2006 Seminar Archive

Rapid Prototyping Technologies Used to Reduce Cost and Time-To-Market in Aerospace and Motorsports

John Murray

Desktop Factory, Inc. (an Idealab Company) 130 W. Union St. Pasadena, CA 91103

Rapid prototyping (RP) technologies have been used since the late 1980s to improve quality and reduce time-to-market. Two market segments that use RP technologies extensively are aerospace and motorsports. While motorsports teams develop and produce components that may have a useful life of only a few hours, aerospace companies produce components that may be required to endure decades. Though their "end use" requirements differ greatly, there are common approaches that aerospace and motorsport organizations use to solve challenging engineering problems.

This presentation will focus on innovative RP strategies that have helped aerospace and motorsports organizations worldwide become more competitive. In this presentation we will explore the use of RP technology for: 1) wind tunnel analysis; 2) rapid casting; 3) ergonomics; 4) "disposable" digital tooling; 5) digital manufacturing, and 6) the future of 3D printing.

RP systems have historically been very expensive to purchase and operate thus limiting their use in education and smaller companies. Fortunately, 3D printers will become much more affordable in the future. Desktop Factory is at the forefront of developing new low-cost 3D printing solutions that will dramatically change how products are designed and manufactured.

John Murray is Vice President of Sales at Desktop Factory. Prior to Desktop Factory, he was Director of Global Business Development for Motorsports and Aerospace at 3D Systems. He has focused on advising companies worldwide on the use of cutting-edge RP applications and has negotiated numerous European technical sponsorships in Formula 1 and World Superbike in addition to NASCAR sponsorships in the U.S. His aerospace work focused on rapid design and manufacturing strategies for large commercial and military aerospace companies in the U.S., Israel, So. America, Japan, the UK and Europe and he has presented at seminars throughout the world on the effective of deployment of RP strategies.

Wednesday, January 11, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Vortices In Stratified And Rotating Fluids

Adam Fincham

Reseach Associate Professor  Aerospace & Mechanical Engineering USC Los Angeles, CA 90089-1191

Late time stratified flows are characterized by extreme anisotropy where the vertical component of velocity w, plays little part in the vortex dynamics and is best described as part of an associated internal wave field. Though quasi-2D in nature in the absence of strong background rotation, these flows exhibit fully 3D vorticity fields as the tendency for layering creates strong vertical shear and promotes a horizontal alignment of the vorticity vector. Standard full field imaging velocimetry measurement techniques capable of providing the component of vorticity perpendicular to the plane of the measurement, are inadequate for diagnosing the complex 3D vortex topology of these flows. Careful exploitation of the inherent anisotropy, and the use of relatively large experimental tanks where the Reynolds number is obtained primarily from the length scale, allows for time resolved, full 3D measurement of all three components of vorticity.

These measurements have confirmed the persistence of a balanced state between horizontal advection and vertical diffusion, that leads to a self similar evolution of the flow structures for late times. For example, the relatively well known stratified dipole, most of the time assumed to be quasi two dimensional, is revealed to have a complex three dimensional vortex topology arising from its self induced propagation. When the buoyancy scale approaches zero, an effective Reynolds number based on vertical diffusion and horizontal advection governs the evolution. Such dipolar structures are believed to characteristic the vortices of the fully turbulent case. Indeed, moderately high Reynolds number towed grid stratified turbulence experiments show a predominance of dipolar type structures, in agreement with recent numerical works. This turbulent case consists of a sea of pancake-like structures separated by highly dissipative horizontal vortex sheets. In this collapsed state, the flow evolves independently of the Froude number and is governed by the effective Reynolds number. Strong background rotation tends to force a vertical alignment of these vortices, eliminating the dominant dissipation mechanism, allowing for a quasi-geostrophic state of columnar cyclonic and anticyclonic vortices. For weaker background rotation there is a pronounced asymmetry between the cyclonic and anticyclonic vortices.

Through analysis of a variety of different experimentally measured flows, the competing effects of rotation and stratification in controlling the flow topology and energy dissipation mechanism will be examined.

Wednesday, January 25, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

The Newtonian Revolution: Interaction of Mathematics with High Technology

Rudolf E. Kalman

Professor Emeritus ETH Zurich, Switzerland

Newton's contributions to physics (and his unamiable personality) have not dimmed in three centuries but his singular genius and his greatest contributions were beginning to be seen only in the second half of the last century. This is the revolution: after basic scientific knowledge is in place further progress can be achieved only by mathematically guided research. And it is not just "applying" mathematics or "mathematizing" physics but a deep and mysterious symbiosis between mathematical thinking and the real world.

(Newton's biggest single result, the gravitational law, was established in this way.) A road-map for high technology. I shall focus on a small part of this dazzling picture: the evolution of system theory since its semi-conscious discovery by Newton (1680's) and its "modern" rediscovery by Foster (1924) and Cauer (1925) to the present, with the precise formulation of the (still) unsolved problems and technical details forming the second part of the lecture.

Wednesday, February 1, 2006 2:00—4:00 PM Gerontology Auditorium

Thermo-Mechanical Effects in Multi-Component Micro-Systems in Electronic Applications

Indranath Dutta

Professor of Materials Science and Mechanical Engineering  Center for Materials Science and Engineering Department of Mechanical & Astronautical Engineering Naval Postgraduate School Monterey, CA 93943

Electronic devices and packages typically comprise micro-to-nano scale multi-component material systems subjected to extreme thermo-mechanical loads. Under these conditions, materials often display unusual, scale-dependent thermo-mechanical effects not observed in macro-systems. This makes it imperative to develop novel experimental approaches to characterize these effects in miniature systems, and develop appropriate constitutive laws to address them in reliability models.

This talk will start with an introduction to thermo-mechanical reliability issues in microelectronic devices and packages. Then, two aspects of ongoing research at the Naval Postgraduate School, which address the above issues, will be presented. The areas covered will include: (1) interfacial creep in micro-systems, with application to interconnect structures in microelectronic devices (i.e., chips) and (2) microstructure-creep interactions in solder joints used in microelectronic packages, with emphasis on the development of a new test approach based on impression creep. Experimental and modeling techniques used to characterize these effects will be outlined, along with the impact of these effects on the reliability of devices and packages during thermo-mechanical cycling.

Indranath Dutta is Professor of Materials Science and Mechanical Engineering and Director of the Composites, Thin Films and Interfaces Laboratory at the Naval Postgraduate School, where he is active in research and instruction in the area of thermo-mechanical behavior of multi-component materials systems. His current research focuses on materials issues in micro-systems packaging and hyper-velocity railguns, with support from NSF, ARO, ONR, SRC and the industry. He was an AFOSR Summer Research Fellow at the Air Force Research Laboratory in 1995, Visiting Fellow at the University of Oxford in 1996, Visiting Consultant at MOTOROLA in 2000, and Visiting Faculty at INTEL Corporation in 2001. He is a recipient of several awards, including the TMS Young Leader Award, NPS Outstanding Research Achievement Award, the Carl E. and Jessie W. Menneken Award for Excellence in Scientific Research at NPS, is listed in Who's Who in the World and Who's Who in America, and is a Fellow of ASM International.

