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机械 & 仪表工业 : 学术学位
Flexure joints are frequently used in precision mechanisms, from motion stages to micro-robots. Due to their monolithic construction and superior wear and loss properties, flexure joints can be used to reduce the mechanism size and increase the positioning accuracy. The compliance of flexure joints,
Electrostatic discharge (ESD) causes a significant percentage of the failures in the electronics industry. The shrinking size of semiconductor circuits, thinner gate oxides, complex chips with multiple power supplies and mixed-signal blocks, larger chip capacitance and faster circuit operation, all
A characterization of micromanipulator controlled dry spinning of micro- and nanoscale polymer fibers.
No current microfabrication technique exists for producing room-temperature, high-precision, point-to-point polymer nanofibers in three dimensions. Producing rounded structures in a third dimension is particularly difficult to accomplish with conventional planar microfabrication techniques. Therefor
Reduced order, inviscid and fully simultaneous viscous-inviscid interaction models of flows in turbomachinery.
The proper orthogonal decomposition technique is applied in the frequency domain to obtain reduced order models (ROM) of the unsteady flow in two-dimensional turbomachinery cascades. The method is applied to both subsonic and transonic flows. Both viscous and inviscid flows are investigated. The vis
Modern urban buses with low floor and considerable over hung design are known to cause poor ride quality and excessive pavement loads. Such performance is partly due to the present status of urban roads and their rapid deterioration. On the other hand, variations in the dynamic tire forces of such v
A dynamic stress theory was developed to provide a uniform solution technique for dynamic stress problems. Dynamic stresses occur during impacts between objects and loads suddenly applied to structures, and these dynamic stresses can be described by closed form equations. The basic dynamic stress eq
An important focus in the glass melting industry, which is an energy intensive industry, is towards greater output and increased energy efficiency in the glass melting process. Conversion to the oxy-fuel-fired furnace from the traditional air-fuel-fired furnace is one means to achieve greater output
When a detonation propagates in an explosive that partially fills a channel, a shock wave can be generated in the air gap between the explosive and its confinement. This is typically referred to as the channel effect. In the air gap, the detonation products behave as a piston, which drives the precu
The elastohydrodynamic behavior of the crankshaft/main-bearings system plays a crucial role in the performance of a multi-cylinder engine. This elastohydrodynamic behavior relates to the tribology of the main-bearings, the dynamics of the engine structure, and the dynamics of the crankshaft. It is a
For the purposes of telecommunications, optical fibers consist of a higher refractive index core and a lower refractive index cladding, which are drawn from a double-layer cylindrical preform. In this study, the thermal transport during the double-layer optical fiber drawing process has been numeric
Numerical simulations of steady and unsteady oblique detonation phenomena with application to propulsion.
Oblique detonations and their propulsive applications were studied by numerically integrating the two-dimensional, reactive Euler equations in a generalized, curvilinear coordinate system. The integration was accomplished using the Roe scheme combined with fractional stepping; nonlinear flux limitin
The goal of this thesis is to develop a general framework for lattice statics analysis of defects in ferroelectric Perovskites. The techniques presented here are general and can be easily applied to other systems as well. We present all the calculations and numerical examples for two technologically
Vibration isolators play a pivotal role in a range of industries from construction to transportation. During the past century the design and optimization of the performance of vibration isolators has attracted enough attention that several criteria have been defined to quantify the performance of th
All real vibrating systems are nonlinear; however, nonlinear behaviors are not always observed in the system dynamics. Input types and levels, boundary conditions, and other characteristics of the experimental environment determine whether or not the nonlinearities surface during testing. Traditiona
Large space structures must be designed to be stowed during launch and deployed once on orbit because the cargo space of a launch vehicle is always limited. The considerations about payload requirement, weight constraint, and ease of storage during launching make highly flexible deployable structure
The objective of this study was to evaluate residential ground-source heat pumps throughout the state of Iowa and use that information to develop educational opportunities for prospective ground-source heat pump owners. The ground-source heat pumps were evaluated based on performance, efficiency, an
The scope of this study is to develop a user-friendly software to evaluate building hourly loads. The following physical phenomena are taken into account: transient thermal conduction through opaque walls, convection and long wave radiation interchange at the internal and external surfaces, solar he
Development of tunable diode laser absorption sensors for a large-scale arc-heated-plasma wind tunnel.
Arc heated wind tunnels are the most reliable high temperature facilities to test thermal protection systems and heat shields. At NASA Ames Research Center, a 60 MW rated interactive heating facility (IHF) with a constricted arc heater and a expansion test cabin has been used to develop thermal prot
The influence of surface perturbations and laminar separation bubble on boundary layer instability by direct numerical solution of the Navier-Stokes equations.
The purpose of this study is to shed more light on the role of surface perturbations and the laminar separation bubble associated with them on the boundary-layer instability and to explore this important flow problem in fluid dynamics further. To accomplish this, the stability characteristics of the
The renewed interest in hypersonic flight has fostered a need to increase our understanding of turbulence and mixing in high Mach number flows. The objective of this work is to aid the development of turbulence models for compressible flows by using direct numerical simulations of compressible homog