We simulate the behavior of a steel ball bearing as it impacts a rigid foundation by solving a discretized version of the dynamic equations of linearized elasticity for a homogeneous, isotropic material. Space is discretized using the finite element method and time is discretized using the implicit trapezoidal method. Impact with a fixed foundation is incorporated into the model using a complementarity condition. This ensures that we have normal forces acting on the bearing only when and where the bearing is in contact with the foundation. After discretization in space, this condition becomes a linear complementarity problem which is solved using an iterative method for solving LCPs that is similar to the Gauss-Seidel method for solving linear systems. The LCP is solved at each time step to determine the normal forces due to contact. By assuming cylindrical symmetry, we are able to simulate the impact of a three-dimensional ball using only two spatial coordinates and two-dimensional finite elements. This decreases the computational cost of a highly refined three-dimensional simulation dramatically. Using this model, we investigate the deformations that occur during and after contact. We hypothesized that dropping a steel ball from even a small height causes plastic deformation. We tested this hypothesis using our model by computing the state of stress inside the ball at various times during the simulation. By comparing the computed maximum shear stress to the yield strength of the material, we can determine if the threshold for plastic deformation is reached. We found that with an impact speed of 2 m/s the stresses induced in the ball are large enough to cause plastic deformation. Because plastic deformation requires energy and is irreversible, it is an important consideration when investigating how high the ball will bounce after contact. To quantify the energy loss due to plastic deformation, we propose a theoretical model capable of describing plastic deformation.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Also available in print.

No description available.

No description available.

Les crises combinées du pétrole, de la biodiversité et des changements climatiques, exigeant, entre autres, la réduction de l'usage des carburants fossiles, font du développement d'énergies alternatives un enjeu majeur. Si bien que l'éthanol, dont la production mondiale a atteint plus de 65 milliards de litres en 2008, constitue désormais un élément clé de la stratégie énergétique de nombreux pays, et que le Canada et les États-Unis (ÉU) le présentent même pour limiter les changements climatiques. Essentiellement dérivées du maïs, les productions d'éthanol aux ÉU premier producteur mondial de carburants végétaux -étaient d'environ 34 milliards de Iitres en 2008 comparées à 900 millions de litres au Canada. Certes, bien que la production de carburants végétaux, ne représente qu'environ 1% de l'ensemble des carburants liquides destinés aux transports dans le monde, elle est néanmoins de plus en plus sujette à controverse. L'aggravation de la crise alimentaire mondiale remet en effet en question cette filière énergivore reposant essentiellement sur des cultures agricoles, notamment le maïs, destinées initialement à l'alimentation. Cette controverse socio-environnementale contribue d'ailleurs au développement d'une 2ième génération de carburants végétaux, dérivée de la cellulose végétale, à qui on promet un avenir bien meilleur, alors que rien n'est moins sûr. La transformation croissante des ressources végétales en énergie destinée aux transports devrait exiger une évaluation approfondie de leurs impacts socio-environnementaux. Or, très peu d'études permettent de dégager un portrait global des carburants végétaux de 1ère génération déjà en production, et de ceux de 2ième génération, toujours en développement. En outre, les plus récents projets de loi au Canada (C-33) et aux ÉU (le US Energy Bill de 2007) favorisent davantage encore le déploiement de ces filières en permettant d'imposer des taux minimums d'éthanol dans l'essence au Canada et en fixant des objectifs nationaux de production (estimés aux É-U à 136 milliards de litres de carburants renouvelables en 2022). Dans ce contexle, ce mémoire vise à analyser dans quelle mesure les carburants végétaux peuvent être considérés, en partie ou en totalité, comme des alternatives viables aux carburants fossiles. Pour ce faire, nous examinerons notamment les impacts socio-environnementaux des carburants végétaux de 1ère et de 2ième génération, à travers les études de cas spécifiques de l'éthanol-maïs et de l'éthanol cellulosique principalement issu de la paille de maïs, deux productions largement développées ou en développement aux ÉU et au Canada. Ce travail de recherche et d'analyse s'appuie sur une importante revue de littérature scientifique, permettant d'appréhender dans toute sa complexité l'évolution des carburants végétaux et notamment la transition amorcée vers ceux de 2ième génération. Comme nous le verrons au fil du texte, la production et l'usage d'éthanol-maïs ont des conséquences socio-environnementales majeures, tant sur la qualité des sols, de l'eau et de l'air, qu'au plan de la biodiversité et de la sécurité énergétique et alimentaire, et elles présentent donc plus de désavantages que de bénéfices. Quant à l'option cellulosique, centrée sur le développement de cultivars à plus fort ratio celulose/lignine et de microorganismes permettant la transformation de la cellulose en éthanol, elle présente autant sinon plus de risques notamment en termes de baisse de productivité des sols agricoles et de risques de contamination génétique des autres variétés végétales naturelles et cultivées. Dans la mesure où ce recours aux carburants végétaux s'inscrit dans une optique incrémentale, modifiant à la marge un aspect relativement mineur de la complexe question de la croissance du transport routier et d'un parc automobile nord-américain particulièrement énergivore, il est fort risqué que l'emballement pour l'option cellulosique accélère sa mise en marché avant que toutes les évaluations requises n'aient été faites, au risque alors de conséquences inattendues, mais aussi importantes que les problèmes qu'on a voulu ainsi éviter ou résoudre. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Biocarburant, Carburants végétaux, Éthanol-maïs, Éthanol cellulosique, Paille de maïs, Sécurité alimentaire, Sécurité énergétique.

