy after the traveler has started moving. Players’ strategies are computed as probabilistic path distributions, a realization of which is the path chosen by the traveler and the ambush location chosen by the ambusher.

A parallel is drawn between the discrete problem, where the traveler moves on a network, and the continuous problem, where the traveler moves in a compact subset of R2. Analytical optimal policies are derived. Assumptions from the Minimal Cut - Maximal Flow literature for continuous domains are used. The optimal value of the game is related to the maximum flow on the environment for sub-classes of games where the reward function for the ambusher is uniform. This proof is detailed in the discrete and continuous setups.

In order to relax the assumptions for the computation of the players’ optimal strategies, a sampling-based approach is proposed, inspired by recent sampling-based motion planning techniques. Given a uniform reward function for the ambusher, optimal strategies of the sampled ambush game are proven to converge to the optimal strategy of the continuous ambush game under some sampling and connectivity constraints. A linear program is introduced that allows for the computation of optimal policies. The sampling-based approach is more general in the sense that it is compatible with constrained motion primitives for the traveler and non-uniform reward functions for the ambusher.

The sampling-based game is used to create example applications for situations where no analytic solutions of the Continuous Ambush Game have been identified. This leads to more interesting games, applicable to real world robots using modern motion planning algorithms. Examples of such games are setups where the traveler’s motion satisfies Dubins’ kinematic constraints and setups where the reach of the ambusher is dependent on the speed of the traveler.

Committee Members:
Prof. Eric Feron (Advisor)
Prof. Panagiotis Tsiotras (AE)
Prof. John-Paul Clarke (AE)
Prof. Sam Coogan (ECE)
Prof. Eric Johnson (Penn State AE)

Travis Smith

(Advisor: Dr. Tim Lieuwen)

“Experimental Investigation of Transverse Acoustic Instabilities”

Monday, October 30, 2017 @ 2 p.m.
Food Processing Technology Building Auditorium
NARA

Abstract:
This work presents 5 kHz stereo PIV and OH PLIF measurements as well as OH* and CH* chemiluminescence measurements of transversely forced swirl flames. The presence of transverse forcing on this naturally unstable flow both influences the natural instabilities, as well as amplifies disturbances that may not necessarily manifest themselves during natural oscillations. By manipulating the structure of the acoustic forcing field, both axisymmetric and helical modes are preferentially excited away from the frequency of natural instability. Additionally, forced and self-excited transverse acoustic instability studies to date have strong coupling between the transverse and axial acoustic fields near the flame. This is significant, as studies suggest that it is not the transverse disturbances themselves, but rather the induced axial acoustic disturbances, that control the bulk of the heat release response.

The work first presents a method for spatially interpolating the phase locked r-z and r-theta planar velocity and flame position data, extracting the full three-dimensional structure of the helical disturbances. These helical disturbances are also decomposed into symmetric and antisymmetric disturbances about the jet core, showing the subsequent axial evolution (in magnitude and phase) of each of these underlying disturbances. Then experiments performed with essentially the same transverse acoustic wave field, but with and without axial acoustics, show that significant heat release oscillations are only excited in the former case. The results show that the axial disturbances at the nozzle exit are the dominant cause of the heat release oscillations. These observations support the theory that the key role of the transverse motions is to act as the “clock” for the instability, setting the frequency of the oscillations while having a negligible direct effect on the actual heat release fluctuations. They also show that transverse instabilities can be damped by either actively canceling the induced axial acoustics in the nozzle (rather than the much larger energy transverse combustor disturbances), or by passively tuning the nozzle impedance to drive an axial acoustic velocity node at the nozzle outlet.

Committee Members:
Dr. Tim Lieuwen              
Dr. Suresh Menon          
Dr. Jerry Seitzman
Dr. Wenting Sun              
Dr. Devesh Ranjan          

Dr. Ellen Yi Chen Mazumdar

Diagnostic Science and Engineering group
Sandia National Laboratories 

“Multi-Modality Sensing and Encoding for Advanced Diagnostic Measurements”

Friday, October 27 @ 11 a.m.
Montgomery Knight Room 317

Abstract:
Many important physical behaviors are often poorly understood because they occur in challenging environments such as within solid propellant flames or near shockwave-induced fragmentation events. To better understand these systems, new diagnostics need to be developed that quickly gather information on multiple modalities.  In particular, I am interested in how encoding mechanisms can be exploited to gather data rapidly and then decoded to elucidate multiple physical phenomena and implement advanced control.  Many mechanisms such as optical diffraction, coherent interference, and magnetic field superposition inherently contain encoding principles, which can be further enhanced with adaptive under-sampling, active feedback control and stochastic system identification algorithms.  In this talk, I describe several multi-modality diagnostic measurement methods and discuss their application to challenging environments.  These include: 1) Digital holography methods for encoding three-dimensional information on two-dimensional sensors, 2) Hyperspectral imaging and adaptive under-sampling, and 3) Remote high speed magnetic field sensing of temperature, vibration, and fluid vorticity.   The talk will conclude with an overview of my vision for how multi-modality sensing and encoding can be utilized for advancing high speed magnetic/optical diagnostics, bio-inspired perception, and miniaturized sensing for distributed state estimation and control.

Dr. Ellen Yi Chen Mazumdar is currently a postdoctoral appointee at Sandia National Laboratories in the Diagnostic Science and Engineering group.  She received her B.S. and M.S. in mechanical engineering from Massachusetts Institute of Technology (MIT).   In 2015, she received her Ph.D. in mechanical engineering from the MIT BioInstrumentation Laboratory under the guidance of Professor Ian W. Hunter.  She received first place in the 2014 MIT de Florez Graduate Design Competition for "outstanding ingenuity and creative development" of a multi-link robotic endoscope.   She was also the recipient of the National Science Foundation Graduate Research Fellowship (2008-2013) and the National Defense Science and Engineering Graduate Fellowship through the Department of Defense (2010-2013).  Her research focuses on developing novel sensors, robots, instrumentation, and mathematical techniques for understanding or controlling physics in challenging environments.

Kaivalya Bakshi

(Advisor: Prof. Evangelos Theodorou)

“PDE Based Stochastic Control: Sampling Algorithms, Optimality Principles and Stability Analysis”

Thursday 2 Nov 2017 @ 9:15 a.m.
Montgomery Knight Building Room 317

Abstract:
Continuous time nonlinear stochastic differential equations (SDEs) with control multiplicative noise are used to model biological motion and sensorimotor systems. Application of the Dynamic Programming Principle (DPP) to the stochastic control problem of such SDEs leads to a fully nonlinear parabolic Hamilton-Jacobi-Bellman (HJB) partial differential equation (PDE) problem. Prior work on solving HJB PDEs, specifically, the linearly solvable framework by Todorov et al. is fundamentally unequipped to solve this fully nonlinear PDE.

In this doctoral thesis a nonlinear Feynman Kac lemma representing the fully nonlinear PDE by a second order Forward Backward SDE (2FBSDE) model is presented. Assumptions necessary for this construction are enunciated. We propose a data efficient sampling algorithm to solve 2FBSDEs which yields the control.

If the goal is optimal control of a large ensemble of stochastic agents, the problem is inherently infinite dimensional. The control in these PDE control problems may be open loop or closed loop, in relation to the state of each agent. In the former case, control feedback for each agent is the density of the ensemble. In the latter, control feedback for each agent is the state of the agent, corresponding to the Mean Field Games (MFG) control. Practical examples of MFG control problems are for air traffic, crowds, code division multiple access control, frequency synchronization in microgrids and unmanned aerial vehicle swarms. Stability properties of multiagent feedback MFG controllers have recently garnered interest in the physics, economics and control communities. Stability of simplistic single integrator MFG control systems has been treated recently by Lions et al. and Caines et. al.

In this work, we deduce a sampling algorithm to compute the open loop PDE control of ensembles governed by a general class of SDEs with jumps. This is done by using the Infinite Dimensional Minimum Principle (IDMP) and results from statistical physics. The relationship between the IDMP and DPP is quantitatively explained by showing the relationship between the costate function and infinite dimensional value function. Further, we propose a study to create a generalized methodology for stability analysis of feedback MFG controllers, for systems more general than single integrator systems. These methods would have direct applications in control problems involving non trivial passive dynamics as well as in study of second order synchronization, such as flocking.

Committee Members:
Prof. Evangelos Theodorou (Advisor)
Dr. Piyush Grover (Principal Research Scientist, MERL)
Prof. Eric Feron (AE)

Xiang Gao

(Adviser: Prof. Wenting Sun)

“The Effects of Ozone Addition on Flame Propagation and Stabilization”

Tuesday, Oct. 24 2017 @ 1:15 p.m.
Montgomery Knight Room 317

Abstract:
Combustion plays a vital role in transportation and power generation. However, concerns of efficiency, emission, and operations at extreme conditions drive combustion to its limits. The relatively slow combustion process is generally attributed to the slow chemical reactions at low temperature conditions, such as radical production process. If the fuel oxidization pathway can be modified to circumvent these rate limiting processes, the ignition and combustion process could be dramatically accelerated. Following this idea, addition of ozone (O₃) is proposed as a potential solution. O₃ is one of the strongest oxidizers. It can be efficiently and economically produced in situ at high pressures, which corresponds to the operating condition of most practical combustion devices. Compared to the time scales in most combustors, the lifetime of O₃ is long enough to allow it being transported to the desired region from an injection location to modify fuel oxidization and control the combustion process.

This dissertation investigates the effects of O₃ addition on some fundamental combustion processes, to serve as a basis for future application on practical combustion systems. These include the propagation of laminar premixed flame and the stabilization of non-premixed jet flames. Previous studies have shown that O₃ addition can enhance flame propagation, stability and ignition, but the dependence on pressure and temperature are not clear yet. Such enhancement is generally attributed to the release of reactive O atoms by the thermal decomposition of O₃. However, this may not be always true as O₃ can react with some fuel directly via ozonolysis reaction before it decomposes.  For unsaturated hydrocarbon, such reactions release significant amounts of heat and are rapid even at room temperature. Therefore, one may expect, at proper conditions, ozonolysis reaction can initiate autoignition and fundamentally changes the flame dynamics. However, very limited studies have been conducted to explore such possibility. The results presented in this dissertation are an attempt to address these questions.

