Seminars

Seminars are held Wednesdays, at 3:30 pm, as Zoom webinars, unless otherwise noted. See the individual announcements for webinar access details.

Archive of Seminar Announcements:

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Keynote Lecture Series Archive

Spring, 2020

Droplet Impingement and its Application in Electronic Cooling

Mahsa Ebrahim

Assistant Professor of Mechanical Engineering
Loyola Marymount University
Los Angeles, CA

The need for cooling of high heat flux electronics is dramatically increasing as the technology developments make the electronic devices more compact and more powerful. Spray cooling is known to be one of the most effective methods of cooling high heat flux applications. However, common issues of dry-out and excessive liquid accumulation make spray cooling an unreliable technique for the cooling of high heat flux electronics. In order to better understand the fundamental physics and heat absorption of spray cooling, single droplet impingement on a heated surface has gained numerous attention. Although extensive research has been performed on single droplet impingement, the literature is sparse regarding the study of the heat transfer at high impact velocities and at micrometer size scale. Upon the impact of the droplet, the surface temperature drops dramatically and rapidly and at higher impact conditions this temperature drop is even more severe. In this work, the hydrodynamic and heat transfer regimes of a single droplet at high impact conditions were identified and mapped. Techniques were developed to enhance the heat absorption and the evaporation rate of each droplet by utilizing an impinging air flow to increase the impact velocity and to control the hydrodynamic phases after the impact and therefore to promote the utilization of spray cooling in high heat flux electronics.

Mahsa Ebrahim is an Assistant Professor of Mechanical Engineering at Loyola Marymount University. She received her Ph.D. degree in Mechanical Engineering from Villanova University and her M.S. and B.S. degrees in Mechanical Engineering from K.N.Toosi University of Technology in Iran. She spent a year of her Ph.D. at the University of Leeds in England as a research scholar. Her research focuses on numerical and experimental thermal-fluid science, spray cooling and droplet impingement, interfacial flows and phase interactions with applications in electronic cooling. She has been an active organizer of the IEEE-ITherm conferences since 2018.

Wednesday, August 26, 2020
3:30 PM
The Zoom webinar is at https://usc.zoom.us/j/95959519165.

host: Sadhal

Research Collaboration with AME Part Time Faculty

Marty Bradley

Senior Technical Fellow
Electra.aero
Falls Church, VA

Marty Bradley invites some of his fellow part time lecturers to discuss collaboration opportunities between their commercial employers and research groups within AME. Marty, Kamal Shweyk, David Lazzara, and Hubert Wong will discuss possible collaboration topics including electric aircraft; alternative fuels – Hydrogen, etc.; environmental analysis; supersonic aerodynamics; design optimization; flight controls; and UAV dynamic requirements.

Marty Bradley is a retired Technical Fellow from Boeing (June 2020) and is now a Senior Technical Fellow for Electra.aero working on a small short takeoff hybrid electric aircraft. He has 36 years of aerospace experience, and is a Part Time Lecturer at USC, teaching AME-481 Aircraft Design. He has a B.S., M.S., E.A.E., and Ph.D. in Aerospace Engineering, all from USC.

Wednesday, September 2, 2020
3:30 PM
The Zoom webinar is at https://usc.zoom.us/j/95556139831.

host: Ronney

Prediction of Real-World External Aerodynamics Using Numerical Simulations

Adrian Lozano-Duran

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

The use of computational fluid dynamics for external aerodynamic applications has been a key tool for aircraft design in the modern aerospace industry. In the last decades, large-eddy simulation with near-wall modeling (wall-modeled LES) has gained momentum as a cost-effective approach for both scientific research and industrial applications. In this talk, we discuss current challenges of wall-modeled LES to become a design tool for the aerospace industry. Our focus is on the working principles and performance of wall-modeled LES for external aerodynamic applications, with emphasis on realistic commercial aircrafts. We examine the computational cost to predict mean flow features and forces for a given degree of accuracy using theory and numerical simulations of the NASA Juncture Flow and the JAXA Standard Model. The vision presented here is motivated by discussions in previous AIAA workshops and the experience acquired at the Center for Turbulence Research during the last years.

