Seminars

Symmetry, Deformations and the Search for Unprecedented Materials from First Principles

Amartya Banerjee

Assistant Professor
Department of Materials Science and Engineering
University of California at Los Angeles
Los Angeles, CA

The mathematical framework of Objective Structures generalizes ideas associated with crystals to atomic/molecular configurations with non-periodic symmetries. Some of the most widely studied structures in materials science, biology and nano-technology can be described as objective structures. The list of objective structures includes nano-tubes, nano-ribbons, buckyballs, tail sheaths and capsids of viruses, many common proteins, graphene and phosphorene sheets as well as molecular bilayers. The presence of high degrees of symmetry in objective structures makes them likely to be associated with remarkable material properties (particularly, collective material properties such as ferromagnetism, ferroelectricity and superconductivity) and their departure from the bulk phase makes them likely to demonstrate such properties in manners that are otherwise unavailable in crystalline systems.

A systematic study of objective structures is likely to lead to the discovery of unprecedented materials. At the same time, formulation and implementation of theoretical and computational methods specifically designed for studying objective structures, is likely to lead to the development of new simulation methodologies in nano-mechanics and materials science.

Following these lines of thought, we have been developing Objective Density Functional Theory (Objective DFT) – a suite of rigorously formulated quantum mechanical theories and numerical algorithms for carrying out ab initio simulation studies of objective structures. Objective DFT is intended to be a natural extension of the traditional Periodic Density Functional Theory method for studying crystalline systems, just as objective structures are a natural generalization of periodic structures. In this talk, I will describe some of the principal mathematical ideas and algorithmic techniques behind Objective DFT, as well as some of the key features and capabilities of this novel computational tool. Additionally, I will highlight how Objective DFT allows the non-periodic symmetries associated with objective structures to be exploited, to investigate non-uniform deformation modes in various nano-materials, from first principles.

Finally, I will discuss some of the many applications that have sprouted from the development of Objective DFT. These include (but are not limited to) the use of the computational packages developed in this work to study the mechanical stability and optical properties of nano-clusters, nano-ribbons and nano-tubes (with potential applications to energy materials and nano-structured meta-materials), ab initio studies of the mechanical and electronic properties of nano-beams, nano-tubes and various 2D materials, as well as the investigation of functional nano-materials with strongly correlated electronic states (with potential applications to the development of novel sensors and quantum hardware materials).

Amartya Banerjee leads the Ab Initio Simulations Laboratory at UCLA, and is an Assistant Professor of Materials Science & Engineering. His research interests include first principles calculations, simulations of energy, quantum and biological materials, mechanics of materials and structures, applications of symmetry principles, multi-scale methods, numerical analysis and scientific computation. Dr. Banerjee obtained his Ph.D. in Aerospace Engineering & Mechanics from the University of Minnesota in 2013. He also holds M.S. degrees in Mathematics, and Aerospace Engineering & Mechanics from the University of Minnesota. He received his undergraduate degree in Aerospace Engineering from the Indian Institute of Technology, Kharagpur, India in 2007. Prior to joining UCLA in 2019, he held postdoctoral appointments at the Computational Research Division of the Lawrence Berkeley National Laboratory, and at the University of Minnesota.

Dr. Banerjee has held visitor positions at the Hausdorff Research Institute for Mathematics, University of Bonn, Germany and the Institute of Mathematics and its Applications, Minneapolis, USA. He has received several awards and travel grants (including the John A. & Jane Dunning Copper Fellowship from the University of Minnesota and the US Junior Oberwolfach Fellowship), and has delivered invited presentations at numerous prestigious research laboratories and universities.

Wednesday, August 25, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: Renuka Balakrishna

Wakes in the Natural Environment

Sutanu Sarkar

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

Environmental wakes are produced by flows past structures which are engineered (e.g., oceanic submersibles, aerial vehicles, wind turbines, urban structures) or in nature (hills, mountain ranges, islands, seamounts). These wakes impact drag on the incident flow as well as transport of material, pollutants and environmental constituents. We will illustrate wake flow physics with a few examples studied using high-resolution simulation. The wake of a blunt object such as a disk will be contrasted with a streamlined object such as a prolate spheroid with respect to mean velocity, turbulence levels, flow instabilities and coherent structures. We will discuss both a constant density fluid and a density-stratified fluid where buoyancy inevitably alters the wake of the body. We will also present an example from nature, an oceanic current past a submerged hill, where we find synchronization of wake vortices with subharmonics of the oscillating tide and also states of high drag.

