No presente trabalho, foi implementada uma formulação de otimização topológica com o objetivo de encontrar o mínimo volume de estruturas contínuas bidimensionais, em estado plano de tensão, sujeitas à restrição de tensão de von Mises. Foi utilizado o Método dos Elementos Finitos para discretizar o domínio, com o elemento não conforme de Taylor. A tensão foi suavizada, calculando-se um valor de tensão para cada nó do elemento. O fenômeno da singularidade foi contornado através do método de relaxação da tensão, penalizando-se o tensor constitutivo. Foi usada uma única medida de tensão global, a normap, resultando na redução do custo computacional do cálculo das sensibilidades. As sensibilidades da função objetivo e da restrição de tensão foram calculadas analiticamente. O problema de otimização topológica foi resolvido por um algoritmo de Programação Linear Sequencial. Os fenômenos da instabilidade de tabuleiro e da dependência da malha foram contornados pela utilização de um filtro de densidade linear. A formulação desenvolvida foi testada em 3 casos clássicos. No primeiro deles, foi testada uma viga curta em balanço, submetida a 3 diferentes tipos de penalização da função objetivo, obtendo-se uma estrutura com 27% do volume inicial, com reduzido número de elementos com densidades intermediárias. No segundo caso, foi testada a mesma estrutura submetida à flexão, chegandose a uma topologia bem definida no formato de duas barras, com 16,25% do volume inicial. No terceiro caso, em que foi utilizado um componente estrutural em formato de “L”, justamente por favorecer o surgimento de concentração de tensão em sua quina interna, o otimizador gerou uma estrutura bem definida, permanecendo, contudo, uma pequena região de concentração de tensão na topologia final. / A topology optimization formulation to search for the minimum volume of twodimensional linear elastic continuous structures in plane stress, subject to a von Mises stress constraint, was implemented in this study. The extended domain was discretized using Taylor nonconforming finite element. Nodal values of the stress tensor field were computed by global smoothing. A penalized constitutive tensor stress relaxation method bypassed the stress singularity problem. A single p-norm global stress measure was used to speed up the sensitivity analysis. The sensitivities of the objective function and stress constraints were derived analytically. The topology optimization problem was solved by a Sequential Linear Programming algorithm. A linear density filter avoided the checkerboard and the mesh dependence phenomena. The formulation was tested with three benchmark cases. In the first case, a tip loaded short cantilever beam was optimized using a sequence of three different objective function penalizations. The converged design had approximately 27% of the initial volume, with a small proportion of intermediate densities areas. In the second case, the same domain was subjected to shear, resulting a well defined two-bar design, with 16.25% of the initial volume. In the third case, an L-shape structure was studied, because it has a stress concentration at the reentrant corner. In this last case, the final topology was well-defined, but the stress concentration was not completely removed.

Context. Simulating realistic fluid behavior in incompressible fluids for computer graphics has been pioneered with the implicit incompressible smoothed particle hydrodynamics (IISPH) solver. The algorithm converges faster than other incompressible SPH-solvers, but real-time performance (in the perspective of video games, 30 frames per second) is still an issue when the particle count increases. Objectives. This thesis aims at improving the performance of the IISPH-solver by proposing a parallel solution that runs on the GPU using CUDA. The solution should not compromise the physical accuracy of the original solution. Investigated aspects are execution time, memory usage and physical accuracy. Methods. The proposed implementation uses a fine-grained approach where each particle is calculated on a separate thread. It is compared to a sequential and a parallel OpenMP implementation running on the CPU. Results and Conclusions. It is shown that the parallel CUDA solution allow for real-time performance for approximately 19 times the amount of particles than that of the sequential implementation. For approximately 175 000 particles the simulation runs at the constraint of real-time performance, more particles are still considered interactive. The visual result of the proposed implementation deviated slightly from the ones on the CPU.

