This thesis concerns one of the upcoming and well discussed subjects withincalculations these days, namely how to perform an analysis of the interactionbetween fluid and structure, called FSI (Fluid Structure Interaction). In the report,evaluations of two different methods of simulating FSI are done. These are knownas Practical FSI (P-FSI) and Direct Coupled FSI (DC-FSI). The methods aredeveloped by Acusim in cooperation with Simulia and the softwares used areAbaqus and AcuSolve.The first part of the thesis is dedicated to explain the general theory and thegoverning equations for FSI. After the general explanation a more delimitatedexplanation regarding P-FSI and DC-FSI are given. After this we show how tosetup and perform the couplings regarding which parameters that need to bedefined and how to perform the analyses using Abaqus and AcuSolve.The last section of the thesis covers the evaluation process. We started withevaluating the methods against a benchmark problem where we compared thecalculation time and accuracy regarding displacements and frequencies. The nextthing we evaluated was how different numbers of modes used in the P-FSIcoupling affects the result. The last thing we evaluated was the robustness of themethods using different mass densities of the structure and different time-stepsizes.The result of the evaluation regarding the criteria: accuracy, calculation time androbustness showed that the P-FSI method is the most efficient method comparedto DC-FSI regarding FSI problems when the structural response is linear.

Ingeniero Civil Mecánico / En el presente trabajo de título se estudia el comportamiento de aneurismas cerebrales, el cual es una patología provocada por el debilitamiento de las paredes en los vasos sanguíneos generando un estiramiento de la estructura con riesgo de ruptura. El objetivo principal de este trabajo consiste en el estudio comparativo a través de simulaciones computacionales FSI (Fluid Solid Interaction) con acople completo de 4 modelos de pared arteriales, 3 hiperlasticos (Valencia, Toth, Costalat) y uno elástico (Valencia Lineal), en 2 geometrías con aneurismas del tipo lateral y 2 terminales. Las variables estudiadas son la presión, los WSS (esfuerzos de corte), deformación y esfuerzos de Von Mises. Para esto se utiliza los software comerciales Ansys-Fluent y Ansys-Estructural. Los principales resultados mostraron que el modelo de Toth y Valencia Lineal tienen un comportamiento muy similar para las variables de estudio, mientras que Costalat y Valencia tienden a parecerse en menor medida. Con respecto a la presión, no se encontraron grandes diferencias entre los autores, comportándose de forma muy similar entre todos, tanto en magnitud como en comportamiento. La concentración de WSS se ubican en las mismas zonas para los 4 autores, difiriendo en magnitud, siendo Costalat el con mayores valores y Toth el con menores. Además, se observa que en las geometrías saculares estos tienden a concentrarse en el sector del cuello, mientras en los terminales a las salidos de los aneurismas. Las mayores deformaciones para todos los autores son siempre en el sector de los aneurismas, cambiando en magnitud para los diferentes modelos. Se obtiene que Toth es el autor con mayores deformaciones en promedio y Costalat el de menores. También se observa que los aneurismas laterales tienen en promedio un 55\% más de deformación que los terminales. Los esfuerzos de Von Mises son los que presentan mayores diferencias entre los autores, llegando incluso a valores de un 40\% entre ellos para los esfuerzos máximos, aunque ninguno supera los limites de ruptura. Costalat es el de mayores valores, mientras Toth el de menores. No se encuentran diferencias significativas entre las distintas geometrías. Por otro lado, se estudia el comportamiento de las simulaciones en general al dejar la pared rígida y con simulaciones FSI con acople en una dirección entre los programas. Resultando que tanto los WSS como los esfuerzos de Von Mises difieren significativamente en comparación a la simulación FSI con acople total. Finalmente, se concluye que para las variables de deformación, WSS y esfuerzos de Von Mises los distintos modelos de pared presentan comportamientos distintos para las simulaciones, mientras que para la presión no hay mayores diferencias.

Tires are the most influential component of the vehicle as they constitute the only contact between the vehicle and the road and have to generate and transmit forces necessary for the driver to control the vehicle. Hydroplaning is a phenomenon which occurs when a layer of water builds up between the tires of a vehicle and the road surface which leads to loss of traction that prevents the vehicle from responding to control inputs such as steering, braking or acceleration. It has become an extremely important factor in the automotive and tire industry to study the factors affecting vehicle hydroplaning. Nearly 10-20% of road fatalities are caused by lack of traction on wet surfaces. The tire tread pattern, load, inflation pressure, slip and camber angles influence hydroplaning to a great extent. Finite Element Analysis, although computationally expensive, provides an excellent way to study such Fluid Structure Interactions (FSI) between the tire-water-road surfaces. Abaqus FSI CEL approach has been used to study tire traction with various vehicle configurations. The tire force data obtained from the Finite Element simulations is used to develop a full vehicle hydroplaning model by integrating the relevant outputs with the commercially available vehicle dynamics simulation software, CarSim. / Master of Science

