Active Control of Separated Flow

Lou Cattafesta

Associate Professor 
Department of Mechanical and Aerospace Engineering
University of Florida
Gainesville, FL

Flow separation incurs a large amount of energy loss and limits the performance of many flow-related devices (e.g., airfoils, diffusers, etc.). Researchers have been trying to mitigate or eliminate flow separation for over a century because of its large potential payoff in practical applications. Numerous active separation control strategies have been attempted on civil and military aircraft and underwater vehicles with varying degrees of success. However, most of the active control approaches are open-loop in nature because of their simplicity but are often time-consuming and expensive. This talk discusses two novel adaptive feedback control approaches designed to reattach a massively separated flow over a NACA airfoil with minimal control effort using piezoelectric synthetic jet actuators and various sensors for feedback. One approach uses an adaptive feedback disturbance rejection algorithm in conjunction with a system identification algorithm to develop a reduced-order dynamical systems model between the actuator voltage and unsteady surface pressure signals. The objective of this feedback control scheme is to suppress the pressure fluctuations on the upper surface of the airfoil model, which results in reduced flow separation, increased lift, and reduced drag. A second approach leverages various flow instabilities in a nonlinear fashion to maximize the lift-to-drag ratio using a constrained optimization scheme – in this case using a static lift/drag balance for feedback. Detailed experiments are described to elucidate the baseline uncontrolled and controlled flow physics, and various technical challenges are addressed and discussed in detail.

Lou Cattafesta is currently an Associate Professor in the Department of Mechanical and Aerospace Engineering at the University of Florida. His primary research interests are active flow control and aeroacoustics. Prior to joining UF in 1999, he was a Senior Research Scientist at High Technology Corporation in Hampton, VA, where he was the group leader of the Experimental and Instrumentation Group. His research at NASA Langley focused on supersonic laminar flow control and pressure- and temperature-sensitive paint measurement techniques. At that time, he became involved in active control of flow-induced cavity oscillations, which provoked his current research interests in active flow control and aeroacoustics. More information regarding his research can be found at http://www.img.ufl.edu. Dr. Cattafesta has co-authored 4 papers that have received AIAA best conference paper awards and 6 US Patents and more than 100 journal and conferences papers. He is an Associate Fellow of AIAA and long-time member of the AIAA Fluid Dynamics Technical Committee.

Wednesday, January 23, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Nonlinear Control and Bioinspired Underwater Vehicle Systems

Kristi A. Morgansen

Assistant Professor 
Department of Aeronautics and Astronautics
University of Washington
Seattle, WA

Underwater locomotion and propulsion for underwater vehicles provide rich applications for the development of control methods for nonlinear systems and underactuated mechanical systems. In the work here, the tasks of modeling and control for agile gait generation for robots built with fin propulsive and maneuvering surfaces are considered.  Previous work for such bioinspired devices has shown that simplified models with quasistatic lift and drag can be used to construct trajectory tracking controls for forward and turning motions that strongly resemble biomimetic motions.  Here we will evaluate the use of such models for agile maneuverability by comparing biomimetic fast start and snap turn data from experiment with simulation data from the model.

Beyond single-vehicle applications, a number of current science applications indicate the need for operation of multivehicle groups composed of different types of vehicles operating in different media (air, water, space).  Recent work in coordinated control of vehicle systems has shown that earlier studies in mathematics, physics, and chemistry with models of interconnected oscillators can be used to construct controls for coordinated vehicles.  Additionally these oscillator models have been demonstrated to have direct connection to Frenet-Serret models of dynamics for nonholonomic systems (e.g. ground vehicles, fixed-wing aircraft, and underwater vehicles).  The work presented here will address the construction of controls for oscilator-based analysis that allow a group of vehicles to track a moving target. Further, when these models are considered in a discrete time setting, effects of intermittent, dynamic and asynchronous communication can be incorporated into the dynamics.  Stability bounds for particular group modes of behavior (identical heading or common point of rotation) can then be determined in the context of limited communication. Results are demonstrated in simulation and experiment with applications drawn from the engineering contexts of autonomous air and underwater vehicles as well as the biological context of schooling fish.

