Seminars

Seminars are held Wednesdays, at 3:30 pm, in Seaver Science Library, Room 150 (SSL 150), unless otherwise noted. Refreshments are served at 3:00 pm. Call (213) 740-8762 for further information.

Archive of Seminar Announcements:

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Keynote Lecture Series Archive

Fall, 2017

Human Health in Long Duration Spaceflight

Allison Anderson

Assistant Professor
Ann and H.J. Smead Aerospace Engineering Sciences
University of Colorado at Boulder
Boulder, CO

Human spaceflight has led to some of the most inspirational achievements of the space program, such as walking on the surface of the Moon or repair of the Hubble space telescope, but not without cost to the astronauts performing these feats. The human body is well adapted to its 1G environment on Earth, but experiences physiologic adaptation when living and working in micro- and hypo-gravity. My research develops technologies to measure and improve human health in space. I will discuss ocular changes astronauts experience in long-duration spaceflight, the cause of which is currently unknown. We are developing non-invasive measures of intracranial pressure and exploring the use of artificial gravity to mitigate these changes. I will also discuss mental health in isolated, confined environments. We have used computer-based training and treatment, including virtual reality, to improve behavioral health outcomes in the Arctic and HI-SEAS Mars simulations. Finally, I will discuss injuries that occur while working and training inside the spacesuit and in-suit sensing systems we built to measure and mitigate performance decrement during extravehicular activity. This research is used not only to improve the health of astronauts, but also to improve health for patients on Earth, soldiers, athletes, and people living and working in extreme environments.

Allison Anderson graduated with a B.S. in Astronautics Engineering from USC in 2007 with a minor in Astronomy. She was involved in the AeroDesign team, the LeapFrog team, the Viterbi Student Ambassadors, and Spirits in Action while at USC. She received an M.S. in Aerospace Engineering and an M.S. in Technology Policy in 2011 from MIT, and a Ph.D. in Aerospace Biomedical Engineering in 2014 from MIT. She received a postdoctoral fellowship from the National Space Biomedical Research Institute to work at Dartmouth Hitchcock Medical Center studying human space physiology. She is currently an Assistant Professor at the University of Colorado – Boulder Smead Department of Aerospace Engineering Sciences.

Wednesday, August 23, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Wall Turbulence Structure in the Atmospheric Surface Layer. Scaling and Implications on Wind Turbine Siting

Michele Guala

Associate Professor
St. Anthony Falls Laboratory
Dept. of Civil, Environmental and Geo Engineering
University of Minnesota
Minneapolis, MN

The atmospheric surface layer, under special geophysical conditions, has been used as a canonical representation of wall turbulence flows at high Reynolds numbers. In this presentation I will describe how hotwire field measurements in the SLTEST (Utah) and Super-large-scale particle image velocimetry (SPIV, Hong et al., 2014, Toloui et al. 2014) during natural snowfalls in Minnesota, gave us the opportunity to explore atmospheric flows with unprecedentedly high spatio-temporal resolution. Results from SPIV measurements in the thermally neutral atmospheric surface layer, collected at the EOLOS field station over relatively flat, snow-covered farmland, will be introduced as a fully rough wall boundary layer with a Reynolds number Re τ ~ 106. The data include three time-resolved 15-minute acquisition periods with a field of view extending from 3 m to 19 m above the ground and up to 14 m wide. The flow statistics are validated and supplemented by sonic anemometers from a meteorological tower immediately downstream of the SPIV field of view. The time-resolved planar measurements provide temporal and spatial characterization of key wall turbulence features at high Reynolds number, including ramp-like structures, spanwise vortices, and uniform momentum zones. In comparing the findings to laboratory studies, Reynolds number similarity and the scaling behavior of characteristic properties will be discussed. The limitations of SPIV measurements will be presented using concepts of particle-turbulence interaction and further observations of snow flake dynamics. The impact of large scale flow measurements and turbulent motions will be discussed in the context of wind energy.

Wednesday, August 30, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Coupled Flow and Geomechanics of Petroleum Reservoirs, Aquifers, and Faults

Birendra Jha

Assistant Professor of Petroleum Engineering
Mork Family Department of Chemical Engineering and Materials Science
USC
Los Angeles, CA

Can we inject and produce fluids out of subsurface reservoirs without causing damaging earthquakes? Can we design and control hydraulic fracturing or “fracking” of rocks to maximize productivity but minimize risks? Will underground sequestration of CO2 lead to induced seismicity and eventually CO2 leakage along faults? Did Indian monsoon rainfall have something to do with the Nepal earthquake? These are some of the questions facing the petroleum industry, geothermal industry, environmental scientists, and the geoscience community-at-large. One way to approach these questions, and the approach that we follow, is physics-based modeling of the underlying processes of fluid flow, rock deformation, and faulting or fracturing. We specialize in computational modeling and simulation of continuum scale coupled flow, transport and geomechanical processes. We develop mathematically rigorous and computationally efficient numerical frameworks and conduct lab experiments to understand, forecast and eventually control these processes in nature. I will present some of the salient features of our computational framework that includes a finite element–finite volume method to solve the flow and deformation problems sequentially. Then I will show results from a few studies that attempt to answer the questions posed in the beginning.

Birendra Jha is an Assistant Professor of Petroleum Engineering in the Mork Family Department of Chemical Engineering and Materials Science at USC. He received his masters in Petroleum Engineering from Stanford University and PhD in Civil and Environmental Engineering from MIT. He has several years of experience in the petroleum industry in India and US. In the Geosystems Engineering and Multiphysics Lab (gemlab.usc.edu) at USC, Birendra’s group conducts research in computational and experimental geomechanics funded by the Department of Energy and the Rose Hills Foundation.

Wednesday, September 13, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Design of Linkage Systems to Draw Specified Curves

J. Michael McCarthy

Professor
Mechanical & Aerospace Engineering
University of California at Irvine
Irvine, CA

Kinematic synthesis is a set of mathematical techniques to calculate the dimensions of a mechanism or robot to achieve a desired task. Since the time of James Watt, whose “parallel motion generator” made the double-acting steam engine practical, engineers and mathematicians have studied curve-drawing linkages for practical as well as theoretical purposes. Recent mathematical results prove that such linkages exist for every algebraic curve, and this talk presents an overview of a variety of techniques to design these linkages. One interesting result is that the equations for kinematic synthesis rapidly expand beyond the ability of current computers to solve completely. On the other hand, because Bezier curves can be written as parameterized trigonometric curves, there is a way to design relatively simple linkage systems that draw Bezier approximations to arbitrary curves.

Michael McCarthy is the Director of UCI’s Performance Engineering Program, having completed a eight year term as the Henry Samueli Professor and Director of the Center for Engineering Science in Design at the University of California, Irvine, which supports the design and execution of team engineering projects across the School of Engineering. He received his Ph.D. at Stanford University, and has taught at Loyola Marymount University and the University of Pennsylvania before joining UCI in 1986.
He has over 200 publications and five books including The Geometric Design of Linkages (Springer 2000, 2nd Ed. 2010). He has served as the Editor-in-Chief of the ASME Journal of Mechanical Design (2002-2007) and is the founding Editor-in-Chief of the ASME Journal of Mechanisms and Robotics (2007-2014). His research team is responsible for the Sphinx, Synthetica and MecGen software packages, which extend computer-aided design to spherical and spatial linkage systems and integrate this process with geometric modeling. He has organized and presented tutorials on the design of linkages and robotic systems at ASME and IEEE conferences, including the NSF sponsored 2012 Workshop on 21st Century Kinematics.
He is a Fellow of the American Society of Mechanical Engineers (ASME), and has received the 2009 ASME Machine Design Award, the 2011 ASME Mechanisms and Robotics Award, and the 2013 Robert E. Abbott Lifetime Service Award from the Design Engineering Division of ASME International. At the 2015 Mechanisms and Robotics Conference, he and his co-author received the A.T. Yang Memorial Award in Theoretical Kinematics for their paper on the design of a linkage system that reproduces the flapping motion of a bird in flight.

