A força propulsiva gerada durante o palmateio é resultado do somatório das forças de arrasto e de sustentação, sendo que a componente que atua na direção do movimento desejado é igual à força propulsiva efetiva. Essas forças podem ser estimadas a partir de equações hidrodinâmicas, porém essas equações não consideram todos os mecanismos que contribuem para a propulsão. Dessa forma, o objetivo geral do presente estudo foi comparar a força propulsiva efetiva calculada a partir das equações hidrodinâmicas e a força propulsiva efetiva medida durante o palmateio de sustentação (na posição vertical, de cabeça para cima) em cada fase do palmateio. Para isso, uma praticante de nado sincronizado realizou palmateio na posição vertical de cabeça para cima durante 15 segundos, enquanto que dados cinemáticos e cinéticos foram obtidos por viodeogrametria 3D e dinamometria respectivamente. A análise gráfica de Bland e Altman foi usada para comparar as forças propulsivas efetivas medida e calculada durante o palmateio. As forças propulsivas efetivas calculada e medida foram diferentes, sendo a medida maior que a calculada. Ainda, os resultados indicaram que o palmateio executado não foi simétrico, isto é, a orientação e a força propulsiva entre a mão direita e a esquerda foram diferentes. Portanto, o achado do presente trabalho destaca a importância de mecanismos instáveis para a propulsão durante o palmateio, já que as forças estimadas por meio das equações hidrodinâmicas apresentaram resultados inferiores, sendo isso observado ao longo de todo o palmateio. / Propulsive force generated during sculling motion results from drag and lift propulsive forces, and the component acting in the direction of motion is the effective propulsive force. These forces may be calculated using hydrodynamic equations, but these equations do not consider all mechanisms that contribute to the propulsion. Thus, the main purpose of this study was to compare the calculated effective propulsive force using the hydrodynamic equations and the measured effective propulsive force during a support sculling motion (vertical position with the head above the water‟s surface) in each phase of sculling. For this, a practitioner of synchronized swimming performed sculling motion in a vertical position with the head above the water‟s surface during 15 seconds, while kinematic and kinetic data were obtained by 3D videogrammetry and dynamometry respectively. Graphical techniques from Bland and Altman were used to compare the measured effective propulsive force and calculated effective propulsive force during sculling motion. The calculated effective propulsive force and the measured effective propulsive force were different, the measured being greater than the calculated. Moreover, the results indicated sculling motion performed was not symmetric, that is, the orientation and propulsive forces between the right and left hands were different. Therefore, the result of this study highlights the importance of the unsteady mechanisms for the propulsion during sculling motion, because the calculated forces using the hydrodynamic equations presented low values throughout the sculling motion.

A força propulsiva gerada durante o palmateio é resultado do somatório das forças de arrasto e de sustentação, sendo que a componente que atua na direção do movimento desejado é igual à força propulsiva efetiva. Essas forças podem ser estimadas a partir de equações hidrodinâmicas, porém essas equações não consideram todos os mecanismos que contribuem para a propulsão. Dessa forma, o objetivo geral do presente estudo foi comparar a força propulsiva efetiva calculada a partir das equações hidrodinâmicas e a força propulsiva efetiva medida durante o palmateio de sustentação (na posição vertical, de cabeça para cima) em cada fase do palmateio. Para isso, uma praticante de nado sincronizado realizou palmateio na posição vertical de cabeça para cima durante 15 segundos, enquanto que dados cinemáticos e cinéticos foram obtidos por viodeogrametria 3D e dinamometria respectivamente. A análise gráfica de Bland e Altman foi usada para comparar as forças propulsivas efetivas medida e calculada durante o palmateio. As forças propulsivas efetivas calculada e medida foram diferentes, sendo a medida maior que a calculada. Ainda, os resultados indicaram que o palmateio executado não foi simétrico, isto é, a orientação e a força propulsiva entre a mão direita e a esquerda foram diferentes. Portanto, o achado do presente trabalho destaca a importância de mecanismos instáveis para a propulsão durante o palmateio, já que as forças estimadas por meio das equações hidrodinâmicas apresentaram resultados inferiores, sendo isso observado ao longo de todo o palmateio. / Propulsive force generated during sculling motion results from drag and lift propulsive forces, and the component acting in the direction of motion is the effective propulsive force. These forces may be calculated using hydrodynamic equations, but these equations do not consider all mechanisms that contribute to the propulsion. Thus, the main purpose of this study was to compare the calculated effective propulsive force using the hydrodynamic equations and the measured effective propulsive force during a support sculling motion (vertical position with the head above the water‟s surface) in each phase of sculling. For this, a practitioner of synchronized swimming performed sculling motion in a vertical position with the head above the water‟s surface during 15 seconds, while kinematic and kinetic data were obtained by 3D videogrammetry and dynamometry respectively. Graphical techniques from Bland and Altman were used to compare the measured effective propulsive force and calculated effective propulsive force during sculling motion. The calculated effective propulsive force and the measured effective propulsive force were different, the measured being greater than the calculated. Moreover, the results indicated sculling motion performed was not symmetric, that is, the orientation and propulsive forces between the right and left hands were different. Therefore, the result of this study highlights the importance of the unsteady mechanisms for the propulsion during sculling motion, because the calculated forces using the hydrodynamic equations presented low values throughout the sculling motion.

