A problem of interest in the power industry is the mitigation of severe torsional oscillations induced in turbine-generator shaft systems due to Subsynchronous Resonance (SSR). SSR occurs when a natural frequency of a series compensated transmission system coincides with the complement of one of the torsional modes of the turbine-generator shaft system. Under such circumstances, the turbine-generator shaft system oscillates at a frequency corresponding to the torsional mode frequency and unless corrective action is taken, the torsional oscillations can grow and may result in shaft damage in a few seconds. <p> This thesis reports the use of a supplementary controller along with the Voltage Source Converter (VSC) HVDC back-to-back active power controller to damp all SSR torsional oscillations. In this context, investigations are conducted on a typical HVAC/DC system incorporating a large turbine-generator and a VSC HVDC back-to-back system. The generator speed deviation is used as the stabilizing signal for the supplementary controller. <p>The results of the investigations conducted in this thesis show that the achieved control design is effective in damping all the shaft torsional torques over a wide range of compensation levels. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating series capacitor compensated transmission lines and VSC HVDC back-to-back systems.

A problem of interest in the power industry is the mitigation of severe torsional oscillations induced in turbine-generator shaft systems due to Subsynchronous Resonance (SSR). SSR occurs when a natural frequency of a series compensated transmission system coincides with the complement of one of the torsional modes of the turbine-generator shaft system. Under such circumstances, the turbine-generator shaft system oscillates at a frequency corresponding to the torsional mode frequency and unless corrective action is taken, the torsional oscillations can grow and may result in shaft damage in a few seconds. <p> This thesis reports the use of a supplementary controller along with the Voltage Source Converter (VSC) HVDC back-to-back active power controller to damp all SSR torsional oscillations. In this context, investigations are conducted on a typical HVAC/DC system incorporating a large turbine-generator and a VSC HVDC back-to-back system. The generator speed deviation is used as the stabilizing signal for the supplementary controller. <p>The results of the investigations conducted in this thesis show that the achieved control design is effective in damping all the shaft torsional torques over a wide range of compensation levels. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating series capacitor compensated transmission lines and VSC HVDC back-to-back systems.

The purpose of this study was to use EMG data of the erector spinae muscles synchronized with three-dimensional video techniques to determine the body's responses to asymmetric lifting under weight belt conditions. The subjects performed static maximum voluntary exertions and dynamic lifts from 0° and 45° from the midline of the body. Three weight belt conditions were used. EMG data revealed significant differences in EMG variables with belt conditions. Weight belt use decreased burst area, peak voltage, and maximum frequency. Kinematic data indicated a significant difference in the left knee and left and right elbow range of motion when the type of lift, symmetric or asymmetric, was considered. Lifting technique also produced a significant effect on the maximum and minimum velocity of the center of mass. The results of the study indicate that weight belt use is an effective means of reducing spinal compression and thus may be helpful in preventing low back injury. / School of Physical Education

The occupation of sheep-shearing is classified as heavy to very-heavy physical work requiring a high level of energy expenditure while performing a repetitive task in a predominantly sustained trunk flexion posture. The task is further complicated by unpredictable animal behaviour. Shearing is considered to carry a high risk of injury particularly to the lumbar spine and epidemiological studies have demonstrated that the prevalence of low back pain (LBP) in shearers is high relative to other occupations. The emergence of a commercial shearing-aid (Warrie Back-Aid TM) that is purported to decrease loading on the spine, reduce injury rate and alleviate symptoms of spinal origin has been welcomed by many sectors of the wool-harvesting industry. However, the precise biomechanical influence of the Warrie Back-Aid TM (WBA) on the sheep-shearing task has not been quantified. The purpose of this study was to investigate the effect of the WBA on three-dimensional kinematics and electromyography of the trunk for 12 experienced shearers during the occupational task of sheep-shearing. Sheep-shearing is a highly patterned process comprised of specific interlinked phases. Nine distinct phases of the shearing-task where the harness was worn during the removal of the sheep�s fleece were investigated. The study used an opto-electronic motion analysis system and rigid body dynamic modelling. The shearer�s trunk and pelvis were considered as a series of three coupled rigid segments; pelvis, lumbar, and thorax with four passive retro-reflective markers defining each segment. The kinematic variables of angular displacement, velocity and acceleration at the thoraco-lumbar and lumbo-pelvic joint centres were calculated for each shearer while shearing with and without the WBA. An eight channel sEMG telemetry system was used to simultaneous record activity in four pairs of trunk muscles. Temporal analysis of the sEMG signal gave information on the duration and relative intensity of trunk muscle activity. The results demonstrated that the task of sheep-shearing required endurance-based muscle activity and the adoption of quasi-static posturing combined with complex asymmetrical trunk motion for extensive periods of the task time. There was considerable variability in the trunk motion of individual shearers despite the pattern-taught and repeatable nature of the shearing task. The introduction of the WBA had no effect on the time taken to shear or trunk kinematics however it resulted in reductions in muscular activity of the trunk extensors. When the complete shearing task was analysed there was a statistically significant reduction in mean intensity of muscle activity for the left multifidus (p = 0.010), right multifidus (p = 0.001), right iliocostalis (p = 0.004) and right longissimus (p = 0.002) when the WBA was used. A reduction in muscular activity of the trunk extensors during the sheep-shearing task may result in a decrease in spinal loading, energy expenditure and muscular fatigue. The clinical recommendation based on the biomechanical results of this and other studies is that the WBA should be incorporated into the practice of sheep-shearing to assist in the reduction of inherent risks associated with the shearing task. Prospective studies into the effect of the harness on LBP are required to endorse this recommendation.