The effects of O₃ addition on the propagation of laminar premixed flames are investigated first, with respect to pressure, initial temperature, O₃ concentration and fuel kinetics. For alkane/air premixed laminar flames, high-pressure Bunsen flame experiments in the present work showed that the enhancement in laminar flame speed (S_L) increases with pressures. Simulation explains this with the finding that at higher pressure, O₃ decomposition becomes a more dominant channel compared to other O₃ consumption pathways. This promotes the release of O atoms, which accelerates flame propagation. The positive relationship between enhancement and pressure makes O₃ addition an attractive technique for high-pressure applications. Regarding the dependence on initial temperature, simulation results show that adding O₃ at higher initial temperature is not as effective as that at lower initial temperature, as another O₃ consumption channel is favored at higher temperature. One can boost such enhancement in S_L by increasing O₃ concentration. A nearly linear relation between the enhancement and O₃ concentration is observed at room temperature and atmospheric pressure. If the fuel is changed from alkanes to C₂H₄, an unsaturated hydrocarbon species, ozonolysis reactions take place in the premixing process. When the heat released from ozonolysis reactions is lost, decrease in S_L is observed. In contrast, if ozonolysis reaction are frozen, either by cooling the reactants to or decreasing the pressure, and enhancement of S_L by O₃ addition has been observed.

The study on flame stabilization with O₃ addition is conducted with a non-premixed jet burner in a quartz tube using C₂H₄ as the fuel. At designed flow conditions, autoignition events are observed in such burner. Filtered chemiluminescence shows that the ozonolysis product, formaldehyde (CH₂O), always accumulates before autoignition happens, which confirms that ozonolysis reactions initiate autoignition. The autoignition timescale is further investigated quantitatively. Overall, the relation between this timescale and inlet velocity is negative. Simulation models are built step by step to interpret this trend. At low Re, this trend is explained by the negative relation between mixing timescale and flow velocity at the present geometry. At high Re, it is attributed to the promoted mixing due to turbulence, which is further confirmed experimentally.

At such autoignitive conditions created by ozonolysis reactions, the stabilization of a lifted non-premixed flame is fundamentally different from the classic ones. It is observed that the ability of a flame to be stabilized at high velocity flows is significantly enhanced. Two mechanisms are proposed to explain this. Firstly, the propagation is enhanced due to the “preprocessing” of fuel by ozonolysis reactions, after which the mass burning velocity of the reactants is increased as shown by simulation. This can increase the propagation by several times. Secondly, the conventional propagation process is circumvented as radicals are generated and thermal energy can be released locally, initiated by ozonolysis reactions. So the propagation is not solely controlled by the diffusion process, and autoignition kernels can be generated at the upstream of the existing combustion zone. This effectively moves the flame front at a speed of more than 100 times of S_L.

In summary, for the premixed laminar flame propagation, the present results explain the pressure, initial temperature, and fuel dependence of enhancement of flame propagation by O₃ addition. A more comprehensive understanding is thus contributed. As for the non-premixed jet, this dissertation provides data and analysis of ozonolysis-activated autoignition events and their enhancing effects on flame stabilization. This includes modeling the relation between the autoignition timescales and chemistry, mixing, and Reynolds number, and proposing two mechanisms that enhance flame stabilization. That is, ozonolysis i) pre-process the reactants to have higher mass burning velocity, and ii) circumvent the propagation by generating autoignition upstream of the original combustion zone.

A global pathway selection (GPS) algorithm is proposed in this work for the systematic generation of skeletal mechanisms. A 28-species mechanism is generated using this algorithm and applied in the 3D simulation of the non-premixed jet flames with O₃ addition. GPS is further extended to a hierarchical framework, Global Pathway Analysis (GPA), to understand the chemical kinetics. A demonstration is given by analyzing the second H₂ explosion limit.

Committee:
Dr. Wenting Sun (AE)
Dr. Jerry Seitzman (AE)
Dr. Timothy Ombrello (AFRL)
Dr. Lakshmi Sankar (AE)
Dr. Jechiel Jagoda (AE)

Dr. Timothy Ombrello

Senior Research Aerospace Engineer
Aerospace Systems Directorate
Air Force Research Laboratory

“Shifting the Paradigm of How Ignition is Approached in a Flowing Environment”

October 24 @ 11:00 a.m.
Montgomery Knight Room 317

Abstract:
Ignition success in real world combustion systems hinges upon multiple local and global parameters. From a global perspective, success is driven by the probability of ignition, as well as how “on demand” the system can respond. More succinctly, how to guarantee that ignition will always occur, and within the shortest time possible. These global parameters are of course governed by local factors, such as the fuel concentration, gas temperature, and velocity and turbulence levels, as well as the quantity of energy deposited, and the volume in which the energy is deposited. Because of all these parameters, energy deposition devices for ignition can be tailored to couple into and enhance the kinetic or fluid dynamic phenomena. The majority of this work has been focused on discrete ignition events where single pulses can be tailored for different levels of excitation or duration. While systems have been developed to pulse repetitively in a burst to increase the probability of ignition, each pulse remained discrete with no coupling between pulses.

Recently, the switching technology in pulsed power systems has allowed for high voltage, high current, high-frequency repetitive pulsed systems to become a reality. The systems are capable of producing short duration pulses (~10 ns) with voltages in excess of 10 kV, at pulse repetition frequencies greater than 100 kHz. The time scale between pulses allows for a synergy between pulses on both fluid dynamic and kinetic time scales that changes the conventional understanding of how ignition is approached.

In this talk, the application of nanosecond-pulsed high-frequency discharges to a range of reactive systems will be discussed; starting with ignition in a quiescent environment to provide a baseline understanding, and building up to ignition in a scramjet cavity-based flame holder. The primary metric for comparison is the total energy, but varying the rate of deposition (i.e. power). Global effects of ignition probability and kernel growth rates will be presented, as well as detailed measurements of temperature and intermediate species.
 

Timothy Ombrello earned his Bachelor of Engineering in Mechanical Engineering from The Cooper Union for the Advancement of Science and Art in 2003, and his Ph.D. in Mechanical and Aerospace Engineering from Princeton University in 2009. Upon completing his graduate degree, he went on to work at the Air Force Research Laboratory, initially as a National Research Council Research Associate for one year before becoming a civilian employee. Currently he is a Senior Research Aerospace Engineer in the Aerospace Systems Directorate, predominately performing research related to high-speed air-breathing propulsions systems, specifically supersonic combustion ramjets. His research covers a wide range of fluid dynamic and combustion challenges, with strong collaborations across academia and industry. His interests lie in performing research and crafting techniques to enhance reactivity for more rapid ignition and more robust flame propagation and stabilization, from fundamental bench-top to supersonic wind tunnel experiments. His contributions thus far have allowed him to be a recipient of the Air Force Research Laboratory’s Early Career Award and Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House.

He serves as a guest editor for IEEE Transactions on Plasma Science and he is an Associate Fellow of the American Institute of Aeronautics and Astronautics.

Chong Zhou

(Advisor: Dr. Lakshmi N Sankar)

“Assessment of Tip Planform Effects on Hover and Forward Flight Aerodynamics of Helicopter Rotors”

Friday Oct. 13^th @ 10:00 a.m.
Weber Room 200

Abstract:

An Assessment of Tip Planform Effects on Hover and Forward Flight from physical point of view is proposed. Preliminary studies have already been completed to assess the effects of planform tip shape on hover performance. The flow field including sectional loads, tip vortex trajectories, and inflow velocity distributions will be examined to identify underlying physical phenomena that influence the previously documented changes to the rotor performance in hover.

Furthermore, all configurations considered in hover will be analyzed in forward flight at a specific advance ratio and shaft incidence angle representative of S-76 which is the baseline of the study, and the rotors will be trimmed for specified thrust values and zero hub moments. It would be examined whether configurations that are efficient in hover are also efficient in forward flight from an induced power and profile power perspective.  The sectional airloads and integrated hub loads will be analyzed to determine whether the changes to the tip shape favorably or adversely affect the vibratory loads.  Underlying physical phenomena (dynamic stall, blade vortex interaction, tip stall) will be identified.

Committee:
Prof. Lakshmi N Sankar
Prof. Daniel P Schrage
Prof. Jonnalagadda V R Prasad

Luke Battey

(Advisor: Prof. L. Sankar)

“A Hybrid Navier-Stokes/Vortex Particle Wake Methodology for Modeling Helicopter Rotors in Forward Flight and Maneuvers”

October 20^th, 2017 @ 11:00 a.m.
Montgomery Knight Room 325

Dr. Daniel P. Shrage
School of Aerospace Engineering
Georgia Institute of Technology

Dr. J.V.R Prasad
School of Aerospace Engineering
Georgia Institute of Technology

Department Head and Professor of Aerospace Engineering and Engineering Mechanics
Department of Aerospace Engineering and Engineering Mechanics
University of Cincinnati

"Development of an Implicit, Overset High-Order Discontinuous Galerkin Simulation Framework"

Guggenheim 442 @ 3:30pm

Abstract:
The discontinuous Galerkin(DG) method for discretizing partial differential equations has been applied in many fields including acoustics, numerical weather predictions, and aerodynamics. Part of the strength of the method exists in its ability to provide arbitrary high-order accuracy, while maintaining a local computational stencil. The local scheme is attractive for use on unstructured grids but is also advantageous for Chimera/Overset structured grids, where traditional challenges with overset schemes such as orphan nodes are eliminated. The ability to represent curved geometry also reduces discretization and interpolation error. The combination of high-order accuracy and straight-forward geometry representation and modification makes the Chimera/Overset-DG discretization an attractive core capability for a framework enabling analysis, modeling, and design.

