2004 Seminar Archive


Fall, 2004

Mode-dependent Thin Film Interfacial Property Measurement by Laser-induced Stress Waves

Junlan Wang

Assistant Professor
Department of Mechanical Engineering
University of California at Riverside
Riverside, CA 92521

Thin films are crucial components in a wide range of multilayer microelectronic and optical devices. They are also desirable candidates for micro-actuators in micro-electro-mechanical systems. Due to the dissimilar nature of the constituents, large residual stress can be induced in the film during the fabrication process which leads to the subsequent failure of the thin film devices. Among the many properties, interfacial adhesion between the thin film and substrate is one of the key parameters influencing the overall reliability and durability of the integrated thin film devices. However, due to the critical dimension of thin films, conventional techniques face challenges to reliably evaluate the thin film interfacial properties.

To address the above challenge, we developed a unique set of laser-induced stress wave techniques to quantitatively investigate the intrinsic strength of a planar thin film/substrate interface. High-amplitude short-duration stress wave pulses generated by laser-pulse absorption are used to delaminate a thin film/substrate interface and the corresponding interfacial stress is calculated from the transient high-speed interferometric displacement measurement using wave mechanics. Depending on the geometry of the substrate, the thin film interfaces can be subjected to a variety of loading modes including tensile, mixed-mode and pure-shear. Systematic studies of similar interfaces failed under different loading conditions reveals that the thin film interfacial failure as well as the adhesion is highly mode-dependent. Significant wrinkling and tearing of the films happens under mixed-mode and pure-shear loading, in great contrast to blister patterns observed in similar films failed under tensile loading. This technique has been further developed to investigate the interfacial adhesion of various thin film/substrate interfaces interesting to semiconductor industry and biomedical applications as well as those under high strain-rate loading for defense applications.

Junlan Wang received her Ph.D. in Theoretical and Applied Mechanics from the University of Illinois at Urbana-Champaign in 2002. She joined the faculty in the Department of Mechanical Engineering at the University of California, Riverside in 2003 after finishing one year post-doctoral research in the Solid Mechanics and Structures group at Brown University. Her research interest is in the mechanics of thin films and coatings, high strain rate materials behavior, size-dependent mechanical behavior of surface micro and nanostructures, and mechanical reliability of multifunctional nanoporous materials. Her recent awards include the SEM Hetenyi Award in 2004, UC Regents Faculty Fellowship in 2004, Faculty Development Award in 2006, UCR College of Engineering Excellence in Teaching Award in 2007, and ASEE Beer and Johnston, Jr. Outstanding New Mechanics Educator Award in 2007.

Wednesday, September 5, 2005
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Multiscale Fluid Flow Studies with Molecular Tagging Diagnostics

Manoochehr Koochesfahani

Professor
Department of Mechanical Engineering
Michigan State University
East Lansing, MI

A brief overview of molecular tagging diagnostics will be presented, along with results from studies in three different flow fields. Molecular tagging methods take advantage of molecules that can be turned into long lifetime tracers upon excitation by photons of an appropriate wavelength. Typically a pulsed laser is used to “tag” the regions of interest, and those tagged regions are interrogated at successive times within the lifetime of the tracer. This approach has been utilized for the measurement of velocity and temperature fields.

The first study presented here considers unsteady flow separation from a pitching airfoil. Boundary-layer resolved measurements of this phenomenon and comparison with complementary computations will be discussed. The second study involves in-cylinder measurements in a motored IC engine. Results from flow mapping of cycle-to-cycle variation in late compression will be presented. Preliminary observations on the possibility of flow control will be discussed. The final study addresses the flow inside a microchannel driven by either a pressure differential or electroosmosis. In-situ measurements of wall friction factor in pressure-driven flow will be compared with theoretical predictions in order to assess the large discrepancies that have been previously reported. Electroosmotically-driven flows involve additional complications, e.g. presence of an electric field and a time-varying temperature field caused by Joule heating. Results will be shown from simultaneous measurements of velocity and temperature within a microchannel for different applied potentials.

