Event Calendar

Nov
15
Thu
Department of Mechanical Engineering Fall Seminar Series @ 210 Hodson Hall
Nov 15 @ 3:00 pm – 4:00 pm

“From fast to ultrafast: the biological world of extreme movement”

Presented by Professor Sheila Patek
Department of Biology, Duke University

Figure 1: Photo Credit, Roy Caldwell

This talk will explore the principles of fast movements in small biological and synthetic systems. I will begin with a classic consideration of power-amplified systems – a class of mechanisms that aims to circumvent the tradeoff between force and velocity – and then build on this tradeoff to incorporate the dynamic interactions among motors, springs, latches and projectiles.  I will explore the current knowledge of these dynamics in both engineered and biological systems and propose ways of thinking about the design of small and fast synthetic systems and strategic analysis of the rich diversity of biological systems.

Figure 2: Photo Credit, Roy Caldwell

Professor Sheila Patek is an Associate Professor in the Biology Department at Duke University.  Patek received her A.B. with honors in Biology from Harvard University followed by a Ph.D. in Biology from Duke University. She was then awarded an interdisciplinary Miller Postdoctoral Fellowship at UC Berkeley. She has received several honors, including a Guggenheim Fellowship, the George A. Bartholomew Award for distinguished contributions to comparative physiology, a Radcliffe Fellowship, a NSF CAREER award, and the Brilliant 10 award from Popular Science magazine. Her research has been funded by the National Science Foundation, National Geographic Society, Hellman Family Foundation, Armstrong Fund for Science, Department of Defense, and others. Patek currently leads a Multidisciplinary University Research Initiative (MURI) funded by the Army Research Office.

Nov
16
Fri
Graduate Seminar in Fluid Mechanics @ 132 Gilman Hall
Nov 16 @ 4:00 pm – 5:00 pm

4:10 pm Presentation

“A New In Vitro Exposure Device to Assess the Health Impacts of Aerosols on the Human Respiratory System

 Presented by LAKSHMANA CHANDRALA (Adviser: Prof. Katz)

Exposure systems for measuring the in-situ time evolution of response of human bronchial epithelial cells to aerosols are essential for understanding the pathogenesis of airway disease. This study describes the design and implementation of a novel Real-Time Examination of Cell Exposure (RTECE) system for assessing the cell’s response to airborne particles. Its major advantage over available commercial devices is the ability to observe the cells in situ throughout the exposure, enabling direct assessment of physiological changes, e.g., morphology, migration, and Ciliary Beat Frequency (CBF) of Human Bronchial Epithelial (HBE) cells. The latter could be used for assessing toxicity. Initially, the performance of the RTECE is compared with the commercial Vitrocell system, which does not allow in situ observations, by exposing HBE cells to cigarette smoke. Measurements of mass deposition, monolayer permeability, and CBF after the exposure show agreement. Subsequently, the cells are observed while being exposed to two cigarettes twice, separated by a rest period of 60 min. Time evolution of CBF is continuously monitored by calculating the Fourier transform of the images. The data reveals that the CBF decreases gradually during the first exposure but recovers to the initial level following a rest period. A similar gradual decrease occurs after the second exposure, but after a short recovery period, the CBF decreases rapidly and never recovers. Furthermore, the contrast images of the cells are continuously recorded for measuring the effect of the smoke on the cell motility. Results show that smoking causes an increase in cell motility.


4:35 pm Presentation

Laminar-to-Turbulence Transition in High-Speed Boundary Layers: A Nonlinear Optimization Approach”

 Presented by REZA JAHANBAKHSHI (Adviser: Prof. Zaki)