The expansion ratio (defined as the ratio of the expanded thickness to the original thickness) of intumescent coatings is the most important quantity that determines their fire protection performance. This thesis explores two possible methods of predicting intumescent coating expansion: an analytical method, and a detailed numerical simulation method using Smoothed Particle Hydrodynamics (SPH).The analytical method is based on a cell-model and predicts bubble growth due to pressure increase in viscous liquid with constant viscosity. It has been extended to non-uniform temperature field and temperature-dependent viscosity of intumescent melt. Accuracy of this extended analytical method is assessed by comparison against the cone calorimeter and furnace fire tests on intumescent coating protected steel plates with different intumescent coating thicknesses, steel plate thicknesses, and heating conditions. The extended analytical method is then used to investigate how intumescent coating expansion and intumescent coating effective thermal conductivity are affected by changing the coating thickness, the steel thickness and the fire condition (including smouldering fire). The main conclusion is that the expansion ratio decreases as the rate of heating increases. Therefore, the intumescent coating properties obtained from the Standard fire exposure may be safely used for slower realistic fires, but would produce unsafe results for faster fires. The second method explores the potential of a meshless numerical simulation: Smoothed Particle Hydrodynamics (SPH). SPH modelling of intumescent coating expansion has been implemented using the SPHysics FORTRAN open-source code as a platform. To check the validity of this modelling method, the modelling results are compared against theoretical solutions for surface tension (Young-Laplace theorem), and available numerical and analytical solutions for bubble expansion. A new algorithm for representing the mass transfer of gas into the bubble using SPH particle insertion and particle shifting scheme is presented to simulate the bubble expansion process. Close agreement with an analytical solution for the initial bubble expansion rate computed by SPH is obtained. Whilst this research has demonstrated the potential of using SPH to numerically simulate intumescent coating expansion, it has also revealed significant challenges that should be overcome to make SPH a feasible method to simulate intumescent coating expansion. The main challenges include:• Simulating gas-polymer flows when expansion is occurring where there are vastly different properties of these two fluids with a density ratio of about 1000. This high density ratio may easily cause numerical pressure noise, especially at the liquid-gas interface.• Extremely high computational cost necessary to achieve sufficient accuracy by using a large number of particles (higher resolution), especially for the multi-phase SPH program, and very small time step for the lighter fluid (air). • The behaviour of intumescent coatings involves expansion ratios on the order of 10-100 with thousands of bubbles which grow, merge and burst. Based on the results of this exploratory research, future improvements are outlined to further develop the SPH simulation method.

[pt] Estruturas submarinas utilizadas nos sistemas de produção de óleo e gás offshore são normalmente projetadas para permanecerem no leito marinho por décadas. Para a grande maioria dessas estruturas a instalação é uma etapa crítica que pode requerer recursos dispendiosos e significativos esforços de engenharia. A descida de estruturas submarinas em regiões de ondas marinhas é uma operação complexa, uma vez que envolve acelerações desses corpos induzidas pelos movimentos das embarcações que, associados com os deslocamentos da superfície do mar, podem levar a significativas cargas de impacto nessas estruturas durante a entrada na água. O estágio inicial do impacto durante a entrada na água tem sido tema de muita pesquisa no último século, desde os trabalhos pioneiros de von Kármán e Wagner sobre a hidrodinâmica do pouso de hidroaviões. O cenário do impacto da proa de navios na superfície do mar também tem sido objeto de estudo, uma vez que pode levar a danos localizados ou mesmo catastróficos ao casco. Diferentes métodos numéricos têm sido aplicados para análise desse problema. A principal contribuição desse trabalho é a utilização do método numérico Smoothed Particle Hydrodynamics (SPH) para estimar as cargas de slamming em corpos rígidos durante a entrada na água considerando superfícies em repouso e sob o efeito de ondas. Inicialmente é introduzida a fundamentação teórica básica sobre o impacto hidrodinâmico, seguida da descrição do método SPH. Aplicações do SPH para simular a entrada na água de corpos rígidos são apresentadas considerando casos em queda livre e com velocidade constante e os resultados são comparados com experimentos e simulações numéricas obtidos na literatura. A presença de ondas regulares durante a entrada na água com velocidade constante também é considerada. Os resultados numéricos obtidos neste trabalho demonstram a viabilidade da abordagem proposta para estimar as cargas de slamming em estruturas submarinas durante a entrada na água. / [en] Subsea structures employed on offshore oil and gas production systems are commonly designed to be laid on seafloor for decades. For most of these structures the installation is a critical stage and may require costly resources and significant engineering effort. Lowering subsea structures through the wave zone is a complex operation as it involves accelerations of these bodies induced by the vessel motion which, associated to the sea surface displacements, may lead to significant impact loads on these structures during water entry. The initial stage of impact during water entry has been a subject of many researches over the past century since the pioneering work of von Kármán and Wagner on the hydrodynamics of an alighting sea plane. The scenario of impact of the forebody of a ship on the sea surface has also been subject of studies, as it may cause localized and eventually catastrophic damage to the hull. Different numerical methods have been applied to the analysis of this problem. The main contribution of this work is the use of the Smoothed Particle Hydrodynamics (SPH) method to estimate slamming loads on rigid bodies during water entry considering both calm and wavy surfaces. A basic theoretical background on hydrodynamic impact load is firstly introduced, followed by the description of the SPH method. Applications of SPH to simulate water entry of rigid bodies considering both free fall and constant velocity cases are presented and results are compared with experiments and numerical simulations from the literature. The presence of regular waves during constant velocity water entry is also considered. The numerical results obtained here demonstrate the effectiveness of the proposed approach to estimate slamming loads on subsea structures during water entry.