Researchers at the University of Cincinnati Gas Turbine Simulation Laboratory have been driving sustained development of Chimera/Overset-DG capabilities for several years. More recently, they have combined lessons learned from previous development efforts and created a software framework based on a core Chimera/Overset-DG capability and thoughtful software engineering. The project is ChiDG: a Chimera-based discontinuous Galerkin framework. The framework is equipped with abstractions for many common components in numerical methods such as time-integrators, nonlinear/linear solvers, and preconditioners so new developers do not have to reinvent the infrastructure and interactions between these components. Additionally, the framework takes a composition-based approach to representing equations. Abstractions exist for defining model coefficients, numerical operators, and composing equation sets from these components. From a software perspective, the framework is written in Modern Fortran(F90-2008), uses CMake and pFUnit to automate configure/build/test activities, and includes an intrinsic automatic differentiation capability to reduce developer burden when implementing new models. The project is open-source under the BSD 3-clause license and hosted on GitHub along with documentation(https://github.com/nwukie/ChiDG).

The framework currently includes Newton-based nonlinear solvers with some globalization approaches for robustness, an FGMRES linear solver, a parallel ILU0 preconditioner, and Euler/RANS equation sets with a Spalart-Allmaras turbulence model. Recent efforts on the ChiDG framework have included the addition of high-order implicit time-integrators along with a Harmonic Balance time-integrator for time-spectral problems. An Arbitrary Lagrangian Eulerian formulation was also added enabling problems with mesh motion or rotating/translating coordinate systems. Current efforts on the ChiDG framework are focused on enabling capabilities for applied problems in external aerodynamics and turbomachinery as well as incorporating adjoint capabilities to drive design and optimization efforts. This talk will discuss the development of ChiDG and provide examples of its capability.

Christopher F. DeGraw

(Advisor) Dr. Marcus Holzinger

“Massive Scale Hardware-in-the-Loop Simulation for Satellite Constellations and Other Multi-Agent Networks”

Monday, October 16 @ 3:00 p.m.
Montgomery Knight Room 317

Given the plans for satellite mega-constellations, there is a lack of rigorously tested operations and control methods for constellations larger than 30 to 50 spacecraft. The purpose of this thesis is to propose the principles behind a robust, modular and scalable system able to provide software-in-the-loop (SWIL) and hardware-in-the-loop (HWIL) simulation capabilities for the advancement of formation and constellation system Technology Readiness Levels (TRL). Additionally, this thesis will develop a first-generation system demonstrating these principles called Constellation Simulation on a Massive Scale, or COSMoS.

The preliminary goals of COSMoS are to:

1. Simulate 47 or more satellites in a constellation to demonstrate scalable capability
2. Connect to external hardware devices in real-time to demonstrate HWIL capability
3. Connect to the Space Systems Design Laboratory Mission Operations Center to demonstrate human interface capability

Currently developing constellation automation capabilities include the implementation of control schemes using a Minimum Lyapunov Error approach developed by Dr. Marcus Holzinger and Dr. Jay McMahon, which will be one of the first algorithms tested on COSMoS. The system will also interact with flight-like and flight-ready hardware with the goal of testing experiment systems for SSDL flight missions and potentially increasing their TRL. Finally, it will also connect to the SSDL Operations Center to assist in the development of human-constellation interactions and ground controller training for SSDL flight missions.

Nandeesh Hiremath

(Advisor:  Dr. Narayanan Komerath)

“Vortex Aerodynamics of Rotors at High Advance Ratio”

October 17, 2017, 2:00 - 4:00 p.m.
Montgomery Knight Building Room 317

Abstract

Rotor operation at high advance ratio is important for high-speed and compound rotorcraft concepts. The operation of helicopter rotors in reverse flow has taken on new significance in the context of co-axial rotors. A rotor moving edgewise at a high advance ratio, encounters reverse flow on parts of the retreating portion of the rotor disc. Predicting rotor stability and pitch link loads is complicated by the presence of unsteady pitch, yaw and rotation effects. Predictions using comprehensive codes have shown large differences from full-scale experimental data. Prior approaches have modeled these using flow separation with airfoil data modified for yaw, vortex shedding, dynamic pitch oscillations and reverse dynamic stall of an airfoil. However, the highly 3-dimensional flow phenomena do not conform to approaches based on 2-dimensional airfoil aerodynamics. The present work delineates the nature of flow around a rotating blade in reverse flow by integrating the results from fixed wing experiments with rotating wing experiments. The work focuses on a strong 3D vortex similar to those seen on delta wings that would develop over the sharp edge at high yaw, providing an avenue for vortex lift aerodynamic analyses. The fixed wing and rotating wing experiments were performed on a tethered rotor blade with NACA0013 profile. Fixed-wing results from load measurements and flow visualization showed that the sharp-edge vortex (SEV) is a primary feature in reverse flow when the blade is yawed either forward or backward. The aerodynamic loads conform with analytical model using Polhamus Suction Analogy, thus showing significant contributions from vortex-induced lift and pitching moments

In summary, it is apparent that the reverse flow regime should be modeled and analyzed as a case of SEV formation under the very sharply swept blade immediately after 180 degrees azimuth. The SEV evolves as the sweep decreases with increasing azimuth. In the regime before 240 degrees, an attached, strengthening SEV may be expected. At some moderate sweep (azimuth beyond 240 degrees in our case) the vortex bursts and detaches from the surface. Thereafter it convects with the blade, but induces strong pressure effects on the blade surface even as far as 300 degrees azimuth. The blunt edge flow is highly 3-dimensional, and has much less flow separation and unsteadiness than might be predicted from 2-dimensional airfoil aerodynamics.

Thesis Committee members:
Dr. Lakshmi Sankar
Dr. Karim Sabra
Dr. Dimitri Mavris
Dr. Tom Thompson (Army)
Dr. Narayanan Komerath (Advisor)

How Do I...?
An informal informational event for  prospective women AE students

Thursday, October 19

4 - 6 p.m.

Student Center Peachtree Room

Refreshments Provided

The Georgia Tech Women in Aerospace Engineering (GT-WAE) wants to meet you!
Drop into this informal session to get more information from current undergrad and grad students about aerospace engineering and....

• Study Abroad Opportunities
• Co-ops
• Internships
• Design
• Graduate School
• Undergraduate Research
• Planning Your Career

Follow GT-WAE on Facebook: GT Women in Aerospace Engineering

Society for Autonomotive Engineers

invites you to an evening with

John Hope Bryant

enterpreneur, author, and founder of

Bryant Motorsports Academy

The Bryant Group Motorsports Academy,will open the doors of inclusion to motorsports. The presentation will include the message of the Motorsports Academy and the Five Rules for Your Economic Liberation from his latest book, The Memo. 

There will be time to network with the speaker. 

Refreshments served

Come to the

11th Annual Aerospace Engineering Expo

Talk with undergrads, grads, and faculty about the challenges and the rewards of an education in aerospace engineering.

This will be catered.

Sponsored by the School of Aerospace Engineering Student Advisory Council (SAESAC)

Monday, October 2, 10:00 a.m. - 3:00 p.m.
Student Success Ctr. President's Suites C & D

Hiring managers from Boeing will be on hand to screen applicants for intern and entry level opportunities (B.S. & M.S. students only).  Select students will be asked to interview for positions, Oct 3-5 on campus.  Business attire is not required for this info session.  You are encouraged to drop by between classes.  Bring your resume!

Aerospace Engineering
Civil Engineering (especially Structural emphasis or interest)
Computer Engineering/Science
Electrical Engineering
Chemical Engineering/Material Science
Mechanical Engineering
Manufacturing Engineering
Mathematics and Systems

Apply online:  https://jobs.boeing.com/

Internships - Job ID 1700011944

Entry Level - Job ID 1700011951

You must apply online to be considered

Vigor Yang

W.R.T. Oakes Professor & Chair
Daniel Guggenheim School of Aerospace Engineering
Georgia Insitute of Technology

"Space Propulsion: Enabling the Future of Space Transportation and Exploration"

Guggenheim 442 @ 3:30 p.m.

Vigor Yang is the William R. T. Oakes Professor and Chair of the School of Aerospace Engineering at the Georgia Institute of Technology.  He has published 10 comprehensive volumes and numerous technical papers on combustion, propulsion and energetics.  He was the recipient of  the Air-Breathing Propulsion Award (2005), the Pendray Aerospace Literature Award (2008), the Propellants and Combustion Award (2009), and the von Karman Lectureship in Astronautics Award (2016) from the American Institute of Aeronautics and Astronautics (AIAA); the Worcester Reed Warner Medal (2014) from the American Society of Mechanical Engineers (ASME); and the Lifetime Achievement Award (2014) from the Joint Army, Navy, NASA, and Air Force (JANNAF) Interagency Propulsion Committee. Dr. Yang was the editor-in-chief of the AIAA Journal of Propulsion and Power (2001-2009) and the JANNAF Journal of Propulsion and Energetics (2009-2012). He is currently a co-editor of the Aerospace Book Series of the Cambridge University Press (2010-).  A member of the U.S. National Academy of Engineering and an Academician of Academia Sinica, Dr. Yang is a fellow of the AIAA, ASME, and Royal Aeronautic Society (RAeS).

Friday, September 29, 2017
11:15am
TSRB Auditorium

Matthew Bopp

Advisor: Dr. Stephen M. Ruffin

"A Time Accurate Fluid-Structure Interaction Framework Using a Cartesian Grid CFD Solver"

Thursday, September 21, 2017 @ 1:00 p.m.
Montgomery Knight, Room 317

Abstract:
The landing of the Mars Science Laboratory (MSL) in 2012 demonstrated the limits of supersonic planetary entry technology through the use of a disk-gap-band parachute deployed from behind the aeroshell capsule. With the eventual goal of sending humans to Mars, the payload requirements are estimated to increase by a factor of 40, far outside the current technological envelope. With a density of less than 1% of Earth's, the Martian atmosphere makes the task of generating aerodynamic drag very challenging. Larger aeroshells produce more drag, but the vehicle is then too large to fit as payload inside a rocket. By utilizing inflatable aerodynamic decelerators, the drag area can be significantly increased, while the pre-deployed configuration has high packing efficiency.