Wednesday, February 8, 2006 3:30 PM Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Molecular Structure Effects On Laminar Burning Velocities At Elevated Temperature And Pressure

Dr. John T. Farrell

Advanced Fuel-Engine Systems ExxonMobil Research and Engineering Company

The laminar burning velocities of 45 hydrocarbons have been measured in a constant volume combustion vessel at an initial temperature of 450 K and pressure of 304 kPa and over the stoichiometry of 0.55< f < 1.4. The burning velocity is determined both from a thermodynamic analysis of the pressure vs time data and from direct flame front measurement via high speed visualization. The results for alkanes and alkenes are consistent with trends previously identified in the literature, i.e., alkenes are faster than the corresponding alkane with the same carbon connectivity. For both alkanes and alkenes, branching lowers the burning velocity. In addition, terminal alkenes and alkynes are found to be slightly faster than internal. The present study includes a greater emphasis on aromatics than previous literature reports. The burning velocities for aromatics show a strong dependence on the type and site of alkyl substitution; methyl substitution lowers the burning velocity more than substitution with larger alkyl groups. For multiple methyl group substitution, meta substitution lowers the burning velocity more than ortho/para. The physical and chemical kinetic bases for the variation of burning velocity with molecular structure are discussed with the aid of elemental flux analyses of simulations using detailed chemical kinetic mechanisms.

Wednesday, February 15, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

New Findings on Utralight Technologies

Mulalo Doyoyo

Assistant Professor  Department of Civil and Environmental Engineering Georgia Institute of Technology Atlanta, GA

Miniaturized strut- and shell-based space-fillers of all-metal materials systems are being used as cores of ultralight sandwich constructions. Modern demands for energy saving and environmental protection are forcing the vehicle-manufacturing industry to develop ultralight concepts including hybrid vehicles and alternate power cells. The key challenge is to develop ultralight technologies without sacrificing safety, cost, and long-term performance criterion. Interest in miniaturized space-fillers is growing rapidly because of their ability to meet these demands. However, in-depth understanding of their topologies, functions, and properties is lacking. This talk presents some of the recent findings on the behavior of ultralight systems with a specific focus on strength-enhancement with direct-action cores (e.g. those with sacrificial microstructures), and energy-absorption enhancement with crushable cores (e.g. fold-fronts vs. auxeticity). The use of “mechanism-based” cores to perform intelligent functions will also be discussed.

References

1. Doyoyo, M., 2006, Hierarchical plasticity of strut-based lattice cores, in preparation.
2. Doyoyo, M. and Hu, J.W., 2006, Plastic failure analysis of an auxetic foam or inverted strut lattice under longitudinal and shear loads, Journal of the Mechanics and Physics of Solids, in press.
3. Doyoyo, M. and Hu, J.W., 2006, Multiaxial failure of strut lattice composed of short and slender struts, International Journal of Solids and Structures, in press.
4. Doyoyo M. and Mohr, D., 2006, Experimental determination of the mechanical effects of mass density gradients in metallic foams under large multiaxial inelestaic deformation, Mechanics of Materials, 38, 4, 325-339.

Mulalo Doyoyo obtained his Ph.D. in Solid Mechanics at Brown University and then worked in the Department of Ocean Engineering at MIT before joining the School of Civil and Environmental Engineering at Georgia Tech. His current research focus is on the development of ultralight technologies in the transportation and biomedical industries.

Wednesday, February 22, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Collective Motion in Engineered and Natural Multi-Agent Systems

Professor  Mechanical and Aerospace Engineering Princeton University

The collective control of mobile, multi-agent systems is motivated by a range of engineering applications that require the coordination of a group of individually controlled systems. A closely related problem focuses on the role of feedback and interconnection in the collective motion of animal groups. Tools from control and dynamical systems can be used to study both engineered and natural mobile networks in a systematic and scalable way. In this talk I will describe recent collaborative work on models for collective motion based on moving particles with steering control. We extend phase models of coupled oscillators to include spatial dynamics and use these models for design and analysis of collective motion patterns. I will describe application to design of an ocean sampling network and to analysis of fish schooling behavior.

Professor Leonard is a 2004 recipient of the MacArthur Prize Fellowship

Wednesday, March 1, 2006 12:00 NOON GFS 101

Enabling Technologies for Nuclear Magnetic Resonance Analysis of Microscopic and Surface-Bound Samples

Garett M. Leskowitz

Lecturer / Postdoctoral Researcher  Department of Chemistry University of California Riverside, CA 92521 and Visiting Assitant Professor  Joint Sciences Center The Claremont Colleges Claremont, CA 91711

Nuclear magnetic resonance (NMR) spectroscopy is an analytical technique with unparalleled information content and flexibility, which is ubiquitous in chemistry, biochemistry, and materials science. Commercial NMR instrumentation relies on magnetic induction, and the signal-to-noise ratio inherent in the signal-detection physics scales very poorly with sample size. The application of NMR to microscopic samples, in particular to thin films at interfaces, has therefore been limited. In this talk, I will describe a recently developed detection method whose sensitivity is predicted to scale favorably down to microscopic samples. The method relies on measurement of sub-nanometer motions of a vibrating magnetic assembly placed near the sample. An important feature of the detection method is its compatibility with homogeneous magnetic fields in the sample volume, which are necessary for optimal sensitivity and spectral resolution. A prototype apparatus confirms proof of principle and quantitatively verifies the theory of signal and noise. Progress and engineering challenges in scaling the prototype down to microscopic and surface-bound samples will also be addressed.

After being active in industrial research and development of fiber-optics based infrared spectroscopy systems, Garett Leskowitz earned his Ph.D. in Physical Chemistry at the California Institute of Technology. He is now a lecturer and postdoctoral research scientist in the Chemistry Department at the University of California, Riverside, and a visiting assistant professor of chemistry at the Joint Sciences Center of the Claremont Colleges. His current research interests include dynamic nuclear magnetic resonance, new magnetic resonance phenomena, and quantum information in spin systems.

Wednesday, March 1, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Towards Verification and Validation of Adaptive Systems for Safety Critical Applications

Naira Hovakimyan

Associate Professor  Department of Aerospace and Ocean Engineering Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0203 e-mail: nhovakim@vt.edu

One of the most important challenges for adaptive control theory is the lack of systematic design methods for guaranteeing transient response with desired specifications. Application of adaptive controllers was largely restricted due to the fact that the system uncertainties during the transient have led to unpredictable/undesirable situations, involving control signals of high-frequency or large amplitudes, large transient errors or slow convergence rate of tracking errors, to name a few. Extensive tuning of adaptive gains and Monte-Carlo runs have been the primary method up today enabling the transition of adaptive control solutions to real world applications. This argument has rendered verification and validation (V&V) of adaptive controllers overly challenging.

This presentation details a theoretical framework for development of novel stable adaptive control architectures for various classes of uncertain systems with guaranteed transient performance for system's both input and output signals and guaranteed stability margins. These synthesis and analysis tools can be used to develop a theoretically justified framework for acceleration of the verification and validation testing of adaptive controllers in safety critical applications. Various aerospace applications will be discussed during the presentation.