Wednesday, September 12, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Homogeneous Microcombustion Studies: Progress and Observations

Mark A. Shannon

James W. Bayne Professor of Mechanical Engineering
Department of Mechanical Science and Engineering
University of Illinois at Urbana-Champagne
Urbana IL, 61801-2906

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. Homogeneously burning hydrocarbons in air at this scale has proved to be more difficult, requiring even higher wall temperatures and better thermal management. 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 19, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Numerical Simulation and Modeling of Complex Turbulent Flows

Kyle Squires

Professor
Arizona State University
Tempe, AZ 85287

Numerical simulation and modeling of the turbulent flows encountered in aerodynamics applications are challenging for several reasons, including the fact that the Reynolds numbers are usually large and the flows often exhibit significant effects of separation. These and other features challenge simulation strategies and have constrained the application of Computational Fluid Dynamics as a tool for analysis and design. Simulation strategies have typically relied on Reynolds-averaged Navier-Stokes (RANS) approaches that are computationally feasible and often sufficient in attached flows though are unable to accurately account for the complex effects characteristic of flow separation. Large Eddy Simulation (LES) is a technique that offers greater fidelity and is a powerful approach away from solid surfaces. Near the wall, however, the computational cost of LES is prohibitive, a fact that will limit its widespread application to high Reynolds number flows for the foreseeable future. These and other considerations have motivated development of hybrid methods, the most popular of these approaches being Detached-Eddy Simulation (DES). DES combines the most favorable elements of RANS and LES models in a single simulation.

In this seminar, development and applications of the method aimed at advancing DES will be reviewed. In natural applications of the technique, attached boundary layers are treated by RANS, exploiting the computational efficiency and relative accuracy of RANS models in attached shear layers. The method becomes an LES in regions away from the wall provided the grid density is sufficient. The range of DES applications to date include an array of “building block” test cases such as the flow over a cylinder, sphere, aircraft forebody, and missile base. In addition, the technique has been applied to complex geometries, including the flows around fighter aircraft. The developing experience base is encouraging expansion of the method beyond the originally intended class of massively separated flows and a brief description of some of the challenges and recent advances will be presented. These include improvements to the method that modify the DES length scale to overcome errors that can arise from the interface between the RANS and LES regions and development of strategies for seeding turbulent fluctuations in boundary layers.

Wednesday, September 26, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Microscopic Mechanisms of Deformation in Amorphous Solids

Mo Li

Associate Professor
School of Materials Science and Engineering
Georgia Institute of Technology

While the fundamental deformation mechanisms in crystalline materials, namely, the dislocation-based process, have long been understood and put into use, our understanding of the microscopic deformation mechanisms in amorphous solids still remains in its infancy despite tremendous efforts made in the past forty years. Amorphous solids contribute to a large fraction of materials used today, including metallic glasses and amorphous semiconductors, granular matters, and many geological materials. They are characterized by metastability and the lack of long-range order, which poses great challenges for experimentalists as well as theorists to have a detailed understanding of how deformation occurs at the atomic or molecular level. In this talk, I will give a brief introduction to the mechanical properties of amorphous solids and in particular, metallic glasses with special emphasis on shear localization or shear banding. I will present the results from extensive atomistic modeling of the changes in the local atomic structure, volume, and mechanical properties in several model systems subjected to various external loadings. The results led us to the establishment of a new model, an extended Ginzburg-Landau theory. We conclude, from these studies, that the microscopic deformation mechanism in amorphous metals is through the process starting from local volume change and then local shear softening to the final breakdown. The implications derived from this study and its applications to other disordered systems such as granular matters and nanocrystalline materials will be briefly mentioned.

Mo Li received his Ph.D. in applied physics in 1994 from California Institute of Technology. He joined Morgan Stanley & Co. in New York after a brief stays as a postdoctoral fellow at Caltech and the Argonne National Laboratory. From 1998 to 2001 he was an assistant professor at the Johns Hopkins University. Currently he is an associate professor at Georgia Institute of Technology.

His research focuses on mechanical properties of amorphous solids and nano-scaled materials, phase transitions in metastable systems, interfaces, and statistical physics and its applications. The approaches used in his research are a blend of those from statistical physics, solid state physics, materials science, metallurgy, mechanics and computational methods. His research focuses on algorithm development, simulation, and theoretical analysis.

