No description available.

Thesis (MScIng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Pour l’industrie automobile, l’identification de sources vibratoires dans un but d’amélioration du confort acoustique est un enjeu majeur. L’identification d’une source vibratoire se résume le plus souvent à la connaissance de sa matrice des fonctions de transfert et des efforts vibratoires au niveau des points de fixation entre la source et son récepteur. Le moyen le plus simple pour effectuer des mesures d’efforts vibratoires est de réaliser des mesures directement à l’aide de capteurs d’effort. Cependant, pour diverses raisons pratiques (accessibilité, encombrement... ), ces efforts vibratoires sont bien souvent impossibles à mesurer de manière directe. Dans ces circonstances on a alors recours à une mesure indirecte des efforts à partir des réponses de la structure en fonctionnement et d’un modèle dynamique de la structure. La mise en œuvre d’une telle démarche est souvent difficile car les problèmes inverses sont en général mal posés au sens d’Hadamard. L’objectif du présent travail de thèse a été l’amélioration de la robustesse de l’identification de source vibratoire par méthode inverse. Le manuscrit est découpé en cinq chapitres : — Le premier chapitre aborde en détail la problématique de la reconstruction des efforts par méthode inverse. On y présente un état de l’art permettant d’appréhender les enjeux et les difficultés de la reconstruction des efforts par méthode inverse. Nous explicitons également dans ce chapitre un certain nombre de relations permettant le couplage des matrices des fonctions de transfert, la caractérisation de la réceptance d’une source vibratoire, la reconstruction des efforts transmis à l’interface, des "réponses libres" et des "forces de blocage" dans le cas général. — Dans le second chapitre sont présentées, dans un premier temps, certaines des méthodes de régularisation du problème inverse les plus utilisées puis dans un second temps nous proposons deux approches de régularisation originales : — La méthode de sélection de points de mesure "CIM". L’objectif de cette méthode est de positionner de manière optimale un ensemble de capteurs de réponse sur la structure étudiée. La méthode opère par itérations initialisées par une matrice des fonctions de transfert contenant tous les points de mesure envisageables et en éliminant progressivement ces derniers pour ne conserver au final que les points de mesure offrant le maximum d’information. — Afin d’éliminer le bruit pouvant entacher les fonctions de transfert et donc améliorer le conditionnement du problème, nous proposons de les lisser à l’aide d’une décomposition modale. Pour ce faire, nous exprimons les fonctions de transfert en fonction des paramètres modaux de la structure, obtenus à l’aide d’une analyse modale expérimentale. Ces méthodes de régularisation ont été validées sur un système numérique simple mais représentatif de la transmission d’efforts vibratoires. — Dans le troisième chapitre nous abordons la prise en compte des incertitudes lors de la reconstruction des efforts par méthode inverse. Nous y présentons en détail la méthode de propagation de l’incertitude nommée "méthode du chaos polynomial". Cette méthode formalise, par un développement en série de polynômes de variables aléatoires, la séparation entre la partie déterministe et la partie stochastique d’une fonction aléatoire. Nous proposons d’utiliser cette méthode afin de propager vers la solution du problème inverse l’incertitude entachant les réponses et le modèle de la structure. Cette stratégie de résolution a été appliquée à un problème numérique représentatif et a fait la preuve de son efficacité comparativement à une méthode de Monte Carlo. — Dans le quatrième chapitre, nous présentons une méthode originale de caractérisation de sources vibratoires que nous avons nommé la méthode du "banc observant". La caractérisation d’une source vibratoire nécessite généralement d’effectuer des mesures au niveau de son interface. [...] / For the automotive industry, the quantification of vibratory forces is a key challenge to improve acoustic comfort. The identification of a vibratory source comes down to the knowledge of its matrix of transfer functions and vibratory forces at the points of attachment between the source and its receiver. The easiest way to measure vibration forces is to take measurements directly using force sensors. However, for various practical reasons, these vibratory forces are often impossible to measure directly. In these circumstances, an indirect measure of vibratory forces is used. The implementation of this approach is often difficult because the inverse problems are generally ill posed in the sense of Hadamard. The objective of this study was to improve the robustness of vibratory source identification by inverse method. The manuscript is divided into five chapters : — The first chapter deals in detail with the problem of the measurement of vibratory forces by inverse method. It presents a state of the art to understand the difficulties of identifying vibrational forces by inverse method. We also explain the relations allowing the coupling of two matrices of transfer functions, the characterization of the receptance of a vibratory source, the reconstruction of the forces transmitted to the interface, the "free answers" and the "blocked forces" in the general case. — In the second chapter are presented, first, some of the methods of regularization of the inverse problem the most used then in a second time we propose two original approaches of regularization : — The method of selecting measuring points "CIM". The objective of this method is to optimally position a set of sensors on the studied structure. The method operates by iterations initialized by a matrix of the transfer functions containing all the possible measurement points and by progressively eliminating them so as to keep only the measurement points offering the maximum of information. — In order to eliminate the noise that could tarnish the transfer functions and thus improve the conditioning of the problem, we propose to smooth them using a modal decomposition. To do this, we write the transfer functions according to the modal parameters of the structure, obtained using an experimental modal analysis. These regularization methods have been validated on a simple numerical system but representative of the transmission of vibratory forces. — In the third chapter we take into account the uncertainties in the reconstruction of the inverse method efforts. We present in detail the method of propagation of uncertainty called "Polynomial Chaos". This method formalizes, by a series development of polynomials of random variables, the separation between the deterministic part and the stochastic part of a random function. We propose to use this method in order to propagate to the solution of the inverse problem the uncertainty affecting the responses and the model of the structure. This strategy has been applied to a representative numerical problem and has proved its effectiveness compared to a Monte Carlo method. — In the fourth chapter, we present an original method of characterization of vibratory sources that we have named the "observing bench" method. The identification of a vibratory source usually requires measurements at its interface. [...]