Beyond single-vehicle applications, a number of current science applications indicate the need for operation of multivehicle groups composed of different types of vehicles operating in different media (air, water, space). Further, such systems are needed to operate with variable levels of autonomy and human interaction. Recent work in coordinated control of vehicle systems has shown that earlier studies in mathematics, physics, and chemistry with models of interconnected oscillators can be used to construct controls for coordinated vehicles. Additionally these oscillator models have been demonstrated to have direct connection to Frenet-Serret models of dynamics for nonholonomic systems (e.g. ground vehicles, fixed-wing aircraft, and underwater vehicles). The work presented here will address the construction of controls for oscillator-based analysis that allow a group of vehicles to track a moving target. Further, when these models are considered in a discrete time setting, effects of intermittent, dynamic and asynchronous communication can be incorporated into the dynamics. Stability bounds for particular group modes of behavior (identical heading or common point of rotation) can then be determined in the context of limited communication. Results are demonstrated in simulation and experiment with applications drawn from the engineering contexts of autonomous air and underwater vehicles as well as the biological context of schooling fish.

Wednesday, April 9, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Impact of Sea-Salt Aerosol on the Weekend Effect

Donald Dabdub

Professor 
Department of Mechanical and Aerospace Engineering 
and
Advanced Power and Energy Program
University of California, Irvine
Irvine, CA

The weekend effect has become an important issue in regulation as it may suggest that controlling NO_x would be counter productive to reducing ozone concentrations. Current hypotheses suggest that the dynamics of NO_x (changes of quantities and timing NO_x emissions rates) explain in part the increase in ozone concentrations. In the past few years there have been new discoveries of atmospheric processes such as the chemistry of sea-salt aerosol in coastal areas. This study quantifies the impact that sea-salt aerosol has on air quality in urban regions. The focus area of this study is the South Coast Air Basin of California.

Particular emphasis will be placed to the impact of sea-salt aerosol to the weekend effect.

Wednesday, February 20, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Prospects for Very Large Space Telescopes: How Mass Scales with Structural Requirements

Lee Peterson

Professor
Gary L. Roubos Endowed Chair
Department Chair (on sabbatical)
Director, Center for Aerospace Structures 
Department of Aerospace Engineering Sciences
University of Colorado
Boulder, CO

A conceptual design framework is presented for studying how the mass of a large space telescope mirror will depend on design disturbances, mirror diameter, and practical structural design constraints. A variety of on-orbit, launch, and ground test design requirements are considered, as are practical constraints on structural truss member properties. While prior work emphasized the trade between structural depth and overall mass fraction, this paper shows how these practical constraints limit the achievable structural depth, and thus define an optimal depth. An example of a tetrahedral support truss for a segmented mirror is presented. For lightly loaded design cases, it is observed that the minimum mass structure is determined by the simultaneous application of minimum allowable tube thickness, a specified strut Euler buckling load, and a specified strut pin-pin frequency. Closed form solutions are derived for the optimal structural depth and areal density. These are shown to be independent of the diameter of the telescope mirror.

Wednesday, February 27, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Inside Polymer Nanocomposites — Interphases and Percolation

L. Cate Brinson

Professor and Chair, Mechanical Engineering Department 
and
Professor, Materials Science and Engineering Department 
Northwestern University
Evanston, IL 60208

Polymeric nanocomposites made by incorporating small amount of nanoscale inclusions into polymer matrices exhibit dramatic changes in thermomechanical properties over the pure polymers. The properties of the nanoscale fillers can be extraordinary, yet the significant changes observed cannot be due to the nanofillers alone. Enhancing their effect is the extremely significant role that the interphase plays in these systems. Given the enormous surface to volume ratio for nanoparticles, the interphase volume fraction can dwarf that of the inclusions themselves and percolate through the composite. In this talk, experimental evidence of the existence of this interphase region is presented for several nanofiller types via local and global glass transition changes and microscopy. We show that by properly controlled functionalization of the nanoscale inclusions, we can impact the properties of the interphase region and consequently control the properties of the nanocomposites. In conjunction with the experimental results, the viscoelastic behavior of multi-phase polymeric nanocomposites is modeled using a novel hybrid numerical-analytical approach that can effectively take into account the existence of the interphase region and be used to elucidate experimental results and aid in materials design. To investigate the concept of percolated interphase, a finite element approach is developed to study the impact of interphase zones on the overall properties of composite. The results have impact on potential commercial applications for nanocomposites including transparent conducting films, wear resistant coatings and hybrid systems for multifunctional performance including sensing and damage tolerance.

