Showing papers by "Mohamed Gad-el-Hak published in 2001"

The MEMS Handbook

Abstract: Part I: Background and Fundamentals Introduction, Mohamed Gad-el-Hak, University of Notre Dame Scaling of Micromechanical Devices, William Trimmer, Standard MEMS, Inc., and Robert H. Stroud, Aerospace Corporation Mechanical Properties of MEMS Materials, William N. Sharpe, Jr., Johns Hopkins University Flow Physics, Mohamed Gad-el-Hak, University of Notre Dame Integrated Simulation for MEMS: Coupling Flow-Structure-Thermal-Electrical Domains, Robert M. Kirby and George Em Karniadakis, Brown University, and Oleg Mikulchenko and Kartikeya Mayaram, Oregon State University Liquid Flows in Microchannels, Kendra V. Sharp and Ronald J. Adrian, University of Illinois at Urbana-Champaign, Juan G. Santiago and Joshua I. Molho, Stanford University Burnett Simulations of Flows in Microdevices, Ramesh K. Agarwal and Keon-Young Yun, Wichita State University Molecular-Based Microfluidic Simulation Models, Ali Beskok, Texas A&M University Lubrication in MEMS, Kenneth S. Breuer, Brown University Physics of Thin Liquid Films, Alexander Oron, Technion, Israel Bubble/Drop Transport in Microchannels, Hsueh-Chia Chang, University of Notre Dame Fundamentals of Control Theory, Bill Goodwine, University of Notre Dame Model-Based Flow Control for Distributed Architectures, Thomas R. Bewley, University of California, San Diego Soft Computing in Control, Mihir Sen and Bill Goodwine, University of Notre Dame Part II: Design and Fabrication Materials for Microelectromechanical Systems Christian A. Zorman and Mehran Mehregany, Case Western Reserve University MEMS Fabrication, Marc J. Madou, Nanogen, Inc. LIGA and Other Replication Techniques, Marc J. Madou, Nanogen, Inc. X-Ray-Based Fabrication, Todd Christenson, Sandia National Laboratories Electrochemical Fabrication (EFAB), Adam L. Cohen, MEMGen Corporation Fabrication and Characterization of Single-Crystal Silicon Carbide MEMS, Robert S. Okojie, NASA Glenn Research Center Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide, Glenn M. Beheim, NASA Glenn Research Center Microfabricated Chemical Sensors for Aerospace Applications, Gary W. Hunter, NASA Glenn Research Center, Chung-Chiun Liu, Case Western Reserve University, and Darby B. Makel, Makel Engineering, Inc. Packaging of Harsh-Environment MEMS Devices, Liang-Yu Chen and Jih-Fen Lei, NASA Glenn Research Center Part III: Applications of MEMS Inertial Sensors, Paul L. Bergstrom, Michigan Technological University, and Gary G. Li, OMM, Inc. Micromachined Pressure Sensors, Jae-Sung Park, Chester Wilson, and Yogesh B. Gianchandani, University of Wisconsin-Madison Sensors and Actuators for Turbulent Flows. Lennart Loefdahl, Chalmers University of Technology, and Mohamed Gad-el-Hak, University of Notre Dame Surface-Micromachined Mechanisms, Andrew D. Oliver and David W. Plummer, Sandia National Laboratories Microrobotics Thorbjoern Ebefors and Goeran Stemme, Royal Institute of Technology, Sweden Microscale Vacuum Pumps, E. Phillip Muntz, University of Southern California, and Stephen E. Vargo, SiWave, Inc. Microdroplet Generators. Fan-Gang Tseng, National Tsing Hua University, Taiwan Micro Heat Pipes and Micro Heat Spreaders, G. P. "Bud" Peterson, Rensselaer Polytechnic Institute Microchannel Heat Sinks, Yitshak Zohar, Hong Kong University of Science and Technology Flow Control, Mohamed Gad-el-Hak, University of Notre Dame) Part IV: The Future Reactive Control for Skin-Friction Reduction, Haecheon Choi, Seoul National University Towards MEMS Autonomous Control of Free-Shear Flows, Ahmed Naguib, Michigan State University Fabrication Technologies for Nanoelectromechanical Systems, Gary H. Bernstein, Holly V. Goodson, and Gregory L. Snider, University of Notre Dame Index

