Dissertations / Theses on the topic 'Fluid-Structure impact'

Violent wave attacking offshore and coastal structures is a complex phenomenon frequently involving air entrapment. A study on fluid/structure impact with air cavity effect is carried out in the framework of velocity potential theory. The purpose is twofold. One is to develop methodologies to tackle the technical difficulties involved. The other is to achieve a better insight into the impact dynamics and the subsequent structure/water/air interaction process, as well as the associated air cavity effect and its acting mechanism. The study starts with axisymmetric problems. Impact by a liquid column on a rigid plate is studied analytically and numerically. The initial singularity at the body-free surface intersection is analysed in detail. The feature of the resulting long thin jet is revealed: providing field solution over larger wetted area without influencing the main impact dynamics. This is favourable in the study of some problems (e.g. steady state solution or local impact over a tiny region), and thus a decoupled shallow water approximation scheme is developed for the computation with long jet. Impact with air cavity of various parameters is studied systematically. Wave impact with air entrapment in practical engineering situations is then focused. A domain decomposition method together with a dual-system technique is developed to provide fully nonlinear simulation on the early impact stage by a plunging wave crest, tackling the large variation in scales involved. Local pressure peak is found to be generated by the sharp turn of the wave surface along the wall. The trapped cavity, governed by an adiabatic law, is found to cause oscillating loading on the wall. The local free jet drawn from the upper cavity surface in each re-contraction stage reveals its distortion and fragmentation mechanism. The initial dimensionless potential energy of the air cavity is found to largely influence its maximum pressure, and the scaling law revealed could be applied to the prediction of impact pressure in practical situations from a laboratory experiment.

Fluid-structure interaction is a well-known and complicated problem. Its formulation requires simplifications in modelling, and usually the presence of gravity is one aspect which is neglected, especially in violent impact. In this thesis we account for the influence of gravity on two physically different but mathematically similar two-dimensional flows. First (in Chapters 2{4), sloshing impact of a standing wave on the lid of a rigid tank, and second (in Chapter 5), impact of a rigid blunt body entering water which is initially at rest. Chapter 1 presents the motivation, literature, aim and structure of the thesis. In Chapter 2, gravity is neglected and model equations are solved analytically, in particular the linearised hydrodynamic problem with and without the lid using the Wagner approximation, time and coordinate stretching, and displacement potential. Chapter 3, introduces gravity into the formulation and the model is solved semi-analytically to determine its influence on the width of the wetted region and on the pressure distribution on the lid during impact. We numerically find the effect of gravity on the moving contact points, hydrodynamic pressure, and surface elevation in Chapter 4. Chapter 5 studies the influence of gravity on the impact of a blunt body entering vertically with a constant speed into an initially at water. All problems are formulated and solved within the Wagner model. In both problems we found visible effects of gravity on the positions of moving contact points after the early stage of impact. Gravity shortens the size of the wetted region. Consequently, the velocities of the contact points are decreased by gravity. The effect of gravity on the surface elevation is shown for both problems. Negative hydrodynamic pressures and forces are found during the sloshing impact stage when gravity is neglected. Numerically, it was found that gravity decreases the hydrodynamic pressure on the lid of the tank. Similarly the hydrodynamic pressure is found to be decreased by gravity in the water-entry problem. Also in the water-entry problem it is shown that gravity increases both the thickness and the mass flux into the spray jets. Also the total energy (potential and kinetic) of the system, and the work done by the body on the fluid are decreased by gravity.

