Event Calendar

Graduate Seminar in Fluid Mechanics: EN.530.807 @ Join online via Zoom: https://wse.zoom.us/j/93762992307
Oct 2 @ 4:00 pm – 5:00 pm

Department of Mechanical Engineering
Join on-line via Zoom: https://wse.zoom.us/j/93762992307
Friday, October 2, 2020 | 4:00 p.m. – 5:00 p.m. (EDT)

“Computational Modeling of Ultrasound Generation in the Larynx of Echolocating Bats”

Presented by CHUANXIN NI
(Advisers: Profs. Rajat Mittal & Jung-Hee Seo)

Echolocating bats produce extremely high-frequency sounds from their larynx using a similar phonating organ as other mammals. Significant knowledge gaps, however, still exist in our understanding of the underlying mechanism of ultrasound generation in bat larynx including the precise role of its anatomical structures during the generating process. One hypothesis is that the unique laryngeal membrane and ventricle structures in the bat larynx may play an important role in the high-intensity ultrasound generation. The objective of this study is to develop and employ a high-fidelity computational model to investigate the mechanism of bat ultrasound production. To build up a model of the bat larynx, high-resolution micro-CT scans are obtained to resolve the unique anatomical structures of bat larynx. Using the geometrical parameters obtained from the scans, a 2D canonical model and a lumped-element model are constructed to investigate the frequency response and the resonance characteristics of the bat larynx and vocal tract. Furthermore, by leveraging the results of this linear acoustic analysis, coupled flow-structure-aeroacoustics interaction simulations are planned to perform on a canonical model of the bat larynx with the laryngeal membranes to resolve the nonlinear behavior of ultrasound generation.

“Instantaneous Pressure Field and Aerodynamic Loads Across a Harmonically Pitching Airfoil”

Presented by JIBU TOM JOSE
(Adviser: Prof. Joseph Katz)

Experimental studies of complex unsteady aerodynamic loads on an airfoil undergoing dynamic stall were performed using a harmonically pitching airfoil. The experiments were performed at a Reynolds number of 45,000 in a refractive index matched water tunnel using a NACA 0015 airfoil with 50mm chordlength, oscillating harmonically between 5o and 20o at a reduced frequency of 0.411. Time resolved stereo PIV data were acquired at 1250 frames/s covering the flow on both sides of the foil simultaneously. Assuming a 2D flow, the pressure field around the airfoil was computed by direct integration of material acceleration calculated from the time-resolved velocity field, using an in-house developed, GPU based, parallel-line, omni-directional code. The formation and development of Leading Edge Vortex, and subsequent dynamic stall vortex, and the existence of a phase lag between the incidence angle and the development of suction side structures during upstroke and downstroke were evident from the data. Growth and migration of the pressure minima from the leading to the trailing edge induced pitch up and pitch down moments, respectively.

Department of Mechanical Engineering 2020 Fall Virtual Seminar Series: Class 530.803 @ https://wse.zoom.us/j/91752450849
Oct 8 @ 3:00 pm – 4:00 pm

“Navigating in a turbulent environment”

Presented by Professor Mimi Koehl
Department of Integrative Biology, University of California, Berkeley

When organisms locomote and interact in nature, they must navigate through complex habitats that vary on many spatial scales, and they are buffeted by turbulent wind or water currents and waves that also vary on a range of spatial and temporal scales.  We have been using the microscopic larvae of bottom-dwelling marine animals to study how the interaction between the swimming or crawling by an organism and the turbulent water flow around them determines how they move through the environment.  Many bottom-dwelling marine animals produce microscopic larvae that are dispersed to new sites by ambient water currents, and then must land and stay put on surfaces in suitable habitats.  Field and laboratory measurements enabled us to quantify the fine-scale, rapidly-changing patterns of water velocity vectors and of chemical cue concentrations near coral reefs and along fouling communities (organisms growing on docks and ships). We also measured the swimming behavior of larvae of reef-dwelling and fouling community animals, and their responses to chemical and mechanical cues.  We used these data to design agent-based models of larval behavior.  By putting model larvae into our real-world flow and chemical data, which varied on spatial and temporal scales experienced by microscopic larvae, we could explore how different responses by larvae affected their transport and their recruitment into reefs or fouling communities.  The most effective strategy for recruitment depends on habitat.

