Event Calendar

Graduate Seminar in Fluid Mechanics @ 316 Hodson Hall
Nov 17 @ 3:00 pm – 4:00 pm

3:00 pm Presentation

 Aerodynamics of Ventilation in Termite Mounds”

 Presented by SHANTANU BAILOOR (Adviser: Prof. Mittal)

Fungus-cultivating termites collectively build massive, complex mounds which are much larger than the size of an individual termite and effectively use natural wind and solar energy, as well as the energy generated by the colony’s own metabolic activity to maintain the necessary condition for the colony survival. We seek to understand the aerodynamics of ventilation and thermoregulation of termite mounds through computational modeling. A simplified model accounting for key mound features, such as soil porosity and internal conduit network, is subjected to external draft conditions. The role of surface flow conditions in the generation of internal flow patterns and the ability of the mound to transport gases and heat from the nursery are examined. The understanding gained from our study could be used to guide sustainable bio-inspired passive HVAC system design, which could help optimize energy utilization in commercial and residential buildings.

3:25 pm Presentation

Strict Nonlinear Bounds on Transition Reynolds Number in High-Speed Boundary Layers

 Presented by REZA JAHANBAKHSHI (Adviser: Prof. Zaki)

Laminar-to-turbulence transition in high-speed flows has significant implications on drag and heat transfer. As a result of its sensitivity to the disturbance environment, small changes in the initial perturbation can lead to unpredictable changes in the transition mechanism and location. Previous computational studies, including direct numerical simulations, have generally started from assumptions grounded in linear theory, e.g. inflow perturbations that are particular or superposition of linear instability waves. Their predictions of transition are therefore dependent on choices informed only by linear theory, and hence are not reliable predictors of performance in realistic environments where transition is triggered by a different free-stream perturbation spectrum.  In this work, we present a new approach that circumvents this deficiency.  We seek strict nonlinear bounds on transition Reynolds number. An ensemble-based variational approach is adopted, where the objective is to compute the inflow disturbance that has a specified initial energy, whose evolution satisfies the non-linear Navier-Stokes equations, and which causes transition to turbulence as far upstream as possible.  Spectral decomposition of this perturbation highlights the essential elements to promote breakdown to turbulence, and the associated transition mechanism.  Most importantly, the present approach provides a strict, nonlinear, minimum bound on transition Reynolds number for a given level of disturbance energy and, as such, a benchmark for robust flow design.

23rd Annual James F. Bell Memorial Lecture in Continuum Mechanics @ 210 Hodson Hall
Nov 20 @ 4:00 pm – 5:00 pm

“Study of Human Diseases at the Intersections of Engineering, Sciences and Medicine”

Presented by Professor Subra Suresh
President-Designate and Distinguished University Professor of Nanyang Technological University, Singapore and Former Director, National Science Foundation

 How do the physical, mechanical and rheological properties of cells influence the onset and progression of human diseases, and vice versa?  How do the dimensions of small constrictions for passage of cells in the human body determine their surface to volume ratios and shapes?  What new platforms do the latest experimental techniques from engineering, physics and chemistry offer for isolating rare circulating tumor cells, vesicles and exosomes for disease diagnostics, therapeutics, and drug efficacy assays?   We discuss these and other related questions as well as some potential clinical applications by recourse to our recent research results at the intersections of engineering, natural sciences, and medicine.   The discussion is guided through specific examples from experiments and computation in the context of infectious diseases, hereditary blood disorders, and human cancers.

Subra Suresh is President-Designate and Distinguished University Professor at Nanyang Technological University, Singapore where he is also a Senior Advisor to Temasek International.  He has previously served as the President of Carnegie Mellon University, Director of the National Science Foundation, and Dean of MIT’s School of Engineering.   He is the first university president and one of 19 Americans to be an elected member of all three branches of the US National Academies – Engineering, Sciences, and Medicine.  He has also been elected to the American Academy of Arts and Sciences, National Academy of Inventors and ten other academies based in Europe and Asia, and has been awarded 12 honorary doctorate degrees.  He has authored three books, 300 research articles and 25 patents.  He has been widely recognized for his research into the properties of engineered and biological materials and their implications for human diseases.  His recent honors include: the 2015 Industrial Research Institute Medal; the 2013 Franklin Medal in Materials Science; the 2012 Timoshenko Medal and the 2011 Nadai Medal of the American Society of Mechanical Engineers; the 2011 Padma Shri award from the President of India; and the 2007 Gold Medal of the Federation of European Materials Societies.   As Director of the National Science Foundation, Suresh launched the Global Research Council, the Graduate Research Opportunities Worldwide (GROW) program, and the NSF Innovation Corps (I-Corps) program in 2011, which has now been replicated by organizations in the US and abroad. He is an independent Director of the Board of HP Inc., Palo Alto, and a member of the Science, Technology and Innovation Council created as an advisory body to the CEO and Management Board of Siemens AG, Munich, Germany.

