This dissertation presents a methodology for the statistical analysis of simulation output data. The analysis deals with the predictability of statistical inferential procedures for means and variances when the data are realizations of correlated and nonnormally distributed random variables. The purpose of the methodology is to improve the predictability of an inferential procedure with respect to the level of confidence in confidence interval analysis, or the power function in hypothesis testing. Conventional methods of statistical analysis for means lead to poor performance in their predictability if the sample observations are subject to strong autocorrelation. In addition, the predictability problem with respect to inferential procedures for variances is compounded by violation of the normality assumption. The methodology presented in this dissertation sets forth a sampling procedure to collect sequences of essentially uncorrelated observations. With these observations at hand, the statistical formulation presented leads to an estimator of the variance of the sample mean, thus yielding inferential procedures for means through the classical techniques. The formulation also leads to an estimator of the variance of the population and inferential procedures for variances are developed with an improved property of robustness. The bias in each estimator is greatly reduced due to the sampling procedure employed. Finally the research includes an algorithm for testing the lag correlation such that the sampling procedure can be actually implemented. The methods for means and variances developed in this research have been compared with corresponding conventional procedures. The comparison is based upon the predictability of the inferential procedure applied to the sample observations generated from autoregressive, simple moving average and M/M/1 queueing models. From the computational and simulation results reported in this research, the methods for means and variances suggested by this research have led to an improvement in the predictability of the analysis. / Ph. D.

One of the local area network medium access control standards created by the Institute of Electrical and Electronic Engineers in IEEE Project 802 is the carrier sense multiple access with collision detection (CSMA/CD) medium access control. Numerous studies have been reported in the literature on the performance of CSMA/CD. These studies show that CSMA/CD performs well under light network load but not well at heavy load. To improve the performance of CSMA/CD under heavy load, a new concept called network partitioning is presented. Network partitioning allows the network to be partitioned into segments when under heavy load. Partition stations then act as bridges between the segments. The impact of network partitioning on network performance was tested using a simulation model of an Ethernet local area network (an implementation of the CSMA/CD medium access control). The simulation results show that network partitioning can improve the performance of CSMA/CD under heavy load.

Thesis (MEng)--University of Stellenbosch, 1995. / AFRIKAANSE OPSOMMING: Die moontlikheid om die warmteoordrag in die reensone van 'n natuurlike trek nat koeltoring te vcrbeter deur die gemiddelde druppel diameter van die sproei te verminder is ondersoek. Eksperimentele wcrk was daarop gerig om tipiese druppelgrootte verspreidings onder druppakking te bepaal, asook die verkryging van werklike verrigtings-data vir verskiJlende pakking en reensone kombinasies in 'n koeltoring toetsfasiliteit. 'n Fotografiese metode wat gebruik maak van beeldverwerkingstegniekc is ontwikkel om die druppelgrootte verspreidings wat in die )meltoring toetsfasiliteit gevind word te bepaal. 'n Rekenaar simulasieprogram wat ontwikkel is deur Dreyer [940Rl] is verder gebruik om reensone verrigtingsdata ( oordragskarakteristieke en druppelgrootte verspreidings) teoreties te vcorspel, vir vergelyking met en evalusie van die eksperimentele resultate. Dit is bewys dat die plasing van 'n laag spatroosters reg onder druppakking die gerniddelde druppeldiameter in die reensone verrninder het, wat gelei het tot 'n ooreenstemmende toename in oordragskarakteristiek. Met die gebruik van 'n rekenaar simulasie program is bereken dat hierdie opstelling die termiese kapasiteit van 'n koeltoring met tot 5 % kan verbeter. / ENGLISH ABSTRACT: The possibility of improving the heat transfer in the rain zone of large natural draft wet cooling towers, by decreasing the mean drop diameter in this region, has been investigated. Experimental studies were aimed at determining typical drop size distributions under trickle packs and obtaining actual performance data for packing and rain zone combinations in a cooling tower test facility. A photography-based method, which utilizes image processing techniques, was develo!Jed t() determine the drop size distributions found in the test facility. A computer simulation program developed by Dreyer [94DRI] was used to theoretically predict rain zone performance data (i.e., transfer coefficients and drop size distribution data) for comparison with and evaluation of the experimental data. I: was found that by placing a layer of splash grids beneath a trickle pack the mean drop diameter in the rain zone was decreased, resulting in corresponding increases in transfer characteristic. Using a computer simulation program it was calculated that this arrangement could increase the thermal capacity of a large natural draft cooling tower by up to 5 %.

