2009 Seminar Archive

Spring, 2009

Simulation and Control of Three-Dimensional Separated Flows around Low-Aspect-Ratio Wings

Kunihiko (Sam) Taira

Postdoctoral Research Associate 
Department of Mechanical and Aerospace Engineering
Princeton University
Princeton, NJ

Micro air vehicles often fly with flow separation on their low-aspect-ratio wings due to the unique design and operational environment. However, three-dimensional flows around such vehicles have not been well understood compared to the classical high-Reynolds-number flows around conventional aircraft. To offer fundamental understanding of the flow field around small-scaled vehicles, a new formulation of the immersed boundary method is developed and used to perform three-dimensional flow simulations around low-aspect-ratio wings at low Reynolds numbers. The study highlights the unsteady nature of separated flows for various aspect ratios, angles of attack, and planform geometries. Following an impulsive start, the short and long time behavior of the wake and the corresponding forces exerted on the wing are examined.

At high angles of attack, the leading-edge vortices are observed to detach in many cases, resulting in reduced lift. Inspired by how insects benefit from the added lift due to the leading-edge vortices, actuation is introduced to increase lift by modifying the three-dimensional dynamics of the wake vortices behind translating wings. Successful control setups that achieve lift enhancement by a factor of two in post-stall flows for low-aspect-ratio wings will be presented.

Wednesday, January 14, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Toward Numerical Simulations of Compressible Multiphase Flows with Applications to Shockwave Lithotripsy and Richtmyer-Meskov Instability

Eric Johnsen

Postdoctoral Fellow 
Center for Turbulence Research
Stanford University
Stanford, CA

Multiphase flows are ubiquitous in nature and in engineering applications, and encompass a range of phenomena as diverse as the dynamics of bubble clouds, the ablation of human tissue by focused ultrasound, and the impact of ocean waves onto naval structures. Though numerical simulations have become common design and analysis tools in fluid dynamics, current multiphase flow algorithms are still in developmental stages, particularly when the flow is compressible.

In the present talk, a compressible multicomponent flow method is presented and applied to study the non-spherical collapse of gas bubbles in the context of shockwave lithotripsy, a medical procedure in which focused shockwaves are used to pulverize kidney stones. The dynamics of non-spherical bubble collapse are characterized, and the damage potential of the shockwaves emitted upon collapse is evaluated by tabulating the wall pressure. In addition, various properties are compared to available experiments and theory, showing good agreement. Furthermore, by using the present results as boundary conditions for simulations of elastic wave propagation within a kidney stone, a new stone comminution mechanism is proposed. Finally, the application of the current method is discussed for simulations of the Richtmyer-Meshkov instability, in which a shock interacts with a perturbed interface.

Eric Johnsen is a post-doctoral fellow at the Center for Turbulence Research at Stanford University. He received his BS in Mechanical and Environmental Engineering from UCSB, and his MS and PhD in Mechanical Engineering from Caltech. For more information, please visit: http://www.stanford.edu/~johnsen.

Wednesday, January 21, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

The Laminar Flame to Turbulent Flame to Detonation Transition: Studies of Non-Kolmogorov Turbulence and Stochasticity

Elaine S. Oran

Senior Scientist for Reactive Flow Physics 
U. S. Naval Research Laboratory
Washington, DC

The transition from a propagating subsonic Laminar flame to a high-speed Turbulent flame and then to supersonic Detonation wave (the LTD transition) involves a series of often dramatic events involving changes in the nature of the reaction wave. Some of the events develop continuously whereas others appear suddenly and with little apparent warning. The LTD transition occurs in highly exothermic energetic materials, for example in hydrogen-air mixtures resulting from gas leaks at hydrogen production and storage facilities as well as in carbon-oxygen mixtures in white-dwarf stars which, after ignition, become thermonuclear supernovae. This presentation describes the properties of the LTD transition using videos made from numerical solutions of the multidimensional, unsteady, chemically reacting, Navier-Stokes equations. The discussion focuses on selected features of the flow, including: formation of a turbulent flame and the nature of the turbulence, creation of hot spots as the origins of detonations, effects of stochastic processes on our ability to make predictions, and comparisons between simulations and experimental data.

Thursday, January 22, 2009
3:00 – 5:00 PM
Davidson Conference Center, Club Room

Refreshments will be served at 3:00 pm.

