Back to Graduate Study in Mechanical Engineering
 
 
 

Our research activities are in computational and experimental heat transfer, fluid mechanics, and combustion. Our efforts are generally split between experimental and computational activities, with the experimental tasks generally complemented by a corresponding computational activity.

Our research work in the computational field includes method/algorithm development activities, development of better physical models in turbulent fluid flows, and heat transfer, and in the application of the predictive procedures to complex problems of practical interest. We have made important contributions in developing solution adaptive algorithms for incompressible and compressible flows with and without heat transfer (see Figure 1 as an example of an adapted mesh for flow over a cone at 16 degrees angle of attack).

We have also made major contributions to the development and testing of improved two-equation turbulence models for both compressible and incompressible flows. Models developed by our group include a functionalized two-equation model to include nonisotropic effects, a compressible k-w model that includes dilatational effects, etc. We are currently involved with direct numerical simulations (DNS) and large eddy simulations (LES) of turbulent flows and heat transfer. We are using results from the DNS and LES calculations to guide the development of improved models. We are also undertaking calculations for two-phase reacting flows and examining models to incorporate droplet/particle-turbulence interactions, and LES-type approaches to incorporate large scale effects.

We have established a state-of the-art laboratory facility in heat transfer and fluid flow that currently houses four medium speed wind tunnels, one low-speed water tunnel, a rotating wind tunnel that simulates a coolant channel of a gas turbine blade, and a gas turbine spray combustor set up for laboratory measurements. Our laboratory is equipped with a two-component Phase-Doppler anemometer for velocity and particle sizing measurements, a one-component Laser-Doppler Anemometer for velocity measurements, hot-wire/cold-wire anemometer systems for velocity and temperature measurements, a Planar Laser Induced Fluorescence System for species and temperature measurements, together with a host of smaller equipment. Our laboratory has the capability of traditional heat transfer measurement techniques using thermocouples and liquid crystals and mass transfer measurement techniques using the naphthalene sublimation technique.

Our research funding comes from diverse federal sources such as NSF, NASA, DOE, SANDIA, EPA, and private sources such as DOW Chemical, GSU, GRI, as well as other state and private sources. We currently have the following ongoing experimental and computational research programs:

· To understand and enhance the heat transport mechanisms in stationary and rotating ribbed gas turbine blade coolant channel flows (see Figure 2 as an example of the use of triangular tabs to increase heat/mass transfer in the ribbed coolant channels).

· To better predict film cooling over turbine blade surfaces.

· To improve fuel efficiency and reduce pollutants in gas turbine spray combustors through active and passive forcing techniques.

· To develop improved turbulence models in stirred chemical reactors.

Selected Publications

S. Acharya, S. Dutta, T. Myrum, & R. S. Baker, "Turbulent Flow Past a Surface-Mounted Two-Dimensional Rib," Journal of Fluids Engineering, 116, 1994, 2, 238-46.

S. Acharya, "Solution Adaptive Techniques in Computational Heat Transfer and Fluid Flow," Computational Mechanics, 1994, 14, 5, 447-67.

S. Dutta & S. Acharya, "Heat Transfer and Flow Past a Backstep with a Nonlinear k-Model and the Modified k-Model," Numerical Heat Transfer, Part A, 1993, 23, 3, 281-302.

T. A. Myrum, X. Qiu, & S. Acharya, "Heat Transfer Enhancement in a Ribbed Duct Using Vortex Generators," International Journal of Heat Mass Transfer, 1993, 36, 14, 3497-508.

A. Harvey, S. Acharya, & S. Lawrence, "Space-Marching Calculations about Hypersonic Configurations Using a Solution-Adaptive Mesh Algorithms," AIAA Journal, 1993, 31, 10, 1809-18.
 top
 

Current Projects

· "Studies of the Agglomerate Morphology and Dynamics in Reacting Flows" sponsored by Air Force Office of Scientific Research

· "Studies of the Effects of Temperature and Composition on the Radiative Properties of Flame Soot" sponsored by National Science Foundation
 top
 

Recent research has been devoted to studies of interior and exterior ballistics, with emphasis on applications in ballistic range testing. This work has been sponsored by the U.S. Air Force Office of Scientific Research. One project is investigating the possibility of using a very light piston in a light gas launcher with a firing cycle tailored to produce multiple compressions. The intent is to facilitate the successful launching of fragile models at high muzzle velocity without destructive model loading. A numerical model of launcher interior ballistics has been validated by experiments in an instrumented launcher facility. The code is now being used to determine launcher design features that will provide the desired launch accelerations.

