Mechanical Engineering Theses and Dissertations
http://hdl.handle.net/2429/35439
2015-09-30T22:47:11ZA modified particle swarm optimization and its application in thermal management of an electronic cooling system
http://hdl.handle.net/2429/37900
Particle Swarm Optimization (PSO) is an evolutionary computation technique, which has been inspired by the group behavior of animals such as schools of fish and flocks of birds. It has shown its effectiveness as an efficient, fast and simple method of optimization. The applicability of PSO in the design optimization of heat sinks is studied in this thesis. The results show that the PSO is an appropriate optimization tool for use in heat sink design.PSO has common problems that other evolutionary methods suffer from. For example, in some cases premature convergence can occur where particles tend to be trapped at local optima and not able to escape in seeking the global optimum. To overcome these problems, some modifications are suggested and evaluated in the present work. These modifications are found to improve the convergence rate and to enhance the robustness of the method. The specific modifications developed for PSO and evaluated in the thesis are: (1) Chaotic Acceleration Factor (2) Chaotic Inertia Factor (3) Global Best Mutation The performance of these modifications is tested through benchmarks problems, which are commonly found and used in the optimization literature. Detailed comparative analysis of the modifications to the classical PSO approach is made, which demonstrates the potential performance improvements. In particular, the modified PSO algorithms are applied to problems with nonlinear constraints. The non-stationary, multi-stage penalty method (PFM) is implemented to handle nonlinear constraints. Pressure vessel optimization and welded beam optimization are two common engineering problems that are used for testing the performance of optimization algorithms and are used here as benchmark testing examples. It is found that the modified PSO algorithms, as developed in this work, outperform many classical and evolutionary optimization algorithms in solving nonlinear constraint problems. The modified PSO algorithm is applied in heat sink design and detailed results are presented. The commercially available software package Ansys Icepak is used in the present work to solve the heat and flow equations in implementing the optimal design variables resulting from the modified PSO algorithms. The main contributions the work are summarized and suggestions are made for possible future work.
2011-10-12T00:00:00ZMixture formation in a partially stratified directly injected natural gas engine
http://hdl.handle.net/2429/37778
A rapid compression machine was redesigned to allow the use of acetone UV laser diagnostics to investigate the mixture distribution that results from the injection of a methane partially stratified charge (PSC) and direct injection (DI) jet. A central composite test matrix was used to investigate the effect of relative injection timing and bulk charge air-fuel ratio upon the mixture distribution. Comparison was made between the distribution that resulted from a capillary injected PSC charge and a bespoke ‘sparkplug insert’ injected charge.
The capillary injected PSC jet was found to preserve a jet-like structure despite its interaction with the direct injection jet, while the effect of the DI jet upon the insert injected fuel was to encourage coalescence of the jets to form a largely homogeneous mixture at the point of injection and near the leading edge of the DI jet. The DI jet, with a weak bulk charge, served to reduce the fluctuations in relative air-fuel ratio compared to PSC injection into air; while the insert injected PSC charge exhibited increased fluctuation levels with advanced relative injection timing. The improved ignition of a partially stratified charge from the introduction of a weak bulk charge had been presumed to work through reductions in fuel concentration gradients, however the findings of the this work suggest that this works in unison with a decrease in fuel concentration fluctuations that increases ignition efficacy. The insert injected PSC fuel demonstrates scalar dissipation rates that are potentially too low to provide robust enough combustion for a viable partially stratified charge approach. The PSC insert engenders more mixing than a capillary injected PSC, but penetrates the DI jet less well. In all cases, and throughout the region of the interaction, there exists a finite probability of encountering pure fuel or the bulk fuel concentration that suggests mixing driven by engulfment rather than entrainment. The PSC ‘sparkplug’ insert offers better opportunity for mixing than the capillary injection and using a stochastic design approach should be pursued further to improve the performance of partially stratified charge combustion for natural gas engines.
2011-10-04T00:00:00ZHole-drilling residual stress measurement in an intermediate thickness specimen
http://hdl.handle.net/2429/37744
The hole-drilling method for measuring residual stresses is generally applied to two extreme cases. In the “thick” case, the specimen depth is very large compared with the hole depth. The far boundary is then sufficiently distant that its effect can be neglected. In the “thin” case, the specimen has the form of a thin plate through which the hole penetrates fully. The thin plate creates plane-stress conditions and it is usually assumed that the associated residual stresses are uniform through the plate thickness. This research focuses on the intermediate case where the specimen has a thickness modestly greater than the hole depth. The far boundary is then near enough to give significant influence, and the through-thickness residual stresses are non-uniform. The finite specimen thickness and non-uniform residual stresses create significant bending deformations of the specimen during hole-drilling that are not present in either extreme case. This bending effect creates out-of-plane deformations that can provide an opportunity for a novel measurement approach. The “intermediate” case is investigated using an analytical model and by finite element analysis. Experimental measurements are made using Electronic Speckle Pattern Interferometry (ESPI), and a comparison is made of the theoretical and experimental results.
2011-10-03T00:00:00ZPIV measurements of flow through forming fabrics
http://hdl.handle.net/2429/37737
Three-dimensional velocity fields in the single phase approach flow to a multiple layer woven forming fabric were measured using Particle Image Velocimetry (PIV). The measurements were conducted on a scale model of a forming fabric in a water/glycerin flow loop. Each strand on the paper side of the model forming fabric had a filament diameter around 15.4mm, and the loop test section was 310mm squared, permitting the measurement of detailed velocity distributions over multiple strands of the fabric. The flow speed in the loop test section were varied to achieve screen Reynolds numbers (Res), calculated based on paper side filament diameter (d), between 15 and 65. PIV measurements showed that the normalized ZD velocity deviation decreases from 19.7% at a plane 0.25d upstream from the forming fabric to 4.2% at a plane 1.5d upstream. The normalized CMD velocity deviation decreases from 15.3% at a plane 0.25d upstream from the forming fabric to 1.9% at a plane 1.5d upstream. The normalized MD velocity deviation decreases from 14.5% at a plane 0.25d upstream from the forming fabric to 2.3% at a plane 1.5d upstream. The highest ZD velocity is about 3.3 times higher than the lowest ZD velocity at a plane 0.25d above the fabric. This ratio decreases to 1.2 at a plane 1.5d above the fabric. These findings show that the flow non-uniformity caused by the fabric weave is restrained to a short distance above the fabric. However, even this non-uniformity is not particularly felt by fibers, whose length scale results in an averaging of the local velocity field. CFD simulations of the same flow were consistent with the PIV measurements.
2011-09-30T00:00:00Z