Classical approaches to evaluate the stability of large woody debris (LWD) introduced in streams for habitat restoration or flood management purposes are usually based on inappropriate assumptions and hydraulic equations. Results suggest that the physics of small cylindrical elements located in large channels cannot be transferred to the case of a large roughness elements placed in small channels. The introduction of LWD in a small channel can generate a significant modification of the upstream hydraulic conditions. This modification has direct implications on the stability of the LWD. Experiments were performed in a controlled environment: a small stream section was represented by a low roughness rectangular flume and LWD were modeled with smooth PVC cylinders. Direct force measurements were performed with a load cell and results were used to identify an equation that evaluates the drag force acting on a large cylindrical element place in a rectangular channel. This equation does not depend on a drag coefficient. Water depths were also measured during the experiments and results were used to develop an approach that evaluates the upstream hydraulic impacts of a large cylinder introduced in a rectangular channel. The effect of the variation of the unit discharge (discharge per unit of width), cylinder size, cylinder elevation from the channel bed, and downstream hydraulic conditions, could be related to the upstream hydraulic conditions with relative success. Dimensionless parameters were developed to increase the versatility of the approach. The application of this approach to field cases is expected to require adjustments, mainly because of the roughness of natural environments differs from the smoothness of the controlled environment described in this work. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

In this work cold model experiments in combination with Comsol modeling have been carried out to investigate the possibilities of a new method for industrial inline measurements of slag viscosities. The method aims at measuring the mass of the drag force as a sphere is dragged upwards in a liquid. The sphere was connected to a balance that was elevated at constant velocity. The liquids used were silicon oils of two different viscosities; 0.1 Pa*s and 0.5 Pa*s. A computer logged the mass from which the viscosity was calculated. Comsol modeling was used to show approximately at which time the drag force is constant, and to investigate the wall effect. The importance of laminar flow is discussed. The results show that the method is more suitable for liquids of higher viscosities. The reason is that the drag force is one order of magnitude lower than the other forces in the system. Since the drag force is directly proportional to the viscosity, it becomes larger with higher viscosity. The Comsol model shows that the drag force becomes constant in a few seconds from start of the movement. Comsol gives approximately the same values for the drag force as can be calculated by hand. The viscosities calculated from the experimental data are between two and five times too large for the higher viscosity tested, and between two and ten times too large for the lower viscosity tested. There is a wall effect for the two containers used in the experiments that can be seen both experimentally and by Comsol. Further work and development of the model has to be done before this method possibly could work for industrial purposes.

No description available.