Another project is involved with assessing the effect of ballistic test model flexibility on the fidelity of aerodynamic characteristics determined by parameter estimation techniques. A major outcome of the work to date is the development of a parameter estimation algorithm that can deal with the solution of implicit state variable rate equations. The algorithm has been applied to the analysis of free-flight ballistic range data for a slender penetrator configuration. In that case, even for bending distortions that were clearly visible in range photographs, model flexibility had no influence on the accuracy of range-acquired aerodynamic coefficients. The work will be extended to other configurations.

Selected Publications

Harkins, T. K. and R. W. Courter, "Aeroelastic Effects on Range-Acquired Aerodynamic Coefficients," AIAA Paper No. 90-0082. Presented at the AIAA Aerospace Sciences Conference, Reno, NV., January 1990.

Hugenroth, J. J. and R. W. Courter, "Wave-Gun Experimentation," Presented at the 46th Meeting of the Aeroballistic Range Association, Minneapolis, MN., September1995.
 top

My research is concerned with turbulent subsonic and supersonic shear flows, interaction between fluid dynamics and combustion, passive and active combustion control in subsonic and supersonic flows, air breathing propulsion, unsteady aerodynamics and aeroacoustics.

I have published 68 papers in refereed journals, am the co-inventor of 12 patents, and have written and presented more than 180 conference papers.

Our work in combustion control is based on altering mixing processes between fuel and oxidizer to improve the combustion process. The passive control work is derived from studies on the effect of nozzle geometry on the evolution of shear flows. Our work on elliptic and other noncircular jets showed that these flows can be used as an efficient passive flow control technique. It allows significant improvements of performance in various practical systems at a relatively low cost, as they rely solely on changes in the geometry of the system. The applications include improved large- and small-scale mixing in low- and high-speed flows, improved combustion efficiency, reduced combustion instabilities, extended flammability limits, noise suppression, and thrust vector control.

Investigations regarding the flow fields of noncircular jets identified new mechanisms of vortex evolution and interaction, flow instabilities, and turbulence generation. Stability theory described the effect of initial momentum thickness distribution, aspect ratio, and radius of curvature on the initial flow evolution. Experiments detected complex vortex evolution and interaction related to self-induction and interaction between spanwise and axial vortices leading to axis switching in the mean flow field. (Figure 1)

Active control work utilized flow excitation amplified by natural flow instabilities to induce large- and small-scale mixing in the flow field through vortex formation and interaction. We have developed the concept of "vortex combustion" in which fuel is injected periodically and synchronously into oxidizer vortices (or vice versa) at a certain phase during the vortex formation. This technique achieves clean and efficient combustion in a well-mixed high temperature environment. The active control work employs open- and closed- loop feedback control, and includes neural network controllers for multi-parameter control. The different concepts were tested in combustors with energy release ranging from 5 kW to 1 MW, (Figure 2) leading to enhanced combustion properties and reduced pollution. Various configurations were tested in areas such as air breathing combustion, furnaces, and waste incineration.

We are also involved in research aimed to reduce aeroacoustic noise, augment heat-transfer, and control vortices over high angle-of-attack delta wings. We are interested in extending this research to include various applications of the new technology of Micro-Electro-Mechanical Systems (MEMS).

Selected Publications

E. Gutmark, Schadow, & K. Yu, "Mixing Enhancement in Supersonic Free Shear Flows," Invited Review for the Annual Review of Fluid Mechanics, 1995, 27, 375-417.

E. Gutmark, K. Schadow, M. Nina, & G. Pita, "Suppression of Combustion Instability by Geometrical Design of the Bluff-Body Stabilizer," J. of Propulsion and Power, 1995, 11, 3, 456-64.

E. Gutmark, T. Parr, K. Wilson, & K. Schadow. "Closed-Loop Control of a Flame and its Application in a Dump Combustor," IEEE Control Systems Magazine, 1993, 13, 2, 73-78.

E. Gutmark, L. Bowman, & K. Schadow, "Flow and Acoustic Features of a Supersonic Tapered Nozzle," Experiments in Fluids, 1992, 13, 49-55.

E. Gutmark, T. Parr, & K. Schadow, "Closed-Loop Amplitude Modulation Control of Reacting Premixed Turbulent Jet," AIAA Journal, 1991, 29, 12, 2155-62.
top
 

mSET, the Microsystems Engineering Team, is a group of faculty within the Department of Mechanical Engineering whose focus is to identify and develop applications for microstructures manufactured using the synchrotron radiation source at LSU's Center for Microstructures and Devices (CAMD). One focus of the group is to inexpensively manufacture sheets covered with microstructures having high aspect ratios (hundreds of microns tall, with widths ranging from a few microns to tens of microns). These sheets will be manufactured using the LIGA process (a German acronym for a three-step process involving lithography, electroplating, and molding). The research effort involves close collaboration both with CAMD personnel and faculty members in the Department of Chemical Engineering. The group will soon be performing tests to demonstrate the benefits of covering surfaces with microstructures in a variety of engineering applications. These applications include heat transfer, acoustics, and composite materials.

mSET is in the middle of an ongoing effort to build a laboratory to manufacture microstructures using the LIGA process. Equipment in the lab includes a resist press and fume hood (lithography), two potentiometers (electroplating), a microscope with attached video camera (characterization), a Class 10,000 cleanroom, and office space.

