2014 Seminar Archive


Spring, 2014

Elastic Filaments in Viscous Fluids

David Saintillan

Department of Mechanical and Aerospace Engineering
University of California San Diego
La Jolla, CA

Flexible elastic filaments are found in a wide range of microscale biological flows, for instance in the form of DNA, actin and microtubules. Understanding the behavior of these biopolymers under various types of forcing is therefore a stepping-stone for the modeling of a broad range of biological processes as well as technological applications involving their transport in microscale devices. In this talk, I will use theory and numerical simulations to analyze two problems involving elastic filaments suspended in viscous fluids. First, the dynamics in simple external flows commonly encountered in microfluidics will be addressed. In simple shear flow, quasi-periodic tumbling of the filament is shown to arise, whereas strain-dominated flows drive a buckling instability for a filament aligned with an axis of compression. This instability in turn has a strong impact on transport properties in complex flow fields such as vortex arrays, where the spatial dispersion of the filaments can be either diffusive or sub-diffusive depending on flow strength and on the importance of thermal fluctuations. Second, the motion and deformation of a filament sedimenting in a gravitational field will be considered. In the weakly flexible case, bending of the filament results in rotation and alignment perpendicular to gravity, whereas we demonstrate that more floppy filaments can again be subject to a buckling instability when aligned with gravity. Consequences of these dynamics for the stability of suspensions of multiple filaments will also be discussed.

Wednesday, January 22, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Role of Microstructure in Predicting Fatigue Performance

Michael D. Sangid

Assistant Professor
School of Aeronautics and Astronautics
Purdue University
West Lafayette, IN 47907

Prediction of fatigue crack initiation has presented engineers with a challenging problem over the years. Classically, predictions are based on a statistical regression of test data. Reducing the necessary certification testing and pushing the envelope of our design allowables has led to a great interest in linking the microstructure of the material to fatigue properties and life prediction. In this presentation, we discuss a model that integrates results of atomic simulations to the continuum level. Our approach is to model the energy of a persistent slip band (PSB) structure and use its stability with respect to dislocation motion as our failure criterion for fatigue crack initiation. Through this methodology, the fatigue life is predicted based on the energy of the PSB, which inherently accounts for the microstructure of the material. Very good agreement is shown between the model predictions and an ensemble of experimental test data. Further efforts for model verification and validation are shown, including how this type of modeling fits within an integrated computational materials science and engineering framework.

Michael D. Sangid received his PhD in Mechanical Engineering from the University of Illinois at Urbana-Champaign (UIUC) in 2010. After his Master’s degree, Dr. Sangid spent two years working in Indianapolis, IN for Rolls-Royce Corporation, specializing in material characterization, fatigue, fracture, and creep of high temperature aerospace materials before resuming his education in 2007. In the fall of 2011, Dr. Sangid started as an assistant professor at Purdue University in the School of Aeronautics and Astronautics, where he continues his work on building computational materials models with experimental verification and validation efforts.

Wednesday, January 29, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Virtual Surgery

Suvranu De

Professor and Department Head
Department of Mechanical, Aerospace and Nuclear Engineering
Rensselaer Polytechnic Institute
Troy, New York

Surgical procedures and devices are traditionally developed on animal models, through extensive trial and error. Similarly, surgical skills are acquired primarily in the operating room on real patients through graded supervision, while training of aviation pilots is now primarily accomplished on sophisticated flight simulators. It is anticipated that virtual surgery systems, that provide immersive computational environments in which the surgeons can interact with three-dimensional organ models using their sense of vision as well as touch, through haptic interface devices, will transform the field of surgery by facilitating discovery of novel surgical procedures, devices and platforms and allowing surgical training to attain competence in a controlled environment that does not expose actual patients to the bare brunt of their “learning curves.” However, developing a virtual surgery system is nontrivial and involves solving or addressing a range of issues including physics-based methods for modeling and simulation in real time; realistic simulation of surgical tool-soft tissue interactions with real-time changes to the model’s topology; soft tissue mechanical property measurement under various pathological conditions (diseased and normal); mathematical modeling of soft tissue behavior; real-time and stable haptic feedback; full connection between 3D deformable anatomical models under various pathological conditions to real-time VR visualizations; validation and performance metrics; and open source architecture for collaborative and incremental research efforts. In this talk we will present some of our recent work in the development and clinical validation of virual surgery systems. Supported by: NIH R01EB010037, R01EB009362, R01EB005807, R01EB014305

Suvranu De is Head of the Department of Mechanical, Aerospace and Nuclear Engineering and Director of the Center for Modeling, Simulation and Imaging in Medicine at Rensselaer Polytechnic Institute. He received his Sc.D. in Mechanical Engineering from MIT in 2001. He is the recipient of the 2005 ONR Young Investigator Award and serves on the editorial board of Computers and Structures and on scientific committees of numerous national and international conferences. He is also the founding chair of the Committee on Computational Bioengineering of the US Association for Computational Mechanics. His research interests include the development of novel, robust and reliable computational technology to solve challenging and high-impact problems in engineering, medicine and biology.

Wednesday, February 5, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Understanding and Controlling Wall-Bounded Turbulent Flows

Mitul Luhar

Postdoctoral Scholar
Graduate Aeronautical Labs
California Institute of Technology
Pasadena, CA

Turbulence is responsible for much of the skin friction generated on airplane fuselages, ship hulls, and inside large-scale pipelines. Even a modest reduction of turbulence in such wall-bounded flows has the potential to yield significant economic and environmental benefits. However, given the difficulty and expense associated with pursuing turbulent flow simulations and experiments at scales relevant to practical situations, the design and evaluation of effective control techniques remains an ongoing challenge. In this talk, I describe a simple theoretical framework that can aid this quest for effective turbulence control. This framework exploits the fact that the governing Navier-Stokes equations act as a directional amplifier to decompose the turbulent flow field into a limited set of high-gain velocity structures, or modes. The effect of any control strategy can then be evaluated on a mode-by-mode basis. I demonstrate the utility of this approach by using one of the earliest proposed feedback flow control techniques as an example*. I show that, with basic assumptions and minimal computation, this approach reproduces trends observed in previous experiment and direct numerical simulation. A mode-by-mode breakdown of control also provides new physical insight and paves the way for future optimization. Finally, I discuss avenues for future development using this framework, especially in terms of making control practicable (e.g., relying only on wall-based sensing, developing entirely passive control strategies).

Mitul Luhar is a Postdoctoral Scholar in the Graduate Aerospace Laboratories at Caltech. He received his PhD in Civil and Environmental Engineering from MIT in 2012. As a graduate student at MIT, Mitul was awarded the Presidential Fellowship as well as the Martin Family Society Fellowship for Sustainability. Prior to joining MIT, Mitul attended Queens’s College at the University of Cambridge, where he earned BA and MEng degrees in Engineering in 2007. His research interests include wall-bounded turbulent flows, coastal hydrodynamics, and flow-structure interaction.

