Fluid simulations are computationally intensive and therefore time consuming and expensive. In the field of visual effects, it is imperative that artists be able to efficiently move through iterations of the simulation to quickly converge on the desired result. One common fluid simulation technique is the Smoothed Particle Hydrodynamics (SPH) method. This method is highly parellelizable. I have implemented a method to integrate a Graphics Processor Unit (GPU) accelerated SPH capability into the 3D software package Houdini. This helps increase the speed with which artists are able to move through these iterations. This approach is extendable to allow future accelerations of the algorithm with new SPH techniques. Emphasis is placed on the infrastructure design so it can also serve as a guideline for both GPU programming and integrating custom code with Houdini.

Zugl.: Stuttgart, University, Diss.

Zugl.: Stuttgart, Univ., Diss., 2009

This PhD thesis reports an investigation into medical coronary stent cutting using three different types of lasers and associated physical phenomena. This study is motivated by a gap in the current knowledge in stent cutting identified in an extensive literature review. Although lasers are widely used for stent cutting, in general the laser technology employed is still traditionally based on millisecond pulsed Nd:YAG lasers. Although recent studies have demonstrated the use of fibre lasers, picosecond and femtosecond lasers for stent cutting, it has been preliminary studies.To further understand the role of new types of lasers such as pulsed fibre lasers, picosecond and femtosecond pulsed lasers in stent cutting, these three lasers based stent cutting were investigated in this project. The first investigation was on a new cutting method using water assisted pulsed (millisecond) fibre laser cutting of stainless steel 316L tubes to explore the advantages of the presence of water compared to the dry cutting condition. Significant improvements were observed with the presence of water; narrower kerf width, lower surface roughness, less dross attachment, absence of backwall damage and smaller heat affected zone (HAZ). This technique is now fully commercialised by Swisstec, an industrial project partner that manufactures stent cutting machines.The second investigation used the picosecond laser (with 6 ps pulse duration in the UV wavelength range) for cutting nickel titanium alloy (nitinol) and platinum iridium alloy. The main achievement in this study was obtaining dross-free cut as well as clean backwall, which may eliminate the need for extensive post-processing. Picosecond laser cutting of stents is investigated and reported for the first time. The third area of investigation was on the use of a femtosecond laser at 100 fs pulse duration for cutting nickel titanium alloy tubes. It was found that dry cutting degraded the cut quality due to debris and recast formation. For improvement, a water assisted cutting technique was undertaken, for the first time, by submerging the workpiece in a thin layer of water for comparison with the dry cutting condition. The final part of the thesis presents a three dimensional numerical model of the laser micromachining process using smoothed particle hydrodynamics (SPH). The model was used to provide better understanding of the laser beam and material interaction (with static beam) including the penetration depth achieved, phase changes, melt ejection velocity, also recast and spatter formation. Importantly, the model also simulated the wet machining condition by understanding the role of water removing the melt ejected during the process which avoided backwall damages. Results with the fibre laser in millisecond pulse duration were used for the validation purposes. The conclusions reached in this project and recommendations for future work are enclosed.The work has resulted in the publication of 3 journal papers and 2 additional journal paper submissions.

An incompressible Smoothed Particle Hydrodynamics (SPH) method is put forward to simulate non-linear and dispersive solitary wave reflection and transmission characteristics after interacting with a partially immersed curtain-type breakwater. The Naviers¿Stokes equations in Lagrangian form are solved using a two-step split method. The method first integrates the velocity field in time without enforcing incompressibility. Then the resulting deviation of particle density is projected into a divergence-free space to satisfy incompressibility by solving a pressure Poisson equation. Basic SPH formulations are employed for the discretization of relevant gradient and divergence operators in the governing equations. The curtainwall and horizontal bottom are also numerically treated by fixed wall particles and the free surface of wave is tracked by particles with a lower density as compared with inner particles. The proposed SPH model is first verified by the test of a solitary wave with different amplitudes running against a vertical wall without opening underneath. Then it is applied to simulate solitary wave interacting with a partially immersed curtain wall with different immersion depths. The characteristics ofwave reflection, transmission, dissipation and impacting forces on the curtain breakwater are discussed based on computational results