Swimming and Flying Somewhere Between the Microscale and Macroscale: Curious Adaptations in Parasitoid Wasps and Other Creatures

Laura Miller

Assistant Professor 
Dept. of Mathematics
U. North Carolina at Chapel Hill
Chapel Hill, NC

Biologists, engineers, physicists, and mathematicians have long studied the fluid dynamics of animal swimming and flying. In most cases, methods of locomotion are divided neatly into high Reynolds number mechanisms (flapping wings and fins, gliding, jet propulsion) and low Reynolds number mechanisms (cilia and flagella). For the most part, mechanisms of locomotion for Reynolds numbers between 0.1 and 10 have not been explored. In these flows, both inertial and viscous effects are significant, and a number of interesting biological adaptations appear. For example, the wings of the smallest insects have a bristled structure. Similar structures are also observed on the appendages of aquatic invertebrates such as copepods and beetles. Some fairyflies use bristled wings to fly in the air and also to swim in the water. In this presentation, the fluid dynamics of locomotion at these Reynolds number is explored. We use computational fluid dynamics and particle image velocimetry (PIV) to characterize the flow around simplified models of flapping wings and fins. The immersed boundary method is used to solve the Navier-Stokes equations around a moving, flexible wing or fin. We then describe thrust and lift generation in air and water over a range of Reynolds numbers and relate the magnitude of these forces to the behavior of the wake behind the flapping appendages. The role of bristled wings in locomotion is also examined. Finally, we describe similar problems in moving and pumping fluids over the same Reynolds number range.

Friday, January 23, 2009
12:00 NOON
Laufer Library (RRB 208)

Vortex Induced Vibrations

A. Leonard

Theodore von Kármán Professor of Aeronautics, Emeritus 
Graduate Aeronautical Laboratories
California Institute of Technology
Pasadena, CA

Vortex shedding from a bluff body can impose significant, time-dependent forces on the body. If the body is freely oscillating, the amplitude of the resulting vibration can lead to disastrous consequences in some instances or, on the plus side, can be the essence of a proposed power generation scheme. The amplitude and frequency of the motion depends on the shape of the body and on four parameters: nondimensional mass, damping coefficient, spring constant or stiffness, and Reynolds number. In some cases, the expected resonant behavior occurs when the vortex shedding frequency is close to the natural vibration frequency of the mechanical system and the damping is low. But there are important ranges of these parameters that yield contrary results. Laboratory and computational experiments of flow past a freely oscillating circular cylinder will be discussed along with a new theoretical approach that requires only three parameters: effective stiffness, damping, and Reynolds number, and takes the mystery out of some of the mysterious results reported in the literature.

Wednesday, January 28, 2009
3:00 PM
Tutor Hall Conference Room, RTH 526

Refreshments will be served.

Computational Analysis of Droplet- and Particle-Laden, Turbulent and Separated High-Speed Flows

Gustaaf Jacobs

Assistant Professor 
Department of Aerospace Engineering
San Diego State University
San Diego, CA

The optimization of fuel droplet/particle and fuel-air mixing improves performance of scramjets and pulse detonation engines and reduces environmental pollution. Understanding the impact of debris in explosions can save lives. The flows in dust explosions and in high-speed combustors are characterized by the intricate interaction between droplets, particles, separated shear layers, turbulence and/or shocks. The tremendous complexity of this interaction has left many questions unanswered. I will discuss our efforts to computationally analyze the droplet- and particle-laden flows. I will first discuss high-fidelity Eulerian-Lagrangian computational methods that model the gas flow equations in the Eulerian frame with high-order methods, while particles are traced along there path in the Lagrangian frame. I will discuss high-order coupling between the two frames and illustrate the performance of the method. I will secondly discuss flow separation, compressibility effects and the droplet dispersion of flows with relevance to the high-speed separated flows in simplified combustor geometries.

Thursday, January 29, 2009
3:30 PM
ZHS 252

Refreshments will be served at 3:15 pm.

On Focusing of Shock Waves

Veronica Eliasson

Postdoctoral Scholar 
California Institute of Technology
Pasadena, CA

In this project we study converging shocks in gas, both experimentally and numerically. The interest in converging shocks stems from their ability to concentrate energy in a small volume. However, it has proven difficult to experimentally obtain a stable cylindrical converging shock wave because initial shape perturbations are amplified during the nonlinear focusing event. In this talk, we address the issue of generating and studying stable converging shocks with various geometrical shapes.