Transition to turbulence causes a significant increase in surface heating and viscous friction on hypersonic vehicles, which are severe performance deficiencies. At the vehicle-design stage, however, it is difficult to accurately account for these effects due the uncertainty of in-flight conditions and the lack of strict bounds on transition Reynolds numbers. We introduce a new approach that can compute the earliest possible transition location paving the way to robust flow design. The nonlinearly most unstable environmental disturbance that causes the fastest route to turbulence in a Mach 4.5 boundary layer flow is evaluated using an ensemble-variational (EnVar) technique. The problem is cast as a constrained optimization, in which the control vector is the inflow disturbance which satisfies the full Navier-Stokes equations and an energy constraint. The EnVar algorithm starts with an ensemble of potential solutions and computes the response of the governing equations to each control vector. The optimization problem is then solved and new candidate solutions are formed. The procedure is repeated until convergence is achieved. For the configuration studied here, the nonlinearly most unstable inflow spectrum is made of a pair of acoustic normal modes and an oblique vorticity wave. The associated transition mechanism cannot be categorized as a classical transition scenario, which highlights the importance of the nonlinear approach developed in current work. Nonlinear energy transfer between the instability modes at the inflow and the instability waves generated later in the flow, feature prominently in the transition scenario. These nonlinear interactions lead to generation of a particular instability wave that contains the characteristics of both vorticity and acoustic modes. This instability grows faster than any linear mode, forms hairpin vortices near the outer edge of the boundary layer and streaks close to the wall, and finally breaks down to turbulence along a relatively short transition zone.

Nov
29
Thu
Department of Mechanical Engineering Fall Seminar Series @ 210 Hodson Hall
Nov 29 @ 3:00 pm – 4:00 pm

“Addressing future aerospace challenges at NASA — how fundamental research matters”

Presented by Dr. Meelan Choudhari
Computational Aerosciences Branch, NASA Langley Research Center  

 Global aviation is forecast to double by mid-2030s and to triple by the mid-century.  Such tremendous growth in air travel will pose unprecedented challenges in minimizing the environmental impact of aviation.  To help address those challenges, NASA is targeting highly ambitious goals to increase the energy efficiency and reduce the emissions of future aircraft. A centerpiece of NASA’s aeronautics research includes new experimental flight demonstration vehicles, the X-planes, that will test advanced technologies and novel designs seeking to overcome these challenges.  However, equally crucial to these aeronautics endeavors as well as to the long-term goals related to space exploration are the fundamental research efforts targeting physics-based prediction tools and novel design concepts related to aerodynamics, aerothermodynamics, structures, and materials.  This briefing will provide a partial overview of NASA’s recent endeavors related to aerodynamics and aeroacoustics, followed by selected examples that focus on recent research in computational fluid dynamics, modeling of laminar-turbulent transition, and airframe noise.

Nov
30
Fri
Graduate Seminar in Fluid Mechanics @ 132 Gilman Hall
Nov 30 @ 4:00 pm – 5:00 pm

4:10 pm Presentation

“Probable Sites of Cavitation Inception and Associated Pressure Field in a Turbulent Shear Layer

 Presented by KARUNA AGARWAL (Adviser: Prof. Katz)

Cavitation inception in a turbulent shear layer occurs preferentially in secondary quasi-streamwise vortices, appearing as intermittent braids between the primary spanwise vortices. High speed imaging of the cavitating structures in the shear layer generated by a backward-facing step enables identification of the most probable regions of cavitation, and therefore high pressure fluctuations. The most likely inception regions are located between 45% to 75% of the reattachment length, well upstream of the peaks in Reynolds stresses. While the distribution of mean flow and turbulence parameters scale with the freestream velocity and reattachment length, the frequencies of cavitation events at corresponding inception indices do not. To explain these trends, the three-dimensional time resolved pressure field is determined by using tomographic PIV data for calculating the acceleration field, and then integrating it spatially to obtain the pressure. With a velocity vector spacing of 247 µm, and temporal resolution of 67 µs, it is possible to characterize the properties of the 1-2 mm diameter quasi-streamwise vortices. To satisfy the stringent temporal and spatial resolution requirements, a physics-based interpolation scheme (from particle velocities to Eulerian grid) is introduced.

