Dissertations / Theses on the topic 'The Newmark method'

The concept of using aluminum as the primary construction material for high speed ships and the hydroelastic behavior of the structure is widely gaining importance as a significant research topic in naval architecture. Aluminum is lighter than steel and hence can be predominantly used in high speed crafts which experiences significant slamming. This thesis work is focused on wedge shaped models. Free fall wedge impact is studied and a FORTRAN 90 computer program is developed to estimate the structural response of the wedge experiencing slamming by the use of matrix methods, finite element techniques and Newmark-Beta numerical time integration methods. The numerical solution is validated by comparison with the static solution. The theoretical hydrodynamic pressures which are used as input for this work was originally developed by using a flat cylinder theory [26]. The wedge drop at 0.6096 m (24 inch) drop height with an impact veloc- ity of v=3.05 m/s is based as the premise and the experimental pressure distributions measured by the pressure-transducers and the theoretical pressure predictions are used as inputs and the structural response is derived. Additionally, the response is compared for three different plate thicknesses and the results are compared against each other. The maximum deflection is comparable to the deflection evaluated from the experiment and tends to attain convergence as well. As the plate thickness reduces there tends to be a significant rise in the deflection values for the wedge plate, in the manner that when the plate thickness is halved there is a deviation of more than 75% in the deflection values as such.

The effects of a composite overwrapped gun barrel with viscoelastic damping layers are investigated. Interlaminar stresses and constrained layer damping effects are described. The Modal Strain Energy method is developed for measuring the extent to which the barrel is damped. The equations of motion used in the finite element analysis are derived. The transient solution process is outlined. Decisions for selected parameters are discussed. The results of the finite element analyses are presented using the program written in FORTRAN. The static solution is solved with a constant internal pressure resulting in a calculated loss factor from the Modal Strain Energy Method. The transient solution is solved using the Newmark-Beta method and a variable internal pressure. The analyses conclude that strategically placed viscoelastic layers dissipate strain energy more effectively than a thick single viscoelastic layer. The optimal angle for maximizing the coefficient of mutual influence in a composite cylinder is not necessarily the optimal angle when viscoelastic layers are introduced between layers.

Nel presente elaborato di tesi viene descritto un metodo di indagine che, mediante prove dinamiche e misure di accelerazione, si propone di identificare eventuali danneggiamenti in strutture reticolari spaziali. L’identificazione consiste, sulla base di dati sperimentali in termini di frequenze proprie del sistema, nel determinare, con la migliore precisione possibile l’area della sezione trasversale degli elementi. Il problema è formulato come un problema di ottimizzazione e l’identificazione è condotta mediante l’utilizzo di Algoritmi Genetici (brevemente GAs). In particolare, una funzione obiettivo misura la differenza tra le grandezze misurate sperimentalmente e le grandezze ottenute numericamente mediante un codice FEM della struttura in esame. Il principio cui sono ispirati gli algoritmi genetici fa sì che questi ricerchino il miglior individuo all’interno di una popolazione che rappresenta le possibili soluzioni del problema. Si riportano i dati ottenuti, mediante prove dinamiche, su una struttura reale, che permettono di ottenere informazioni sui parametri modali: frequenze proprie e smorzamento. Si confrontano, infine due differenti tipi di sensori di accelerazione, dimostrando la validità e i possibili benefici dell'utilizzo di sensori con tecnologia MEMS nell'ambito della misura delle vibrazioni.