Structural designs barely consider the dynamic scenario of a well-developed impinging wave hitting the structure. The usual area of focus is on static and stability factors (e.g. drag, inertia, resistive forces related to weight, buoyancy, sliding etc). Even the "Factor of Safety" which is regularly used in designs to account for unknown and/or unforeseen situations which might occur implies a degree of uncertainty about the dynamic scenario of breaking waves in the coastal environment. In the present study the hydrodynamics of a coastal structure-turbulent bore interaction was studied by examination (two-dimensional) of the singular case of a plunging breaking wave forming a well developed turbulent bore which impacted on a model sea wall structure. The turbulent bore impact event was found to display similar characteristics to the impact event of other wave shapes, in particular that of a plunging breaker. Examination of the impact event confirmed the conversion of nearly all horizontal velocity to vertical velocity during the "flip through" event. In accordance with theoretical expectations the location of maximum pressure was found to occur just below the still water level (SWL). Resulting pressure data in the present study consisted of two blunt spikes as opposed to the "church-roof" (high spike) shape seen in other results. The shape of the pressure data was attributed to the following: firstly, to the initial impact of the protruding jet of the breaking wave which causes the first maxima, secondly, to the sensor encountering the bulk of the entrapped air hence causing the drop in pressure between the blunt spikes and lastly, to the inherent hydrostatic pressure combined with the compression of the entrapped air bubbles, by the subsequent forward motion of the water within the wave, which causes the second maxima. The point of maximum pressure was found to always be within the second maxima. Observation of the turbulent bore-structure interaction showed that the consequential maximum pressure was a direct result of the compression of entrapped air by the weight of the water in the wave as it continued forward onto the structure combined with the inherent hydrostatic pressure of the wave. The project was conducted in an attempt to contribute to the vast knowledge of coastal structure-wave interactions and to add to the understanding of the physics and characteristics of breaking waves. Whilst numerous studies and experiments have been carried out on the phenomenon of breaking waves by previous researchers the current project highlights the advent of new equipment and technological advances in existing methods.

Abstract In this paper, the mechanical properties of carbon-fiber reinforced polyether-ether ketone (PEEK) with and lay-up subject to impact and temperature reaction have been investigated.The drop-weight impact tests were performed by a 4mm diameter semi spherical nosed projectile. Incident impact height adopts 0.8m and 1.6m incident height. After impact testing, the static tension tests were performed to measure the ultimate strengths and elastic modulus at 25¢J¡B75¢J¡B125¢J¡B145¢J,so that the effects of stacking sequence and the damage mechanism subjected impact at elevated temperature was obtained. By the parametric study and research , there are very important results as follow: The destructive crack of AS4/PEEK laminates subject to impact were arised from the tension sides toward the pressure sides, and the lay-up was more serious than the lay-up. Although more excellent ultimate strength than the lay-up, the must be quantities of decay When the incident height increase as well as elevated temperature. Keywords: Composite, Impact, Temperature, Strength, Elastic Modulus, Fracture.

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This field study evaluates the impact of replacing existing 17-inch Cathode Ray Tube (CRT) monitors with 19 and 21-inch CRT monitors and 18.1-inch Flat Panel Displays (FPDs) on matrices of productivity, visual comfort, and physical discomfort among 30 employees within a large insurance company (Policy Service and Claims). Metrics were analyzed over a five (5) month period. During Phase One (initial eight weeks) of the study, metrics were gathered weekly on 17-inch CRT monitors to establish a baseline of data on productivity, visual comfort and physical discomfort. During Phase Two (12 weeks), each subject used the 19-inch CRT, 21-inch CRT and 18.1-inch FPD for two weeks, respectively interspersed with other subjects in the study utilizing 17-inch monitors for the same time period. Initially, it appears that the 19-inch monitor enables users to enter more keystrokes per hour ( x19 =1894) than its 17-inch counterpart ( x17=1721) which would be a productivity enhancement. However, this value is not statistically significant (p>0.34). Analysis of additional performance metrics yielded similar results (p>0.2). The users’ level of visual comfort increased with all test display units over their existing 17-inch counterpart (p<0.023), but the data was not meaningful due to the minute difference between their mean values (&#8710;<0.75). Physical discomfort metrics were analyzed among all of the monitor treatments. Most employees were relatively comfortable through the duration of the study. Mean values across all physical discomfort metrics measured were less than one on a Borg scale of zero to ten, but none of the values among treatments were significant (p>0.31). Anecdotally, the users preferred the larger monitors.

Capital-intensive and technology-intensive semiconductor industry in Taiwan to flourish, resulting in a specific cluster effect, the global semiconductor-related industries, such as equipment, materials, components and other inputs are also competing to take food off such big cake. As the related industries focusing on in Taiwan, multinational company, due to the cultural differences between the various members and organizations within the internal structure, continued to have an impact on Taiwan subsiderary. Foreign companies, according to the investment, technology position and existed market position, have varying degrees of local impact. The impact of parent company host culture and subsiderary local culture in Taiwan also interact with the factors mentioned above. To meet demands of parent company, oftently caused trouble in local business operation. In this study, a subsidiary (case company) of a MNC of semiconductor quartz manufacturing industries in Taiwan, via the differences of attitudes and issue resolving, disposition among the MNCs to explore the operation impact of cultural differences between the multi-national members. As a result of cultural differences, conflict and contradiction, a subsidiary of multinational companies in Taiwan found that the culture impact can be switched from resistance to assistance and maneuver to help creating a favorable business environment.