New technologies bring with them the requirement to study their behavior, and characterize their flight limits. Wind tunnel tests are difficult due to scaling concerns, and flight tests are costly and time consuming. Thus, accurate computational modeling of the fluid-structure interactions (FSI) is critical in the development of aerodynamic decelerators. Much of the current research in FSI focuses on high fidelity analysis, which is often very computationally expensive, and requires significant user intervention. The current work fills a mid-fidelity niche where the analysis time and human interaction is reduced, by utilizing an adaptive, Cartesian grid framework for solving the computational fluid dynamics (CFD).

A time accurate, partitioned coupling strategy is employed to study FSI applied to flexible materials under high dynamic pressure loads. The structural dynamics is solved using LS-DYNA, and care must be taken at the interface boundary conditions to reduce numerical errors. The development of this tool has relied on a complete re-write of the in-house CFD code, NASCART-GT, where significant improvements have been made in computational efficiency and scalability. CFD simulations with prescribed motions are studied in order to validate the fluid dynamics of high speed flows with non-stationary boundary conditions, and to study the effects of solution-based grid adaption for these simulations. The interaction with rigid body dynamics is presented in simulations of the free flight dynamics of the MSL capsule. FSI simulations are then presented for a series of test cases, where the physics is validated for the unsteady, time accurate coupling of 1-D piston motion and 2-D beam deformation. Finally, steady state and time accurate simulations of an inflatable aerodynamic decelerator demonstrate the effectiveness of the current methodology in furthering the development of decelerator technologies.

Committee:
Dr. Stephen M. Ruffin, Advisor (AE)
Dr. Michael D. Barnhardt (NASA Ames)
Dr. Julian J. Rimoli (AE)
Dr. Lakshmi N. Sankar (AE)
Dr. Marilyn J. Smith (AE)

Self-Driving Cars and Ethics: An Overview of Design Challenges

a talk by

Dr. Jason Borenstein

Friday, September 22
11:15 a.m.
TSRB Auditorium

About the Talk:
Engineers are in the process of developing and deploying a broad range of vehicles with varying levels of autonomy.  As these vehicles start to appear on the roads more regularly, the importance of examining the extensive collection of ethical issues that could emerge becomes increasingly pressing.  Key ethical issues that warrant examination include potential “Trolley problems” and complexities associated with design decisions to take the human driver “out of the loop” from operating a vehicle.  Given how unpredictable interactions between human users and automated systems may be, engineers will need to work with various stakeholders in the effort to uphold public safety.

About the Speaker
Jason Borenstein, Ph.D., is the Director of Graduate Research Ethics Programs and Associate Director of the Center for Ethics and Technology. His appointment is divided between the School of Public Policy and the Office of Graduate Studies. He is an assistant editor of the journal Science and Engineering Ethics, co-editor of the Stanford Encyclopedia of Philosophy’s Ethics and Information Technology section, and an editorial board member of the journal Accountability in Research.  He is also editor for Research Ethics for the National Academy of Engineering's Online Ethics Center for Engineering and Science. Dr. Borenstein’s research interests include bioethics, engineering ethics, robot ethics, and research ethics. His work has appeared in numerous professional journals including AI & Society, Communications of the ACM, Science and Engineering Ethics, the Journal of Academic Ethics, Ethics and Information Technology, IEEE Technology & Society, Accountability in Research, and the Columbia Science and Technology Law Review.

"Unified Approach for Accurate and Efficient Modeling of Composite Rotor Blade Dynamics” 

Professor Dewey Hodges

2014 Nikolsky Lecturer for the American Helicopter Society

Farshad Shirani

Advisors: Professor Wassim M. Haddad and Professor Rafael de la Llave

"Mathematical Analysis of a Mean Field Model of Electroencephalographic Activity in the Neocortex"

4:30 p.m., Tuesday, September 19, Montgomery Knight, Room 317

Abstract
The electroencephalographic recordings from the scalp are essential measures of mesoscopic electrical activity in the neocortex. Such spatio-temporal electrical activity can effectively be modeled using the mean field theory. The mean field model of the electroencephalogram developed by Liley et al., 2002, is one of these models that has been widely used in the literature to study different patterns of rhythmic activity in the conscious and unconscious states of the brain. This model is presented as a system of coupled ordinary and partial differential equations with periodic boundary conditions.

In this doctoral thesis, this model is mathematically analyzed using the theory of partial differential equations and infinite-dimensional dynamical systems. Specifically, existence, uniqueness, and regularity of weak and strong solutions of the model are established in appropriate function spaces, and the associated initial-boundary value problems are proved to be well-posed. Moreover, sufficient conditions are developed for the phase spaces of the model to ensure nonnegativity of certain quantities, as required by their biophysical interpretation. Semidynamical system frameworks are established for the model and it is proved that the semigroups of weak and strong solution operators possess bounded absorbing sets for the entire range of biophysical values of the parameters of the model. Challenges towards establishing a global attractor for the model are discussed and it is shown that there exist parameter values for which the constructed semidynamical systems do not possess a compact global attractor due to the lack of the asymptotic compactness property. A bifurcation analysis is performed on a finite-dimensional approximation of the model with respect to variations in critical parameters of the model. The various emerging behaviors at each set of parameter values are qualitatively studied by numerically solving the equations of the model using finite element software packages. Finally, using the theoretical results developed in this thesis, instructive insights are provided into the complexity of the behavior of the model and computational analysis of the model.

Committee:

• Professor Wassim M. Haddad, School of Aerospace Engineering, Georgia Institute of Technology
• Professor Rafael de la Llave, School of Mathematics, Georgia Institute of Technology
• Professor John-Paul B Clarke, School of Aerospace Engineering, Georgia Institute of Technology

Andrew J. Greenhill

Advisor: Dr. Amy Pritchett

“Enhanced Flight Vision Systems: Presence of Runway Markings and Visibility Effects on Pilot Performance”

9:00 AM, Friday, September 15^th, 2017
Bradley Building, Bradley Conference Room

Abstract:

This proposal defines a research plan to investigate the effects of visibility range and runway marking on pilot performance with enhanced flight vision systems. The motivation behind this experiment is to observe the implications of sensor technologies in general aviation. This research hopes to provide some insight into the possible concerns of enhanced flight vision systems with regards to pilot performance. The background section of this proposal describes some of the current sensor technologies in use today with enhanced flight vision systems (EFVS). The current sensors described are millimeter wave radar, forward-looking infrared and light detection and ranging; each of these sensors have capabilities and constraints that could affect the display shown to the pilot. In addition to sensor technologies, pilot visual cues and situational awareness is discussed. The objective of this research is twofold: first, find the effect, if any, the visibility range of an EFVS system affects the pilot performance on approach and landing. Secondly, find the effect that the absence of runway markings in EFVS has on the pilot performance during approach and landing. The approach that will be taken is to modify the visual cues presented to the pilot that directly affect the pilot’s performance and situational awareness. The visual cues were chosen since they have been shown to be used on approach and landing and can be directly related to current sensor technologies.

Professor and Department Chair
Department of Mechanical and Aerospace Engineering
University of Florida

Guggenheim 442 @ 3:30 p.m.

Alexei Poludnenko

Department of Aerospace Engineering
Texas A&M University

"Turbulent Combustion: From a Jet Engine to an Exploding Star"

September 14 @ 11 am
Montgomery Knight Room 317

Abstract:
Turbulent reacting flows are pervasive both in our daily lives on Earth and in the Universe. They power modern society being at the heart of many energy generation and propulsion systems, such as gas turbines, internal combustion and jet engines. At the same time, they also power the Universe through the energy produced in stellar interiors – both quiescently, as in the Sun, and also violently, as in the most powerful explosions in the Universe known as Type Ia supernovae. Despite this ubiquity in Nature, turbulent reacting flows still pose a number of fundamental questions concerning their structure and dynamics often exhibiting surprising and unexpected behavior. In recent years, the advent of large-scale direct numerical simulations (DNS) has allowed the detailed exploration of the reacting flow dynamics in extreme, previously inaccessible regimes characterized by high flow speeds, significant compressibility effects, and strong coupling between exothermic reactions and the turbulent flow. Such combustion regimes are fundamental to the operation of many modern propulsion applications from scramjets to detonation-based engines. Furthermore, in certain cases these regimes can now be studied with remarkable realism using full-scale combustors, realistic fuels, and engine-relevant conditions. This talk will present an overview of a range of phenomena recently discovered in DNS of high-speed, premixed, turbulent reacting flows. These include intrinsic instabilities of reacting turbulence, onset of catastrophic transitions, e.g., spontaneous detonation formation, qualitative changes in the nature of the turbulent cascade in the presence of exothermic reactions, as well as the onset of distributed burning regimes at high turbulent intensities. I will discuss challenges presented by these findings both in the context of our theoretical understanding of reacting flows, and also in the context of modern modeling paradigms, such as Large Eddy Simulations.

Bio:
Alexei Poludnenko received his Bachelor degree in Physics and Mathematics from the National University “Kyiv-Mohyla Academy” in Kyiv, Ukraine, and Masters and Ph.D. degrees in Physics and Astronomy from the University of Rochester. Upon graduation, he joined the Department of Energy ASC Flash Center at the University of Chicago as a postdoctoral researcher. Subsequently, Dr. Poludnenko worked at the Naval Research Laboratory first as a National Research Council postdoctoral fellow and later as a permanent research staff member. Currently, he is an associate professor in the Department of Aerospace Engineering at the Texas A&M University. His research includes theoretical and computational studies of turbulent combustion in chemical and thermonuclear systems, numerical algorithm development for computational fluid dynamics, and high-performance computing. Dr. Poludnenko was a recipient of the Distinguished Paper Award at the 36^th International Symposium on Combustion, the 2016 François Frenkiel Award for Fluid Mechanics of the American Physical Society Division of Fluid Dynamics, and the Alan Berman Research Publication Award of the US Naval Research Laboratory.

Dr. Andrew J. Aspden

Thermofluid Dynamics
Newcastle University

"ADNS Perspective on the Turbulent Premixed Flame Regime Diagram"

Tuesday August 29 @ 2 p.m.
Food Processing Technology Building Auditorium
NARA complex

Abstract:
Over the last decade or so, three-dimensional Direct Numerical Simulation (DNS) with detailed chemistry has provided unique insight into the small-scale interactions between turbulence and premixed flames.  In this talk, a DNS perspective will be presented of the turbulent premixed flame regime diagram, primarily through canonical flame-in-a-box calculations.  Interpretation of the dimensionless groups will be considered, along with consequences for the demarcations between burning regimes.  Topics of particular focus will include the influence of Karlovitz number and the transition towards distributed burning, effects due to Lewis numbers of different species, and the response observed in chemical distribution.