In this study composite materials were tested in different fluid environments to determine the role of Fluid Structure Interaction with these composites under a lower velocity impact. The purpose of this research is to develop a better understanding of possible marine applications of composite materials. This was done using a low velocity impact machine and two composite types. The first composite is made from a multi-ply symmetrical plain weave 6 oz. E-glass skin. The test area of the composites is 12 in by 12 in (30.5 cm by 30.5 cm) with clamped boundary conditions. The testing was done using a drop weight system to impact the center of the test area. A Plexiglas box in conjunction with the impact machine was used to keep the top of the composite sample dry while it was submerged in approximately 15 inches (38.10 cm) of water. The second composite type was constructed using the same methods, but was made from a Carbon Fiber Reinforced Polymer (CFRP) instead of the E-glass skin. These samples were pre-cracked and tested using the same impact machine in 15 inches (38.10 cm) of water. The overall size of these samples was 42 cm long and 3 cm wide forming a long thin rectangular shape. The test area of these samples was a 20 cm long section of the sample with the outsides being clamped to achieve the desired boundary conditions. Two variations of these samples were tested. The first was reinforced with Multi-Walled Carbon Nanotubes (MWCNTs) and the second had no reinforcements at the interface layer in front of the pre-cracks. Output from both tests was recorded using strain gauges and a force impact sensor. The results show that an added mass from the water plays a large role in the Fluid Structure Interaction with composites due to the similar densities of water and the composites.

Ce travail de thèse porte sur l’étude numérique de la propagation d’ondes de choc dans les écoulements compressibles multiphasiques et en interaction (fluide-structure). Deux approches sont étudiées pour la résolution numérique de la partie fluide : L’approche ALE (Arbitrary Lagrangian Eulerian) et l’approche lagrangienne SPH (Smoothed Particle Hydrodynamics) ; la partie structure, quant à elle, est résolue par une approche classique EF (Éléments finis). L’étude des méthodes ALE et SPH constituent les deux principaux axes de recherche. La problématique des coups de bélier dans l’ingénierie nucléaire est abordée dans cette thèse. Lors d’un coup de bélier, les nombreuses réflexions d’ondes de choc dans les tuyauteries nucléaires peuvent faire baisser la pression de l’eau en dessous de sa pression de saturation et générer localement de la cavitation. Le modèle HEM (Homogeneous Equilibrium Model) de changement de phase proposé par Saurel et al. (1999) à trois équations est étudié et appliqué aux coups de bélier. Les résultats obtenus sont comparés aux données expérimentales. Malgré l’utilisation des techniques de renormalisation en SPH, des instabilités (oscillations numériques) se développent à l’interface entre les particules de matériaux différents. Ces instabilités restreignent l’utilisation des schémas SPH classiques pour des problèmes à faible ratio de densité. Afin de résoudre les problèmes de choc, le schéma proposé par Hu et Adams (2006) est adapté au régime fortement compressible en considérant le couplage entre la densité et la longueur de lissage. Les différents schémas SPH sont comparés entre eux pour les problèmes de chocs multiphasiques en 1-D et 2-D. Les résultats SPH sont validés avec la solution exacte pour les problèmes 1-D et la solution ALE pour les problèmes 2-D
This thesis focuses on the numerical study of the propagation of shock waves in compressible multiphase flows and fluid structure interaction. Two approaches are being studied for the numerical solution of the fluid part: the ALE approach (Arbitrary Lagrangian Eulerian) and the Lagrangian SPH (Smoothed Particle Hydrodynamics) approach; while the structure part is solved by a conventional FE (Finite Element). The numerical investigation of the ALE and SPH methods are the two main areas of research.Water Hammers phenomena occuring in nuclear industries are investigated in this thesis. During a Water Hammer, the shock waves reflections in nuclear piping may drop locally the water pressure below its saturation pressure and generate cavitation. The three equations HEM (Homogeneous Equilibrium Model) phase change model proposed by Saurel et al. (1999) is studied and applied to solve water hammers. The obtained results are compared with experimental data. Despite the use of renormalization techniques in SPH, instabilities (numerical oscillations) are developed at the interface between particles from different materials. These instabilities restrict the use of traditional SPH schemes to problems with low density ratio. In order to solve the shock problems in the compressible regime, the scheme originally proposed by Hu and Adams (2006) is adapted to fully compressible regime (FC-SPH) by considering the coupling between the density and the smoothing length. The different SPH schemes are compared for 1-D and 2-D multiphase shock problems. Validation is performed in comparison with exact solutions for 1-D problems and ALE solution for 2-D problems

The growth of the nuclear power industry has provided a considerable stimulus for investigations into fluid-structure interaction problems. The safety case for nuclear reactors requires an understanding of the impact response of structures enclosing or surrounded by fluids. In many cases the structural response is in excess of that which can be predicted by elastic analyses and both material and geometrical non-linearities must be considered. The understanding of the interaction between the structure and the contained fluid poses additional problems which, in the extreme loading conditions envisaged, have received little attention. There is a lack of data relating to basic fluid-structure interaction problems involving dynamic plastic structural impact. Two sets of experiments are described which were carried out to provide some such data. The first set of experiments considered beams, both fully clamped (leading to large membrane forces) and partially clamped (preventing rotational and transverse motion while allowing the beam material to be fed in from the supports), struck centrally by a projectile. The second set of experiments considered a circular plate clamped around its periphery, sealing a volume of fluid, and struck centrally by a projectile. The shape of the plates and beams as they deformed were recorded, as were the pressure variations during the tests. In both sets of experiments the main contribution of the fluid to the beam or plate response was to localise the deformations. The early deformation of the beams was limited to the centre half span and the deformation only spread to the ends of the beams as the supporting effect of the fluid was lost due to the fluid escaping. In the plate experiments, where a good seal could be achieved, the deformation throughout was localised compared with a similar plate in air. The deformation in these cases was limited to a central disc of approximately half the plate diameter. The pressures recorded during the tests suggest that the fluid response was predominantly incompressible. A finite element program was written to model the response of beams and circular plates (axisymmetric problems). A brief history of the finite element method, the background theory and the development of the method to treat non-linear, large displacement, dynamic problems are given. The results are presented for a number of beam and plate problems, both those described above and other problems for which data was available. The finite element program was found to give good predictions of the deforming shapes of both the beams and the plates. No detailed analysis of the fluid was carried out, but two types of approximation to the effect of the fluid were investigated. Firstly a time varying pressure pulse (based on the measured pressure pulses) or a pressure loading derived from the beam velocity (acoustic and incompressible fluid approximations) were used to represent the loading on the beam due to the fluid. Secondly a mass was added to the plate mass to represent the inertia of the fluid. The applied pressure loading worked to a limited extent for the beams but no one pressure pulse shape gave good results for both end fixities. The best results for the plate problem were achieved with the added mass approach. Finally a number of areas of experimental and computational work are identified, which it is felt would benefit from further study.

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The objective of this research is to examine the added mass effect that water has on the dynamic response of a sandwich composite under impact, particularly impact leading to failure. Because sandwich composites are much less dense than water, fluid structure interaction plays a large part in the failure. Composite samples were constructed using vacuum assisted transfer molding, with a 6.35 mm balsa core and symmetrical plain weave 6 oz E-glass skins. The experiment consisted of three phases. First, using threepoint bending, strain rate characteristics were examined both in air and under water. After establishing that the medium had no effect on the beam response under different strain rates, but confirming that previously established relationships between strain rate and ultimate strength for axially loaded glass composites can be applies to sandwich construction in bending, the experiment progressed to impact testing where each specimen, again a one inch wide beam, was subjected to progressively increasing force. The data from this phase showed that submerged samples failed at lower drop heights and lower peak forces with a failure mode dominated by center span skin compression failure. Beams in air were able to withstand higher drop heights and peak forces. Dry sample failure mode was dominated by skin compression failure at the clamped support with occasional evidence of shear failure through the core adjacent to the clamped support. The data from this study will increase understanding of sandwich composite characteristics subjected to underwater impact.