Naira Hovakimyan received her Ph.D. in Physics and Mathematics in 1992, in Moscow, from the Institute of Applied Mathematics of Russian Academy of Sciences. Upon her Ph.D. she joined the Institute of Mechanics, Armenian Academy of Sciences, as a research scientist, where she worked till 1997. In 1997 she has been awarded a governmental CNRS postdoctoral scholarship to work in INRIA, France. She is the recipient of the SICE International scholarship for the best paper of a young investigator in the VII ISDG Symposium (Japan, 1996). The subject areas in which she has published include differential pursuit-evasion games, optimal control of robotic manipulators, robust control, adaptive estimation and control. In 1998 she was invited to the School of Aerospace Engineering of Georgia Tech, where she worked as a research faculty member until 2003. In 2003 she joined the Department of Aerospace and Ocean Engineering of Virginia Tech as an associate professor. She is the author of over 100 refereed publications. She is senior member of the IEEE (CSS, NNS), Associate fellow of AIAA, member of AMS, ISDG, and is serving as Associate Editor for the IEEE Control Systems Society, IEEE Transactions on Neural Networks, IEEE Transactions on Control Systems Technology, Computational Management Science of Springer, International Journal of Control, Systems and Automation. She is the 2004 and 2006 recipient of Pride@Boeing award. Her current interests are in the theory of adaptive control and estimation, neural networks, stability theory and are supported by AFOSR, ONR and The Boeing Co.

Wednesday, March 8, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Numerical Simulations of Biological Locomotion in Fluid Media

Jeff Eldredge

Assistant Professor  Mechanical and Aerospace Engineering Department University of California at Los Angeles Los Angeles, CA

Intrinsic to many forms of locomotion in nature is the dynamic interaction of a flexible surface—wing, caudal fin, or the body itself—with the fluid in which the organism is immersed. Analysis of such problems with conventional grid-based computational approaches is cumbersome because of the need to constantly regenerate the grid in response to the motion. Furthermore, in the moderate Reynolds number regime where many insects, fish, and biologically inspired vehicles function, viscous and inertial processes are both important, and vorticity plays a crucial role. In recognition of these characteristics, the viscous vortex particle method (VVPM) is shown to provide an intuitive simulation approach for investigation of this class of problems. In contrast with a grid-based approach, the method solves the Navier-Stokes equations by tracking computational particles that carry smooth blobs of vorticity and exchange strength with one another to account for viscous diffusion. In this way, computational resources are focused on the physically relevant features of the flow, and there is no need for artificial boundary conditions. Vorticity is created at the fluid-body interface in exactly such measure necessary to enforce the no-slip condition and diffused to adjacent particles. The method is extended to dynamically coupled problems, in which the bulk motion of the body is simultaneously solved for with the fluid motion. Application of the method to several two-dimensional model problems is presented, including single and multiple flapping wings, locomotion of a three-linkage fish, and the flapping of a wing section composed of two rigid ellipses connected by a torsion spring.

Wednesday, March 22, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Design for Fault Prevention & Health Management in Complex Aerospace Systems

Dr. Irem Y. Tumer

Senior Research Scientist  Group Lead Complex Systems Design Group Intelligent Systems Division NASA Ames Research Center

Designing and building vehicles for NASA's increasingly complex aerospace missions has never been more challenging. Success depends heavily upon the ability to meet the stringent requirements of safety, reliability, and performance while having to push the limits of structural integrity, material durability, and autonomous operation. Designers are expected to anticipate every possible contingency and account for interactions among components that cannot be thoroughly planned, understood, anticipated, or guarded against. As a result, it is not only critical to "design out" failures when possible, but also to "design in" the capability to detect, diagnose, and recover from failures throughout the mission lifecycle when they do occur. To meet this need, the aerospace industry as a whole has been moving towards the concept of an integrated systems health management (ISHM) capability for the next generation aerospace vehicles and systems, including aircraft, crewed spacecraft, and robotic explorers. A key challenge in the acceptance of an ISHM capability by designers and system engineers is to ensure these systems are not designed and implemented as an afterthought, but rather as a critical subsystem to be designed concurrently with the overall system and/or vehicle. To address this challenge, we assert that the ISHM capability has to be introduced into the system-level design as early as possible in the requirements and architecture definition phases. Our work focuses on two main aspects of this problem: 1) developing methodologies to introduce failure analyses and risk assessment practices as early as possible in the design lifecycle; and, 2) developing systems-level design methodologies to seamlessly incorporate health management functionality into the design of vehicles and systems. In this talk, I will give an overview of various research projects we have ongoing to address these challenges.

Dr. Tumer leads the Complex Systems Design and Engineering group in the Intelligent Systems Division at NASA Ames Research Center. Her research group focuses on the overall problem of designing highly complex and integrated aerospace systems with reduced risk of failures, developing formal methodologies and approaches for complex system design, and integrated fault detection, diagnosis, and management. Dr. Tumer leads and supervises various projects addressing the prediction and prevention of failures and risks early in design, has published over 70 articles on various research topics in her areas of expertise, including 20 journal articles and 40 fully refereed conference articles. She is an active member of ASME, has been Chair of the Design for Manufacturing Conference in 2002, Program Chair for the same conference in 2001, and session chair, review coordinator, panel organizer, track organizer for International Design Theory and Methodology, Design Automation, and Design for Manufacturing and Lifecycle Conferences, as well as an active participant in other conferences on system design and health management. Within NASA, she has served as the project manager for the Core Risk Research element of NASA's Engineering for Complex Systems program from 2002 through 2004; she is currently deputy Principal Investigator for the Exploration Technology Development Program's Integrated Systems Health Management Project (focus on solid rocket, liquid engine, and spacecraft systems health management technology and architecture research). In addition, she is heavily involved with the Exploration Systems Mission Directorate's Crew Launch Vehicle and the Crew Exploration Vehicle Integrated Systems Health Management design projects, as well as the Aeronautics Research Mission Directorate's Aviation Safety Program's Aging Aircraft and Integrated Vehicle Health Management projects. She received her Ph.D. in Mechanical Systems & Design from The University of Texas at Austin. She has been with NASA since 1998, first as an in-house contractor, then as a NASA employee since 2000 (GS-15 level since 2005).

Friday, March 24, 2006 12:00 NOON Stauffer Science Lecture Hall, Room 100 (SLH 100)

Kinetic Modeling of Microscale Gas Flows

Alina Alexeenko

WiSE Postdoctoral Fellow  Aerospace and Mechanical Engineering Department University of Southern California Los Angeles, CA 90089 e-mail: alexeenk@usc.edu

Development of microsystems such as lab-on-chip analytical sensors, flow control, and propulsion devices will take a giant leap forward if accurate and cost-effective numerical modeling is available in areas where experimental flow diagnostics is limited or impossible. Gas flows in such microsystems are characterized by low Reynolds and relatively large Knudsen numbers, and large surface-to-volume ratios. This leads to a flow regime in microdevices that is drastically different from their macroscale counterparts. Due to significant flow non-equilibrium the constitutive relations for the stress tensor and heat flux that appear in the Navier-Stokes equations break down, and the modeling must be based on a microscopic, kinetic description of the gas flow.