A shock tube is used to transform an initially planar shock into a cylindrical ring-shaped shock. These cylindrical shock waves are then further transformed into different geometrical shapes during the focusing phase by two methods. One method consists of changing the shape of the outer boundary of the test section of the shock tube, while the other introduces cylindrical obstacles in specific patterns inside the test section. As a result, a polygonal shape is most often obtained and depending on the number of sides of the shock, either a Mach or regular reflection occurs at the corners during the focusing event.

The shock wave focusing is also studied numerically using Euler equations of gas dynamics for a gas obeying the ideal gas law with constant specific heats with a high-order accurate Godunov method. The governing equations are discretized on body-fitted overlapping structured grids, and adaptive mesh refinement is used to dynamically track the shocks and contact surfaces. Two problems are analyzed; an axisymmetric model of the shock tube used in the experiments and a cylindrical shock wave diffracted by cylinders in a two-dimensional test section.

Schlieren photographs of a converging shock perturbed by 8 cylinders.

Veronica Eliasson has been working as a postdoc at GALCIT, Caltech since Oct. 2007. She is working on a joint project with Prof. Paul Dimotakis and Prof. Ares Rosakis investigating converging shocks in water, where the liquid-solid coupling between the confined water and the surrounding material is of interest.

Wednesday, February 11, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Pulsed Jetting in the Mechanical and Biological Worlds

Paul S. Krueger

Associate Professor 
Department of Mechanical Engineering
Southern Methodist University
Dallas, TX 75275

Nature boasts a wide array of organisms utilizing jet propulsion, or more properly, pulsed-jet propulsion. Squid and jellyfish are some of the more well-known members of this group. It is often assumed that this form of locomotion requires high velocity, inefficient jets to be effective. Studies of mechanically generated fully-pulsed jets (pulsed jets with a period of no flow between pulses), on the other hand, have revealed a spectrum of possible flows ranging from vortex rings for short jet pulses to vortex rings followed by trailing jets for longer pulses. Jet pulses producing isolated vortex rings obtained a thrust benefit from over-pressure at the nozzle exit plane during vortex ring formation, a result with potential benefits for biological and/or mechanical pulsed-jet propulsion. In this talk the propulsive efficiency of brief squid (juveniles and adults), longfinned squid (hatchlings), and a self-propelled, mechanical pulsed-jet vehicle (“Robosquid”) will be assessed using direct measurement of the jet hydrodynamics with digital particle image velocimetry (DPIV). The results for the juvenile and adult squid show that they utilize the spectrum of jet flows available with the propulsive efficiency of isolated vortex rings being significantly greater than the longer jet pulses. The performance of Robosquid mirrors these results with propulsive efficiency increasing as pulse duration decreases for pulse durations that produce isolated vortex rings. Surprisingly, squid hatchlings outperformed their larger counterparts, a result which is attributed to a range of factors including the hatchlings’ preference for shorter pulses and their proportionately larger funnel diameters. A simple model for propulsive efficiency of pulsed jets incorporating nozzle exit over-pressure associated with the unsteady flow physics will be presented. The model explains the key experimental results in terms of over-pressure effects associated with vortex ring formation and predicts efficiencies that increasingly outperform steady jets as scale (i.e., Reynolds number) is reduced for pulsed jets with short, high-frequency pulses.

Paul Krueger received his B.S. in Mechanical Engineering in 1997 from the University of California at Berkeley. He received his M.S. in Aeronautics in 1998 and his Ph.D. in Aeronautics in 2001, both from the California Institute of Technology (Caltech). In 2002 he joined the Mechanical Engineering Department at Southern Methodist University where he is currently an Associate Professor. He is a recipient of the Rolf D. Buhler Memorial Award in Aeronautics and the Richard Bruce Chapman Memorial Award for distinguished research in Hydrodynamics. In 2004 he received the Faculty Early Career Development (CAREER) Award from the National Science Foundation and he was elected the ASME North Texas Section Young Engineer of the Year in 2009. His research interests include unsteady hydrodynamics and aerodynamics, vortex dynamics, vortex-boundary interactions, bio-fluid mechanics, and pulsed-jet propulsion.

Wednesday, February 18, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Microstructure as Derived from X-Ray Line Broadening

Tamás Ungár

Department Materials Physics
Eötvös University
Budapest, Hungary

X-ray diffraction peaks broaden either when crystallites become small or if the crystal is distorted by lattice defects. Size broadening is independent of diffraction order, however, strain broadening increases with diffraction order. Planar defects, especially stacking faults or twin boundaries produce a mixture of size and strain. hkl dependence of the different microstructure features can be very different allowing separation. A brief summary of the principles and specific case studies will be presented for nanomaterials and conventional grain size structural materials, including the effect of twinning in hexagonal metals.

Wednesday, February 25, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Sea Level Rise: How the Oceans Respond to a Warming World

Josh Willis

Jet Propulsion Laboratory
Pasadena, CA

As the planet heats up, over 80 percent of the excess heat goes toward warming the oceans. In essence, the oceans are the Earth’s heat capacitors, absorbing the heat from global warming and setting the time scale for climate change. As they warm, ocean waters expand, causing sea level rise. Rising ocean levels are one of the most serious and visible consequences of global warming. However, projections of future sea level rise remain very crude and have so far underestimated the actual rate of rise. To accurately project sea level rise, it is important to understand its causes. Since 2003, two new global ocean observing systems have begun to address this issue. The Argo array of profiling floats now provides nearly global observations of temperature and salinity in the upper ocean, and the Gravity Recovery and Climate Experiment (GRACE) satellites provide monthly estimates of the ocean’s total mass. Using data from these and other instruments, the first attempts to explain the causes of present data sea level rise have been made. Results suggest that although warming and thermal expansion played a large role in sea level rise during the 1990s, the melting of glaciers and ice sheets is accelerating and may have become the dominate source in recent years.

Wednesday, March 4, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Alternative Fuels for Commercial and Military Aviation

Marty Bradley

Technical Fellow 
The Boeing Company
Huntington Beach, CA

Boeing is working with our military and commercial aviation customers to develop alternative fuels for aviation. In this presentation, Dr. Bradley will discuss a range of alternative fuel options and show why Boeing is concentrating on drop-in replacement fuels for aviation. Synthetic fuels and biofuels will be compared and evaluated for energy efficiency, environmental impact, and sustainability. The suitability of biomass feedstocks will be compared. Dr. Bradley will also discuss recent developments involving progress toward the certification of alternative fuels and recent highly successful commercial and military flight demonstrations.

Wednesday, March 11, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

The Looming Crisis of Air Traffic Capacity—Can Vortex Dynamics Help?

Fazle Hussain

Cullen Distinguished Professor and
Director, Institute of Fluid Dynamics and Turbulence 

Department of Mechanical Engineering
University of Houston
Houston, TX
Moore Distinguished Scholar
California Institute of Technology
Pasadena, CA

By 2025, the air traffic capacity will be tripled, demanding a tripling of runways at major airports of the world. Primarily mandated by aircraft separation for safe flight, this is not only already a challenge during takeoffs and landings, but will become a major problem also during cruise in the crowded skies. Motivated by this scenario, we propose a method of breaking up the trailing vortices and inducing their rapid decay so that separation between aircraft can be significantly reduced, thus minimizing the need for additional runways and flight delays. We study via direct numerical simulation the evolution of a vortex column embedded in fine-scale turbulence. We then explore three potential mechanisms for core perturbation growth:

  • (a) centrifugal instability due to vortex circulation overshoot,
  • (b) Kelvin wave growth in the core due to resonance with the external turbulence, and
  • (c) transient growth of perturbations in the normal-mode-stable vortex.

We show that transient growth of bending waves can produce orders of magnitude growth in core turbulence and hence possible breakup of trailing vortices and their faster decay—particularly at Reynolds numbers relevant to aircraft trailing vortices.

Wednesday, March 25, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Inertial Effects in Fluid Locomotion

Steve Childress

Courant Institute of Mathematical Sciences
New York University
New York, NY

Inertial effects emerge in fluid locomotion as the Reynolds number reaches the range 1-10. The transition to flapping flight in a small mollusc suggests a bifurcation to thrust production at a finite Reynolds number. We describe a simple table-top experiment where this bifurcation could be observed. In order to study models at arbitrary Reynolds number we revisit the classic problem of swimming of a sheet, studied by G.I. Taylor in Stokes flow. At finite and large Reynold number Taylor’s result is modified. The known results are reexamined for large Reynolds number using boundary-layer theory, and the nature of the expansions is clarified for wave-like motions of the sheet. We apply this approach to recoil swimming, a mechanism of locomotion that is known to work in a perfect fluid, thus extending the theory to a slightly viscous fluid.