Monday, February 10, 2014
11:00 AM
The Laufer Library (RRB 208)

Digital Microstructure and Material Design: Building a Bridge to Link Computational Materials Science to Applications

Mo Li

Professor
School of Materials Science and Engineering
Georgia Institute of Technology
Atlanta, Georgia

Material development and application have been main drivers to the advancement of human society. What makes our time unique is that we have the ability to deal with a large amount of data and the unprecedented computing power. These two features define the next stage of material development and also the competitiveness of our industry. Two key issues arise as a result: (1) How, through computing, can we link materials science with materials design and application and vice versa?(2) What the challenges do we face in building such a digital bridge? In this talk, I will address these questions through examples drawn from our own work on microstructure quantification and application in material design. From the ancient Damascus sword to high temperature alloys in modern jet engines, we witness a long history of human endeavor in making desired properties by controlling the microstructures in polycrystalline materials. Microstructure in polycrystalline materials, either coarse-grained or nano-crystalline, is characterized by complex topological structure of grain boundary networks. Those networks are composed of an array of geometric entities with different dimensions. Collectively, the networks contribute to the materials’ properties. In this talk, I present algorithms and numerical methods in polycrystalline samples we have recently developed, and how we use them for exploration and material design. Such quantitative methods, unavailable before, enable detailed and rigorous treatment of microstructures in a wide range of applications including both atomistic simulation and continuum modeling. If time permits, I will also discuss crystal grain nucleation and growth and their relations to microstructures.

Wednesday, February 12, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Numerical Simulation of Transition to Turbulence and Thermoacoustic Instabilities: Analysis and Modeling

Taraneh Sayadi

Postdoctoral Fellow
Laboratoire d’Hydrodynamique
Ecole Polytechnique
91128 Palaiseau cedex, France

The flows encountered in relevant engineering devices are often turbulent, and therefore involve a vast range of spatial and temporal scales. This is the case in energy conversion systems, where a variety of complex phenomena such as transition, separation, combustion, and thermoacoustic instabilities occur. These phenomena are of different nature, and their intricate coupling makes their understanding and prediction particularly challenging. Laminar to turbulent transition has been a subject of intensive experimental, theoretical, and numerical research. Direct numerical simulations (DNS) of controlled transitions are carried out for flat plate boundary layers. The modes of dynamical importance are extracted using dynamic mode decomposition (DMD). A few low-frequency modes are shown to provide a good estimate of the Reynolds shear stress gradient within the transitional region. This is of interest since large eddy simulation (LES) fails at predicting the rise to the overshoot of the skin-friction coefficient. The analysis shows that although the shapes and frequencies of the low-frequency modes are independent of the resolution, their amplitudes are underpredicted in the LES, resulting in the underprediction of the Reynolds shear stress. In addition, during the conversion process, the unsteady nature of the transitional and turbulent flow can affect the performance of the subsequent stages. These thermoacoustic instabilities are notoriously difficult to predict and control. A dedicated solver is introduced and applied to a modeled configuration, which enables the generation of accurate time series relevant to such systems. As opposed to frequency domain analysis typically used in this context, this approach is shown to capture linear and non-linear multi-modal dynamics.

Taraneh Sayadi is currently a postdoctoral fellow in the LadHyX laboratory in Ecole Polytechnique (France). She received a Bachelor of Science degree in September 2005 from Sharif University of Technology (Tehran, Iran), and continued her studies at the Technical University of Munich (Germany), where she received a Master of Science degree in Mechanical Engineering in August 2007. In September 2012 she completed a Ph.D. degree under the guidance of Professor Parviz Moin at the Center for Turbulence Research; at Stanford University. Her research focuses on the direct and large eddy simulation of complex turbulent flows with the objective of designing reduced-order models and control strategies. She is also interested in thermoacoustic instabilities relevant to energy conversion and transportation systems as well as data driven spectral analysis techniques and their integration with large-scale data processing tools. She may be reached at sayadi(at)ladhyx(dot)polytechnique(dot)fr

Thursday, February 13, 2014
4:00 PM
Laufer Library (RRB 208)

Refreshments will be served.

Information-Driven Sensorimotor Learning and Control

Silvia Ferrari

Professor of Engineering and Computer Science
Department of Mechanical Engineering and Materials Science
Graduate Program on Wireless Intelligent Sensor Networks (WISeNet)
Laboratory for Intelligent Systems and Controls (LISC)
Duke University, Durham, NC

Unmanned ground, aerial, and underwater vehicles equipped with on-board wireless sensors are becoming crucial to both civilian and military applications because of their ability to replace or assist humans in carrying out dangerous yet vital missions. As they are often required to operate in unstructured and uncertain environments, these mobile sensor networks must be adaptive and reconfigurable, and decide future actions intelligently based on the sensor measurements and environmental information. Recent work on geometric and information-driven sensor path planning has shown that the performance of these sensors can be significantly improved by planning their paths based on probabilistic sensor models, and on the geometric characteristics of the workspace and of the sensor field-of-view or visibility region. This talk discusses a general framework by which the expected information value of sensor measurements can be described by information theoretic functions in closed form, and, consequently, used to obtain path planning and control laws for active sensing and information gathering. This talk also presents new learning and control algorithm for developing adaptive controllers that are biologically realizable in-vitro and in-vivo, and, thus, can be used toward neuroscience research aimed at reverse engineering biological brains.

Silvia Ferrari is Professor of Engineering and Computer Science at Duke University, where she directs the Laboratory for Intelligent Systems and Controls (LISC). She is a member of the Duke Institute for Brain Sciences (DIBS) and of the information Initiative at Duke (iID). Her principal research interests include information-driven planning and control, learning and approximate dynamic programming, and distributed optimal control. She received the B.S. degree from Embry-Riddle Aeronautical University and the M.A. and Ph.D. degrees from Princeton University. She is a senior member of the IEEE, and a member of ASME, SPIE, and AIAA. She is the recipient of the ONR young investigator award (2004), the NSF CAREER award (2005), and the Presidential Early Career Award for Scientists and Engineers (PECASE) award (2006).

Wednesday, February 19, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Integrated Simulation and Diagnostics of Multi-Physics Turbulent Fluid Flows: From the Geometry of Turbulence to Hypersonic Flight Propulsion

Ivan Bermejo-Moreno

Postdoctoral Research Fellow
The Center for Turbulence Research
Stanford University
Stanford, CA

The success of numerical simulations in the prediction and understanding of turbulent flows with complex multi-physics often requires the integration of high-fidelity modeling approaches, massively-parallelizable computational frameworks and novel diagnostic methodologies. In this talk, I will address these issues by first presenting recently developed diagnostic techniques for the geometric study of turbulent structures, showing application to canonical, fundamental problems such as homogeneous isotropic turbulence and its interaction with shock waves. The latter will lead to progressively addressing several modeling aspects in turbulent flow simulations of increasing geometric and physical complexity, including internal, wall-bounded compressible flows with and without chemical reactions. Simulations of shock/turbulent-boundary layer interactions of multiple strengths in a duct will be presented to gain insight into the effects of confinement imposed by side walls in practical engineering applications. The integration of these modeling efforts will culminate in the simulation of the HIFiRE-2 hydrocarbon-based scramjet engine. Comparisons with experimental data will be provided for validation, as well as to highlight the complementary nature of simulations and experiments. The use and importance of supercomputers for these simulation efforts will be emphasized. I will finish with an outlook of future research challenges and opportunities on the path to exascale computing.

Ivan Bermejo-Moreno is currently a postdoctoral research fellow at the Center for Turbulence Research, Stanford University. He received his M.Sc. and Ph.D. degrees in aeronautics from the California Institute of Technology, and his aeronautical engineering degree from the School of Aeronautics at the Polytechnic University of Madrid, Spain. He worked in the space industry for two years before being awarded a Fulbright Fellowship to pursue his master’s and doctoral studies at Caltech, where he was a recipient of the Rolf D. Buhler Memorial Award, the William F. Ballhaus Prize and the Hans G. Hornung Prize.