In recent years, faster, lighter and bigger are the key issues in a modern racing yacht for extreme performance. As a result, many yachts have experienced various structural failures caused by the hydrodynamic impact or ’hydro-impact’ phenomenon by slamming. The structural failure by hydro-impact originates from the facts that the external hydro-impact load and fluid structure interaction effect is somewhat misled and when applying the load into current structural design, the ’dynamic’ load is typically, manipulated in a ’static’ way with fluid structure interaction effect, generally, ignored. In this thesis, the hydro-impact load by slamming, its fluid structure interaction effect and dynamic response of the local structure of the yacht are studied. Firstly, to acquire insight into the hydro-impact phenomenon, a series of drop tests and seakeeping-slamming tests are carried out with various sensing instruments of pressure transducers, accelerometer and ’slam patch system’ - a specific application form of generally known pressure panel - are installed. The slam patch system is designed and implemented to investigate the hydro-impact loads and fluid structure interaction effect of slamming. Afterward, the measured hydro-impact loads are summarised via statistical manipulations with regard to pressure and duration time. Secondly, impact pressure by the rules and regulations of various organisations are provided to compare it with the experimental results and structural response calculations. The applicability of the rules and regulations on the high performance racing yacht is also pointed out. Finally, the manipulated loads are used as input data to simulate the transient response of local structure of the yacht structure. Throughout this study, the dynamic and fluid structure interaction effect by hydroimpact phenomenon on local composite structure can be easily visualised and calculated in a conservative way through conventional finite element analysis work.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2009.
Thesis Advisor: Kwon, Young W. Second Reader: Didoszak, Jarema M. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Composite, Carbon, Low Velocity Impact, Fluid Structure Interaction. Includes bibliographical references (p. 49-50). Also available in print.

Les impacts hydrodynamiques entre structures solides et liquides jouent un rôle crucial dans des domaines comme l'ingénierie côtière, l'aéronautique et les énergies renouvelables. Cette thèse se focalise sur l'effet peu exploré de l'aération, où l'air sous forme de bulles ou de poches modifie significativement les forces d'impact et les réponses hydrodynamiques. L'objectif central de cette thèse est d'approfondir notre compréhension des effets de l'aération sur les dynamiques complexes d'impact hydrodynamique. Cette recherche se concentre sur deux configurations expérimentales distinctes : l'impact d'une plaque plane sur une surface d'eau calme et l'impact d'un jet d'eau aéré sur une plaque plane. L'enjeu est d'examiner l'influence de l'aération sur les pressions d'impact et les fréquences d'oscillation post-impact. Pour atteindre ces objectifs, des dispositifs expérimentaux ont été conçus pour chaque cas d'étude. Ces expériences modèles nous offrent la possibilité de contrôler avec précision des paramètres cruciaux tels que la vitesse d'impact, les dimensions de la plaque, la pression ambiante, etc. Parallèlement, une attention particulière a été portée à la mesure des taux d'aération et des pressions d'impact, permettant ainsi une analyse rigoureuse des résultats. Pour l'impact de la plaque, les observations ont montré que les pressions maximales d'impact et les impulsions dévient de la théorie de von Karman, principalement à cause de l'effet amortissant de l'air. La diminution de la pression ambiante augmente les pressions d'impact, suggérant une atténuation de l'effet de coussin d'air. Concernant l'impact d'un jet d'eau aéré, une diversité de régimes d'écoulement, tels que les régimes à bulles, en bouchons, agités, et annulaires a été identifiée. L'interaction entre le nombre d'injecteurs, la pression d'air, et les caractéristiques des bulles illustre une interdépendance significative. Les effets de l'aération sur les pressions d'impact et les fréquences d'oscillation démontrent que des structures plus grandes induisent des oscillations plus lentes et des pressions adimensionnelles augmentées
Hydrodynamic impacts between solid structures and liquids play a crucial role in various strategic fields such as coastal engineering, aeronautics, and renewable energy. This thesis focuses on the less explored effect of aeration, where the presence of air in the form of bubbles or air pockets significantly alters impact forces and hydrodynamic responses. The central objective of this thesis is to deepen our understanding of aeration's effects on complex hydrodynamic impact dynamics. This research concentrates on two distinct experimental setups: the impact of a flat plate on a calm water surface and the impact of an aerated water jet on a flat plate. The challenge is to examine how aeration influences impact pressures and post-impact oscillation frequencies. To achieve these objectives, experimental setups were designed for each case study. These model experiments allow us to precisely control crucial parameters such as impact velocity, plate dimensions, ambient pressure, etc. Special attention was also given to measuring aeration rates and impact pressures, enabling rigorous analysis of the results. For the plate impact, observations showed that maximum impact pressures and pressure impulses deviate from the von Karman theory, mainly due to the damping effect of air. Reducing ambient pressure increases impact pressures, suggesting a reduction of the air cushion effect. Regarding the impact of an aerated water jet, a diversity of flow regimes, such as bubble, slug, churn, and annular flows, were identified. The interaction between the number of injectors, air pressure, and bubble characteristics demonstrates a significant interdependence. The effects of aeration on impact pressures and oscillation frequencies show that larger structures induce slower oscillations and increased dimensionless pressures