Two kinetic approaches will be discussed, with examples of applications to gaseous microsystems: a micronewton thruster; the microscale roughing pump known as the Knudsen compressor; and a resonant microbeam pressure sensor. The first approach, the direct simulation Monte Carlo (DSMC) method, is a stochastic technique based on the atomistic description of a gas as a collection of moving and colliding particles. The DSMC method has proved to be a very powerful numerical tool for modeling high-speed rarefied gas flows, such as high-altitude hypersonic flight. However, this stochastic approach currently has limited application to low-speed gas systems, due to inherent statistical scatter and low signal-to-noise ratios. It also becomes increasingly computationally costly as the flow Knudsen number decreases towards the continuum flow regime. Moreover, the DSMC method is explicit in time, which imposes additional limits to its application in low-speed microflows. An alternative numerical approach is to obtain a deterministic solution, based on the discrete ordinate method, to the ellipsoidal statistical (ES) model kinetic equation. The primary advantage of this modeling technique is its high computational efficiency compared to pure stochastic methods. Last but not least, techniques for solution of the ES model equation are readily amenable to multiphysics/multiscale simulations. This is an essential feature for describing the flow physics of micro/nano-flows, where surface potential wells, mobile adsorbed gases, and the details of a bounding surface's lattice structure can all have uniquely important influences on the flow.

Wednesday, March 29, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Research in High-Speed Jet Noise

Dennis K. McLaughlin

Professor of Aerospace Engineering  Aerospace Engineering Department Penn State University University Park, PA

This seminar describes experiments on model supersonic jets in the Penn State anechoic chamber jet noise facility. The experiments are designed to produce aeroacoustic data on shock containing and perfectly expanded round jets and jets issuing from rectangular nozzles with and without thrust vectoring. Acoustic overall sound pressure levels, spectra, and directivity are measured for a number of jet flowfield conditions as well as the nonlinear effects during propagation to the far field. Optical Deflectometry provides information on the noise producing turbulence in the jet flow fields.

The experiments are part of a larger program at Penn State and Wyle Laboratories that also involves the computational simulation of the jet flow near field, development of an algorithm to predict the propagation nonlinear effects, as well the inclusion of these developments into a dynamic model for use in airport and community noise impact studies.

Wednesday, April 5, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Low Pressure Performance of Micro/Meso Scale Knudsen Compressors

Y.-L. Han

Department of Aerospace & Mechanical Engineering University of Southern California Los Angeles, CA

Continuing advances in MEMS fabrication capabilities and strategies are beginning to facilitate significant progress in miniaturizing the functionality of many conventional and unconventional thermo/mechanical machines. A significant number of these evolving devices require micro/meso-scale gas pumps or compressors in order to create complete, miniaturized systems. One option is the Knudsen Compressor, named in 1994 by Pham-van-Diep et al [1]. Knudsen Compressors are solid-state, micro/meso-scale gas pumps or compressors with no moving parts. Based on the rarefied flow phenomenon of thermal creep, Knudsen Compressors operate by imposing a temperature gradient across a high porosity, low thermal conductivity transpiration membranes [2]. Studies have shown that a Knudsen Compressor with an aerogel membrane, can be operated efficiently by either resistive or radiant heating techniques over a pressure range from about ten atmospheres down to 250 Torr [3][4]. Employing different 'membrane' configurations, Sone and Sugimoto have recently studied several meso/macro-scale thermal creep (thermal transpiration) pumps at pressures of around 2 Torr and lower.[5][6]

At low pressures (< 1Torr), relevant issues encountered for providing efficient operation of micro/meso-scale Knudsen Compressors include; large membrane channel sizes, required because of relatively large molecular mean free paths; and "reverse" thermal creep in the connector sections due to finite connector channel to membrane channel size ratios. Mechanically machined aerogel membranes with circular channels have already been studied; results have shown that they are attractive candidates as Knudsen Compressor membranes at low pressures.[7] The performance of these membranes has also been found limited by rarefaction effects in the connector section such as reverse thermal creep flow, and related induced internal flows.[8] The principal goal of this study was to investigate in greater detail than previously reported[8] the fundamental limitations encountered in reducing a micro/meso-scale Knudsen Compressor's operating inlet pressures to as low as 10 mTorr (10-5 atm). Both experiments and simulations were employed in this investigation.

For the experimental studies[9] aerogel membranes, incorporating mechanically machined 500 mm high, 0.5 mm long, and 1cm wide rectangular, supplementary flow-channels, were used for the investigation of a Knudsen Compressor stage's performance at low pressures. For connector section Knudsen numbers greater than about 0.1, the pressure ratio gain through an entire stage was seriously impacted by the connector section's reverse thermal creep flow. This finding is consistent with earlier circular channel results [8][9].

Direct Simulation Monte Carlo (DSMC) technique codes were constructed for further investigations of the reverse thermal creep flow in connector sections [9]. A two-dimensional simulated domain was adopted to mimic a simplified, rectangular channel, single stage Knudsen Compressor. The effects of the reverse thermal creep flow in simulated connector sections, for several connector to membrane channel size ratios and several wall temperature distributions, have been obtained in the simulations. The simulation results were in good agreement with appropriate theoretical predictions based on available flow coefficients [10].

This investigation quantifies, using the results of both experiments and simulations, the importance of reverse thermal creep induced flows in the connector sections of low pressure, single stage micro/meso-scale Knudsen Compressors. As the connector section Knudsen number rises above about 0.1, the performance of Knudsen Compressors, with either rectangular or circular channels, will be progressively decreased by reverse thermal creep induced flows in the connector sections

References: [1] Pham-Van-Diep, G., Keeley, P., Muntz, E. P., Weaver, D. P., 19th RGD, 1995. 715-721. [2] Muntz, E.P., Sone, Y., Aoki, K., Vargo, S., and Young, M., J. Vac. Sci. Technol.. A1 (2002): 214. [3] Vargo, S.E., PhD Dissertation,, Los Angeles, CA: University of Southern California, 2000. [4] Young, M., PhD Dissertation,, Los Angeles, CA: University of Southern California, 2004. [5] Sone, Y., Sugimoto, H., 23rd RGD, 2003, pp. 1041-1048. [6] Sugimoto, H., Sone, Y., 24th RGD, 2005, pp. 168-173. [7] Han, Y.L., Young, M., Muntz, E.P., Shiflett, S., 24th RGD, 2005, pp. 162-167. [8] Han, Y. L., Young, M., Muntz, E.P., Proceedings of IMECE 2004-61807. [9] Y-L Han, PhD Dissertation, Los Angeles, CA: University of Southern California, 2006. [10] Sharipov, F.M., Phys. Fluids. 9-6 (1996): 262.

Wednesday, April 12 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Vortex Generation in Flows Around Solid Bodies

Stefan G. Llewellyn-Smith

Asst. Professor of Environmental Engineering  Department of Mechanical and Aerospace Engineeering University of California, San Diego La Jolla, CA

It is well known that the singularity at the sharp trailing edge of a body in two-dimensional potential flow is removed by the Kutta condition, which specifies the circulation about the body. We examine a different approach to computing the unsteady flow about such bodies in potential flows, in which each edge sheds vortices to ensure boundedness of the velocity at the edge. This requires equations for the motion of the vortices. We review the history of such equations, from Legendre to Howe via Cheng, Brown, Michael and Rott. A simple complex variable formulation is used to examine the validity of the equations.

