Event Calendar

Sep
14
Thu
Mechanical Engineering 2017 Fall Seminar Series: Class 530.803 @ 210 Hodson Hall
Sep 14 @ 3:00 pm – 4:00 pm

“Intervertebral disc biomechanics with swelling and injury”

Presented by Professor Grace O’Connell, Department of Mechanical Engineering, University of California, Berkeley

The musculoskeletal system is comprised of large load bearing soft tissues that absorb and distribute the complex loads placed on the joint. Degeneration of these tissues, including articular cartilage and the intervertebral disc of the spine, is the leading cause of disability in Americans, contributing to over $130 billion in medical costs. These tissues have limited ability to self heal, and current treatment options, including total joint replacement with a device comprised of metal and plastic components, significantly alters the loading environment. This talk will focus on recent advances in understanding disc biomechanics with hydration and injury. Furthermore, I will discuss recent advances in large-scale development of biological treatment options through cartilage tissue engineering.

Dr. Grace D. O’Connell is an Assistant Professor in the Department of Mechanical Engineering at the University of California, Berkeley. She is the co-director of the Berkeley Biomechanics Laboratory, and her research interests are in soft tissue mechanobiology and tissue engineering. O’Connell received her BS degree in Aerospace Engineering from the University of Maryland and her PhD in Bioengineering from the University of Pennsylvania, where her research focused on intervertebral disc biomechanics with age, degeneration, and injury. She then conducted a postdoctoral research in cartilage tissue engineering with Dr. Clark Hung at the University of Columbia. O’Connell’s research group is currently evaluating the role of tissue swelling and stress homeostasis in injured and degenerated intervertebral discs. She has received many awards including the 2017 ACS Polymeric Materials: Science and Engineering (PMSE) Young Investigator Award and the Signatures Fellow for Innovation. She is also an active member of the American Society of Mechanical Engineering – Biomechanics Division and is the Scholarship Chair for the Golden Gate Section of the Society of Women Engineers.

Sep
15
Fri
Graduate Seminar in Fluid Mechanics 530.807 @ 316 Hodson Hall
Sep 15 @ 3:00 pm – 4:00 pm

3:00 p.m. Presentation

Large Eddy Simulation Including Population Dynamics Model for Polydisperse Droplet Evolution in Turbulence

 Presented by ADITYA KANDASWAMY AIYER (Adviser: Prof. Meneveau)

Previous studies have shown that dispersion patterns of oil droplets in the ocean following a deep sea oil spill depend critically on droplet diameter. Hence predicting the evolution of the droplet size distribution is of critical importance for predicting macroscopic features of dispersion in the ocean. We adopt a population dynamics model of polydisperse droplet distributions for use in LES. We generalize a breakup model from Reynolds averaging approaches to LES in which the breakup is modeled as due to bombardment of droplets by turbulent eddies of various sizes. The breakage rate is expressed as an integral of a collision frequency times a breakage efficiency over all eddy sizes.An empirical fit to the integral is proposed in order to avoid having to recalculate the integral at every LES grid point and time step. The fit is tested by comparison with various stirred tank experiments. As a flow application for LES we consider a jet of bubbles and large droplets injected at the bottom of the tank. The advected velocity and concentration fields of the droplets are described using an Eulerian approach. We study the change of the oil droplet distribution due to breakup caused by interaction of turbulence with the oil droplets.

Acknowledgement: This research was made possible by a grant from the Gulf of Mexico Research Initiative.


3:25 p.m. Presentation

Flow-Induced Flutter of Multiple Inverted Flags for Improved Energy Harvesting

 Presented by AARON RIPS (Adviser: Prof. Mittal)

Multi-inverted flag configurations undergoing flow-induced flutter have been studied using a coupled fluid-structure interaction solver. Both tandem and side-by-side configurations are examined to better understand the dynamics and energy harvesting potential of these systems, and to identify configurations that enhance energy harvesting. Parametric sweeps over the separation distance demonstrate a rich variety of coupling modes and system dynamics. A number of operational regimes have been identified for this two-flag system and correlated to the vortex dynamics. Simulations indicate that the coupling between flags can be used to enhance overall energy harvesting potential.