[Truncated abstract] The hydrodynamics of wave impact on offshore structures is not well understood. Wave impacts often involve large deformations of water free-surface. Therefore, a wave impact problem is usually combined with a free-surface problem. The complexity is expanded when the body exposed to a wave impact is allowed to move. The nonlinear interactions between a moving body and fluid is a complicated process that has been a dilemma in the engineering design of offshore and coastal structures for a long time. This thesis used experimental and numerical means to develop further understanding of the wave impact problems as well as to create a numerical tool suitable for simulation of such problems. The study included the consideration of moving boundaries in order to include the coupled interactions of the body and fluid. The thesis is organized into two experimental and numerical parts. There is a lack of benchmarking experimental data for studying fluid-structure interactions with moving boundaries. In the experimental part of this research, novel experiments were, therefore, designed and performed that were useful for validation of the numerical developments. By considering a dynamical system with only one degree of freedom, the complexity of the experiments performed was minimal. The setup included a plate that was attached to the bottom of a flume via a hinge and tethered by two springs from the top one at each side. The experiments modelled fluid-structure interactions in three subsets. The first subset studied a highly nonlinear decay test, which resembled a harsh wave impact (or slam) incident. The second subset included waves overtopping on the vertically restrained plate. In the third subset, the plate was free to oscillate and was excited by the same waves. The wave overtopping the plate resembled the physics of the green water on fixed and moving structures. An analytical solution based on linear potential theory was provided for comparison with experimental results. ... In simulation of the nonlinear decay test, the SPH results captured the frequency variation in plate oscillations, which indicated that the radiation forces (added mass and damping forces) were calculated satisfactorily. In simulation of the nonlinear waves, the waves progressed in the flume similar to the physical experiments and the total energy of the system was conserved with an error of 0.025% of the total initial energy. The wave-plate interactions were successfully modelled by SPH. The simulations included wave run-up and shipping of water for fixed and oscillating plate cases. The effects of the plate oscillations on the flow regime are also discussed in detail. The combination of experimental and numerical investigation provided further understanding of wave impact problems. The novel design of the experiments extended the study to moving boundaries in small scale. The use of SPH eliminated the difficulties of dealing with free-surface problems so that the focus of study could be placed on the impact forces on fixed and moving bodies.

The cylinder block/valve plate interface is a critical design element of axial piston machines. In the past, extensive work has been done at Maha Fluid Power Research center to model this interface were a novel fluid structure thermal interaction model was developed which accounts for thermal and elasto-hydrodynamic effects and has been proven to give an accurate prediction of the fluid film thickness. This paper presents an in-depth investigation of the impact of the elastic deformation due to pressure and thermal loadings of the end case/housing on the performance of the cylinder block/valve plate interface. This research seeks to understand in a systematic manner the sensitivity of the cylinder block/valve plate interface to the structural design and material properties. A comparison between simulations results is done by utilizing different end case designs and material compositions, both in the valveplate and end case solids.

Cette etude porte sur les vibrations dans le vide ou en contact avec un fluide, d'une plaque elastique infinie soumise a un impact ponctuel normal a sa surface. La reponse, en deplacement et en deformation, a un impact de bille a ete calculee dans le vide par une methode analytique de transformees integrales dans le temps et l'espace, parallelement a des mesures d'extensometrie. Dans le cas du couplage, le deplacement sous l'effet d'une force harmonique ponctuelle a ete etudie en fonction de la frequence

This research has developed an innovative road safety barrier system that will enhance roadside safety. In doing so, the research developed new knowledge in the field of road crash mitigation for high speed vehicle impact involving plastic road safety barriers. This road safety barrier system has the required feature to redirecting an errant vehicle with limited lateral displacement. Research was carried out using dynamic computer simulation technique support by experimental testing. Future road safety barrier designers may use the information in this research as a design guideline to improve the performance and redirectional capability of the road safety barrier system. This will lead to better safety conditions on the roadways and potentially save lives.