Mimi Koehl, a Professor of the Graduate School in the Department of Integrative Biology at the University of California, Berkeley, earned her Ph.D. in Zoology at Duke University.  She studies the physics of how organisms interact with their environments, focusing on how microscopic creatures swim and capture food in turbulent water flow, how organisms glide in turbulent wind, how wave-battered marine organisms avoid being washed away, and how olfactory antennae catch odors from water or air moving around them. Professor Koehl is a member of the National Academy of Sciences and the American Academy of Arts and Sciences, and is a Fellow of the American Physical Society.  Her awards include a MacArthur “genius grant”, a Presidential Young Investigator Award, a Guggenheim Fellowship, the John Martin Award (Association for the Sciences of Limnology and Oceanography, for “for research that created a paradigm shift in an area of aquatic sciences”), the Borelli Award (American Society of Biomechanics, for “outstanding career accomplishment”), the Rachel Carson Award (American Geophysical Union, for “cutting-edge ocean science”), and the Muybridge Award (International Society of Biomechanics “highest honor”).

Graduate Seminar in Fluid Mechanics @ Join online via Zoom
Oct 9 @ 4:00 pm – 5:00 pm

Department of Mechanical Engineering
Join on-line via Zoom: https://wse.zoom.us/j/93762992307
Friday, October 9, 2020
4:00 p.m. – 5:00 p.m. (EDT)

“Deep Operator Neural Networks (DeepONets) for Prediction of Instability Waves in High-Speed Boundary Layers”

(Advisers: Profs. Charles Meneveau & Tamer Zaki)

We show how DeepONets can predict the amplification of instability waves in high-speed flows. In contrast to traditional networks that are intended to approximate functions, DeepOnets are designed to approximate operators and functionals. Using this framework, we train a DeepONet that takes as inputs an upstream disturbance and a downstream location of interest, and provide as output the amplified profile at the downstream position in the boundary layer. DeepONet thus approximates the linearlized Navier-Stokes operator for this flow. Once trained, the network can perform predictions of the downstream flow for a wide variety of inflow conditions without the need to calculate the whole trajectory of the perturbations, and at a very small computational cost compared to discretization of the original flow equations.

“The Effect of Seams on the Aerodynamics of Baseballs: A Computational Study”

Presented by JOHN SCHEFFEY
(Adviser: Prof. Rajat Mittal)

The aerodynamic force on a ball due to its rotation, known as the Magnus effect, has long been observed and studied in baseball and other ball sports. Experimental studies have examined the effects of pitch speed, spin rate, and seam height on these forces, but the underlying effect of the presence of a seam is not as well understood. Recently, there has been interest in the potential existence of “non-Magnus” forces, which are thought to be caused by certain seam orientations in ball flight. In this study, we present numerical simulations of flows past rotating spheres at varying orientation angles of rotation and investigate the effects of baseball seams on the aerodynamics of such bodies. Simulations are performed at Reynolds numbers of 500 and 1000 and spin ratios of 0.25 and 0.5. We examine the role that baseball seams play in modifying the wake and producing asymmetry, leading to transverse forces that generate deviations in the trajectory of pitched and batted balls.

