An existing analytical model, in use by Spoornet for the past two decades for calculating rail stresses on railway track, was revisited and improved. The model provided engineers with an easy-to-use program for evaluating track capacity and authorizing heavier loads on track. The model was modified to calculate rail and track component stresses more accurately. These modifications include the incorporation of current best practices and presentation of guidelines for the engineer on how to determine some input parameters which are normally difficult to obtain. Firstly it was determined which input parameters the model was the most sensitive to. Thereafter it was determined whether or not the correct information would generally be readily available for those sensitive parameters. The most sensitive parameters were further investigated and test results, as well as best practice analytical methods, were used to establish nominal input values and guidelines for determining such values. This research was necessary to establish whether or not the currently used analytical model still provided railway engineers with a useful tool and whether or not more modern and popular tools could validate or replace it. After some modifications to the analytical model, it was proved that it provides engineers with a suitably accurate tool for calculating rail and track component stresses, without the need to build time-consuming models of the track under investigation. It showed that the model, after some modifications, is current with calculational methods in recent publications and provides an immediate answer to "what-if" questions without the need to run lengthy analyses. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Nous étudions des fluctuations qui sont omniprésentes dans des collisions entre particules aux hautes énergies. Ces fluctuations peuvent être de nature classique ou quantique et nous allons considérer ces deux cas. D'abord, nous étudions les fluctuations quantiques qui sont présentes dans des collisions entre protons. Celles-ci sont calculables en théorie quantique des champs, et nous allons nous concentrer sur une certaine classe de diagrammes dans ce cadre. Dans un second temps nous allons étudier des fluctuations qui sont présentes dans des collisions entre particules plus lourdes que le proton. Celles-ci sont décrites par les lois quantiques de la nature qui donnent les positions des nucléons dans le noyau, ou bien des fluctuations classiques, d'origine thermique, qui affectent l'évolution hydrodynamique du milieu produit dans une collision. Les fluctuations dans des collisions entre protons peuvent être calculées analytiquement jusqu'à un certain ordre en théorie quantique des champs. Nous allons nous concentrer sur des diagrammes à une boucle, d'une topologie donnée. Ces diagrammes aux boucles donnent des intégrales, qui typiquement sont difficiles à calculer. Nous allons démontrer comment des outils des mathématiques modernes peuvent être utilisés pour faciliter leur évaluation. En particulier, nous allons étudier des relations entre des coupures d'un diagramme, la discontinuité à travers d'un branchement et le coproduit. Nous allons démontrer comment l'intégrale originale peut être reconstruit à partir de l'information contenue dans le coproduit. Nous nous attendons à ce que ces méthodes seront utiles pour le calcul des diagrammes avec des topologies plus difficiles et ainsi aident au calcul des nouvelles amplitudes de diffusion. A la fin, nous étudions les deux types de fluctuations qui ont lieu dans des collisions entre ions lourds. Celles-ci sont liées soit à l'état initial de la matière, soit à l'état intermédiaire produit dans une telle collision. Les fluctuations de l'état initial ont été mesurées expérimentalement, et on voit qu'elles donnent lieu à des non-Gaussianités dans le spectre final de particules. Nous allons démontrer comment ces non-Gaussianités peuvent être comprises comme des positions et des énergies d'interaction aléatoires des 'sources' dans les noyaux entrant en collision. En plus, nous étudions le bruit hydrodynamique dans le milieu produit juste après une collision. Le comportement de ce milieu est celui d'un fluide à basse viscosité. / We study fluctuations that are omnipresent in high-energy particle collisions. These fluctuations can be either of either classical or quantum origin and we will study both. Firstly, we consider the type of quantum fluctuations that arise in proton-proton collisions. These are computable perturbatively in quantum field theory and we will focus on a specific class of diagrams in this set-up. Secondly, we will consider the fluctuations that are present in collisions between nuclei that can be heavier than protons. These are the quantum laws of nature that describe the positions of nucleons within a nucleus, but also the hydrodynamic fluctuations of classical, thermal origin that affect the evolution of the medium produced in heavy-ion collisions. The fluctuations arising in proton-proton collisions can be computed analytically up to a certain order in perturbative quantum field theory. We will focus on one-loop diagrams of a fixed topology. Loop diagrams give rise to integrals that typically are hard to evaluate. We show how modern mathematical methods can be used to ease their computation. We will study the relations among unitarity cuts of a diagram, the discontinuity across the corresponding branch cut and the coproduct. We show how the original integral corresponding to a given diagram can be reconstructed from the information contained in the coproduct. We expect that these methods can be applied to solve more complicated topologies and help in the computation of new amplitudes in the future. Finally, we study the two types of fluctuations arising in heavy-ion collisions. These are related either to the initial state or the intermediate state of matter produced in such collisions. The initial state fluctuations are experimentally observed to give rise to non-Gaussianities in the final-state spectra. We show how these non-Gaussianities can be explained by the random position and interaction energy of `sources' in the colliding nuclei. Furthermore, we investigate the effect of hydrodynamical noise in the evolution of the medium produced just after a collision. This medium behaves like a fluid with a very low viscosity, and so the corresponding evolution is hydrodynamical.