Mechanical Engineering Fall Seminar Series: Class 530.803 @ 210 Hodson Hall
Nov 30 @ 3:00 pm – 4:00 pm

“Pumping by oscillating plate arrays: viscous to inertial transitions in mayfly nymphs”

Presented by Professor Ken Kiger, Department of Mechanical Engineering, University of Maryland

Mayfly nymphs are aquatic insects, many of which can generate ventilation currents by beating two linear arrays of external plate-like gills.  The oscillation Reynolds number associated with the gill motion changes with animal size, varying from Re ~ 2 to 30 depending on the age of the animal. This range of Re is interesting, as it represents an approximate boundary between the classical analytical realms of Stokesian and Eulerian dynamics. In this context, mayflies provide a novel system model for studying adaptations associated with transitions from a more viscous- to inertia-dominated flow. Observation of the gill plate kinematics and the mean flow field of the species C. triangulifer reveal that the mayfly makes a transition in stroke motion when Re > 5 (corresponding to a change from a “rowing” to a “flapping” type of motion), which is consistent with speculations in the literature that a boundary may exist for this transition. Our effort is directed to understand how the mayfly nymph effectively transits this intermediate regime using a combined technique of experimental measurement and numerical simulation. Time-resolved PIV measurements within the inter-gill space reveal the basic elements of the flow consist of vortex rings generated by the strokes of the individual gills. For the larger Re case, the phasing of the plate motion generates a complex array of small vortices that interact to produce an intermittent dorsally directed jet. For Re < 5, distinct vortices are still observed, but increased diffusion creates vortices that simultaneously envelope several gills, forcing a new flow pattern to emerge and preventing the effective use of the high Re stroke kinematics. Thus we argue the transition in the kinematics is a reflection of a single mechanism adapted over the traversed Re range, rather than a shift to a completely new mechanism.

Dr. Kiger is a Professor and Director of Undergraduate Studies in the Department of Mechanical Engineering and an Affiliate Faculty in the Fischell Department of Bioengineering at the University of Maryland where he has been a faculty member since 1995.   Dr. Kiger’s research interests are in the area of experimental fluid mechanics and turbulence, with an emphasis on two-phase flows and biological fluid mechanics. His work in two-phase flows have focused on particle-turbulence interaction, which has required the development of novel instrumentation approaches to resolve the momentum coupling between the phases, primarily in solid-liquid flows. His research interests in biological applications relate to hemodynamics, cardiovascular mechanics pertaining to cardiogenesis, disease, and artificial pumping devices, as well as the study of bio-locomotion of animal flight and respiration.

Graduate Seminar in Fluid Mechanics @ 316 Latrobe Hall
Dec 1 @ 3:00 pm – 4:00 pm

3:00 pm Presentation

 Modeling of Yawed Wind Turbines”

 Presented by CARL SHAPIRO (Advisers: Profs. Meneveau & Gayme)

Although yawing wind turbines has the potential to increase or control total wind farm power output, wake deflection and the formation of a counter-rotating vortex pair complicate efforts to describe the wake. Here we derive expressions for the initial transverse velocity and magnitude of the shed counter-rotating vortex pair formed in a yawed turbine wake. The streamwise velocity deficit in the inviscid wake is then obtained using classical momentum theory. This inviscid model is compared to simulations and found to more accurately predict the initial transverse velocity and wake skewness angle than existing models. We use the inviscid model as initial conditions in a dynamic wake model that is used to describe the turbulent downstream evolution of the wake. This wake model is found to predict the centerline of the deflected wake in wind tunnel experiments.

3:25 pm Presentation

Detailed Characterization of the Flow Induced by Pitching and Heaving Foil Controlled by a Novel Electromagnetic Suspension System

 Presented by JIBU JOSE (Adviser: Prof. Katz)

