4:10 pm Presentation
“An Improved Generalized Model of Wind Turbine Wakes”
Presented by CARL SHAPIRO (Advisers: Profs. Meneveau & Gayme)
Simple wake models are needed to develop improved wind farm designs and for use in operational controllers to regulate wind farm power production and reduce structural loads. From the Reynolds-averaged Navier-Stokes, we derive a one-dimensional partial differential equation model. We apply a mixing-length model for the eddy viscosity in the wake that leads to linear downstream wake expansion, with a rate specified using a top-down model for a developing wind turbine array boundary layer (Meneveau 2012, J. Turbulence) where the friction velocity evolves non-monotonically downstream. The streamwise velocity deficits are distributed using a super-Gaussian function that smoothly transitions from a top-hat profile close to the turbine to a Gaussian profile farther downstream. Finally, large-eddy simulations are used to validate the improved wake model.
4:35 pm Presentation
“Turbulent Boundary Layer Over a Compliant Surface”
Presented by JIN WANG (Adviser: Prof. Katz)
Previous simultaneous time-resolved measurement of the 3D flow structure and deformation of a compliant wall by a turbulent channel flow involved wall stiffness too high to affect the flow, resulting in one-way coupling between flow and deformation. The current experiments focus on cases with deformations extending to several wall units aimed at generating two-way coupling. Guided by theoretical analysis, the required Young’s Modulus (0.15Mpa), shear speed (6m/s), and thickness (5mm) of the compliant surface is achieved. The large field of view (70×35 mm^2) deformation measurements elucidate that the advection speeds are fixed at 0.66 U0. Corresponding deformation amplitudes range from sub-micron to serval wall units with U0 increasing from 1 m/s to 6 m/s. The scale of deformation fits well with the predictions of the Chase model. The boundary layer flow is measured using high resolution 2D PIV which can resolve the viscous sublayer. The mean velocity profiles of flow over the compliant wall deviates slightly from the rigid wall at viscous sublayer and buffer region for low flow speeds when the deformation is smaller than the wall unit. At higher flow speeds, the influence of compliant wall deformation extends to the log layer, resulting a decrease of velocity magnitude.
No equations, no variables, no parameters, no space, no time: Data and the modeling of complex systems
Presented by Professor Yannis G. Kevrekidis, Bloomberg Distinguished Professor
Chemical and Biomolecular Engineering & Applied Mathematics and Statistics
Johns Hopkins University
Obtaining predictive dynamical equations from data lies at the heart of science and engineering modeling, and is the linchpin of our technology. In mathematical modeling one typically progresses from observations of the world (and some serious thinking!) first to equations for a model, and then to the analysis of the model to make predictions. Good mathematical models give good predictions (and inaccurate ones do not) – but the computational tools for analyzing them are the same: algorithms that are typically based on closed form equations.
While the skeleton of the process remains the same, today we witness the development of mathematical techniques that operate directly on observations -data-, and appear to circumvent the serious thinking that goes into selecting variables and parameters and deriving accurate equations. The process then may appear to the user a little like making predictions by “looking in a crystal ball”. Yet the “serious thinking” is still there and uses the same -and some new- mathematics: it goes into building algorithms that jump directly from data to the analysis of the model (which is now not available in closed form) so as to make predictions. Our work here presents a couple of efforts that illustrate this “new” path from data to predictions. It really is the same old path, but it is travelled by new means.
Micro Mechanical Methods for Biology (M3B)
Presented by Professor Liwei Lin
University of California, Berkeley
Next-generation autonomous microfluidic components, circuits and systems have been widely investigated for the past decades by researchers from various disciplines, including mechanical engineering, electrical engineering, bioengineering, chemistry and biology. They key focuses have been making microfluidic systems with functions similar to microelectronics with possible applications related to biological/medical problems. This talk will start with the discussions on the background information on the development of microfluidic components and systems. It will then followed with specific progresses from my laboratory in relevant topics, including: (1) the application of optofluidic lithography in the making and demonstration of microfluidic diodes with three different versions: bead-based operations, swing check valves, and spring check valves; (2) micro mechanical platforms for cell mechanobiology to control the cellular functions with two approaches: bi-axial control of substrate stiffness using micropost arrays of varying diameter, and tri-axial stiffness control using microscale springs; and (3) microfluidics based on the 3D printing techniques.
Professor Liwei Lin received PhD degree from the University of California, Berkeley, in 1993. He was an Associate Professor in the Institute of Applied Mechanics, National Taiwan University, Taiwan (1994~1996) and an Assistant Professor in Mechanical Engineering Department, University of Michigan (1996~1999). He joined the University of California at Berkeley in 1999 and is now James Marshall Wells Professor at the Mechanical Engineering Department and Co-Director at Berkeley Sensor and Actuator Center (BSAC), an NSF/Industry/University research cooperative center. His research interests are in design, modeling and fabrication of micro/nano structures, sensors and actuators as well as mechanical issues in micro/nano systems including heat transfer, solid/fluid mechanics and dynamics. Dr. Lin is the recipient of the 1998 NSF CAREER Award for research in MEMS Packaging and the 1999 ASME Journal of Heat Transfer best paper award for his work on micro scale bubble formation. He led the effort to establish the MEMS division in ASME and served as the founding Chairman of the Executive Committee from 2004~2005. He is an ASME Fellow and has 20 issued US patents in the area of MEMS. He was the general co-chair of the 24th international conference on Micro Electro Mechanical Systems at Cancun, Mexico. Currently, he serves as a subject editor for the IEEE/ASME Journal of Microelectromechanical Systems and the North and South America Editor of Sensors and Actuators –A Physical.
4:10 pm Presentation
“Systematic Experimental Evaluations Aimed at Optimizing the Geometry of Axial Casing Groove in a Compressor”
Presented by HUANG CHEN (Adviser: Prof. Katz)
Our recent studies have shown that skewed semicircular axial casing grooves reduce the stall flowrate by 40%, but causes a 2.4% reduction in peak efficiency. Velocity measurements have demonstrated that the periodic inflow into the grooves entrains substantial fractions of the leakage flow and the tip leakage vortex (TLV), reduces the elevated circumferential velocity surround the TLV, which plays a key role in the onset of stall, and causes periodic variations in the relative flow angle around the blade leading edge. Near the best efficiency point, the TLV entrains secondary flows from the groove back into the passage. It is not clear which of these phenomena plays a primary role in the suppression of stall or causes adverse effects at high flowrates. Hence, the present study involves use of a series of grooves, all with the same inlet, but different outflow orientations, aimed at decoupling the different effects. The tests are performed in the JHU refractive index matched facility using the same one and a half stage transparent compressor. All the grooves have the same ramped inlet aligned with the positive circumferential direction, but outlets aligned at different directions. A U-shaped groove has an outlet aligned in the negative circumferential direction, and an “S” groove is aligned in the opposite direction. Another pair is aligned with and against the flow at the exit from the inlet guide vane (IGV). All the grooves increase the pressure rise at low flow rates significantly, suggesting that it is associated with the periodic suction of the TLV by the commonly shaped inlet. The U-shaped groove extends the stall margin even further than the semicircular ones, but causes a similar peak efficiency loss. The S groove extends the stall margin by 35%, less than the U groove, but does not cause a loss of efficiency at high flow rates. Both grooves with outlets aligned with and against the IGV wake delay the stall to a lesser extent than the U and S grooves. Efficiency loss only occurs when the outlet is aligned against the IGV wake. Hence, the performance degradation at high flow rates appears to be associated with the periodic increase in flow angles near the leading edge of the blade caused by the negatively aligned outflow from the grooves. When this flow is suppressed by realigning the outlet, the efficiency loss is suppressed.
4:35 pm Presentation
“Population Balance Modeling to Study Evolution of Jet with Polydisperse Oil Droplets in a Large Eddy Simulation Framework”
Presented by ADITYA KANDASWAMY AIYER (Adviser: Prof. Meneveau)
In the context of oil spills, knowledge of the dispersed phase droplet size distribution and its evolution is critical for accurate prediction of many macroscopic features of the oil plumes. In this study, we adopt a population dynamics model for polydisperse droplet size distributions and implement it in a Large Eddy Simulation framework. This allows us to study the evolution of the number density of droplets due to turbulent transport and droplet breakup. Modeling breakup based on turbulent fluctuations and droplet-eddy collisions is a popular method that has been adopted in the literature, in which the breakup occurs primarily due to the bombardment of droplets by turbulent eddies. Existing models assume the scale of droplet-eddy collision to be in the inertial scale of turbulence. In this work we extend the breakup kernels to the entire spectrum of turbulence using generalized structure functions. Our model includes a dimensionless model coefficient that is fitted by comparing the model predictions with a dataset obtained from an experiment performed by C. Li and Katz (2017). Moreover, we develop a new parameterization for the breakup frequency over a wide parameter range to reduce numerical computations in our LES. As a flow application for LES we consider a jet in crossflow with oil being released at the source of the jet. We model the number density fields of the polydisperse droplets using an Eulerian approach. We compare the droplet size distribution obtained from our simulations with published experimental data.
“Understanding the Cheetah Tail: A Robotics Perspective”
Presented by Dr. Amir Patel, Senior Lecturer
Department of Electrical Engineering, University of Cape Town
In our quest to develop the next generation of legged robots, we should look to nature for inspiration. The cheetah (Acinonyx Jubatus) presents a prime example of specialization as even though it is the fastest land animal, it is also one of the most maneuverable. Furthermore, when one views these maneuvers, the cheetah appears to be actively (and rapidly) swinging its lengthy tail in response to the prey’s attempts at evasion. But as it stands, the current literature does not provide a categorical answer as to why the cheetah swings its tail?
The public sphere of knowledge views the cheetah tail as being lengthy and muscular and is often considered to be used as either a “rudder”, or “counterweight” employed for balance. Indeed, the biological literature has also anecdotally described the tail in a similar manner. However, the mechanisms for using the tail are still not well understood and no definitive kinematic data on the cheetah tail motion exists.
My PhD research involved investigating the various cheetah tail motions using mathematical modelling, control engineering and physical robotics. Here it was shown that a rigid inertial tail could be used to stabilize high-speed turns, rapid linear accelerations, as well as longer duration turns on a wheeled robotic platform. Additionally, I discovered that the aerodynamics of the cheetah tail could also assist stabilization when moving at high-speed.
Consummation of the investigation however requires experimental motion data from live cheetahs. Obtaining this data has been challenging, as standard animal sensor collars treat the animal as a point mass and cannot provide information about the legs, spine or tail. To this end, I have recently developed a novel motion capture system for cheetahs using on-animal cameras and a smartphone.
In this seminar, I will present work done during my sabbatical at Carnegie Mellon and Johns Hopkins this year. I have attempted to close the loop on my previous work by analyzing the kinematic data obtained from free-running cheetahs in South Africa. Firstly, I have developed a novel contact-implicit trajectory optimization method to enable generating optimal motions of rapid maneuvers of a multibody cheetah model and compare them to the animal motion data. Secondly, I have captured several hours of multi-camera footage of cheetahs in South Africa and implemented a state-of-the-art markerless motion capture algorithm to track the 3D whole-body kinematics of the animals. Lastly, I have improved on my previous aerodynamic tail investigation by performing dynamic (actuated) wind tunnel tests and use these to develop an aerodynamic robotic tail.
Amir Patel is a Senior Lecturer in the Department of Electrical Engineering at the University of Cape Town (UCT) in South Africa. After completing his BSc Eng (Mechatronics) at UCT, he designed flight control systems for the aerospace industry. Following this, he completed his PhD in Mechatronics (also at UCT) and became a full-time academic. His overarching research goal is to understand manoeuvrability in legged animals and robots. More specifically, he utilises optimal control, physical robots as well novel motion capture systems to understand the dynamics of transient locomotion such as acceleration, turning and gait termination in legged systems. He is on academic sabbatical in the USA and spent January – June 2018 at Carnegie Mellon University. He is currently a visiting scholar in Noah Cowan’s LIMBS Lab at Johns Hopkins University till December 2018.
4:10 pm Presentation
“Difficulty of State Estimation from Wall Measurements in Turbulent Channel Flow”
Presented by QI WANG (Adviser: Prof. Zaki)
Reconstructing the state of turbulent channel flow from wall measurements is formulated as an adjoint variational problem. We seek an estimate of the initial condition of the flow that can accurately reproduce the measurements. The cost function to minimize is therefore the difference between the estimated measurements and the true sensor data. The fundamental limitations in state estimation are examined in detail by evaluating the Hessian matrix of the cost function, in the vicinity of the true solution. The diagonal components of the Hessian and its leading eigen-modes capture the highest sensitivity of the measurements to the flow state. Their peak sensitivity is concentrated in the near-wall region, and the sensitivity decays quickly into the bulk of the channel. The structure of the eigenmodes exposes the fundamental difficulty of estimating the flow state from wall measurements.
4:35 pm Presentation
“Entrainment during Droplet Crossing at Oil – Water Interface”
Presented by OMRI RAM (Adviser: Prof. Katz)
High speed imaging examines processes occurring prior to, during and after initially quiescent oil or water droplets cross an oil-water interface. Using sugar water and silicone oil with nearly (but not exactly) the same refractive index enables visualization of the time evolution of the interfaces by coherent inline illumination. The well-established rupturing of the thin water layer above the oil droplet or oil layer below the water droplet before the droplet ejects rapidly into its own phase follow similar patterns. However, while the water droplet migrates away from the interface while generating secondary flows, the oil droplet remains attached to the interface and maintains its shape long after the crossing. Hence, a layer containing multiple droplets forms above the interface when the oil is injected continuously. The lingering interference pattern on the surface of each droplet suggests that it remains separated from the bulk oil by a thin film whose signature diminishes with time. The current research aimed at characterizing this film, as well as elucidating the difference between the behavior of falling water and rising oil droplets.