The work in this thesis focuses on the use of explicit finite element analysis (FEA) in the modelling of fluid-structure interaction of panel-water impacts. Paper A, considers modelling of a two-dimensional rigid wedge impacting a calm water surface. From analytical methods and results of a systematic parameter study a generalised approach for determination of fluid discretization and contact parameters in the modelling of arbitrary hull-water impact situations is developed and presented. In paper B the finite element modelling methodology suggested in paper A is evaluated for elastic structures by a convergence study of structural response and hydrodynamic load. The structural hydroelastic response is systematically studied by a number of FE-simulations of different impact situations concerning panel deadrise, impact velocity and boundary conditions. In paper B a tentative method for dynamic characterization is also derived. The results are compared with other published results concerning hydroelasticity in panel water impacts. The long-term goal of this work is to develop design criteria, by which it can be determined whether the loading situation of a certain vessel type should be regarded as quasi-static or dynamic, and which consequence on the design a dynamic loading has.

L’émergence de bruits auparavant inaudibles dans les réservoirs à carburants automobiles requiert des constructeurs une meilleure compréhension des phénomènes physiques intervenants au sein de leurs produits. Dans cette thèse, différents travaux ont été conduits autour de l’étude du ballottement de fluide dans une cuve rigide rectangulaire partiellement remplie de fluide et soumise à une excitation extérieure. La première partie présente un état de l’art sur le sloshing suivant trois approches complémentaires - approche analytique, approche numérique et approche expérimentale - permettant d’orienter les travaux. Dans une deuxième partie, une étude préliminaire sur le sloshing dans une cuve rectangulaire soumise à une excitation harmonique forcée est réalisée. La confrontation des résultats numériques entre une approche linéaire - basée sur la théorie d’écoulement potentiel tenant compte de la viscosité du fluide [Schotté et Ohayon, 2013] - et une approche non linéaire commerciale – basée sur la résolution des équations de Navier-Stokes - permet de définir un paramètre de linéarité. Ce dernier permet de déterminer les cas de sloshing qui nécessitent une résolution non linéaire et ceux pour lesquels la théorie linéaire suffit pour prédire le phénomène. La troisième partie de ce document présente une étude expérimentale du ballottement de fluide dans une cuve rectangulaire rigide soumise à un freinage automobile. Deux niveaux de remplissage créant deux types d’impacts contre les parois (avec et sans enfermement de poche d’air) ont été analysés. Les essais menés ont permis de mesurer les forces engendrées par le mouvement du fluide, les pressions d’impact en paroi ainsi que le champ de vitesse par méthode Particle Image Velocimetry (PIV). Ce chapitre constitue une importante base de données expérimentales ayant permis d’étudier précisément le phénomène physique. L’étude est complétée par une confrontation des résultats expérimentaux avec des résultats Computational Fluid Dynamics (CFD). Enfin, pour conclure ce mémoire, une étude du sloshing dans un réservoir en tenant compte de la Fluid-Structure Interaction (FSI) est présentée. Le choix du couplage a été porté sur un schéma partitionné itératif faible avec, dans un premier temps, une approche potentielle instationnaire, puis avec une approche Volume Of Fluid (VOF) pour la physique fluide. Les limites d’un tel couplage dans le cas d’étude d’un réservoir partiellement rempli de fluide et attaché de manière flexible en fonction du rapport de masse fluide-réservoir ont été mises en évidence. La correction du schéma de couplage par l’effet de masse ajoutée présentée dans [Song et al., 2013] permet la résolution d’un système couplé quel que soit le rapport de masse en jeu et améliore de manière significative la convergence en réduisant également fortement le temps de calcul
The present thesis focuses on an investigation of the sloshing phenomenon in a partially filled fuel tank submitted to a harmonic excitation motion. In the first part, the confrontation of numerical results between a linear approach - taking into account viscosity - and a nonlinear approach based on a commercial code leads to define a parameter of linearity. This parameter allows determining cases of sloshing who require non-linear resolution and those who need a linear theory to predict the phenomenon. An experimental study of fluid sloshing in a rectangular tank submitted to an automotive braking is conducted. Tests leaded allow measuring global forces engendered by the motion of the fluid, pressure of fluid impact and velocity field by PIV. This chapter provides an important data base and helps to investigate on the physical phenomenon. This study is completed by CFD results. To conclude, a numerical model for fluid-structure interactions is presented. Limits of this segregated partitioned coupling in case of sloshing in tank flexibly attached are highlighted, depending mostly on the mass ratio between fluid and tank structure. An added-mass term is integrated to the corrected staggered scheme ensuring systematically the convergence of the coupled solution and reducing significantly the iterations required

