Ce travail de recherche est dédié à la compréhension des mécanismes physiques de l’érosion de cavitation dans un fluide compressible à l’échelle fondamentale de l’implosion d’une bulle de cavitation. Suite à l’implosion d’une bulle de vapeur à proximité d’une surface solide, des très hautes pressions sont générées. Ces pressions sont considérées responsables de l’endommagement (érosion) des surfaces solides observé dans la plupart des applications. Notre approche numérique démarre avec le développement d’un solveur compressible capable de résoudre les bulles de cavitation au sein du code volumes finis YALES2 en utilisant un simple modèle de mélange homogène des phases fluides. Le solveur est étendu à une approche ALE (Arbitraire Lagrangien Eulérien) dans le but de mener des simulations d’interaction fluide-structure sur un maillage mobile. La réponse du matériau solide est calculée avec le code de calcul éléments finis Cast3M, et nous a permis de mener des simulation avec un couplage d’abord monodirectionnel, ensuite bidirectionnel, entre le fluide et le solide. On compare des résultats obtenus à deux dimensions, puis à trois, avec des observations expérimentales. On discute les chargements de pression estimés, et les réponses de différents matériaux pour des implosions de bulle à des différentes distances de la surface. Enfin, à travers l’utilisation de simulations avec couplage bidirectionnel entre fluide et solide, on identifie l’amortissement des chargements de pression pour les différents matériaux. / This research is devoted to understanding the physical mechanism of cavitation erosion in compressible liquid flows on the fundamental scale of cavitation bubble collapse. As a consequence of collapsing bubbles near solid wall, high pressure impact loads are generated. These pressure loads are believed to be responsible for the erosive damages on solid surface observed in most applications. Our numerical approach begins with the development of a compressible solver capable of resolving the cavitation bubbles in the finite-volume solver YALES2 employing a simplified homogenous mixture model. The solver is extended to Arbitrary Lagrangian-Eulerian formulation to perform fluid structure interaction simulation with moving mesh capabilities. The material response is resolved with the finite element solver Cast3M, which allowed us to perform one-way and two-way coupled simulations between the fluid and solid domains. In the end, we draw comparisons between 2D and 3D vapor bubble collapse dynamics and compare them with experimental observations. The estimated pressure loads on the solid wall and different responses of materials for attached and detached bubble collapses are discussed. Finally, the damping of pressure loads by different materials is identified with two-way coupled fluid-structure interaction.

Le travail présenté a pour objectif la prédiction numérique de la résistance résiduellede grandes structures vis-à-vis d’évènements accidentels, tels que ceux rencontrés p.ex. dans le cas de la collision de navires ou d’impact d’oiseaux en aéronautique. Cesévènements peuvent dans certain cas conduire à la rupture, qui est ici considéréeductile. La difficulté de cette étude, consiste à reproduire dans une méthodologieunifiée basée sur la méthode des éléments finis les étapes successives menant àla ruine ultime de la structure. Ces étapes sont : l’endommagement ductile, lalocalisation de la déformation et la propagation de la fissure. Un élément essentiel pour la conception d’un modèle de fissuration ductile prédictif est le traitement numérique de la phase transitoire critique de localisation de la déformation induite par l’endommagement dans une bande de matière étroite.A cet effet, trois points de vue différents en termes de champ de déplacement àtravers la bande de localisation sont proposés. Ces trois approches se distinguentpar le type de discontinuité considérée : forte, faible et régularisée (expression nonlinéaire). Un cadre variationnel consistant est élaboré pour chacune des trois approches.Ainsi la cinématique enrichie est incorporée dans la formulation de l’élément fini enutilisant la méthode des éléments finis enrichis (X-FEM). Puis, la performance deces méthodes est évaluée vis-à-vis de leur capacité à modéliser la phase transitoireentre endommagement diffus (mécanique des milieux continus) et propagation defissure (mécanique de la rupture). Ces travaux sont réalisés dans le contexte dematériaux ductiles. D’après les analyses réalisées, la combinaison du modèle de ’discontinuité fortecohésive’ et la X-FEM semble être la plus prometteuse des trois approches