Bio:
Dr. Apsden joined Newcastle University in January 2017 as a Lecturer of Thermofluid Dynamics.  He obtained an MMath from the University of Oxford in 2002, followed by a PhD in Applied Mathematics from the University of Cambridge in 2006. He was awarded a Glenn T Seaborg Fellowship at the Lawrence Berkeley National Laboratory, where he was a member of the Center for Computational Sciences and Engineering for five years. Before joining Newcastle University, he was a Lecturer of Applied Mathematics at the University of Southampton, a Lecturer of Computational Fluid Dynamics at Cranfield University, and before that a Lecturer of Engineering Sciences at the University of Portsmouth. Andy's research interests include analysis and simulation of fluid mechanics, turbulence, combustion, and type Ia supernovae.
 

Fokion N. Egolfopoulos

William E. Leonhard Professor in Engineering
Department of Aerospace and Mechanical Engineering
University of Southern California

"Understanding Reacting Flows under Engine-Relevant Conditions:  Historical Trends and Some Recent Developments"

Thursday, October 5, 2017 @ 11:00 a.m.
Montgomery Knight Room 317

Abstract:
Combustion science is nearly 100 years old and major advances have been made since Nikolai Semenov determined in the 1920’s that “mechanisms of chemical reactions and in particular chain reactions” is essential towards the understanding of “combustion and explosion processes.”  Many believe that the most profound example of the contributions of combustion science remains the notable reduction of pollutant emissions since the 1970’s, which was achieved through the understanding of their formation mechanisms.  However, there are many open-ended questions regarding the relevance of the current state of combustion science to applications that operate at high pressures and temperatures in the presence of highly turbulent flows, and involve complex multicomponent liquid fuels.  In order to characterize with confidence the operational behavior and limits of engines after identifying the controlling mechanisms, the science that needs to be tackled is rather complicated under such extreme conditions and in many ways it appears to be a daunting task.  In this presentation, some issues will be discussed in the context of the engine-relevant thermodynamic and flow parameter space, and possible ways to move forward will be outlined through examples that are based on recent developments.

Fokion N. Egolfopoulos is a William E. Leonhard Professor of Engineering in the Department of Aerospace and Mechanical Engineering at the University of Southern California.  He obtained his Diploma degree in 1981 from the National Technical University of Athens, and his Ph.D. degree in 1990 from the University of California at Davis after having spent the last two years of his doctoral research at Princeton University.   He was a recipient of the Silver Medal of the Combustion Institute at the Twenty-Second International Combustion Symposium.  He is a Fellow of the American Society of Mechanical Engineers (ASME) and an Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA).  Since January 2009 he is the co-Editor in Chief of Combustion and Flame, after having served as an Associate Editor of the journal from January 2003 until December 2008.

Timothy Edward Dawson

(Advisor: Prof. Vigor Yang)

“Flame Response Modeling for Linear Stability Analysis of Staged-Combustion Rocket Engines”

Tuesday, September 5^th, 2017 @ 1:30 p.m.
Montgomery Knight Building Room 317

Abstract:
Recent efforts led by the Air Force Research Laboratory (AFRL) aim to help transition US-based rocket manufacturing from conventional gas-generator cycle Liquid Rocket Engines (LREs), such as the Saturn V's F-1 engine and Space Shuttle Main Engine (SSME), to higher performance closed-cycle designs such as the oxidizer-rich staged combustion (ORSC) cycle employed in many Russian-developed engines including the RD-180. Even as conventional LREs are being driven to higher chamber pressures to meet the requirements of next-generation payload delivery, combustion instabilities remain nearly impossible to predict a priori. These high-amplitude pressure oscillations become exceedingly dangerous as the energy density of the thrust chamber assembly (TCA) increases, leading to catastrophic structural failures and expensive engine testing programs. Bringing instability prediction on-line in the design process would both reduce costs and improve safety drastically, and one particularly promising avenue combines the robust modal analysis of a linearized acoustic solver with the detailed physics captured by high-fidelity simulations, providing a framework by which rapid prototyping of engine designs becomes computationally feasible.

The proposed research investigates a novel approach for modeling the response of TCA injectors to acoustic excitation, using Large Eddy Simulation (LES) to capture the detailed physics in turbulent reacting flowfields representative of full scale ORSC engines. Single element simulations will be conducted on both full and reduced computational domains, while reduced-domain multi-element simulations are proposed to specifically investigate proximity effects of both bordering elements and combustion chamber walls. Dynamic Mode Decomposition (DMD) is used to precompute the combustion response terms for incorporation into a COMSOL-based linearized acoustics model for rapid prediction of natural acoustic modes and their associated linear growth rates. Single and multi-element sub-scale ORSC experiments conducted by the Georgia Tech Combustion Lab and NASA Marshall Space Flight Center (MSFC) serve as benchmarks for both direct validation of the LES accuracy and demonstration of the predictive capabilities of the overall framework.

Committee Members:
Dr. Vigor Yang (Advisor)                                     
Dr. Timothy Lieuwen
Dr. Lakshmi Sankar

Nick P. Breen

(Advisor: Dr. Krish K. Ahuja)

“Comparison Between Beamforming and Nearfield Contours for Source Location in Subsonic and Supersonic Jets of Various Geometries”

2:00 PM, Thursday, September 21, 2017
Montgomery Knight, Room 317

Abstract:
In the context of aeroacoustics, source location refers to a methodology that allows identification of locations of noise sources of a given frequency in the noise-producing region of the flow. The need to understand and reduce aircraft noise emissions has led numerous researchers to apply various source location techniques to jet noise. There are a number of applications where the knowledge of the location of sources of various frequencies along the length of the jet is required. Prior to 1985, several methods for determining jet-noise source locations were explored: acoustic mirrors, microphone arrays, two microphone methods, causality correlation and coherence techniques, nearfield contour surveys, and automated source breakdown. More recently there have been developments in the microphone array, notably acoustic beamforming, and two microphone method techniques. Most of the older techniques, while they would successfully produce source location results, require significant amount of time to acquire data at each jet condition; this requirement is often caused by the necessity to move microphones, while the jet is running on condition, to obtain source locations at all frequencies. The acoustic beamformer, on the other hand, is not required to be moved during the acquisition of data, resulting in very rapid tests compared to most other source location methods.

                In this work, the acoustic beamformer is analyzed as a jet noise source location tool. This method is compared against nearfield noise contours, an older well-developed method for jet noise source location, to see how consistent the two methods are for a variety of subsonic and supersonic jet conditions. Preliminary results show that these two methods agree fairly well for subsonic jet conditions. This work also examines how the noise source distributions of subsonic jets change due to low Reynolds number effects and due to nozzle geometry. The effects of pressure ratio, both on and off design condition, on the supersonic jet noise sources are analyzed. The noise source distributions of round twin jets are examined as a function of Mach number and separation distance. Attempts are made to empirically model the above results. Schlieren flow visualization videos are used in tandem with source location, to better explain how the noise source distributions change.

Aero Maker Space

is seeking applications from qualified students to serve as trained staff for our facility, located in the Weber Building on the AE campus.

The deadline to apply is August 22 at 11:59 p.m.

To apply, visit: https://docs.google.com/forms/d/e/1FAIpQLSefCGIlDAT7f5dREAoU9DMgfQSSiAHP-qV686Wo3xsOjVzQ6g/viewform?usp=sf_link

you are invited to a

Information Session

Undergraduate Research Opportunities at the Aerospace Systems Design Lab

Tuesday, August 22 @ 11 a.m.
Weber Building CoVE Auditorium,  3rd floor

Find out about the opportunities available to get started with engineering research. Hundreds of engineers got their start at ASDL. You might be the next one.

Students from multiple disciplines are invited to an information session for the

TARGIT and RANGE Satellite Missions

Tuesday, August 22 @ 6 p.m.
Guggenheim 442

Bring your resume!

A limited number of student research positions are available for two upcoming small-sat missions that are being run by AE Prof. Brian Gunter.

1. The Ranging And Nanosatellite Guidance Experiment (RANGE) is a two-satellite formation that will complet e assembly in the Fall of 2017 and will launch and commence operations in the Spring of 2018.

2.  The Tethering And Ranging mission of the Georgia Institute of Technology (TARGIT)  is a NASA-sponsored cubesat project that will deploy and conduct 3D lidar imaging on an inflatable target while in orbit, with an expected launch date in 2019.

Looking for: all majors & class ranks, esp. those interested in electronics, optics/lasers, and programming
Minimum Commitment:  8 hrs/wk, or 2 credit hours, in the lab
Contact: Prof. Brian Gunter brian.gunter@ae.gatech.edu
More info: bgunter.gatech.edu
NOTE: Only US citizens or permanent residents may participate

Career Information Session

featuring recruiters from

Bell Textron

Wednesday, September 13
5:30 - 7 p.m.
Guggenheim Building of the School of Aerospace Engineering

Bring your resume and your A-game. There will be pizza and drinks provided.

This is sponsored by the Georgia Tech Chapter of the American Helicopter Society (AHS) and the Vertical Lift Research Center of Excellence (VLRCOE)

“Perspectives from Saturn: Cassini’s Two-Decade Exploration of the Ringed Planet and the Grand Finale"

Michael Staab, M.S. AE
JPL engineer

Project Manager
NASA Revolutionary Vertical Lift Technology
NASA Langley Research Center

Guggenheim 442 @ 3:30 p.m.