This thesis investigates turbulent wall-bounded flows using the Smoothed Particle Hydrodynamics (SPH) method. The first part focuses on the SPH method itself in the context of the Navier-Stokes equations with a special emphasis on wall boundary conditions. After discussing classical wall boundary conditions a detailed introduction to unified semi-analytical wall boundary conditions is given where the key parameter is a renormalization factor that accounts for the truncated kernel support in wall-bounded flows. In the following chapter it is shown that these boundary conditions fulfill energy conservation only approximately. This leads to numerical noise which, interpreted as form of Brownian motion, is treated using an additional volume diffusion term in the continuity equation where it is shown to be equivalent to an approximate Riemann solver. Two extensions to the boundary conditions are presented dealing with variable driving forces and a generalization to Robin type and arbitrary-order interpolation. Two modifications for freesurface flows are then presented, one for the volume diffusion term and the other for the algorithm that imposes Robin boundary conditions. The variable driving force is validated using a Poiseuille flow and the results indicate an error which is five orders of magnitude smaller than with the previous formulation. Discretising the wave equation with Robin boundary conditions proves that these are correctly imposed and that increasing the order of the interpolation decreases the error. The two modifications for flows under the influence of external forces significantly reduce the error at the free-surface. Finally, a dam break over a wedge demonstrates the capabilities of all the proposed modifications. With the aim of simulating turbulent flows in channels, the thesis moves on to extending the unified semi-analytical wall-boundary conditions to three dimensions. The thesis first presents the consistent computation of the vertex particle mass. Then, the computation of the kernel renormalization factor is considered, which in 3-D consists of solving an integral over a two dimensional manifold where the smoothing kernel intersects the boundary. Using a domain decomposition algorithm special integration areas are obtained for which this integral can be solved for the 5 th -order Wendland kernel. This algorithm is successfully applied to several validation cases including a dam break with an obstacle which show a significant improvement compared to other approximative methods and boundary conditions. The second part of this thesis investigates turbulent flows, in particular turbulent channel flow. This test case is introduced in detail showing both the physical properties as well as established numerical methods such as direct numerical simulation (DNS) and large eddy simulation (LES). In the penultimate chapter several SPH simulations of the turbulent channel flow are shown. The first section deals with a quasi DNS of the minimal-flow unit, a channel flow with a minimal domain size to sustain turbulent flow structures. The Eulerian statistics are compared to literature and show good agreement except for some wall-normal quantities. Furthermore, preliminary Lagrangian statistics are shown and compared to results obtained from a mesh-based DNS. The final simulation shows a LES of a full-sized channel at Reynolds number Re τ = 1000. The Eulerian statistics are compared to literature and the discrepancies found are explained using simulations of the Taylor-Green vortex, indicating that the momentum is not transferred appropriately due to an unresolved velocity-pressure-gradient tensor.

