2025 Seminar Archive

Turbulence as the Stability of Three Fundamental Flow Structures

Johan Hoffman

Professor
Division of Computational Science and Technology
KTH Royal Institute of Technology.
Stockholm, Sweden

Turbulence theory builds on two main results: (i) the Navier-Stokes equations from about 200 years ago, a set of partial differential equations with the viscosity as the sole empirical parameter that under given flow conditions describe the evolution of velocity and pressure; and (ii) a statistical theory from almost 100 years ago, which under the assumptions of statistical homogeneity and isotropy states that there exists an inertial subrange of scales where energy dissipation is independent of viscosity so that the energy spectrum satisfies a certain power law. Two important developments are: (iii) the extension of the statistical theory into a theory of non-uniform, localized energy dissipation, referred to as intermittency; and (iv) the Onsager conjecture that turbulence can be modelled by weak solutions to the inviscid Euler equations, hence, without viscosity at all. In this talk we present a model of turbulence in the form of three fundamental flow structures: rigid body rotation, pure strain, and shear flow; each with its own distinct stability property. Rotation is stable and can exist for a long time; shear is linearly unstable and only exits for a short time before transforming into rotation (roll-up); and strain is exponentially unstable, therefore, only exists in short instants before transforming into shear (compression) or rotation (vortex stretching). This model connects (i)-(iv) and is consistent with classical fluid mechanics phenomena driven by flow instabilities, such as the Kelvin-Helmholtz instability, boundary layer transition to turbulence, and the turbulent flow separation (d’Alembert paradox). Further, we show how this model can be used to construct a mechanistic model of the turbulent energy cascade.

Johan Hoffman is professor and deputy head of the division of computational science and technology at KTH Royal Institute of Technology in Stockholm. He is a founder of the FEniCS open source software project, and he combines fundamental research in mathematics, fluid mechanics, and computational science with applied research in interdisciplinary collaborations with industry and society. He earned his Ph.D. in applied mathematics at Chalmers University, was a postdoc fellow at the Courant Institute at New York University, and has been a visiting researcher at Oxford University, University of Chicago, Stanford University, University of Heidelberg, UPC Barcelona, the Auckland Bioengineering Institute, and the Basque Center for Applied Mathematics.

Monday, August 25, 2025

12:00 NOON

Laufer Conference Room (OHE 406)

 

host: Oberai

Ice Sculpturing with Laminar Flow

Xiaojing (Ruby) Fu

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

This talk examines the physics of unsaturated water flow through subfreezing porous media and its role in shaping ice solidification within confined environments.

At the centimeter-to-meter scale, we use a nonequilibrium infiltration model to study refreezing structures that emerge during gravity-driven infiltration. Two freezing-induced mechanisms are shown to hinder infiltration: (i) partial freezing of infiltrating water, which reduces effective infiltration rates and can be characterized by a freezing Damköhler number, and (ii) the formation of secondary fingers—new flow paths that disrupt primary channels—leading to homogenization of the flow field and reduced infiltration efficiency. Preliminary experimental observations are presented to test these model predictions.

At the millimeter-to-centimeter scale, we investigate water imbibition in a subfreezing Hele-Shaw cell. Water at 0 °C is injected at a constant rate into a radial cell cooled by a temperature-controlled aluminum block. By varying flow rate and subcooling, we identify how solidification dynamics and flow morphology evolve across regimes.

These studies are motivated by the need to understand fundamental processes in cold-region hydrology, including snowpack, glacier, and permafrost evolution. Beyond the cryosphere, the insights extend to broader nonequilibrium solidification problems relevant to additive manufacturing, freeze casting, lava flows, and natural terrace landform development.

Xiaojing (Ruby) Fu is an assistant professor in Mechanical and Civil engineering at California Institute of Technology, where she leads the group on Mechanics and Physics of Porous Media Flow. Her group combines mathematical theory, computation and laboratory experiments to advance our predicative capability of field-scale applications in a wide range of geoscience problems, including hydrology, gas hydrate systems and soil biogeochemistry, geologic carbon sequestration and geothermal systems. A primary focus of her current work is on understanding the physics of freezing flow through porous media.