Os Procedimentos de Comparações Múltiplas (PCM) podem ser utilizados para comparar médias de tratamentos. Há muitos testes de comparações múltiplas e, para escolher o melhor, devem ser levados em conta o controle do erro tipo I (testes exatos, conservadores ou liberais) e o poder desses testes. Para melhorar o seu desempenho, em relação ao erro tipo I e poder, métodos de reamostragem bootstrap têm sido utilizados em alguns estudos sobre PCM. O teste de Student-Newman-Keuls (SNK) possui boas qualidades estatísticas que poderiam ser melhoradas com o uso do bootstrap. Assim, os objetivos deste trabalho foram propor uma versão utilizando o bootstrap paramétrico do teste de comparações múltiplas SNK (SNKB), avaliar o desempenho do teste SNKB e compará-lo com o teste SNK. O desempenho foi avaliado pelas taxas de erro tipo I por experimento e pelo poder por meio de um estudo de simulação Monte Carlo em condições de normalidade e não normalidade dos resíduos. Foram realizadas N=1000 simulações de experimento com k tratamentos (k = 5, 10, 20 e 80) com r repetições (r = 4, 10 e 20). Diferentes hipóteses sobre as médias foram consideradas. Sob H0 completa, as médias foram consideradas todas iguais, sob H1, as médias foram todas diferentes, considerando a mesma variância, e, sob H0 parcial, foram considerados dois grupos cujas médias eram diferentes entre si. Ambos os testes apresentaram valores de taxas de erro tipo I próximos do nível nominal de 0,05 sob H0 completa e normalidade. Sob H0 completa e não normalidade, os testes SNK e SNKB controlaram as taxas de erro tipo I por experimento na maior parte dos casos simulados para k=5 e k=10, enquanto que, para k=20 e k=80, ambos os testes foram considerados liberais em alguns cenários. Sob H0 parcial, o teste SNKB foi liberal em todos os casos simulados, enquanto que o teste SNK foi, em geral, conservador para δ ≤ 2 e liberal para os demais valores de δ. O poder do teste proposto em geral superou o poder do teste original nas situações de normalidade e não normalidade. Assim, em situações práticas, se as diferenças entre as médias dos tratamentos forem pequenas (δ ≤ 2), o teste SNK é mais indicado por controlar o erro tipo I e apresentar valores de poder satisfatórios. Nos demais casos, o teste SNKB é mais recomendado, apesar de ambos serem liberais para δ ≥ 4, se a situação for de H0 parcial. Além disso, os testes SNK e SNKB foram aplicados em dados reais de um experimento delineado para avaliar os controles químico e mecânico de pragas da gravioleira com o objetivo de comparar os resultados obtidos pelos dois testes.<br>Multiple Comparisons Procedures (MCP) are used to compare treatment means. There are many tests with this purpose and to choose the best one, two features must be analysed: the control of type I error rate (exact, conservative or liberal tests) and the power. Bootstrap resampling methods have been used in some studies to improve the performance of MCP. The Student-Newman-Keuls (SNK) test shows good statistical qualities that can be improved with the use of bootstrap. Therefore, this study aimed to propose a SNK parametric bootstrap version (SNKB) and compare it with the original SNK test. The performance was evaluated by experimentwise error rates and power using a Monte Carlo simulation study considering normal and non-normal situations. We considered N = 1000 simulations of k treatments (k = 5, 10, 20 e 80) with r repetitions (r = 4, 10 and 20). Under null hypothesis, the means were considered all equal, under H1 the means were all different, but the variance was the same and, under partial H0, we considered two groups with different means. Both tests showed type I error rates values close to the nominal level of 0.05 under H0 and normality. Under H0 and non-normality, both tests controlled the experimentwise error rates in most simulated cases for k=5 and k=10, whereas, for k=20 and k=80, the tests were considered liberal in some scenarios. Under H0 partial, the SNKB test was liberal in all simulated cases, while SNK test was generally conservative for δ ≤ 2 and liberal to other δ values. In general, the power of the proposed test surpassed the power of original test under normality and non-normality. Thus, in practice, if the differences between the treatment means are small (δ ≤ 2), the SNK test works better given that it controls the type I error and the power is satisfactory. In the other cases, the SNKB test is recommended, although both are liberal for δ ≥ 4, if we are under partial H0. Furthermore, the tests were applied to a real experiment designed to evaluate the chemical and mechanical controls of pests soursop in order to compare the results of both tests.<br>Fundação de Amparo à Pesquisa do Estado de Minas Gerais - FAPEMIG

Nous étudions l’analyse asymptotique en relativité générale sous deux aspects: le peeling et le scattering (diffusion) conforme. Le peeling est construit pour les champs scalaires linéaire et non-linéaires et pour les champs de Dirac en espace-temps de Kerr (qui est non-stationnaire et à symétrie simplement axiale), généralisant les travaux de L. Mason et J-P. Nicolas (2009, 2012). La méthode des champs de vecteurs (estimations d’énergie géométriques) et la technique de compactification conforme sont développées. Elles nous permettent de formuler les définitions du peeling à tous ordres et d’obtenir les données initiales optimales qui assurent ces comportements. Une théorie de la diffusion conforme pour les équations de champs sans masse de spîn n/2 dans l’espace-temps de Minkowski est construite.En effectuant les compactifications conformes (complète et partielle), l’espace-temps est complété en ajoutant une frontière constituée de deux hypersurfaces isotropes représentant respectivement les points limites passés et futurs des géodésiques de type lumière. Le comportement asymptotique des champs s’obtient en résolvant le problème de Cauchy pour l’équation rééchelonnée et en considérant les traces des solutions sur ces bords. L’inversibilité des opérateurs de trace, qui associent le comportement asymptotique passé ou futur aux données initiales, s’obtient en résolvant le problème de Goursat sur le bord conforme. L’opérateur de diffusion conforme est alors obtenu par composition de l’opérateur de trace futur avec l’inverse de l’opérateur de trace passé<br>This work explores two aspects of asymptotic analysis in general relativity: peeling and conformal scattering.On the one hand, the peeling is constructed for linear and nonlinear scalar fields as well as Dirac fields on Kerr spacetime, which is non-stationary and merely axially symmetric. This generalizes the work of L. Mason and J-P. Nicolas (2009, 2012). The vector field method (geometric energy estimates) and the conformal technique are developed. They allow us to formulate the definition of the peeling at all orders and to obtain the optimal space of initial data which guarantees these behaviours. On the other hand, a conformal scattering theory for the spin-n/2 zero rest-mass equations on Minkowski spacetime is constructed. Using the conformal compactifications (full and partial), the spacetime is completed with two null hypersurfaces representing respectively the past and future end points of null geodesics. The asymptotic behaviour of fields is then obtained by solving the Cauchy problem for the rescaled equation and considering the traces of the solutions on these hypersurfaces. The invertibility of the trace operators, that to the initial data associate the future or past asymptotic behaviours, is obtained by solving the Goursat problem on the conformal boundary. The conformal scattering operator is then obtained by composing the future trace operator with the inverse of the past trace operator

The semi-classical black hole tunnelling method is a useful technique to calculate black hole temperature and understand black hole thermodynamics. I will investigate the black hole tunnelling method in detail. I will compare two different approaches used to calculate black hole tunnelling. The tunnelling method can be applied to a broad range of spacetimes and I will show this explicitly in order to demonstrate the robustness of the tunnelling technique. In particular, I will apply the tunnelling method to spacetimes including: Rindler (the method can recover the Unruh temperature), and more general spacetimes (such as Kerr-Newman and Taub-NUT). I will also discuss the 5d Kerr-Gödel spacetimes in detail (while showing a previous unobserved property of these spaces). Once the parameter space of Kerr-Gödel is understood in detail, I will show how the tunnelling method can also be successfully applied to the Kerr-Gödel black hole. Finally, the key result of my thesis involves extending the tunnelling method to model fermion emission. The previous tunnelling calculations all involved the emission of scalar particles. I will model the emission of spin-1/2 fermions from various spacetimes including the Rindler spacetime and general non-rotating black holes. I will also model the emission of charged spin-1/2 fermions from the Kerr-Newman spacetime to show that the method is also applicable to rotating spacetimes. In all these cases I show that the correct Hawking temperature (Unruh temperature in the case of Rindler) is recovered for spin-1/2 fermion emission. Although this final result is not surprising, it is an important result because it confirms that Dirac particles will radiate from the black hole at the same temperature as scalar particles. It has always been assumed that this is the case but there is very little literature involving fermion radiation of black holes. So the results of my calculations are twofold, I demonstrate that Dirac particles are emitted at the same temperature as scalar particles from a black hole and it shows how robust the semi-classical tunnelling technique is.