Wednesday, March 5, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Development of Upconversion Nanophosphors for Bioimaging and Photodynamic Therapy in Cancer Treatment

Yiguang Ju

Department of Mechanical and Aerospace
Princeton University
Princeton, NJ

Upconversion nanophosphors provide new opportunities for bioapplications because of their stable optical property, increased light penetration depth in tissue, low toxicity, and reduced background scattering compared to conventional markers. First, the seminar will give a review of the recent progress of synthesis of rare-earth (erbium and ytterbium) doped upconversion nanophosphors by using combustion and in-solution thermolysis methods. Second, the particle morphology and the luminescence properties with infrared excitation are investigated. The correlations between the nanoparticle fluorescence, particle crystal structure, synthesis temperature, and precursor conditions are summarized. The dynamic dependence of particle luminescence time on particle size and phonon energy will be analyzed. The kinetic mechanism of the non-linear dependence of the luminescence intensity on the excitation power is discussed. Third, the ability of specific targeting of functionalized upconversion nanophosphors on surfaces coated by biotins will be demonstrated. Finally, the efficacy of photodynamic therapy by using upconversion nanophosphors on singlet oxygen production and lung cancer tissue growth are presented.

Wednesday, April 12, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Micro and Miniature Technologies of Advanced Energy and Thermal Systems (Fuel Cells and Heat Pipes)

Amir Faghri

United Technologies Endowed Chair Professor in Thermal-Fluids Engineering 
Department of Mechanical Engineering
University of Connecticut
Storr, CT

The 21^st century will see the development of a wide range of active miniaturized energy devices with application in energy management and power sources, electronic cooling, energy storage and bioengineering. Although these active devices are effective, they are often cumbersome and inefficient considering the auxiliary supporting devices such as pumps, fans, and other moving parts they require for operation. A more efficient and novel approach involves use of passive small energy and thermal devices with no moving parts. Two research thrusts will be presented in this talk.

We propose a new miniature passive direct methanol fuel cell (DMFC) that includes a fuel cell stack and ancillary systems with no moving parts. This system uses passive approaches for fuel storage and delivery, air breathing, water management, CO₂ release, and thermal management. The performance characteristics of the passive miniature DMFC system will be presented.

Increasing component densities of the integrated circuit (IC) and packaging level have led to serious challenges in thermal management problems in electric cooling. Micro heat pipes are one of the promising cooling devices because of their high efficiency, reliability and cost effectiveness. Theoretical and experimental analysis performed on micro and miniature heat pipe arrays reveals a 300% improvement in effective thermal conductivity at high heat fluxes over conventional approaches.

Dr. Faghri is currently the United Technologies Endowed Chair Professor in Thermal-Fluids Engineering. He was the Dean of the School of Engineering from 1998-2006, and the Head of the Mechanical Engineering Department from 1994-1998 at the University of Connecticut. Dr. Faghri developed major initiatives and incentives to promote quality research and graduate education, including establishing the Connecticut Global Fuel Cell Center with significant support from the federal and state governments, as well as the private sector. Dr. Faghri has authored seven books and edited volumes, more than 260 archival technical publications (including 160 journal papers), and 11 U.S. patents. His latest textbook, Transport Phenomena in Multiphase Systems, was published by Elsevier in 2006. He has served as a consultant to several major research centers and corporations, including Los Alamos and Oak Ridge national laboratories, ExxonMobil, and Intel Corporation as well as serving on the boards of directors of both publicly-traded and private companies. Dr. Faghri has served as a principal investigator conducting research in the area of thermal management and multiphase transport phenomena for applications ranging from advanced cooling systems to alternative energy systems including fuel cells, solar energy systems and thermal energy storage devices. Dr. Faghri has received numerous external research contracts and grants from the National Science Foundation, National Aeronautics & Space Administration, Department of Defense, Department of Energy, and various industries. Dr. Faghri has received many honors and awards, including the 1998 American Institute of Aeronautics & Astronautics (AIAA) Thermophysics Award, the 1998 American Society of Mechanical Engineering (ASME) Heat Transfer Memorial Award and the 2005 ASME James Harry Potter Gold Medal.

Dr. Faghri received his M.S. and Ph.D. degrees from the University of California at Berkeley, and a B.S. with highest honors from Oregon State University.

Friday, March 14, 2008
12:00 Noon
Kapriellian Hall of Engineering, Room 144 (KAP 144)

Refreshments will be served at 3:15 pm.