Wednesday, August 27, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202

 

host: Maghsoodi

Data-Driven Nonlinear Stability Analysis in Aeroelastic Systems

Amin Ghadami

Research Assistant Professor
Sonny Astani Department of Civil and Environmental Engineering
University of Southern California
Los Angeles, CA

The demand for increased fuel efficiency in aircraft and the necessity to address structural damage caused by sudden loading are driving an interest in new aircraft designs with lighter, more slender, and flexible configurations. Increased flexibility results in diverse nonlinear response phenomena due to complex fluid-structural interactions, making the system susceptible to unexpected instabilities in their dynamics, emphasizing the necessity to incorporate nonlinear stability analysis early in the design process. However, performing such analysis in aeroelastic systems remains challenging with traditional approaches. Despite the existence of analytical and numerical methods for performing such analysis, their use is limited in systems with large dimensionality or when an accurate mathematical model is lacking, leaving time-marching simulations as the common alternative, though they are computationally expensive and difficult to interpret. In this talk, I will present recently developed data-driven techniques for nonlinear stability analysis in aeroelastic systems. In particular, I will demonstrate that a combined use of invariants in nonlinear dynamics and data-driven methods offers an alternative to demanding analytical, computational, and experimental processes for nonlinear stability analysis in aeroelastic systems. Applications of this approach to models of highly flexible wings and experimental configurations prone to flutter instabilities will be demonstrated.

Amin Ghadami is a Research Assistant Professor of Civil and Environmental Engineering and Aerospace and Mechanical Engineering at the University of Southern California. He received his Ph.D. in mechanical engineering in 2019, followed by a postdoctoral position at the University of Michigan-Ann Arbor from 2019 to 2022. His research is at the intersection of nonlinear dynamics and data-driven techniques with applications in mechanical and aerospace systems and structures. Dr. Ghadami is the recipient of the 2025 AFOSR Young Investigator Program Award for his research on nonlinear stability analysis of aeroelastic systems. He is also the recipient of several other honors and awards, including the University of Michigan Ivor K. McIvor Award, which recognized the excellence of his PhD research in applied mechanics. He is a member of the Technical Committee of Multibody Systems, Nonlinear Dynamics, and Control as well as the Technical Committee of Dynamics and Control of Systems and Structures within American Society of Mechanical Engineers (ASME).

Wednesday, September 3, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Ronney

Hierarchical Learning and Control for Agile and Adaptive Legged Robots

Quan Nguyen

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

Optimization-based control methods, such as model predictive control (MPC) and trajectory optimization, are essential to advancing the locomotion capabilities of legged robots. However, for successful deployment in real-world environments, legged robots must be capable of rapid adaptation to unknown terrain, robust handling of model uncertainties, and effective interaction with unknown objects to perform practical manipulation tasks.

In this talk, I will present a hierarchical model predictive control framework that enables legged and humanoid robots to perform dynamic loco-manipulation tasks. I will also highlight our recent work on adaptive force-based control that enables legged robots to handle significant model uncertainty. These strategies allow the robots to interact robustly with unknown objects, particularly in scenarios involving the transport of heavy loads over rough terrain.

Finally, I will discuss how we extend our hierarchical control principles into the domain of reinforcement learning to acquire long-term adaptive behaviors in both control actions and trajectory planning for legged and humanoid robots.

Quan Nguyen is an Assistant Professor of Aerospace and Mechanical Engineering at the University of Southern California. He is also the Chief Scientific Officer of VinMotion, a humanoid robotics company established by Vingroup, the largest private enterprise in Vietnam. Prior to joining USC, he was a Postdoctoral Associate in the Biomimetic Robotics Lab at the Massachusetts Institute of Technology (MIT). He received his Ph.D. from Carnegie Mellon University (CMU) in 2017 with the Best Dissertation Award.

His research interests span different learning and control approaches for highly dynamic robotics, including nonlinear control, trajectory optimization, adaptive control, and reinforcement learning. His work was featured widely in many major media channels, including CNN, BBC, NBC, IEEE Spectrum, etc. Nguyen won the Best Presentation of the Session at the 2016 American Control Conference (ACC) and the Best System Paper Finalist at the 2017 Robotics: Science & Systems conference (RSS). He is also a recipient of the 2020 Charles Lee Powell Foundation Faculty Research Award.

Wednesday, September 10, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Ronney

Robots and Sensors for Movement Rehabilitation: What Have We Learned and What Comes Next?

David Reinkensmeyer

Professor
Departments of Mechanical and Aerospace Engineering, Anatomy and Neurobiology, Biomedical Engineering, and Physical Medicine and Rehabilitation
University of California at Irvine
Irvine, CA

A fundamental goal of movement rehabilitation following neurologic injuries such as stroke is to enhance sensorimotor plasticity through targeted movement practice. Over the past 40 years, researchers have developed robotic and sensor-based technologies to facilitate and quantify this practice. In this talk, I will describe key insights into post-stroke motor control that have emerged from these technologies. I will also discuss recent findings that reveal which individuals benefit most from robot-assisted training and why, highlighting the role of somatosensory feedback in what appears to be a reinforcement learning-driven process. Finally, I will provide examples of mechatronic rehabilitation technologies that have successfully transitioned into clinical and home settings, inviting discussion on the design factors that drive their adoption and impact.