Experimental studies of aeroelastic flutter are quite limited due to the challenge in probing this complex flow‐structure interaction. To characterize the flow response to bending and torsion, which involve interaction of two or more modes of vibration, experiments have been performed using pitching and heaving foil. Unlike spring-mass or cam systems used to generate restoring forces and moments used in literature, we have designed a novel electromagnetic apparatus allowing controlled heaving and pitching of a hydrofoil suspended in a water tunnel to study this aeroelastic flutter. It can generate linear and nonlinear electromagnetic forces facilitating both active or passive controls of the hydrofoil’s angular and vertical motions. It could be used for generating restoring forces constraining the motion of the foil or for prescribing time-varying heaving and pitching. The springs have been replaced with custom designed linear motors and oil cooled rotary motors. Being an electronic device, it can generate linear or non‐linear restoring forces it response to the displacement, velocity, and acceleration of the hydrofoil. They control a modified NACA 0015 acrylic hydrofoil bounded by end plates, which is mounted in the test section of a water tunnel extension to the JHU refractive index matched facility, facilitating unobstructed optical access. Signal provided by four bi-axial MEMS accelerometers installed in the endplates are used for monitoring the (near) real-time pitch and heave, as a feedback for the LabVIEW based control system.  The index matched experiment is designed to perform simultaneous acceleration and 3D time resolved velocity measurements, which could be used to compute the motion profile and the pressure distribution over the hydrofoil.

Mechanical Engineering Fall Seminar Series: Class 530.803 @ 210 Hodson Hall
Dec 7 @ 3:00 pm – 4:00 pm

“Implementation of New Materials into Orthopedic Implants”

Presented by Dr. Ken Gall, Professor and Chair, Mechanical Engineering and Materials Science, Duke University

We will discuss the translation of a diverse set of new material technologies into orthopedic implants.  In all the applications, the implementation of the new materials was accelerated by basic research leading to a new fundamental understanding of the relationship between processing, structure, and mechanical properties of the constituent materials.  The examples span implants and new materials that have been successfully used in over ten thousand patients, to materials yet to be cleared in a device by the FDA.  The topics to be overviewed include: The development and understanding of deployable shape memory polymers to mitigate damage when reattaching soft tissue to bone.  A fundamental breakthrough on the processing and machinability of shape memory alloys to enable a paradigm shift in the success of large bone intramedullary fusion devices. A new approach to the formation of an interconnected surface porosity in a high strength polymer that results in the first ever FDA clearance and clinical success of an all polymer spinal fusion cage with porosity.  Finally, a 3D printed, bio-mimetic elastomer is shown to have early promise as a reliable and long-term soft tissue replacement or scaffold.

Professor Gall is currently the Chair of Mechanical Engineering and Materials Science at Duke University and his technical expertise is in the discovery and mechanical properties of novel materials.  His contributions to the scientific community range from the creation and understanding of multiple new functional biomaterials to the discovery of a new phase transformation in gold nanowires.  He has over 200 publications that have been cited over 13,500 times, and his publication H-index is 66.  Over the past 20 years he has given over 300 presentations at conferences, companies, and universities.  In addition to his research and teaching, he has consulted for multiple companies, the US Military and the US Intelligence Community.  He has also served as an expert witness in various patent and product litigations involving materials in the biomedical device space.  Finally, he is a passionate entrepreneur who has founded multiple medical device start-up companies, including MedShape and Vertera which have been sold in part or fully to large public companies.  He works closely with early stage companies to commercialize new technologies in the medical device space.

Graduate Seminar in Fluid Mechanics 530.807 @ 316 Hodson Hall
Dec 8 @ 3:00 pm – 4:00 pm

3:00 p.m. Presentation

Transition in Three-Dimensional Boundary Layer Forced By a Free-Stream Wake Flow

 Presented by RIKHI BOSE (Advisers: Prof. Zaki)

Lifting surfaces often operate with a sweep angle relative to the free stream. In favorable pressure gradient boundary layers, this configuration is prone to the amplification of cross-flow instabilities. In the present work, transition in three-dimensional boundary layers due to an upstream wake, akin to the interaction in multi-element airfoils is studied using direct numerical simulations. A cylinder is placed above the leading edge of the flat plate, and its turbulent wake interacts with the three-dimensional, favorable-pressure-gradient boundary layer beneath it. The sweep angle is 45 degrees and the Reynolds number is 800 based on the free-stream speed, the leading-edge half thickness and the fluid viscosity. The instability and transition processes are studied starting from the initial receptivity stage all the way through the onset of turbulence. Disturbances penetrate the boundary layer in two stages: right at the leading edge through pressure perturbations and also downstream where the wake diffuses with the boundary layer. Boundary-layer disturbances are streaky prior to breakdown into turbulent spots. Counterintuitively, in such a scenario, transition may be promoted in favorable pressure gradient due to emergent crossflow vortices.