Selected Publications

E. Barbero & K. Kelly, "Predicting High Temperature Ultimate Strength of Continuous Fiber Metal Matrix Composites," Journal of Composite Materials, 1993, 27, 12, 1214-35.

K. Kelly & E. Barbero, "Predicting Longitudinal Creep of a Continuous Fiber Metal Matrix Composite," International Journal of Solids and Structures, 1993, 30, 24, 3417-29.

K. Kelly, K. Koai, & S. Motakef, "Model-Based Control of Thermal Stresses During LEC-Growth of GaAs Part 1: Validation of Thermal Model," Journal of Crystal Growth, 1991, 113, 254-64.

K. Kelly, K. Koai, & S. Motakef, "Model-Based Control of Thermal Stresses During LEC-Growth of GaAs II. Crystal Growth Experiments," Journal of Crystal Growth, 1991, 113, 265-78.

S. Motakef, K. Kelly, & Keith Koai, "Comparison of Calculated and Measured Dislocation Density of LEC-Grown GaAs Crystals," Journal of Crystal Growth, 1991, 113, 279-88.
top
 

Areas of Research:

Environment-induced embrittlement, plasma-assisted processing of materials, tribology of thin films and modified surfaces, processing-microstructure-property relationship.

Current Research Projects:

"Applications and Mass Production of High Aspect Ratio Micro-Structures" (ARPA/ESTO).

"Microstructure-Corrosion and -SCC Relationship in Al-Li Alloy Weldments" (Lockheed Martin/NASA).

"Corrosion Behavior of 2195 Al-Li Alloys" (AGARD).

"Environment-Assisted Cracking Under Mixed-Mode Loading" (NATO).

Selected Recent Publications:

"Environment-Induced Deformation Localization During Transgranular Stress Corrosion Cracking", K. Lian and E.I. Meletis, Corrosion 52, No.5, 347-355 (1996).

"A Study of the Wear Mechanism of Diamond-Like Carbon Coatings", L. Yan, A. Erdemir and E.I. Meletis, Surface and Coatings Technology 82, Nos.1-2, 48-56 (1996).

"Deformation Evolution During Initiation of Transgranular Stress Corrosion Cracking", E.I. Meletis and K. Lian, International Journal of Fracture 79, 165-178 (1996).

"Study of the 3-D Region Around a Crack Tip by Caustics", M. Konsta-Gdoutos and E.I. Meletis, International Journal of Fracture 82, R11-R17 (1996).

"On the Mechanism of Intensified Plasma-Assisted Processing", A. Adjaottor, E. Ma and E.I. Meletis, Surface and Coatings Technology 89, 197-203 (1997).

"Evidence of Graphitization of Diamond-Like Carbon Films During Sliding Wear", Y. Liu and E.I. Meletis, Journal of Materials Science 32, 3491-3495 (1997).

"Influence of Environmental Parameters on the Frictional Behavior of DLC Coatings", Y. Liu, A. Erdemir and E.I. Meletis, Surface and Coatings Technology 94-95, 463-468 (1997).

"Calculation of Hydrogen Buildup in the Neighborhood of Intergranular Cracks", T.I. Zohdi and E.I. Meletis, Journal of the Mechanical Behavior of Materials 9, No. 1, 23-33 (1998).

"Characterization of Plasma Nitrided Pure Titanium by X-Ray Absorption Spectroscopy", V.A. Palshin, E.I. Meletis, P. Schilling, R. Tittsworth, Journal of Materials Science, (1998).

 
 top
 

I am currently involved in two distinct areas of research:

· Biomechanics of the human knee, and

· High aspect ratio microsystem design and fabrication.

The first focus area is directed toward understanding the control of complex joints in the human body. The initial hypothesis was that reconstructive surgery might be avoided if the muscles could be trained to compensate for the absence of ligament(s). This is a case of a problem driving the development of the necessary tools. As a first step, we are trying to understand the kinematics of the knee joint. We have developed a mathematical model to identify all of the possible displacements of the knee as limited by the passive (nonmuscular) constraints, the displacement workspace of the knee (Figure 1). We are also working on improved parameter measurements for input to the model, including developing a 6-axis ultrasound scanner for mapping joint surfaces, and improved kinematic measurements for testing the validity of the model. The next step is to study how the joint moves and how the passive constraints, such as the ligaments and articular surfaces, affect the mobility of the joint. The approach is similar to that taken for displacement, to find a velocity workspace for the joint.