Electronically Tunable Nanomaterials

Horst Hahn

Professor 
Forschungszentrum Karlsruhe
Institute for Nanotechnology and Joint Research Laboratory Nanomaterials
Technische Universität Darmstadt
Darmstadt, Germany

The properties of materials are typically controlled in a static manner by the microstructure. This implies control of the grain size, defect concentration, structure and metastability. As long as the microstructure does not change during the use of the material, the properties of the material are fixed, or irreversible. In contrast, in semiconducting materials, properties can be tuned by the application of an external field due to the space charge regions which extend far from the interfaces. In metallic systems, this effect cannot be observed unless the dimensions of the structures are in the nanometer regime. The reason for this different behavior is the small spatial dimension of the space charge regions due to the effective screening of the induced charges by the conduction electrons.

In nanoporous metals and thin films exposed to appropriate electrolytes, it has been demonstrated that substantial changes of physical properties can be induced by the application of a potential between the nanostructured metal and a counter electrode. Examples of the changes of surface stresses and the electrical resistivity of thin gold films and nanoporous gold will be presented. A simple model is proposed based on the modification of the electron density distribution at the interface of the metal and the electrolyte. Effectively, the corresponding change of the effective thickness of the sample is the major cause of the observed resistivity change.

Additionally, a transparent conducting oxide, ITO, in a nanoparticulate form has been prepared from a dispersion using spin coating. The observed resistivity changes, i.e. the on/off ratio can be as large as 2.000, i.e. 200.000%, between the different values of the control potential. Moreover, the device exhibits field effect transistor behavior identical to a conventional semiconductor, but in this case observed in a material with a large charge carrier density exhibiting metallic conduction behavior. Additionally, the mobility is exceeding 20 cm²/Vs. The device can be used for printable electronics and transparent electronics.

Wednesday, April 2, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

NanoRobotic Systems

Lixin Dong

Senior Research Scientist, Head of NanoRobotics Group 
Swiss Federal Institute of Technology (ETH)
Zurich, Switzerland

Progress in robotics over the past years has dramatically extended our ability to explore the world at a variety of scales extending from the edges of the solar system down to individual atoms. At the bottom of this scale, technology has been moving toward greater control of the structure of matter, suggesting the feasibility of achieving thorough control of the molecular structure of matter atom by atom. Nanorobotics represents the next stage in miniaturization for maneuvering nanoscale objects. Nanorobotics is the study of robotics at the nanometer scale, and includes robots that are nanoscale in size and large robots capable of manipulating objects that have dimensions in the nanoscale range with nanometer resolution. Nanorobotic systems emphasize the engineering aspect of nanorobotics and include the manufacturing and application technologies of nanorobotic manipulation systems, nanoelectromechanical systems (NEMS), and nanorobots (nano-sized robots, which have yet to be realized).

The well-defined geometry, exceptional mechanical properties, and extraordinary electrical characteristics of carbon nanotubes (CNTs) qualify them for structuring such systems. Relative displacements between the atomically smooth, nested shells in multiwalled carbon nanotubes (MWNTs) can be used as robust nanoscale motion enabling mechanisms for applications such as bearings, oscillators, shuttles, switches, memories, syringes, and actuators. The hollow structures of CNTs can serve as containers, conduits, pipettes, and coaxial cables for storing mass and charge, or for transport. On the other hand, novel helical nanostructures are created through a top-down fabrication process in which a strained nanometer thick heteroepitaxial bilayer such as SiGe/Si and InGaAs/GaAs curls up to form 3D structures with nanoscale features such as tubes, coils, rings, and spirals. Because of their interesting morphology, mechanical, electrical, and electromagnetic properties, potential applications of these nanostructures include springs, electromechanical sensors, magnetic field detectors, chemical or biological sensors, and inductors.

Shrinking device size to nanometer scales presents many fascinating opportunities such as manipulating nanoobjects with nanotools, measuring mass in zeptogram ranges, sensing forces at piconewton scales, and inducing gigahertz motion, among other new possibilities waiting to be discovered. Nanorobotic manipulation is a promising technology for structuring, characterizing and assembling nano building blocks into NEMS. Combined with recently developed nanofabrication processes, the technological progress on building nanorobotic systems from shell engineered CNTs and rolled up SiGe/Si and InGaAs/GaAs helical nanostructures is presented focusing on nanotube linear servo motors, nanorobotic spot welders using copper-filled nanotubes, and helical nanobelt motion converters.