Vibratory gyroscopes are inertial sensors, used to measure rotation rates in a number of applications. The performance of these sensors is limited by imperfections that occur during manufacture of the resonators. The effects of resonator imperfections, in piezoelectric vibratory gyroscopes, were studied. Hamilton's principle and the Rayleigh-Ritz method provided an effective approach for modeling the coupled electromechanical dynamics of piezoelectric resonators. This method produced accurate results when applied to an imperfect piezoelectric vibrating cylinder gyroscope. The effects of elastic boundary conditions, on the dynamics of rotating thin-walled cylinders, were analyzed by an exact solution of the Flügge shell theory equations of motion. A range of stiffnesses in which the cylinder dynamics was sensitive to boundary stiffness variations was established. The support structure, of a cylinder used in a vibratory gyroscope, should be designed to have stiffness outside of this range. Variations in the piezoelectric material properties were investigated. A figure-of- merit was proposed which could be used to select an existing piezoceramic material or to optimize a new composition for use in vibratory gyroscopes. The effects of displacement and velocity feedback on the resonator dynamics were analyzed. It was shown that displacement feedback could be used to eliminate the natural frequency errors, that occur during manufacture, of a typical piezoelectric vibrating cylinder gyroscope. The problem of designing the control system to reduce the effects of resonator imperfections was investigated. Averaged equations of motion, for a general resonator, were presented. These equations provided useful insight into the dynamics of the imperfect resonator and were used to motivate the control system functions. Two control schemes were investigated numerically and experimentally. It was shown that it is possible to completely suppress the first-order effects of resonator mass/stiffness imperfections. Damping imperfections, are not compensated by the control system and are believed to be the major source of residual error. Experiments performed on a piezoelectric vibrating cylinder gyroscope showed an order of magnitude improvement, in the zero-rate offset variation over a temperature range of 60°C, when the control systems were implemented. / Ph. D.