The second focus area is in the design and fabrication of high aspect ratio microsystems. In this case, the tool is driving the search for applications. At LSU we have the Center for Advanced Microstructures and Devices (CAMD), a synchrotron X-ray source. The X-rays are used for micromachining via X-ray lithography as one step of the LIGA process, which combines X-ray lithography for deep (500-1000 mm), high aspect ratio structures (>100:1) (Figure 2), electrodeposition, and plastic molding. We have formed a group in the College of Engineering, the Microsystems Engineering Team (µSET), which is working to use this tool to fabricate structures and devices for different applications. Our projects range from fundamental fabrication issues to a broad range of applications, including a micromachined gyroscope, micromachined gas sensors for process control and environmental detection, advanced instrumentation for biology, and tools for least-invasive medicine. The last project is taking a tool developed for the biomechanics research and micromachining it so that it can be used in arthroscopic surgery.

Sample Projects

"Mapping the Kinematic Workspaces of the Human Knee" (NSF)

"Microsystems for Least-Invasive Medicine" (NSF)

"A Micromachined Vibrating Cylinder Angular Rate Gyroscope" (SatCon Technology, Cambridge, Massachusetts)

"Microfabricated Thermoelectric Probes and Probe Arrays for Highly Localized Temperature Sensing and Control" w/W. Wang (NSF)

Selected Publications

M. Zhang & M. C. Murphy, "Mapping the Displacement Workspace of the Human Knee," Proceedings, 19th Annual Meeting of the American Society of Biomechanics, Palo Alto, California, 1995, K. R. Williams, ed., 257-58. (submitted to J. Biomechanics).

Y. M. Desta, M. C. Murphy, M. Madou, & J. Hines, "Integrated optical bench for a CO2 sensor," Micromachining and Microfabrication '95, Austin, Texas, Society of Photo-optical Instrumentation Engineers (SPIE), 1995.

S. Akkaraju, Y. M. Desta, B. Q. Li, & M. C. Murphy, "Electrochemical Post-Processing of LIGA Structures," presented at HARMST'95-First International Conference on High Aspect Ratio Microsystem Technology, Karlsruhe, Germany, July 1995 (to appear in Microsystems Technologies).
 top
 

My areas of expertise include experimental, theoretical, and computational fluid dynamics, and multiphase flow with and without phase-change. I have more than 10 years of experience in experimental fluid mechanics and have developed and applied nonintrusive techniques based on light-scattering methods (Laser/Phase-Doppler technique) and image-processing aided visual methods (Particle Image Velocimetry), for the measurement of carrier and dispersed phase velocities and particle/droplet/bubble size in dispersed, two-phase flows.

I am also an expert on large-scale turbulent structures, nonlinear stability and transition, and have conducted theoretical and computational work in these areas. I have studied mixing and transport control through large-scale-structure excitation and have developed a model incorporating the effect of large-scale structures on the motion and dispersion of particles.

My more recent experience extends to mass/heat transfer measurement in gas-turbine blade cooling channels and the experimental study of gas-turbine combustor flow dynamics, as well as the direct numerical and large eddy simulations (DNS, LES) of gas-turbine combustor flows. I have lengthy experience in thermo/fluid and mechanical design, having designed laboratory and industrial facilities and supervised numerous design projects. I have acted as a consultant for FIAT in Italy and for local industry.

I have received more than 1.6 million dollars funding for my research in these areas from federal (NASA, DOE) and state sources and my collaboration with local industry has resulted in over $100K of research funding and $260K in independent projects involving design.

I have taught undergraduate and graduate fluid dynamics, and thermodynamics, undergraduate fluid mechanics and instrumentation laboratories, and have developed graduate courses in turbulence, two-phase flow, and experimental methods. I have also taught short courses in fluid mechanics for the LSU Division of Continuing Education and local industry.

Selected Publications

R. Hibbs, S. Acharya, D. E. Nikitopoulos, Y. Chen, & T. A. Myrum, "Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel with Cylindrical Vortex Generators," ASME-Int. Gas Turbine Inst. Conference, 1996, Birmingham, United Kingdom, June 10-13, 1996.

A. L. Tassin & D. E. Nikitopoulos, "Nonintrusive Measurement of Bubble Size and Velocity," Experiments in Fluids, 1995, 19, 121-32.

D. E. Nikitopoulos & E. E. Michaelides, "A Phenomenological Model for Dispersed, Bubbly Flow in Pipes," AIChE Journal, 1995, 41, 1, 12-22.

D. E. Nikitopoulos, "Mach Number Scaling of Single-Component Two-Phase Flow," ASME Journal of Fluids Engineering, 1993, 115, 772-78.