Wednesday, September 20, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Acoustic Nanofluidics

James Friend

Professor
Medically Advanced Devices Lab
University of California, San Diego
Center for Medical Devices and Instrumentation
Department of Mechanical and Aerospace Engineering
University of California, San Diego
La Jolla, CA

Acoustic waves have found new utility in microfluidics, providing an enormously powerful ability to manipulate fluids and suspended particles in open and closed fluid systems. In this talk, we cover some fundamental and powerful concepts of acoustic wave generation and propagation often overlooked in the literature, and follow it with exploration of new phenomena observed at the nanoscale. In fact, the usefulness of acoustic waves at the micro-scale is even more compelling at the nano-scale, in ways not predicted by classical theory. Particle deagglomeration, fluid pumping, pattern formation, and other curious physical phenomena will be shown in the context of potentially useful applications. Along the way, the fascinating underlying physics tying together the acoustics, fluid dynamics, and free fluid interface in these systems will be described.

James Friend James Friend is a Professor in the Center for Medical Devices and Instrumentation, Department of Mechanical and Aerospace Engineering, at the University of California, San Diego, having received his PhD in mechanical engineering from the University of Missouri-Rolla in 1998. His research interests are diverse, but principally lie in exploring and exploiting acoustic and vibration phenomena at small scales. He has over 260 peer-reviewed research publications, including 138 journal papers and eight book chapters, and 27 patents in process or granted, completed 33 postgraduate students and supervised 18 postdoctoral staff, and been awarded over $25 million in competitive grant-based research funding over his career. He has been fortunate to receive an AIAA Jefferson Goblet Student Paper Award and an ASME Best Paper of Conference Award for a single talk at the AIAA/ASME/AHS/ASC/ASCE Structural Dynamics & Mechanics Conference in 1996; excellence in teaching, early career research, and research awards from the Monash Faculty of Engineering in 2006, 2008, and 2011, respectively; a Future Leader award from the Davos Future Summit in 2008; a Top 10 emerging scientific leader of Australia by Microsoft and The Australian newspaper award in 2009; an award as the corresponding author of one of the top 50 papers of the past 50 years of Applied Physics Letters in 2012; and the IEEE Carl Hellmuth Hertz Ultrasonics Award from the IEEE in 2015.

Wednesday, September 27, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Predator Sensing and Evasion in Fish

Matthew McHenry

Professor
Ecology & Evolutionary Biology
University of California at Irvine
Irvine, CA

The ability to survive encounters with predators is fundamental to the biology of a broad diversity of species. However, it is largely unclear how prey animals sense and evade predators. We study how the sensory and motor systems of fishes facilitate predator evasion with a focus on zebrafish (Danio rerio), where the adults prey on larvae of the same species. We have learned that the flow-sensitive lateral line system is necessary for survival by rapidly triggering a ‘fast start’ escape response. By replicating these conditions with a predator robot and modeling the flow stimulus with computational fluid dynamics, we were able to examine the cues that prey fish use to sense a predator. We similarly modeled the visual stimuli presented by a predator’s approach. For both stimuli, we found that larvae direct their escape rapidly with coarse directionality. By examining these interactions with pursuit-evasion game modeling, we found that these directional responses are effective due to the high speed of the escape relative to the slow approach of the predator. Therefore, zebrafish survive encounters with a predator using either visual or flow cues that trigger a poorly-directed, but fast, escape response.

Matt McHenry is a Professor of Ecology and Evolutionary Biology at UC Irvine. Since his freshman year at Vassar College, Matt has studied biomechanics and sensing in aquatic animals. He earned a doctorate with Mimi Koehl at UC Berkeley and completed postdoctoral studies with George Lauder at Harvard. His lab’s research is supported by the National Science Foundation and the Office of Naval Research.

Wednesday, October 4, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Engineering Reverse Innovations: Using Emerging Markets’ Constraints to Drive the Creation of High-Performance, Low-Cost, Global Technologies

Amos Winter

Ratan N. Tata Career Development Associate Professor
and
Director, Global Engineering and Research (GEAR) Laboratory
 
Department of Mechanical Engineering
Massachusetts Institute of Technology
http://gear.mit.edu/

This presentation will demonstrate how the Global Engineering and Research (GEAR) Lab at MIT characterizes the unique technical and socioeconomic constraints of emerging markets, then uses these insights with engineering science and product design to create high-performance, low-cost, globally-relevant technologies. The talk will focus on three areas of GEAR Lab’s research: high-performance, low-cost prosthetic feet; low-pressure, low-power drip irrigation, and solar-powered desalination. We have created a novel method of connecting the mechanical design of a foot to its biomechanical performance, which allows the stiffness and geometry to be optimized to induce able-bodied walking kinematics and kinetics. This theory has resulted in a single-part foot architecture which can be made of nylon to hit a $10 price point for developing countries, and which will be ruggedized and customizable for the US military/veteran population. By characterizing the coupled fluid/solid mechanics within drip irrigation emitters, we have designed new drippers that operate at 1/7th the pressure of existing products. This technology can cut the overall pressure, pumping power, and energy usage of drip irrigation systems by approximately 50%, and lower the capital cost of off-grid systems by up to 40%. GEAR Lab elucidated a disruptive market opportunity in arid countries for photovoltaic-powered electrodialysis (PV-ED) desalination, which requires half the energy and reduces water wastage from 60% to <10% compared to reverse osmosis. These market insights have led to new spiral-wound and voltage-controlled architectures which substantially reduce capital cost, as well as co-optimized PV and ED systems that are 40% less expensive than current technology. These projects demonstrate how rigorous engineering theory combined with insights on emerging market constraints can yield high-value solutions relevant to poor and rich countries alike.

Amos Winter is the Ratan N. Tata Career Development Associate Professor of Mechanical Engineering at MIT. His research focuses on machine and product design for developing and emerging markets. Prof. Winter earned a BS from Tufts University (2003) and an MS (2005) and PhD (2011) from MIT, all in mechanical engineering. He received the 2010 Tufts University Young Alumni Distinguished Achievement Award, the 2012 ASME/Pi Tau Sigma Gold Medal, was named one of the MIT Technology Review’s 35 Innovators Under 35 (TR35) for 2013, and received the MIT Edgerton Faculty Achievement Award and an NSF CAREER award in 2017. Prof. Winter is also the principal inventor of the Leveraged Freedom Chair (LFC) developing world wheelchair, which was a winner of a 2010 R&D 100 award, was named one of the Wall Street Journal’s top innovations in 2011, received a Patents for Humanity award from the U.S. Patent and Trademark Office in 2015, and was the subject of “Engineering Reverse Innovations”, winner of the 2015 McKinsey Award for the best article of the year in Harvard Business Review.

Tuesday, October 10, 2017
11:00 AM
Ronald Tutor Hall, Room 211 (RTH 211)

Bioinspired Robots: Embracing the Environment

Mark R. Cutkosky

Fletcher Jones Professor
Dept. of Mechanical Engineering
Stanford University
Stanford, CA

As we bring robots out of the laboratory and into the world, one of the most important lessons we can learn from nature is how to exploit interactions with materials and surfaces in the environment. Examples of robots that need to take advantage of surface interactions include multimodal flying/climbing robots, microtugs, and free-flying robots that grasp objects using gecko-inspired adhesives. These robots use specialized materials and mechanisms to manage interactions with the surfaces they contact. In each case dynamic models and tests lead to computed “envelopes” of conditions for which the robot is expected to perform reliably – for example, to latch onto a surface without slipping or bouncing off. As contact takes place the dynamics are typically fast, so passive properties of mechanisms are more effective than closed-loop control to dissipate energy, distribute forces and stabilize the robot. Nature offers many examples of structures and functional materials that help to manage these interactions. Investigations of surface interactions also allow us to discover new opportunities for synergy when combining multiple locomotion modes (e.g., flying and climbing). Here again, we find parallels in nature.

Mark R. Cutkosky Mark R. Cutkosky is the Fletcher Jones Professor in the Dept. of Mechanical Engineering at Stanford University. He joined Stanford in 1985, after working in the Robotics Institute at Carnegie Mellon University and as a design engineer at ALCOA, in Pittsburgh, PA. He received his Ph.D. in Mechanical Engineering from Carnegie Mellon University in 1985.
Cutkosky’s research activities include robotic manipulation and tactile sensing and the design and fabrication of biologically inspired robots. He has graduated over 47 Ph.D. students and published extensively in these areas. He consults with companies on robotics and human/computer interaction devices and holds several patents on related technologies. His work has been featured in Discover magazine, The New York Times, National Geographic, Time magazine and other publications and has appeared on PBS NOVA, CBS Evening News, and other popular media.
Cutkosky’s awards include a Fulbright Faculty Chair (Italy 2002), Fletcher Jones and Charles M. Pigott Chairs at Stanford University, an NSF Presidential Young Investigator award and Times Magazine Best Innovations (2006) for the Stickybot gecko-inspired robot. He is a fellow of ASME and IEEE and a member of Sigma Xi.
Cutkosky’s laboratory and research can be found at http://bdml.stanford.edu.