26th Annual James F. Bell Memorial Lecture in Continuum Mechanics @ Zoom
Oct 13 @ 3:00 pm – 4:00 pm

ZOOM LINK: https://wse.zoom.us/j/98427352821 | Passcode 781551

“Soft Material Characterization by Magnetic Resonance Phase Field Imaging”

Presented by Professor Ellen M. Arruda Tim Manganello/BorgWarner Department Chair of Mechanical Engineering and the Maria Comninou Collegiate Professor of Mechanical Engineering at the University of Michigan

The characterization of the mechanical properties of soft materials, including elastomers and the soft tissues of knee and shoulder joints has been a major focus of my laboratory. Obtaining the mechanical properties of soft tissues is particularly challenging for a number of reasons, the first of which is that they are very soft, and direct gripping is fraught with problems. They are also anisotropic, therefore testing in multiple directions and deformation states is typically required. Our interest in developing full-knee computational models necessitates accurate constitutive models of the soft tissues of the knee. Finite element (FE) models of the knee can provide specific information on individual tissue contributions with respect to global joint function, as well as the coupling and coordination among tissues during macroscopic joint motions. Computational models offer precise, full-field, and complete descriptions of deformation manifesting from normal motions, injury causing activities, injured and diseased joints, and reconstructive procedures. FE models further have the potential to conduct clinically meaningful, individualized joint analyses.

In this talk I will show how geometric effects, heterogeneous deformation, and experimental uncertainty have manifested as subject-to-subject variability in the mechanical response of the anterior cruciate ligament (ACL). I will describe our use of full-field methods to overcome these challenges and the tremendous opportunity they afford in characterization of the non-linear, anisotropic mechanical properties of soft tissues. Specifically, we have pioneered a new experimental method for finite strain characterization of soft materials using the phase field signal during in-situ mechanically deforming materials with magnetic resonance imaging. We have validated our approach using a well-characterized elastomer and recently applied the approach to the bundles of the ACL and the patellar tendon of the knee. We add to our approach to virtual fields method of characterization. Time permitting I will also describe our very recent efforts to also characterize materials without assuming a constitutive model a priori.

Professor Ellen M. Arruda is the Tim Manganello/BorgWarner Department Chair of Mechanical Engineering, and the Maria Comninou Collegiate Professor of Mechanical Engineering at the University of Michigan. She also holds courtesy appointments in Biomedical Engineering and in Macromolecular Science and Engineering. Professor Arruda earned her BS degree in Engineering Science (with Honors) and her MS degree in Engineering Mechanics from Penn State, and her PhD degree in Mechanical Engineering from MIT. Professor Arruda teaches and conducts research in the areas of theoretical and experimental mechanics of macromolecular materials, including polymers, elastomers, composites, soft tissues and proteins, and in tissue engineering of soft tissues and tissue interfaces. Her recent honors and awards include the 2019 Nadai medal from the American Society of Mechanical Engineers, the 2018 Rice medal from the Society of Engineering Science, the 2015 Outstanding Engineering Alumnus Award from the Pennsylvania State University, the 2014 Distinguished Faculty Achievement Award from the University of Michigan, the Ann Arbor Spark Best of Boot Camp award 2012, and the 2012 Excellence in Research Award by the American Orthopaedic Society for Sports Medicine. Professor Arruda has more than 100 papers in scientific journals. She also holds thirteen patents. Her H-index is 35 (ISI). Professor Arruda is a Fellow of the American Society of Mechanical Engineers, the American Academy of Mechanics, and the Society of Engineering Science. She is currently President of the American Academy of Mechanics. She is a member of the National Academy of Engineering (class of 2017).

Mechanical Engineering Virtual Info Session @ Zoom
Oct 15 @ 10:30 am – 11:30 am

This one-hour session will give you a broad overview of the graduate programs in the Department of Mechanical Engineering offered at Johns Hopkins University. Panelists will provide a program overview, areas of research, admissions requirements, and discuss life in Baltimore. In addition, you will have the opportunity to ask any questions you may have.