étudiéespour allier physique et numérique. Le développement d’un tel modèle est discutéen détail. Enfin, deux critères supplémentaires sont définis : le premier pour lepassage de l’endommagement diffus au modèle de bande cohésive et un deuxièmepour le passage du modèle de bande cohésive à la rupture. / The present work aims at numerically predicting the current residual strengthof large engineering structures made of ductile metals regarding accidental events,e.g. ships collision or bird strike in aviation, which may potentially lead to failure.With this aim in view, the challenge consists in reproducing within a unified finiteelement (FE)-based methodology the successive steps of micro-voiding-induceddamage, strain localization and crack propagation, if any.A key ingredient for a predictive ductile fracture model is the proper numericaltreatment of the critical transition phase of damage-induced strain localizationinside a narrow band. For this purpose, three different viewpoints in terms ofdisplacement field across the localization band are proposed involving a strong,weak and (non-linearly) regularized discontinuity, respectively.A consistent variational framework is elaborated for each of the three methods,whereby the enriched kinematics is embedded into the FE formulation using theeXtended FEM. Then, within a comparative procedure, the performance of thesemethods is assessed regarding their ability of modeling the transition phase betweendiffuse damage (continuum mechanics framework) and crack propagation (fracturemechanics framework), always in the context of ductile materials.According to the aforementioned analyses, the combination of the strong discontinuitycohesive model and the X-FEM appears to be the most promising of thethree studied approaches to bring together physics and numerics. The developmentof such a model is discussed in detail. Finally, two supplementary criteria aredefined: the first one for the passage from diffuse damage to the cohesive bandmodel and the second one for the passage from the cohesive band model to thecrack.

On assiste aujourd’hui à une évolution des systèmes électroniques nomades vers des fonctionnalités plus avancées. Cette complexification des systèmes électroniques nomades nécessite une augmentation de la puissance de calcul des puces électronique, ce qui se peut se traduire par une utilisation d’une technologie CMOS agressive, mais qui se complète aujourd’hui par une technique appelée intégration 3D. Il ne s’agit donc plus d’une évolution classique à l’échelle du transistor suivant la loi de Moore mais à celle de l’échelle plus large du boîtier / système, on parle alors de la loi de « More than Moore ». L’empilement tridimensionnel (3D) des puces électroniques engendre une augmentation de la densité de puissance totale dissipée par unité de surface de l’empilement final. Cette puissance, résultant essentiellement de l’effet joule dans les transistors et l’interconnexion, est une source de chaleur qui contribue à l’augmentation de la température globale de la puce. L’objectif global de cette thèse est d’étudier les échanges thermiques dans un empilement de puces 3D durant leur fonctionnement. On s’attachera à comprendre les effets géométriques ou matériaux de l’empilement ainsi que l’impact du placement des TSV, Bumps ... sur ces échanges thermiques. L’étude s’appuie sur des simulations numériques validées par des mesures expérimentales sur des empilements 3D. Ces études numérique et expérimentale auront comme finalité de déduire des règles de dessin thermiques qui seront validées sur le dessin de circuits basiques ou plus complexes. Dans la suite, ces différents objectifs seront motivés et abordés en détail. L’établissement d’un modèle thermique basé sur des simulations en éléments finis d’un procédé industriel CMOS 65 nm 3D permettra d’aborder le problème de modélisation de la manière la plus précise possible. En effet, les précédentes simulations ont utilisé des modèles compacts – donc de moindre précision que les éléments finis – et un procédé générique qui ne reflète pas toutes les propriétés des matériaux, et en particulier celles des interfaces. Les résultats ainsi obtenus seront validés par des mesures sur des puces empilées réalisées dans le procédé considéré. Dans cette partie expérimentale, l’objectif est de déterminer une cartographie de la température dans un empilement 3D en utilisant des capteurs embarqués dans le silicium, et ce sous différentes conditions d’opération de la puce 3D. Il en ressortira un modèle numérique validé et calibré par des mesures expérimentales. / Today we are witnessing an evolution of mobile