Lixin Dong is Senior Research Scientist at Swiss Federal Institute of Technology (ETH, Zurich), where he leads the NanoRobotics Group in the Institute of Robotics and Intelligent Systems (IRIS). He received the B.S. and M.S. degrees in Mechanical Engineering from Xi’an University of Technology (XUT) in 1989 and 1992, respectively. He became Research Associate in 1992, Lecturer in 1995, and Associate Professor in 1998 at XUT. He has served as the head of the Department of Mechatronics Engineering at XUT from 1997 to 1999. He received his Ph.D. degree in Micro Systems Engineering from Nagoya University in 2003, and became Assistant Professor at Nagoya University in 2003. In 2004 he joined ETH Zurich as a Research Scientist. His main research interests include nanorobotics, mechatronics, nanoelectromechnical systems (NEMS), mechnochemistry, and biomedical devices. He received the IEEE T-ASE Googol Best New Application Paper Award in 2007, Best Conference Paper Award at the Int. Conf. on Control Sci. and Engr. (ICCSE2003), and Finalist in the Best Paper Competition at IEEE-ICRA2007, IROS2005, and ICRA2001. He has been awarded the Science and Technology Advancement Prize by the Ministry of Education of China in 1999, by Shaanxi Province Government in 1999 and 1995, by Xi’an City Government in 1999, and by the Ministry of Machine-Building Industry of China in 1998 and 1992. He serves on the editorial board of the IEEE Trans. on Nanotechnology and the IEEE Trans. on Automation Science and Engineering.

Wednesday, April 9, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Novel Nanoscale Materials for the National Ignition Facility

Juergen Biener

Nanoscale Synthesis and Characterization Laboratory
Lawrence Livermore National Laboratory
Livermore, California 94550

Current designs of targets for the National Ignition Facility (NIF) require the development of novel nanoscale materials such as ultra-low density nanoporous metal foams, nanocrystalline metal and diamond films. This talk will provide an overview of the challenges and opportunities associated with the synthesis of these nanoscale materials, and discuss applications beyond NIF targets.

Prepared by LLNL under Contract DE-AC52-07NA27344

Dr. Juergen Biener was born in 1961 in Augsburg, Germany. He studied chemistry at the Ludwig-Maximilians-Universität in Munich and conducted his doctoral research in the field of surface science at the Max-Planck-Institute of Plasma Physics (IPP) in Garching. In 1997 he received a fellowship from the German Academic Exchange Service (DAAD) to work with Bob Madix at Stanford University on metal oxide model catalysts. In 2000 he returned to the IPP to continue his research on plasma-wall interactions. In 2003 he accepted a visiting scientist position at the Center for Imaging and Mesoscale Structures at Harvard University where he developed a new view of the reactivity of gold surfaces. Currently, he is one of the leaders in the Nanoscale Synthesis and Characterization Laboratory at the Lawrence Livermore National Laboratory. His research interest lies at the intersection of surface chemistry, physics and mechanics of nanostructured materials.

Wednesday, April 16,2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Long Actuator Delays – Extending the Smith Predictor to Nonlinear Systems

Miroslav Krstic

Harold W. Sorenson Professor of Control Systems 
Dept. of Mechanical & Aerospace Engineering
University of California at San Diego
La Jolla, CA

One would be hard pressed to find “long actuator delays” and “nonlinear control” co-existing in the same sentence in the existing control literature, which is due to the infinite dimensionality and the potential for finite escape time instability in the underlying problems. On the 50th anniversary of Otto Smith’s invention of the “predictor” feedback for compensating long actuator delays for linear systems, a method that has since become one of the favorite tools in chemical process control and many other applications, I am pleased to present an approach for synthesizing a predictor feedback to go along with any stabilizing nominal nonlinear controller, with actuator delay of any length. Interestingly, Smith’s idea was actually an elementary version of “infinite dimensional backstepping,” which I have been developing over the last few years for PDE problems such as Navier-Stokes, MHD, Euler and Timoshenko beams, and other systems in mechanics. By employing the backstepping point of view to construct Lyapunov-Krasovskii functionals, it becomes possible to prove several forms of robustness of predictor feedbacks, including robustness to both underestimating and overestimating the length of the actuator delay. The latter is a particularly subtle result because it involves a non-standard dynamic perturbation – the controller (inadvertently) inserts an additional infinite-dimensional state to an already infinite-dimensional feedback loop.