Wednesday, February 26, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

What Can We Learn Through Computation?

Petros Koumoutsakos

Professor of Computational Science
ETH Zürich
Zürich, Switzerland

The solution of many important scientific and societal problems of our century, such as energy, health and the environment hinge on the fusion of mathematics and information technology.

Computational science is the new scientific field emerging from this fusion.

In this talk I will describe research challenges in computational science as it is implemented to understand, predict and solve problems across disciplinary boundaries. I will demonstrate research practices using examples ranging from cavitation and fish swimming to cancer induced angiogenesis.

Professor Petros Koumoutsakos holds the Chair of Computational Science at ETH Zurich (2000-present). He received his Diploma (1986, National Technical University of Athens) and Master’s (1987, University of Michigan, Ann Arbor) in Naval Architecture, followed by a Master’s (1988) and PhD in Aeronautics and Applied Mathematics (1992) from the California Institute of Technology. He was an NSF fellow in parallel computing (1992-1994, Center for Research on Parallel Computation) at the California Institute of Technology and a research associate (1994-1997) with the Center for Turbulence Research at NASA Ames/Stanford University. Professor Koumoutsakos is Fellow of the American Physical Society and Fellow of the American Society of Mechanical Engineers. He has published 1 monograph, 3 edited volumes, 8 book chapters and over 180 peer reviewed articles. His research explores the interfaces of multiscale modeling, high performance computing, optimization and uncertainty quantification. Applications range from aerodynamics to nanofluidics and from cancer induced angiogenesis to artificial fish schools.

Thursday, February 27, 2014
3:00 PM
Grace Ford Salvatori, Room 118 (GFS 118)

Refreshments will be served.

Learning Combustion from Expanding Flames

Fujia Wu

Ph.D. Candidate
Department of Mechanical and Aerospace Engineering
Princeton University
Princeton, New Jersey

Quantitative prediction of combustion phenomena and their active control require fundamental understanding of chemical kinetics as well as the associated flow which is frequently turbulent. Both processes pose formidable challenges due to species complexity, nonlinearity and the large range of length and time scales. Expanding flames, laminar or turbulent, implemented in a specially-designed dual-chamber fan-stirred vessel, not only have tractable initial and boundary conditions but can also be achieved with high pressures and large Reynolds numbers. Consequently it is suitable for the study of various aspects of combustion, as will be demonstrated by three problems of interest, namely the determination of laminar flame speeds, flamefront instabilities, and flame dynamics in turbulent flows. Specifically, when a flame is in quiescence and free from flame-front instabilities, high fidelity laminar flame speeds can be acquired and subsequently used to partially validate and develop chemical kinetic models. Second, with increasing pressure and molecular diffusivity of the deficient species, intrinsic flame-front hydrodynamic and diffusional-thermal instabilities are promoted which in turn accelerate the flame. This self-acceleration of flames is systematically quantified. Finally, when the flame propagates into a near-isotropic turbulent flow, turbulent combustion of premixed flames is then studied, resulting in well-defined data and fundamental understanding of the underlying turbulent flame structure and propagation mechanism.

Fujia Wu is a Ph.D. candidate in Mechanical and Aerospace Engineering at Princeton University, working with Professor Chung K. Law. He received his Bachelor degree in Vehicle Engineering in 2006 and a Masters in Engineering Thermophysics in 2008, both from Tsinghua University in Beijing, China. In 2010, he received a Masters in Mechanical and Aerospace Engineering from Princeton University. His dissertation research is on the dynamics, instabilities and chemistry of laminar and turbulent flames. His research accomplishments and presentations have been recognized through multiple awards of various nature.

Monday, March 3, 2014
11:00 AM
Laufer Library (RRB 208)

Refreshments will be served.

Experiments on the Rayleigh-Taylor and Richtmyer-Meshkov Instabilities

Jeffrey W. Jacobs

Department Head, Elwin G. Wood Distinguished Professor
Department of Aerospace and Mechanical Engineering
University of Arizona

Rayleigh-Taylor and Richtmyer-Meshkov instabilities are two very fundamental fluid phenomena that are of importance to the fields of astrophysics, inertial fusion and supersonic combustion. Rayleigh-Taylor instability occurs whenever a heavy fluid lies over a lighter one in a constant gravitational field and Richtmyer-Meshkov instability is the related fluid instability that is generated when the acceleration is impulsive in nature, such as that generated by a shock wave that passes over an interface separating two differing density gases. Experiments will be presented carried out in four experimental apparatuses. Incompressible Rayleigh-Taylor instability is generated by accelerating a two-liquid system downward at a rate greater than gravity in one of two drop towers driven either by a weight and pulley system or by linear induction motors. Richtmyer-Meshkov instability is studied in experiments that utilize a shock wave to impulsively accelerate an interface generated by flowing light and heavy gases from opposite ends of a vertical shock tube. In addition, compressible Rayleigh-Taylor instability is generated in an expansion tube in which an expansion wave is used to produce a non-constant but continuous acceleration acting on a gas interface. In all of these experiments initial perturbations are generated by harmonically oscillating the fluids either horizontally to produce standing internal waves having sinusoidal shape, or vertically to produce Faraday resonance resulting in more random short wavelength perturbations. Diagnostics used include planar laser induced fluorescence, planar Rayleigh scattering, shadowgraph and ordinary backlit imaging to visualize the flows. Experimental measurements will be compared to existing theory and models.

Jeff Jacobs has been a faculty member with the Department of Aerospace and Mechanical Engineering at the University of Arizona since 1990 where he now serves as the department head. He received his B.S., M.S. and Ph.D. degrees in engineering from UCLA and after receiving his Ph.D., he was a research fellow at Caltech from 1987 through 1990. He is a recipient of the Presidential Young Investigator Award from the National Science Foundation and the François Frenkiel Award for Fluid Mechanics from the American Physical Society. His research interests include hydrodynamic stability with emphasis in flows with accelerated interfaces, gas dynamics, turbulent mixing, and optical flow diagnostic techniques.

Wednesday, March 5, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Towards Realistic Direct Numerical Simulations of Turbulent Combustion

Ankit Bhagatwala

Postdoctoral Research Fellow
Combustion Research Facility
Sandia National Laboratories
Livermore, CA 94550

Combustion remains the primary source of energy for power generation and transportation and will likely continue to do so well into this century. Combustors typically operate at high Reynolds numbers in a turbulent environment for high efficiency. My research fills the gap in our understanding of fundamental chemical and fluid dynamic processes underlying these systems through Direct Numerical Simulations (DNS) that resolve all relevant chemical and fluid dynamic time and length scales. I will present results from two recent DNS studies at Sandia. The first study is based on a new engine concept called Homogeneous Charge Compression Ignition (HCCI), with potential diesel-like efficiency with low NOx and soot, that relies primarily on autoignition of the fuel/air mixture rather than flame propagation, as in traditional SI engines. Two and three-dimensional simulations were performed with parametric variations in thermal and mixture stratification. A special feature of these simulations is the use of compression heating through mass source/sink terms to emulate the compression and expansion resulting from piston motion. The second study is a comparison between a DNS of a temporally evolving planar slot jet flame and experimental measurements within a spatially evolving axisymmetric jet flame with dimethyl ether (DME), a bio-alcohol, as the fuel. Joint scalar statistics of OH and CH2O (formaldehyde) are compared between DNS and experiment. The efficacy of OH/CH2O product imaging as a surrogate for peak heat release rate is investigated. I will conclude with some thoughts and ideas about the future direction of DNS based approaches.