Tsunamis are among the most terrifying and complex physical phenomena potentially affecting almost all coastal regions of the Earth. Tsunami waves propagate in the ocean over thousands of kilometres away from their generating source at considerable speeds. Among several other tsunamis that occurred during the past decade, the 2004 Indian Ocean Tsunami and the 2011 Tohoku Tsunami in Japan, considered to be the deadliest and costliest natural disasters in the history of mankind, respectively, have hit wide stretches of densely populated coastal areas. During these major events, severe destruction of inland structures resulted from the action of extreme hydrodynamic forces induced by tsunami flooding. Subsequent field surveys in which researchers from the University of Ottawa participated ultimately revealed that, in contrast to seismic forces, such hydrodynamic forces are not taken into proper consideration when designing buildings for tsunami prone areas. In view of these limitations, a novel interdisciplinary hydraulic-structural engineering research program was initiated at the University of Ottawa, in cooperation with the Canadian Hydraulic Centre of the National Research Council, to help develop guidelines for the sound design of nearshore structures located in such areas. The present study aims to simulate the physical laboratory experiments performed within the aforementioned research program using a single-phase three-dimensional weakly compressible Smoothed Particle Hydrodynamics (SPH) numerical model. These experiments consist in the violent impact of rapidly advancing tsunami-like hydraulic bores with individual slender structural elements. Such bores are emulated based on the classic dam-break problem. The quantitatively compared measurements include the time-history of the net base horizontal force and of the pressure distribution acting on columns of square and circular cross-sections, as well as flow characteristics such as bore-front velocity and water surface elevation. Good agreement was obtained. Results show that the magnitude and duration of the impulsive force at initial bore impact depend on the degree of entrapped air in the bore-front. The latter was found to increase considerably if the bed of the experimental flume is covered with a thin water layer of even just a few millimetres. In order to avoid large fluctuations in the pressure field and to obtain accurate simulations of the hydrodynamic forces, a Riemann solver-based formulation of the SPH method is utilized. However, this formulation induces excessive numerical diffusion, as sudden and large water surface deformations, such as splashing at initial bore impact, are less accurately reproduced. To investigate this particular issue, the small-scale physical experiment of Kleefsman et al. (2005) is also considered and modeled. Lastly, taking full advantage of the validated numerical model to better understand the underlying flow dynamics, the influence of the experimental test geometry and of the bed condition (i.e. dry vs. wet) is investigated. Numerical results show that when a bore propagates over a wet bed, its front is both deeper and steeper and it also has a lower velocity compared to when it propagates over a dry bed. These differences significantly affect the pressure distributions and resulting hydrodynamic forces acting on impacted structures.

Currently, the accurate prediction of the impact of an extreme wave on infrastructure located near shore is difficult to assess. There is a lack of established methods to accurately quantify these impacts. Extreme waves, such as tsunamis generate, through breaking, extremely powerful hydraulic bores that impact and significantly damage coastal structures and buildings located close to the shoreline. The damage induced by such hydraulic bores is often due to structural failure. Examples of devastating coastal disasters are the 2004 Indian Ocean Tsunami, 2005 Hurricane Katrina and most recently, the 2011 Tohoku Japan Tsunami. As a result, more advanced research is needed to estimate the magnitude of forces exerted on structures by such bores. This research presents results of a numerical model based on the Smoothed Particle Hydrodynamics (SPH) method which is used to simulate the impact of extreme hydrodynamic forces on shore protection walls. Typically, fluids are modeled numerically based on a Lagrangian approach, an Eulerian approach or a combination of the two. Many of the common problems that arise from using more traditional techniques can be avoided through the use of SPH-based models. Such challenges include the model computational efficiency in terms of complexity of implementation. The SPH method allows water particles to be individually modeled, each with their own characteristics, which then accurately depicts the behavior and properties of the flow field. An open source code, known as SPHysics, was used to run the simulations presented in this thesis. Several cases analysed consist of hydraulic bores impacting a flat vertical wall as well as a sloping seawall. The analysis includes comparisons of the numerical results with published experimental data. The model is shown to accurately reproduce the formation of solitary waves as well as their propagation and breaking. The impacting bore profiles as well as the resulting pressures are also efficiently simulated using the model.