Thesis--Kansaneläkelaitos, 1989. / Added t.p. with thesis statement inserted.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Massas de pães são preparadas a partir da mistura de farinha de trigo, água, sal e fermento. Ao entrar em contato com a água e sofrer amassamento mecânico, a farinha de trigo tem a propriedade, quase exclusiva, de produzir uma massa coesa e viscoelástica, por conter proteínas formadoras de glúten. O processo de mistura pela qual passam as massas de pães, seguido de etapas de fermentação é fundamental para o bom desenvolvimento da massa e qualidade final do pão acabado. As análises de textura (back extrusion e extensibilidade) e volume, em massa crua de pão, podem avaliar o desenvolvimento e a qualidade de massas, eficácia de formulações e a eficiência dos ingredientes usados na melhoria do desenvolvimento da massa e do pão acabado. O projeto teve como objetivo elaborar formulações de massas de pães por diferentes processos de fermentação e testá-las através das análises de textura por extensibilidade e back extrusion, e volume sendo esta última sugerida para esse fim. Também foi testada a substituição de parte da farinha de trigo por triticale. As formulações utilizadas incluíram diferentes métodos de preparo de massas, como método direto e indireto, sendo nove formulações propostas. Pelo método direto o fermento seco instantâneo é adicionado diretamente à farinha e em seguida os demais ingredientes da formulação são adicionados, em uma única fase, seguido das etapas de mistura e fermentação. Já para as massas elaboradas de forma indireta, preparou-se uma massa fermentada denominada esponja, que foi feita com parte da farinha e da água e todo fermento seco instantâneo da formulação, deixada fermentar durante uma hora. Em uma segunda fase, a esponja foi adicionada ao restante dos ingredientes, seguido das etapas de mistura e fermentação. Os resultados das análises mostraram as diferenças do comportamento reológico de massas preparadas por diferentes processos fermentativos e a influência dos ingredientes como, o iogurte, adicionado por conter substâncias que são encontradas em pães fermentados naturalmente, resultando no aumento dos parâmetros reológico das massas contendo esse ingrediente. / Dough of bread are prepared from the mixture of flour wheat, water, salt and yeast. By contacting the water and suffer mechanical kneading the flour has property, almost exclusively, to produce a cohesive dough and viscoelasticity, which contain gluten-forming proteins. The mixing process through which runs the dough of bread, followed stages of fermentation is essential for the dough development and final quality of the finished bread. The analysis of texture (back extrusion and extensibility) and the volume dough of raw bread, can measure the development and quality of dough, formulation\'s effectiveness and efficiency of ingredients used in enhancing development of dough and the finished bread. The project had the object to develop formulations of doug for different fermentation processes and test them through the analysis of texture by extensibility and back extrusion, the latter being suggested for this purpose. Also was tested the substitution of part of the flour for triticale. The formulations used included different methods of preparation of dough, as a direct and indirect method, being nine formulations proposed. Through direct method the instant dry yeast is added directly to flour and then other ingredients formulation are added in a single phase, followed by stages of mixing and fermentation. To the dough produced in an indirect way, has been prepared a fermented dough called sponge, which is made with part of the flour and water and all instant dry yeast used in the formulation, and left to ferment for one hour. In a second phase, the sponge was added to the rest of the ingredients, followed the steps of mixing and fermentation. The analysis results showed the differences of rheological behavior of doughs prepared by different fermentation processes and the influence of ingredients as yogurt, added to contain substances that are found in naturally fermented breads, resulting in the increase of rheological parameters of the dough containing this ingredient.

No description available.

No description available.

In a world where fuel economy and crash safety is becoming an important factor in the automotive industry, the need for materials with very high strength-to-weight ratio is growing rapidly. One of the materials used for this purpose is the boron steel 22MnB5. Since the material has very high mechanical yield limit it is hard to produce parts using cold forming, which is the standard procedure for sheet metal forming. Therefore, the use of hot stamping is increasing. Hot stamping enables manufacturing of boron steel parts with good dimensional accuracy and low spring back. However, some amount of spring back is still present during the process. In this thesis, spring back of a hot formed 22MnB5 A-pillar is investigated using computer simulations in the software LS-DYNA. The main focus was to develop a process for simulating spring back in hot stamping. The work started with simulations of the forming and quenching stages of the hot stamping process, both on a full size and on a smaller section of the blank. Simultaneously as the simulations, a literature study was also conducted. The literature study was aimed at finding hints and information on how to build the simulations. Furthermore, interviews were made with experts on both LS-DYNA and hot stamping. A process for spring back evaluation was then created and written as an LS-DYNA keywordfile. In the developed spring back simulation, the part is taken out of the press right after the quenching is finished and placed in a space where it can cool and move freely. The simulation is conducted until the part reaches room temperature. After the quenching is done, data containing temperatures, stresses and strains of the part is exported. This data is then included in the spring back simulation where the part is cooled to room temperature. During the cooling, the stresses, strains and temperatures are equalized until the spring back reaches a steady state. The results indicate that the developed method for spring back evaluation can be used to foresee shape deviations for the intended part and process.