xii, 205 leaves : photos., diags., tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1978

The need to attenuate noise transmitted into enclosed spaces such as aircraft cabins, automobiles and mining cabins has provided the impetus for many active noise control studies. Studies into active interior noise control began with a pressure squared cost function utilising multiple error sensors and control sources in an attempt to produce global control of the interior sound field. This work found problems with observability of the primary disturbances and a large number of error sensors and control sources were required to produce global control. Since this early work in the 1980's, many new acoustic based cost functions have been developed to improve on the performance of the pressure squared cost function. This thesis will focus on one novel acoustic cost function, virtual error sensing. Virtual error sensing is a relatively new technique which produces localised zones of attenuation at a location remote to the physical sensors. The practical advantage of this method is the people within these enclosed spaces are able to observe a reduction in sound pressure level without their movement being restricted by error sensors located close to their ears. The aim of this thesis is to further investigate the performance of forward-difference virtual error sensors in order to understand the factors that affect the accuracy of the pressure prediction at the virtual location and use this information to develop more accurate and efficient forward- difference virtual sensors. These virtual sensors use linear arrays of microphones containing two or more microphone elements and a linear or quadratic approximation is used to predict the sound at the virtual location. The prediction method determines the weights applied to each microphone signal to predict the sound pressure level at the virtual location. This study investigates susceptibility of the sensors to corruption as a result of phase and sensitivity mismatch between the microphones, as well as in the location of the elements in the error sensing array. A thorough error analysis of the forward-difference virtual microphones was performed in a one-dimensional sound field and in a plane wave sound field. The accuracy of the quadratic virtual microphone was found to be strongly affected by the presence of short wavelength extraneous noise. From this study, two novel virtual error sensing techniques were developed, namely; higher-order virtual sensors and adaptive virtual sensors. The higher-order virtual error sensors still employ the linear and quadratic prediction method but extra microphone elements are added to the array. The aim of these higher-order virtual microphones is to produce a more accurate prediction of the pressure at the virtual location by spatially filtering out any short wavelength extraneous noise that may corrupt the prediction. These virtual sensors were tested in a realtime control scenario in both a one-dimensional reactive sound field and in a free field. This work found that the higher-order virtual microphones can improve the prediction accuracy of the original virtual sensors but are still prone to problems of phase, sensitivity and position errors. Finally, the adaptive LMS virtual sensors were investigated in a SIMULINK simulation and tested experimentally using real-time control in a one-dimensional sound field. It was hoped that an adaptive LMS algorithm could overcome previous difficulties arising from inherent and transducer errors by adapting the weights of the signals from the sensing elements which form the array. The algorithm adapts the sensing microphone signals to produce the same signal as the microphone at the virtual location. Once this has been achieved, the sensing microphone weights are fixed and the microphone at the virtual location is removed, thus creating a virtual microphone. The SIMULINK simulation allowed the performance of the fixed weight and virtual microphones to be investigated in the presence of only phase errors, sensitivity errors and position errors and in the presence of all three combined. This work showed that the adaptive virtual sensors had the ability to compensate for the errors. The number of modes used in the simulations was varied to observe the performance of all virtual sensors in the presence of higher-order modes. The prediction accuracy of the fixed weight virtual sensors was found to be greatly affected by the presence of higher-order modes. The use of the adaptive virtual microphones to produce localised zones of quiet was examined experimentally using real-time control. The study found the real-time control performance is superior to that of the fixed weight higher-order virtual microphones and the original forward-difference virtual microphones. / Thesis (Ph.D.)--School of Mechanical Engineering, 2003.

<p>Tendon healing is a slow process and the tendon may not regain its initial mechanical properties after rupture. Mechanical stimuli have shown to have positive effect on tendon healing. This study is the first to investigate the effect of vibration stimuli on healing tendons. Vibration was also compared to treadmill running, which has previously been used for mechanical stimuli.63 female Sprauge-Dawley rats were used. A 3 mm segment was removed from the Achilles tendon and the tendon was left to heal. The animals were subjected to 15 min of daily exercise, vibration or treadmill running or acted as controls without exercise. The study was divided into three experiments. Experiment 1; the animals had full time cage activity and was randomized into running, vibration and control group. Experiment 2; the animals were unloaded and randomized into vibration, running and control group. There was also a control group with full time cage activity in experiment 2. Experiment 3; the animals were unloaded and randomized into vibration and placebo group. 14 days after surgery the animals were killed and mechanical testing of the Achilles tendons was performed. The results showed no significant difference between the groups in experiment 1. Experiment 2 showed that controls with full time cage activity had higher peak load, stiffness and cross sectional area than unloaded running, vibration and control groups. In experiment 3, there was no significant difference between vibration and placebo group. In conclusion, this study shows that vibration, as applied here, does not affect tendon healing.</p>