Flow Control: The Future

Abstract: The subject of e ow control, particularly reactive e ow control, is broadly introduced, leaving some of the details to other papers in this special volume of the Journal of Aircraft . The ability to manipulate a e owe eld actively or passively to effect a desired change is of immense technological importance. In general, methods of control to achieve transition delay, separation postponement, lift enhancement, drag reduction, turbulence augmentation, and noise suppression are sought for both wall-bounded and free-shear e ows. An attempt is made to present a unie ed view of the means by which different methods of control achieve a variety of end results. The important advances in the e eld of e ow control that took place during the past few years are discussed. Spurred by the recent developments in chaos control, microfabrication and neural networks, reactive control of turbulent e ows is now in the realm of the possible for future practical devices. HEability to manipulate a e owe eld actively or passively to effect a desired change is of immense technological importance, and this undoubtedly accounts for the subject being more hotly pursuedbyscientistsandengineersthananyothertopicine uidmechanics.The potential benee ts of realizingefe cient e ow-controlsystems range from saving billions of dollars in annual fuel costs for land, air,and seavehiclesto achieving economically andenvironmentally more competitive industrial processes involving e uid e ows. Methodsofcontroltoeffecttransitiondelay,separationpostponement,lift enhancement, drag reduction, turbulence augmentation, and noise suppression are considered. Prandtl 1 pioneered the modern use of e ow control in his epoch-making presentation to the Third International Congress of Mathematicians held at Heidelberg, Germany. In just eight pages, Prandtl introduced the boundary-layer theory, explained the mechanics of steady separation, opened the way for understanding the motion of real e uids, and described several experiments in which the boundary layer was controlled. He used active control of the boundary layer to show the great ine uence such control can exert on the e owpattern. Specie cally, Prandtl used suction to delay boundary-layer separation from the surface of a cylinder. NotwithstandingPrandtl’ s 1 success,aircraftdesignersinthethree decades following his convincing demonstration were accepting lift anddragofairfoilsaspredestinedcharacteristicswithwhichnoman could or should tamper. 2 This predicament changed mostly due to the German research in boundary-layer control pursued vigorously shortly before and during World War II. In the two decades following the war, extensive research on laminar e ow control, where the boundary layer formed along the external surfaces of an aircraft is kept in the low-drag laminar state, was conducted in Europe and the UnitedStates,culminatinginthesuccessfule ighttestprogramofthe X‐21,wheresuctionwasusedtodelaytransitiononasweptwingup to a chord Reynolds number of 4 :7£10 7 . The oil crisis of the early 1970s brought renewed interest in novel methods of e ow control to reduce skin-friction drag even in turbulent boundary layers. In the 1990s, the need to reduce the emissions of greenhouse gases and to constructsupermaneuverablee ghterplanes,faster/quieterunderwater vehicles, and hypersonic transport aircraft, for example, the U.S. National Aerospace Plane, provides new challenges for researchers in the e eld of e ow control.

Micro-Air-Vehicles: Can They be Controlled Better?

Abstract: Micro-air-vehicles (MAV) are small, autonomous, aerial vehicles designed for reconnaissance and difficult to reach missions. Microelectromechanical systems (MEMS) are extremely small machines in which electronic and mechanical components are combined on a single silicon chip using photolithographic micromachining techniques. The question of whether MEMS can help improve the performance of futuristic MAV is pondered. The treatment focuses on the lifting and control surfaces of MAV, particularly the fixed-wing type. Two additional ideas are advanced to improve the performance of the lifting surfaces of MAV: effecting chaotic mixing to energize the laminar boundary layer and thus delay separation; and using genetic algorithms to optimize the shape of the airfoil section

Flow physics in MEMS

Abstract: Interest in microelectromechanical systems (MEMS) has experienced explosive growth during the past few years. Such small devices typically have characteristic size ranging from 1 mm down to 1 micron, and may include sensors, actuators, motors, pumps, turbines, gears, ducts and valves. Microdevices often involve mass, momentum and energy transport. Modeling gas and liquid flows through MEMS may necessitate including slip, rarefaction, compressibility, intermolecular forces and other unconventional effects. In this article, I shall provide a methodical approach to flow modeling for a broad variety of microdevices. The continuum-based Navier–Stokes equations — with either the traditional no-slip or slip-flow boundary conditions — work only for a limited range of Knudsen numbers above which alternative models must be sought. These include molecular dynamics (MD), Boltzmann equation, Direct Simulation Monte Carlo (DSMC), and other deterministic/probabilistic molecular models. The present paper will broadly survey available methodologies to model and compute transport phenomena within microdevices.

The logarithmic law in turbulent boundary layers: the debate continues

Abstract: In the present research, we analyze the experimental and DNS data sets of canonical turbulent boundary layers from six independent groups. For the range of momentum-thickness Reynolds numbers of 500‐27,320, we determine the best-fit values for the parameters appearing in the standard logarithmic law and the power law. The result is that neither the standard logarithmic law nor the proposed alternative power law is valid throughout the entire overlap region. The remedy for the problem is an extension of the logarithmic law to higher orders concerning the von Karman number. It is found that the standard inner logarithmic law with κ=0.393 and Clog=4.568 is the envelope of this generalized law for an infinite von Karman number δ + . The appropriate outer