Dec
6
Thu
Department of Mechanical Engineering Fall Seminar Series @ 210 Hodson Hall
Dec 6 @ 3:00 pm – 4:00 pm

“Multiscale Process-Structure Simulations for Additive Manufacturing in Metals”

Presented by Professor Greg Wagner
Mechanical Engineering, Northwestern University

Additive manufacturing (AM) brings advantages for the fabrication of metal parts compared with traditional techniques, including the ability to create complex geometries with reduced production lead time and less material waste. However, the intricacy of the additive process and the extreme thermal environments involved can lead to material defects, heterogeneous microstructures, and wide variation in properties, leading to unpredictable and sometimes inferior performance of AM-built parts. Computational simulation can be used to understand and predict the effects of various process parameters on the resulting material, and to suggest strategies to optimize ultimate part performance. In this talk, I present modeling approaches at several length scales that are important in predicting material structure in AM. These include the part scale, where geometry and build strategy affect the thermal history throughout the material; the melt pool scale, where fluid flow and phase change dictate the heat transfer in the solidifying material; and the material microscale, where repeated re-melting and the competition between grain growth and nucleation can lead to unusual grain structures. Novel computational methods and tools are used at each scale, and to couple across scales. Finally, I discuss ideas for developing reduced order models to more efficiently material structure for a given set of process parameters.

Greg Wagner received his Ph.D. in Mechanical Engineering from Northwestern University in 2001. He spent over 12 years as a staff member and later manager in the Thermal/Fluid Science and Engineering department at Sandia National Laboratories in Livermore, CA, where his work included multiscale and multi-physics computational methods, multiphase and particulate flow simulation, extended timescale methods for atomistic simulation, and large-scale engineering code development.  In January 2015 he joined the faculty of the Mechanical Engineering department at Northwestern. His current research focuses on applying novel simulation methods and high performance computing to multiphase flows and flows with complex and moving geometries. He is the author or co-author of over 50 journal articles, and his awards include the Zienkiewicz Prize for Numerical Methods in Engineering. He is an associate editor for Computer Modeling in Engineering & Sciences and Journal of Micromechanics and Molecular Physics.

Dec
7
Fri
Graduate Seminar in Fluid Mechanics @ 132 Gilman Hall
Dec 7 @ 4:00 pm – 5:00 pm

4:00 pm Presentation

“Computational Modeling of Hemodynamics and Blood Washout in the Patient-Specific Left Atrial Appendages

 Presented by CHUANXIN NI (Advisers: Dr. Jung-Hee Seo & Prof. Mittal)

The left atrial appendage (LAA) is a small chamber-like organ connected to the left atrium (LA). Studies have shown that this structure is implicated in thrombus formation and thromboembolic events for patients with atrial fibrillations. However, due to its highly complex and variable shape, the blood flow patterns and the mechanism of thrombogenesis inside the LAA are poorly understood. The aim of this study is to analyze the hemodynamics inside patient-specific LA/LAAs via computational fluid dynamics (CFD) modeling and to understand the potential for thrombus formation in the LAA. Patient-specific LA/LAA geometries are derived from high-resolution CT scans and the blood flowrate profiles at the mitral annulus are obtained from ultrasound Doppler measurements. Direct numerical simulation is carried out using a sharp-interface immersed boundary method. An Eulerian transport equation for the blood residence time is also solved inside the fluid domain to investigate the blood transportation and coagulation potential in the LAA. In this study, several patient-specific cases with different LAA shapes and heart conditions are considered and the blood flow patterns and washout in the LAA are compared for these cases.


4:25 pm Presentation

Compressing DNS Datasets using a Sub-Domain Re-Simulation Algorithm”

 Presented by ZHAO WU (Adviser: Prof. Meneveau)