Thesis (MSc)--University of Stellenbosch, 2004 / ENGLISH ABSTRACT: A variety of computational techniques are used to calculate structural, thermodynamic and transport properties of two specific Platinum Group Metal (PGM) complex systems. The first system consists of a PGM complex ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- or [RhCl6]3-) with sodium counter-ions in a water solution at 30ºC and at a concentration of 0.106 mol/dm3. The second system under consideration is that of a PGM complex ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- or [RhCl6]3-) with sodium counter-ions in a water solution in the presence of four poly (ethylene oxide) (PEO) chains at 30ºC and at a concentration of 0.013 mol/dm3. A conformational study of the two types of dihedral angles in a PEO chain (-C-O-C-Cand -O-C-C-O-) is performed and the extreme flexibility of the polymer is confirmed. Dihedral angle distributions of the two dihedral angles are calculated and explained in terms of the potential energy surface obtained from the conformational study. The solvation geometries of the PGM complexes are confirmed and the results are contrasted with those in the system where the polymer (PEO) is present. It is concluded that the effect of the polymer on the structure and degree of solvation is negligible. The free energy of solvation values of the PGM complexes are calculated to provide insight into their structural characteristics such as solvation shell volume and geometry. The structural and thermodynamic properties of the PGM complexes in solution are also used to explain the trends observed in the calculated diffusion coefficients. Comments are made on the accuracy of the calculated diffusion coefficients as well as the legitimacy of the mechanistic speculations which results from them. Suggestions regarding possible future improvements to the computational methods are made. / AFRIKAANSE OPSOMMING: Verskeie berekenings tegnieke is aangewend om die strukturele, termodinamiese en verplasings eienskappe van twee spesifieke Platinumgroep Metaal (PGM)-kompleks sisteme te bereken. Die eerste sisteem bestaan uit die PGM-kompleks ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- of [RhCl6]3-) met natrium teenione in water by 30ºC en met ‘n konsentrasie van 0.106 mol/dm3. Die tweede sisteem bestaan uit die PGM-kompleks ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- of [RhCl6]3-) met natrium teen-ione in water in die teenwoordigheid van vier poli-etileenoksied (PEO) kettings by 30ºC en met ‘n konsentrasie van 0.013 mol/dm3. ‘n Studie is gemaak van die konformasies van die twee soorte dihedrale-hoeke in ‘n PEOketting (-C-O-C-C- en -O-C-C-O-) en die insense buigbaarheid van die polimeer is hiermee bevestig. Die dihedrale-hoek-verspreidings van die twee tipes dihedrale hoeke is bereken en word verduidelik in terme van die potensiёle energie kromvlakke soos bereken tydens die konformasie analiese. Die geometrie van die solvasie van die PGM-komplekse is bereken en vergelyk met die sisteme waar die polimeer (PEO) teenwoordig is. Hieruit word afgelei dat die effek van die polimeer op die struktuur en graad van solvasie van die komplekse minimal is. Die vrye energie van solvasie van die PGMkomplekse is bereken met die doel om insig in te win oor die stukturele eienskappe soos byvoorbeeld die volume van die solvasie sfeer en die geometrie daarvan. Die strukturele en termodinamiese eienskappe van die PGM-komplekse in oplossing word ook gebruik om die neigings in die berekende diffusie koёffisiente te verduidelik. Opmerkings word gemaak aangaande die akkuraatheid van die berekende diffusie koeffisiente asook die geldigheid van die meganistiese spekulasies wat daaruit gemaak word. Voorstelle word ook gemaak rakende toekomsige verbeterings aan die reken tegnieke.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

A new method for transient simulation of integrated circuits has been developed and investigated. The method utilizes expansion of circuit variables into Chebyshev series. A prototype computer simulation program based on this technique has been implemented and applied in the transient simulation of several MOS circuits. The results have been compared with those generated by SPICE. The method has been also combined with the waveform relaxation technique. Several algorithms were developed using the Gauss-Seidel and Gauss-Jacobi iterative procedures. The algorithms based on the Gauss-Seidel iterative procedure were implemented in the prototype software. They offer substantial CPU time savings in comparison with SPICE without compromising the accuracy of solutions. A description of the prototype computer simulation program and a summary of the results of simulation experiments are included.

A simulation program has been developed to facilitate the investigation and analysis of power semiconductor devices under the reverse-bias condition. The electrostatic potential distribution is solved by using Poisson's equation alone, with particular attention to the neighborhood of avalanche breakdown. Because of its generality and efficiency, the program emerges as a powerful engineering tool for the design of power devices incorporating special junction termination techniques. Results are presented for a DMOS structure to illustrate the improvement in breakdown voltage when a field plate is applied. Numerical solution techniques for solving elliptic partial differential equations in a multi-material domain are discussed. The discretization of this domain is nonuniform in general due to its highly nonuniform physical parameters. By careful selection of grid lines near interfaces, the difference equation coefficients are considerably simplified. The resultant matrix of coefficients is symmetric even though Neumann boundary conditions are specified.

The objective of this research was to develop a framework whereby the United States Naval Surface Forces could be provided with better information to determine their overall readiness capability. This study utilized the new Readiness Assessment and Reporting Standard (S9410-AN-STD-010/AEGIS) as a guide. Also, a System Design Methodology was used as a tool to develop mathematical models for generating the readiness capability for a particular system. The specific system selected for demonstrating this framework was the Gun Weapon System (GWS) being developed for the Arleigh Burke DDG-51 Class Destroyer.

The computer program WHEEL is a mathematical model which predicts off-road vehicle performance characteristics. The program was developed using empirical relationships resulting from mobility tests on conventional-sized trucks and tires. The model was subsequently validated by comparing the model's predicted values of vehicle performance parameters, such as net drawbar pull, slip, sinkage and torque, with field test results for conventional-sized vehicles. However, validity of the model for predicting the off-road mobility of vehicles with large diameter tires was not established. The purpose of this study was to provide this validation. Values of net drawbar pull and slip for a Case 2390 tractor with 70.2" diameter driven wheels predicted by computer program WHEEL compare favorably with traction data obtained from tractor performance tests conducted by the University of Arizona Department of Agricultural Engineering. Therefore, the model may be used confidently to analyze performance of vehicles with large diameter wheels.

This thesis describes the simulation of the IBM SYSTEM/7. The research leading to this thesis involved the development of a PL/I computer program that runs on an IBM 360/50 computer and simulates the IBM SYSTEM/7. Various methods of simulation are examined and guidelines for computer simulation of another computer are established. The SYSTEM/7 simulator (SIM/7) is the heart of this thesis. SIM/7 simulates the IBM SYSTEM/7 entirely with software as opposed to an emulator which involves the combined use of hardware and software to perform the simulation process. This thesis contains a general introduction to computer simulation, reason for simulation, a user's guide for SIM/7 and a definition of the SYSTEM/7 processor using the Vienna Definition Language.