Wednesday, April 8, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

[CANCELED] Processing of Bulk Nanocrystalline Oxide Materials for Optical and Magnetic Applications

Javier E. Garay

Assistant Professor 
Department of Mechanical Engineering
Materials Science and Engineering Program
University of California, Riverside

Nanocrystalline materials display significantly different properties and behaviors than their microcrystalline counterparts, yet their direct application in products has been hindered by the difficulty in producing them reliably and efficiently. One reason is that consolidation of nanocrystalline powders usually results in large grain size increase and therefore loss of enhanced nanocrystalline properties. Recently, the versatile material processing technique of spark plasma sintering (SPS) has proven effective in overcoming the grain growth challenge—it is now possible to efficiently produce viable nanocrystalline parts. The method draws its effectiveness from large electric current densities that serve to heat the materials and also alter the processing kinetics. After an overview of our processing techniques, I will present results on large-sized, fully dense oxides with grain sizes much less that 100 nm. The materials have very different properties than traditional materials. Properties presented include improved visible light transmittance, enhanced toughness, and ferri-antiferromagnetic coupling leading to exchange bias. The results will be discussed in terms of crystal length scale effects and proximity of nanoscale phases.

Wednesday, April 15, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Geometrical Evolution Problems at Low Reynolds Numbers: Reduced Models

Darren Crowdy

Imperial College London
London, UK

In this talk we report on some mathematical techniques for modelling evolving geometries at low Reynolds numbers. Two problems will be discussed, both involving free capillary surfaces. The first is a study of organisms swimming in Stokes flows in the presence of free surfaces. An idealized mathematical model is presented whereby the swimmer’s interaction with a free capillary surface is captured. The second problem is of industrial importance involving the optimal design of thin optic fibres with microstructure. There is much interest in reducing transmission loss in optic fibres by careful design of the microstructure imparted to a fibre during the “drawing process” in which molten glass is pulled through a casting die. During this process, geometrical changes in the microstructure take place owing to capillary effects resulting in the need to understand a highly nonlinear inverse problem. New ideas for modelling this process will be described.

Wednesday, April 22, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Fabrication of Bulk Metallic Glass Foams via Severe Plastic Deformation

Suveen N. Mathaudhu

Materials Engineer 
Weapons and Materials Research Directorate
U.S. Army Research Laboratory
Aberdeen Proving Ground
Aberdeen, MD

Personnel protection for soldiers requires thin, shock-absorbing components in composite vest plate. Metallic foams exhibit outstanding energy absorption, due to ductile densification by plastic deformation of their struts. Foams based on bulk metallic glasses (BMG), which have the highest strength of any metals, and as such, should be optimal. An obstacle to the use of BMG foams is the brittle behavior. However, recent demonstrations show that the thin, sub-millimeter, struts of BMG foams are ductile in compression, with outstanding energy absorption. The work presented here will demonstrate that equal channel angular extrusion (ECAE) can be used to create composites of BMG powders and metallic powders (Cu, Ni, W) which can subsequently be converted to BMG open-cell foams by leaching of the metallic second phase. These foams show excellent mechanical properties and particularly high energy absorption. Comparisons with similar melt cast BMG foams will be made. The talk will cover the overview of severe plastic deformation processing, metallic glass powder consolidation and foam fabrication by ECAE.

Dr. Suveen Mathaudhu is a Materials Engineer with the Weapons and Materials Research Directorate of the U.S. Army Research Laboratory. Dr. Mathaudhu received his B.S. in Mechanical Engineering from Walla Walla College (College Place, WA) and his PhD in Mechanical Engineering from Texas A&M University (College Station, TX). Upon graduating, he accepted a post-doctoral fellowship, and subsequently a civil servant position at the U.S. Army Research Laboratory (Aberdeen Proving Ground, MD) with the purpose of establishing a deformation processing laboratory for research on advanced materials of interest to the DoD.