The goal of this master’s thesis is to examine the influence of eccentricity on the behaviour of forces between the piston and cylinder liner and on balancing of the crank mechanism for given parameters of the diesel engine. Another aim of this paper is to propose an appropriate balancing of the crank mechanism followed by stress analysis considering torsional vibration for a chosen value of eccentricity.

This thesis deals with vibration diagnostics of electrical machines. The thesis describes vibrations and their measurement. The next section concernes the diffrent modes of elctrical machines. Vibration of machines are divided into electrical causes and mechanical causes. Practical part deals with the measurement of vibration on the machines and their subsequent analysis. The result of the practical part is determining the fault of the measured induction motors.

There are approximately 4000 railway bridges in Sweden managed by the Swedish Administration of Transport (Trafikverket), of which a common construction type is the reinforced concrete (RC) trough bridge, which is a structure that consists of a slab carried by two longitudinal main beams which transfer loads towards the supports. A substantial amount of the RC trough bridge population is approaching the end of their service lives which consequently implies that the replacement of some of these bridges can be expected in the near future. Extending their service lives can yield positive effects from a financial- as well as an environmental perspective, and therefore it is highly beneficial to evaluate their capacities as realistically as possible. One factor that may help improve accuracy during the determination of their capacities is an evaluation of how it is affected by the location of the railway track on the bridge.  In current design codes defined by Trafikverket, consideration is taken to horizontal track displacement for a minimum displacement of 0.1 m if there doesn’t exist data suggesting that a larger displacement is prevalent on the bridge. However, Trafikverket has received data which suggest that a considerable number of bridges could experience load eccentricities which exceed the standard minimum value. This raises the question whether or not 0.1m is the most optimal limit value for load eccentricity on railway bridges. For RC trough bridges, a larger load eccentricity may result in one main beam carrying a larger portion of the load which will decrease the axle load which the bridge can carry. It is therefore important to evaluate the influence of larger horizontal displacements than what is currently is considered as a preventive action.   In addition, several studies on Swedish concrete bridges constructed during the 20th century have pointed to a significant increase in concrete compressive- and tensile strength over time. This suggests that it is possible that a considerable amount of RC trough bridges have a higher capacity than what was originally intended, and further research is required in order to understand the behaviour of these bridges when key material parameters are altered.        There are three main tasks which this master thesis seeks to complete. The first part is a detailed analysis of a database named BaTMan (Bridge and Tunnel Management) that belongs to Trafikverket. In this analysis parameters such as span length, age, material type and damages for every identified railway bridge is extracted and further processed in Microsoft Excel in order to gain a clear overview of the RC trough bridge population. The second task regards the development of a non-linear finite element model of a typical RC trough bridge named Lautajokki. The model is analysed using ATENA Science and its behaviour is verified against test results obtained during a full-scale test of the bridge performed by Paulsson et al. (1996). The last task is to use the devolved model to perform a parametric study where the effects of changes in load eccentricity, compressive strength as well as tensile strength is studied.