D. E. Nikitopoulos & J. T. C. Liu, "Nonlinear Binary-Mode Interactions in a Developing Mixing Layer," Journal of Fluid Mechanics, 1987, 179, 345-70.
 top
 

Our major research effort is in Composite Materials and Composite Piping Systems, which consists of the following four areas:

· Advanced Development of Heat Activated Couplings/Joints for Composite and Alloy Pipes

· Buckling Analysis of Thick-Walled Composite Cylinders

· Advanced Development of Energy-Conserving Composite Pipe Using Corrugated Layers

· Determination of the Damage Tolerance of Laminated Composites Due to Low Velocity Impact

Each of these areas is briefly discussed below.

Advanced Development of Heat Activated

Couplings/Joints for Composite and Alloy Pipes

The use of heat couplings is a quick and cost-effective joining method for composite-to-composite and composite-to-alloy materials. In this approach, a prepreg laminate composite that contains thermoset resins and fiberglass reinforcements is wrapped around the ends of components that are to be joined. A shrink sleeve made of thermoplastic material is placed over the prepreg laminate. When curing the shrink sleeve and the prepreg laminate by using a thermal blanket, the shrink sleeve shrinks and compresses the prepreg to obtain good adhesion and the required mechanical properties. The main technical barrier is the nonuniform cure of the prepreg laminate due to the nonuniform heating of the current existing thermal blanket and the different thermal conductivities of composite and alloy materials. The final outcome to be obtained form this project is to develop an easy-to-operate, cost-effective, and commercially viable thermal joining technology for composite-to-composite and composite-to-alloy components.

Buckling Analysis of Thick-Walled Composite Cylinders

Composite materials were developed for many applications because of their prestigious advantages of light weight and high strength. Even advanced composite materials have been brought into the market since the 1960s and the failure criteria and buckling analyses have received tremendous attention, however, most of the buckling analyses were developed based on thin-wall assumption and cannot be applied to thick-walled structures. A buckling analysis of cylindrical composite structures is being conducted. The three buckling modes included in this project are external pressure, axial compression, and torsion. In order to simulate the real situation, combinations of these modes are being studied. Energy method together with laminated anisotropic plate theory are utilized to derive the governing equations. Computer algorithms are being developed in order to solve the systems of equations and determine the buckling loads. Once these models have been developed, optimal designs of composite structures can be achieved with design parameters such as fiber orientations, stacking sequence, and thickness, etc.

Advanced Development of Energy-Conserving Composite Pipe Using Corrugated Layers

The objective of this study is to develop a new energy-conserving composite pipe using corrugated layers. While composite pipe has been successfully used for transporting materials at relatively high temperatures in industry, very little attention has been paid to the thermal energy loss. Specific fibers and resins can be combined to give desired mechanical and thermal properties. These properties include strength, stiffness, corrosion resistance, and thermal conductivity. Energy is one of the focus areas in many petrochemical and defense industries. In order to optimize the energy characteristics of the pipe, a potentially innovative approach is to add a corrugated (round, rectangular, honeycomb) sublayer impregnated with the epoxy vinyl ester resin matrix to form a "dead air" space between the resin liner and the structural wall.

Determination of the Damage Tolerance of Laminated Composites Due to Low Velocity Impact

The objective of this study is to develop a standardized impact test procedure and post-impact damage evaluation procedure through experimental and analytical study of the structural integrity of laminated composites with low-velocity impact damage. The penalties of either conservative estimations of the composite's damage tolerance or nonconservative estimations must be overcome. This is an important area of research because invisible impact damage can contribute up to 60 percent loss in the structure's compressive strength. The following two tasks are being conducted.

Task I (Experimental Aspect)-to develop standardized test for laminated composites under low-velocity impact and standard post-impact evaluation procedures. Standard post-impact test for material properties will also be developed.

Task II (Analytical Aspect)-to apply failure criteria to the evaluation of damage caused by low-velocity impact, and to establish the relationship between post-impact laminate strength and the relevant factors. Micro- and macro- mechanics are utilized.

Selected Publications

A. Huille, C. Yang, & S. S. Pang, "Buckling Analysis of Thick-Wall Composite Pipe Under Torsion," ASME Trans-Journal of Pressure Vessel Technology, in press.

M. A. Stubblefield, S. S. Pang, & V. A. Cundy, "Heat Loss in Insulated Pipe-The Influence of Thermal Contact Resistance: A Case Study," Composites Engineering, 1996, 27B, 1, 85-93.

S. S. Pang, C. Yang, & Y. Zhao, "Impact Response of Single-Lap Composite Joints," Composites Engineering, 1995, 5, 8, 1011-27.