Adrian Lozano-Duran is a Postdoctoral Research Fellow at the Center for Turbulence Research at Stanford University hosted by Prof. Moin. He received his PhD in Aerospace Engineering from the Technical University of Madrid in 2015 at the Fluid Mechanics Lab. advised by Prof. Jiménez. The overarching theme of his research is physics and modeling of wall-bounded turbulence via theory and computational fluid mechanics. His work covers a wide range of topics, such as turbulence theory and modeling by machine learning, large-eddy simulation for external aerodynamics, geophysical and multiphase flows, among others.

Wednesday, September 9, 2020
3:30 PM
The Zoom webinar is at https://usc.zoom.us/j/99375525323

host: Bermejo-Moreno

Robotics Meets Physics

Daniel Goldman

Dunn Family Professor Professor
School of Physics
Georgia Institute of Technology
Atlanta, Georgia

Robots will soon move from the factory floor and into our lives (e.g. autonomous cars, package delivery drones, and search-and-rescue devices). However, compared to living systems, robot capabilities in complex environments are limited. I believe the mindset and tools of physics can help facilitate the creation of robust self-propelled autonomous systems. This “robophysics” approach – the systematic search for novel dynamics and principles in robotic systems -- can aid the computer science and engineering approaches which have proven successful in less complex environments. The rapidly decreasing cost of constructing sophisticated robot models with easy access to significant computational power bodes well for such interactions. Drawing from examples in the work of my group and our collaborators, I will discuss how robophysical studies have inspired new physics questions in low dimensional dynamical systems (e.g. creation of analog quantum mechanics and gravity systems) and soft matter physics (e.g. emergent capabilities in ensembles of active “particles”), have been useful to develop insight for biological locomotion in complex terrain (e.g. control targets via optimizing geometric phase), and have begun to aid engineers in the creation of devices that begin to achieve life-like locomotor abilities on and within complex environments (e.g. semi-soft myriapod robots).

Daniel I. Goldman is a Dunn Family Professor in the School of Physics at the Georgia Institute of Technology and a Georgia Power Professor of Excellence. Prof. Goldman became a faculty member at Georgia Tech in January 2007. He is an adjunct member of the School of Biology and is a member of the Interdisciplinary Bioengineering Graduate Program.

Prof. Goldman's research program broadly investigates the interaction of biological and physical systems with complex materials like granular media. In particular, he integrates laboratory experiment, computer simulation, and physical and mathematical models to discover principles of movement of a diversity of animals and robots in controlled laboratory substrates.

He received his S.B. in physics at the Massachusetts Institute of Technology in 1994. He received his PhD in Physics in 2002 from the University of Texas at Austin, studying nonlinear dynamics and granular media. From 2003-2007 he did postdoctoral work in the Department of Integrative Biology at UC Berkeley studying locomotion biomechanics.

Prof. Goldman is a Fellow of the American Physical Society (2014), and has received an NSF CAREER/PECASE award, a DARPA Young Faculty Award, a Burroughs Wellcome Fund Career Award at the Scientific Interface, and the UT Austin Outstanding Dissertation in Physics (2002-2003).

Wednesday, September 16, 2020
3:30 PM
The Zoom webinar is at https://usc.zoom.us/j/96536533521

host: Kanso

The Hydrodynamics of Sea Lion Swimming

Megan Leftwich

Associate Professor
School of Engineering & Applied Science
George Washington University
Washington, DC

California Sea Lions are highly maneuverable swimmers, capable of generating high thrust and agile turns. Their main propulsive surfaces, the foreflippers, feature multiple degrees of freedom, allowing their use for thrust production (through a downward, sweeping motion referred to as a “clap”), turning, stability and station holding (underwater “hovering”). To determine the two-dimensional kinematics of the California sea lion fore flipper during thrust generation, digital, high definition video is obtained using the specimen at the Smithsonian National Zoo in Washington, DC. Single camera videos are analyzed to digitize the flipper during the motions, using 10 points spanning root to tip in each frame. Digitized shapes were then fitted with an empirical function that quantitatively allows for both comparison between different claps and for extracting kinematic data. The resulting function shows a high degree of curvature (with a camber of up to 32%). Analysis of sea lion acceleration from rest shows thrust production in the range of 150-680 N and maximum flipper angular velocity (for rotation about the shoulder joint) as high as 20 rad/s. Analysis of turning maneuvers indicate extreme agility and precision of movement driven by the fore flipper surfaces. This work is being extended to three-dimensions via the addition of a second camera and a sophisticated calibration scheme to create a set of camera-intrinsic properties. Simultaneously, we have developed a robotic sea lion foreflipper to investigate the resulting fluid dynamic structures in a controlled, laboratory setting.