Details TBA

Matthew J. Miller

(Advisor: Dr. Karen Feigh)

9:00am, Monday, August 14th, 2017
GT Library (ground floor west), Wilby Room

“Decision Support System Development for

Human Extravehicular Activity”

Abstract:

Human spaceflight is arguably one of mankind's most challenging engineering feats, requiring carefully crafted synergy between human and technological capabilities. One critical component of human spaceflight pertains to the activity conducted outside the safe confines of the spacecraft, known as Extravehicular Activity (EVA). Successful execution of EVAs requires significant effort and real-time communication between astronauts who perform the EVA and the ground personnel who provide real-time support. As NASA extends human presence into deep space, the time delay associated with communication between the flight crew and Earth-bound support crew will cause a shift from real-time to delayed communication. A decision support system (DSS) is one possible solution to enhance astronauts’ capability to identify, diagnose, and recover from time critical irregularities during EVAs without relying on real-time ground support.

The contributions of this thesis are two fold. The first is domain specific and addresses the known deficiencies that will impact future human EVA operations. The second is methodological and generalizable across many domains. This thesis demonstrates that Cognitive Work Analysis (CWA) can be applied to yield design insight in the form of high level design requirements amenable to traditional systems engineering. Beginning with the first two phases of CWA, a broad work domain analysis of EVA is made to identify the system constraints on EVA operations. Subsequently, Control Task Analysis models were developed that yielded a set of DSS design requirements in the form of cognitive work and information relationship requirements which reflect the underlying states of knowledge associated with supporting EVA operations. Furthermore, this thesis demonstrates how a subset of those requirements, along side envisioning and testing within a future work context, can yield prototype DSS designs suitable for supporting future EVA operations. Finally, this thesis included a human-subject study to evaluate the resultant prototypes against the requirements to demonstrate both validity of the requirements and the verification of the design. As a result, this thesis contributes the underlying science needed to design a DSS within the EVA work domain for future mission operations.

Committee Members:
Prof. Karen M. Feigh (Advisor, AE)
Prof. Amy R. Pritchett (AE)
Prof. David A. Spencer (AE)
Dr. Ute M. Fischer (LMC)
Dr. Kerry M. McGuire (NASA JSC)

Lee Whitcher

(Advisor: Dr. Eric N. Johnson)

Monday, August 7th, 2017 @ 9am
Montgomery-Knight Building, Room 317

“Design Considerations for the Control and Performance Optimization of a VTOL UAV Using the Coanda Effect”

Abstract:

The Coanda effect is a phenomenon of fluid dynamics whereby a jet exhibits a strong tendency to become attached to, and flow around, a nearby surface. Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) utilizing the Coanda effect for lift generation have a number of potential benefits, including: (a) the creation of a large aerodynamically-neutral payload/systems bays, (b) a high payload-carrying ability for its size, and (c) the use of an enclosed rotor, enabling it to withstand contact with its surroundings.

Coanda effect UAVs have undergone some study, but remain a largely under-investigated and certainly un-optimized VTOL configuration. This proposed research aims to address this by:

• Developing a physics-based model for the aircraft’s flight dynamics
• Developing a robust flight controller for hover and low-speed flight
• Developing analytical and numerical methods to predict performance characteristics
• Incorporating this knowledge into an optimization strategy for maximizing the aircraft’s potential as a safer VTOL UAV for use in urban and otherwise challenging environments
• Validating all of the above works with experimental data gained from static and flight tests

Committee:
Dr. Eric N. Johnson, School of Aerospace Engineering, Georgia Institute of Technology
Dr. Daniel P. Schrage, School of Aerospace Engineering, Georgia Institute of Technology
Dr. J.V.R. Prasad, School of Aerospace Engineering, Georgia Institute of Technology
Dr. Magnus Egerstedt, School of Aerospace Engineering, Georgia Institute of Technology
Dr. Tony J. Dodd, Dept.of Automatic Control and Systems Engineering, University of Sheffield (UK)
Dr. Suraj Unnikrishnan, Lockheed Martin Sikorsky

Kyuman Lee

(Advisor:  Professor Eric N. Johnson)

“Adaptive Filtering for Vision-Aided Inertial Navigation”

3:00 p.m. Wednesday, July 26, 2017
Montgomery Knight Building Room 317

Abstract: 
With the advent of unmanned aerial vehicles (UAVs), a major area of interest in the research field of UAVs has been vision-aided inertial navigation systems (V-INS). Many missions of UAVs—reconnaissance, damage assessment, exploration, and other guidance, navigation, and control (GNC) tasks—often demand V-INS in more operational environments such as indoors, hostilities, and disasters. In V-INS, inertial measurement unit (IMU) dead reckoning generates the dynamic models of UAVs, and vision sensors extract information about the surrounding environment and determine features or points of interest. With these sensors, the most widely used algorithm for estimating vehicle and feature states of V-INS is an extended Kalman filter (EKF). The design of the standard EKF does not inherently allow for time offsets between the timestamps of the IMU and vision data, and the necessary assumption of the EKF is Gaussian and white noise. In fact, sensor-related delays, correlations of noise, or outliers that arise in various realistic conditions are unknown parameters. A lack of compensation of unknown parameters leads to a serious impact on the accuracy of the navigation systems. To compensate for uncertainties of the parameters, we require modified versions of the estimator or the incorporation of other techniques into the filter.

The main purpose of this thesis is to develop adaptive and robust V-INS for UAVs, in particular, those for situations pertaining to such unknown parameters. First, to fuse measurements with unknown time delays, this study incorporates parameter estimation and constrained filtering into state estimation. In addition, we use machine-learning techniques (e.g., the kernel embedding of distributions) to handle unknown correlations and dependences of each noise source. Unfortunately, few researchers have treated correlated noise in V-INS in great detail. Finally, typicality and eccentricity data analysis (TEDA) detects the real-time outliers of the IMU and vision data, and variational approximation for Bayesian inference derives how to compute the optimal precision matrices of both propagation and measurement outliers. Results from both Monte Carlo simulation and flight testing validate the improved accuracy and reliability of V-INS employing these adaptive filtering frameworks.

Committee Members:
Prof. Eric N. Johnson (Advisor), School of Aerospace Engineering
Prof. Eric Feron, School of Aerospace Engineering
Prof. E. Glenn Lightsey, School of Aerospace Engineering
Prof. Marcus J. Holzinger, School of Aerospace Engineering
Prof. Byron Boots, School of Interactive Computing

Doctoral Defense by

Matthew Gross

Advisor: Dr. Mark Costello

“Smart Projectile Parameter Estimation Using
Meta-Optimization”

Monday, July 31, 2017 @ 1 p.m.
Montgomery-Knight Room 317

Nishant Jain

(Advisor: Dr. Jerry M. Seitzman)

“Combustion and Flow Characteristics of Staged Combustors with Multiple Large Jets in Confined Crossflow”

Monday, July 24, 2017, 11 a.m.-12:00 p.m.
Montgomery Knight building, Conference room 317

Abstract:
Staged combustion offers many advantages in high performance aero-propulsion and power generation applications that demand increasingly robust gas turbine engines with reduced emissions. Air-staged combustors primarily rely upon rapid mixing and rapid combustion which occurs in a confined environment with multiple large jets carrying significant amounts of mass and momentum into a high temperature vitiated crossflow. The proposed thesis focuses on elucidating the mixing and combustion processes under conditions relevant to applications in non-premixed (Rich-Quench-Lean, RQL) and premixed (Lean-Quench-Lean, LQL) staged combustors. To this effect, experimental and analytical investigations will be performed in a simplified atmospheric laboratory setup using geometries, air split ratios, jet configurations and other flow parameters that are relevant to practical applications.

With the goal of determining mixing and flow field characteristics that are unique to highly confined multiple jets in crossflow, high speed planar and stereo PIV techniques will be employed. The thesis will examine the impact of jet-jet and jet-wall interactions on mixing for two jet configurations, namely, parallel jets and staggered-opposed jets. Moreover, high speed OH* chemiluminescence imaging of highly confined reacting jets in a high temperature, vitiated crossflow will be performed to understand the controlling flame characteristics such as flame stabilization mechanisms, liftoff height and burnout distance. Reduced order chemical kinetic modeling (e.g., autoignition and consumption-based flame speed analysis) will also be used to interpret the results obtained from the flame measurements. Essentially, the temporally and spatially resolved velocity and mixing results will be used together with the high speed chemiluminescence and reduced order modeling to investigate the interplay of flow and combustion characteristics in staged combustion architectures.

Proposal committee members:
Dr. Jerry M. Seitzman (advisor)
Dr. Jechiel I. Jagoda
Dr. Timothy C. Lieuwen

Andrew T. Bellocchio

(Advisor: Prof. Daniel Schrage,)

“Balancing Maintenance Free Operating Period Rotorcraft with Cost Capability Analysis”

2:00 pm, Friday, July 28, 2017
Weber SST III, Collaborative Visualization Environment (CoVE)

Abstract:

For the past 50 years, the paradigm of on-condition rotorcraft maintenance has yielded to random failures and subsequent unscheduled maintenance that regularly disrupt flight operations.  The British Ultra-Reliable Aircraft Pilot Program of the late 1990s introduced the paradigm of Maintenance Free Operating Period (MFOP) as a solution.  An MFOP aircraft is a fault tolerant, highly reliable system that minimizes disruptive failures for an extended period of operations.  After the MFOP, a single Maintenance Recovery Period (MRP) consolidates the repair of accrued faults and inspections in order to restore aircraft’s reliability for the next MFOP cycle.  An MFOP strategy provides assurance to the user that flight operations will continue without disruption for the duration of the MFOP at a given survivability rate.

The U.S. Department of Defense recently adopted MFOP as its maintenance strategy for the next generation of rotorcraft named the Future Vertical Lift (FVL) Family of Systems.  The U.S. military desires uninterrupted flight operations to enable a more expeditionary force that operates from remote, austere bases.  An initial goal of a 100-flight hour MFOP at 90% availability will be necessary to support such deployments; yet, today’s fleet has the system reliability to fly less than ten hours without significant repair at 75% availability.  Beyond FVL, the military desires to transition to near-zero maintenance with an MFOP between 480 hours and 720 hours.  The challenge presented is to achieve an order of magnitude improvement to meet the FVL target and set the conditions for near-zero maintenance while still remaining affordable.