S. S. Pang, G. A. Van Beek, & R. H. Lea, "Development of an Advanced Electrically Conductive Fiber Reinforced Plastics Pipe," Polymer Composites, 1995, 16, 5, 409-14.
 top
 

I am interested in various topics in materials science and engineering. For example, I am studying the structure and properties of hard magnetic materials based on Nd-Fe-boride and on the rare earth-iron compounds with the crystal structure Ln2T17, LnT12, and LnT13. The effects of solid solution formation with important alloy additives as well as carbon are studied. In the area of high Tc superconductor materials, I am working with Prof. Nagarajan of the University of Madras to synthesize useful products out of the 2223-type oxide superconductor based on Cu-O. Defects in thin films and their influence on properties are of special focus.

Another important area of study is corrosion science and engineering. I have been studying the corrosion mechanisms of steels in air and in salt water. The area of surface modification with a view to improve the properties is of special interest here. I am trying to find how the materials can be given permanent protection through simple surface modifications. Using IR-absorption spectra from the rust products, I hope to be able to predict the performance of surface modified steel components.

Polymeric and metallic coatings applied on metals provide protection from corrosion. Likewise, corrosion inhibitors protect the metals by offering suitable surface shields or protective layers. Degradation of coatings and corrosion inhibitors due to temperature cycling is a problem and the mechanisms are being studied. This work is in collaboration with Prof. Yu.I. Kuznetsov of the Russian Academy of Sciences, Moscow.

I am also carrying out several studies on the properties of composites. Current doctoral efforts involve: characterization of polymer-wood composites; surface modifications of ceramics (SiC) with a view to improve the properties of ceramic-matrix composites, particularly their toughness; and study of high temperature mechanical and thermal properties of intermetallic (TiAl and Ni3Al) composites, potentially useful at high temperatures. Crack growth characteristics in composites and in high temperature materials at high temperatures and their fracture toughness characterization at high temperatures are to be studied, particularly under conditions of degradation. In this work, I am collaborating with Prof. Prabhu-Gaonkar of the Department of Metallurgical Engineering at Indian Institute of Technology, Bombay.

Selected Publications

H-S Li, R. C. Mohanty, A. Raman, & C. G. Grenier, "Magnetic Properties of Nd2Fe14-xBexB," J. Magnetism and Magnetic Materials, in press.

A. Raman & P. Labine, "Temperature Effects on Inhibitors and Corrosion Inhibition," in Reviews on Corrosion Inhibitor Science and Technology, 1996, 2, III-1-12, A. Raman & P. Labine, eds.NACE International, Houston, Texas.

B. Kuban, A. Raman, & R. J. Gale, "Electrochemical Studies of Initial Corrosion Processes on Weathering Steels in Chloride Solutions," J. Electrochem. Soc. India, 1995, 44, 3, F61-F-74.

S. Nasrazadani & A. Raman, "The Application of Infrared Spectroscopy to the Study of Atmospheric Rust Systems, II. Study of Cation Deficiency in Magnetite, Corrosion Science, 1993, 34, 8, 1355-65.

V. Sridharan, T. Nagarajan, & A. Raman, "Thermogravimetric Studies of Y1Ba2Cu3O7-x Superconductors," J. Materials Science, 1992, 27, 4483-88.

A. Raman, B. Kuban, & A. Razvan, "The Application of Infrared Spectroscopy to the Study of Atmospheric Rust Systems, I. Standard Spectra and Illustrative Applications," Corrosion Science, 1991, 32, 12, 1295-1306.
 top
 

Selected Publications

Kong, L. and M. Sabbaghian, "Design of Engagement Mechanism for Roller Chain Drives, ASME Transaction," Journal of Mechanical Design, 118, September 1996.

Grewal, A.S. and M. Sabbaghian, "Load Distribution Between Threads in Threaded Connections," ASME Transaction, Journal of Pressure Vessel Technology, 118, November 1996.

Herrington, Paul and M. Sabbaghian, "Fatigue Failure of Composite Bolted Joints," Journal of Composite Materials, 1993, 27, No. 5, 491-512.

Herrington, P.D. and M. Sabbaghian, "Effect of Radial Clearance Between Bolt and Washer on the Bearing Strength of Composite Bolted Joints," Journal of Composite Materials, 1992, 26, No. 12, 1826-1843.

Boudjelida, K., A. H. Ghosn, & M. Sabbaghian, "A More Accurate Method for Predicting the Prestresses in a Multilayer Wrapped Cylindrical Vessel," ASME Transaction, Journal of Pressure Vessel Technology, August 1991, 113, No. 3, 459-464.
 top
 

Our group is concerned with the design of high speed and very low wear rotating machines. Such machines commonly require special bearing and sealing technologies that offer contact-free rotation and precise control of the rotating shaft. One machinery component that offers both contact free performance and high bandwidth shaft control is magnetic bearings.