Sep
21
Thu
Department of Mechanical Engineering 2017 Fall Seminar Series: Class 530.803 @ 210 Hodson Hall
Sep 21 @ 3:00 pm – 4:00 pm

“Lapping dogs, skittering frogs, and insect blood: an organismal biomechanics perspective”

Presented by Professor Jake Socha
Dept. Biomedical Engineering and Mechanics, Virginia Tech

Our lab studies the comparative biomechanics of animal locomotion, respiration, circulation, and feeding. We also dabble in bio-inspired engineering, borrowing principles from animals to design new engineered devices. In this talk, I’ll discuss multiple projects on how vertebrate animals move in and on fluids, and how insects move fluids within their bodies. In the area of locomotion, our work has focused on skittering frogs that hop on the water surface and jump into the air from a floating position, and how flying snakes traverse gaps in the arboreal environment. In the area of insect physiology, we have been exploring how blood is pumped in the insect heart, which includes imaging studies using synchrotron x-rays and Doppler ultrasound, and additional measurements of blood viscosity. I’ll also briefly talk about how dogs drink, because who doesn’t love a good dog story?

Dr. Jake Socha is an associate professor in the Department of Biomedical Engineering and Mechanics at Virginia Tech. He earned a B.S. in physics and biology from Duke University in 1994 and a Ph.D. in biology (with a focus on biomechanics) from the University of Chicago in 2002. After graduate school, he was the Ugo Fano Postdoctoral Fellow at Argonne National Laboratory, studying insect flow systems using synchrotron x-ray imaging at the Advanced Photon Source. His research program at Virginia Tech combines both interests, investigating the biomechanics and functional morphology of flows in and around organisms. Current research foci include: the behavior, biomechanics, and aerodynamics of gliding flight in vertebrates, particularly flying snakes; and the biomechanics and physiology of internal convective flows involved in breathing, feeding, and circulation in insects. Prior to entering science, he was a member of the Teach for America national teacher corps, serving as the sole high school science teacher at Centerville High School in southern Louisiana.

Sep
22
Fri
Graduate Seminar in Fluid Mechanics 530.807 @ 316 Hodson Hall
Sep 22 @ 3:00 pm – 4:00 pm

3:00 p.m. Presentation

The Behaviors of Tip Leakage Vortex in the Tip Region of an Aviation Compressor Rotor

 Presented by YUANCHAO LI (Adviser: Prof. Katz)

The blade tip flow in a compressor rotor has been studied experimentally in the JHU refractive index matched facility for years. This presentation summarizes the measurements performed to date and highlights the features associated with the tip leakage vortex (TLV). TLV is commonly observed in all the turbomachines tested in our lab, including the current compressor with different tip gaps at different operating conditions. The mean and instantaneous behaviors of these vortical structures are reviewed, including the high spatial variation of the 3D velocity field near vortex center and the elevated turbulence level associated with multiple vortical filaments. Furthermore, a quasi-2D analysis is performed to evaluate the wall effect on the spatial migration of TLV. The velocity induced by the ‘image vortex’ in the other side of the endwall turns out to be in the same order of magnitude as the measured migration speed away from the blade. And the trends for different tip gaps and flow rates can be favorably explained using the vortex strength and the distance between vortex center and the endwall. In the end, the effects of axial casing grooves on the TLV are presented briefly, together with an introduction to the on-going measurement campaign with varied groove geometries.


3:25 p.m. Presentation

Numerical Study of Separating Turbulent Boundary Layer

 Presented by WEN WU (Advisers: Profs. Mittal & Meneveau)

Flow physics and modelling of separating turbulent boundary layers (TBLs) are investigated. On one hand, we examined the separating TBLs over smooth and rough plates using large-eddy simulation (LES). Streamline detachment occurs earlier and the separation region is substantially larger for the rough-wall case, due to the momentum deficit by roughness. Coincidence of various separation criteria does not hold in the rough-wall case and the causes are revealed. The separated shear layer exhibits higher turbulent kinetic energy (TKE) in the rough-wall case. Besides, the growth of the TKE there begins earlier relative to the separation point, and the peak TKE occurs close to the separation point. Momentum deficit caused by the roughness, again, plays a critical role in these changes. On the other hand, a modification to a scale-adaptive-type subgrid-scale model is proposed, and is applied to the wall-modelled LES of separating TBLs. The new model shows better accuracy of predicting the separation point compared with the dynamic eddy viscosity model. Such improvement is achieved by reducing the contribution of the resolved TKE, which contains numerical and model errors due to the poor grid resolution near the surface, to the total one.