Wednesday, October 3, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

On Instability Waves and the Noise Generated by Turbulent Jets

Tim Colonius

Mechanical Engineering Department
California Institute of Technology
Pasedena, CA

Reduction of jet noise remains an important goal for commercial and military aircraft, as well as a challenging problem for experimental and computational fluid dynamics. We present analysis and results from recent experiments that suggest that the pressure fluctuations associated with large-scale structures in turbulent jets are well modeled by linear instability waves of the mean velocity profile. An 80 microphone phased-array was used to measure pressure fluctuations just outside the jet shear layers of turbulent jets over a range of subsonic Mach numbers and temperature ratios. Measured pressures are decomposed into azimuthal modes and compared to predictions of linear instability theory based using measured and/or predicted mean flow profiles. Agreement in terms of streamwise evolution, phase speed, and radial decay are demonstrated. The near-field pressure measurements are also projected to the far-field using a Kirchhoff surface approach and compared with the directly measured far-field. We also analyze serrated (chevron) nozzles in an attempt to understand how they reduce low frequency noise.

Work supported by the Aeroacoustics Research Consortium and the Naval Air Systems Command.

Wednesday, October 10, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Highly Nonlinear Dynamics in Solids: a new Horizon in Wave Propagation

Chiara Daraio

Assistant Professor of Aeronautics and Applied Physics
California Institute of Technology
Pasedena, CA

The discovery of novel highly nonlinear dynamic phenomena in multiscale artificial composite systems (metamaterials) will be presented. Emphasis will be given to the new tunable properties provided by the high nonlinearity in the specific cases of granular materials and carbon nanotubes. This research was conducted for designing and constructing optimized macro-, micro- and nano-scale structural configurations of materials and for studying their nonlinear acoustic behavior. Variation of composite arrangements of the fundamental elements with different elastic properties in a linear 1-D chain-of-spheres, Y-junction or 3-D configurations led to a variety of novel physical phenomena and interesting wave properties. Potential applications can be found in the area of mechanical, structural and biomedical engineering as well as security and communications systems. The characterization of mechanical and electronic properties of carbon nanostructures with different atomic arrangements and microstructures, exhibiting an exciting highly nonlinear behavior, will also be discussed.

Chiara Daraio’s interests reside at the interface of materials science, condensed matter physics and solid mechanics, particularly in the design, development and testing of multi-scale metamaterials; phononic crystals; responsive soft matter; highly nonlinear solitary waves; mechanical and electronic properties of nano and biomaterials. http://www.daraio.caltech.edu

She received her Laurea degree (Equivalent to a master degree) in Mechanical Engineering from the Universita’ di Ancona, Universita’ Politecnica delle Marche, Ancona, Italy (2001). She received her M.S. (2003) and Ph.D. degrees (2006) in Materials Science and Engineering from the University of California, San Diego. She has been a guest researcher at the Lawrence Berkeley National Laboratories, NCEM, since 2003 and won several awards. Among these, she is a Gold Medal winner of the MRS Graduate Student Award (2005) and winner of the AIM young investigator award (2006). She published over 30 peer reviewed papers, one book chapter and one patent.

Wednesday, October 17, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Applying Realistic Chemistry in Direct Numerical Simulations

Tianfeng Lu

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

Direct numerical simulations (DNS) of reacting flows invoking realistic chemistry constitute the ultimate approach to producing results of high fidelity. This would allow for the solution of a broad range of problems from first principles, such as fuel utilization, pollutant emissions, climate change, as well as biochemical cycles and human health. However, DNS with detailed chemistry has been computationally unaffordable due to the high dimension of variables and the mandatory fine resolutions that are required both spatially and temporally. Recently, DNS of turbulent reactive flows with realistic hydrocarbon fuels have been successfully carried out on supercomputers in collaboration with Sandia National Laboratories, following a significant reduction in both the dimension and the stiffness of the involved detailed kinetics. Most of the major difficulties faced in the reduction process, such as variable elimination from large-scale nonlinear systems and analytic solution of quasi steady state equations, have plagued the scientific community for decades. To solve each of these problems satisfactorily, we have developed a suite of new techniques involving graph theory, binary integer programming, singular perturbation, and spectral analysis. In this talk, representative components of these methods will be discussed and their potential impacts on other fields will be outlined.

Wednesday, October 31, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Modeling Combustion with Detailed Chemistry

Zhuyin Ren

Postdoctoral Research Associate
Sibley School of Mechanical and Aerospace Engineering
Cornell Universiy
Ithaca, NY

Combustion modeling is now playing an important role in the design and optimization of advanced combustion devices such as internal combustion engines and gas turbine combustors. For high-fidelity combustion modeling, it is essential, though challenging, to resolve the highly nonlinear turbulence-chemistry interaction and to predict the emissions of pollutants such as NOx and particulates. This requires the accurate description of turbulent mixing as well as the use of detailed chemistry.

In this talk, recent progresses in PDF methods for turbulent reactive flows, particularly the sensitivity analysis, will be described and demonstrated. Then the talk will focus on presenting the ICE-PIC dimension-reduction method and the ISAT storage-retrieval method for the efficient implementation of detailed chemistry in combustion modeling. The theoretical basis, validation, and computational efficiency of these methods will be described. This talk will also describe the x2f_mpi software for efficient chemistry calculations in large-scale parallel simulations. It will conclude with a discussion on applying the ICE-PIC, ISAT, x2f_mpi algorithms to incorporate detailed chemistry in combustion simulations.

Wednesday, November 7, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Measuring Unsteady Efficiency and Performance of Biological and Bio-Inspired Propulsors

John O. Dabiri

Professor
Graduate Aeronautical Laboratories and Bioengineering
California Institute of Technology
Pasadena, CA

This talk will describe the development of new experimental and analytical tools to extract the governing mechanisms of animal swimming and flying from empirical observations. The approach advocated presently avoids direct use of the vorticity field in favor of a Lagrangian, particle-tracking perspective. The benefits of this strategy are demonstrated in laboratory studies of the bluegill sunfish and various jellyfish species. These laboratory observations are complemented by inexpensive computational models and a new in situ field apparatus, which enables a SCUBA diver to make velocimetry measurements normally confined to artificial laboratory environments. The principles derived from these studies are applied to fluid dynamic problems as varied as autonomous underwater vehicle design, cardiovascular flow diagnostics, and wind energy harvesting.

Wednesday, November 14, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Examination of the Link Between Aerosol Properties and Cloud Droplet Activation Efficiency

Don Collins

Associate Professor
Department of Atmospheric Sciences
Texas A&M University
College Station, Texas 77843

Among the factors contributing to the overall uncertainty in the indirect effect of aerosols on climate is the still inadequately understood relationship between particle size, composition, and critical supersaturation. Applying the results of laboratory studies of the activation efficiency of relatively simplistic aerosols to predict CCN concentration for an ambient aerosol for which only an incomplete description of its size distribution and composition is available is undoubtedly challenging, as is reflected in the varied success of several recent CCN closure efforts. Whereas an understanding of the link between composition and critical supersaturation is ultimately needed, insight into the factors controlling activation can be gained through an improved understanding of the relationship between hygroscopic growth under subsaturated conditions and cloud droplet formation under supersaturated conditions.

I will describe both our recent efforts aimed at quantifying the link between critical supersaturation and hygroscopicity, and our recent development and use of an instrument that permits quantification of the link between critical supersaturation and composition.

Wednesday, November 21, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Global Modes and Aerodynamic Sound Generation In Self-Excited Hot Jets

Lutz Lesshafft

Postdoctoral Fellow
University of California at Santa Barbara
Santa Barbara, CA

One of the most remarkable phenomena in the field of aerodynamic instability is the spontaneous bifurcation of a steady flow towards a selforganized state of intrinsic oscillations. Similar to the von Kármán vortex street in cylinder wakes, hot jets constitute another class of such globally unstable flows: whereas an isothermal jet behaves as an amplifier of external perturbations, sufficiently heated jets display intrinsic oscillations in the form of regularly spaced ring vortices.