Mechanical Engineering 2018 Spring Seminar Series: Class 530.804 @ 210 Hodson Hall
Feb 1 @ 3:00 pm – 4:00 pm

“Toward harnessing the full potential of urban winds: a case study of Hess Tower”

Presented by Professor Daniel Araya, Department of Mechanical Engineering, University of Houston

Using wind turbines in urban areas supports an increasing demand for energy that comes with rapid population growth in a sustainable way. The challenge that has been largely neglected, however, is that urban environments are characterized by relatively low wind speeds, large velocity gradients, and significant wind fluctuations, all of which degrades wind farm efficiency. Hess Tower, built in 2010, is a 29-story office building situated in the heart of downtown Houston, TX. Unique to the building is a roof structure that was engineered to house ten vertical-axis wind turbines (VAWTs). Despite detailed wind tunnel measurements to predict the flow conditions on the roof before the building was constructed, the Hess VAWTs were removed soon after construction when one of the turbines failed and fell to the ground. In this talk, I will present new in-situ measurements taken on the roof of Hess Tower and compare this with the pre-construction wind tunnel data to assess the accuracy of the predicted flow field. I will also present results from recent wind tunnel experiments conducted in our lab to examine the effects of VAWT blade curvature on turbine performance and wake development. We find that a simple change in the helical twist of the blades plays a significant role in the VAWT aerodynamics, which has implications for both for small-scale urban VAWT use and large-scale arrays.

Daniel Araya is an assistant professor in the Mechanical Engineering department at the University of Houston (UH). He received his B.S. and M.S. in Aerospace Engineering from Texas A&M University, and M.S. and Ph.D. in Aeronautics from Caltech. He leads an experimental laboratory at UH with a focus on understanding complex vortex interactions in unsteady flows. Applications of current interest to the lab include urban wind farming, vertical-axis wind turbines, and multirotor vehicles.

Mechanical Engineering 2018 Spring Seminar Series: Class 530.804 @ 210 Hodson Hall
Feb 8 @ 3:00 pm – 4:00 pm

“Trabecular Meshwork Biomechanics and Therapies in Glaucoma”

Presented by Professor C. Ross Ethier, Wallace H. Coulter Department of Biomedical Engineering at Georgia Institute of Technology & Emory University School of Medicine

Glaucoma is the second most common cause of blindness, and elevated intraocular pressure (IOP) is a causal risk factor for the development of glaucomatous optic neuropathy. Further, lowering IOP is the only treatment that helps slow vision loss in glaucoma. The trabecular meshwork is a specialized tissue that is primarily responsible for controlling IOP through as-yet unknown mechanisms, and is thus a major target of study and therapy development. In this talk I will describe interesting features of the flow through the trabecular meshwork and adjacent tissues, including a shear-stress mediated signaling pathway for IOP control. I will then describe how the stiffness of the trabecular meshwork, determined by atomic force microscopy and inverse finite element modeling, may interact with this signaling pathway. Finally, I will describe efforts to regenerate the trabecular meshwork using stem cells loaded with magnetic nanoparticles and steered to a target location in the eye by an external magnetic field.

Professor Ethier holds the Lawrence L. Gellerstedt, Jr. Chair in Bioengineering and is a Georgia Research Alliance Eminent Scholar in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Institute of Technology & Emory University School of Medicine. Prior to joining Georgia Tech, he was Head of the Department of Bioengineering at Imperial College, London for 5 years, and Director of the Institute of Biomaterials and Biomedical Engineering at U. of Toronto for 2 years before that. He received his Ph.D. from MIT in 1986, his S.M. from MIT in 1983, his M. Math. from Waterloo in 1982 and his B.Sc. from Queen’s in 1980. His research is in the biomechanics of cells and whole organs, with specific emphasis on ocular biomechanics. He works on developing treatments for glaucoma, the second most common cause of blindness, and for SANS, a syndrome affecting astronauts which is a major NASA human health concern. He is a leading engineer working in the field of glaucoma, and has developed a new paradigm of how pressure within the eye is regulated and how the sclera plays a major and unexpected role in influencing vision loss in glaucoma. He has published approximately 170 refereed journal articles and two books, and received both Steacie and Humboldt Fellowships. His work has attracted approximately 9700 citations and has an h-index of 58 (Google Scholar).