REGISTER HERE: https://wse.zoom.us/webinar/register/WN_B24fPKxtSvOnACaD_DjbzA

Learn more about Mechanical Engineering Graduate Studies at Johns Hopkins: https://me.jhu.edu/graduate-studies

Mechanical Engineering 2020 Fall Virtual Seminar Series: Class 530.803 @ Join online via Zoom
Oct 29 @ 3:00 pm – 4:00 pm

Meeting ID: 917 5245 0849 | Passcode: 605594

“Soft, shape, sense: Fabricating hierarchically-patterned soft mechanical sensors”

Presented by Professor Kristen Dorsey
Assistant Professor of Engineering, Smith College

Physically-soft mechanical sensors are poised to unlock exciting new applications in wearable devices, robotics, and human-machine interfaces. This interdisciplinary area borrows from materials science, mechanical engineering, and electrical engineering to realize physically soft sensors that can measure deformations such as strain, torsion, and pressure. A promising development in soft mechanical sensors is hierarchically-patterned structures within the sensor, which enables both deformation selectivity and the ability to tune sensing properties.

I will discuss work and challenges related to fabricating hierarchically-patterned sensors. I will also present work in enhancing the selectivity of stretchable sensors, towards tuning a wearable sensor for measuring human body motions and using origami patterns to improve mechanical selectivity between pressure and strain.

Dr. Kris Dorsey is an assistant professor of engineering in the Picker Engineering Program at Smith College. She was a President’s Postdoctoral Fellow at the University of California, Berkeley and University of California, San Diego. Dr. Dorsey graduated from Carnegie Mellon University with a Ph.D. in Electrical and Computer Engineering and earned her Bachelors of Science in Electrical and Computer Engineering from Olin College. She founded The MicroSMITHie Lab at Smith College to investigate micro- and miniature-scale sensor design and to prepare undergraduates for graduate study in engineering. Her current research interests include novel morphology soft sensors, stability concerns for soft-material sensors, and sensors for soft robots and wearable devices. Dr. Dorsey has co-authored several publications on hyperelastic strain sensors, novel soft lithography processes, and the stability of gas chemical sensors. In 2019, she received the NSF CAREER award.

Mechanical Engineering 2020 Fall Virtual Seminar Series: Class 530.803 @ Join online via Zoom
Nov 5 @ 3:00 pm – 4:00 pm

Meeting ID: 917 5245 0849 | Passcode: 605594

“Mechanics of the extracellular matrix and its biophysical consequences”

Presented by Professor Herbert Levine
Professor of Physics and Bioengineering, Northeastern University

In order to metastasize, cancer cells must leave the primary tumor and transit through collagen-rich fibrous material known as the extra-cellular matrix (ECM). This material has interesting mechanical properties, properties which directly affect its reciprocal interaction with cells. This talk will provide an introduction to recent efforts to formulate simple yet informative mathematical models of ECM behavior and compare these to increasing quantitative experimental data.

Dr. Herbert Levine is a Professor of Physics and Bioengineering at Northeastern University and has adjunct faculty positions at Rice University and MD Anderson Cancer Center. For several decades Dr. Levine has been an acknowledged leader in applying methods from physical science to living systems. He has served as chair of the Biological Physics division of the American Physical Society and the Biological Physics interest group of the National Academy of Sciences, to which he was elected in 2011. He is on the editorial board of PNAS, has been an associate editor of Physical Review Letters, and recently finished a term as editor-in-chief of Physical Biology. Currently he is the lead of the Northeastern branch of a National Science Foundation Physics Frontier Center devoted to theoretical biological physics and the coordinator of an international network of graduate students working on the physics of living systems.

Future Leaders in Mechanical and Aerospace Engineering: Celebrating Diversity and Innovation
Nov 11 @ 2:00 pm – 3:00 pm

This nationwide online seminar series highlights research contributions by graduate students and postdocs from groups that are underrepresented among Mechanical Engineering and Aerospace Engineering faculties.

In addition to providing exposure and mentorship opportunities to the speakers, the seminar series will create a network among underrepresented students and faculty allies in MAE departments across the country.