La reponse dynamique de divers materiaux soumis a des impacts de jets ou d'ondes de surpression a ete simulee a l'aide d'un modele elastoplastique. Les geometries des empreintes ainsi generees numeriquement ont ete comparees a celles d'empreintes observees experimentalement sur des echantillons soumis a la cavitation d'eau et de mercure. On a constate que l'emission d'une onde de surpression etait la cause principale des dommages observes. Une etude parametrique du phenomene d'onde de supression a ete effectuee. Cette etude a servi de base pour le trace d'histogrammes classant le nombre d'impacts et/ou le volume deforme des empreintes en fonction des caracteristiques geometriques des trous ou des parametres hydrodynamiques des impacts. L'influence de la vitesse de l'ecoulement, de l'effet d'echelle, des caracteristiques du fluide et des proprietes mecaniques des materiaux sur l'agressivite de l'ecoulement a pu etre evaluee pour des eprouvettes soumises a l'erosion de cavitation dans sa phase d'incubation. Pour approfondir les connaissances en ce qui concerne le phenomene d'onde de supression et son interaction avec une paroi solide, un code de calcul 2d axisymetrique en fluide compressible a ete developpe. Ce modele, associe au programme de calcul mecanique du solide a servi de base a la mise en uvre d'un code de calcul traitant le couplage fluide-structure dans le cadre de l'erosion de cavitation

This thesis analyses the impact of granular aggregates with structures using experiments and numerical simulations. Original contributions include an insight into multiple factors affecting the loading and damage to the structures, along with study of numerical parameters important for realistic prediction of the interaction between the granular media and structures. It extends the current understanding related to such interactions, with an underlying motivation to guide strategies in order to reduce the structural damage. The response of structures impacted by granular media (sand or soil) is of significant research interest for many applications. One of the applications is for landmine explosions which causes ejection of soil from ground and damage to structures impacted by this ejected soil. Experimentation is done in a laboratory setting where the cylindrical sand slugs are generated at high speed using an impulse provided by a piston. This induces a velocity gradient along the slug, because of which the slug expands during the flight before impacting the target. Deformable as well as rigid flat targets are considered in two orientations relative to the incoming slug: perpendicular (i.e. normal orientation) and inclined at an angle of 45°. The targets are supported by force transducers to capture the loading from the slug. Simulations are performed using a combination of discrete particle and finite element schemes, which enables the analysis of the fully coupled interaction between the flowing granular media and the structure. A contact model involving multiple parameters is used for inter-particle and particle-target contact. Firstly, a numerical analysis is performed to characterise the temporal evolution of slugs and their impact on monolithic beams constrained at the ends. Out of all the parameters used for inter-particle contact definition in discrete particle method, only the contact stiffness is found to effect the velocity gradient in the slug before it impacts the target. Other factor influencing the gradient is the acceleration provided by the piston. A strong dependence of beam deflection on the stand-off distance is observed due to the velocity gradient in the slugs. As the second step, the effect of target surface properties on the transmitted momentum is analysed. Experiments are done by applying coatings of different hardness and roughness on the target surface impacted by sand slugs. For normally oriented targets, the transmitted momentum is observed to be insensitive to the change in surface coating. In contrast, for inclined targets, a significant influence of coatings is observed. Additionally, the momentum transmitted to the inclined targets is always less than that for normal targets. Numerical analysis of this surface effect reveals that assuming the slug particles to be spherical shape in simulations does not capture the particle/target interactions accurately and under-predicts the frictional loading on the target. Following this, a detailed numerical study is done to understand the effect of the shape of particles in the slug. Simple shaped non-spherical particles are constructed by combining spherical sub-particles. With increasing angularity of particles in the slug, the frictional loading on the target is shown to increase. This results in an increase of momentum transmitted to inclined targets. For normally oriented targets however, the particle shape does not affect the overall transmitted momentum, which is a behaviour similar to that observed when studying the effect of target surface properties. In addition, effect of fracture of particles in the slug is analysed by using beam connections between sub-particles that break during the impact with the target. If the fracture results in increasing particle angularity, the transmitted momentum increases, whereas the situation reverses if fracture results on more spherical shaped particles. Lastly, a strategy to reduce the loading on the targets is analysed by using sacrificial coating on the target surface. In experiments, this coating is placed on the rigid target surface using a lubricant at their interface. When impacted by the slug, this coating slides on the target surface, resulting in a reduction of frictional loading on the target. If the friction at the coating/target interface vanishes, the transmitted momentum approaches the theoretical minimum value. Simulations are used to first validate the experimental observations and then to extend the concept of sliding coatings using deformable targets. Both the transmitted momentum and deflections depended on the thickness of the target and coating. When a coating is used, the deflections increase due to reduction in target thickness. It is found that the best strategy to reduce the damage to the target is to use least possible thickness of the coating and minimise the friction at the interface between the coating and the target. The presented work examines many of the factors that affect the loading on the target impacted by granular slugs, in addition to characterising the expansion of slugs before the target impact. The analysed factors include those already known such as target stand-off distance, inclination and unveils others such as target surface properties and granular properties. The numerical analysis discloses important parameters and shows the effect of particle shape, highlighting the shortcomings of widely used spherical particle assumption in the numerical studies. A strategy using a sacrificial coating to reduce damage to the target is also analysed.