A numerical implementation similar to that of Cortelezzi and Leonard is presented, and the motion of a flat plate in a given velocity field is examined. Forces and couples are calculated. The motion of a freely-falling plate is then investigated. Extensions to flexible structures are outlined.

Finally the whole notion of a moving singularity in a fluid is examined briefly, historically and mathematically.

This work is funded by NSF CTS-0133978.

Wednesday, April 19, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Fabrication Of Proton Exchange Membrane Fuel Cell Bipolar Plates By Selective Laser Sintering

David Bourell, Ph.D.

Temple Foundation Professor  The University of Texas at Austin Laboratory for Freeform Fabrication 1 University Station, C2200 Austin, TX 78712-0292

Presented is a new manufacturing technique involving Selective Laser Sintering (SLS) for fabrication of proton exchange membrane fuel cell bipolar plates. A material system for bipolar plate fabrication was identified to satisfy both the cell performance requirements and SLS operation restrictions. The structure of the constituent powders and the fabrication process will be described. Carbonization and liquid epoxy infiltration are necessary following the completion of the SLS green part. The finished SLS bipolar plate showed impressive surface finish and mechanical strength, and a single fuel cell was assembled with two SLS end plates and membrane electrode assembly in between. Computational modeling (FLUENT) of various bipolar plate channel designs will be compared to experimentally prepared samples. This research was funded by the State of Texas Technology Development and Transfer Program (Grant number 003658) and the U.S. Office of Naval Research (Grant number N000140010334).

Wednesday, April 26, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Discrete Mechanics, Optimal Control and Formation Flying Spacecraft

Sina Ober-Blöbaum

A new approach to the solution of optimal control problems for mechanical systems is proposed. It is based on a direct discretization of the Lagrange-d'Alembert principle for the system (as opposed to using, for example, collocation or multiple shooting to enforce the equations of motion as constraints). The resulting forced discrete Euler-Lagrange equations then serve as constraints for the optimization of a given cost functional. We numerically illustrate the method by optimizing the reconfiguration of a group of formation flying spacecraft as motivated by the Darwin (ESA) and TPF (NASA) space missions. This is joint work with Jerry Marsden (Caltech) and Oliver Junge (TU Munich).

Tuesday, May 2, 2006 2:00 PM Laufer Library (RRB 208)

[Canceled] Homogeneous Microcombustion Studies: Progress and Observations

Mark A. Shannon

J.W. Bayne Professor  Department of Mechanical Science and Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801

In the past few years, there has been an intense interest in building very small engines, power plants, and high temperature microchemical reactors, all running on the combustion of hydrocarbon fuels (due to their high inherent energy densities). While most systems employ catalytic and heterogeneous combustion processes, we wished to create and study high-temperature flames confined within burners with the smallest gap below 1 mm in length. The problem we immediately confronted is that flames either could not be created within narrow confined structures, or quenched quickly, similar to that which occurs in flame arrestors. We hypothesized that if we could have hot enough walls with low enough radical recombination probabilities, we could create and sustain homogeneous combustion in burners with sub-millimeter gaps. Therefore, we investigated a number of different wall materials and burner configurations, and found that flames of hydrogen, methane, propane, butane, and acetylene mixed with oxygen can be sustained in cavities as small as 100 microns, provided that the walls are sufficiently "quenchless." In addition, we have observed unusual flame structures at this scale, and flame dynamics that strongly vary with changes in temperature profiles. In this talk, I will present the experiments that we have conducted towards developing microcombustion-based systems, some of the observations I find interesting, what we now know is happening within the structures, and the many open questions that remain to be answered (hopefully!) by many of the excellent researchers working in combustion studies throughout the U.S. and world.

Mark A. Shannon is the Director of a NSF Science and Technology Center, the WaterCAMPWS, which is a multiple university and government laboratory center for advancing the science and engineering of materials and systems for revolutionary improvements in water purification for human use. He is also the Director of the Micro-Nano-Mechanical Systems (MNMS) Laboratory at the University of Illinois at Urbana-Champaign, a 1600 sq. ft class 50 cleanroom laboratory devoted to research and education in the design and fabrication of micro- and nanoelectromechanical systems (MEMS & NEMS), microscale fuel cells and gas sensors, high-temperature microchemical reactors and microcombustors, micro-nanofluidic sensors for biological fluids. He is also the Chair of the Instrument Systems Development Study Session for the National Institutes of Health. He is the James W. Bayne Professor of Mechanical Engineering at UIUC, and is an affiliate of the Beckman Institute of Advanced Science and Engineering, and the Departments of Electrical and Computer Engineering and Bioengineering. He received his B.S. (1989) M.S. (1991) and Ph.D. (1993) degrees in Mechanical Engineering from the University of California at Berkeley. He received the NSF Career Award in 1997 to advance microfabrication technologies, the Xerox Award for Excellence in Research, is a former Kritzer Scholar (2004) and Willet Faculty Scholar (2005) in the College of Engineering at UIUC, and received the BP Innovation in Education Award in 2006.

Wednesday, September 13, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Intelligent Pen-Based Interfaces and Their Applications to CAD and Education

Tom Stahovich

Associate Professor  Department of Mechanical Engineeering University of California, Riverside Riverside, CA

Sketching with pencil and paper has always been an important means of communication and problem-solving for designers and engineers. There are a variety of reasons for this. For example, sketches are a convenient tool for examining geometric, temporal, and other such relationships, which cannot be described easily in words. Similarly, the simplicity and ease of creating a sketch allows one to focus on problem solving rather than the communication medium. Yet, despite the importance of sketches in engineering practice, traditional engineering software can do little with them. We are working to change this by creating sketch understanding techniques that enable software to work directly from the kinds of sketches engineers ordinarily draw. This talk will present techniques for interpreting free-hand sketches and transforming them into models suitable for use with engineering analysis tools. The talk will also present examples of pen-based engineering tools we have developed with our techniques. Finally, the talk will conclude with a discussion of recent applications of this work to the development of pen-based educational software.

Dr. Stahovich received a B.S in Mechanical Engineering from UC Berkeley in 1988. He received an S.M. and Ph.D. from MIT in 1990 and 1995 respectively. He conducted his doctoral research at the MIT Artificial Intelligence Lab. After serving as an Assistant and Associate Professor of Mechanical Engineering at Carnegie Mellon University in Pittsburgh, PA, Dr. Stahovich joined the Mechanical Engineering Department at UC Riverside in 2003. He also currently holds cooperative appointments in the Computer Science and Electrical Engineering Departments at UC Riverside. His research interests include pen-based computing, design automation, and design rationale management.

Wednesday, September 20, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

The Situation of Chinese Manufacturing and Theory of Modern Design

Y.B. Xie

Professor  Shanghai Jiaotong University and Xi'an Jiaotong University Shanghai, People's Republic of China

The problem with Chinese manufacturing is that how China can become a strong manufacturing country from a big manufacturing country? The situation is: 1. Lake of new Knowledge with Chinese own property. 2. Lake of the capability of discovering and describing new Knowledge with Chinese own property. 3. Lake of the Knowledge of inserting new technologies in new design, say capability of matching, of making optimum life cycle performance and of meeting the life cycle constrain requirements. Our strategy and the activities for solving the problem are developing a distributed resource environment in China, any enterprise anywhere can ask and obtain Knowledge Service for design activities providing by intelligent resource units outside of the enterprise via internet or other tools in such an environment. Some theoretical results coming from the activities form what we called the Theory of Modern design.