David Reinkensmeyer is Professor in the Departments of Mechanical and Aerospace Engineering, Anatomy and Neurobiology, Biomedical Engineering, and Physical Medicine and Rehabilitation at the University of California at Irvine. He received the B.S. degree in electrical engineering from the Massachusetts Institute of Technology and the M.S. and Ph.D. degrees in electrical engineering from the University of California at Berkeley, studying robotics and the neuroscience of human movement. He carried out postdoctoral studies at the Rehabilitation Institute of Chicago developing robotic devices for rehabilitation therapy after stroke before becoming a assistant professor at U.C. Irvine in 1998. He is co-inventor of the T-WREX upper extremity training device, which was commercialized as ArmeoSpring, and the MusicGlove finger training device. He was Editor-in-Chief of the Journal of Neuroengineering and Rehabilitation for 10 years and is co-director of the NIDILRR COMET Robotic Rehabilitation Engineering Center, co-editor of the of the book Neurorehabilitation Technology, and a fellow of the National Academy of Inventors.

Wednesday, September 17, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Maghsoodi

—Laufer Lecture—

Probing Turbulence Physics Using High Fidelity Numerical Simulations with Application to Model-Based Engineering

Parviz Moin

Franklin P. and Caroline M. Johnson Professor of Mechanical Engineering
Center for Turbulence Research
Stanford University
Stanford, CA

High fidelity numerical simulations have provided unprecedented comprehensive datasets for the study of the mechanics of turbulent flows. A brief review of fundamental research on the structure and mechanics of wall-bounded turbulent flows will be presented with particular emphasis on the role played by large scale numerical simulations in conducting controlled experiments of discovery. Although incorporation of the results from these simulations into practical engineering models remains an important area of research, a key insight gained from these novel numerical experiments has been the demonstration of the independence of self-sustaining dynamics of near wall-turbulence from the outer layer structures. In retrospect this insight has been underpinning the success of the so-called wall modeled LES of complex wall bounded turbulent flows.

I will conclude by presenting recent progress in large eddy simulation of complex flows, specifically for prediction of aircraft performance at the edges of flight envelope. Recent work has demonstrated that leveraging large eddy simulation with appropriate wall/subgrid-scale models and low dissipation numerical methods on modern computer architectures offers a tractable path towards meeting industry’s stringent accuracy and affordability requirements. The success of these calculations in predicting important quantities of practical interest is further evidence of the robust nature of near wall turbulence.

Parviz Moin is the Franklin P. and Caroline M. Johnson Professor of Mechanical Engineering and the Founding Director of the Center for Turbulence Research (CTR) and the Institute for Computational and Mathematical Engineering (ICME) at Stanford University. Professor Moin pioneered the use of Direct Numerical Simulation for the study of turbulence physics, and has written widely on the structure of turbulent shear flows. His current interests include numerical simulation of complex multi-physics turbulent flows. Professor Moin is a Fellow of the American Physical Society, AIAA, and the American Academy of Arts and Sciences. He is a member of the United States National Academy of Engineering, and the National Academy of Sciences.

Wednesday, September 24, 2025

Reception at 2:30 PM

Seminar at 3:30 PM

Michelson Hall, Room 101 (MCB 101)

 

host: Ronney

Advanced Manufacturing for Extreme Environment Spacecraft Applications at NASA JPL/Caltech

Douglas Hofmann

Senior Research Scientist
Materials Development and Manufacturing Technology Group
Jet Propulsion Laboratory
Pasadena, CA

For the past 15 years, NASA’s Jet Propulsion Laboratory has had a robust research activity in advanced materials and manufacturing, with focus on the development of new metal alloys and manufacturing technologies for extreme environment spacecraft and rovers. This has involved the creation of many new applications for advanced materials, such as innovative spacecraft shielding, cryogenically capable gears for space applications, novel robotics applications, and lightweight wheels for planetary rovers, among others. The research has spanned the technology development spectrum, from early prototyping through successful infusion of hardware on the Mars Perseverance Mars rover and on the Europa Clipper flagship spacecraft. This talk will give an overview of some of the technologies and applications that have been developed as part of this materials and manufacturing effort.