Manufacturing processes inevitably induce a state of residual stress into materials and products. These residual stresses pose a large potential problem, in terms of dimensional stability and reduced fatigue life. Ideally, residual stresses should be reducible to low levels. There are three methods in general usage for the relaxation of these stresses, - Annealing, Shakedown and Vibratory Stress Relief (VSR). A previous study had suggested that vibration during and/or after welding may usefully modify residual stresses due to welding. This has been termed Vibratory Weld Conditioning (VWC). A comparative study of the methods is presented in section 1.4. The use of VSR, though widespread, has been adopted on a case-by-case basis, due to the lack of understanding of the processes at work. The purpose of this work was to investigate and validate the VSR/VWC method as a proposed alternative to the processes mentioned above. In order to do this a series of tests were devised in which the specimens were welded as a mechanism of stress induction. The residual stresses were measured before and after welding and vibration by means of a scanning X-ray diffractometer. In Chapter 1, the study of Residual Stress (source, formation etc), Welding Metallurgy and a comparison of VSR/VWC with other treatment methods are presented. In Chapter 2, a detailed review of literature is presented, where the accessible literature on VSR/VWC to date are included. In Chapter 3, the theoretical background of Modal Analysis, the Measurement of Dynamic Induced Stress and Measurement of Residual Stressesis discussed. In Chapter 4, the FE analysis of different structures is presented. In the FE analysis, different properties of the structures were determined using the FE model to aid the VSR/VWC study. The experimental investigations are presented in Chapter 5, which is divided into the following parts: Modal Analysis (experimental), Calibration of the X-ray measurements, VSR/VWC treatments, Cryogenic treatment, Fatigue Test and Metallurgical Investigation of VSR/VWC treated specimens. At the outset of the experimental work, the calibration of the X-ray diffractometer was carried out. After calibration of the X-ray and the X-ray Elastic Constant the error band of the diffractometer was significantly reduced. The practical modal analysis of the "8" frame was carried out to determine the modal characteristics of the frame to aid the VSR investigation of the frame. The VSR/VWC treatments are divided into "during welding" and "post weld" treatments and are presented in 10 different experiments. First, the "during welding" treatments were carried out. Investigation was started with application of tensile and compressive static stress to the specimens during welding and cooling. It was observed that the tensile induced stress decreased, and compressive induced stress increased the residual stresses. Rigid body motion (RBM) vibration showed no effect on the residual stresses. The cantilever beam test of the flexural vibration test showed some important characteristics, where the longitudinal residual stresses were found to decrease with application of small-induced stress. An increase in applied stress or time of vibration did not cause any more reduction. The transverse residual stresses increased with application of small-induced stresses. With increase in the applied stress the residual stresses decreased. High frequency vibration in both RBM and flexural vibration was found to be ineffective in reducing the residual stresses. The flexural vibration of the Four-Roller Supported beam showed a very confusing result, where no particular trend of the residual stresses was found. The combined mode of vibration (longitudinal and flexural) treatment showed no effect on residual stresses. The "post weld" treatment of the specimens showed a significant reduction in the residual stresses, where the reduction in the residual stresses were found to be a function of applied stress, while the vibration time effect was found to be negligible. A complex shape of reduction in the residual stresses were found along the width of the specimens, which made it impossible to develop any plastic flow model for the reduction in the residual stresses. Torsional test revealed a very important property of the residual stresses, where the residual stresses were found to decrease by a significant amount with application of very small induced stress. High induced stress only redistributed the residual stresses. Cryogenic treatment caused no reduction in the residual stresses. Contrarily the same specimen showed a significant reduction after VSR treatment. The fatigue test showed an increased fatigue life of the VSR treated specimens, while the thermally treated specimens showed a decreased fatigue life. The vibrated specimens showed highly oriented ferrite crystals in directions with Miller [111] to the stress axis. The hardness of the VSR treated specimens was found to increase significantly in comparison to the unvibrated specimens.

In this report a relationship is established between the variables of compaction temperature, compaction effort, mixture gradation and, density, air void content and stability of asphalt mixtures. The Marshall method of mix design was used, and Vibratory Kneading Compactor was utilized for compaction. Results include Marshall Stability and density-air void analysis for 4 and 6-inch specimens. It was found that the densities generally increased with increase of compaction temperatures and compaction efforts. From selected sets of 6-inch specimens, 4-inch cores were obtained. Density and stability studies were carried out on these cores and the results obtained were found to have the same trends. The air void content and voids in the mineral aggregates decreased with the increase of compaction effort. Stability increased with the increase in density. All the results found, indicate strong effects of compaction temperature and compactive effort on the amount of air voids, VMA, density, and stability of the mixes used.

abstract: Humans constantly rely on a complex interaction of a variety of sensory modalities in order to complete even the simplest of daily tasks. For reaching and grasping to interact with objects, the visual, tactile, and proprioceptive senses provide the majority of the information used. While vision is often relied on for many tasks, most people are able to accomplish common daily rituals without constant visual attention, instead relying mainly on tactile and proprioceptive cues. However, amputees using prosthetic arms do not have access to these cues, making tasks impossible without vision. Even tasks with vision can be incredibly difficult as prosthesis users are unable to modify grip force using touch, and thus tend to grip objects excessively hard to make sure they don’t slip. Methods such as vibratory sensory substitution have shown promise for providing prosthesis users with a sense of contact and have proved helpful in completing motor tasks. In this thesis, two experiments were conducted to determine whether vibratory cues could be useful in discriminating between sizes. In the first experiment, subjects were asked to grasp a series of hidden virtual blocks of varying sizes with vibrations on the fingertips as indication of contact and compare the size of consecutive boxes. Vibratory haptic feedback significantly increased the accuracy of size discrimination over objects with only visual indication of contact, though accuracy was not as great as for typical grasping tasks with physical blocks. In the second, subjects were asked to adjust their virtual finger position around a series of virtual boxes with vibratory feedback on the fingertips using either finger movement or EMG. It was found that EMG control allowed for significantly less accuracy in size discrimination, implying that, while proprioceptive feedback alone is not enough to determine size, direct kinesthetic information about finger position is still needed. / Dissertation/Thesis / Masters Thesis Bioengineering 2016