His current research interests include:

  • Ultrafine-grained and nanostructured materials by severe plastic deformation
  • Microstructural optimization and homogenization
  • Consolidation of metastable particulate materials
  • Processing-Microstructure-Property relationships of refractory metals and ultralightweight metals
  • Finding ways of celebrating when the L.A. Lakers win the NBA championship this season
Wednesday, April 29, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

The Role of Thermal Undulations in Adhesion of a Biological Membrane

L.B. Freund

H. L. Goddard University Professor
Professor of Engineering 

Divisions of Engineering
Brown University
Providence, RI 02912

Fibroblasts and other tissue secreting cells have the ability to adhere to extracellular matrix and to migrate in the course of tissue generation. Adhesion occurs through specific bonding of integrins, large transmembrane protein molecules in the cell wall, to ligands in the surrounding tissue. Integrins are mobile in the cell wall and diffuse randomly in a normal thermal environment. The mean density of integrins in the cell wall is normally too low for adhesion to occur casually upon contact. Instead, adhesions form gradually as a few integrins become immobilized in a small region. Such focal adhesion regions usually grow to about a micron or two in diameter.

Such adhesion patches have been studied at a coarse scale by means of a number of experimental approaches. In a departure from this trend, Arnold et al. [ChemPhysChem 5 (2004) 383] carried out experiments in which they were able to study the process of cell adhesion at the scale of individual binding sites. Among their observations was the discovery that there appeared to be an upper bound on spacing of integrin bond sites for tight adhesions to form. Furthermore, the critical value of this density was found to be essentially uniform among the four cell types examined. This raises the tantalizing question as to whether or not this remarkable finding can be understood in terms of a fundamental physical phenomenon across the cell types. In this presentation, the question will be examined from the point of view of classical statistical mechanics with bonding being represented by a well in the potential energy landscape of the system. It will be shown that thermal fluctuations arising from immersion of the membrane in a heat bath can account for the appearance of a critical bond site spacing.

L. B. Freund received his Ph.D. degree from Northwestern University in 1967. He is the author or co-author of over 190 published articles on stress waves in solids, fracture mechanics, seismology, computational mechanics, dislocation theory, thin films, microstructure evolution in films, and engineering education, plus monographs on Dynamic Fracture Mechanics and on Thin Film Materials. His current research interests include: mechanics of biological materials (cell adhesion, molecular transport in cell walls) and mechanics of thin film materials (evolution of microstructure, influence of strain on quantum mechanical transport, lattice mismatched heterostructures). Freund presently serves as Associate Editor of the Proceedings of the National Academy of Sciences and as President of the International Union of Theoretical and Applied Mechanics. He is an elected member of the National Academy of Sciences, the National Academy of Engineering, and the American Academy of Arts and Sciences. For a complete bio please visit his website:http://www.engin.brown.edu/people/Faculty/facultypage.php?id=1106970192 

Wednesday, May 6, 2009
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Fall, 2009

Technological Entrepreneurship in Innovations for Emergence of New Industries

Shuichi Ishida

Professor of Innovation and Social Systems Research 
Ritsumeikan University
Kyoto, Japan

Innovation in industry is a process that involves an enormous amount of uncertainty, human creativity, and opportunity. Over the years, scholars have studied patterns of successful industrial innovation, but the identification of patterns does not suggest that successful innovation is entirely predictable. This research attempts to develop a practical and theoretical model of industrial innovation. Further research on the dynamics of innovation was required to development a concrete operational model to account for the role of key persons who are able to bridge over product innovation and process innovation differences. He examined the method for evaluating the strategy of firms which technology is positioned between the fluid and transitional phase of Abernathy-Utterback Model and in particular, discussed the efforts of core human resources who play a key role in the technological strategies, as well as how they are utilized. He expected to find that the strategic allocation of key individuals-multi performers would emphasize company-wide technological strategies. His research target is to address a number of epoch making product developments such as Electric Vehicle, Li-ion Battery, Fuel Cell, stuff like that, and to provide a framework for thinking about the important issues of technological entrepreneurship. Issues addressed in his future research include the following:

  • The role of key individuals in industrial innovation
  • The relationship between regional agglomeration process and technological entrepreneurship by key individuals who plays an important role of innovation and knowledge-based network creation
  • How ‘rising’ new industry firms can successfully renew their SCM as one generation of technology succeeds another (for example, EV, fuel cell, etc.). In case, who plays an important role of technological entrepreneurship?

Dr. Shuichi Ishida is a Professor of Innovation and Social Systems Research at Ritsumeikan University (Rits MOT), KYOTO, JAPAN. He received his Ph.D. in the field of R&D management from Hokkaido University (2000) and in the field of Social System Engineering from Kyoto University (2008). He has done research on R&D organization, knowledge-based networking, construction project management and industrial agglomeration development, along with theoretical modeling, ‘action research’ at several companies with specific core technologies, and some governmental projects. Prior to joining Rits MOT faculty in 2004, he developed some frontier devices of Li-ion Battery as an engineer at Sony after finishing his masters of Nuclear Engineering at Research Laboratory for Nuclear Reactors in Tokyo Institute of Technology. And next, he worked as a research fellow at the Japan Society for the Promotion of Science (JSPS) and an associate professor of product development at Hokkai-Gakuen University, Sapporo, JAPAN.

Thursday, September 17, 2009
1:30 PM
Laufer Library, (RRB 208)

Turbidity Currents Interacting with the Seafloor

Eckart Meiburg

Department of Mechanical Engineering
University of California at Santa Barbara
Santa Barbara, CA 93106

We will present high-resolution, Navier-Stokes based simulations and linear stability investigations of turbidity currents, and their two- way interaction with the seafloor. The turbidity currents we consider are driven by particles with negligible inertia that are much smaller than the smallest length scales of the buoyancy-induced fluid motion. For the mathematical description of the particulate phase an Eulerian approach is employed, with a transport equation for the particle-number density.

We will discuss some effects due to complex topography. Furthermore, we will analyze the linear stability problem of channel and sediment wave generation by turbidity currents. A novel linear instability mechanism is identified that can potentially create both of these topographical features. Its relation vis-a-vis the classical lee wave mechanism is discussed. In addition, results will be shown regarding the unsteady interaction of a gravity current with a submarine structure, such as a pipeline.

Wednesday, October 14, 2009
3:30 PM
Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Effect of Plasma Discharges on Spacecraft: An Experimental View

Timothy P. Graves

Electric Propulsion and Plasma Science Section
The Aerospace Corporation
2310 E. El Segundo Blvd.
El Segundo, CA 90245-4609

Successful satellite design and operation requires proper understanding of the many plasma phenomena associated with spaceflight. Various types of plasma discharges affect satellite components on-orbit, and in some cases, they can lead to critical failures in susceptible hardware. Some key examples of these phenomena are electrostatic discharge (ESD), plasma propulsion effects, and RF/microwave plasma discharges. The Aerospace Corporation’s Electric Propulsion and Plasma Science Section continues to experimentally research these areas to improve current understanding and provide necessary data to avoid potential satellite failures. In this talk, the plasma physics and mitigation strategies associated with the aforementioned plasma discharges will be discussed. Additionally, the unique experimental capabilities and techniques developed in Aerospace laboratories will be described with specific emphasis on how the data are used to improve satellite design and operation. Recent experiments include laboratory ESD formation and measurement on solar panel coupons, NASA’s Evolutionary Xenon Thruster (NEXT) plume measurements, satellite communication and plasma thruster electromagnetic interference, and the effect of surface contamination on multipactor discharge.

Wednesday, October 28, 2009
3:30 PM
Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Challenges in Modeling Soot Formation in Turbulent Hydrocarbon Flames

Guillaume Blanquart

Department of Mechanical Engineering
California Institute of Technology
Pasadena, CA

Understanding and modeling soot particle dynamics in combustion systems is a key issue in the development of low emission engines. In engines, soot particles are formed as a result of complex hydrocarbon chemistry and are subject to a turbulent flow field which controls ultimately the yield of soot particles. In this work, we will detail the strategies used to model the various chemical and physical processes encountered both in laminar and turbulent flames. More precisely, we will consider the impact of the chemistry on the inception of the first soot particles, the geometrical and statistical representation of fractal aggregates, the oxidation and fragmentation of particles under lean conditions, and finally the turbulent transport of soot in complex unsteady flows. For each of these cases, we will compare our results with experimental measurements and discuss the differences. Finally, we will show preliminary results for the first Large Eddy Simulation of a sooting turbulent jet diffusion flame with detailed chemical and soot models. This last simulation highlights the challenges in modeling soot evolution in turbulent flames due to the nonlinear interactions between the particles and the gas-phase turbulent combustion processes.

Wednesday, November 4, 2009
3:30 PM
Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Gravity Currents Propagating Over an Array of Bottom Obstacles

George Contantinescu

Associate Professor 
Department of Civil and Environmental Engineering
IIHR-Hydroscience and Engineering
University of Iowa
Iowa City, IA 52242

Highly resolved 3-D Large Eddy Simulation (LES) is used to study the interaction between a lock-exchange gravity current with a large volume of release and an array of bottom-mounted large-scale obstacles in the form of 2-D dunes or square ribs. The study of the interaction between a gravity current and an array of obstacles is important for many practical applications. For example, arrays of obstacles are often used as protective measures on the hilly terrains and on the skirts of the mountains to stop or slow down gravity currents in the form of powder-snow avalanches. Even if they do not arrest the flow, the retarding obstacles reduce the impact of the avalanche with the buildings situated downstream of the obstacles. The temporal variation of the impact forces on the obstacles is analyzed. This information is needed for the design of the retarding obstacles. Additionally, simulation results are used to understanding how this variation is related to the passage of the backward propagating hydraulic jumps and the different flow structures that develop within the flow. The loose bed surface over which the gravity current propagates in the environment is often not flat. Bed forms, typically in the form of ripples, dunes or anti-dunes are present at the seafloor or river bed. The presence of large-scale bedforms provides an additional mechanism for energy dissipation and can substantially modify the capacity of a compositional gravity current to entrain sediment with respect to the case of a flat bed. LES is used to understand how the shape and the relative size of the large-scale obstacles (roughness elements) affect the front velocity, the structure of the current, the energy balance, the bed shear distributions and sediment entrainment capacity of the current as it propagates over a loose bed. Finally, scale effects are investigated between Reynolds numbers at which most of the laboratory studies are conducted (Re~104) and Reynolds numbers that are within the lower range of those encountered in the field (Re=106).

Wednesday, November 11, 2009
3:30 PM
Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Gas-Phase Nanomaterials Synthesis and In-Situ Laser-Based Diagnostics

Stephen D. Tse

Associate Professor 
Department of Mechanical and Aerospace Engineering
Rutgers—the State University of New Jersey
Piscataway, NJ

Gas-phase synthesis of materials has demonstrated a history of scalability and offers the potential for high-volume commercial production, at reduced costs. Flame synthesis of ceramic oxide nanoparticles and semiconducting metal-oxide nanostructures will be discussed. Plasma synthesis affords the synthesis of non-oxide materials, such as Group III-Nitride nanopowders, which will be discussed.

Al2O3 and TiO2 nanoparticles are produced from corresponding organometallic vapor precursors using an axisymmetric stagnation-point premixed flat flame impinging on a cooled substrate under uniform electric field application. Other nanostructures, such as WO2.9 nanowires, ZnO nanoribbons, and MO2 nanoplates are also synthesized, whereby growth occurs by the vapor-solid mechanism, with local gas-phase temperature and chemical species strategically specified at the substrate for self-synthesis. Finally, cubic-BN and cubic-GaN nanopowders (which are especially attractive for photonic and structural applications) are synthesized using a plasma process, for subsequent consolidation into bulk nanomaterials.

Laser-based spectroscopy is utilized to characterize the gas-phase flow field (e.g. temperature, species concentrations). Additionally, a novel technique of using Raman spectroscopy to diagnose nanoparticle presence and characteristics (in aerosol form) during synthesis has been applied. This technique serves as a sensitive and reliable way to characterize particle composition and crystallinity (e.g. anatase versus rutile) and delineate the phase conversion of nanoparticles as they evolve in the flow field.

Stephen D. Tse received his B.S.E. in Engineering Physics from Princeton University in 1991, and his M.S. and Ph.D. in Mechanical Engineering from the University of California at Berkeley in 1994 and 1996, respectively. He was a Post-doctoral Researcher and Research Staff Member at Princeton University from 1997 to 2000. In 2001, he joined Rutgers University as an Assistant Professor, receiving his tenure in 2006. He is presently an Associate Professor and the Outreach Director in the Department of Mechanical and Aerospace Engineering.

Prof. Tse’s research focus is in the thermal sciences, involving applications in nanomaterials synthesis, CVD, and combustion and propulsion. He has designed experiments and diagnostics that have flown on the Space Shuttle or are being planned for the International Space Station. While at U.C. Berkeley, he was supported by a NASA Graduate Student Research Fellowship. He received the 1998 AIAA Best Paper Award in Microgravity Science and Space Processing, and the 2001 AIAA Best Paper Award in Propulsion and Combustion. He is an Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA), and is a member of the American Society of Mechanical Engineers (ASME), the Combustion Institute, and the Materials Research Society. He is Chair of the AIAA Microgravity and Space Processes Technical Committee, and is Chair of the Public Policy Committee on the ASME Board of Government Relations.

Wednesday, November 18, 2009
3:30 PM
Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.