Wednesday, April 23, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Towards Dislocation Dynamics in Carbon Nanotubes and Graphene

Elif Ertekin

Department of Mechanical Engineering
University of California at Berkeley
Berkeley, CA

The mechanical properties of graphene-like systems are proving to be quite unique; for instance, carbon nanotubes demonstrate elongations exceeding 200% at under tensile loading at high temperature.  I will describe some of our recent computational efforts at understanding the role of defects in the plastic deformation of carbon nanotubes and graphene sheets.  We have developed a topological, continuum theory of defect energetics in carbon nanotubes and graphene, which accurately reproduces ab initio results for a variety of defect geometries.  I will describe our theory in detail and show how we can use it explore deformation mechanisms via both Kinetic Monte Carlo and dislocation dynamics.  Time-permitting, I will also discuss more recent work in modeling the growth of carbon nanotubes by catalyst-assisted chemical vapor deposition, emphasizing again the role of defect topology in nanotube synthesis.

Wednesday, April 30, 2008
3:30 PM
Seaver Science Library, Room 150 (SSL 150)

Refreshments will be served at 3:15 pm.

Combustion Chemistry: Contributions From Theory

Stephen J. Klippenstein

Chemical Sciences and Engineering Division
Argonne National Laboratory
Argonne, IL, 60439

A quantitative understanding of the chemistry of combustion is central to the improved performance of combustion devices. Advanced engine designs require an enhanced understanding of the ignition process. There is also continued interest in decreasing the production of pollutants such as NO_x and soot particles. Chemical models of combustion employ rate coefficients for hundreds to thousands of reactions. The past 10 years have seen a major advance in the predictive capabilities of gas phase theoretical chemical kinetics. Thus, many of the rate coefficients in combustion models are now being obtained from theoretical studies. We will review our contributions to the kinetics of some key combustion reactions including studies of (i) NO_x formation and removal, (ii) aromatic ring formation, (iii) fuel decomposition, and (iv) hydrocarbon oxidation. These studies will illustrate the recent progress in theoretical kinetics, while also emphasizing the synergy provided by detailed comparisons with experiment.

Wednesday, September 3, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Development of Multilayer Thermoelectric Energy Harvesters by CMOS Process

Shih-Ming Yang

Professor 
Department of Aeronautics and Astronautics
National Cheng Kung University
Taiwan, ROC

A novel micro thermo-electric generator (μTEG) design is developed to harvest thermal gradient. Compared with conventional in-plane and cross-plane design, the μTEG is in hybrid configuration in which the heat flux from the top to bottom surface is confined passing through the in-plane P- and N-thermolegs. The thermolegs (thermal couples) of poly silicon are isolated by a cavity to prevent heat loss and maintain the temperature gradient thereby improving the output power. Analyses show that the μTEG performance can be further improved by stacking multilayered thermolegs and adapting low-dimensional thermoelectric materials. Design verification on a two-layered μTEG by TSMC 0.35μm 2P4M CMOS foundry process shows that the thermoleg design of 120 × 4 μm (length x width) has the highest power factor of 0.0427 μW/cm² K² and voltage factor of 3.417 V/cm²K². The energy harvesters can be applied to autonomous sensor nodes.

Wednesday, September 10, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

New Metric for Regulation of Diesel Vehicle Emissions

Heejung Jung

Professor 
Dept. of Mechanical Engineering & CE-CERT
University of California
Riverside, CA 92507

As regulatory limits in California and the US for 2007 heavy-duty diesel engines introduce dramatic reductions in PM emissions, there is considerable interest in new emission metrology that can more accurately measure low PM levels. One such metrology, particle number measurement, has been extensively investigated in Europe as part of Europe’s Particle Measurement Program (PMP) for light-duty diesel vehicles. This program has put forth a new methodology, including instrument specifications and sampling protocols, for “solid” particle number measurements. While counting only solid particles results in better precision, it may not be fully indicative of the diesel PM exhaust components of interest from a health effects perspective. The PMP protocol still represents a significant advancement as it is currently the only methodology with low enough detection limits to produce precise measurements of Diesel Particulate Filter (DPF) equipped engines. Evaluation study of the PMP methodology will be presented.

Heejung Jung received his Ph.D. from the University of Minnesota, and received both his M.S. and B.S. degrees from Seoul National University in Mechanical Engineering. Upon completion of his masters, he joined Hyundai Motor Company as a research engineer. He later completed his postdoc research at UC Davis before joining UCR. His current research focus areas are diesel PM emissions, nanoparticle synthesis, and air quality.