Alumina is one of the most commonly used engineering ceramics for a variety of applications ranging from microelectronics to prosthetics due to its desirable properties. Unfortunately, conventional machining techniques generally lead to fracture, tool failure, low surface integrity, high energy consumption, low material removal rate, and high tool wear during machining due to high hardness and brittleness of the ceramic material. Laser machining offers an alternative for rapid processing of brittle and hard engineering ceramics. However, the material properties, especially the high thermal expansion coefficient and low thermal conductivity, may cause ceramic fracture due to thermal damage. Striation formation is another defect in laser cutting. These drawbacks limit advanced ceramics in engineering applications. In this work, various lasers and machining techniques are investigated to explore the feasibility of high-quality laser machining different thicknesses of alumina. The main contributions include: (i) Fibre laser crack-free cutting of thick-section alumina (up to 6-mm-thickness). A three-dimensional numerical model considering the material removal was developed to study the effects of process parameters on temperature, thermal-stress distribution, fracture initiation and propagation in laser cutting. A rapid parameters optimisation procedure for crack-free cutting of thick-section ceramics was proposed. (ii) Low power CW CO2 laser underwater machining of closed cavities (up to 2-mm depth) in alumina was demonstrated with high-quality in terms of surface finish and integrity. A three-dimensional thermal-stress model and a two-dimensional fluid smooth particle hydrodynamic model (SPH) were developed to investigate the physical processes during CO2 laser underwater machining. SPH modelling has been applied for the first time to studying laser processing of ceramics. (iii) Striation-free cutting of alumina sheets (1-mm thickness) is realised using a nano-second pulsed DPSS Nd: YAG laser, which demonstrates the capability of high average power short pulsed lasers in high-quality macro-machining. A mechanism of pulsed laser striation-free cutting was also proposed. The present work opens up new opportunities for applying lasers for high-quality machining of engineering ceramics.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22047号 / 工博第4628号 / 新制||工||1722(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 後藤 仁志, 教授 細田 尚, 准教授 KHAYYER,Abbas / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The shaped charges on the market today ranges from about 20 to 200 mm in diameter but there is a need of smaller sizes for example in applications where a small projectile with a high speed is needed or to equip or take out drones with. The objective of this thesis work was to develop a miniaturized shaped charge with dimensions smaller than those available today and preferably with a diameter down to 10 mm. The project was conducted at Karlstad University in collaboration with Saab Dynamics AB. The process used during this project was to start with a feasibility study to obtain information about the limits on dimensions in order to investigate how small dimensions can be used for the casing and liner with respect to manufacturability. The feasibility study was conducted by studying academic literature, contacting companies with expertise within the field of manufacturing. A previously used shaped charge was used as a starting point and the dimensions was scaled in accordance with the objective. The influence of the design parameters was examined using the γSPH module in IMPETUS Afea. The liner material used was restricted to oxygen-free high thermal conductivity copper and different materials for the casing was tested. Two material selections for the casing were made with the aid of Granta Edupack. It has been concluded that it is possible to manufacture a miniaturized shaped charge with dimensions down to about ten mm. Both a design for a jet forming shaped charge and an explosively formed penetrator was developed during the project. The resulting projectile for the explosively formed penetrator had a velocity of 2450 m/s, a total length of 7.3 mm and 3.5 mm in diameter, and the jet forming shaped charge had a jet tip velocity of 7060 m/s and was able to penetrate 38-mm into an AISI 4340 steel target according to the models used in IMPETUS Afea. A prototype was planned but due to cost restrictions, it is left as future work. / Riktad sprängverkan (RSV)-laddningarna som finns på marknaden idag sträcker sig från ungefär 20 till 200 mm i diameter. Det finns dock ett behov för storlekar mindre än detta, till exempel i tillämpningar där en liten projektil med hög fart krävs, alternativt att utrusta eller sänka drönare med. Målet med detta examensarbete var att utveckla en miniatyriserad RSV-laddning med dimensioner mindre än vad som finns tillgängligt idag och helst med en diameter neråt tio mm. Projektet utfördes på Karlstads universitet i samarbete med Saab Dynamics AB. Processen som användes under detta projekt gick ut på att börja med en förstudie for att erhålla information om gränserna för mått för att undersöka hur små dimensioner som kan användas för höljet och linern med avseende på tillverkningsbarhet. Förstudien genomfördes genom att studera akademisk litteratur och kontakta företag med expertis inom tillverkningsområdet. En tidigare använd RSV-laddning användes som startpunkt och dimensionerna justerades i enlighet med målet. Påverkan av parametrar på prestanda undersöktes genom att använda γSPH modulen i IMPETUS Afea. Det använda materialet för linern begränsades till OFHC koppar och olika material för höljet testades. Två materialval gjordes för höljet med hjälp av Granta Edupack. Slutsatsen som kan dras utifrån arbetet är att det är möjligt att tillverka miniatyriserade RSV-laddningar med dimensioner neråt tio mm. Både en design för en strålbildande RSV-laddning och en projektilbildande RSV-laddning utvecklades under projektet. Den resulterande projektilen för den projektilbilande RSV-laddningen hade en fart på 2450 m/s, en längd av totalt 7.3 mm och 3.5 mm i diameter och den strålbildande RSV-laddningen hade en spetsfart på 7060 km/s och kunde penetrera 38 mm AISI 4340 stål enligt modellen som användes i IMPETUS Afea. En prototyp planerades men på grund av kostnadsrestriktioner lämnades det som framtida arbete.