Graduate Seminar in Fluid Mechanics @ 132 Gilman Hall
Feb 9 @ 4:00 pm – 5:00 pm

4:00 pm Presentation (New Time)

 Modeling and Simulations of Fused Deposition Modeling”

 Presented by HUANXIONG XIA (Adviser: Prof. Tryggvason)

A fully resolved model is developed for FDM (Fused Deposition Modeling) process, one of the well-known additive manufacturing processes, to understand the underlying physical behaviors, where the objects are built by depositing filaments of hot polymers that fuse together when they solidify. The process is embedded in a hexahedral computational domain, where both the polymer and the ambient air are included. A finite volume/front tracking method and one-fluid formulation are used to model the behaviors of fluid flow, heat transfer, volume shrinkage, residual stress as well as the moving immiscible interface. The extrusion of the polymer is modeled by using a volume source inside a rigid body with an open outlet, which is moving along a specific path. A temperature and shear-rate depend viscosity and a modified neo-Hooke stress model are applied for the polymer to describe its viscoelastic behavior and find the solid stress. The model is computed by an implicit projection scheme with second-order accuracy both for time integration and space derivation. The accuracy and convergence properties are tested by grid refinement studies for a simple setup involving two short filaments, one on top of the other. The effect of the various injection parameters, such as nozzle speed, cooling condition, depositing and bridging space are briefly examined and the applicability of the approach to simulate the construction of simple multilayer objects is shown. The fully resolved model can be helpful to understand the physical mechanism, predict the process, model the other relevant novel processes, and provide “ground truth” results for the simplified/reduced order model that is suitable for the part-scale simulations.

4:25 pm Presentation (New Time)

Experimental Investigation of Compliant Wall Surface Deformation in Turbulent Boundary Layer

 Presented by JIN WANG (Adviser: Prof. Katz)

In our previous work, correlations between a compliant wall surface deformation and turbulent channel flow are studied by Tomographic PIV (TPIV) and Mach-zehnder Interferometer (MZI). In the ongoing experiment, a softer compliant surface with Young’s modulus reduced from 1 MPa to around 100 KPa is used. The material is a mixture of 88% Dow Corning Sylgard 527 and 12% Sylgard 184 by weight. The Young’s modulus is chosen to increase the amplitude of deformation so that a two-way coupling instead of one-way coupling in the stiffer surface experiment is expected. The coating thickness (l0=5mm) is tuned to guarantee that large amplitude surface deformation with a length scale of 3l0 predicted by the Chase model can be captured in our limited FOV.  Corresponding shear wave speed for the softer compliant surface, calculated from ct=(G/ρc)1/2 is around 5.37 m/s. Thus, a designed flow speed around 6 m/s is capable of trigger the static divergence wave. MZI and TPIV will be used to measure the surface deformation and the 3D velocity, volume pressure is calculated from the TPIV data via a GPU-based, parallel-line, omni-directional integration method. Measurement of large field of view (>50x50mm2) deformation will be implemented using MZI to study the large scale deformation, followed by a simultaneous measurement of velocity by TPIV and deformation by MZI in a small field of view (<20×20 mm2).  In this talk, the large field of view MZI experiment results will be presented and discussed.

Mechanical Engineering 2018 Spring Seminar Series: Class 530.804 @ 210 Hodson Hall
Feb 15 @ 3:00 pm – 4:00 pm

“Elephant trunks, cat tongues, and the Ig Nobel Prize”

Presented by Professor David Hu, Mechanical Engineering and Biology, Georgia Institute of Technology

Fluid mechanics can appear in surprising places.  Elephants suck air at speeds comparable to a vacuum cleaner, picking up potato crisps without breaking them.  Cats have hairy surface areas equal to that of a ping pong table.  Their tongue is covered in small spines that wick saliva, enabling them to coat the many pockets between their fur.  A routine diaper led the presenter to the universal law of urination and the Ig Nobel Prize Ceremony at Harvard University.  The audience will learn how to write simple mathematical models to rationalize everyday phenomena and to turn chance observations into opportunities for worldwide engagement with science.

He has defended his work from a senator:


Videos of his ant and frog works are in the New York Times: 



Dr. David Hu is a mechanical engineer who studies the interactions of animals with water.  His team has discovered how dogs shake dry, how insects walk on water, and how eyelashes protect the eyes from drying.  Originally from Rockville, Maryland, he earned degrees in mathematics and mechanical engineering from M.I.T., and is now Associate Professor of Mechanical Engineering and Biology and Adjunct Professor of Physics at Georgia Tech.  He is a recipient of the National Science Foundation CAREER award for young scientists, the Ig Nobel Prize in Physics, and the Pineapple Science Prize (the Ig Nobel of China).  He serves on the editorial board of Nature Scientific Reports and The Journal of Experimental Biology.   His work has been featured in The Economist, The New York Times, Saturday Night Live, and Highlights for Children.  He has defended basic research in a Scientific American article, Confessions of a Wasteful Scientist.  He lives with his wife Jia and children Harry and Heidi in Atlanta, Georgia.

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