I received my B.S and M.S degrees in Naval Architecture and Ocean Engineering from the Indian Institute of Technology Madras in 2005 where my Masters thesis was focused on compliant coatings for their potential to reduce skin friction drag. I received my Ph.D. in Aeronautics and Astronautics from Stanford in 2011, working on spherical shock-turbulence interaction and Richtmyer-Meshkov instability in spherical geometry. After my Ph.D., I joined the Combustion Research Facility at Sandia National Laboratories (SNL) as a postdoctoral research fellow where I am working on petascale simulations of turbulent combustion with application to internal combustion engines and gas turbines. My work at SNL is part of a broader DOE Combustion Energy Frontier Research Center (CEFRC) focused on developing predictive models for 21st century transportation fuels.

Monday, March 10, 2014
2:00 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served.

Bio-Inspired Soft Robotics: New Ways of Sensing, Actuation, and Integration

Yong-Lae Park

Assistant Professor
Robotics Institute and the School of Computer Science
Carnegie Mellon University

Innovation in soft sensor and actuator technologies is extremely important for future robots with medical applications, such as human rehabilitation and minimally invasive surgeries, where close interactions between human and machines are are critical. This talk will describe the design and manufacturing processes for developing biologically inspired soft robots for healthcare, focusing on three specific areas: soft artificial skin sensors, soft artificial muscle actuators and soft wearable robots for human assistance and rehabilitation. The talk will also discuss advanced manufacturing technologies for building multi-material and multi-functional 3-D soft smart composite microstructures.

Yong-Lae Park is an Assistant Professor in the Robotics Institute and the School of Computer Science at Carnegie Mellon University. Prior to joining CMU in 2013, Prof. Park completed his Ph.D. degree in Mechanical Engineering from Stanford University (2010), and conducted postdoctoral research in the School of Engineering and Applied Sciences and the Wyss Institute for Biologically Inspired Engineering at Harvard University. His research focuses on bio-inspired design and manufacturing of soft robots and microrobots. He is the winner of the Best Paper Award from the IEEE Sensors Journal, in 2013, a NASA Tech Brief Award from the NASA Johnson Space Center, in 2012, and a Technology Development Fellowship for independent postdoctoral research from the Wyss Institute at Harvard University, in 2010. His paper on soft artificial skin was selected as a cover article of the IEEE Sensors Journal, and his work on soft wearable robots was recently featured in Discovery News, New Scientist, and Pittsburgh Post-Gazette.

Wednesday, March 12, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

—John Laufer Lecture—

A Stretchy, Curvy Future for Electronics: From Brain Interfaces to Fly’s Eye Cameras

John A. Rogers

Swanlund Chair Professor
Department of Materials Science and Engineering
University of Illinois at Urbana/Champaign
Urbana, Il

Recent advances in materials, mechanics designs and fabrication techniques enable construction of high performance optical, electronic and mechanical microsystems that can flex, bend, fold and stretch, with ability to accommodate large (>>1%) strain deformation, reversibly and in a purely elastic fashion. Such systems open up new engineering opportunities in bio-inspired device design and in intimate, multifunctional interfaces to biological systems. This talk summarizes fundamental and applied aspects of two specific examples: (1) hemispherical digital imagers that incorporate essential design features found in the arthropod eye and (2) injectable, cellular-scale light emitting diodes for wireless control of complex behaviors in animal models, via the techniques of optogenetics.

Professor John A. Rogers obtained BA and BS degrees in chemistry and in physics from the University of Texas, Austin, in 1989. From MIT, he received SM degrees in physics and in chemistry in 1992 and the PhD degree in physical chemistry in 1995. From 1995 to 1997, Rogers was a Junior Fellow in the Harvard University Society of Fellows. He joined Bell Laboratories as a Member of Technical Staff in the Condensed Matter Physics Research Department in 1997, and served as Director of this department from the end of 2000 to 2002. He is currently Swanlund Chair Professor at University of Illinois at Urbana/Champaign, with a primary appointment in the Department of Materials Science and Engineering. He is also Director of the Seitz Materials Research Laboratory. Rogers’s research includes fundamental and applied aspects of materials and patterning techniques for unusual electronic and photonic devices, with an emphasis on bio-integrated and bio-inspired systems. He has published more than 400 papers and is inventor on over 80 patents, more than 50 of which are licensed or in active use. Rogers is a Fellow of the IEEE, APS, MRS and AAAS, and he is a member of the National Academy of Engineering. His research has been recognized with many awards, including a MacArthur Fellowship in 2009, the Lemelson-MIT Prize in 2011 and, in 2013, the MRS Mid-Career Researcher Award, the ASME Robert Henry Thurston Award and the Smithsonian Award for American Ingenuity in the Physical Sciences.

Wednesday, March 26, 2014
1:00 PM
Davidson Conference Center (DCC), Club Room

Reception at Noon PM in the Vineyard Room
Refreshments at 2:00 PM in the Vineyard Room

Structure of Highly Turbulent Premixed Flames

Guillaume Blanquart

Assistant Professor
Mechanical and Civil Engineering Department
California Institute of Technology
Pasadena, CA

In turbulent premixed flames, an important quantity is the relative magnitude of the scales of turbulence to that of the flame. This ratio is referred to as the Karlovitz number (Ka). In the case of low to moderate Ka numbers, the flame is “thinner” than any turbulent scales and is often referred to as a “flamelet”. A lot of studies in the past have focused on characterizing this limit, both from a theoretical and modeling point of view. Unfortunately, the combustion regimes found in aircraft combustors are characterized by a high Ka number, for which a lot less is known. The objective of the present work is gain insight into the structure of turbulent premixed flames under relevant conditions, i.e. highly turbulent (high Ka number) and for realistic fuels (large hydrocarbons). The present work relies on the use of high fidelity Direct Numerical Simulations (DNS). I will start the presentation by addressing two important requirements for these simulations, namely an efficient (i.e. skeletal and yet accurate) chemical model to describe the fuel oxidation and an efficient time integration scheme for the stiff chemical source terms. With these tools in hand, we can analyze the intrinsically two-way coupling of highly turbulent flames. In particular, I will address the effects of turbulence on the chemistry and I will focus on the chemical structure of the resulting turbulent flame. I will also discuss the particular effects the flame has on the incoming turbulence and compare these effects to those found in low Ka flames.

Guillaume Blanquart is an Assistant Professor in the Mechanical and Civil Engineering Department at Caltech. He received his BS and his first MS in Applied Mathematics from École Polytechnique, France, in 2002. He received a second MS in Aeronautics and Astronautics in 2004 and his PhD in Mechanical Engineering in 2008, both from Stanford University. He continued as a Postdoctoral Scholar under the supervision of Professor Heinz Pitsch at Stanford University before joining Caltech in 2009. He received the NSF Career Award in 2011 and the DOE Early Career Award in 2011. His research is funded currently by the DOE, NSF, AFOSR, Boeing, and Energent.