Magnetic bearings utilize magnetic forces to maintain separation between the rotating and stationary surfaces in a machine.

Active magnetic bearing (AMB) systems are comprised of electromagnets arranged circumferentially about a shaft for this purpose. AMB systems are unstable unless a feedback system is employed. To this end, displacement sensors sense the position of the shaft in the bearing. This signal is fed back to a controller which then commands appropriate electromagnet coil currents from a power amplifier. In this way, separation is maintained between the bearing surfaces and the shaft is stabilized within the bearing.

Noncontacting stabilization of the shaft within the bearing stator allows the shaft to rotate at speeds that are limited only by the journal material strength and fracture toughness. Magnetic bearings can rotate at speeds of greater than 2-10 times that of different rolling element bearings, which yields many process benefits. However, one difficulty in rotating shafts at high speed is overcoming increased power losses.

Increased power losses in machinery bearings result in lower machine efficiency and higher operating temperatures. Although power losses for magnetic bearings are significantly smaller than those of rolling element and journal bearings, at high speed these losses cannot be neglected. Predicting such power losses for magnetic bearings is very difficult and normally requires spin-down testing in a vacuum. An alternative method that is significantly less expensive is to predict the power losses from a set of temperature measurements using a nonlinear iterated least squares parameter estimation. This method has been shown experimentally to be highly effective at estimating power losses when the signal-to-noise ratio of the temperature measurements is large. Figure 1 shows simulated errors due to instrumentation and the data reduction algorithm when using this method. The results clearly indicate the accuracy of the method when the signal-to-noise ratio is large.

In addition to shaft stabilization, which is typically accomplished through PID control, magnetic bearing control objectives normally include shaft vibration suppression. Vibration suppression becomes important at high rotational speeds as the running speed approaches or exceeds flexible modes of the rotor. Such control must be robust to uncertainties and changes in the rotor model, such as those induced by the gyroscopic effect.

The need for robust controllers requires the use of more advanced control techniques such as m-synthesis and H· control. Figure 2 shows a comparison of shaft control using PD control and shaft control using mu-synthesized, H· control. The objective of the control is to minimize the deflection of the rotor tip (the point at zero axial length). This result shows the effectiveness of advanced H· control as the rotor is lifted by the magnetic bearings to attain minimum tip deflection in the low frequency range. Although tradeoffs do exist, advanced control objectives for rotating shafts can be accomplished effectively through magnetic bearings.

Selected Publications

L.S. Stephens & C.R. Knospe, "Effect of Pole Arrangement on Core Loss in Laminated High-Speed Magnetic Journal Bearings," IEEE Transactions on Magnetics, 1996.

C. R. Knospe & L. S. Stephens, "Side Pull and Stiffness of Magnetic Bearing Radial Flux Return Paths," ASME Journal of Tribology, 117, 1996.

L. S. Stephens & C. R. Knospe, "Determination of Power Losses in High- Speed Magnetic Journal Bearings Using Temperature Measurements," Experimental Heat Transfer, 8, 1995, 33-56.

L. S. Stephens, "Design and Control of a High Speed Machining Spindle on Magnetic Bearings," Doctoral Dissertation, University of Virginia, August 1995.

L. S. Stephens, S. G. Tewani, & K. E. Rouch, "Theory for An Active Dynamic Vibration Absorber," Proceedings of the ASME 13th Biennial Conference on Mechanical Vibration and Noise, Miami, Florida, September 22-25, 1991.
 top
 

I am a control scientist and a fuzzyologist. My research interests center on the development of embedded microprocessor/DSP-based controllers for real-time control applications. I have a strong interest in contemporary approaches to controller design including fuzzy, neural, genetic algorithm, and artificially intelligent control algorithms and novel software/hardware approaches, including multiprocessor and massively parallel-based controller architectures. I am also a member of the mechatronics community and am active in the development of novel curricula and laboratory experiences for mechanical engineering education.

Selected Publications

S. Shenoi, M. Timmerman, & K. Ashenayi, "Implementation of a Learning Fuzzy Controller," IEEE Controls, 15, 3, 1995, 73-80.

D. Gardner, K. Ashenayi, M. Timmerman, & S. Shenoi, "Autonomous Control Hardware for Real-Time Applications," Proceedings IEEE Conference on Fuzzy Systems, Orlando, Florida, 1994.

S. Shenoi, M. Timmerman, & K. Ashenayi, "Implementation of an On-Line Adaptive Fuzzy Controller in Low-End Hardware," Journal of Engineering Applications of Artificial Intelligence, 7, 5, 1994, 533-43.