Wednesday, September 24, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Environmental Technology Challenges & Entrepreneurship

Anthony Michaels

Managing Director 
Proteus Environmental Technologies
Los Angeles, CA 90071

The entrepreneurial spirit that creates new and profitable companies is one of the most effective methods for spreading new technologies and innovations throughout the human population and across the Earth’s landscape. This can be for both better and worse. Damaging technologies with good local economics can quickly spread a form of pollution or an impact on human or environmental health. At the same time, a novel solution to a compelling environmental challenge can gain widespread use through the self-reinforcing power of markets. Environmental scholarship within universities is one of the most creative sources of innovation, however many challenges exist for using markets to spread those innovative solutions to our homes, towns and lives. These challenges reside in the university culture, the sources of funding – the valley of death – and within the traditions and practices of the business community. However, I have a great optimism about the potential for markets to take some of the best academic scholarship, apply it to some of the largest human environmental challenges and make a major improvement in the quality of life and the sustainability of our society.

I will present a few examples based on my own USC experience – one made more real by my personal choice to leave academia and form Proteus Environmental Technologies, a company designed specifically to help universities commercialize their academic environmental discoveries. Biofuels are a renewable energy source that illustrates both the strengths and weaknesses of new environmental technologies. Algae-based fuels have the greatest promise, but have significant challenges, both biological and technical. The systems at full scale require well-mixed bio-reactors with cost effective methods for re-introducing carbon and nutrients. Extracting algae and processing becomes a dynamic problem as the extraction process shifts the algal ecosystem towards cells that escape extraction. It is also the largest capital cost in an algae farm. Scaling itself is an interesting challenge as individual farms must be at the scale of 1000s of hectacres and a meaningful solution may require 10-20 million hectacres. In the end, nobody wants algae for its own sake, it must be a product that fits into the current or future energy or food markets. The technologies to transform 1,000s of tons per day of green powder to a coal substitute, a liquid fuel or an animal feed must parallel the development of an algae farm and have a strong feedback on the design choices for the farm and its crop. Microbial fuel cells are a biological curiosity with the potential to transform energy production world wide. Again, scaling is key. How do we take a device at the scale of liters and make a facility that can process a million cubic meters per day? The technical challenges range from the biology of biofilms, the materials for anodes and cathodes to the fluid mechanics of dilute solutions that must interact with those biofilms, all at a reasonable cost.

Wednesday, October 1, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Particle Transport In Unsteady, Separated Flow

Gustaaf (Guus) Jacobs

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

Particle-laden and droplet-laden flows occur in many important natural and technological situations, e.g. aerosol transport and deposition, spray combustion in gas turbine engines, fluidized bed combustion, plasma spray coating and synthesis of nanoparticles. Particles frequently interact with a flow that separates from a wall. Liquid droplets are, for example, injected into the flow that separates at a sudden expanding geometry in dump combustors. Sand particles well up in the separated flow behind hills or plankton is dispersed in the detached flow behind uneven ocean floor obstacles. Mixing levels and drag overhead crucial to the combustor performance, pollution levels or plankton concentration are strongly affected by the flow separation and particle dynamics. In this talk I will discuss the physics of particles in a separated flow in the Lagrangian frame (i.e. the frame moving with the particle) and the computation of these flows with high-fidelity computational methods. After a brief discussion of the characteristics and advantages of high-order discontinuous spectral element methods for simulation of unsteady particle-laden separated flow, I present recent criteria that identify the separation location and angle of fluid particles from walls in unsteady and three dimensional setting. The Lagrangian dynamics of finite sized particles is discussed and compared to the Lagrangian fluid particle motion and Lagrangian coherent structures.

Wednesday, October 15, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Generation and Degeneration of Long Internal Waves in Lakes

Takahiro Sakai

Ph.D. Candidate 
USC Department of Aerospace & Mechanical Engineering

The nonlinear evolution, generation and degeneration of wind-driven, basin-scale internal waves in lakes are investigated employing weakly-nonlinear, weakly-dispersive evolution models. The models studied are based on rational, asymptotic approximations of the hydrodynamic equations of motion, and include a two-layer model, a multi-modal model, and a large-lake model with the effect of earth’s rotation. It is found that nonlinearity, in conjunction with the dispersive nature of the fluid medium, plays a principle role in (i) the early stage of degeneration of basin-scale waves through nonlinear steepening and subsequent generation of oscillatory waves; and (ii) the transfer of energy among multiple vertical modes in the internal field. Strong dependence of these nonlinear processes on the background stratification, the lake geometry, the horizontal extent of a lake, and the spatio-temporal wind stress function are demonstrated and quantified through a series of numerical simulations of the different models.