Wednesday, April 2, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

High-Order Discontinuous Galerkin Simulation of Flapping Wings Designed for Energetically Optimal Flight

Per-Olof Persson

Assistant Professor
Department of Mathematics
University of California, Berkeley

The numerical simulation of flapping flight is a challenging problem, partly because of the large deformations of the computational domain, the transitional flows, and the complex geometries. We present our recent results with high-order accurate discontinuous Galerkin methods, which are capable of accurately solving complex flow problems on unstructured meshes. We generate tetrahedral meshes using the DistMesh mesh generator and the Delaunay refinement method. A nonlinear elasticity analogy is used both for curving the elements to align with the boundaries and for deforming the mesh due to the moving domains, which are modeled by a mapping-based high-order accurate Arbitrary Lagrangian-Eulerian formulation. The equations are discretized using the Compact DG method, and solved efficiently in parallel using Newton-Krylov solvers and optimized element ordering. We demonstrate our solvers in the setting of a multi-fidelity framework for inverse design of flapping wings. A panel method-wake only energetics solver is used to define the energetically optimal wing shapes and flapping kinematics. Candidate designs are then simulated using our high-order solvers, to gain insight into practical wing designs, the influence of viscous effects, and when faster low-fidelity simulation tools can be sufficiently accurate.

Per-Olof Persson is an Associate Professor of Mathematics at the University of California, Berkeley, since July 2008. Before then, he was an Instructor of Applied Mathematics at the Massachusetts Institute of Technology, from where he also received his Ph.D. in 2005. His current research interests are in high-order discontinuous Galerkin methods for computational fluid and solid mechanics, with applications to many important problems such as the simulation of flapping flight and vertical axis wind-turbines, quality factor predictions for micromechanical resonators, and noise prediction for aeroacoustic phenomena.

Wednesday, April 9, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Towards Automated Manufacturing of Geometrically-Complex Heterogeneous Structures

Satyandra K. Gupta

Professor
Department of Mechanical Engineering
and
Institute for Systems Research at the Advanced Manufacturing Lab
University of Maryland
College Park, MD

Biological creatures often utilize geometrically-complex heterogeneous structures to exhibit remarkable capabilities. The geometric complexity arises due the large number of features in the structure and the underlying shape complexity of the individual features. The heterogeneity manifests itself at multiple size scales due to the use of multiple different materials. Many application areas such as robotics, bio-medical devices, thermal management systems, and aerospace structures can significantly benefit from utilizing geometrically-complex heterogeneous structures. The traditional approach to manufacturing that involves fabricating constituent components and assembling them together is not well suited to realize such structures in a cost-effective manner. This seminar will begin by describing a new manufacturing process called in-mold assembly. This process integrates customized mechanisms inside the mold to morph the mold cavity during the molding operation to enable the realization of geometrically-complex heterogeneous structures. These mechanisms are realized using 3D printing and serve the role of robots during in-mold assembly. This automates the manufacturing operation by eliminating the need for post-molding assembly operations. The material is assembled in the liquid state during in-mold assembly, and hence articulated heterogeneous structures that would have been otherwise impossible to realize can be made. This process is inherently parallel in nature, and hence a large number of assembly operations can be performed concurrently in a cost effective manner. This process also eliminates the need for manually handling small parts and hence can also be used to perform assembly at small size scales. Topics covered during the seminar will include thermo-mechanical characteristics of the in-mold assembly process at macro and mesoscale and the associated process model. The second part of the seminar will describe computational foundations for automatically designing, optimizing, and fabricating molds to enable digital manufacturing of the desired structures from CAD models. This part will also describe mold design solutions and manufacturability rules associated with the in-mold assembly of polymer composite structures. The final part of the seminar will describe how in-mold assembly is being used to realize novel bio-inspired robots, bio-medical devices, and polymer heat exchangers.

Satyandra K. Gupta is a Professor in the Department of Mechanical Engineering and the Institute for Systems Research at the University of Maryland, College Park. He is the director of the Advanced Manufacturing Laboratory. He was the founding director of the Maryland Robotics Center. Prior to joining the University of Maryland, he was a Research Scientist in the Robotics Institute at Carnegie Mellon University. Currently, he is on an IPA assignment at the National Science Foundation and serves as a program director in the Division of Information and Intelligent Systems. He manages National Robotics Initiative. Dr. Gupta’s interest is broadly in the area of automation. He is specifically interested in automation problems arising in Engineering Design, Manufacturing, and Robotics. He is a fellow of the American Society of Mechanical Engineers (ASME). He has served as an Associate Editor for IEEE Transactions on Automation Science and Engineering, the ASME Journal of Computing and Information Science in Engineering, and SME’s Journal of Manufacturing Processes. Dr. Gupta has received several honors and awards for his research contributions. Representative examples include: a Young Investigator Award from the Office of Naval Research in 2000, a Robert W. Galvin Outstanding Young Manufacturing Engineer Award from the Society of Manufacturing Engineers in 2001, a CAREER Award from the National Science Foundation in 2001, a Presidential Early Career Award for Scientists and Engineers (PECASE) in 2001, Invention of the Year Award in Physical Science category at the University of Maryland in 2007, Kos Ishii-Toshiba Award from ASME Design for Manufacturing and the Life Cycle Committee in 2011, and Excellence in Research Award from ASME Computers and Information in Engineering Division in 2013. He has also received six best paper awards at conferences and 2012 Most Cited Paper Award from Computer Aided Design Journal.

Friday, April 11, 2014
3:30 PM
Grace Ford Salvatori, Room 101 (GFS 101)

Refreshments will be served at 3:15 pm.

Joint seminar with the USC Center for Applied Mathematical Sciences

Explorations in Biofluids: A Tale of Two Tails

Lisa J. Fauci

Pendergraft Nola Lee Haynes Professor of Mathematics
Tulane University
New Orleans, LA

In the past decade, the study of the fluid dynamics of swimming organisms has flourished. With the possibility of using fabricated robotic micro swimmers for drug delivery, or harnessing the power of natural microorganisms to transport loads, the need for a full description of flow properties is evident. At a larger scale, the swimming of a simple vertebrate, the lamprey, can shed light on the coupling of neural signals to muscle mechanics and passive body dynamics in animal locomotion. We will present recent progress in the development of a multiscale computational model of the lamprey that examines the emergent swimming behavior of the coupled fluid-muscle-body system. At the micro scale, we will examine the function of a flagellum of a dinoflagellate, a type of phytoplankton. We hope to demonstrate that, even when the body kinematics at zero Reynolds number are specified, there are still interesting fluid dynamic questions that have yet to be answered.

Lisa Fauci was educated in the New York City public school system, received her B.S. at Pace University, and later her Ph.D. in Mathematics at the Courant Institute of Mathematical Sciences, NYU in 1986. She joined the faculty of Tulane University in New Orleans the same year. She was the founding Director of the Center for Computational Science at Tulane in 2001, currently serves as an Associate Director, and is the Nola Lee Haynes Pendergraft Professor of Mathematics. She has held visiting positions at New York University and the University of Utah, and has lectured throughout the world. Her research lies at the interface of mathematics, scientific computing and biology.