With the development of computer speed, researchers are able to perform larger and larger direct numerical simulations (DNS). In 2013, Lee et al. (SC’13) used 260 million CPU hours to run the then world record DNS channel flow at Reτ=5200 with 121 billion grid points. In 2015, Yeung et al. (PNAS 2015) performed an isotropic turbulence DNS on a 81923 grid. Simple calculations show a single snapshot of velocity and pressure would cost 2TB and 8.8TB for the two DNS respectively, in single precision. Clearly, storing the time-resolved results would not be feasible in the current storage approach. To overcome this difficulty, we are experimenting with a novel algorithm to store the dataset. Once the original DNS (termed big DNS below) is performed, spatiotemporal subsampling will be stored. When a user requests values at a particular grid point, a re-simulation of the sub-domain (termed re-simulation below), which contains the querying grid point, will be performed, with boundary conditions from the subsampling. We have found that we have to perfectly match the numerical scheme of the re-simulation with the big DNS to produce machine precision errors. The re-simulation errors will be linearly proportional to the errors, if any, introduced in the re-simulation, which could be caused by using different numerical schemes or incorrect boundary conditions.

Jan
31
Thu
Department of Mechanical Engineering 2019 Spring Seminar Series: Class 530.804 @ 26 Mudd Hall
Jan 31 @ 3:00 pm – 4:00 pm

Cracking and buckling: defect driven mechanics of collagen and DNA

Presented by Dr. Keir Neuman
Laboratory of Single Molecule Biophysics, National Heart, Lung, and Blood Institute
National Institutes of Health

Defects in macroscopic beams decrease the mechanical stability and promote buckling and cracking under compressive and torsional stress.  For example, a twisted hose will buckle and form an interwound plectoneme at a pre-formed kink.  At the microscopic scale of biological polymers such as collagen and DNA, defects on the scale of thermal energy can result in unusual behaviors with important physiological consequences.  I will describe a spontaneous periodic buckling phenomenon in fibrillar type I collagen that exposes the otherwise impervious surface of collagen to binding and degradation by matrix metalloproteinases (MMPs).  These spontaneous defects migrate over the surface of the collagen while maintaining their periodicity that far exceeds the intrinsic length scales of collagen. The dynamic yet periodic defects can be explained with a simple internal strain model that provides a mechanistic explanation for the inhibition of MMP degradation by the application of external load.  Defects in DNA occur spontaneously due to damage and errors in replication or repair.  We find that supercoiling can localize a single mismatch in many thousands of base-pairs of DNA and we propose that this may be a mechanism to facilitate mismatch and damage recognition by repair enzymes.  Furthermore, the unusual buckling kinetics at mismatches and the direct observation of an intermediate state provide strong evidence supporting a recently proposed torsional buckling pathway.

Keir Neuman graduated cum laude with a B.A. in physics and applied math from the University of California, Berkeley in 1994 and received his Ph.D. in physics from Princeton University in 2002. He did postdoctoral research with Steven Block at Stanford University from 2002 to 2004, and was a Human Frontiers Fellow with David Bensimon and Vincent Croquette at the Laboratoire de Physique Statistique at the École Normale Supérieure in Paris, France from 2004 to 2007. Dr. Neuman joined the NHLBI as a tenure-track Investigator in 2007 and was promoted to senior investigator in 2015. Dr. Neuman is a member of the Biophysical Society, the Optical Society of America, and the American Physical Society.

Feb
7
Thu
Department of Mechanical Engineering 2019 Spring Seminar Series: Class 530.804 @ 26 Mudd Hall
Feb 7 @ 3:00 pm – 4:00 pm

Critical Ruga Structures for Molecular Self-Assembly and Adhesion/Friction Control in Soft Materials

Presented by Professor Kyung-Suk Kim
Director of the Center for Advanced Materials Research, Professor of Engineering
Brown University

Morphologies and electronic states of solid surfaces are often used to control guided self-assembly of molecules as well as adhesion and friction in bio and nanotechnology. Here, we first present nanomechanical analysis of peculiar crinkle-ruga formation in multilayer graphene. The ‘crinkle’ is one of subcritical ruga structures, and a quantum-flexoelectric crinkle in graphene was discovered recently [1-3]. The quantum-flexoelectric crinkle in graphene localizes electric surface line-charge within 0.86 nm width along crinkle valleys and ridges. Controlling the charge localization, the crinkle is used as a molecular manipulator. The graphene crinkles attract and align bio-molecules, or nano-particles. Herein, we present detailed mechanisms of critical crinkle formation in graphene, which is revealed by quantum/continuum hybrid analysis. Then, presented are verifications of the crinkle formation and associated self-assembly of molecules with an AFM atomic lattice interferometry [4]. In addition, also presented will be how multi-scale ruga structures control adhesion and friction in soft-material structures.