electronic systems to more advanced features. The complexity of mobile electronic systems requires an increase in computing power of electronic chips, which can lead to the use of aggressive CMOS technology, but which now completed with a technique called 3D integration. It is more of a classical evolution across the transistor following Moore's law but that of the wider scale of the packaging / system, it is called the law of "More than Moore". Three dimensional (3D) stack of electronic chip generates an increase in the density of total power dissipated per unit area of the final stack. This power, essentially resulting in the Joule effect transistors and interconnection, is a source of heat which contributes to increase the overall temperature of the chip. The global objective of this thesis is to study the heat transfer in a 3D stack of chips during operation. We will seek to understand the geometric or materials effects of the stack and the impact of the placement of TSV, Bumps ... on these heat exchanges. The study is based on numerical simulations validated by experimental measurements on 3D stacks. These numerical and experimental studies have as a goal to deduce thermal design rules that will be validated in the drawing of basic or more complex circuits. In the following, these goals will be motivated and discussed in detail. The establishment of a thermal model based on finite element simulations of an industrial process 3D CMOS 65 nm will address the problem of modelling the most accurate way possible. Indeed, previous simulations used compact models - so that the lower accuracy of finite elements - and a generic method that does not reflect all of the properties of materials, and in particular interfaces. The results obtained will be validated by measurements on stacked chips carried out within the process concerned. In the experimental part, the objective is to determine a thermal mapping in a 3D stack using sensors embedded in the silicon, and under different conditions of 3D chip process. This will provide a numerical model validated and calibrated by experimental measurements.

Vid beräkning av grundkonstruktioner tillämpas ofta Winkler-modellen där jorden ersätts med en fjäderbädd som motsvarar jordens styvhet, en så kallad bäddmodul. Samverkanseffekter försummas ofta i dagens sätt att ansätta bäddmoduler och konsekvensen av detta blir att oförutsedda dragspänningar uppstår. Syftet med undersökningen är att ge konstruktörer ett underlag så de kan välja en beräkningsmodell som ger beräkningsförutsättningar vid dimensionering av grundkonstruktioner som tar hänsyn till samverkanseffekter. Målet är att påvisa hur samverkanseffekter och ansättning av bäddmodul påverkar delar av grundkonstruktionen med hänsyn till moment. Tre olika metoder för att beräkna bäddmoduler och två olika sätt att ansätta dessa har studerats med avseende på hur moment uppträder i grundkonstruktionen. Sex modeller har analyserats i datorprogrammet FEM-Design genom fyra valda sektioner i grundkonstruktionen. Resultatet visar att val av bäddmodul inte påverkar formen på momentkurvan men att det maximala momentet kan variera stort. Resultatet påvisar även att det uppstår zoner med dragspänning i konstruktionens överkant som en effekt av samverkan. / The Winkler-model is often applied when calculating foundation slabs. The model intend to replace the subgrade with a bedding of vertical springs that corresponds with the stiffness of the soil. The integration of the foundation slab is often neglected in todays approved methods of implementing subgrade modulus. The consequence of this overlook may cause unforeseen tensile stress in the foundation. The purpose of this study is to support engineers in their decision of choosing a model and provide proper conditions designing slabs taking into account for interplay of the whole foundation structure. The aim is to demonstrate how the interplay in the construction and the application of the subgrade modulus affects parts of the foundation regarding bending moment. Three different methods of calculating subgrade modulus and two ways of application have been studied with purpose to illustrate how bending moment appear in the structure. Four sections have been selected to represent the structural behavior to analyze six model cases in the FEM-Design program. The result indicates the choosing of subgrade modulus affect maximum value of bending moment although the appearance of the momentum curve are not affected. Results also show that zones of tensile stress occur at the top of the foundation as an effect of integration effects of the whole structure.

Neste trabalho foi desenvolvida uma formulação alternativa para o acoplamento entre o método dos elementos de contorno (MEC) e o método dos elementos finitos (MEF) para análise não linear geométrica de estruturas reticuladas ligadas a meios contínuos bidimensionais heterogêneos, aplicado a problemas de interação solo-estrutura. O solo foi considerado com comportamento elástico linear e modelado via MEC por meio de uma formulação alternativa à clássica técnica de sub-região permitindo a consideração de múltiplas inclusões mais ou menos rígidas do que o material padrão e de linhas de carga internas aos domínios. Este código foi então acoplado ao programa AcadFrame, baseado no MEF posicional para análise não linear geométrica de pórticos com consideração de cinemática exata. O acoplamento numérico foi realizado por meio de uma formulação algébrica onde a matriz de rigidez do solo e a força de contato são condensadas e somadas à matriz e ao vetor de forças internas da estrutura a cada iteração no processo de Newton-Raphson. Em ambos os programas foi utilizada uma generalização do grau de aproximação dos elementos através dos polinômios de Lagrange, o que permite a utilização de elementos curvos de alta ordem. Foi utilizada ainda a técnica dos mínimos quadrados para reduzir as oscilações de forças de superfície no contato. Os resultados obtidos de forma geral são bastante satisfatórios e comprovam a eficiência da formulação. O trabalho permite a análise de problemas de edificações apoiadas sobre solos estratificados com múltiplas inclusões e linhas de carga. Permite tanto a análise de elementos apoiados diretamente sobre o solo (sapatas, radies) quanto de elementos internos e em qualquer direção, como no caso de estacas verticais ou inclinadas. Pode-se inclusive considerar as estacas passando por diferentes camadas de solo. A aplicação pode ser estendida ainda a outros problemas elásticos, acoplamento entre peças mecânicas e análise de materiais compostos. / This work presents an alternative coupling of the boundary element method (BEM) and the finite element method (FEM) to create a computer program for non linear geometric analysis of frames coupled to continuous domains, applied to soil-structure interaction. A linear elastic behavior is considered for the soil, modeled by BEM. An alternative formulation is adopted for the classic sub-region technique, allowing the consideration of multiple inclusions and load lines inside the soil domain. The BEM computational code is coupled to the AcadFrame software, based on positional FEM for non linear geometric analysis of frames, considering exact kinematics. The numerical coupling is made by an algebraic formulation where the soil stiffness matrix and contact forces are condensed and added to the structure matrix and internal forces for each iteration on Newton-Raphson process. On both programs it is adopted a generalization of the element degree assuming the Lagrange polynomials, which allows the use of curved high order elements. It was also implemented the least square method in order to obtains better and smoother results of surface forces in the contact interface. The obtained results are satisfactory and prove the formulation efficiency. The program allows the analysis of buildings supported by layered soils with multiples inclusions and load lines. It considers directly supported elements over the soil (footing foundations, radies) and internal elements in any direction, like vertical and diagonal piles. It can also consider piles going through different layers of the soil. This formulation can be applied to other elastic problems like coupling between mechanic pieces and composite material analysis.

Le développement et l'exploitation de réservoirs géothermiques profonds s'accompagnent généralement d'une sismicité induite - un effet secondaire indésirable. Cette recherche est axées sur l'utilisation de simulations numériques pour étudier la propagation des fractures hydrauliques et la réactivation de failles préexistantes lors de la stimulation hydraulique des réservoirs afin de mieux comprendre le comportement du réservoir fracturé et de réduire le risque potentiel de sismicité induite.La sismicité induite est d'abord étudiée du point de vue de l'utilisation de la loi de conservation de l'énergie afin d'expliquer le mécanisme de génération d'ondes élastiques à partir d'une rupture de roche. Ensuite, une approche approximative est proposée pour calculer les accélérations de pointe (PGA) induites par le glissement de faille. Les PGA calculés à la surface du sol servent à évaluer la perception humaine des ondes sismiques et le potentiel de dégradation des structures. / The development and the exploitation of deep geothermal reservoirs are usually accompanied with induced seismicity - an unwanted side effect. This research is focused on using numerical simulations to investigate the propagation of hydraulic fractures and the reactivation of pre-existing faults during the hydraulic stimulation of the reservoirs in an effort to better understand the fractured reservoir behavior and to reduce the potential risk of induced seismicity.The induced seismicity is studied first from the standpoint of using the law of energy conservation in order to explain the mechanism of generating elastic waves from rock failure. Then an approximate approach is proposed to calculate the peak ground accelerations (PGAs) that are induced by the fault slip. The computed PGAs on ground surface are used to assess the human perception of the seismic waves and the damage potential to structures.