Wednesday, April 16, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Toward Accurate Combustion Simulations with Stiff Chemistry

Tianfeng Lu

Assistant Professor
Department of Mechanical Engineering
University of Connecticut

Practical combustion systems involve complex and stiff chemistry that is difficult to simulate, particularly when strong chemistry-turbulence interactions are present. Accurate resolution of chemistry and its response to flow variation is key to create a predicting power for chemically reacting flows, and it requires efficient and accurate methods for mechanism reduction, stiff chemistry solver, direct flame simulations, computational diagnostics, and combustion modeling, etc. This presentation will show our effort on theoretical and numerical development in response to these challenges. Specifically, reduced mechanisms were obtained for gasoline, diesel, kerosene, and renewable fuels, such as ethanol and biodiesel, using systematic approaches of directed relation graph (DRG), analytically solved linearized quasi steady state approximations, and dynamic chemical stiffness removal. New integration schemes will be introduced for efficiently solving stiff chemistry coupled with transport when conventional solvers are not applicable. For computational diagnostics, chemical explosive mode analysis (CEMA) and bifurcation analysis will be presented for systematic identification of critical flame features in complex flow fields, such as local ignition/extinction, flame instabilities, and flame fronts. Results from collaborative efforts on direct numerical simulation (DNS) with the nonstiff reduced mechanisms and CEMA will be shown for turbulent jet flames and homogeneous charge compression ignition combustion. These methods may also be extended to solve other problems involving multi-timescales and large data, e.g. in biological systems and informatics.

Tianfeng Lu received his B.S. and M.S. in Engineering Mechanics from Tsinghua University in 1994 and 1997, respectively, and Ph.D in Mechanical and Aerospace Engineering from Princeton University in 2004. Since then he has been a postdoctoral fellow and a research staff at Princeton. He joined the Department of Mechanical Engineering in the University of Connecticut as an Assistant Professor in 2008. Lu’s primary research interest is in combustion and computational fluid dynamics with special interests in mechanism reduction, stiff chemistry solver, and computational flame diagnostics. He is a member of the Combustion Institute, Associate Fellow of the AIAA, and the recipient of the inaugural Irvin Glassman young investigator award from the Eastern States Section of the Combustion Institute.

Thursday, April 17, 2014
11:00 AM
Laufer Library (RRB 208)

Refreshments will be served at 10:45 am.

Integration of Geometry and Analysis

Ahmed A. Shabana

Richard and Loan Hill Professor of Engineering
Department of Mechanical and Industrial Engineering
University of Illinois at Chicago

A necessary step in the design of mechanical and aerospace systems is performing flexible multibody system (MBS) analysis. This step is necessary in order to accurately determine the stresses resulting from different loading conditions. Nonetheless, this design step can be very costly and time consuming and requires the use of at least three different computer codes. A computer aided design (CAD) software is required for the solid modeling, a finite element (FE) code is required to develop the analysis mesh, and a flexible MBS code is needed as the main processor for performing the analysis. There are serious compatibility problems rooted in the FE kinematic description when these different codes are used. Because of these fundamental problems, a successful integration of CAD and analysis (I-CAD-A) was not feasible. Furthermore, because of the need for accurate geometric description (kinematics), the field of computational mechanics is currently witnessing significant changes that will lead to new generation of FE and MBS computational algorithms. With the introduction of new FE formulations such as the absolute nodal coordinate formulation (ANCF), it is feasible to develop a new generation of software that allows for successful integration of CAD and analysis. This lecture provides an overview of some of the approaches used in the deformation analysis and explains the need for using accurate geometry description in the analysis and design of MBS applications.

Ahmed Shabana is a Professor of Mechanical Engineering at the University of Illinois at Chicago (UIC). He joined the faculty of the Department of Mechanical Engineering at UIC in 1983 after receiving his Ph.D. degree from the University of Iowa. His research interest is in the area of large scale computations as applied to dynamic systems. Dr. Shabana is the author of several books in the areas of multibody system dynamics, vibration, and railroad vehicle system. He is a Fellow of ASME.

Wednesday, April 23, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Mobile Teaching for Engineering Education

Bingen Yang

Professor
Dept. of Aerospace and Mechanical Engineering
University of Southern California
Los Angeles, CA

This presentation is about the results from an on-going project on teaching innovations that is jointly undertaken by me and USC Viterbi DEN. In this talk, I will show you step-by-step on how to quickly convert your normal teaching with paper note/blackboard-writing and PPT/Keynote presentation to mobile teaching with mobile devices (tablets and smart phones) and iclouding computing. The benefit of mobile teaching is multi-fold:

  • Versatile in presentations (integration of different types of course materials)
  • High-quality and high-resolution real-time note writing
  • High portability and easy set-up
  • Reduced effort and time for course preparation (by at least 50%)
  • e-Grading made possible
  • Multi-media enrichment of lectures and enhancement of instructor-student interactions
  • Mostly green or paperless
  • Instant back-up and convenient data transfer through the cloud

The proposed mobile teaching is easy to learn, and is viable for both DEN and non-DEN classes.

Wednesday, April 30, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.


Fall, 2014

Wonderful Fluids: From Hovering Hats to Bacterial Waves

Eva Kanso

Associate Professor
Department of Aerospace & Mechanical Engineering
University of Southern California
Los Angeles, CA

I am happy to respond to the AME graduate students who recommended that I give a department seminar. Please join me as I take you on a tour of some of the recent research activities in my biodynamics lab, emphasizing some unintuitive results in biological solid-fluid interactions that can be simply described as wonderful!

Wednesday, September 10, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Diagnostics and Modeling of Plasma Assisted Combustion Kinetics

Igor V. Adamovich

Professor
Department of Mechanical and Aerospace Engineering
The Ohio State University
Columbus, OH

Recent experimental studies of repetitive nanosecond pulse discharges demonstrate their significant potential for plasma assisted ignition and combustion. The main advantage of using these discharges for ignition is efficient generation of electronically excited and radical species, such as O and H atoms, as well as OH. In recent experiments, time-resolved temperature, N2 vibrational level populations, absolute O, H, and OH number densities, and ignition delay time are measured in premixed hydrocarbon-air, hydrogen-air, and hydrogen-oxygen-argon flows excited by repetitive nanosecond pulse discharges in plane-to-plane and point-to-point geometries. Time-resolved temperature and OH number density in lean H2-air, CH4-air, C2H4-air, and C3H8-air mixtures are measured by picosecond, broadband Coherent Anti-Stokes Raman Spectroscopy (CARS) and by OH Laser-Induced Fluorescence (LIF). Time-resolved, spatially resolved temperature and absolute number densities of OH and H in Ar-O2-H2 mixtures are measured by UV Rayleigh scattering, LIF, and Two-Photon Absorption LIF (TALIF), respectively. The results demonstrate that ignition occurs due to efficient generation of radical species in the discharge, and provide insight into the kinetic mechanism of low-temperature plasma assisted ignition. Time-resolved electron density, electron temperature, and electric filed in transient nanosecond pulse discharges are measured by Thomson scattering and psec CARS / 4-wave mixing. The results are compared with kinetic modeling calculations, showing the need for development of an accurate, predictive low-temperature plasma / fuel chemistry model applicable to fuels C3 and higher.

The principal challenges in development of a predictive kinetic model include (i) lack of “conventional” chemical kinetics mechanisms validated at low temperatures, and (ii) lack of data on rates and products of reactions of excited species generated in the plasma, and their coupling with fuel-air plasma chemistry. “Conventional” combustion chemistry mechanisms have been developed for relatively high temperature conditions, and their applicability below ignition temperature, common in plasma assisted combustion environments, needs to be critically evaluated. This requires time-resolved measurements of radical species concentrations during low-temperature fuel oxidation, when an initial pool of primary radicals (O, H, and OH) is generated in the plasma, such as in the late afterglow of an electric discharge. This approach allows isolating relatively slow “conventional” low-temperature fuel oxidation reactions triggered by the radicals from the reactions of excited species generated in the discharge, which decay relatively rapidly. A complementary approach is to focus on kinetics of “rapid” reactions of excited species in the electric discharge and their effect on production of radicals in the early afterglow. These experiments would provide key data on coupling of molecular energy transfer processes in the plasma with “conventional” chemical reactions. Time-resolved measurements of temperature, excited species, and radical species concentrations are critical for characterization of the nonequilibrium reacting mixture at these conditions. Kinetic modeling of recent experiments in nanosecond pulse electric discharges in air suggest that the role of electronically excited N2* molecules on chemical reactions in the afterglow, such as NO generation reactions, has been significantly underestimated in the past. Further experiments in fuel-air mixtures are expected to provide additional data on the role of these excited species on low-temperature fuel-air chemistry.