  • Watch the seminar here: http://bit.ly/MAEFutureLeaders (join by phone: 172 929 8293, access code: S9ejUZVS8u6)

  • Speaker 1: Matthew Clarke, Ph.D. student at Stanford University, “Prediction of the Operational Envelope of Electric Aircraft Through Robust Battery Cycle-Life Modeling” (Advisor: Juan Alonso)

  • Speaker 2: Jeremy Epps, Ph.D. student at Georgia Institute of Technology, “An Analysis of Wake Interactions of a Novel Aerial Modular Robotic System” (Advisor: Mitchell Walker)

  • Faculty Mentors: TBD

  • Host: Allison Okamura (Stanford University)

Graduate Seminar in Fluid Mechanics @ https://wse.zoom.us/j/93762992307
Nov 13 @ 4:00 pm – 5:00 pm

Join on-line via Zoom: https://wse.zoom.us/j/93762992307
Friday, November 13, 2020
4:00 p.m. – 5:00 p.m. (EST)

“The Dynamics of Inertial Particles in a Under-Expanded Sonic Jet”

(Adviser: Prof. Rui Ni)

Particle-laden flows are ubiquitous in nature and in many engineering applications, covering a large range of spatial and temporal scales from the formation of planetary disks to the supersonic plume-surface interaction during Lunar and planetary landing. As particles traverse a series of expansion and compression waves in the compressible flow regime, they could potentially significantly modulate the flow characteristics as the particle mass loading increases. In this study, a high-speed under-expanded sonic jet is seeded with monodisperse solid particles, with mean diameters of 29.5 μm, 41.5 μm, and 98 μm. A range of mass loadings were used, and particles were tracked using a ultra-high-speed system to obtain their Lagrangian particle trajectories, velocities, and accelerations. The results acquired from this unique system provide a set of new high-fidelity experimental data for studying high-speed particle-laden flows and may reveal new insights into the physics of inertial particles traveling through compressible media. Earlier results of this work are compared with numerical simulations performed at the University of Michigan, which show good agreement between the two studies.

This work was supported by a NASA Space Technology Graduate Research Opportunity.

“Experimental Investigation of the 3D Flow Structure around a Pair of Cubes Immersed in the Inner Part of a Turbulent Channel Flow”

Presented by JIAN GAO
(Adviser: Prof. Joseph Katz)

The origin and evolution of the three-dimensional flow structures around a pair of roughness cubes embedded in the inner part of a turbulent channel flow (Reτ=2300) are measured using microscopic dual-view tomographic holography. The cubes’ height, a=1 mm, corresponds to 91 wall units or 3.9% of half channel height. They are aligned in the spanwise direction and separated by a, 1.5a, and 2.5a. This study focuses on the mean flow structure, and the data resolution allows detailed characterization of the open separated regions upstream, along the sides, on top, and behind the cubes, as well as measurements of wall shear stress from velocity gradients. The flow features a horseshoe vortex, a vortical canopy engulfing each cube, a near wake arch-like vortex, and multiple interacting streamwise vortices. Most of the boundary layer vorticity is entrained into the horseshoe vortex. The canopy, consisting of wall-normal vorticity to the sides, and spanwise vorticity on top of the cube, originates from the front surface. The streamwise vortices originate from realignment of the other components along the corners of the front surface. Merging of streamwise structures around and behind each cube causes formation of a large streamwise vortex rotating in the same direction as the inner horseshoe leg, with remnants of the outer leg under it. This merging occurs earlier and the entire flow structure becomes more asymmetric with decreasing spacing. Peaks and minima in the distributions of the bottom wall shear stress are associated with the formation of and interactions among the near-wall vortices.