Wednesday, October 11, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Field Cancerization in Head and Neck Squamous Cell Carcinoma

Jasmine Foo

Associate Professor
School of Mathematics
University of Minnesota, Twin Cities
Minneapolis, MN

High rates of local recurrence in tobacco-related head and neck squamous cell carcinoma (HNSCC) are commonly attributed to unresected fields of precancerous tissue. Because they are not easily detectable at the time of surgery without additional biopsies, there is a need for noninvasive methods to predict the extent and dynamics of these fields. Here, we developed a spatial stochastic evolutionary model of tobacco-related HNSCC at the tissue level and calibrated the model using a Bayesian framework and population-level incidence data from the Surveillance, Epidemiology, and End Results (SEER) registry. Our model predicted a strong dependence of the local field size on age at diagnosis. Similarly, the probability of harboring multiple, clonally unrelated fields at the time of diagnosis was found to increase substantially with patient age. This work highlights the importance of spatial structure in models of epithelial carcinogenesis and suggests that patient age at diagnosis may be a critical predictor of the size and multiplicity of precancerous lesions.

Wednesday, October 18, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Thermoacoustic Dynamics in Aeronautical Gas Turbine Combustors

Adam Steinberg

Associate Professor
University of Toronto Institute for Aerospace Studies (UTIAS)
University of Toronto
Toronto, Ontario
Canada

Thermoacoustic instability in combustion systems refers to the tendency for small perturbations to grow into sustained high-amplitude oscillations, driven by feedback between heat release and pressure dynamics. This seminar will explore various aspects of thermoacoustic instabilities that were studied experimentally in a practical aeronautical gas turbine combustor using optical measurement techniques. Specific challenges arising in the application of optical diagnostics to high-pressure, liquid-fueled combustors will be addressed. We then will discuss two types of thermoacoustic behavior. The first involves apparently spontaneous increases and decreases in oscillation amplitude that occurred at particular operating points. The second pertains to conditions exhibiting steady and intense oscillations, but with extreme sensitivity between the operating point and oscillation amplitude. Both of these behaviors can be explained using the experimental data. Such insights help guide engine designers to more robust systems, and provide important information regarding the application of computational fluid dynamics simulations to thermoacoustically oscillating combustion systems.

Adam Steinberg is an Associate Professor at the University of Toronto Institute for Aerospace Studies, where he holds a Canada Research Chair (Tier II) in Turbulent Reactive Flows. His research focuses on the application of laser-based measurement techniques to solve problems in fundamental and applied thermo-fluids, with particular emphasis on aerospace and power generation systems. He obtained his PhD from the University of Michigan in 2009, and worked at the German Aerospace Center (DLR) before joining the University of Toronto in 2011. He is the recipient of the inaugural Hiroshi Tsuji Early Career Research Award from the Combustion Institute, as well as several other distinctions. He is a member of the Editorial Board of Combustion and Flame and the AIAA Propellants and Combustion Technical Committee, and is a Colloquium Co-Chair for the International Symposium on Combustion.

Wednesday, October 25, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

On the Physical Mechanisms of Droplet/Turbulence Interaction

Antonino Ferrante

Associate Professor
William E. Boeing Department of Aeronautics and Astronautics
University of Washington
Seattle, WA

The interactions of liquid droplets with turbulence are relevant to both environmental flows and engineering applications, e.g., rain formation and spray combustion. The physical mechanisms of droplet-turbulence interaction are largely unknown. The main goal of this research is to investigate the physical mechanisms of droplet-turbulence interaction for both non-evaporating and evaporating droplets.

Droplets in turbulent flows behave differently from solid particles, e.g., droplets deform, break up, coalesce and have internal fluid circulation. We have developed a new pressure-correction method for simulating incompressible two-fluid flows with large density and viscosity ratios. The method’s main advantage is that, for example, on a 10243 mesh, our new pressure-correction method using the FFT-based parallel Poisson solver is forty times faster than the standard method using multigrid. In general, the new pressure-correction method could be coupled with other interface advection methods such as level-set, phase-field, or front-tracking. We have coupled the pressure-correction method with a volume-of-fluid method for its properties of being mass conserving and sharp-capturing of the interface.