Xie, You-Bai, Professor of Shanghai Jiaotong University and Xi'an Jiaotong University, Member of the Chinese Academy of Engineering. His fields are tribology and design theory and methodology. He has published more than 350 papers and there were 50 students obtained their Master Degrees and 47 students obtained their Doctor Degrees under his supervision.

Wednesday, September 27, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Mechanics of Stretchable Electronics

Yonggang Y. Huang

Shao Lee Soo Professor  Department of Mechanical and Industrial Engineering University of Illinois at Urbana-Champaign Urbana, Illinois

Stretchable electronics is important in the development of next-generation electronics since it has many applications such as portable electronics, flexible display, small optical sensor and compact digital camera, sensors and drive electronics for artificial muscles, structural monitors wrapped around aircraft wings, and surgeon's gloves studded with stretchable sensors that can monitor a patient's vital signs. However, silicon is an intrinsically brittle material and is not stretchable. We have produced a stretchable form of silicon that consists of sub-micrometer single crystal elements structured into shapes with microscale periodic, wave-like geometries (Science, v 311, pp 208-212, 2006). When supported by an elastomeric substrate, this wavy silicon can be reversibly stretched and compressed to large strains without damaging the silicon. The amplitudes and periods of the waves change to accommodate these deformations, thereby avoiding significant strains in the silicon itself. Dielectrics, patterns of dopants, electrodes and other elements directly integrated with the silicon yield fully formed, high performance wavy metal oxide semiconductor field effect transistors, pn diodes and other devices for electronic circuits that can be stretched or compressed to similarly large levels of strain. There are many mechanics problems in stretchable electronics, and I will discuss a few in this talk.

Wednesday, October 4, 2006 1:00 PM Hedco Auditorium (HNB 101)

Refreshments will be served at 3:15 pm.

The Health Effects of Combustion-Generated Particles

Ian M. Kennedy

Professor  Departments of Mechanical and Aeronautical Engineering, Biomedical Engineering, and Electrical and Computer Engineering University of California Davis Davis, CA

The link between exposure to fine particles in the atmosphere and adverse health effects has been well-established by epidemiological studies. Most of the fine and ultrafine material of concern derives from combustion sources and is largely a mixture of elemental and organic carbon, metals, and inorganic compounds such as sulfates. When inhaled by people, the particles can be taken-up by cells in the lung. The particles can also penetrate into the circulatory system and lodge in organs such as the liver and heart. The mechanism for their impact on health is not entirely understood although the generation of reactive oxygen species such as the OH radical is a major focus. The inflammation that can be caused by these reactive species can exacerbate pre-existing ailments. Combustion conditions in mobile and stationary sources can affect the reactivity of aerosols and their ability to generate reactive oxygen species. Combustion conditions can also affect the speciation of transition metals, the morphology of particles and their composition, and their size, all parameters that may lead to adverse health effects. This presentation will review the current state of knowledge about sources, transport, transformation and fate of fine and ultrafine particles that arise from combustion sources. The impact of combustion conditions on the potential for adverse health impacts will be given particular attention.

Wednesday, October 4, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Scaling Effects on High Strength, High Porosity Nanoporous Metal Foams

Andrea M. Hodge

Materials Scientist  Nanoscale Synthesis and Characterization Laboratory Lawrence Livermore National Laboratory Livermore, CA

A comprehensive study including nanoindentation, pillar compression tests and MD simulations of nanoporous Au foams will be presented in order to elucidate on the relationship between mechanical properties, relative density and foam ligament size at the nanoscale. Scaling equations for yield strength and Young's Modulus were investigated using 20% to 42% relative density foams with ligament sizes ranging from 10 to 940 nm. Overall, this study demonstrates that, at the nanoscale, the foam strength is no longer governed by the relative density, but rather by the size of the ligaments. Additionally, experimental results show that nanoporous foams present a new type of high strength, low density material.

Wednesday, October 11, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Forming, Counting, and Breaking Individual Biological Bonds: Applications for Drug Delivery and Single Cell Signal Transduction

Todd Sulchek

Staff Scientist  Biosecurity and Nanosciences Laboratory Lawrence Livermore National Laboratory Livermore, CA

Protein molecules commonly operate in complexes to perform their function. For example, cell surface receptors often cluster at the site of complementary ligands so as to efficiently transduce binding. A special case of improved functionality through complexed protein binding is demonstrated in a new class of therapeutics in which monovalent antibody binding elements are combined to form multivalent complexes that dramatically increase drug specificity and residency time. However, traditional methods of analysis cannot directly measure the bond lifetime of drug molecules that can bind with a distribution of valencies. Therefore, a single molecule binding assay is illuminating.

We have developed a method using single molecule dynamic force spectroscopy to determine the binding strength of antibody-protein complexes as a function of binding valency in a direct and simple measurement. We used the atomic force microscope (AFM) to measure the force required to rupture a single complex formed by the MUC1 protein, a cancer indicator, and therapeutic antibodies that target MUC1.

We show for the first time that the valency of stochastic, multivalent bond formation can be distinguished with a "molecular counter" in the form of a soft polymer linker. As a result, we independently measure both the valency and the composite bond strength for the interaction. The effective bond lifetime rises dramatically with the number of molecular bonds, from several minutes for a single antibody-antigen bond to many days for three antibody-antigen bonds. Moreover, our results support the theoretical prediction for unbinding dynamics of multiple parallel bonds. We furthermore describe current experiments in which we study cell signal transduction using controlled delivery of protein stimuli.

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

Refreshments will be served at 3:15 pm.

Social Biological Organisms: Aggregation Patterns and Dynamics

Chad Topaz

Assistant Professor and Assistant Director of Center of Excellence in Teaching  Center of Excellence in Teaching Rossier School of Education USC

Biological aggregations such as insect swarms, bird flocks, and fish schools are arguably some of the most common and least understood patterns in nature. These groups are thought to arise chiefly from "social forces" acting on individual organisms, including attraction (for protection and mate choice) and dispersion (for collision avoidance). In this talk, I will discuss recent work on continuum (fluid-like) and agent-based models for aggregations. The models describe phenomena such as vortex swarming, population clumping, and group migration. The goal is to determine the relationship between individuals' microscopic rules for movement and the macroscopic properties of the group (such as size, density, and velocity).

Wednesday, October 25, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Investigation of Transport Phenomena in Micro/Nano/Subnano-Scale Channels applied in Knudsen Compressors and Continuous Trace Gas Preconcentrators

Yen-Lin Han

Postdoctoral Research Associate  Department of Aerospace & Mechanical Engineering Los Angeles, CA 90089-1191

Investigation of transport phenomena is one of the major research topics in micro/nano/subnano-scale (M/N/SN-scale) technologies. Practical applications include concentration, separation, mixing, delivering, pumping, etc. Two specific devices, Knudsen Compressors and Continuous Trace Gas Preconcentrators, have been selected to illustrate the utilization of transport phenomena in micro/nano-scale flows.