After receiving his master’s degree in mechanical and aerospace engineering in 1987 from Moscow Institute of Physics and Technology, Igor Abamovich was a research associate in the Aerothermodynamics Laboratory at the A.V. Lykov Heat and Mass Transfer Institute of the Soviet Academy of Sciences in Minsk, USSR. In 1993 he earned his Ph.D. in chemical Physics from Ohio State then worked as a research scientist and a post-doctoral researcher in the Nonequilibrium Thermodynamics Laboratories at Ohio State. Since 2009, he has been a professor in the Department of Mechanical and Aerospace Engineering at Ohio State with research interests in the kinetics of gases and plasmas at extreme thermodynamic disequilibrium; sustaining and stability control of high-pressure weakly ionized plasmas; high-speed flow control by plasmas; nonequilibrium MHD flows; plasma assisted combustion; molecular energy transfer processes; electron and ion kinetics; and chemical reactions among excited species.

Wednesday, September 17, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

High Speed and Multidimensional Combustion Diagnostics

Lin Ma

Associate Professor
Department of Aerospace and Ocean Engineering
Department of Mechanical Engineering
Virginia Tech, Blacksburg, VA 24060

This talk describes our efforts to enable high speed and multidimensional measurements in turbulent combustion systems, which have been long desired for resolving the inherent three-dimensional spatial features and temporal dynamics of turbulent flames. This talk uses several examples to introduce our recent work on multidimensional diagnostics using tomography, and to discuss the unique opportunities that they can enable. Examples include the multidimensional measurements of mixture fraction, temperature fields, chemical species distribution, and instantaneous 3D flame topography. Combined with ruggedized hardware and robust data analyzing algorithms, such measurements have been successfully demonstrated in both laboratory flames and also practical combustion systems including a model scramjet combustor.

From 2000-2006, Lin Ma worked as a graduate research assistant in the High Temperature Gasdynamics Laboratory (HTGL) at Stanford University. Dr. Ma started his faculty career in 2006 after completing his PhD work, focusing on multidimensional laser diagnostics. His work on 2D mixture fraction measurement was recognized by the National Science Foundation with a CAREER award. He is also active in teaching and professional services. His teaching and research efforts were recognized by a Board of Trustee Award, and he is an active member of several professional organizations and technical committees.

Wednesday, October 1, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

On the Connection between Wave Resonance, Shear Instability and Oscillator Synchronization

Anirban Guha

Postdoctoral Fellow
Atmospheric and Oceanic Sciences
University of California at Los Angeles
Los Angeles, CA

Homboe (Geophys. Publ., 24, 1962, pp. 67–112) postulated that resonant interaction between two or more progressive, linear interfacial waves produces exponentially growing instabilities in idealized (broken-line profiles), homogeneous or density-stratified, inviscid shear layers. We have generalized Holmboe’s mechanistic picture of linear shear instabilities by (i) not initially specifying the wave type, and (ii) providing the option for non-normal growth. We have demonstrated the mechanism behind linear shear instabilities by proposing a purely kinematic model consisting of two linear, Doppler-shifted, progressive interfacial waves moving in opposite directions. Moreover, we have found a necessary and sufficient condition for the existence of exponentially growing instabilities in idealized shear flows. The two interfacial waves, starting from arbitrary initial conditions, eventually phase-lock and resonate (grow exponentially), provided the necessary and sufficient condition is satisfied. The theoretical underpinning of our wave interaction model is analogous to that of synchronization between two coupled harmonic oscillators. We have re-framed our model into a nonlinear autonomous dynamical system, the steady-state configuration of which corresponds to the resonant configuration of the wave interaction model. When interpreted in terms of the canonical normal-mode theory, the steady-state/resonant configuration corresponds to the growing normal mode of the discrete spectrum. The instability mechanism occurring prior to reaching steady state is non-modal, favoring rapid transient growth. Depending on the wavenumber and initial phase-shift, non-modal gain can exceed the corresponding modal gain by many orders of magnitude. Instability is also observed in the parameter space, which is deemed stable by the normal-mode theory. Using our model we have derived the discrete spectrum non-modal stability equations for three classical examples of shear instabilities: Rayleigh/Kelvin-Helmholtz, Holmboe and Taylor-Caulfield. We have shown that the necessary and sufficient condition provides a range of unstable wavenumbers for each instability type, and this range matches the predictions of the normal-mode theory.

Wednesday, October 8, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Random Walks, Markov Chains, and Cancer Progression Models from Longitudinal and Autopsy Data

Paul Newton

Professor
Department of Aerospace & Mechanical Engineering
University of Southern California
Los Angeles, CA

We will describe models of metastatic cancer progression using Markov chain modeling on a directed graph of nodes that are the various anatomical sites where metastatic tumors can form for a given type of primary cancer. We use metastatic tumor distributions gathered from historical autopsy data, as well as current longitudinal data sets to estimate the transition probabilities (stochastic parameters) from site to site. This creates a systemic network diagram from which we can calculate reduced two-step diagrams using the fact that the systems converge to their steady-state distribution after roughly two steps. The diagrams are used to categorize metastatic sites as ‘sponges’ or ‘spreaders,’ as well as to run hypothetical therapeutic scenarios based on Monte Carlo simulations of progression with mean first-passage times as a surrogate timescale measure. A useful metric which we describe is the notion of metastatic entropy and how is correlates with graph conductance dictating Markov convergence rates, mixing times, and complexity. If time permits, we will describe a more fine-scale cell based model which is driven by a stochastic Moran process acting on a heterogeneous population of cells trafficking across the directed graph to various sites, governed by a fitness landscape, with simple point-mutations, interacting via the prisoner’s dilemma paradigm in which the cancer cells are the ‘defectors’ and the healthy cells are the ‘cooperators.’

Wednesday, October 15, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Vortex Breakdown, Instability, and Sensitivity of a T-Junction Flow

Kevin K. Chen

Viterbi Fellow
Department of Aerospace & Mechanical Engineering
University of Southern California
Los Angeles, CA

The fluid flow through a T-shaped pipe bifurcation (with the inlet at the bottom of the “T”) is a very familiar occurrence in both natural and man-made systems. Everyday examples include industrial pipe networks, microfluidic channels, and blood flows near the heart and brain. Yet, many questions about the flow physics remain, and prior analyses have been rudimentary. This seminar addresses three important questions: 1) How does the flow evolve with Reynolds number? 2) What are the important flow structures? 3) Lastly, where in the flow do the stability eigenvalues exhibit high sensitivity to dynamical perturbations? Much of this research focuses on the relation between vortex breakdown in the outlet pipes and the regions of stability, receptivity, and sensitivity as defined by linear global stability theory. The vortex breakdown, which occurs above a Reynolds number of 320, gives rise to recirculation regions near the junction; a supercritical Hopf bifurcation first occurs at a Reynolds number of 556. Regions of growth are concentrated in the outlet pipes, but regions of receptivity to initial conditions and external disturbances are confined to small regions near the walls of the inlet and junction. Finally, the flow is most sensitive to localized feedback and to base flow modifications in the recirculation regions, which we explain using an inviscid Lagrangian short-wavelength theory. To the best of our knowledge, this is the most complicated flow for which anyone has observed the relation between sensitivity and recirculation.