We performed direct numerical simulation (DNS) of finite-size, non-evaporating droplets of diameter approximately equal to the Taylor lengthscale in decaying isotropic turbulence. We studied the effects of Weber number, viscosity ratio and density ratio. We derived the turbulence kinetic energy (TKE) equations for the two-fluid, carrier-fluid and droplet-fluid flow. This allows us to explain the pathways for TKE exchange between the carrier turbulent flow and the flow inside the droplet. The role of the interfacial surface energy is explained through the power of surface tension term of the two-fluid TKE equation. Also, we derive the relationship between the power of surface tension and the rate of change of total droplet surface area. This allows us to explain how droplet deformation, breakup and coalescence plays a role on the temporal evolution of TKE. Our DNS results show that increasing Weber number, the droplet to fluid density or viscosity ratios increases the decay rate of the two-fluid TKE relative to that of single-phase flow. Via analysis of the DNS results, the revealed physical mechanisms will be presented.

Recently, we have also extended the volume-of-fluid method to simulate evaporating droplets. The verification and validation of the method and the DNS results will be presented in comparison to theory and experiments.

Antonino Ferrante is an Associate Professor of the William E. Boeing Department of Aeronautics & Astronautics at the University of Washington (UW). In 2004, he received the Ph.D. in Mechanical and Aerospace Engineering from the University of California, Irvine, where he continued his research as Postdoctoral Scholar until 2007. From 2007 to 2009, he was Postdoctoral Scholar in Aeronautics at the California Institute of Technology at GALCIT. In 2009, he joined the UW as Assistant Professor where was tenured in 2015. Ferrante is recipient of the NSF CAREER Award (2011). His research is focused to the understanding of the physical mechanisms of complex flows, e.g. multiphase and wall-bounded turbulent flows, and enable that through the development of parallel computational methodologies for simulating such flows on supercomputers.

Wednesday, Date November 1, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

The Effects of Stable Density Stratification Initially Homogeneous, Isotropic Turbulence

James J. Riley

PACCAR Professor of Engineering
Department of Mechanical Engineering
University of Washington
Seattle, WA

Stable density stratification occurs in various situations in the atmosphere and in the oceans. For example, in the atmosphere stable density stratification is found near the tropopause and above, and often in nocturnal boundary layers, while in the oceans it usually is observed below the mixed layer. And, through its effects on turbulent mixing, stable stratification has relevance to a number of important issues such as the overall ocean thermal energy balance and the transfer rates of heat and chemicals to/from the atmosphere.

In this seminar the results are presented of a study of the effects of stable density stratification on the simplest of turbulent flows, initially homogeneous, isotropic turbulence, using direct numerical simulations. Simulations were carried out at an initially moderate Froude number, but for a range of initial Reynolds numbers such that, for the high Reynolds number cases, the flows had buoyancy Reynolds numbers in the hundreds, similar to typical oceanic values. A number of aspects of the flows have been addressed, including their energetics, the behavior of various velocity and length scales describing the flows, their mixing characteristics, and their spectral behavior. In particular, how the behavior of the flows depend on the local Froude and buoyancy Reynolds numbers is emphasized. It is found, for example, that as the flows decay, stratification modifies them such that, compared to non-stratified cases, the energy decay rates decreased, the growth rate of the horizontal scales increased, while the growth rates of the vertical scales became negative. These results are consistent with the analysis of Davidson (J. Fluid Mech., 2010), based upon the behavior of the effects of density stratification on the large-scale motions. On the other hand if the buoyancy Reynolds number becomes too low, then the flows, especially the vertical velocity, begin to decay much more rapidly. It is also found, for example, that the behavior of the spectra of the velocity gradient tensor is consistent with the heuristic arguments of Lilly (J. Atmos. Sci., 1983) and the scaling arguments of Billant & Chomaz (Phys. Fluids, 2001). Finally, previous results of the USC group (e.g., Spedding J. Fluid Mech., 1997) are interpreted in terms of the Froude and buoyancy Reynolds numbers.