Douglas Hofmann is a Senior Research Scientists, Principal Scientist, and founding member of the Materials Development and Manufacturing Technology Group at JPL. He is founder of the JPL Metallurgy Facility, co-founder of JPL’s Additive Manufacturing Center and has been a Visiting Associate and Lecturer in Applied Physics and Materials Science at Caltech for 15 years. He holds an M.S. and Ph.D. from Caltech in Materials Science and Engineering and a B.S. and M.S. in Mechanical Engineering from U.C. San Diego. He is a recipient of several awards, including the 2012 Presidential Early Career Award for Scientists and Engineers from President Obama, and the inaugural Young Innovator in the Materials Science of Additive Manufacturing Award from The Minerals, Metals and Materials Society. He is a 2024 Fellow of the National Academy of Inventors. Doug has over 35 granted patents in materials and manufacturing and has successfully founded two commercial NASA spinoff companies that are exclusively licensing JPL technology.

Wednesday, October 1, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Chen

Autonomy On-Orbit and Beyond: Expanding Mission Capabilities in Extreme Environment Robotics

Keenan Albee

Assistant Professor
Department of Astronautical Engineering
University of Southern California
Los Angeles, CA

Autonomy is essential to making rapid decisions in safety-critical situations and dealing with tasks too complex for a human teleoperator. Within the space robotics community, the confluence of enhanced processing power, algorithmic maturity, and growing acceptance of autonomy in risk-averse domains is leading to a renaissance in its use. This talk explores some of the enduring algorithmic and safety challenges of working with increasing complexity in space and extreme environment robotics autonomy; in particular, the problem of motion planning and control under uncertainty will be explored in the context of providing robot motion that is safe, real-time, and tailored to the needs of real robotic systems. This work is framed in the context of novel planning and control techniques in microgravity close proximity operations and planetary surface robotics, demonstrating, respectively, 1) planning, control, and state estimation for autonomous on-orbit rendezvous with an uncharacterized tumbling target; and 2) highly-constrained model predictive control for roving in unknown environments. Flight demonstrations of these techniques will be discussed for the Astrobee free-flyers aboard the ISS, and the Cooperative Autonomous Distributed Robotic Explorer (CADRE) rovers launching to the Moon.

Keenan Albee is an Assistant Professor at the University of Southern California and former Robotics Technologist in the Maritime and Multi-Agent Autonomy group at the NASA Jet Propulsion Lab. He received a Ph.D. in Aeronautics and Astronautics (Autonomous Systems) from MIT in 2022 under a NASA Space Technology Research Fellowship. His research focuses on model-aware autonomy for space and extreme environment robotics, leveraging real-time tools to make autonomous robotic operations safer and more efficient. His work includes the first autonomous on-orbit rendezvous with an uncharacterized tumbling target—demonstrated on the Astrobee robots aboard the ISS—and multiple planning and multi-agent decision-making algorithms aboard the fully autonomous CADRE lunar rovers launching to the Moon. His research interests span extreme environment robotics, safe motion planning and control under uncertainty, and novel extreme environment systems development with a “theory to practice” philosophy of real-world field hardware validation.

Wednesday, October 8, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Luhar

USC Space Engineering Research Center Overview for AME

David Barnhart

Research Professor
Department of Astronautical Engineering
USC
Los Angeles, CA

A jointly supported center between the Department of Astronautical Engineering and the Information Sciences Institute has built up its research portfolio dedicated to Space. The Space Engineering Research Center (or SERC) was formed in 2006 with a single faculty member and now has 9 PhD’s, 3 full time staff, and supports 20-30 masters students and 10 summer intern undergrads on various space related research projects. The goal of the talk is to introduce the basics of SERC, impactful projects, and potential opportunities to help faculty/PhD students in AME in any way to secure additional resources and collaborate on new innovations in the space domain

David Barnhart is an active Research Professor in the Department of Astronautical Engineering at USC, the Director/Co- Founder of the USC Space Engineering Research Center and co-founder/CEO of Arkisys Inc.

David has specialized in developing innovative technologies and architectures for 2nd generation space morphologies, RPO technologies/techniques, and new business applications to in space activities. At USC David specializes in developing innovative technologies and architectures for 2nd generation space morphologies, rendezvous and proximity operations technologies/techniques, and hands-on projects with students, faculty and staff through an “engineering teaching hospital” construct. The SERC created and launched USC’s first three satellites in 2010, 2012 and 2021, and is working on its 4th for 2026. Over 250 students have graduated through the SERC’s hands-on training capabilities and every summer hosts US and international student interns. As part of SERC funded activities USC was part of the creation of CONFERS, and built and launched the first payload onto the ISS Astrobee free flying platform. Patented technology that came out of SERC from David and his students has provided the commercial basis for a company’s creation to develop orbital tugs and debris capture technology, and was featured by NASA on the ISS.