Knudsen Compressors are solid-state, micro/meso-scale gas pumps or compressors with no moving parts. Based on the rarefied flow phenomenon of thermal creep, Knudsen Compressors operate by imposing a temperature gradient across a high porosity, low thermal conductivity transpiration membrane. Knudsen Compressors with an aerogel membrane (mean channel size > 20 nm) operated by the radiant heating technique have been studied over a pressure range from about atmospheric pressure down to 10-5 atm. At low pressures, mechanically machined aerogel membranes with circular or rectangular channels have been found to be attractive candidates as Knudsen Compressor membranes. The performance of these membranes has also been found limited by rarefaction effects in the connector section such as "reverse" thermal creep flow and by membrane exit vortices. The Direct Simulation Monte Carlo (DSMC) technique was employed for further investigations of these effects in connector sections of Knudsen Compressors at low pressures. A two-dimensional simulated domain was adopted to mimic a simplified, rectangular channel, single stage Knudsen Compressor. The effects of the "reverse" thermal creep flows and membrane exit vortices have been visualized in the simulations.

The Continuous Trace Gas Preconcentrator is an innovative nano-channel flow application. The operating theory and the preliminary design of the preconcentrator are based on three separation mechanisms: mass separation, quantum separation, and size separation. The separation membranes are an array of aligned channels with nanometer to sub-nanometer size and relatively short lengths. As a consequence of mass separation, size, or quantum separation, the membranes inhibit target molecules from passing through the capillaries while allowing the carrier gas to pass more freely. With a suitable membrane, such as single-walled or multi-walled carbon nanotube membranes, the continuous trace gas preconcentrator is expected to have an excellent performance with a factor of 100 to 1000 times or more increase in the target molecule concentration. The ability to align multi-walled carbon nanotubes has been successfully demonstrated with the construction of a 1cm x 1cm multi-walled array of carbon nanotube towers, and the process of fabricating multi-walled carbon nanotube membranes is ongoing. Fabrication and characterization of a proof-of-concept continuous micro/meso-scale preconcentrator is under way.

It is expected that further research on Knudsen Compressors and Continuous Trace Gas Preconcentrators will yield significant advances in the basic understanding of M/N/SN-scale channel flows as well as efficient micro devices.

Tuesday, October 31, 2006 3:30 PM Laufer Library (RRB 208)

Geophysical Vortex Streets: The Dynamics that Determines Their Late-Time Behavior - or - Why Jupiter Has a New Red Spot

Phil Marcus

Professor of Fluid Mechanics  Department of Mechanical Engineering University of California at Berkeley Berkeley, CA

Rotating, stratified 3D flows often act as if they were nearly 2D and the inverse cascade of energy often leads to large, turbulent vortices and jets. In general, the flows are not unique, and there are several basins of attraction of the flow - each characterized by its own pattern of vortices and jet streams. The transport properties of each pattern vary markedly, so in a geophysical, or climate-change context, the robustness of each pattern and how patterns are selected due to small changes in the environment are important. We explore pattern selection, and present a physical model that works well in correctly predicting the outcomes of long-term numerical simulations. This study was originally motivated by the behavior of the long-lived vortical storms on Jupiter, and we show the relationship between the results of this study and Jupiter's new (as of March 2006) red spot.

Wednesday, November 1 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Observations of Ice Sheet Dynamics in a Warming Climate from Space

Eric Rignot

Senior Research Scientist  Jet Propulsion Laboratory National Aeronautics and Space Administration Pasadena, CA

A little over ten years ago we knew very little about the state of mass equilibrium of ice sheets in Antarctica and Greenland. The nature of our knowledge has changed considerably with the advent of satellite techniques capable of measuring ice motion, surface elevation and more recently gravity. In this presentation, I will review the technique I have been using for the past ten years to study glacier dynamics in Greenland and Antarctica and determine their state of mass balance: satellite radar interferometry. It has been employed to detect ice motion, grounding lines, flow speed up and other detailed features associated with ground water migration at an unprecendented level of precision and spatial details. I will discuss how it has been used in combination with other data to come up with new estimates of the present-day evolution of ice sheets, how these results compare to other techniques (some of which published results as recently as a few weeks ago), and how these results (do not) match predictions made by numerical models that international panels of experts rely on to predict future sea level rise.

This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Admistration's Cryosphere Science Program.

Wednesday, November 8, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Biomedical Ultrasound

Kirk Shung

Professor of Biomedical Engineering  Medical Ultrasonic Transducer Resource University of Southern California Los Angeles, CA 90089-1111

Ultrasound has been used in medicine for many years. There are two major applications of ultrasound: diagnosis and therapy. As a diagnostic tool, its major advantages over other imaging modalities like magnetic resonance imaging, x-ray, CT and nuclear imaging lie in that it is non-invasive, capable of producing images in real-time, more cost-effective and portable. Ultrasound has been found to be of clinical value in many medical disciplines including OB/GYN and cardiology. As the frequency is further increased, applications in ophthalmology, dermatology and small animal imaging are being explored.

Ultrasound therapy has recently also received much attention. Higher than diagnostic ultrasound intensities have been used to treat tumor and to perform selective surgery. Current efforts are targeted toward cellular applications since it has been shown that ultrasound can be used to modulate cell membrane permeability.

Wednesday, November 15, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Energy Loss Mechanisms in Micromechanical Resonators

Dr. Julie Zhili Hao

Assistant Professor  Department of Mechanical Engineering Old Dominion University Norfolk, VA

Micromechanical resonators are of great interests for a wide range of applications, such as rotation rate sensors (gyroscopes), electrical filters, and physics research instruments. For their practical applications, quality factors (Q) or energy loss mechanisms of micromechanical resonators are of critical importance, as a higher Q in these devices translates to higher sensitivity, lower motional resistance, better stability, and lower power consumption. Therefore, it is desirable to design and fabricate micromechanical resonators with ultra-high Q or very little energy loss. To this end, we need to understand and analyze energy loss mechanisms in such devices, not only for improving their performance, but also for establishing the fundamental limit of the Q. In fact, arising from its own nature, each loss mechanism in a micromechanical resonator exhibits a unique phenomenon that is governed by its related theory and can be analytically expressed and experimentally characterized. In this talk, I will discuss the analytical and experimental study on support loss and thermoelastic damping (TED) in micromechanical resonators. From this study, the closed-form expressions for their quantitative evaluation are obtained, shedding significant insights into the geometrical design and choice of materials in high-Q micromechanical resonators.

Julie Z. Hao received the B.S and M.S. degrees in Mechanical Engineering from Shanghai Jiao Tong University, Shanghai, in 1994 and 1997, respectively. She received her doctoral degree in Mechanical Engineering from the University of Central Florida in 2000. Her dissertation topic was the research and development of a MEMS-based cooling system for microelectronics. After graduation, Dr. Hao worked as a MEMS Engineer in industry for two years and was involved in the development of optical MEMS and microfluidic products. From 2002-2006, she worked in the Integrated MEMS Laboratory at the School of Electrical and Computer Engineering, Georgia Institute of Technology. In July 2006, Dr. Hao joined the Department of Mechanical Engineering, Old Dominion University. Her research focuses on the development of MEMS devices for sensory, biomedical, and communications applications. These include high precision gyroscopes, bulk-mode resonators, high-Q biosensors, as well as microfluidic devices. Also, Dr. Hao works on the analytical and experimental study of complex multidisciplinary micromechanics that is critical for the performance of MEMS devices and microsystems.