Comparison of direct numerical simulation results to theoretical predictions, derived from Ginzburg-Landau model equations, demonstrates that these self-sustained oscillations in subsonic hot jets are dominated by the dynamics of a nonlinear wave front, which separates an oscillating flow region from the upstream steady flow. The bifurcation towards a state of self-sustained synchronized oscillations (‘nonlinear global mode’) is due to the existence of an absolutely unstable region in the underlying base flow. A linear stability analysis allows us to predict the naturally selected frequency, as well as the critical temperature ratio for the onset of global instability.

Both the near- and the far-field of the jet are resolved via DNS: the acoustic field generated by such a synchronized vortex street is found to be that of a compact dipole, with maximum acoustic intensity in the axial direction of the jet. A numerical analysis of the Lighthill equation reveals that this radiation pattern is due to strong entropy fluctuations within the jet.

Figure 1: Self-sustained synchronized oscillations in a hot jet: isosurfaces and isocontours of vorticity. (Lesshafft, Huerre & Sagaut 2007: Phys. Fluids 19)

Wednesday, November 28, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Overall Electromagnetic Properties of Multifunctional Composites

Alireza V. Amirkhizi

Graduate Student
Center of Excellence for Advanced Materials
Department of Mechanical and Aerospace Engineering
University of California at San Diego
La Jolla, CA 92093

Composite materials are used for their excellent structural performance. Load-bearing properties are traditionally the only aspects for which a composite structure is designed. Recent technological advances have made it possible to reach beyond this limited view. Inspired by biological systems, we seek to develop engineering materials that exhibit multiple functionalities in addition to providing structural integrity. I will present my research on embedding periodic arrays of scattering elements within composites to modify and tune their overall electromagnetic properties. A number of techniques for numerical and analytical modeling of the periodic media are discussed. Based on these methods we have designed and fabricated composites with tuned electromagnetic properties. Examples include fiber-reinforced polymer composites with embedded arrays of straight wires or coils. In both cases, the overall dielectric constant of the medium is reduced and can even be rendered negative within microwave frequencies. The coil medium can exhibit chiral response. Solutions for eliminating this behavior as well as a method for calculation of the bianisotropic material parameters are presented. One can achieve similar modification of the overall properties at higher frequencies by reducing the length scale. For example, we demonstrated that a polymer film with embedded nano-strips of gold can demonstrate negative dielectric constant in infrared regime. An example of a structural composite is fabricated and tested for which the magnetic permeability is altered and even turned negative. Finally, a general method for homogenization of the electromagnetic properties of periodic media based on the microstructure is presented.

Wednesday, December 5, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.

Lessons on Structure from the Structure of Viruses

RICHARD D. JAMES

Russell J. Penrose Professor
and
Distinguished McKnight University Professor

University of Minnesota
Minneapolis, MN 55455

As the most primitive organisms, occupying the gray area between the living and nonliving, viruses are the least complex biological system. One can begin to think about them in a quantitative way, while still being at some level faithful to biochemical processes. We make some observations about their structure, formalizing in mathematical terms some rules-of-construction discovered by Watson and Crick and Caspar and Klug. We call the resulting structures objective structures. It is then seen that objective structures include many of the most important structures studied in science today: carbon nanotubes, the capsids, necks, tails and other parts of many viruses, the cilia of some bacteria, DNA octahedra, buckyballs, actin and collagen and many other common proteins, and numerous atomic-scale rods, springs and wires now being synthesized. Objective structures also have an intriguing relation to the crystalline and noncrystalline structures adopted by elements in the Periodic Table. The rules defining them relate to the basic invariance group of quantum mechanics. We develop a methodology for computing such structures. Some of the nonperiodic structures revealed by the formulas exhibit beautifully subtle relations of symmetry. This common mathematical structure paves the way toward many interesting calculations for such structures: the likelihood of unusual electromagnetic and other collective properties, simplified schemes for exact molecular dynamics of such structures, phase transformations between them, defects and failure, new x-ray methods of determination of structure not relying on crystallization, and their growth by self-assembly.

Friday, December 7, 2007
3:30 PM
Stauffer Science Lecture Hall, Room 102 (SLH 102)

Refreshments will be served at 3:15 pm.