Sep
29
Fri
Graduate Seminar in Fluid Mechanics @ 316 Hodson Hall
Sep 29 @ 3:00 pm – 4:00 pm

3:00 pm Presentation

 “An Adjoint Variational Data-Assimilation Approach for Flow-State Estimation

 Presented by MENGZE WANG (Adviser: Prof. Zaki)

Numerical predictions of laminar-to-turbulence transition are very sensitive to initial and boundary conditions, across flow regimes.  For example, the relative phases of instability waves can significantly shift transition onset in channel flow even if the initial disturbance energy is unchanged.  An analogous problem where significant progress has been achieved is numerical weather prediction: small changes in the initial conditions can significantly alter forecasts. The prediction accuracy can be appreciably enhanced by incorporating measurements in the initial condition, which can be accomplished using adjoint variational techniques.   In this work, a discrete adjoint Navier-Stokes algorithm is derived, implemented and validated.  It is subsequently used within a variational approach to estimate the state of Tollmien-Schlichting waves within channel flow, using wall information. State estimation of transitional and fully turbulent channel flow will be considered in future work.


 3:25 pm Presentation

The Restricted Nonlinear Large Eddy Simulation Framework and Applications in Wind Energy

 Presented by JOEL BRETHEIM (Advisers: Profs. Meneveau & Gayme)

The restricted nonlinear (RNL) model is a reduced-order model of turbulent wall-bounded shear flow which has been shown to accurately reproduce certain statistical features of wall-turbulence in low to moderate Reynolds numbers. Recently we have extended the RNL model to arbitrarily high Reynolds numbers by developing a large eddy simulation (LES) framework for the RNL system. We present our latest results from simulations of this new RNL-LES system, drawing comparisons with prior direct numerical simulations of the RNL system and with LES. We identify a new method to determine a priori the important streamwise lengthscales to include for simulations of a band-limited version of the RNL-LES system. Finally, we present new results from applying the RNL-LES simulation framework to simulations of wind farms.

Oct
5
Thu
Mechanical Engineering Fall Seminar Series @ 210 Hodson Hall
Oct 5 @ 3:00 pm – 4:00 pm

“Application of characterization, modelling, and analytics towards understanding process-structure linkages in metallic 3D printing”

Dr. Michael Groeber, Senior Materials Research Scientist
Metals Branch/Materials State Awareness Branch, Air Force Research Laboratory, WPAFB

Additive manufacturing presents both extreme potential and concern for component design. The ability to locally tailor processing path opens the door to sophisticated new designs with heterogeneous properties.  However, accounting for this heterogeneity, before exploiting it, requires the ability to link local processing state to properties/performance of local material.  A concern with current geometry-based design approaches, such as topology optimization, is not directly accounting for material property changes as geometry updates are made.  Given current closed and fixed scanning strategies of most commercial systems, local processing paths are potentially altered significantly with seemingly minor macroscopic geometry changes and are unable to be avoided.

This talk will present methods for combining process monitoring, thermal modelling and microstructure characterization together to draw process-to-structure relationships in metal additive manufacturing.  The paper discusses heterogeneities in the local processing conditions within additively manufactured components and how they affect the resulting material structure.  Methods for registering a fusing disparate data sources are presented and some effort is made to discuss the utility of different data sources for specific microstructural features of interest.  It is the intent that this paper will highlight the need for improved understanding of metallic additive manufacturing processes and show that combining experimental data with modelling and advanced data processing and analytics methods will accelerate that understanding.

Additionally, this talk will outline building ICME modules that predict microstructure (grain size, texture, void Vf, etc.) from processing history and predict performance (E, σys, hardening rate, εf, etc.) from microstructure.  These modules will be designed to interface with topology optimization codes to dynamically account for material properties as geometry updates are made.  The work is being demonstrated using a laser-based powder-bed fusion process on nickel superalloy IN625 for thin-walled structures.  Highly-pedigreed data sets of in-situ monitoring data (beam path, thermal measurements), post-build characterization (CT, RUS, 3D Optical and SEM) and mechanical testing (milli-tensile, HEDM, notch and torsion testing) will be collected and provided to the open community.  Challenges problems will be commissioned to benchmark the current modeling capabilities in process-structure and structure-properties.  Finally, challenge results will be used in novel forecasting techniques akin to weather forecasting strategies of model aggregation.  This talk will present the current state of the program and the vision for community involvement.