Mechanical Engineering Fall Virtual Seminar Series: Class 530.803 @ Join online via Zoom
Nov 19 @ 3:00 pm – 4:00 pm

Meeting ID: 917 5245 0849 | Passcode: 605594

“Extended lifetime of respiratory droplets in a turbulent vapor puff and its implications on airborne disease transmission”

Presented by Professor Detlef Lohse
Physics of Fluids Group, University of Twente

To mitigate the COVID-19 pandemic, it is key to slow down the spreading of the life-threatening coronavirus (SARS-CoV-2). This spreading mainly occurs through virus-laden droplets expelled at speaking, screaming, shouting, singing, coughing, sneezing, or even breathing. To reduce infections through such respiratory droplets, authorities all over the world have introduced the so-called 2-meter distance rule or 6-foot rule. However, there is increasing empirical evidence, e.g. through the analysis of super-spreading events, that airborne transmission of the coronavirus over much larger distances plays a major role, with tremendous implications for the risk assessment of coronavirus transmission. It is key to better and fundamentally understand the environmental ambient conditions under which airborne transmission of the coronavirus is likely to occur, in order to be able to control and adapt them.

Here we employ direct numerical simulations of a typical respiratory aerosol in a turbulent jet of the respiratory event within a Lagrangian-Eulerian approach with 5000 droplets, coupled to the ambient velocity, temperature, and humidity fields to allow for exchange of mass and heat and to realistically account for the droplet evaporation under different ambient conditions. We found that for an ambient relative humidity of 50% the lifetime of the smallest droplets of our study with initial diameter of 10 _m gets extended by a factor of more than 30 as compared to what is suggested by the classical picture of Wells, due to collective effects during droplet evaporation and the role of the respiratory humidity, while the larger droplets basically behave ballistically. With increasing ambient relative humidity the extension of the lifetimes of the small droplets further increases and goes up to 150 times for 90% relative humidity, implying more than two meters advection range of the respiratory droplets within one second. Smaller droplets live even longer and travel further. We also show that for low ambient temperatures the problem is even more serious, as the humidity saturation level of air goes down with decreasing temperature. Our results may explain why COVID-19 superspreading events can occur for large ambient relative humidity such as in cooled-down meat-processing plants or in pubs with poor ventilation. We anticipate our tool and approach to be starting points for larger parameter studies and for optimizing ventilation and indoor humidity controlling concepts, which both will be key in mitigating the COVID-19 pandemic.

This is joint work with Kai Leong Chong, Chong Shen Ng, Naoki Hori, Morgan Li, Rui Yang, and Roberto Verzicco.

Professor Detlef Lohse studied physics at the Universities of Kiel & Bonn (Germany), and got his PhD at Univ. of Marburg (1992). He then joined Univ. of Chicago as postdoc. After his habilitation (Marburg, 1997), in 1998 he became Chair at Univ. of Twente in the Netherlands and built up the Physics of Fluids group. Since 2015 he is also Member of the Max Planck Society and of the Max-Planck Institute in Göttingen and since 2017 Honorary Professor at Tsinghua Univ., Beijing. Lohse’s present research interests include turbulence and multiphase flow, micro- and nanofluidics (bubbles, drops, inkjet printing, wetting), and granular & biomedical flow. He does both fundamental and more applied science and combines experimental, theoretical, and numerical methods. Lohse is Editor of J. Fluid Mech. and Ann. Rev. Fluid Mech. (among others journals) and serves as Vice-Chair for the Executive Board of the Division of Fluid Dynamics of the American Physical Society and Member of the Executive Board of IUTAM. He is Member of the (American) National Academy of Engineering (2017), of the Dutch Academy of Sciences (KNAW, 2005), the German Academy of Sciences (Leopoldina, 2002) and Fellow of APS (2002). He won various scientific prizes, among which the Spinoza Prize (NWO, 2005), the Simon Stevin Meester Prize (STW, 2009), the Physica Prize of the Dutch Physics Society (2011), the AkzoNobel Science Award (2012), two European Research Council Advanced Grants (2010 & 2017), the George K. Batchelor Prize (IUTAM, 2012), the APS Fluid Dynamics Prize (2017), the Balzan Prize (2018), and the Max Planck Medal (2019). In 2010, he got knighted to become “Ridder in de Orde van de Nederlandse Leeuw”. Website: http://pof.tnw.utwente.nl

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