M.Tech. / There is a general lack of understanding of the laboratory compaction test based on the vibrating hammer method. The impact method of testing soil in the laboratory is conservatively used by engineers for design and construction control purposes even when the specified mode of compaction on site is vibratory. Furthermore, the effects of vibratory compaction are not fully understood, and hence this mode of compaction in the field has not always been effectively utilized. The objective of this research project was to determine whether the vibrating hammer method could be used in the laboratory for design and control purposes, through an investigation of its operating characteristics, and a comparison of its effectiveness against that of the impact method, following a study of the compaction properties of a range of different soils used in road and embankment construction. The results of the study showed that the vibrating hammer can be used in place of impact in the laboratory for non-cohesive soils and gravels. In one instance, vibratory compaction produced maximum dry densities for a decomposed granite which were almost 5 % higher than that for impact compaction. Cohesive soils reached maximum compaction at moisture contents which were 7 % wetter under the vibratory mode as opposed to those for impact, but at lower densities. This showed that field densities under vibratory compaction would be difficult to achieve when the laboratory control method was based on impact. The research showed that electrical power input to the vibrating hammer must be carefully regulated in order to maintain specified standards which are based on a fixed frequency. Further study based on operation at different frequencies would be required to determine whether the vibrating hammer would be suitable for cohesive soils having natural frequencies lower than the current standard specified.

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Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / There are currently well established compaction methods being used in laboratories globally to prepare specimens for material testing. None of these methods provides the repeatability and reproducibility, ease of execution or simulation and correlation to field compaction desired by engineers. The research presented in this report was aimed at the development of a new or adapted compaction method for bituminous stabilized materials (BSM) that would address the aforementioned factors, by making use of a vibratory hammer. Along with this, a new protocol was to be established. The initial vibratory hammer that was tested was the Kango 637®. This specific vibratory hammer suffered irreparable damage to the gearbox during the research. A replacement Kango hammer could not be purchased, therefore a substitute hammer was purchased i.e. a Bosch GSH 11E®, for which back-up service and replacement parts are readily available throughout South Africa. Significant progress had been made with the development of a laboratory compaction protocol for BSM using the Kango Hammer. The specifications of the Bosch® hammer showed it was superior in terms of power, weight and other technical features. Comparative testing was therefore carried out. This allowed for the adaptation of the results achieved to that point. Extensive experimentation was then carried out using two types of BSM i.e. foamed bitumen (80/100 bitumen) and bitumen emulsion (60/40 Anionic Stable Grade) stabilized material. The initial material used for the experimentation was a G2 quality graded crushed stone. Additional material was also obtained from a recycling project taking place along the N7 near Cape Town. The N7 material was used to perform correlation experiments so as to determine how representative the laboratory compacted specimens were to field compacted material. Results showed that the vibratory hammer is capable of producing specimens for testing in the laboratory as well as providing a possible benchmark method for accurately controlling the quality of work on site i.e. field density control. This was done by identifying the time to and level of refusal density compaction. The level of refusal density compaction was expressed as a percentage of Mod AASHTO compaction and using current specifications, a potentially new site compaction level specification was determined. In order to asses the material applicability of the vibratory hammer compaction method, tests regarding moisture sensitivity analysis were carried out on a G5 material. The vibratory compaction protocol includes a specification for the type of hammer, guide-frame, surcharge weight, compaction moisture and number of layers. Vibratory compaction can be used to prepare two types of specimens: • Specimens for triaxial testing with a diameter of 150mm and a height of 300mm • Specimens for laboratory testing with a diameter of 150mm and a height of 125mm. Tests showed that the material properties prove to have an influence on the compactability of the material. Material from the N7 recycling project had been milled out thus altering the grading and including some RAP. This in turn influenced compaction. The vibratory hammer moisture curve was found to shift slightly to the left when compared to the Mod AASHTO moisture curve. The variability of the vibratory hammer was found to be well below the specified variability of 15%. Repeatability experiments on G5 material indicate that vibratory hammer compaction may be used on lesser quality granular materials. A recommended procedure for the compaction of BSM was developed following the experimentation results.