The Master's thesis deals with the creation of the numerical model that serves to analysis of the acoustic properties of separating construction of a wooden structure. The work includes theoretical basis for solving the subject, it discusses the airborne sound insulation of separating structures, focuses on wooden buildings, describes a computing environment ANSYS and model creation in it. More variants of model were compiled, CLT panel and frame construction. Model itself is using scripting language APDL and each step of creation is described. The results of numerical simulations describe the distribution of pressure in front and behind the separation construction. Results are compiled into graphs and single value of weighted airborne sound insulation is evaluated. In conclusion individual results of model variants are compared, model accuracy improvements are discussed.

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Sediment erosion is a major challenge for run-of-river power plants, especially during flood periods. Due to the high content of hard minerals such as quartz and feldspar carried in the river, substantial damage is observed on the turbine components. Material is gradually removed, thus the efficiency of the turbine decreases and the operating time of the turbine reduces. Hydro power plants situated in areas with high sediment concentration suffer under hard conditions, where turbine components could be worn out after only a short period of three months. This short life expectation causes trouble for energy production since the replacement of new turbine parts is a time consuming and costly procedure. It is desirable to design a Francis runner which will withstand sediment erosion better than the traditional designs. The literature states that an expression for erosion is velocity to the power of three. By reducing the relative velocities in the runner by 10%, the erosion will decrease almost 30%. The objective is to improve the design of a Francis turbine which operates in rivers with high sediment concentration, by looking at the design parameters in order to reduce erosion wear. A Francis turbine design tool was developed to accomplish the parameter study. In the search for an optimized Francis runner, several design proposals were compared against a reference design by evaluating the turbine’s performance. The hydraulic flow conditions and the prediction of erosion on the turbine components are simulated by analyzing the models with a Computational Fluid Dynamic (CFD) tool. A Fluid Structure Interaction (FSI) analysis ensures that the structural integrity of the design is within a desired value. Results from this research show that it is feasible to design a runner with an extended lifetime, without affecting the main dimensions and hydraulic efficiency.

This work details the development of a computational tool that can accurately model strongly-coupled fluid-structure-interaction (FSI) problems, with a particular focus on thin-walled structures undergoing large, geometrically non-linear deformations, which has a major interest in, amongst others, the aerospace and biomedical industries. The first part of this work investigates improving the efficiency with which a stable and robust in-house code, Elemental, models thin structures undergoing dynamic fluid-induced bending deformations. Variations of the existing finite volume formulation as well as linear and higher-order finite element formulations are implemented. The governing equations for the solid domain are formulated in a total Lagrangian or undeformed conguration and large geometrically non-linear deformations are accounted for. The set of equations is solved via a single-step Jacobi iterative scheme which is implemented such as to ensure a matrix-free and robust solution. Second-order accurate temporal discretisation is achieved via dual-timestepping, with both consistent and lumped mass matrices and with a Jacobi pseudo-time iteration method employed for solution purposes. The matrix-free approach makes the scheme particularly well-suited for distributed memory parallel hardware architectures. Three key outcomes, not well documented in literature, are highlighted: the issue of shear locking or sensitivity to element aspect ratio, which is a common problem with the linear Q4 finite element formulation when subjected to bending, is evaluated on the finite volume formulations; a rigorous comparison of finite element vs. finite volume methods on geometrically non-linear structures is done; a higher-order finite volume solid mechanics procedure is developed and evaluated. The second part of this work is concerned with fluid-structure interaction (FSI) modelling. It considers the implementation and coupling of a higher order finite element structural solver with the existing finite volume fluid-flow solver in Elemental. To the author’s knowledge, this is the first instance in which a strongly-coupled hybrid finite element–finite volume FSI formulation is developed. The coupling between the fluid and structural components with non-matching nodes is rigorously assessed. A new partitioned fluid-solid interface coupling methodology is also developed, which ensures stable partitioned solution for strongly-coupled problems without any additional computational overhead. The solver is parallelised for distributed memory parallel hardware architectures. The developed technology is successfully validated through rigorous temporal and mesh independent studies of representative two-dimensional strongly-coupled large-displacement FSI test problems for which analytical or benchmark solutions exist. / Dissertation (MEng)--University of Pretoria, 2012. / Mechanical and Aeronautical Engineering / unrestricted

Please read the abstract (Summary) in the 00front part of this document / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted