Mechanical Engineering Commons^™

Modeling And Simulation Of Optical Characteristics Of Microelectromechanical Mirror Arrays, Peter C. Roberts

Theses and Dissertations

MEMS (Micro-Electro-Mechanical Systems) micromirror devices can be used to control the phase of a propagating light wavefront, and in particular to correct aberrations that may be present in the wavefront, due to either atmospheric turbulence or any other type of fixed or time and space varying aberrations. In order to shorten the design cycle of MEMS micromirror devices, computer software is developed to create, from MEMS micromirror device design data, a numerical model of the MEMS device. The model is then used to compute the far field diffraction pattern of a wavefront reflected from the device, and to predict the …

Artificial Cochlea Design Using Micro-Electro-Mechanical Systems, George C. Dalton Ii

Theses and Dissertations

The use of Micro-Electro-Mechanical Systems (MEMS) in the design of an artificial cochlea is investigated in depth. Interdigitated finger (comb), cantilever, bridge, and mirror resonators are presented as possible devices used to implement the artificial cochlea. These resonators are demonstrated to be extremely high Q devices, capable of being tuned with a simple DC bias. This suggests a possible change to existing cochlea models that claim highly complex AC feedback as being responsible for changes in the damping of the basilar membrane. The new cochlea model presented here, using MEMS to approximate the tuning of the basilar membrane, may be …

Microelectromechanical Isolation Of Acoustic Wave Resonators, James R. Reid Jr.

Theses and Dissertations

Microelectromechainical systems (MEMS) is a rapidly expanding field of research into the design and fabrication of actuated mechanical systems on the order of a few micrometers to a few millimeters. MEMS potentially offers new methods to solve a variety of engineering problems. A large variety of MEMS systems including flip-up platforms, scanning micromirrors, and rotating micromirrors are developed to demonstrate the types of MEMS that can be fabricated. The potential of MEMS for reducing the vibration sensitivity of surface acoustic wave and surface transverse wave resonators is then evaluated. A micromachined vibration isolation system is designed and modeled. A fabrication …

Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick

Theses and Dissertations

This research conducted the first demonstrated use of a micro-electro-mechanical structure (MEMS) mirror array to correct a static optical aberration. A well-developed technique in adaptive optics imaging systems uses a deformable mirror to reflect the incident wave front to the imaging stage of the system. By matching the surface of the deformable mirror to the shape of the wave front phase distortion, the reflected wave front will be less aberrated before it is imaged. Typical adaptive optics systems use piezo-electric actuated deformable mirrors. This research used an electrostatically actuated, segmented mirror array, constructed by standard MEMS fabrication techniques, to investigate …

High-Pressure Oxidation Rates For Large Coal And Char Particles, James A. Mathias

Theses and Dissertations

The main objective of this study was to investigate the factors that influence the oxidation rate of large (five to eight millimeters in diameter) coal and char particles. To accomplish this, experiments were performed in which the gas temperature, gas velocity, particle size, partial pressure of oxygen, and total pressure were varied. The experiments were performed with the cantilever balance attachment and the high pressure controlled profile reactor.

Approximately 90 combustion experiments were performed with Pittsburgh, Utah Blind Canyon, and Wyodak-Anderson coal. These experiments were performed at atmospheric pressure with air and varied gas temperature, gas velocity, and particle size. …

Numerical Analysis Of Two And Three Dimensional Recessed Flame Holders For Scramjet Applications, Douglas L. Davis

Theses and Dissertations

This study investigated the flame holding properties of recessed cavities in supersonic flow using numerical analysis techniques. A simplified analytical model indicated that an important property for flame holding was the lower residence time. Several chemical kinetic rate models for hydrogen and hydrocarbon combustion were compared. The perfectly stirred reactor model also indicated that trace species diffusion should increase flame spreading rate, and that heat loss reduces flame holding limits. After nonreacting calibration, two-dimensional simulations confirmed the perfectly stirred reactor results for blowout limits. Also, the effect of trace species diffusion on flame spreading was shown to be negligible, and …

The Development And Evaluation Of The Knife Finite Element, Brett W. Clark

Theses and Dissertations

This thesis presents the development and evaluation of the knife finite element which is a degenerate case of a hexahedral element. The knife connectivity is an artifact of automatic all-hexahedral mesh generators. Currently, knives are propagated to the surface of the mesh for removal. However since this disturbs the surface mesh, other alternatives are needed. This thesis investigates the option of leaving the knife connectivity in the mesh and treating it as a valid finite element. The shape functions and stiffness matrix for the knife element are derived and evaluated using theoretical and practical evaluations. It is concluded that the …

Reaction Based Grasp Force Assignment, Mark W. Hunter

Theses and Dissertations

An iterative method is developed by which the contact forces required to apply an arbitrary wrench (six elements of force and moment) to a stably grasped object may be calculated quickly. The assignment of contact forces, given a required object wrench, is accomplished with the use of fuzzy logic. This concept is referred to as the fuzzy logic reactive system (FLRS). The solution is versatile with respect to goals inherent in the rulebase and the input parameters, and is also applicable for an arbitrary number of contacts. The goal presented in this research, to illustrate the concept of the FLRS, …

Structures And Techniques For Implementing And Packaging Complex, Large Scale Microelectromechanical Systems Using Foundry Fabrication Processes, John H. Comtois

Theses and Dissertations

Microelectromechanical Systems, or 'MEMS' is a broad new field of research into devices that range in size from a few microns to a few millimeters. Much of the technology supporting MEMS research is borrowed from the microelectronics industry; so MEMS holds out the promise of batch fabrication of microminiaturized machines that can be easily integrated with electronics. This dissertation research investigated structures and methods for implementing and packaging complex, large scale microelectromechanical devices and systems using commercially available foundry fabrication processes. It specifies methods for creating and packaging large, complex MEM systems, allowing the exploration of new MEMS architectures at …

An Investigation Of The Characteristics Of Regenerative Heat Exchangers, Timothy J. Murphy

Theses and Dissertations

The objective of the current research was to investigate the effects of reducing screen thickness on the volume and compactness factor of stacked, wire-screen regenerators. An improved transient step-change method was devised which integrated experimental data with a numerical model of the flow to determine the heat transfer coefficient and friction factor. The improvements to the approach are: (1) the measured inlet temperature trace is used, (2) the heat transfer coefficient is based on a parameter called the sponge effect delay time, and (3) the important effect of the tube surrounding the matrix is included in the numerical model. The …

Simultaneous Composite Tailoring And Bending Control Optimization For Damping The Torsional Vibration Of A Plate, Douglas W. Dehart

Theses and Dissertations

A method for the simultaneous structural and control optimization for torsional vibration of a composite plate which simulates a spacecraft solar array structure was developed in this study. Included in the optimization of the plate are the location of the piezoceramic actuators and sensors that provide bending/torsion actuation, the control gains, and the orientation of the graphite fibers in the composite plies. This research included the effects of using composite tailoring to promote the coupling of the twisting-bending mode to enhance the damping system. The plate was modeled by classical lamination plate theory using a linear elastic strain-displacement theory. This …