Sutanu Sarkar received his B. Tech. from IIT Bombay, M. S. from Ohio State University and Ph. D. from Cornell University. After 4 years as a staff scientist at ICASE, NASA Langley Research Center, he joined UCSD where he currently holds the Blasker Chair of Environmental Engineering, is a Distinguished Professor in the department of Mechanical & Aerospace Engineering (MAE), and is an affiliate professor at the Scripps Institution of Oceanography. He was Chair of MAE from 2009-2014. He has broad interests in the simulation and modeling of turbulent flows. He has worked in problems concerning the environment, energy, aerospace and propulsion. His current research interests are turbulence and mixing in the ocean and atmosphere, wakes and boundary layers of engineered structures in the natural environment, and renewable energy. He has received a NASA group achievement award (1994), the Bessel Award from the Humboldt Foundation (2001), and was elected Fellow, American Physical Society (2006), Associate Fellow, AIAA (2009) and Fellow, ASME (2010). He is an associate editor of JFM.

Wednesday, September 1, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: AME Department

Turbulence in Vegetation Canopies – From Biometeorology to Wildfires

Tirtha Banerjee

Assistant Professor
Department of Civil and Environmental Engineering
University of California at Irvine
Irvine, CA

The traditional motivation behind studying the dynamics of turbulent wind flow in vegetation canopies has been to understand the nature of mass, momentum and energy exchange between the land surface and the atmosphere. The nature of this interaction determines the microclimate in a forest environment where plants exchange carbon and water and its understanding is relevant for a plethora of applications ranging from ecology, hydrology, agriculture and the modeling of weather and climate. However, the fundamental nature of turbulence in a vegetation canopy is significantly different from the atmospheric surface layer lying above, which means that scaling laws and exchange coefficients from traditional wall bounded flows are not applicable. In a forest canopy, momentum absorption happens not only at the ground surface but throughout the depth of the canopy, resulting in a unique ‘roughness sub layer’. Instead of a log-layer, the mean velocity profile is inflected, second order moments are variable with height and skewnesses are large. Large scale coherent structures impart significant impact on the turbulence dynamics. Sweeping motions arising out of downdraft motions of counter-rotating vortices dominate eddy fluxes. A mixing layer model is found to be a better model for describing canopy flows. High frequency measurements and computational fluid dynamics modeling, especially Large Eddy Simulations (LES) has been instrumental in revealing the nature of canopy turbulence in the last few decades. Now this knowledge is being used to push the frontiers of our limited understanding of how wildland fires behave. The main controls on wildland fire behavior – fuel (canopy and grasslands), weather and topography are strongly influenced by fine scale physics of canopy turbulence. We will demonstrate that further developments in the understanding of canopy turbulence can benefit wildfire modeling tools and developing actionable management strategies.

Tirtha Banerjee is an Assistant Professor at the Department of Civil and Environmental Engineering, University of California, Irvine. He received his Bachelor of Science degree in Civil Engineering from Jadavpur University, Calcutta, India in 2011. During his undergraduate studies, he conducted research in the areas of structural dynamics and Aerospace Engineering in India and Germany as a DAAD (German Academic Exchange Service) Fellow. Upon completion of his undergraduate studies in 2011, he moved to the U.S. and joined Duke University in Durham, NC, as a Ph.D. student and conducted theoretical, numerical and experimental studies involving environmental fluid dynamics and turbulent flows. He received his Ph.D. in 2015 and joined the Karlsruhe Institute of Technology (KIT) in Germany for postdoctoral research in atmospheric boundary layer dynamics. He relocated to the U.S. in early 2017 to join the Los Alamos National Laboratory (LANL) in New Mexico and started working on wildfires, ecosystem disturbance as well as wind energy resources. At LANL he received a Chick Keller Postdoctoral Fellowship in 2017 and a Director’s Fellowship in 2018. He joined UC Irvine in fall 2019. Research in the Boundary Layers and Turbulence Lab led by Banerjee studies mass, momentum and energy exchange between the land surface and the atmosphere using a range of theoretical, numerical and experimental techniques. He currently serves as an associate editor of the journal Earth Systems and Environment (Springer) and as an editorial board member of the journal Agricultural and Forest Meteorology (Elsevier).

Wednesday, September 8, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: Luhar

Simulation of Bubbly, Cavitating Flows with Application to Shock- and Ultrasound-Based Medical Therapies

Tim Colonius

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

Models and numerical methods for simulating bubbly, cavitating flows have benefitted from recent advances in sharp and diffuse interface-capturing schemes, but many challenges remain to be solved before they can be routinely used to predict the complex, multiscale flows associated with important applications in engineer ing and medicine. In particular, the complex phase boundary, small length scales, and fast time scales associated with the dynamics of bubbles and clouds of bubbles strain existing algorithms and computational resources. In this talk, I will review different formulations for multiphase/multicomponent flows that involve large changes in volume, including methods that explicitly resolve the material interface, and ones that model the mixture as either homogeneous, or as a dilute dispersion of spherical bubbles. These methods are demonstrated in applications involving the high-intensity ultrasound and shock waves used for medical imaging and intra- and extra-corporeal manipulation of cells, tissue, and urinary calculi. Such waves are currently used to treat kidney stone disease, plantar fasciitis, and bone nonunion, and they are being investigated as a technique to ablate cancer tumors and mediate drug delivery. In many applications, acoustic waves induce the expansion and collapse of preexisting or newly cavitating bubbles. The resulting bubble dynamics generate large, localized stresses and strains that can be beneficial or deleterious depending on how effectively they can be controlled. I will describe efforts aimed at simulating the collapse of bubbles, both individually and in clusters, in order to characterize these mechanical stresses and strains.

Tim Colonius is the Frank and Ora Lee Marble Professor of Mechanical Engineering at the California Institute of Technology. He received his B.S. from the University of Michigan in 1987 and M.S and Ph.D. in Mechanical Engineering from Stanford University in 1988 and 1994, respectively. He and his research team use numerical simulations to study a range of problems in fluid dynamics, including aeroacoustics, flow control, instabilities, shock waves, and bubble dynamics. Prof. Colonius also investigates medical applications of ultrasound, and is a member of the Medical Engineering faculty at Caltech. He is a Fellow of the American Physical Society and the Acoustical Society of America, and he is Editor-in-Chief of the journal Theoretical and Computational Fluid Dynamics. He was the recipient of the 2018 AIAA Aeroacoustics Award and the 2021 APS Stanley Corrsin Award.

Wednesday, September 15, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at
https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: AME Department

Dragonfly’s Titan Entry and Descent System and DrEAM Instrumentation Suite

Aaron Brandis

Senior Research Scientist
Aerothermodynamics Branch
NASA Ames Research Center
Moffett Field, CA

This presentation will discuss the entry and descent phase for the Dragonfly missions arrival at Titan, a moon of Saturn. Dragonfly is a rotorcraft lander mission designed to take advantage of Titan's environment to sample materials and determine surface composition in different geologic settings, and even to search for chemical signatures that could indicate water-based and/or hydrocarbon-based life. The DrEAM instrumentation suite will take measurements of pressure, temperature and heatflux around the aeroshell during the Dragonfly entry.

Dr Brandis is a senior research scientist employed by AMA Inc in the Aerothermodynamics branch at NASA Ames Research Center. He is the PI for NASA’s Entry Systems Modeling project, Dragonfly aerothermal lead and PI for Dragonfly’s Titan entry instrumentation, known as DrEAM. His research focuses on shock layer radiation with the NEQAIR code and EAST shock tube facility.

Wednesday, September 22, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: AME

Initiated Chemical Vapor Deposition of Polymer Coatings and Membranes

Malancha Gupta

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

Initiated chemical vapor deposition (iCVD) is a solventless process that can be used to synthesize polymer films and coatings with a range of functionalities including hydrophilicity, hydrophobicity, light-responsiveness, and thermo-responsiveness. This talk will present the mechanism, capabilities, and advantages of the iCVD process. We will demonstrate that the iCVD process can be used to modify the surface properties of fibers, membranes, and microfluidic channels for applications in textiles, separations, and diagnostics. We will also demonstrate that polymers can be deposited onto low vapor pressure liquids including ionic liquids and silicone oils to fabricate ultrathin freestanding polymer films, nanoparticles, core-shell particles, and gels. We will also show that lowering the temperature of the substrate below the freezing point of the monomer leads to the formation of polymer membranes. These membranes can be deposited onto porous substrates to create hierarchical porous-on-porous structures that can enable improved filtration for water purification and sensor applications.

Malancha Gupta is the Gabilan Distinguished Professor at the Mork Family Department of Chemical Engineering and Materials Science at the University of Southern California. She received her B.S. in chemical engineering from The Cooper Union in New York City in 2002. She received her Ph.D. in chemical engineering from Massachusetts Institute of Technology in 2007 under the guidance of Professor Karen Gleason. From 2007-2009, she was a postdoctoral fellow in the department of chemistry and chemical biology at Harvard University working under the guidance of Professor George Whitesides. Her current research interests include polymer coatings and thin films, chemical vapor deposition, ionic liquids, and microfluidics. She has mentored 16 doctoral students and published 68 peer-reviewed manuscripts. She received the Jack Munushian Early Career Chair in 2013, the National Science Foundation CAREER award in 2013, and the USC Viterbi School of Engineering Junior Faculty Award in 2014. She was director of the chemical engineering program from 2018-2020 and she has served as chair of the Women in Science and Engineering (WiSE) engineering committee at USC since 2015.

Wednesday, September 29, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: Luhar

Rethinking Compressible Turbulence: From New Regimes to Extreme Simulations

Diego A. Donzis

Associate Professor
Department of Aerospace Engineering
Texas A&M University
College Station, TX

Compressible turbulence is much more common than incompressible turbulence and plays a critical role in countless natural and engineering systems such as astrophysical flows, high-speed aerodynamics, turbulent combustion, among many others. However, much less is known about compressible turbulence due to its larger parameter space; the additional complexity associated with coupling between hydrodynamics and thermodynamics; and the greater challenges to develop theory, attain realistic conditions in simulations, and conduct carefully controlled experiments.

In the first part of this talk I will review recent work that highlights some qualitative differences observed in compressible turbulence using a massive database of very well-resolved direct numerical simulations. After some illustrations of specific compressibility effects on turbulent flows, I will show why current approaches as "corrections" to well-known laws in incompressible turbulence present fundamental problems and then `provide a new alternative interpretation of statistical equilibria in an expanded parameter space in which new compressible universal scaling laws can be found. In the second this part, I will present current computational challenges to achieve more realistic conditions and a novel numerical approach in which the main well-known obstacles towards simulations on exascale systems and beyond can be removed. We will present some examples for smooth flows as well as flows with shocks and reactions.

Diego A. Donzis is an associate professor and Director of Graduate Programs in the Department of Aerospace Engineering at Texas A&M University where he directs the Turbulence and Advanced Computations Lab (TACL). He received his PhD from the Georgia Institute of Technology and continued his research at the University of Maryland and the International Centre for Theoretical Physics, Italy. His main interests are in high-performance computing at extreme scales, and the physics of turbulence and turbulent mixing in incompressible and compressible flows. Among his major recognitions Dr. Donzis received an NSF CAREER award, the Francois Frenkiel Award from the American Physical Society, TAMU Dean of Engineering Excellence Award, three TEES Faculty Awards for research, the McElmurry Teaching Excellence Award, and is a best graduate from Argentina by the National Academy of Engineering. In 2018, he was named a Presidential Impact Fellow by Texas A&M University for his scholarly influence. He is an AIAA Associate Fellow.

Wednesday, October 6, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: AME

Dynamics of Acoustically Coupled Combustion Instabilities

Ann Karagozian

Distinguished Professor
Department of Mechanical and Aerospace Engineering
UCLA
Los Angeles, CA

Acoustically-coupled combustion instabilities can result in large scale, potentially catastrophic pressure oscillations in aerospace propulsion systems, including liquid rocket engines (LREs) and gas turbine engines. A fundamental understanding of the interactions among flow and flame hydrodynamics, acoustics, and reaction kinetics is essential to determining combustor stability and controlling combustion processes. Over the past several years our group at the UCLA Energy and Propulsion Research Laboratory has been pursuing fundamental experiments that can shed light on combustion instabilities and their control, including exploration of the effects of external acoustic perturbations on liquid nanofuel combustion as well as gas-phase fuel jet combustion for alternative geometrical configurations. The dynamics of phenomena such as periodic liftoff and reattachment, periodic partial extinction and reignition, and full extinction are explored and quantified via phase-locked OH* chemiluminescence and high speed visible imaging. Proper orthogonal decomposition (POD) modes and phase portraits extracted from time-resolved imaging enables characterization of characteristic signatures associated with different phenomena. Understanding such signatures enables development of reduced order models that can impact eventual combustion control strategies.

Ann Karagozian is a Distinguished Professor in the Department of Mechanical and Aerospace Engineering at UCLA and heads the UCLA Energy and Propulsion Research Laboratory and the UCLA-Air Force Research Laboratory Collaborative Center for Aerospace Sciences. Her research interests lie in fluid mechanics and combustion as applied to improved energy efficiency, reduced emissions, and advanced air breathing and rocket propulsion systems. Professor Karagozian was a member of the Air Force Scientific Advisory Board for over 15 years, serving as SAB Vice Chair from 2005-2009 and twice receiving the Air Force Decoration for Exceptional Civilian Service. She is a Member of the National Academy of Engineering and is a Fellow of the American Institute of Aeronautics and Astronautics (AIAA), the American Physical Society (APS), and the American Society of Mechanical Engineers (ASME). She received her B.S. in Engineering from UCLA and her M.S. and Ph.D. in Mechanical Engineering from the California Institute of Technology. She is a member of the Board of Trustees of the Institute for Defense Analyses (IDA) and is an alumna of and mentor for the IDA Defense Science Study Group. Prof. Karagozian also recently became the Inaugural Director of The Promise Armenian Institute, an endowed scholarly and cross-disciplinary outreach entity at UCLA.

Wednesday, October 13, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: Bermejo-Moreno

Capillary Flows of Suspensions

Alban Sauret

Assistant Professor
Department of Mechanical Engineering
University of California at Santa Barbara
Santa Barbara, CA

Interfacial flows of multiphase systems containing a dispersed solid or liquid phase occur in a broad range of manufacturing, environmental, and bioengineering processes. However, the classical capillary dynamics is strongly modified when the length scale of the liquid becomes comparable to the particle size. This configuration may lead to a failure of classical models based on a rheological approach. For instance, particles can destabilize thin-films, lead to defects in additive manufacturing, reduce transport efficiency, and result in the contamination of substrates.

In this talk, I will present some of our recent studies that characterize the role of interfaces in suspension dynamics. I will first describe the formation of a thin-film of suspension on a substrate to illustrate how the particles are entrained and deposited depending on the flow configuration and suspension properties. I will discuss how these results can be used to develop passive capillary filtering and sorting mechanisms. The second part of the talk will characterize how particles can modify the formation of droplets and the atomization of suspension sheets and ligaments. Our approach, bridging different length and time scales, describes how the bulk behavior and local heterogeneities contribute to the dynamics of multiphase capillary objects.

Alban Sauret is an Assistant Professor in the Department of Mechanical Engineering at UC Santa Barbara. He graduated with a BS and an MS in Physics from ENS Lyon (France) and earned a Ph.D. in Mechanical Engineering from the University of Aix-Marseille (France) in 2013. During his graduate studies, he was awarded a Geophysical Fluid Dynamics Fellowship from the Woods Hole Oceanographic Institution. He then worked as a Postdoctoral Fellow at Princeton University from 2013 to 2014 and then spent four years as a tenured CNRS Research Scientist in a joint academic and industrial laboratory, while also being a visiting research scholar at NYU Tandon School of Engineering. He joined UC Santa Barbara in 2018. His research aims at understanding the dynamics of multiphase systems. He is particularly interested in the couplings between the fluid dynamics, interfacial effects, and particle transport mechanisms involved in environmental and industrial processes. Alban Sauret was named a Soft Matter Emerging Investigators in 2017, was elected a UC Regents Junior Faculty Fellow in 2019, and received the NSF CAREER Award in 2020. His past results were highlighted in various media, including the Los Angeles Times, The Wall Street Journal, and Science Friday.

Wednesday, October 20, 2021

3:30 PM

Seaver Science Library, Room 202 (SSL 202)

The Zoom webinar is at https://usc.zoom.us/j/97427241653?pwd=UGd2aXY2b3dsQkxMdzdvcnNBMjRJZz09.

host: AME

host: Balakrishna

host: Kanso

host: Ronney