David has served as a senior space Project Manager at DARPA (Defense Advanced Research Projects Agency), pioneering cellular spacecraft morphologies, satbotics, space robotics and low cost high volume manufacturing on the Phoenix and SeeMe projects. He represented the first DARPA space project at the United Nations COPUOS in Vienna Austria addressing new technology pushing the need for updates to space regulations and policy issues for next generation ISAM and space servicing activities. This +$500M program is still operating and will be the first major ISAM mission from the USG in over 20 years.

Prior to USC and DARPA David helped initiate two commercial space companies; co-founding and serving as VP and CFO for Millennium Space Systems in Los Angeles CA (a Boeing Co.); and elected member of a startup in Bremen Germany, Vanguard Space, one of the first companies working commercial spacecraft servicing in early 2000.

David started his career as a civilian for the Air Force Research Labs spending over 13 years helping to birth several notable innovations in micro-miniature electronic technologies, micro-chemical/electric propulsion systems, some of the first small satellites for remote observations, and the first independent RPO missions. David has a BS from Boston University and ME from Virginia Tech both in Aerospace and Ocean engineering. He has published over 80 research papers and articles, holds 10 copyrights and patents, is a Board Member on CONFERS and Industry Oversite Board member on COSMIC (the two major space servicing sectors industry/academic consortiums), and speaks on 2nd generation space technologies nationally and internationally.

Wednesday, October 15, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Ronney

Sensing and Imaging Gas Dynamics in Extreme Environments: Rockets to Wildfires

Mitchell Spearrin

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

Extreme environments typified by high temperatures and/or high pressures present unique engineering challenges. Energy and environmental flows at such extreme conditions often involve complex, temporally-dynamic and spatially-heterogenous domains governed by competing physics of fluid dynamics, heat transfer, and chemical kinetics that are poorly understood. To improve understanding and predictive capability of these flow fields, quantitative sensing and imaging methods for temperature, species, and other fluid properties are needed. This talk examines the challenges and potential of laser spectroscopy for quantitative sensing in extreme environments with application to dynamic thermo-fluid systems at multiple scales. Basic and applied research areas are highlighted, including (1) photo-physics characterization of supercritical fluids, (2) development of advanced laser absorption imaging techniques, and (3) applied sensing and imaging in studies of advanced rocket propulsion and fire dynamics. Forward-looking research supported by emerging areas of photonics and data science are also discussed in the context of diverse engineering applications.

Mitchell Spearrin is a Professor of Mechanical and Aerospace Engineering at the University of California Los Angeles (UCLA), where he directs the Laser Spectroscopy and Gas Dynamics Laboratory. His research spans fundamental spectroscopic studies of collisional and radiative properties of gases, optical diagnostic methods development, and experimental investigations of non-equilibrium flow physics and advanced propulsion and power technologies. Recent extensions of Dr. Spearrin’s research include planetary entry thermochemical kinetics, toxicant formation in fires and environmental health monitoring. Dr. Spearrin was recently recognized with the U.S. Presidential Early Career Award for Scientists and Engineers (PECASE) and Hiroshi Tsuji Early Career Researcher Award from the Combustion Institute. Dr. Spearrin completed his Ph.D. at Stanford University, working in the High Temperature Gas Dynamics Laboratory. Prior to his academic career, Dr. Spearrin worked for Pratt & Whitney Rocketdyne as a combustion devices development engineer.

Wednesday, October 22, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Xu

Integrating Physical Intelligence with Artificial Intelligence: Autonomous Design and Manufacturing of Material Systems

Wei Chen

Wilson-Cook Professor in Engineering Design
Professor and Chair
Department of Mechanical Engineering
Northwestern University
Evanston, IL

Achieving superior performance in future material systems hinges on optimizing the heterogeneity of materials and structures. However, the design and fabrication of such advanced systems present significant challenges, requiring the integration of knowledge across multiple domains—including materials science, manufacturing, structural mechanics, and design optimization. This talk introduces a paradigm shift toward unifying “physical intelligence” with artificial intelligence (AI) to realize “embodied intelligence” in material systems. By combining data-driven generative design with physics-based modeling and simulation, we enable seamless integration of predictive materials modeling, advanced manufacturing, and design optimization—accelerating the development and deployment of next-generation materials. We will present state-of-the-art design methodologies that leverage statistical inference and AI techniques for the design of nano- and microstructured materials and programmable metamaterials responsive to external stimuli, covering methods such as machine learning, mixed-variable Latent Variable Gaussian Process (LVGP) modeling, Bayesian optimization, differentiable simulation, topology optimization, and generative design. The talk will also highlight recent advances in digital twins for autonomous co-design and manufacturing, using additive manufacturing as an example to showcase how these tools are transforming the landscape of intelligent material systems.