Ett undersöknings- och utvecklingsarbete för att lösa ett problem med att dränkbara pumpar i ett vattenavrinningssystem gick sönder med perioder på två år i genomsnitt, utfördes i samarbete med Cementa AB i Skövde. Orsak till pumpars haveri söktes och fanns vara bristande rutiner och kunskap om det underhåll pumparna krävde. För att lösa detta problem utvecklades riktlinjer för nyinköp av torruppställda pumpar för att möjliggöra kontinuerligt underhåll. Då möjligheter för placering av torruppställd pump saknades utvecklades ett pumpfundament för placering av torruppställd pump. Krav för utvecklingsarbetet togs fram i samarbete med Cementas underhållsavdelning och teoretisk dimensionering av dränkbara länspumpars dåvarande volymflödeskapacitet utfördes. Krav utvärderades och viktades med hjälp av parvis jämförelse. Dimensionering och kontroll av hållfasthet för utvecklat pumpfundamentet utfördes med hjälp av Finita Element Analyser i programvaran Pro/Engineer Creo 1.0 Mechanica. Kontroll av hållfasthet i infästning av pumpfundamentet samt svetsfogar utfördes analytiskt. Arbetet resulterade i en rekommendation till Cementa AB i Skövde att ta in offerter på nya torruppställda pumpar med hjälp av utvecklade riktlinjer och att tillverka det pumpfundament som tagits fram inom ramen för examensarbetet, för att placera nya pumpar på. Att noggrant följa de underhållsinstruktioner som pumpar har och att underlätta för personal att utföra detta underhåll ansågs kunna bidra till att pumpar skulle få en längre och mer ekonomisk livslängd. / A development project to solve problems with why submersible pumps in a run-off system broke down with periods of two years, on average, was performed in collaboration with Cementa AB in Skövde. Reason for the pumps breakdowns was searched and found to be inadequate procedures and missing knowledge of the maintenance required on the pumps. To solve this problem, guidelines for the purchase of new dry pit pumps were developed to allow for continuous maintenance. As the possibilities of placing a dry well pump did not exist at Cementa, a pump foundation was developed. Requirements for the development work were produced in cooperation with Cementas maintenance department and theoretical dimensioning of the submersible bilge pumps volume flow capacity was performed. Requirements were evaluated and weighted using Pairwise comparison. The design and control of the strength of the developed pump foundation was performed using finite element analysis in the software Pro/Engineer Creo 1.0 Mechanica. Controls of the strength of the attachment of the pump foundation and welds were performed analytically. The work resulted in a recommendation to Cementa AB in Skövde to bring in quotes on the new dry-pit pumps using the developed guidelines and to manufacture the pump foundation developed within the framework of the thesis. Cementa was also recommended to carefully follow the maintenance instructions for pumps and make it easier for staff to perform this maintenance. This was recommended to ensure that new pumps would have a longer and more economical lifetime.

In this thesis a theory for large deformation of plates is presented. Herein aspects of the common 3D-theory for large deformation with the Kirchhoff hypothesis for reducing the dimension from 3D to 2D is combined. Even though the Kirchhoff assumption was developed for small strain and linear material laws, the deformation of thin plates made of isotropic non-linear material was investigated in a numerical experiment. Finally a heavily deformed shell without any change in thickness arises. This way of modeling leads to a two-dimensional strain tensor essentially depending on the first two fundamental forms of the deformed mid surface. Minimizing the resulting deformation energy one ends up with a nonlinear equation system defining the unknown displacement vector U. The aim of this thesis was to apply the incremental Newton technique with a conformal, C^1-continuous finite element discretization. For this the computation of the second derivative of the energy functional is the key difficulty and the most time consuming part of the algorithm. The practicability and fast convergence are demonstrated by different numerical experiments.