The femur is the longest limb bone found in humans. Almost all the long limb bones found in terrestrial mammals, including the femur studied herein, have been observed to be loaded in bending and are curved longitudinally. The curvature in these long bones increases the bending stress developed in the bone, potentially reducing the bone’s load carrying capacity, i.e. its mechanical strength. Therefore, bone curvature poses a paradox in terms of the mechanical function of long limb bones. The aim of this study is to investigate and explain the role of longitudinal bone curvature in the design of long bones. In particular, it has been hypothesized that curvature of long bones results in a trade-off between the bone’s mechanical strength and its bending predictability. This thesis employs finite element analysis of human femora to address this issue. Simplified human femora with different curvatures were modeled and analyzed using ANSYS Workbench finite element analysis software. The results obtained are compared between different curvatures including a straight bone. We examined how the bone curvature affects the bending predictability and load carrying capacity of bones. Results were post processed to yield probability density functions (PDFs) for circumferential location of maximum equivalent stress for various bone curvatures to assess the bending predictability of bones. To validate our findings on the geometrically simplified ANSYS Workbench femur models, a digitally reconstructed femur model from a CT scan of a real human femur was employed. For this model we performed finite element analysis in the FEA tool, Strand7, executing multiple simulations for different load cases. The results from the CT scanned femur model and those from the CAD femur model were then compared. We found general agreement in trends but some quantitative differences most likely due to the geometric differences between the digitally reconstructed femur model and the simplified CAD models. As postulated by others, our results support the hypothesis that the bone curvature is a trade-off between the bone strength and its bending predictability. Bone curvature increases bending predictability at the expense of load carrying capacity.

<p>Induction machines convert more than 55% of electrical energy into various other forms in industrial and domestic environments. Improved performance, especially by reduction of losses in induction machines hence can significantly reduce consumption of electricity. Many design and control methods are adopted to make induction machines work more efficiently, however certain design compromises are inevitable, such as skewing the rotor to improve the magnetic noise and torque characteristics increase the cross current losses considerably in a cage rotor, degrading the efficiency of the motor. Crosscurrent losses are the dominating stray losses which are dependent on several factors among them are percentage skew and the contact resistance between the rotor bars and laminations. It is shown in this thesis that implementing a design change which has non-skewed asymmetrical distribution of rotor slots can serve the same purpose as skewing i.e., reduction of the magnetic noise, thereby avoiding the negative effects of skewing the rotor slots especially by reducing the cross-current losses.</p><p>Two design ethodologies to introduce asymmetry in rotor slots are proposed and the key performance characteristics like torque ripple, radial air gap forces are computed both numerically and analytically. Radial forces obtained from the finite element method are coupled to the analytical tool forcalculating the magnetic noise. A spectral method to calculate and separate the radial forces into vibration modes and their respective frequencies is proposed and validated for a standard 4-pole induction motor. The influence of rotor slot number, eccentricity and skew on radial forces and magnetic noise are studied using finite element method in order to understand the vibrational and acoustic behavior of the machine, especially for identifying their sources. The validated methods on standard motors are applied for investigating the asymmetrical rotor slot machines.</p><p>Radial air gap forces and magnetic noise spectra are computed for the novel dual and sinusoidal symmetrical rotors and compared with the standard symmetrical rotor. The results obtained showed reduced radial forces and magnetic noise in asymmetrical rotors, both for the eccentric and noneccentric cases. Based on the results obtained some guide lines for designing  asymmetrical rotor slots are established. Magnitudes of the harmful modes of vibration observed in the eccentric rotors, which usually occur in reality, are considerably reduced in asymmetrical rotors showing lower sound intensity levels produced by asymmetrical rotors. The noise level from mode-2 vibration in a 4-pole standard 15 kW motor running with 25% static eccentricity is decreased by about 6 dB, compared to the standard rotors. Hence improved performance can be achieved by removing skew which reduces cross current losses and by employing asymmetrical rotor slots same noise level can be maintained or can be even lowered.</p><p> </p><p> </p>