Wei Chen is the Wilson-Cook Professor in Engineering Design and Chair of Department of Mechanical Engineering at Northwestern University. Directing the Integrated DEsign Automation Laboratory (IDEAL- http://ideal.mech.northwestern.edu/), her current research involves the use of statistical inference, AI, and uncertainty quantification techniques for design of emerging materials systems including microstructural materials, metamaterials and programmable materials. She serves as the Design Thrust lead for the newly funded NSF Engineering Research Center (ERC) on Hybrid Autonomous Manufacturing, Moving from Evolution to Revolution (HAMMER), where she works on digital twin systems for concurrent materials and manufacturing process design. Dr. Chen is an elected member of the National Academy of Engineering (NAE) and American Academy of Arts and Sciences (AAA&S). She served as the Editor-in-chief of the ASME Journal of Mechanical Design, the Chair of the ASME Design Engineering Division (DED), and the President of the International Society of Structural and Multidisciplinary Optimization (ISSMO). She currently serves as the chair of the ASME Mechanical Engineering Department Heads Executive Committee (MEDHEC). Dr. Chen is the recipient of the 2025 ASME Barnett-Uzgiris Product Safety Design Award, 2022 Engineering Science Medal from the Society of Engineering Science (SES), ASME Pi Tau Sigma Charles Russ Richards Memorial Award (2021), ASME Design Automation Award (2015), Intelligent Optimal Design Prize (2005), ASME Pi Tau Sigma Gold Medal achievement award (1998), and the NSF Faculty Career Award (1996). She received her Ph.D. from the Georgia Institute of Technology in 1995.

Wednesday, October 29, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Jin

Soft Elastic Composites: Microstructure evolution, macroscopic multi-physics response, instabilities and associated soft modes

Pedro Ponte Castañeda

Professor
Department of Mechanical Engineering and Applied Mechanics
Graduate Group in Applied Mathematics and Computational Sciences
University of Pennsylvania
Philadelphia, PA

Soft elastic composite materials can undergo large deformations under normal operating conditions and, in many applications, such as in robotics and prosthetics applications, they are designed with the objective of undergoing controlled deformation by means of externally applied magnetic, electrical, pneumatic or other types of fields. They include porous, particle- and fiber-reinforced rubbers, thermoplastic and magnetorheological elastomers, dielectric elastomer composites, polymer foams, muscle and other biological tissues. As a consequence of the finite deformations involved, their microstructure evolves with the deformation and their constitutive or rheological behavior can be highly nonlinear and strongly anisotropic. This presents a challenge for the application of homogenization methods, which were originally developed to characterize the effective material parameters of composites, such as, for example, the thermal conductivity of a two-phase composite material, or the Young’s modulus of an isotropic metal polycrystal. In this presentation, I will give an overview of several methods that have been recently developed to characterize the multi-physics constitutive response of soft composites, as well as the evolution of the microstructure and the possible development of instabilities in such material systems. In addition, I will present some explicit examples, including those leading to a certain type of ‘twining’ instabilities and associated soft modes of deformation.

Pedro Ponte Castañeda is Raymond S. Markowitz Faculty Fellow and Professor in Mechanical Engineering & Applied Mechanics, Applied Mathematics & Computational Science, and Mathematics (secondary) at the University of Pennsylvania. He earned a B.S. in Mechanical Engineering and a B.A. in Mathematics from Lehigh University, and a Ph.D. in Applied Mathematics from Harvard University. He was Assistant Professor of Mechanical Engineering at the Johns Hopkins University (1987-90) and Professor of Mechanics at the École Polytechnique (2004-08). He has held visiting positions at the C.N.R.S. (France), Cambridge University, IMDEA Materials (Spain) and the University of Stuttgart. His honors include the Humboldt Senior Research Award (2013) and the ASME Warner T. Koiter Medal (2016).

Wednesday, November 5, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Plucinsky

Field-assisted Additive Manufacturing of Bio-inspired Structures

Yong Chen

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

The development of bio-inspired structures has revolutionized material science and engineering, offering unprecedented mechanical, functional, and aesthetic capabilities. However, traditional additive manufacturing (AM) techniques often fall short in replicating the complex anisotropic and hierarchical features observed in natural systems. This talk explores the emerging paradigm of field-assisted additive manufacturing, where external fields of force, electric, magnetic, and acoustic, are integrated into the AM process to engineer advanced bio-inspired structures. By leveraging these fields, it becomes possible to control the alignment of particles, fibers, or cells during deposition, creating architectures with tailored properties such as directional strength, functional gradients, and dynamic responsiveness. Key methodologies in the integration for controlled spatial patterning and alignment will be discussed. Case studies will demonstrate how these approaches can be utilized to fabricate materials with exceptional biomimetic features. The talk will conclude with remarks and thoughts on future AM developments and potential opportunities for mechanical and aerospace engineers. Attendees will gain insights into how field-assisted strategies can push the boundaries of AM, paving the way for next-generation materials in various fields.

Yong Chen is a professor of Aerospace and Mechanical Engineering at the University of Southern California (USC). His research focuses on additive manufacturing (3D printing) and related modeling, control, material, and application. He has published 1 edited book, 4 book chapters, and nearly 200 publications in refereed journals and conferences, as well as 19 issued and pending U.S. patents. His work has been recognized by over 15 Best/Outstanding Paper Awards in major design and manufacturing conferences and research journals. Other major awards he received include the NSF CAREER Award, USC’s Innovation Commercialization Awards, and invitations to the National Academy of Engineering Frontiers of Engineering Symposiums. Dr. Chen is a Fellow of the American Society of Mechanical Engineers (ASME). He has served as conference/program chair and keynote speaker at several international design and manufacturing conferences. At USC, Dr. Chen teaches students design and manufacturing-related courses. Nine Ph.D. students and post-doctors from his group have landed faculty positions in North American Universities.

Wednesday, November 12, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Zhao

3D Printing Active Electronics

Michael C. McAlpine

Professor
Department of Mechanical Engineering
University of Minnesota
Minneapolis, MN

The ability to three-dimensionally pattern active electronic devices (including semiconductors) represents a transformative approach to creating active electronics without the need for a cleanroom or conventional microfabrication facilities. This could enable the generation of active electronics on-the-fly, using only source inks and a portable 3D printer, to realize electronics anywhere, including in resource limited environments. Interfacing active devices with the body in 3D could impact a variety of fields, such as biomedical devices, wearable electronics, bioelectronics, smart prosthetics, and human-machine interfaces. Developing the ability to 3D print various classes of materials possessing distinct properties will enable the freeform generation of active electronics in unique functional, interwoven architectures. Yet, achieving seamless integration of these diverse materials via 3D printing is a challenge which requires overcoming discrepancies in material properties in addition to ensuring that all the materials are compatible with the 3D printing process. Our group has developed strategies for three-dimensionally integrating diverse classes of electronic materials using a custom-built 3D printer to create fully 3D printed active electronic devices. As proofs of concept, we have 3D printed quantum dot-based light-emitting diodes (QD-LEDs), polymer-based photodiodes on curvilinear surfaces, flexible displays, and skin-interfaced hybrid electronics. These results represent a series of critical steps toward the 3D printing of high performance, active electronic integrated materials and devices.

The McAlpine Research Group are the inventors of 3D printing functional materials & devices. Michael C. McAlpine is a Professor of Mechanical Engineering at the University of Minnesota and the Founder and Director of the 3D Electronics Center (3DE). He received a B.S. (2000) in Chemistry with honors from Brown University, and a Ph.D. (2006) in Chemistry from Harvard University. His research interests are focused on 3D printed active electronics, with recent breakthroughs in 3D printed OLED displays and 3D printed bionic eyes (one of National Geographic’s “12 innovations that will revolutionize the future of medicine”). He has received several awards for this work, including the Presidential Early Career Award for Scientists and Engineers (PECASE), and the National Institutes of Health Director’s New Innovator Award.

Wednesday, November 17, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Zhao

Electrokinetic Phenomena in Nanoconfinement: From Molecular Structure to Flow Control

Thomas Petersen

Assistant Professor
Sonny Astani Department of Civil and Environmental Engineering
University of Southern California
Los Angeles, CA

This seminar investigates electrokinetic phenomena in nanoscale confinement. I first explore how surface charge patterning and geometric undulations control flow in corrugated, charge-patterned nanochannels. Performing fully nonlinear Poisson-Nernst-Planck-Stokes (PNPS) simulations, I demonstrate three flow regimes—surface-gradient-induced electroosmosis, electrokinetically inhibited flow, and pressure-dominated flow—and show how charge placement and Debye screening enable selective ionic current control for envisioned applications of desalination and energy harvesting. As the PNPS equations are performed on continuum concentration fields, much detail about the molecular interactions between water molecules and co- and counter-ions is omitted in the formulation.