The goal of the proposed research is to measure the balance between capability, availability, dependability, and life cycle cost of an MFOP rotorcraft.  It will utilize a Petri net-like state space in an integrated Discrete Event Simulation to model the MFOP, MRP, and their survivability as operational metrics.  The work will identify which subsystem(s) limit the MFOP of an aircraft and which components drive MRP higher.  It will explore the relationship between MFOP and MRP as well as their cost and vehicle performance implications.  It will test the hypothesis that an operational commander has some control over MFOP by varying the MRP through an aggressive lifing policy.  Ultimately, the work will demonstrate an application of Cost Capability Analysis to inform decision makers on vehicle design and technology trade decisions in a near-zero maintenance context.

Committee Members:
Prof. Daniel Schrage, Advisor
Prof. Dimitri Mavris
Dr. Vitali Volovoi

Michael X. Grey

(Advisor:  Prof. Karen C. Liu)

Tuesday, June 20th, 2017 @ 12:00pm EDT
Technology Square Research Building (TSRB) 222

“High Level Decomposition for Bipedal Locomotion Planning”

Abstract:
Legged robotic platforms offer an attractive potential for deployment in hazardous scenarios that would be too dangerous for human workers. Legs provide a robot with the ability to step over obstacles and traverse steep, uneven, or narrow terrain. Such conditions are common in dangerous environments, such as a collapsing building or a nuclear facility during a meltdown. However, identifying the physical motions that a legged robot needs to perform in order to move itself through such an environment is particularly challenging. A human operator may be able to manually design such a motion on a case-by-case basis, but it would be inordinately time-consuming and unsuitable for real-world deployment.

This thesis presents a method to decompose challenging large-scale motion planning problems into a high-level planning problem and a set of parallel low-level planning problems. We apply the method to quasi-static bipedal locomotion planning. The method is tested in a series of simulated environments that are designed to reflect some of the challenging geometric features that a robot may face in a disaster scenario. We analyze the improvement in performance that is provided by the high- and low-level decomposition, and we show that completeness is not lost by this decomposition.

Committee Members:
Dr. C. Karen Liu (Advisor), School of Interactive Computing, Georgia Institute of Technology

Dr. Aaron D. Ames (Advisor), Mechanical and Civil Engineering & Control and Dynamical Systems, California Institute of Technology

Dr. Magnus Egerstedt, School of Electrical and Computer Engineering, Georgia Institute of Technology

Dr. Kris Hauser, Department of Electrical and Computer Engineering & Department of Mechanical Engineering and Computer Science & Department of Computer Science, Duke University

Dr. Matt Zucker, Engineering Department, Swarthmore University

Shane V. Lympany

(Advisor: Dr. Krish K. Ahuja)

“Acoustic Damping Mechanisms of Propellant Injectors”

Friday, June 23, 2017 @ 10:00 a.m.
Montgomery Knight, Room 317

Abstract:
Combustion instabilities in liquid rocket engines are caused by coupling between the combustion process and pressure oscillations in a combustor, and they are characterized by the frequencies and shapes of the acoustic modes of the combustion chamber. Acoustic resonators are commonly installed in combustors to provide passive acoustic damping and prevent combustion instabilities. Previously, it has been proposed that the propellant injectors in a combustor can be tuned to act as half-wave resonators and provide acoustic damping, which requires a thorough understanding of the acoustic damping mechanisms of injectors.

In this work, the acoustic damping of propellant injectors is measured experimentally. A new experimental facility is developed to measure the sound power reflection, transmission, and dissipation under the conditions of mean flow, high amplitude, high temperature, and higher-order modes. The effects of common design parameters – namely, the typical features of an injector, the number of injectors, the ratio between the cross-sectional area of the injectors and the combustion chamber, and the position of the injectors – on the absorption coefficient are investigated experimentally using the new facility. The effects of mean flow, high amplitude, high temperature, and higher-order modes are also investigated. Measurements of the fraction of sound power dissipated by the injectors and the velocity flow field at the ends of the injectors are used to elucidate the physical mechanisms responsible for the acoustic damping. Attempts are made to quantify the separate contributions of viscous dissipation and the conversion of sound to vorticity. An analytical model incorporating these acoustic damping mechanisms is developed to predict the absorption coefficient of the injectors for each of the measured geometric parameters and operating conditions.

Toshinobu Watanabe

(Advisor: Dr. Eric N. Johnson)

“Monocular Vision Based Obstacle Avoidance”

Friday, June 9, 2017 @ 11:00 a.m.
Montgomery Knight Building - Room 317

Abstract:
Obstacle avoidance is one of the most important and expensive topics in Autonomous Robotics because it is an essential task for an autonomous vehicle to find an obstacle and avoid it. Any robotics designers use LIDAR, stereo camera and so on to be able to obtain more accurate sensing data. However, these approaches are more expensive than a single camera and need a specific device. Currently, many fields use UAVs for many objectives. Especially, photographing uses it from movie filming to personal use, and they have a single camera. Therefore, although the monocular camera-based recognition technique is a challenging task, its technique can be applied to a wider range, like an existing vehicle and a cheaper vehicle with fewer sensors. For this reason, this proposal mentions the monocular camera-based obstacle avoidance technique.

In this work, this technique can be separated into two parts: a mapping and a path planning. The mapping technique is designed by a monocular vision as input, which consists of the filter technique to obtain a point cloud and an occupancy grid map. The filter includes the pre-filter for initial convergence and an Extended Kalman Filter (EKF) for final localization and mapping. The occupancy grid map updates a probability of obstacle existence, and the octree data structure adds scalability and efficient memory management to the occupancy grid map. The path planning algorithm is designed based on the octree data structure, which consists of three parts: a new A* algorithm, a tree-based trajectory generation technique, and an additional lateral trajectory. The first A* algorithm can work on the octree data structure and outputs a free corridor. The second technology generates a trajectory in that corridor. The additional lateral trajectory improves the obstacle detection.

Committee Members:
Dr. Eric N. Johnson         
Dr. Eric Marie J Feron                    
Dr. Jonnalagadda V R Prasad
Dr. Hao-Min Zhou           
Dr. Patricio Antonio Vela

Chief Scientist, Aerospace Systems Directorate
Air Force Research Laboratory

Guggenheim 442 @ 3:30p.m.

Details TBA

Timothy Gallagher

(Advisor: Dr. Suresh Menon)

“A Generalized Maccormack Scheme For Low Mach Number, Chemically-Reacting Large-Eddy Simulations”

Friday, June 2, 2017 @ 1:00 PM
Guggenheim Building, Room 442

Abstract:
Chemically reacting flows contain a wide range of regimes with many velocity and time scales. The increasing access to computational resources enables higher-fidelity simulations of these flows. In order to take advantage of these capabilities, numerical schemes must be robust, efficient and accurate in all of the regimes present in the flow. Pressure-based schemes are suitable for many low Mach number flows, but are limited to low velocities and relatively small temperature variations. Density-based schemes struggle to converge in low-speed flows due to the time-step restrictions imposed by the acoustic velocity, which may be orders of magnitude larger than the convective velocity. Furthermore, such codes may exhibit excessive numerical dissipation due improper scaling of the dissipative properties of the scheme. Chemical reactions introduce another set of temporal scales associated with the kinetics mechanism used to model the system. These scales are often much smaller than the convective or acoustic scales and impose additional restrictions on the time-step. This disparity requires numerical schemes designed to handle the challenges that occur in low Mach number, chemically reacting flows. Analysis of density-based schemes at the low Mach number limit suggests that the development of improved, robust preconditioning with suitable operator splitting techniques leads to improved solution fidelity.

In this work, a dual-time framework with low-Mach preconditioning is developed for complex, chemically reacting large-eddy simulations. A new version of the well-known MacCormack scheme is proposed and the resulting scheme improves the solution quality significantly at low Mach numbers. An established ordinary differential equation solver for stiff systems treats the stiffness associated with the chemical source terms. Methods to couple the PDE and ODE solvers in both pseudo-time and in physical time are proposed and analyzed. Validation of the non-reacting scheme and the coupled reacting scheme using canonical test cases demonstrates the improved solution fidelity and simulations of representative industrial applications demonstrate the combined scheme.

Committee Members:

Dr. Suresh Menon          
Dr. Stephen Ruffin                          
Dr. Marilyn Smith            
Dr. Lakshmi Sankar
Dr. Yingjie Liu                    
Dr. Venkateswaran Sankaran     
Dr. Vaidyanathan Sankaran

Keir C. Gonyea

(Advisor: Prof. Robert D. Braun)

“Use of the Mars Atmosphere to Improve the Performance of Supersonic Retropropulsion”

Monday May 8, 2017, 12:30pm
Montgomery Knight Room 317

Abstract:

NASA has landed seven vehicles on the surface of Mars using parachutes for supersonic descent. These parachutes are unsuited to future high mass missions due to inflation, drag, and aerothermodynamic complications. Supersonic retropropulsion is a candidate technology to replace supersonic parachutes, but is hindered by its large associated propellant mass. Atmospheric-breathing propulsion systems may reduce this mass constraint by ingesting oxidizer from the surrounding atmosphere. However, the Martian atmosphere, which is composed of primarily carbon dioxide, necessitates that metal fuels be used in order to combust the available oxidizer.  

This thesis advances the state of the art of atmospheric-breathing supersonic retropropulsion (ABSRP) by providing the first exploration into the feasibility and potential performance of ABSRP as a technology solution for high-mass Mars missions. Specific advancements are made using systems analysis methods and computational models. 

ABSRP propulsion performance is assessed via a suite of analysis tools, which are developed to simulate metal – CO2 combustion performance and sensitivity to both the engine design and operating regime. These tools include an equilibrium combustion simulation to evaluate engine efficiency, a finite-rate kinetics simulation to investigate the time-dependent phenomena, and a particle burning simulation to assess diffusion effects. Case studies are presented for ABSRP relevant mixtures and conditions to predict propulsion performance of the ABSRP engine across a range of conditions and verify that reasonably sized combustion chambers can provide complete combustion of the propellant. 