The piston ring in a marine two-stroke diesel engine operates in demanding conditions, involving high temperatures and pressures. Its main purposes are to seal the combustion chamber of the engine, minimize the frictional contact against the cylinder liner and transfer heat from the piston. The development of new piston ring designs for marine diesel engines is mainly based on engineering knowledge and expertise but is somewhat unstructured. A new method which may be used to overcome this lack of structure is to simulate the working conditions for the piston ring. This is the main objective of this thesis work, to invent a simulation method which allows accurate and distinct results to be obtained and thereby knowledge about piston ring performance. The simulation method is based on a three-dimensional geometric model of the piston ring, where the radial geometry should be described by the lathe curve from industry. It should also be implemented and function automatically as a simulation tool. In short terms, the calculated stresses and strains in the material, the contact pressure against the cylinder liner and the piston ring twist should be evaluated. The simulation tool should be able to model two different types of piston ring designs, namely straight cut design and CPR design, and both with optional dimensions. Validation of the results are performed with a simulation model which uses fewer dimensions, but also utilizes engineering knowledge from the marine industry. In addition to this, some more advanced investigations have been performed in order to demonstrate the capacity and power of the simulation tool. The simulation method appears to perform well and according to the simple model, but it also shows good prediction in more advanced investigations. For example, piston rings in overheated engines tend to twist more than usual, which could be seen in real investigations, and the behavior is easily recreated with the simulation tool. Also investigations with reduced cross sections, which is well known within high-speed engines, are performed. The method is executed automatically with the developed simulation tool which is based on ANSYS, a commercial simulation software. This software, that is commonly used in development work, uses a finite element method to solve the problem. The simulation tool is used as an external input which configures the geometry, finite element formulation and the result rendering. / Kolvringen i en marin tvåtaktsmotor arbetar under krävande förhållanden i form av hög temperatur och högt tryck. Dess huvudsyften är att täta motorns förbränningskammare, minimera friktion mot cylindern och transportera värme från kolven. Utvecklingen av nya kolvringsmodeller för marint bruk är huvudsakligen baserat på ingenjörskunskap och expertkunnande vilket dock lett till en viss osäkerhet. En modern metod för att bemästra denna osäkerhet är att simulera kolvringen och dess förhållanden i motorn. Det huvudsakliga målet är att skapa en simuleringsmetod som ger noggranna och tydliga resultat och därav kunskap om kolvringens påfrestningar och egenskaper under drift av motorn. Simuleringsmetoden är skapad för en tredimensionell geometri som är beskriven av bl.a. den svarvkurva som används inom industrin. Metoden skall även vara implementerad och fungera automatiskt som ett beräkningsverktyg vilket inom en rimlig tidsrymd skall beräkna intresseområden såsom spänningar, kontakttryck och twist. Det skall även vara konstruerat så att två olika kolvringmodeller skall kunna simuleras, nämligen rakskuren ring och gastät ring, och båda med valbara dimensioner. Simuleringsmetoden är bekräftad genom att jämföra med en enklare simuleringsmodell samt teknisk kunskap och resonemang. Utöver att bekräfta modellen genomförs även en del mer avancerade undersökningar för att kunna återge simuleringsverktygets verkliga effektivitet. Resultaten återger rätt karaktär och i rätt storleksordning i jämförelse med den enklare modellen men visar även på sanningenliga resultat vid mer avancerade tester. Exempelvis har överhettade motorer ofta en förstärkt twist, vilket är uppmärksammat vid mätningar, och sådana effekter kan återges med simuleringsverktyget. Även tester med förändrade tvärsnittsprofiler, vilka ofta används inom fordonsindustrin, och vilken effekt dessa profiler får på twistningen har genomförts. Metoden och det automatiska simuleringsverktyget är implementerat i den kommersiella programvaran ANSYS. Programmet använder sig av finita elementmetoden för att lösa problem och är ett vanligt program inom flera olika utvecklingsområden. Verktyget används som en extern inläsning till programmet vilket konfigurerar geometrin, finita elementformuleringen och resultatrenderingen.

Der Vortrag beschreibt numerische Singularitäten bei der h- und p-FEM, wie sie erkannt werden und welche Lösungen möglich sind bzw. was nicht vermieden werden kann.