Thursday, November 16, 2006 3:30 PM, Laufer Library (RRB 208)

Refreshments will be served at 3:15 pm.

Engineering New Treatments for Cardiovascular Disease Via Optimal Design and Physiologic Simulation

Alison L. Marsden

Postdoctoral Fellow  Stanford University Stanford, CA

Rigorous modeling and optimization of treatments for cardiovascular disease according to engineering principles provide a framework for testing new surgeries and interventions at no risk to patients. Ultimately these tools have the potential to complement doctors’ clinical judgement and experience to improve outcomes for patients suffering from both congenital and acquired heart disease. In this talk I will discuss the application of computational fluid dynamics to the Fontan surgery, a treatment for severe congenital heart defects in which a patient is born with only one functioning ventricle. Patient specific geometric models were used to evaluate the performance of current Fontan surgical designs by quantifying fluid-mechanical efficiency under physiologic conditions including rest, graded exercise, and respiration (Marsden, et. al, Ann Biomed Eng, to appear). This work inspired a new "y-graft" design of the Fontan surgery. Evaluation of the new design demonstrates improved efficiency and lower Fontan pressures.

Optimization is commonly used in engineering industry for design, but neither simulation or optimization are currently used to test surgical designs in advance of trying them on patients. Optimization of new surgical designs for patient specific models such as the Fontan surgery requires methods that are appropriate for expensive fluid mechanics problems with little or no gradient information. Efficient derivative-free surrogate-based optimization methods have been previously successful in reducing aerodynamic noise generated by airfoils in turbulent flow (Marsden, et. al J Fluid Mech, to appear). A similar set of tools is now being applied to fully couple optimization algorithms with time-dependent simulations of blood flow. I will present two model problems for optimization that are representative of important cardiovascular problems, a vessel bifurcation and an end-to-side anastomosis. Next, I will discuss the application of optimization tools in future work for the design of the Fontan surgery. Finally, I will describe the potential broad impact of optimization in designing devices and surgical procedures for congenital heart disease, coronary artery disease, and peripheral vascular disease.

Friday, November 17, 2006 1:00 PM Grace Ford Salvatori Hall, Room 107 (GFS 107)

Chemical Kinetic Modeling of Alkane Ignition

Tim Barckholtz

Planning Advisor  ExxonMobil Research and Engineering Fairfax, Virginia

This talk will summarize work on extending high temperature kinetic models to lower temperatures, for which the ignition process is significantly different than that at high temperatures. A single, unified model has been constructed for the combustion of all alkane isomers from CH₄ through C₅H₁₂ as well as for n-C₆H₁₄, n-C₇H₁₆, and iso-C₈H₁₈. A variety of techniques were used in the assembly of the model. Sophisticated ab initio calculations were employed for the prediction of the isomerization rates of peroxy radicals; abstraction rates were generated by using linear free-energy relationships; and many rates were derived empirically or semi-empirically. The complete, pressure-dependent model has over 700 chemical species and 11,000 reactions. The performance of the model is quite good with respect to the prediction of ignition delays in rapid compression machines and other experimental devices. Finally, a methodology for the drastic reduction of reacting species in this model will be summarized, in which the sub-model for n-heptane can be reduced from approximately 250 species to less than 40 for use in CFD codes.

Wednesday, November 29, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

Dynamics of Nonlinear Coupled Nanomechanical Resonators

Ron Lifshitz

Senior Lecturer in Physics  School of Physics and Astronomy Raymond and Beverly Sackler Faculty of Exact Sciences Tel Aviv University Tel Aviv 69978, Israel (On sabbatical at California Institute of Technology)

We are studying the dynamics of nonlinear coupled oscillators, motivated by recent experiments with arrays of micromechanical and nanomechanical resonators at Caltech and Cornell. We have obtained exact results for the parametric excitation of small arrays using secular perturbation theory [1], as well as an amplitude equation to describe the slow dynamics of the parametric excitation of large arrays [2]. I will focus on these results to explain the intricate experimentally-observed response curves, and to suggest further experiments. If time permits, I will say a few words about our model of synchronization, which is based on reactive coupling and nonlinear frequency pulling [3, 4] (rather than the more common linear dissipative models).

[1] Lifshitz and Cross, Phys. Rev. B 67 (2003) 134302 [2] Bromberg, Cross, and Lifshitz, Phys. Rev. E 73 (2006) 016214 [3] Cross, Zumdieck, Lifshitz, and Rogers, Phys. Rev. Lett. 93 (2004) 224101 [4] Cross, Rogers, Lifshitz, and Zumdieck, Phys. Rev. E 73 (2006) 036205

Wednesday, December 6, 2006 3:30 PM Stauffer Science Lecture Hall, Room 100 (SLH 100)

Refreshments will be served at 3:15 pm.

3D Direct Numerical Simulations of Autoigntion in Turbulent Non-Premixed Flows with 1-Step and Reduced Chemistry

Terese Løvås

Lecturer in Future Energy Conversion Technologies  Department of Engineering Queen Mary University of London UK

The autoignition of non-premixed flows is important for diesel and Homogenous Charge Compression Ignition (HCCI) engines, and it is also now a concern in the new lean premixed pre-vapourised (LPP) gas turbines. Because typically in diesel engines the ignition time is longer than an estimated turbulent timescale, the common understanding until early 1990's was that the ignition is not affected by the turbulence, but that is purely driven by the chemistry. However, it was later recognised that turbulence may affect the ignition time and the subsequent flame development significantly. Deeper knowledge of how the fluid mechanics affect autoignition will assist the design of the low-polluting HCCI engines and the new LPP gas turbines.

In the talk results from a set of 3D Direct Numerical Simulations (DNS) of autoignition in turbulent non-premixed flows will be discussed. Both a simple 1-step mechanism and a complex chemistry consisting of a 22-species n-heptane mechanism are employed to investigate spontaneous ignition timing and location. The results from simple chemistry showed that the previous findings from 2D DNS, that ignition ocurred at the most reactive mixture fraction (ξ_MR) and at small values of the conditional scalar dissipation rate (N|ξ_MR), are valid also for 3D turbulent mixing fields. However, in the Negative Temperature Coefficient regime (NTC), the most reactive mixture fraction is very rich and ignition seems to occur at high values of scalar dissipation. This is not consistent with a previous conjecture that the first appearance of ignition is correlated with the low-N content of the conditional probability density function of N.

The treatment of reliable chemistry in complex flow codes is of great importance for the correct predictions of control parameters such as ignition time and flame temperatures. However, the inclusion of detailed chemistry in such complex flow codes is demanding in terms of both computational time and memory requirements. This is because the chemical reaction system is governed by a set of stiff differential equations determining the time evolution of each chemical species based on consumption and production through chemical reactions. Much effort is devoted to developing methods to eliminate the species governed by the shortest time. A method for reducing reaction mechanisms will be discussed which is based on a time-scale analysis much similar to typical model reduction techniques. This enables the set of variable that are transported in the flow codes to be significantly reduced. Also, a procedure to automatically optimize the sparsity of the Jacobian matrix governing the chemical evolution is implemented resulting in a significant computational speed-up.

Wednesday, December 13, 2006 3:30 PM Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.