The propulsion system results are used in an ABSRP vehicle model, which accounts for the variable engine performance across different flight regimes. This model is used to search the design space and determine the characteristics and performance of ABSRP architectures relative to competing propulsive solutions. The investigation includes an assessment of feasible and unfeasible regions of the design space in addition to design trends for optimal configurations. Mass favorable vehicles of multiple architectures are compared to understand their relative performance in order to ultimately determine the potential applicability of atmospheric-breathing propulsion for Mars descent.

Committee:
Dr. Robert D. Braun (advisor)
Dr. Jechiel I. Jagoda
Dr. Jerry M. Seitzman
Dr. Brian J. German
Dr. Aaron H. Auslender

Alfredo Valverde

Dr. Panagiotis Tsiotras (Advisor)

“Dynamic Modeling and Control of Spacecraft Robotic Systems using Dual Quaternions”

May 10^th @ 4:00 pm
Montgomery Knight Room 317

Abstract:

As of 2014, the space servicing market has a potential revenue of $3-$5B per year due to the ever-present interest to upkeep existing orbiting infrastructure. In space servicing, there is a delicate balance between system complexity and servicer capability. Basic module-exchange servicers decrease the complexity of the servicing spacecraft, but is likely to require a more complex architecture of the serviced satellite (the host) in terms of electrical and mechanical connections.

With increasing dexterity of the servicing satellite, host satellites can remain closer to flight-proven heritage architectures, which is a practice commonly adopted to increase reliability of space missions. This increased dexterity can be provided through the on-orbit exchange of end-effector tools appended to a robotic arm. The dynamic coupling of the arm and the base has been the subject of intense academic scrutiny and its understanding is essential to the implementability and success of robotic servicing missions.

In this work, we propose a framework to implement the different phases of a servicing mission based on dual quaternion algebra. First, we propose a dual quaternion 6-{DOF} pose-tracking controller that adaptively estimates the mass properties of a spacecraft using the concurrent learning framework. Next, we provide a generalizable case study of the derivation of the dynamic equations of motion for a spacecraft with a serial robotic manipulator. This derivation uses a Netwon-Euler approach, and its results are validated against an analogous derivation that uses a decoupled representation of translational and rotational dynamics

Future work will include the generalization of this framework to contain [endif]--> robotic arms with [endif]--> links. Additionally, for the case of a one-arm system, a pose-stabilizing controller of the end-effector will be proposed in the context of differential dynamic programming, as well as a pose-tracking controller that will follow the concept of control-computed torque. The results will then be used to simulate the autonomous rendezvous and capture of an orbiting object. Finally, an algorithm will be proposed to estimate the mass properties of said captured object.

Committee Members:

• Dr. Panagiotis Tsiotras (Advisor)
• Dr. Marcus J. Holzinger
• Dr. Patricio A. Vela

Pratibha Raghunandan

 (Advisor: Prof. Stephen M. Ruffin)

“Internal Energy Modeling of Hypersonic Weakly Ionized Non-Equilibrium Flows”

May 1, 2017 @ 3 p.m.
Weber 200

Abstract:

            The dissociation and ionization of gases in high temperature flows, typical for planetary re-entry vehicles, require computation of finite rate chemistry and thermal non-equilibrium. This work presents the implementation of non-equilibrium flow physics capabilities in an unstructured Cartesian grid-based adaptive solver. The thermo-chemical non-equilibrium solver incorporates multiple multi-temperature models that simulate various types of energy exchanges between the constituent atoms/ molecules. The modeling of such energy exchanges can provide different effective temperatures to define a chemical reaction, which in turn can yield significant differences in non-equilibrium chemical and thermal relaxation rates.

            A two temperature model, involving a single translational and a single vibrational temperature, is compared to a multi-vibrational, single translational model for different gases/gaseous mixtures; the effects of composition of gases on the relaxation rates are discussed for these cases. Furthermore, the effects of the inclusion of a separate electron temperature on the vibration-translation relaxation rates in ionized flows are discussed. The study of the differences brought about by such relaxation rates in two-dimensional thermo-chemical non-equilibrium flows is proposed.

            The thermo-chemical non-equilibrium modeling in hypersonic flows yields considerable differences in resultant chemistry and shock stand-off distances in comparison with chemical non-equilibrium flows, and significant differences with equilibrium models. This particularly has an impact on the prediction of electron and ion densities in weakly ionized gases, the accurate modeling of which are very important for radio blackout mitigation and plasma-aerodynamic flow control. It is identified that accurate modeling of energy exchanges at the macroscopic level along with the simulation of thermal inhomogeneities are imperative to successfully replicate ground-based tests in a computationally efficient manner, as well as capture the flow physics associated with shock waves traveling through weakly ionized gases. This proposed work will investigate such underlying physics through the appropriate modeling of internal energy for the high speed flows of interest.

Committee:
Dr. Stephen Ruffin (Advisor)
Dr. Suresh Menon
Dr. Wenting Sun

Department of Mechanical and Aerospace Engineering

Princeton University

“Turbulent Combustion Modeling for Large Eddy Simulation: Finding Simplicity in Complexity”

May 2 @ 1:30pm
Montgomery Knight Rm 317

Abstract:

Turbulent combustion modeling is a challenging multi-physics, multi-scale modeling problem.  Both turbulence and combustion are already difficult multi-scale problems, and the combination of the two brings in new interactions across various length and time scales that fundamentally change both the combustion processes and the turbulence.  This seminar will focus on the modeling of unresolved, small-scale details of the combustion processes and the many chemical species involved.

Large Eddy Simulation (LES) models for turbulent combustion generally fall into two distinct classes subject to an inherent trade-off: models that are very general in their description of the underlying combustion processes but computationally intensive versus models that make very constraining assumptions about the underlying combustion processes but are computationally efficient.  In the latter class of models, the combustion processes are typically constrained to low-dimensional manifolds obtained by assuming combustion occurs in a single asymptotic mode: premixed flames, nonpremixed flames, or homogeneous reactions.  For multi-modal combustion, the current state-of-the-art is to apply the “best” asymptotic model locally.  However, recent LES results in a laboratory-scale turbulent flame exhibiting partially premixed combustion demonstrate the inherent shortcomings of this approach not only in selecting the “best” asymptotic model but also in relying solely on asymptotic models.

In the final portion of the seminar, a new, generalized combustion model will be presented that seeks to break the inherent trade-off above.  The model relies on a more detailed manifold description that can capture not only all of the asymptotic modes of combustion in their respective limits but also intermediate regimes.  Key characteristics of the model will be discussed, and algorithmic challenges and opportunities in coupling the model with LES will be highlighted.

About the speaker:

Michael E. Mueller is an Assistant Professor in the Department of Mechanical and Aerospace Engineering at Princeton University, an associated faculty member in the Princeton Institute for Computational Science and Engineering, and an associated faculty member in the Andlinger Center for Energy and the Environment.  He received a BS degree in mechanical engineering from The University of Texas at Austin in 2007, a MS degree in mechanical engineering from Stanford University in 2009, and a PhD degree in mechanical engineering from Stanford University in 2012 before moving to Princeton in 2012.  His expertise is the computational modeling of turbulent reacting flows, where he utilizes a multi-fidelity approach leveraging first-principles calculations for physics discovery for the development of physics-based models for engineering calculations.  Areas of current interest within his research group include multi-modal turbulent combustion, pollutant emissions, and combustion-affected turbulence.  In addition, he is active in areas of applied computational science including the development of new approaches to uncertainty quantification and the development of new numerical algorithms and their implementation on emerging architectures.

Tejas Puranik

 (Advisor: Prof. Dimitri N. Mavris)

“A Methodology for Quantitative Data-Driven Safety Assessment for General Aviation”

Thursday, May 4, 2017 @ 9:00 a.m.

Weber Space Science and Technology Building
Collaborative Visualization Environment (CoVE)

Abstract:

The safety record of aviation operations has been steadily improving for the past few decades, however, accident rates in General Aviation (GA) have not improved significantly compared to scheduled airline operations. Per the Federal Aviation Administration (FAA), the demand for air travel and traffic is predicted to grow steadily through 2036 at a rate of approximately 1.8% annually with GA set to receive a much-needed revitalization. However, safety remains a major hurdle and with such a large increase in expected operations, there is an ever-increasing demand for improving safety of GA operations

Various data-driven safety programs such as Flight Data Monitoring (FDM) that exist in commercial aviation domain have percolated in GA with the aim of improving safety. These programs typically feature a continuous cycle involving data collection from on-board recorders, retrospective analysis of flight data records, identification of operational safety exceedances, design and implementation of corrective measures, and monitoring to assess their effectiveness. While these programs have been shown to be effective in reducing accident rates, there are certain obstacles in their widespread implementation in the GA domain. The variability in recorded parameters in GA, heterogeneity in GA fleet, different missions flown, etc. are some of the important hurdles. Additionally, existing techniques of analysis such as exceedance detection are designed to identify known unsafe conditions but are potentially blind to safety-critical conditions that may be captured in flight data records but are not present in the set of predefined safety events.

The overarching objective of this dissertation is to develop a methodology that can provide objective metrics for quantifying GA flight safety, enable identification of anomalous operations, and provide predictive capabilities that will complement existing approaches. The methodology presents the use of energy-based metrics as objective currency that can be used for quantifying safety across the heterogeneous GA fleet. These metrics are defined using recorded flight data and aircraft performance models. An anomaly detection framework is then developed using these metrics for identifying different types of anomalies (flight-level and instantaneous) in GA operations. A novel technique of calibrating aircraft performance models used in defining these metrics is proposed using data available in the public domain. The obtained calibrated models are further refined by employing Bayesian updating using actual flight data records. Finally, the calibrated performance models and a flight simulation model will be utilized to construct an offline surrogate model that approximates boundaries or limits of the performance envelope and can be queried online to identify when the aircraft might be drifting outside its safety space. Once the methodology is developed, its implementation on a set of real flight data records will be demonstrated through various experiments to highlight its widespread applicability.

Committee members:
      1.  Prof. Dimitri Mavris (Advisor)
           School of Aerospace Engineering, Georgia Institute of Technology
      2.  Dr. Simon Briceno
           School of Aerospace Engineering, Georgia Institute of Technology
      3.  Prof. Karen Marais
           School of Aeronautics and Astronautics, Purdue University