[1] M. Kothari, M. H. Cha and K.-S. Kim, “Critical curvature localization in graphene. I. Quantum- flexoelectricity effect,” Proceedings of the Royal Society A. doi: 10.1098/rspa.2018.0054, 2018.

[2] M. Kothari, M. H. Cha, V. Lafevre and K.-S. Kim, “Critical curvature localization in graphene. II. Nonlocal flexoelectricity-dielectricity coupling, Proceedings of the Royal Society A. doi: 10.1098/rspa.2018-0671, 2018.

[3] R. Li, M. Kothari, A. Landauer, M. Cha, H. Kwon, & K.-S. Kim, “A New Subcritical Nanostructure of Graphene—Crinkle-Ruga Structure and Its Novel Properties,” MRS Advances, 1-7. doi:10.1557/adv.2018.432, 2018.

[4] B. K. Jang, J. Kim, H. J. Lee, K .-S. Kim, C. Wang, “Device and method for measuring distribution of atomic resolution deformation,” United States Patent, Patent Number 9,003,561: issued on April 7, 2015.

Kyung-Suk Kim has 38 years of experience as an engineering scientist and is currently Professor of Engineering at Brown University.  He received his Ph.D. (1980) in Solid Mechanics from Brown University. He taught at TAM Department, University of Illinois, Urbana-Champaign for 9 years until he joined Brown as Professor of Engineering in 1989. He served as a board member (2012-2015) and the Representative of the Society of Engineering Science (SES) to U.S. National Committee for Theoretical and Applied Mechanics (2016-2018). His research interests are in scale-bridging mechanics, and nano and micromechanics of solids. Through his research on dynamic properties of solids, adhesion and friction, ruga mechanics of soft materials and stability of nanostructures, he has invented numerous new scientific instruments, including various interferometers, and analytical methods. He has advised more than 40 Ph.D. students and postdocs. His work has been recognized through various awards including the Melville Medal (1981), JEP best paper award (1999), the Drucker Medal from ASME (2016), the John Simon Guggenheim Fellowship (1996), the Ho-Am Prize in Engineering (2005), the Kwan-Ak Distinguished Alumni Award of Seoul National University (2012), and the Engineering Science Medal from the Society of Engineering Science (2012). His research on “New Math for Designer Wrinkles” was selected as one (# 30) of the Top 100 Science Stories, in Discover (2015). He will deliver the William, M. Murray Lecture of the Society of Experimental Mechanics in 2019.

Feb
14
Thu
Department of Mechanical Engineering 2019 Spring Seminar Series: Class 530.804 @ 26 Mudd Hall
Feb 14 @ 3:00 pm – 4:00 pm

Control of Reaction Fronts for Rapid Energy-Efficient Manufacturing of Multifunctional Polymers and Composites

Presented by Professor Nancy R. Sottos
Department of Materials Science and Engineering &
The Beckman Institute for Advanced Science and Technology
University of Illinois at Urbana Champaign

Reaction-diffusion processes are versatile, yet underexplored methods for manufacturing that provide unique opportunities to control the spatial properties of materials, achieving order through broken symmetry. The mathematical formalism and derivation of equations coupling reaction and diffusion were presented in the seminal paper by Alan Turing [Phil. Trans. R. Soc. Lond. B 237, 37,1952], which describes how random fluctuations can drive the emergence of pattern and structure from initial uniformity. Inspired by reaction-diffusion systems in nature, this talk describes a new manufacturing platform technology predicated on the exploitation of an autocatalytic (self-propagating) polymerization reaction occurring in a system undergoing reaction and diffusion of its ingredients.  The system uses the exothermic release of energy to provide a positive feedback to the reaction. In turn, this stimulates further exothermic energy release, and a self-propagating reaction “front” that rapidly moves through the material – a process called frontal polymerization.  The self-sustained propagation of a reaction wave through the material gives rise to entirely new ways of manufacturing high performance composites using rapid, energy efficient methods at greatly reduced costs, including 3D printing of thermosetting polymers and composites. Controlling the reaction wave by simple thermal perturbations gives rise to symmetry breaking events that can enable complex, emergent pattern formation and control over growth, topology, and shape.