Michael Groeber is currently a Senior Material Research Scientist in the Metals Branch of the Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio.  Dr. Groeber’s research projects focus on the quantification and representation of microstructure for improving process and property modeling.  Dr. Groeber is the principal developer/inventor of DREAM.3D, a unique software package that integrates several digital microstructure tools that will facilitate the advancement of Integrated Computational Material Science and Engineering (ICMSE) in the Air Force and outside.  Additionally, Dr. Groeber has worked on creating autonomous, multi-modal data collection systems that integrate real-time analysis to optimize microstructure data collection and analysis.  Recently, Dr. Groeber has focused on applying these developments to advancing the understanding of additive manufacturing.  Dr. Groeber received a Bachelors of Science degree in Materials Science and Engineering from the Ohio State University in 2003, followed by a Ph.D. from the Ohio State University in 2007.  Dr. Groeber has published over 30 peer reviewed journals, 3 book chapters and presented over 15 invited international presentations.

Oct
6
Fri
Graduate Seminar in Fluid Mechanics @ 316 Hodson Hall
Oct 6 @ 3:00 pm – 4:00 pm

3:00 pm Presentation

 “Computational Modeling and Analysis of Aeroelastic Wing Flutter

 Presented by KARTHIK MENON (Adviser: Prof. Mittal)

Aeroelastic flutter is ubiquitous in aeronautics; of particular relevance here is the flutter of aircraft wings, helicopter rotor blades, flexible wing MAVs and UAVs, and long-endurance aerial systems such as airships and solar powered air-vehicles. Here, we attempt to understand some fundamental aspects of this problem via immersed boundary method based numerical simulations of canonical bodies. We report findings on the effect of body geometry on the dynamics of flutter involving coupled pitch-heave oscillations. We also explore flow-induced flutter of airfoils in pre and post-stall configurations, including the effect of stiffness and pitch axis location. Finally, a novel force decomposition method is used to provide some insight into the flutter dynamics and associated unsteady flow physics.


3:25 pm Presentation

Improvements of Four-Way Coupled Euler/Lagrange Numerical Models by Multi-Scale Simulations and High Performance Computing

 Presented by AMIR ESTEGHAMATIAN (Adviser: Prof. Zaki)

Particle-laden flows are observed in different natural phenomena and industrial applications. Owing to the diversity of temporal and spatial scales, this class of flows exhibit highly nonlinear and rich dynamics. Accordingly, a wide range of particle/fluid numerical models with various levels of complexity/assumptions exists in the literature. In this talk, we focus on one particular class of numerical models which has gained much popularity in simulation of meso-scale systems: four-way coupled Euler/Lagrange models (EL). In the EL model while the particles motion is handled in a direct fashion, the fluid field remains unresolved at the scale of particles. As compared to Particle Resolved Simulations (PRS), we evaluate the performance of the EL model in prediction of first- and second-order moment statistics of particles motion in a bi-periodic fluidization configuration. We show that while the integral properties of the system is well-predicted by the EL model, particle fluctuations are underestimated particularly in the transverse direction with respect to the mean axial flow. In this work, we have explored two different directions in improving the EL model: (a) improving the inter-phase coupling scheme and (b) introducing a stochastic formulation for the drag law derived from the PRS results. The new stochastic drag law, which incorporates information on the first and second-order moments of the PRS results, shows promises to recover the appropriate level of particles fluctuations.

Oct
12
Thu
Mechanical Engineering Fall Seminar Series: Class 530.803 @ 210 Hodson Hall
Oct 12 @ 3:00 pm – 4:00 pm

“Direct Numerical Simulations of Complex Multiphase Flows”

Presented by Professor Gretar Tryggvason
Department Head and Charles A. Miller, Jr. Distinguished Professor
Department of Mechanical Engineering, Johns Hopkins University