“Single-molecule measurements of force transmission by integrin heterodimers in living cells”
Presented by Professor Alexander Dunn, Chemical Engineering, Stanford University
Integrins are heterodimeric transmembrane adhesion proteins that link the cytoskeleton to the extracellular matrix (ECM), and hence play a central role in the construction of complex, multicellular tissues. Although integrins are required for both cellular traction generation and for sensing mechanical cues such as substrate rigidity, the magnitude of the forces born by integrin heterodimers was unclear. We used FRET-based molecular tension sensors to determine the magnitude and origins of the forces experienced by individual integrins in living cells. We found that this distribution was highly skewed, with the majority of integrins bearing loads of ~2 pN, while a tiny subpopulation experienced forces >11 pN. Further experiments revealed that this distribution was controlled in a modular manner: integrin heterodimer usage controlled the number and stability of cellular connections to the ECM, while the proteins that link integrins to the cytoskeleton regulated the distribution of loads borne by individual integrin complexes. These and other observations support a general model for how cells create the regulated and dynamic adhesion complexes that are a defining feature of multicellular life.
Alex Dunn is an Associate Professor in the Department of Chemical Engineering at Stanford University. His research focuses on understanding how living cells sense mechanical stimuli, with particular interests in stem cell biology and tissue engineering. Dr. Dunn worked as a postdoctoral scholar with James Spudich in the Department of Biochemistry at the Stanford University School of Medicine. He received his Ph.D. at the California Institute of Technology under the direction of Harry Gray, where his work focused on understanding the catalytic mechanism selective C-H bond oxidation by cytochrome P450 enzymes. His work has been recognized with numerous awards, including the Hertz Fellowship, Jane Coffin Childs Postdoctoral Fellowship, the Burroughs Wellcome Career Award at the Scientific Interface, and NIH Director’s New Innovator Award.
“The Hexagon KH-9 Spy Satellite, its workings and importance to world peace”
Presented by Mr. Phil Pressel
Retired: United Technologies Corporation
Mr. Pressel will explain how the stereo camera system worked in perfect synchronization with the incredible amount (30 miles of film for each camera) of fast moving film (200 inches per second) linearly and in rotation. This satellite was and still is considered the most complicated satellite ever put in orbit. It was also one of America’s best and most successful spy satellites. It was launched on the Titan IIID or the Titan 34D from Vandenberg Air Force Base.
Mr. Pressel’s presentation will show some photographs that the system took of some Russian assets and of some cities in the US. The Air Force ran all of the launches from Vandenberg AFB and actually ran the program from 1972 when the CIA turned it over to them.
The following is a more detailed list of what Mr. Pressel will discuss:
Mr. Phil Pressel retired after over 50 years working in the aerospace industry, of which for 30 years he worked for the Perkin-Elmer Corporation in Danbury, CT (now United Technologies Corporation). He was the project engineer in charge of the design of the stereo cameras for the formerly top secret Hexagon KH-9 spy satellite, the last film-based satellite. He and his wife live in San Diego and keep busy traveling, writing, consulting and doing volunteer work. He is a Holocaust survivor and describes his and his parents’ wartime escape from the Nazis living in hiding in several cities in France in his first book “They Are Still Alive”.
Since the Hexagon program was declassified in September 2011, he has lectured on the Hexagon program to many national technical organizations and museums including the Wright-Patterson Air Force Base Museum in Dayton, Ohio, the Smithsonian Air & Space Museum and the Spy Museum in DC. He is an accomplished public speaker and has been interviewed by numerous publications including the Associated Press, National Public Radio, various newspapers, a CBS TV affiliate in San Diego and online at Space.com. He was seen on CNN on September 4, 2016, in a one-hour documentary called “Declassified” about the Hexagon Program. Mr. Pressel has written a book, “Meeting the Challenge: the Hexagon KH-9 Reconnaissance Satellite”, on the importance of the Hexagon program to United States security. He also has a blog about Hexagon that can be accessed at www.hexagonkh9.com.
“From fast to ultrafast: the biological world of extreme movement”
Presented by Professor Sheila Patek
Department of Biology, Duke University
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.
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.
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.