L'objectif de ce travail est d'établir un cadre théorique favorable à la détermination et au contrôle des efforts radiaux dans les moteurs électriques synchrones. Le besoin d'une modélisation susceptible d'être utilisée pour le contrôle en temps réels des efforts écarte naturellement les classiques méthodes numériques de calcul des champs. Aussi, notre volonté de représenter de façon la plus synthétique qui soit l'état magnétique de la machine nous conduit à proposer une modélisation qui intègre de façon intrinsèque un maximum d'informations concernant la machine comme le caractère localisé des courants dans les encoches et les nombreuses symétries liées au bobinage de la machine. Cette modélisation est basée sur une discrétisation du champ d'entrefer qui consiste à considérer le champ constant sous chaque dent statorique.

Residual vibrations degrade the performance of many systems. Due to the lightweight and flexible nature of space structures, controlling residual vibrations is especially difficult. Also, systems such as the Space Shuttle remote Manipulator System have frequencies that vary significantly based upon configuration and loading. Recently, a technique of minimizing vibrations in flexible structures by command input shaping was developed. This document presents research completed in developing a simple, closed- form method of calculating input shaping sequences for two-mode systems and a system to adapt the command input shaping technique to known changes in system frequency about the workspace. The new techniques were tested on a three-link, flexible manipulator.

In this study, particle impact damping is measured for a cantilever beam with a particle-filled enclosure attached to its free end. Many particle materials are tested: lead spheres, steel spheres, glass spheres, tungsten carbide pellets, lead dust, steel dust, and sand. The effects of particle size are also investigated. Particle diameters are varied from about 0.2 mm to 3 mm. The experimental data collected is offered as a resourceful database for future development of an analytical model of particle impact damping.

Internal friction has been known to be a cause of whirl instability in built-up rotors since the early 1900's. This internal damping tends to make the rotor whirl at shaft speeds greater than a critical speed, the whirl speed usually being equal to the critical speed. Over the years of research, though models have been developed to explain instabilities due to internal friction, its complex and unpredictable nature has made it extremely difficult to come up with a set of equations or rules that can be used to predict instabilities accurate enough for design. This thesis deals with suggesting improved methods for predicting the effects of shrink fits on threshold speeds of instability. A supporting objective is to quantify the internal friction in the system by measurements. Experimental methods of determining the internal damping with non-rotating tests are investigated, and the results are correlated with appropriate mathematical models for the system. Rotating experiments were carried out and suggest that subsynchronous vibration in rotating machinery can have numerous sources or causes. Also, subsynchronous whirl due to internal friction is not a highly repeatable phenomenon.

No description available.

Tendon healing is a slow process and the tendon may not regain its initial mechanical properties after rupture. Mechanical stimuli have shown to have positive effect on tendon healing. This study is the first to investigate the effect of vibration stimuli on healing tendons. Vibration was also compared to treadmill running, which has previously been used for mechanical stimuli.63 female Sprauge-Dawley rats were used. A 3 mm segment was removed from the Achilles tendon and the tendon was left to heal. The animals were subjected to 15 min of daily exercise, vibration or treadmill running or acted as controls without exercise. The study was divided into three experiments. Experiment 1; the animals had full time cage activity and was randomized into running, vibration and control group. Experiment 2; the animals were unloaded and randomized into vibration, running and control group. There was also a control group with full time cage activity in experiment 2. Experiment 3; the animals were unloaded and randomized into vibration and placebo group. 14 days after surgery the animals were killed and mechanical testing of the Achilles tendons was performed. The results showed no significant difference between the groups in experiment 1. Experiment 2 showed that controls with full time cage activity had higher peak load, stiffness and cross sectional area than unloaded running, vibration and control groups. In experiment 3, there was no significant difference between vibration and placebo group. In conclusion, this study shows that vibration, as applied here, does not affect tendon healing.

No description available.