Nancy Sottos is the Donald B. Willet Professor of Engineering in the Department of Materials Science and Engineering and the Beckman Institute at the University of Illinois Urbana-Champaign.  Sottos started her career at Illinois in 1991 after earning a Ph.D. from the University of Delaware.  Her research interests include self-healing polymers and advanced composites, mechanochemically active polymers, tailored interfaces and novel materials for energy storage. Sottos’ research and teaching awards include the ONR Young Investigator Award, Scientific American’s SciAm 50 Award, the Hetényi Best Paper Award in Experimental Mechanics, the M.M. Frocht and B.J. Lazan Awards from the Society for Experimental Mechanics, the Daniel Drucker Eminent Faculty Award, an IChemE Global Research Award and the Society of Engineering Science Medal. She is a Fellow of the Society of Engineering Science and the Society for Experimental Mechanics.

Feb
15
Fri
Graduate Seminar in Fluid Mechanics @ 132 Gilman Hall
Feb 15 @ 4:00 pm – 5:00 pm

4:10 pm Presentation

 Formation of Compound Droplets by Turbulent Buoyant Oil Jet and Plume”

 Presented by XINZHI XUE (Adviser: Prof. Katz)

Buoyant jet and plume are important in many engineering and environmental applications. In the regime of high Reynolds and Ohnesorge number, knowledge breakup of a liquid jet in another immiscible liquid is limited, however, it is relevant to e.g., to oil well blowout on the sea floor. In this study, refractive index matched silicone oil and sugar water are used as surrogate to crude oil and seawater. Their density, viscosity ratio, and interfacial tension are closely matched with the original liquids. Simultaneous planar laser-induced fluorescence and particle image velocimetry are applied to dissect the jet center plane for flow visualization, as well as quantitative concentration and velocity measurements. Initially, the oil jet entrains water layers as the shear layer rolls up along the jet periphery. While a few droplets form in this process, the primary fragmentation of oil to ligaments occurs 6-12 and 7-13 nozzle diameters downstream of the nozzle at Re=1358 and 2122, respectively. In both cases, compound droplets, containing multiple water droplets, some with smaller oil droplets, form regularly. The origin of some of the encapsulated water droplets can be traced back to the entrained water ligaments. They persist for at least up to 30 nozzle diameters – the current measurement range. Random forest-based segmentation is applied to measure the compound droplet statistics, showing that this phenomenon increases the overall interfacial area by 23% and 15% for Re=1358 and 2122, respectively, increasing with droplet size. The interior water droplets are also less deformed than the exterior oil droplets and ligaments, indicating that the interior interfaces are subjected to less shear. Such longer-lived quiescent interfaces might facilitate increased biochemical interaction between the oil and the water.


4:35 pm Presentation

Vortex Shedding from a Circular Cylinder in Shear-Thinning Carreau Fluids

 Presented by SHANTANU BAILOOR (Advisers: Profs. Mittal & Zaki)

Results from numerical simulations of two-dimensional, shear-thinning Carreau fluid flow over an unconfined circular cylinder are presented in this paper. Parametric sweeps are performed over the various Carreau model parameters, and trends of the time-averaged force coefficients and vortex characteristics are reported. In general, increased shear-thinning results in lower viscous forces on the body but greater pressure forces, resulting in a complex non-monotonic drag response. Lift forces generally increased with shear-thinning due to the dominant pressure contribution. The decrease in fluid viscosity also led to shorter vortex formation lengths and the consequent rise in the Strouhal frequency of vortex shedding. It is expected that these results will be useful for verification of computational models of unsteady non-Newtonian flows.

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