James J. Riley is the PACCAR Professor of Engineering at the University of Washington. He received his PhD from the Johns Hopkins University in 1972, having worked under the guidance of Stanley Corrsin. After a year as a post-doctoral fellow at the National Center for Atmospheric Research, he spent ten years in industry at Flow Research Company in Kent, Washington, ultimately as the Director of the Fluid Mechanics Division. He joined the University of Washington in 1983, where he is now a Professor in the Department of Mechanical Engineering, and an Adjunct Professor in both the Departments of Applied Mathematics and of Aeronautics and Astronautics. While on sabbatical at the Joseph Fourier University in Grenoble, France, Riley occupied the Visiting Chair in Industrial Mathematics. More recently he was a Senior Fellow at the Isaac Newton Institute for the Mathematical Sciences at Cambridge University. Riley’s research interests have included particle dispersion in turbulent flows, waves and turbulence in stably-stratified and in rotating fluids, boundary layer and shear layer transition and turbulence, fluid/compliant surface interactions, and chemically reacting turbulent flows. He is an associate editor of the Journal of Fluid Mechanics and of the Journal of Turbulence, and until recently was a member of the editorial boards of the Annual Review of Fluid Mechanics and of the Applied Mechanics Reviews. Riley is a member of the National Academy of Engineering, and of the Washington State Academy of Sciences.

Wednesday, Date November 8, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Unsteady Combustion Problems in Modern Energy and Propulsion Systems

Tim Lieuwen

Professor
Daniel Guggenheim School of Aerospace Engineering
Georgia Institute of Technology
North Avenue, Atlanta, GA

The operational limits of modern power generation and propulsion devices are strongly influenced by the combustor. For example, combustion instabilities have emerged as one of the leading challenges associated with low emissions combustion technologies. More fundamentally, the combustion instability problem involves the nonlinear interactions of harmonic flow disturbances with flames in a highly turbulent flow. This talk will describe the key processes controlling the flame response – flame anchoring, excitation of wrinkles by flow oscillations, tangential convection of wrinkles upon the flame, and kinematic restoration.

Tim Lieuwen is a professor and the David S. Lewis, Jr. Chair at Georgia Institute of Technology, and the Executive Director of the Strategic Energy Institute. He has a Ph.D. in mechanical engineering and is a licensed professional engineer in the state of Georgia. He leads a diverse research group investigating a range of problems associated with clean power, energy, and combustion, including such issues as emissions, efficiency, and alternative fuels. Prof. Lieuwen has edited/written four books, written 7 book chapters and over 300 papers, and received 5 patents.

Wednesday, November 15, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Learning from Fish: The Mechanics of Aquatic Propulsion

Iman Borazjani

Associate Professor
Department of Mechanical and Aerospace Engineering
SUNY Buffalo
Buffalo, NY

The grand challenges facing society today, let it be environment, energy, or health, typically involve fluids whose flow physics are not well-understood. To investigate the flow physics and even discover new ones, computational tools can play a major role. Nevertheless, simulating flows with complex shapes and moving boundaries, fluid-structure interactions, pulsatile flows, and at a resolution to resolve are relevant scales is quite challenging. We have overcome many of these challenges using our computational framework, parallelized to efficiently utilize high-performance computing clusters, which handles moving bodies using a sharp-interface immersed boundary method, and solves the flow equations and the immersed bodies in a fully implicit manner using a Newton-Krylov method with an analytical Jacobian. The method has been validated against experimental and benchmark data, and applied to several application from cardiovascular flows, aquatic swimming, wind turbines, and suspension of complex-shaped particles to drive discovery and provide insights into the flow physics. In this talk, we will show how numerical simulations provide us the capability to test hypothetical cases, which are quite difficult to test experimentally with live fish, e.g., we cannot ask a fish to swim with a desired kinematics. We will discuss the main mechanisms of propulsion for fish based on our simulations and show that our results agree with the reactive force theory. In addition, we discuss how the discovery of the leading edge vortex in simulations of aquatic swimming has resulted in new ideas for flow control in engineering applications. At the end, future challenges and research directions are discussed.

Iman Borazjani is an associate professor at the department of mechanical and aerospace engineering SUNY Buffalo and will move to Texas A&M in January 2018. He got his PhD, MSc, and BSc degrees in mechanical engineering from University of Minnesota, Georgia Tech, and Sharif University in 2008, 2005, and 2002, respectively, and was a post-doctoral researcher at the St Anthony Falls Laboratory, University of Minnesota. He is the recipient of the 2013 Scientific Development award from American Heart Association, the 2013 Doctoral New Investigator from American Chemical Society, 2015 NSF CAREER, and 2017-18 Fulbright award.

Wednesday, November 29, 2017
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

To Be (High-Order), Or Not To Be: A Perspective on Next-Generation Computational Tools for Engineering Applications

Gianmarco Mengaldo

Senior Postdoctoral Scholar
Division of Engineering and Applied Science
California Institute of Technology
Pasadena, CA

Advanced computational tools in applied science are becoming increasingly crucial for the analysis, design and decision-making processes commonly required to drive technological and societal innovation. In engineering, high-fidelity simulations constitute an essential mean to provide otherwise unreachable insights that can significantly improve the understanding of complex systems. An area of particular interest is computational fluid dynamics (CFD), where the adoption of high-fidelity simulation technologies, namely large-eddy simulation (LES) is considered of paramount importance to advance the fields where a detailed understanding of flow physics is critical (CFD Vision 2030 Study, Slotnick et al. 2014). LES can provide substantial advantages over more commonly used steady-state tailored techniques. In fact, LES can significantly extend the simulation predictive skills to off-design conditions that include unsteady separated flows, thus providing high-resolution data that can be used in the analysis and design processes as well as to devise reduced-order models.

The key enabler to develop such high-fidelity CFD tools is the underlying numerical discretization, as it drives the accuracy, robustness and time-to-solution of the simulations. In this talk, I will provide an overview of the challenges that CFD is facing in the near future focusing on key aspects that the community needs to consider to push the current boundaries, namely (i) the development of numerical discretizations that can accurately handle complex geometries and that are competitive in terms of time-to-solution and robustness, (ii) the better understanding of numerical vs. physical dissipation to improve LES models and (iii) the co-design of software and hardware to achieve extreme computational performance on heterogeneous computing architectures. The discussion will primarily debate whether high-order finite element methods (also referred to as spectral element methods (SEM)), are a valid choice to build high-fidelity tools for next generation CFD or low-order alternatives are also an adequate option. From this perspective, I will show how SEMs are extremely competitive to describe unsteady separated flows over complex geometries for applications where accuracy is of paramount importance. On the other hand, I will emphasize the role of low order methods – e.g. mimetic finite-volume immersed boundary formulations – in effectively tackling problems with moving surfaces, where body-fitted discretizations may struggle, and for applications where resolution and accuracy are weaker constraints. The talk will also include some ideas from the weather community, where similar issues are being discussed. While the initial question might not have a definitive answer, I hope to provide a clearer view on its implications and on how “to be high-order” can be extremely competitive for certain applications and less for others.

Gianmarco Mengaldo is a senior postdoctoral scholar at the California Institute of Technology and he actively collaborates with Imperial College London, the Massachusetts Institute of Technology, University of Cologne and the European Centre for Medium-Range Weather Forecast (ECMWF), the world leader in numerical weather prediction. Gianmarco graduated among the top of his class from Politecnico di Milano, one of the most prestigious Italian universities, with a master of science in aerospace engineering. He went on to obtain a PhD from Imperial College London in aeronautical engineering, where he worked on novel approximation strategies for partial differential equations, including discontinuous Galerkin and flux reconstruction approaches, using the spectral element library Nektar++. During the PhD, he joined McLaren Racing for an internship in the Formula 1 R&D department where he worked on the aerodynamic design of the competing car. After the PhD, Gianmarco worked for one year at ECMWF leading the technical side of a project, ESCAPE, devoted to test several numerical algorithms for weather and climate simulations on emerging computing technologies and he contributed building the new data-structure for handling different numerical discretization for massively parallel weather applications. Currently, he is working at the California Institute of Technology, where he is developing next generation numerical algorithms for multi-scale and multi-physics problems, with applications that include energy harvesting, bio-inspired micro aerial vehicles and drones, among others. He is also an active senior developer of Nektar++, where he leads the development of discontinuous spectral element discretizations for compressible flow problems and continues his collaboration with ECMWF on a range of topics, including the evaluation of different numerical discretization strategies for weather and climate applications on next generation hardware.

Monday, December 4, 2017
11:00 AM
Laufer Library (RRB 208)