Yes / Aquatic vegetation can significantly affect flow structure, sediment transport, bed scour and water quality in rivers, lakes, reservoirs and open channels. In this study, the lattice Boltzmann method is applied for performing the two dimensional numerical simulation of the flow structure in a flume with rigid vegetation. A multi-relaxation time model is applied to improve the stability of the numerical scheme for flow with high Reynolds number. The vegetation induced drag force is added in lattice Boltzmann equation model with the algorithm of multi-relaxation time in order to improve the simulation accuracy,. Numerical simulations are performed for a wide range of flow and vegetation conditions and are validated by comparing with the laboratory experiments. Analysis of the simulated and experimentally measured flow field shows that the numerical simulation can satisfactorily reproduce the laboratory experiments, indicating that the proposed lattice Boltzmann model has high accuracy for simulating flow-vegetation interaction in open channel. / National Natural Science Foundation of China (grant number: 11861003 and 11761005)

Des études numériques ont montré que la taille de la cellule de maillage peut avoir un effet drastique sur la modélisation du lit fluidisé circulant avec des petites particules. En effet, la taille de la cellule doit être de l’ordre de quelques diamètres de particules pour prédire avec précision le comportement dynamique d’un lit fluidisé. En conséquence, les simulations numériques d’ Euler-Euler des processus industriels sont généralement effectuées avec des grilles trop grossières pour permettre la prédiction des effets de ségrégation locale. La modélisation appropriée, qui prend en compte l’influence des structures non résolues, a déjà été proposée pour les simulations monodispersés. Dans ce travail, l’influence des structures non résolues sur un mélange binaire de particules est analysée et on propose des modèles pour tenir compte de cet effet dans des simulations de lit fluidisé polydispersés. Pour atteindre cet objectif, des simulations Euler-Euler de références sont réalisées avec un raffinement du maillage aboutissant à une solution indépendante de la taille de la cellule. Ce type de simulation numérique est très coûteux et se limite à des configurations très simples. Dans ce travail, la configuration se consiste en un lit circulant périodique 3D, qui représente la région établie d'un lit circulant. Parallèlement, une approche filtrée est développée où les termes inconnus, appelés contributions de sous-maille, doivent être modélisés. Les filtres spatiaux peuvent être appliqués aux résultats de simulation de référence afin de mesurer chaque contribution de sous-maille apparaissant dans l’approche théorique filtrée. Une analyse est réalisée afin de comprendre et de modéliser l’effet de la contribution des termes de sous-maille. L’opération de filtrage fait apparaître de nouveaux termes, les termes de sous-maille. Un terme filtré est la somme d’un terme résolu, obtenus à partir des champs filtrés, et d’ un terme de sous-maille. L’analyse de l’équation filtrée de quantité de mouvement montre que les contributions résolues de la traînée des particules fluides et la collision entre particules surestiment les effets de transferts de quantité de mouvement filtrés. L’analyse de l’équation filtrée de l’énergie cinétique des particules montre que la production résolue par le cisaillement moyen et par le mouvement relatif moyen des particules sous-estime contribution filtrée. Des modèles fonctionnels sont proposés pour les contributions de sous-maille de la traînée et des collisions inter-particule. / Detailed sensitivity numerical studies have shown that the mesh cell-size may have a drastic effect on the modelling of circulating fluidized bed with small particles. Typically, the cell-size must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Hence, the Euler-Euler numerical simulations of industrial processes are generally performed with grids too coarse to allow the prediction of the local segregation effects. Appropriate modelling, which takes into account the influence of unresolved structures, have been already proposed for monodisperse simulations. In this work, the influence of unresolved structures on a binary mixture of particles is investigated and models are proposed to account for those effect on bidisperse simulations of bidisperse gas-solid fluidized bed. To achieve this goal, Euler-Euler reference simulations are performed with grid refinement up to reach a mesh independent solution. Such kind of numerical simulation is very expensive and is restricted to very simple configurations. In this work, the configuration consists of a 3D periodical circulating fluidized bed, that could represent the established zone of an industrial circulating fluidized bed. In parallel, a filtered approach is developed where the unknown terms, called sub-grid contributions, appear. They correspond to the difference between filtered terms, which are calculated with the reference results then filtered, and resolved contributions, calculated with the filtered fields. Then spatial filters can be applied to reference simulation results to measure each sub-grid contribution appearing in the theoretical filtered approach. A budget analysis is carried out to understand and model the sub-grid term. The analysis of the filtered momentum equation shows that the resolved fluid-particle drag and inter-particle collision are overestimating the momentum transfer effects. The analysis of the budget of the filtered random kinetic energy shows that the resolved production by the mean shear and by the mean particle relative motion are underestimating the filtered ones. Functional models are proposed for the subgrid contributions of the drag and the inter-particle collision.