To address this limitation, I present a classical density functional theory (cDFT) framework. By explicitly including excluded volume effects, hydrogen bonding between water molecules, dispersion interactions, and electrostatic correlations, the model reproduces experimental observations of molecular layering near graphene and mica surfaces. The framework reveals how ion-specific properties and surface texture govern the electric double layer organization and demonstrates that multivalent ions generate attractive stresses between like-charged surfaces through out-of-plane structuring.

Thomas Petersen started working as an Assistant Professor in the Sonny Astani Department of Civil and Environmental Engineering in Fall 2022. Prior to arriving at the University of Southern California, he spent three years as a Senior Research Engineer at ExxonMobil, where he developed technologies to improve the integrity of wells during construction and operation. Specifically, he worked on composite fluid and solid systems that reduce pressure and stress developments in confined, high-temperature, and high-pressure environments. Before his research experience in industry, he obtained his Ph.D. (2019) on Mechanics of Materials and S.M. (2015) in Civil and Environmental Engineering from the Massachusetts Institute of Technology and received his B.S. (2011) in Civil Engineering with a Minor in Mathematics from North Carolina State University.

Wednesday, December 3, 2025

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

 

host: Plucinsky

Formation and Evolution of Turbulence in Convectively Unstable Internal Solitary Waves of Depression Shoaling over Gentle Slopes in the South China Sea

Peter Diamessis

Professor
School of Civil and Environmental Engineering
Cornell University
Ithaca, NY

The shoaling of high-amplitude Internal Solitary Waves (ISWs) of depression in the South China Sea (SCS) is examined through large-scale parallel turbulence-resolving high-accuracy/resolution simulations. A select, near-isobath-normal, bathymetric transect of the gentle SCS continental slope is employed together with stratification and current profiles obtained by in-situ measurements. Three simulations of separate ISWs with initial deep-water amplitudes in the range [136m, 150m] leverage a novel wave-tracking capability for a propagation distance of 80km and accurately reproduce key features of in-situ-observed phenomena with significantly higher spatiotemporal resolution. The interplay between convective and shear instability and the associated turbulence formation and evolution are further studied, as a function of deep-water ISW amplitude, in-part revealing processes previously not observed in the field. Across all three waves, the convective instability develops in a similar fashion: heavier water entrained from the wave rear plunges into its interior, giving rise to transient, yet distinct, subsurface vortical structures which transition to turbulence. Ultimately, a gravity current is triggered which horizontally advances through the wave interior and mixes it down to the pycnocline base. Although the waveform remains distinctly symmetric, Kelvin-Helmholtz billows emerge near the well-mixed ISW trough, disturb the wave’s trailing edge and give rise to an active wake. The wake's perturbation kinetic energy is nonlinearly dependent on deep-water wave amplitude and can become a sizable fraction of the kinetic energy of the deep-water ISW, suggesting the wake is a primary mechanism of water column mixing. The talk will conclude with potential interpretations on the origins of the above gravity current as a form of frontogenesis and the associated challenges of measuring such phenomena in the field.

Peter Diamessis joined the CEE faculty in January 2006. He received his undergraduate degree in Mechanical Engineering from the National Technical University of Athens (NTUA), Greece in 1995. From 1996 to 2001, he pursued graduate studies at the Mechanical and Aerospace Department (formerly Applied Mechanics and Engineering Sciences Dept.) of the University of California, San Diego. Following completion of his PhD studies, Diamessis became a postdoctoral researcher in the fluid dynamics group at the Aerospace and Mechanical Engineering at the University of Southern California where he focused on the development and implementation of numerically stable spectral multidomain techniques and the numerical investigation of stably stratified turbulent wakes and 2-D instabilities under internal solitary waves. Diamessis's recent and ongoing work involves the continued development of spectral multidomain schemes for more complex flow geometries and the application of element-based techniques to other disciplines such as structural mechanics and soil chemistry. The physically focused component of his efforts consists of the study of high Reynolds number stratified wakes and the evolution of the radiated internal wave field and its interaction with the subsurface region, the investigation 3-D turbulence and resuspension under internal solitary waves, the study of nonlinear effects in internal waves propagating through variable environments and the application of stability analysis to environmental boundary layers.

Friday, December 12, 2025

11:00 AM

Laufer Conference Room, (OHE 406)

 

host: Spedding