D. Gardner, C. H. Chen, S. Shenoi, M. Timmerman, & K. Ashenayi, "Practical Autonomous Control Hardware for Real-Time Applications," Advances in Fuzzy Theory and Technology, Vol. II, P. P. Wang, ed., Duke University, Durham, North Carolina, 1994, 303-25.

C. Ume & M. Timmerman, "Microprocessor Systems Design for Control-Oriented Projects," Journal of Microcomputer Applications, 15, 1992, 241-52.
 top
 

The general research focus in the Interactive Modeling Research Laboratory (IMRL) is the development and evolution of intelligent geometric modeling tools that will one day form the core of a self-contained, computer-based prototyping environment encompassing conceptual design, detailed engineering analyses, simulation, testing, and ultimately planning and production of a marketable product. Much progress has been made in this field during the past three decades, yet much work remains to be done, and IMRL projects seek to address some of the shortcomings of contemporary modeling systems. Although concentrating primarily on mechanical design, our investigations into fundamental modeling problems are applicable to numerous other technical arenas, including medicine and the basic sciences. The following paragraphs summarize some of our ongoing research projects.

Wireframe to Solid Model Conversion

Geometric modeling history has demonstrated that wireframe and surface models, although not as informationally complete as solids modelers, serve a valuable role in geometric design. We have characterized the fundamental limitations of this problem and developed the most general and robust algorithm for extracting accurate face topologies. Several unresolved issues in wireframe-to-solid conversion will continue to be the focus of ongoing research efforts, including automatic surface detailing and the development of new and improved algorithms for extracting three-dimensional geometry from the two-dimensional wireframe models (technical drawings). Each new development contributes to the automation.
  top

   My research interests have been concentrated in the fields of dynamic systems and control, sensors and actuators, microsystems, and microfabrication. The following are some of the typical research projects that are currently on-going.

DESIGN AND MICROFABRICATION OF A HIGH-PRECISION SUPERCONDUCTOR MICROSENSOR FOR WEAK MAGNETIC FIELD DETECTION

   The goal of this project is to design, simulate, construct, and test a high precision superconductor magnetic field microsensor. The sensor will have a microsize and integrated signal processing circuit. The operation principle of the microsensor is based on the giant magnetoresistivity of the Y-Ba-Cu-O ceramic superconductors at low magnetic field. Due to the sharp jump of resistivity at low magnetic field, high precision measurements of magnetic fields can be expected. The proposed microsensor has a simple structure, is easy to operate, and may be suitable for both analog and digital operation. The prototype microsensor will be fabricated with the microfabrication technology that is based on lithography and masked electro-chemical deposition.

MICROFABRICATED THERMOELECTRIC PROBES AND PROBE ARRAYS FOR HIGHLY LOCALIZED TEMPERATURE SENSING AND CONTROL

The purpose of this research effort, done in collaboration with Dr. M. C. Murphy, is to design, analyze, fabricate, and test a thermoelectric microprobe or array of such probes. Depending on the specific applications targeted, they can be used either for precision temperature measurement of micro-subjects or for highly localized cooling, heating, and simultaneously in-situ temperature sensing and control. The microprobes will have the capability of accurately controlling the temperature of microsized objects (cells, tissue, or neurons) at a target level. They can be potentially used in various applications of biological and medical researches. The X-ray mask for this project has been made to electroplate bismuth telluride and bismuth antimony, which are required for cooling.

   Other research projects include microrelays for high power applications ( in collaboration with Dr. M. C. Murphy); advanced materials ( such as high magnetostrictive materials) for microsystems ( in collaboration with Drs. M.C. Murphy and E. Ma).

Selected Publications

W.Wang & T.He, "A High Precision, Five-Degeree-of-Freedom Micropositioner Based on Electromagnetic Driving Principle", Review of Scientific Instruments, 67, 1, 1996, 312-17.

I. Busch-Vishniac, B. Buckman, W. Wang, & D. Qian, "Noncontact Position Measurement Systems Using Optical Sensors", U.S. Patent 5,367,373, issued in November 22, 1994.

C. Narayanan, A. Bruce Buckman, I. Busch-Vishniac, & W. Wang, "Position Dependence of the Transient Response of a Position-Sensitive Detector Under Periodic Pulsed Light Modulation", IEEE Transactions on Electron Devices, 40,9,1993, 1688-94.

D. Qian, W. Wang, I.J. Busch-Vishniac, & A.B. Buckman, "A Method for Measurement of Multiple Light Spot Positions on One Position-Sensitive Detector (PSD)", IEEE Transactions, on Instrumentation and Measurements, 42, 1, 1993, 14-18.

W. Wang & I. J. Busch-Vishniac, "A High Precision Micro-Positioner Based on Magnetostriction Principle", Review of Scientific Instruments, 63,1,249-54,1992.
 top