Wednesday, October 22, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Self-Similarity in the Inertial Region of Wall Turbulence

Joe Klewicki

Professor
Department of Mechanical Engineering
University of New Hampshire
Durham, NH
and
Department of Mechanical Engineering
University of Melbourne
Parkville, Victoria, Australia

The inverse of the von Karman constant, κ, is the leading coefficient in the equation describing the logarithmic mean velocity profile in wall bounded turbulent flows. Previous research (J. Fluid Mech., 638, 2009, 73; J. Fluid Mech., 718, 2013, 596.) demonstrates that the asymptotic value of κ derives from an emerging condition of dynamic self-similarity on an interior inertial domain, and that these dynamics induce a geometrically self-similar hierarchy of scaling layers. First-principles based analyses are used to reveal a number of properties associated with the asymptotic value of κ. The development leads toward, but terminates short of, analytically determining a value for κ. This analysis does, however, suggest the distinct possibility that κ = Φ-2 = 0.381966…, where Φ – (1 + √5)/2 is the golden ratio. Empirical measures derived from the theory are used to explore the veracity and implications of κ = Φ-2. Consistent with the differential transformations underlying the invariant form admitted by the governing mean equation, it is further demonstrated that the value of κ arises from two geometric features associated with the inertial turbulent motions responsible for momentum transport. One nominally pertains to the shape of the relevant motions as quantified by their area coverage in any given wall-parallel plane, and the other pertains to the changing size of these motions in the wall-normal direction. Data from direct numerical simulations and higher Reynolds number experiments convincingly support the self-similar geometric structure indicated by the analysis.

Joseph Klewicki holds joint appointments in the Departments of Mechanical Engineering at the University of Melbourne, Australia and the University of New Hampshire. He is a Fellow of the American Society of Mechanical Engineers (ASME) and a Distinguished Alumnus of the Michigan State University (MSU) Department of Mechanical Engineering. He received his BS (1983), MS (1985) and PhD (1989) degrees from MSU, Georgia Tech and MSU respectively. His areas of specialization include experimental methods in fluid mechanics, turbulent and unsteady flows, vorticity dynamics, boundary layers, atmosphere surface layer phenomena.

Wednesday, October 29, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Mechanics of Materials at Extreme Environment, at Different Time and Length Scale: A Digital Image Based Approach

Addis Kidane

Assistant Professor
Mechanical Engineering Department
University of South Carolina
Columbia, SC

Understanding the failure mechanism of materials at extreme condition is essential and at the same time challenging. There have been different approaches proposed over the years to studying materials response at extremely aggressive environment, for example high pressure, ultrahigh temperature. With the advent of high speed imaging systems and computer processing power, these days, high quality images can be taken as fast as 200 million frames / sec and one can study the failure mechanisms at such a high events by carefully analyzing the digital images taken during testing. We used a digital image based approach and characterize the deformation mechanism of materials at different loading conditions, at different time and length scale and temperature. In this talk, different examples such as, shock loading of rigid foams and pre-stressed composite, local heterogeneity in polycrystalline materials and deformation of materials at temperature above 1000 °C will be presented.

Addis Kidane is an assistant professor of Mechanical Engineering at the University of South Carolina. He got his Ph.D. from the University of Rhode Island in 2009 and spent 2 years at California Institute of Technology as a postdoctoral scholar before he moved to Columbia. His research interests are in the areas of failure and fracture of materials at extreme conditions, functionally graded materials, digital image based experimental analysis. He is a recipient of the 2013 Haythornthwaite Research Initiation Grants, from the ASME Applied Mechanics Division and the 2014 AFOSR Young Investigator Research Program (YIP) award.

Wednesday, November 5, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Failure Modes of Sandwich and Cellular Materials

E.E. Gdoutos

Professor
Northwestern University
Evanston, Illinois
and
School of Engineering
Democritus University of Thrace
Xanthi, Greece

Sandwich structures consisting of strong and stiff facings and light weight cores offer improved stiffness and strength to weight ratios compared to monolithic materials. Under flexural loading the facings carry almost all of the bending, while the core takes the shear loading and helps to stabilize the facings. Facing materials include metals and fiber reinforced composites. The latter are being used in advanced applications due to the large strength-to-weight ratio. The core materials mainly include honeycombs, cellular foams and wood. In the present seminar the failure behavior of composite sandwich beams subjected to three- and four-point bending will be presented. The beams were made of unidirectional carbon/epoxy facings and various core materials including PVC closed-cell foams, a polyurethane foam and an aluminum honeycomb. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. It was established that the initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions. The crack growth behavior of polymeric foams under mixed-mode loading conditions will also be presented. Polymeric foams are anisotropic materials and crack kinking occurs even though the applied load is perpendicular to the crack plane. The stress analysis of the plate was performed by finite elements. Crack trajectories for various angles of the orientation of the axes of orthotropy of the material with respect to the applied load were obtained.

Wednesday, November 12, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Fluid Mechanics of Drinking and Diving

Sunghwan (Sunny) Jung

Assistant Professor
Department of Biomedical Engineering and Mechanics
Virginia Tech
Blacksburg, VA

Drinking is defined as the animal action of taking water into the mouth, but to fluid mechanists, it is simply one kind of fluid transport phenomena. Classical fluid mechanics show that fluid transport can be achieved by either pressure-driven or inertia-driven processes. In a similar fashion, animals drink water using pressure-driven or inertia-driven mechanisms. For example, domestic cats and dogs lap water by moving the tongue fast, thereby developing the inertia-driven mechanism. We will investigate how cats and dogs drink water differently and discuss the underlying fluid mechanics.

Diving is the activity of falling from air into water, which is somewhat dangerous due to the impact. Humans dive for entertainments less than 20 meters high, however seabirds dive as a hunting mechanism from more than 20 meters high. Moreover, most birds including seabirds have a slender and long neck (13~25 vertebrae) compared to many other animals, which can potentially be the weakest part of the body upon axial impact compression. Motivated by the diving dynamics, we investigate the effect of surface and geometric configurations on structures consisting of a beak-like cone and a neck-like elastic beam. A transition from non-buckling to buckling is characterized and understood through physical experiments and an analytical model.

Sunghwan (Sunny) Jung is a faculty member in the Department of Biomedical Engineering and Mechanics (formerly, Department of Engineering Science and Mechanics), Virginia Tech. Dr. Jung received his PhD in Physics at the University of Texas at Austin and spent two years at the Courant Institute, NYU. Prior to Virginia Tech, he was a math instructor at MIT for two years. His research interests are a variety of fluid mechanics problems occurring in biological systems.

Wednesday, November 19, 2014
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Lost in Fathoms: A Conversation on Art and Science Collaborations at Dawn of the Anthropocene

Anais Tondeur

Visual Artist

Jean-Marc Chomaz

Director of Research at CNRS
Paris, France

Monday, December 1, 2014
11:00 AM – 12:30 PM
Hughes Aircraft Electrical Engineering Building (EEB), Room 132

For more information, click here.