Na análise de estruturas é comum a consideração da concentricidade entre vigas e placas. Estudos numéricos em pavimentos de laje nervurada, onde os espaçamentos das vigas são pequenos, mostram que a consideração da excentricidade entre placa e a viga resultam em redução dos deslocamentos na estrutura, entretanto não existem estudos sobre a influência da excentricidade em pavimentos com poucas vigas. Este trabalho apresenta a análise numérica de pavimentos com dimensões usuais considerando ou não a excentricidade com o objetivo de verificar a influência da excentricidade no comportamento da estrutura. As análises mostraram diferenças de deslocamentos e tensões nas estruturas estudadas. O efeito de excentricidade pode ser incluído através da modificação da matriz de rigidez do elemento finito de viga. Todos os pavimentos foram analisados com o software ANSYS com elementos de placa e viga que representassem os modelos do trabalho. / It\'s usual practice on structural analysis of buildings slabs to assume the concentricity between plates and beams. Numerical studies in waffle-slabs, where the distance between beams is small, showed that the eccentricity of beam to plate results in reduction of stresses and displacements of the system, however there is not similar study about the influence of eccentricity in slabs with few beams. This work presents numerical analysis results of at slabs with usual dimensions considering or not plate-beam eccentricity, aiming at evaluating its influence in structural behavior. The analysis showed differences of displacements and stress in studied structures. The effects of eccentricity can be included by modifying the stiffness matrix of the beam finite element. All slabs were analyzed with ANSYS program with suitable beam and plate elements.

[pt] A presente dissertação trata do projeto, construção e ensaio preliminar de um novo modelo do compressor Kopelrot. É uma máquina de deslocamento positivo baseada em seis patentes depositadas desde 1998. Esta tecnologia está em desenvolvimento há aproximadamente 8 anos, tendo gerado artigos e dissertações, assim como a construção de dois protótipos. É apresentada, inicialmente, uma revisão dos trabalhos publicados sobre a tecnologia Kopelrot. Foram construídos junto ao novo modelo de compressor Kopelrot um novo sistema de acionamento e uma base para a fixação de ambos a um motor elétrico. Durante a elaboração dos desenhos foram realizadas simulações preliminares da geometria para definir a fabricação de algumas peças importantes. A base permite regular a excentricidade entre os eixos de centro do compressor e do sistema de acionamento e, dessa forma, variar a vazão volumétrica do compressor. Simulou-se a variação de volume no interior da câmara com o conjunto compressor Kopelrot/Sistema de acionamento, ajustado para 5 excentricidades diferentes, a fim de mapear o comportamento do Kopelrot quando sua capacidade é variada, deslocando-se os eixos de centro do compressor e do sistema de acionamento. Para as excentricidades escolhidas, foram calculadas, a partir de modelo termodinâmico simplificado, as variações de pressão, temperatura e massa no interior da câmara do compressor. Valores globais de potência consumida e eficiência volumétrica também foram calculados. Durante o funcionamento do protótipo identificaram-se alguns problemas tipicamente encontrados em tecnologias inovadoras. Devido a esses problemas, não foi possível a realização dos testes do compressor operando em condições normais de pressão. / [en] The present dissertation addresses the design, construction, simulation and preliminary tests of an innovative positive displacement rotary compressor. A review is presented on the previous works, papers and dissertations, based on this new this new Kopelrot technology. A new prototype, employing a new driving system, was manufactured. The main feature of the machine is that, by adjusting the eccentricity between compressor cylinder and driving mechanisms axis, a variable capacity device is obtained. Design, manufacturing and assembly of components and subsystems of the compressor are presented in detail. Design data of the compressor allowed for a simple thermodynamic simulation model to be developed. Main conclusions of the simulation are that a full positive displacement compression cycle can be attained with the Kopelrot technology and that use of discharge and suction valves is required in order to have the compressor operating under different conditions.

The aim of the thesis is to focus on the different methods of analysis of vibration signals. Focusing on the physical fundamentals of vibrations and a description of their origin in an electrical machine. Describe the vibration sources from mechanical across the electromagnetic to the aerodynamic. Defining the current defects of electric machines and sensors suitable for the measurement of vibrations in an electric machines. Introduction to the methods of analysis of vibration signals in the time and frequency domain. Then using some of these methods for the analysis of vibration signals measured asynchronous motors with different manufacturer defined production defect. The conclusion is composed from the comparison between measured and analyzed results.