Yes / This research paper presents an incompressible smoothed particle hydrodynamics (ISPH) technique to investigate a regular wave overtopping on the coastal structure of different types. The SPH method is a mesh-free particle modeling approach that can efficiently treat the large deformation of free surface. The incompressible SPH approach employs a true hydrodynamic formulation to solve the fluid pressure that has less pressure fluctuations. The generation of flow turbulence during the wave breaking and overtopping is modeled by a subparticle scale (SPS) turbulence model. Here the ISPH model is used to investigate the wave overtopping over a coastal structure with and without the porous material. The computations disclosed the features of flow velocity, turbulence, and pressure distributions for different structure types and indicated that the existence of a layer of porous material can effectively reduce the wave impact pressure and overtopping rate. The proposed numerical model is expected to provide a promising practical tool to investigate the complicated wave-structure interactions. / Nazarbayev University Seed Grant, entitled “Environmental assessment of sediment pollution impact on hydropower plants”. S. Shao also acknowledges the Royal Society Research Grant (2008/R2 RG080561)

This work presents a partitioned approach to simulating free-surface flow interaction with hyper-elastic structures in which a smoothed particle hydrodynamics (SPH) solver is coupled with a finite-element (FEM) solver. SPH is a mesh-free, Lagrangian numerical technique frequently employed to study physical phenomena involving large deformations, such as fragmentation or breaking waves. As a mesh-free Lagrangian method, SPH makes an attractive alternative to traditional grid-based methods for modeling free-surface flows and/or problems with rapid deformations where frequent re-meshing and additional free-surface tracking algorithms are non-trivial. This work continues and extends the earlier coupled 2D SPH-FEM approach of Yang et al. [1,2] by linking a double-precision GPU implementation of a 3D weakly compressible SPH formulation [3] with the open source finite element software Code_Aster [4]. Using this approach, the fluid domain is evolved on the GPU, while the CPU updates the structural domain. Finally, the partitioned solutions are coupled using a traditional staggered algorithm. / Ph. D.

L'étude porte sur l'impact de vagues sur une paroi rigide en deux dimensions. Les travaux de modélisation numérique ont été réalisés à partir du code JOSEPHINE, utilisant la méthode Smoothed Particle Hydrodynamics (SPH), développé au sein du laboratoire LOMC. La méthode choisie repose sur une approximation faiblement compressible des équations d'Euler. Dans un premier temps, l'étude d'un cas académique de l'impact d'un jet triangulaire a permis de valider et améliorer le schéma numérique permettant la modélisation d'impacts violents. Les pressions d'impacts ont été étudiées et comparées à d'autres résultats analytiques et numériques. Dans un second temps, l'impact d'une vague solitaire déferlante a été modélisé. Les pressions d'impact ont été déterminées et comparées avec celles issues d'expériences. Après une analyse numérique approfondie des simulations mono-phasiques, un modèle diphasique a été spécifiquement développé pour tenir compte à la fois des phases eau et air. Le modèle SPH diphasique a permis d'améliorer la qualité des résultats, notamment pour le cas « air pocket impact », où une poche d'air est emprisonnée lors de l'impact. Le but final de ce travail est d'étudier la survivabilité des récupérateurs d'énergie marine adossés à des structures côtières lors d'événements météorologiques violents. / The present manuscript focuses on the wave impact on a rigid wall in two dimensions. The numerical computations were performed using a Smoothed Particle Hydrodynamics (SPH) software named JOSEPHINE, developed at the LOMC laboratory. The software is based on a weakly-compressible SPH model, where Euler equation of motion is solved. Firstly, an academic test case, the impact of a triangular jet was used to validate and improve the numerical scheme to model violent impacts.The impact pressures were studied and compared to analytical and other numerical results. Secondly, the impact of a breaking solitary wave was modelled.The impact pressures were determined and compared with those obtained in the experiments. After a depth numerical analysis of mono-phase flow computations, a two-phase model was developed specifically to consider both water and air phases. The two-phase SPH model improved the results quality, especially for the case "air pocket impact", where an air pocket is trapped during the impact. The ultimate goal of this work is to study the survivability of coastal structures equipped with a marine energy recovery device during severe weather events.

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Fluids are important to the Visual Effects Industry but extremely hard to control and simulate because of the complexity of the governing equations. Fluid solvers can be divided into two categories, those of the Eulerian point of reference and those of the Lagrangian. Both categories have different advantages and weaknesses and hybrid methods are popular. This thesis examines Smoothed Particle Hydrodynamics, a Lagrangian method for physically based uid simulations. To allow the artist the exibility given by shorter simulation times and increased number of iterations, the performance of the solver is key. In order to maximize the speed of the solver it is implemented entirely on the GPU, including collisions, volumetric force fields, sinks and other artist tools. To understand the implementation decisions, it is important to be familiar with the CUDA programming model. Thus, a brief explanation of CUDA is given before the exact implementation of the methods are explained. The results are presented along with a performance comparison as well as a discussion of the different parameters which can be fed to the solver. Some thoughts on possible future extensions can be found in the conclusion.