Diferentes tipos de sólitons têm sido observados em meios ópticos não-lineares, e seus comportamentos individuais descritos pela equação não-linear de Schrödinger e pela equação não-linear de Schrödinger generalizada, em diferentes dimensões e geometrias. Entretando, há situações onde muitos sólitons são gerados formando uma densa rede de sólitons. Nestes casos, é impossível desprezar as interações entre os sólitons e temos que considerar a evolução da estrutura como um todo. A teoria das ondas de choque dispersivas em meios fotorrefrativos e a teoria da difração não-linear de intensos feixes de luz propagando-se em meios fotorrefrativos com um fio refletor incorporado a esse meio foi desenvolvida, e verificamos que está em excelente acordo com nossas simulações numéricas. No caso da formação de sólitons em condensados, fizemos cálculos numéricos realísticos dentro da aproximação de campo médio usando a equação de Gross-Pitaevskii, incluindo também um potencial de confinamento, um potencial móvel e um potencial dipolar. A maioria dos resultados puderam ser comparados com experimentos recentes. / Different kinds of solitons have already been observed in various nonlinear optical media, and their behavior has been explained in the frameworks of such mathematical models as the nonlinear Schrödinger and generalized nonlinear Shrödinger equations for different dimensions and geometries. However, there are situations when many solitons are generated so that they can comprise a dense soliton train. In such situations, it is impossible to neglect interactions between solitons and one has to consider the evolution of the structure as a whole rather than to trace the evolution of each soliton separately. The theory of optical shock waves in photorefractive media and the theory of nonlinear diffraction of light beams propagating in photorefractive media with embedded reflecting wire was developed and agrees very well with our numerical simulations. In the condensate soliton formation case, we did numerical calculations in the mean field approach using the Gross-Pitaevskii equation, adding a trap potential and a moving potential and a potential of the dipole-dipole interaction. The main results were also checked by recent experiments.

This doctoral thesis reports analytical and numerical results for the electrostatic response of a dusty plasma to a moving test charge. Two important physical aspects of dusty plasmas, namely grain size distribution and grain charging dynamics were taken into account. In the first case, a dusty plasma in thermal equilibrium and with a distribution of grain sizes is considered. A size distribution is assumed which decreases exponentially with the grain mass for large sizes and gives a simple smooth reduction for small sizes. The electrostatic response to a slowly moving test charge, using a second order approximation is found and the effects of collisions are also investigated. It turns out that for this particular size distribution, there is a remarkably simple result that the resulting effective distribution for the electrostatic response is a kappa (generalized Lorentzian) distribution. In the second case, we present an analytical model for the shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging for cases both with and without the collision effects. The response potential is treated as a power series in test charge velocity. Analytical expressions for the response potential are found up to second order in test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. It is concluded that the dynamical charging of the grains in a dusty plasma enhances the shielding of a test charge. To clarify the physics, a separate study is made where the charging is approximated by using a time delay. The resulting potential shows the delayed shielding effect explicitly. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. The wake potential of a fast moving test charge in the case of grain charging dynamics was also found. It was observed that the grain charging dynamics leads to a spatial damping and a phase shift in the potential response. Finally, combining these two physical aspects, generalized results for the electrostatic potential were found incorporating the terms from both grain size distribution and grain charging dynamics. The generalized results contain the previous work where these two effects were studied separately and which can now be found as special limiting cases. This kind of work has relevance both in space and astrophysical plasmas. / QC 20100920