Monday, October 20,2008
3:30 PM
The Laufer Library, Room 208 (RRB 208)

The Art and Science of Large-Scale Disasters

Mohamed Gad-el-Hak

The Caudill Eminent Professor of Biomedical Engineering and Chair of Mechanical Engineering 
Virginia Commonwealth University
Richmond, Virginia

Large-scale disasters adversely affect considerable number of people, devastate sizable geographical area, and tax the resources of local communities and central governments. Disasters can naturally occur, but humans can also cause their share of devastation. There is also the possibility of anthropogenic calamity: humans’ actions causing a natural disaster to become more damaging than it would otherwise. The art and science of large-scale disasters aim at better prepare scientists, engineers, first responders, and above all politicians to deal with manmade and natural disasters. The last annus horribilis in particular has shown the importance of being prepared for large-scale catastrophes, and how the world can get together to help clean out the consequent mess. In this talk, both the art and science of predicting, preventing and mitigating natural and manmade disasters are broadly discussed. The laws of nature govern the evolution of any disaster. In some cases, as for example weather-related disasters, those first-principles laws could be written in the form of field equations, but exact solutions of these often nonlinear differential equations are impossible to obtain particularly for turbulent flows, and heuristic models together with intensive use of supercomputers are necessary to proceed. In other cases, as for example earthquakes, the precise laws are not even known and prediction becomes more or less a black art. Management of any type of disaster is more art than science. Nevertheless, much can be done to alleviate the resulting pain and suffering.

Wednesday, November 5, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Minimal Mass Structures for Control

Robert Skelton

Professor 
Department of Mechanical and Aerospace Engineering
University of California at San Diego
San Diego, CA

An optimization of a structure before, and independent of, control design leads to high energy controllers with little cooperation between the dynamics of the controller and the dynamics of the structure. Some optimization problems have been solved to minimize mass while maitianing a high degree of controllability. Two examples are given: Optimal structures under compressive loads and optimal structures under bending loads. The bending case solves a problem that has been open since the work of Michell in 1904, when he solved the infinitely complex case (a continuum of material), leaving the optimal discrete case open.

Wednesday, November 12, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Aerodynamic Separation and Invariant Manifolds: Recent Progress on a Century-old Problem

George Haller

Mechanical Engineering Department
Massachusetts Institute of Technology
Cambridge, MA

Flow separation–the detachment of fluid from a boundary– is a major cause of performance loss in engineering devices such as diffusers, airfoils and jet engines. In a landmark 1904 paper on boundary layers, Ludwig Prandtl derived a criterion for flow separation from no-slip boundaries in steady two-dimensional incompressible flows. Despite widespread effort, however, no unsteady or three-dimensional extension of Prandtl’s criterion has emerged in the fluid dynamics literature.

In this talk, I discuss recent success in extending Prandtl’s criterion to unsteady three-dimensional compressible flows as well as to slip boundaries. This new separation theory relies on advanced dynamical systems concepts such as nonhyperbolic invariant manifold theory and aperiodic averaging. Remarkably, these techniques render exact separation criteria that cannot be obtained from first principles. I show numerical and experimental results confirming the generalized separation criteria and discuss applications to flow control and pollution tracking.

Wednesday, November 19, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Converging Shocks in Water

Veronica Eliasson

Postdoctoral Scholar 
GALCIT
California Institute of Technology
Pasadena, CA

Fluid-solid interactions present a challenging and coupled problem. This presentation will focus on converging shocks in water confined in an elastic body. Both experiments and simulations will be considered. The overarching goal is to provide quantitative results for shock-focusing in a converging geometry in water, and provide a better understanding of the response of the surrounding material and how it affects the focusing event.

To create a converging shock in water, a projectile launched from a gas gun impacts on a liquid contained in a converging geometry. The impact on the liquid initiates a shock wave which, during the focusing phase, builds up high pressure. Consequently, the shock in the liquid transmits to the solid. As a result, the waves in the material are then influencing the wave propagation in the liquid, creating a coupled problem.

Simulations are performed with Overture(LLNL), a finite difference code with overlapping grids and adaptive mesh refinement. Three types of simulations are considered to help quantify the experimental data: simulations of converging shocks in water in a rigid confinement, simulations of wave propagation in the surrounding material, and simulations with a solid-liquid coupling using Euler equations for the fluid domain and linear elasticity equations in the solid domain.

Results have the potential to enhance the design of marine structures subjected to dynamic loading, as well as improve the techniques used to generate high-speed liquid jets.

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, December 3, 2008
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.