Tübingen, Universiẗat, Diss., 2001.

No description available.

No description available.

Techn. University, Diss., 2004--Berlin.

A numerical method commonly referred to as smooth particle hydrodynamics (SPH) is implemented in two dimensions for solid mechanics in general and fracture mechanics in particular. The implementation is tested against a few analytical cases: a vibrating plate, a bending plate, a modus I crack and a modus II crack. A conclusion of these tests is that a better way of treating a shortcoming of SPH called tensile instability is needed. A study is made on the best choice of a vital parameter called the smoothing radius, and it is found that a good choice of the smoothing radius is roughly 1.5 times the initial particle spacing.

A complete understanding of the cooling process when hot rolling steel is essential to understanding how the quality of the steel is connected to the cooling. This is why it is of great interest to simulate this process. However traditional CFD methods are too expensive in terms of CPU time. Knowing that video games successfully simulate fluids in reasonable time, those methods could be useful for simulating the cooling process in steel manufacturing. This would mean a loss in accuracy that could be acceptable. In this thesis different methods used for fluid simulations have been studied. The Smoothed Particle Hydrodynamics (SPH) method has been chosen. The method has been implemented for simulating the cooling process in MATLAB, which is a matrix operation based programming tool. Convincing results have been achieved for a big scale, but problems still remain for an implementation on a small scale.

Universiẗat, Diss., 2000--Tübingen. / Gedr. Ausg. in Selbstverl. Stefan Kunze, Tübingen.

With the growing threat of orbital debris impacts to space structures, the development of space shielding concepts has been a critical research topic. In this study, numerical simulations of the hypervelocity impact response of stacked aluminum 6061-T6 sheets were performed to assess the effects of layering on penetration resistance. This work was initially motivated by set of experimental tests where a stack of four aluminum sheets of equal thickness was observed to have a higher hypervelocity ballistic resistance than a monolithic aluminum sheet with the same total thickness. A set of smoothed particle hydrodynamic simulations predicted a 40% increase in the ballistic limit for a 6-layer target compared to a monolithic sheet. In addition, the effect of variable sheet thickness and sheet ordering on the impact resistance was investigated, while still maintaining a constant overall thickness. A set of thin layers in front of a thick layer generally lead to a higher predicted ballistic limit than the inverse configuration. This work demonstrates an increase in the performance of advanced space shielding structures associated with multi-layering. This suggests that it may be possible to dramatically improve the performance of such structures by tailoring the material properties, interfaces, and layering concepts.

Ce mémoire présente une nouvelle méthode pour simuler de l'air en interaction avec des solides en se basant sur le modèle particulaire Smoothed Particle Hydrodynamics (SPH). Après avoir rappelé les bases de SPH ainsi que ses variantes incompressibles WCSPH et PCISPH pour simuler de l'eau, nous présentons un modèle de simulation d'air réaliste permettant de simuler des effets aérodynamiques. Par exemple nous arrivons à faire léviter une balle dans un flux d'air grâce à une gestion des interactions air-solide dans les deux sens. Nous proposons aussi une initialisation simple et rapide pour échantillonner rapidement l'air avec des particules SPH tout en prenant en compte les objets solides de la scène 3D. La technique consiste à échantillonner le domaine en se basant sur une grille uniforme puis à abaisser progressivement la densité cible appellé aussi densité au repos poussant les particules d'air à occuper tout l'espace de la simulation. Cette diminution s'arrête lorsque la densité cible vaut la densité moyenne des particules, c'est-à-dire la somme des densités des particules divisée par le nombre total de particules de fluides. Les résultats obtenus ont été comparés avec des expériences réelles dans le but de valider notre modèle.

The effect of vegetation on the dissipation of waves is important in understanding the vegetation's role in protecting coastal communities during extreme events such as hurricanes and tsunamis. Numerical modeling makes it possible to study the flow through vegetation fields, but it is important to understand the flow dynamics around one piece of vegetation and validate the numerical model used, before the dynamics of an entire vegetated patch can be modeled and understood. This project validated GPUSPH, a Lagrangian mesh-free numerical model, by determining the optimal characteristics to obtain accurate simulations for flow through a flume with and without an obstruction. The validation of GPUSPH and determination of optimal characteristics was accomplished by varying model particle spacing, sub-particle scale (SPS) turbulence inclusion in the conservation of momentum equation, and kernel weighting function for two test cases. The model particle spacing sets the initial distance between the moving grid points, known as particles, in the system. The SPS turbulence term is intended to account for turbulence generated at the sub-particle scale between the particles. The kernel weighting functions used are the quadratic kernel and the cubic spline kernel. These kernels determine how much influence surrounding particles have on the flow characteristics of an individual particle. The numerical results of these tests were compared with experimental results to obtain conclusions about the accuracy of these simulations. Based on comparisons with experimental velocities and forces, the optimal particle spacing was found to occur when the number of particles was in the high 100,000s for single precision calculations, or mid-range capabilities, for the hardware used in this project. The sub-particle scale turbulence term was only necessary when there was large-scale turbulence in the system and created less accurate results when there was no large-scale turbulence present. There was no definitive conclusion regarding the best kernel weighting function because neither kernel had overall more accurate results than the other. Based on these conclusions, GPUSPH was shown to be a viable option for modeling free-surface flows for certain conditions concerning the particle spacing and the inclusion of the subparticle scale turbulence term.