Megan C. Leftwich is an Associate Professor in the Department of Mechanical and Aerospace Engineering at The George Washington University. She holds a Ph.D. in Mechanical and Aerospace Engineering from Princeton University and a B.S.E. degree from Duke University. Prior to joining GW, she was the Agnew National Security Postdoctoral Fellow at Los Alamos National Lab from 2010 to 2012. Her current research interests include the fluid dynamics of rotating airfoils, high performance jetting for aquatic locomotion, unsteady activation for undulatory propulsion, and the fluid dynamics of human birth. Prof. Leftwich has a deep interest in diversity in technical fields and STEM education from the first year through the Ph.D. Professor Leftwich is an Office of Naval Research 2017 Young Investigator Award Recipient. Additionally, she is the winner of the Curriculum Vitae of Megan C. Leftwich 2019 Early Career Researcher Award at George Washington University, the 2018 SEAS Dean’s Faculty Recognition Award, the 2017 SEAS Outstanding Young Researcher Award and the 2016 SEAS Outstanding Young Teacher Award. Her work on unsteady propulsion has been profiled in over 20 popular media venues including: Wired, CNN's Great Big Story, the Smithsonian Magazine and the New York Times.

Wednesday, January 29, 2020
3:30 PM
The Zoom webinar is at https://usc.zoom.us/j/99786894408

host: Kanso/Luhar

Pulmonary Hypertension Assessed Using Mathematical Modeling Integrating Imaging and Time-Series Data

Mette Olufsen

Professor
Department of Mathematics
NC State University
Raleigh, NC

Cardiovascular disease management involves interpreting imaging data, time-series data, and single-valued markers often measured over several visits. While each data type provides insight into the disease state, these snapshots cannot easily be integrated to provide insight into disease predictions. In this talk, we demonstrate how to interpret the disease state using multiscale mathematical modeling integrating computed tomography (CT) images with blood pressure measurements from right heart categorization. We use these models to characterize patient-specific remodeling in the proximal and distal vasculature. We calculate patient-specific nominal parameter values using morphometric and invasively measured hemodynamic data, use sensitivity analysis to determine what parameters best inform the data, and a Bayesian approach to infer identifiable subject-specific parameters and propagate the uncertainty of pressure and flow predictions to all large vessels. We also validate frequency domain results assessing change in wave-propagation and wave-intensity with the disease. For the micro-vasculature, we conduct a morphometric analysis characterizing changes in the arterial networks' branching structure by extracting skeletonized networks from the micro-CT images and using a custom algorithm to represent the network as a connected graph. We determine subject-specific fractal parameters and analyze how these changes with PH. Our model and data analysis outcomes are combined to understand the link between spatially distributed etiologies and global hemodynamics and shed light on the prospect of combining the model and graph-based morphometric analysis of vascular trees.

Dr. Olufsen, Professor, has been associated with the NCSU Mathematics Department since 2001. She got her Ph.D. in Applied Mathematics from Roskilde University, Denmark in 2001, for which she developed a 1D systemic arterial model for use in an Anesthesia Simulator. After graduating, she spent three years at Boston University, working with Nancy Kopell and Ali Nadim.

At NCSU her main focus has been on developing patient-specific models for understanding the cardiovascular system and its control. Her recent work has focused on using modeling to understand pulmonary hypertension integrating imaging and time-series data. She has mentored more than 20 graduate students (two who are Assistant Professors at USC) and a large number of undergraduate students. She has published more than 100 manuscripts and organized numerous workshops and conferences including SIAM Life Sciences. She served as a scientific advisor for the Mathematical Biosciences Institute at Ohio State and is currently the director for the NCSU Research for Undergraduates Program.

Wednesday, September 30, 2020
3:30 PM
A Zoom webinar invitation will be posted here.
host: Sadhal

Tackling Complex Flow Problems via Numerical Simulation: From Jumping Fish and Heart Valves to River Flooding and Wind Energy

Fotis Sotiropolous

Dean, College of Engineering and Applied Sciences
and
State University of New York Distinguished Professor of Civil Engineering
Stony Brook University
Stony Brook, NY

Simulation-based engineering science has emerged as a powerful approach for tackling the major societal problems of our time related to human health, environmental sustainability, and renewable energy. Fluid mechanics problems frequently at the center of many of these challenges are often so complex that simulation-based research is the only viable approach for tackling them. Examples range from disease promoting blood flow patterns in the human heart and bioinspired swimming robots to extreme flooding in waterways and harnessing renewable energy from wind, currents, and waves. Accurate numerical simulation of such flows poses a formidable challenge to even the most advanced computational methods available today. In this talk I will discuss the advances we have made in my group to develop a powerful computational framework, the Virtual Flow Simulator (VFS), which can: handle arbitrarily complex geometries encountered in real-life applications; simulate fluid-structure interaction for rigid and flexible bodies; account for two-phase flows and free surface effects; and carry out coherent-structure-resolving simulations of turbulent flows in arbitrarily complex domains with dynamically evolving boundaries. The ability of the method to yield striking new insights into the physics of a broad range of real-life problems will be demonstrated by discussing applications in aquatic biology, cardiovascular engineering, turbulence and transport processes in natural waterways, and wind and marine and hydrokinetic energy. Future grand challenges and opportunities for simulation-based fluid mechanics research will also be discussed.

Fotis Sotiropoulos serves as Dean of the College of Engineering and Applied Sciences and SUNY Distinguished Professor of Civil Engineering at Stony Brook University. Before joining Stony Brook University, he was the James L. Record Professor of Civil Engineering; Director of the St. Anthony Falls Laboratory; and Director of the EOLOS wind energy research consortium at the University of Minnesota, Twin Cities (2006-2015). Prior to that, he was on the faculty of the School of Civil and Environmental Engineering at the Georgia Institute of Technology, with a joint appointment in the G. W. Woodruff School of Mechanical Engineering (1995-2005). His research focuses on simulation-based engineering science for tackling complex, societally relevant fluid mechanics problems in energy, environment and human health applications. He has authored over 190 peer reviewed journal papers and book chapters and his research results have been featured on the cover of several prestigious journals. He has been awarded the 2019 American Geophysical Union (AGU) Hydrology Days Borland Lecture in Hydraulics, the 2017 Hunter Rouse Hydraulic Engineering Award from the American Society of Civil Engineers (ASCE), a 2014 distinguished lecturer of the Mortimer and Raymond Sackler Institute of Advanced Studies at Tel Aviv University, and a Career Award from the National Science Foundation. Sotiropoulos is a Fellow of the American Physical Society (APS) and the American Society of Mechanical Engineers (ASME) and has twice won the APS Division of Fluid Dynamics Gallery of Fluid Motion (2009, 2011).

Wednesday, October 7, 2020
3:30 PM
A Zoom webinar invitation will be posted here.

host: Pahlevan

Tunable Porous and Patterned Surfaces for Turbulence Control

Mitul Luhar

Department of Aerospace & Mechanical Engineering
USC
Los Angeles, CA

Control of wall-bounded turbulent flows has been an important area of research for several decades. However, the development of effective control techniques has been hindered by the limited availability of computationally tractable models that can guide design and optimization. This talk describes extensions of the resolvent analysis formalism that seek to address this limitation. Under the resolvent formulation, the turbulent velocity field is expressed as a superposition of propagating modes (‘resolvent modes’) identified via a gain-based decomposition of the Navier-Stokes equations. Control is introduced into this framework via changes to the boundary conditions or through additional forcing terms in the governing equations. These changes alter the structure and gain of resolvent modes, whereby a reduction in gain is shown to be indicative of mode suppression and drag reduction. This modeling framework reproduces previous observations for passive control techniques such as sharkskin-inspired riblets, compliant walls, and anisotropic porous materials with minimal computation. Ongoing work builds on these observations to develop optimization routines for riblet shape and to design, fabricate, and test porous materials that can passively control turbulent flows

Mitul Luhar joined the Department of Aerospace and Mechanical Engineering at USC as Assistant Professor in January 2015 and was appointed as the Henry Salvatori Early Career Chair in 2020. He has received the AFOSR Young Investigator Program award as well as the NSF Career award. Prior to joining USC, Mitul was a Postdoctoral Scholar in the Graduate Aerospace Laboratories at Caltech. He earned his Ph.D. in Civil and Environmental Engineering from MIT in 2012, and his B.A. and M.Eng. degrees in Engineering from Cambridge University in 2007.

Wednesday, October 21, 2020
3:30 PM

A Zoom webinar invitation will be posted here.