Direct numerical simulations (DNS), where every continuum length and time scale are fully resolved, allow us to follow the evolution of complex flows for sufficiently long time so that meaningful statistical quantities can be gathered. Results for relatively simple multifluid and multiphase systems with bubbles and drops in turbulent flows are now available, but new challenges are emerging. First of all, DNS of very large systems are yielding enormous amount of data that, in addition to providing physical insights, opens up new opportunities for the development of lower order models that describe the average or large-scale behavior. Recent results for bubbly flows and the application of statistical learning tools to extract closure models from the data suggest one possible strategy. Secondly, success with relatively simple systems calls for simulations of more complex problems. Multiphase flows often produce features such as thin films, filaments, and drops that are much smaller than the dominant flow scales and are well-described by analytical or semi-analytical models. Recent efforts to combine semi-analytical models for thin films using classical thin film theory, and to compute mass transfer in high Schmidt number bubbly flows using boundary layer approximations, in combination with fully resolved numerical simulations of the rest of the flow, are described.

Gretar TryggvasonGretar Tryggvason is the Charles A. Miller, Jr. Distinguished Professor at the Johns Hopkins University and the head of the Department of Mechanical Engineering.  He received his PhD from Brown University in 1985 and was on the faculty of the University of Michigan in Ann Arbor until 2000, when he moved to Worcester Polytechnic Institute as the head of the Department of Mechanical Engineering. Between 2010 and 2017, he was the Viola D. Hank professor at the University of Notre Dame and the chair of the Department of Aerospace and Mechanical Engineering. Professor Tryggvason is well known for his contributions to computational fluid dynamics; particularly the development of methods for computations of multiphase flows and for pioneering direct numerical simulations of such flows. He served as the editor-in-chief of the Journal of Computational Physics 2002-2015, is a fellow of APS, ASME and AAAS, and the recipient of several awards, including the 2012 ASME Fluids Engineering Award.

Oct
13
Fri
Graduate Seminar in Fluid Mechanics @ 316 Hodson Hall
Oct 13 @ 3:00 pm – 4:00 pm

3:00 pm Presentation

 “Structured Light Methods: A Brief Review and its Application in Measuring Deformation of Bat Wings

 Presented by SUBHRA SHANKHA KOLEY (Adviser: Prof. Katz)

Structured light method is a non-contact 3D surface measuring technique based on active stereo. In this method an arrangement of dots or stripes of varying intensity/color is projected on an object which is recorded on a camera. The geometric shape of the object distorts the projected pattern; this distortion is used to find the 3D surface shape of the object. In this talk, I would be reviewing the basic working principle of structured light along with the various types of structured light techniques. The structured light patterns are mainly divided in two categories where the patterns can either be coded temporally (i.e., over a sequence of images) or they can be coded spatially (single shot). I would also discuss the specific structured light pattern which would be used in my experiments to measure the deformation of bat wings.


3:25 pm Presentation

Scalar Source Reconstruction from Limited Remote Measurements

 Presented by VINCENT MONS (Adviser: Prof. Zaki)

Reconstructing the characteristics of a scalar source from limited remote measurements in a turbulent flow is a problem of great interest for environmental monitoring, and is challenging due to several aspects. Firstly, the numerical estimation of the scalar dispersion in a turbulent flow requires significant computational resources. Secondly, in actual practice, only a limited number of observations are available, which generally makes the corresponding inverse problem ill-posed. In this presentation, data assimilation approaches are considered to infer the scalar source localization in a turbulent channel flow at Reτ = 180. Non-intrusive ensemble-based variational techniques are employed, and their performance is compared with adjoint-based data assimilation. Strategies to decrease the number of numerical simulations performed in the assimilation process are discussed. The problem of optimal sensor placement in the framework of ensemble-based data assimilation is also investigated in order to enhance the quality and robustness of the source reconstruction from noisy measurements.

Oct
19
Thu
Mechanical Engineering Fall Seminar Series: Class 530.803 @ 210 Hodson Hall
Oct 19 @ 3:00 pm – 4:00 pm

“Dynamic traction forces exerted on the extracellular matrix mediate cellular response to microenvironment stiffness”

Presented by Professor Sergey Plotnikov
Department of Cell & Systems Biology, University of Toronto

I will be presenting our recent work on how adherent cells probe stiffness of their microenvironment through integrin-based focal adhesions. Particularly, we have been employing live cell imaging, traction forces microscopy, and mathematical modeling to understand dynamics of cellular forces exerted on the extracellular matrix. I will focus my talk on an intriguing discovery we made of how two functionally distinct cytoskeletal domains contribute to cell mechanosensing by driving calcium influx at the focal adhesions.

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