Over the last decade, an increase in earthquake occurrence in Oklahoma and Kansas has been linked to oilfield wastewater injection disposal, particularly into the regionally underpressured Arbuckle Group. The Arbuckle is hydraulically connected to Precambrian basement through an extensive fracture system, which transmits pressure perturbations from wastewater injections to seismogenic depths. Previous studies have convincingly attributed induced seismicity to pore pressure diffusion and solid elastic stressing, both resulting from fluid waste injection. Recent work adds to the physical understanding of injection-induced seismicity by demonstrating that the density differential between injection fluids and formation brines may also drive fluid pressure into the seismogenic basement. In this thesis, variable density groundwater flow is modeled in a numerical simulation comprising parts of the Anadarko Basin, the Anadarko Shelf, the Cherokee Platform, and the Nemaha Fault Zone as well as injection data from 2006-2018. Results show buoyancy forces interacting with regional stratigraphic dip to force density-driven pressure transients into the deep Anadarko Basin, aligning with previously unexplained earthquakes in that region.
Master of Science
Increased earthquake activity in Oklahoma and Kansas over the last decade is linked waste disposal related to hydrofracking. Oil and gas produced in the fracking process is often mixed with large amounts of water that is too salty to be used for public or industrial purposes, thus this water is disposed of via injection into deep rock layers in the upper portion of the Earth's interior, or crust. This injection disturbs the crust to trigger earthquakes where none have been historically observed. Previous studies examining this phenomenon assume that the rock layers of the crust lie flat and level; simplify the nature of major faults, or cracks, in the crust; and do not consider differences in water chemistry between injected water and water that already occupies the crust. The study developed in this thesis considers the effect of these three factors with regard to how they influence the extent of the linkage between waste water injection and earthquakes in Oklahoma and Kansas.

Ce travail de thèse porte sur les outils statistiques pour l'évaluation des maxima de charges de sloshing dans les cuves de méthaniers. Selon les caractéristiques du navire, son chargement et les conditions de navigation, un ballotement hydrodynamique est observé à l'intérieur des cuves, phénomène communément appelé sloshing. La détermination des charges qui s'appliquent à la structure est basée sur des mesures de pression d'impact au moyen d'essais sur maquette. Les maxima de pression par impact, extraits des mesures, sont étudiés. La durée d'un essai est équivalente à 5 heures au réel et insuffisante pour déterminer des maxima de pression associés à de grandes périodes de retour (40 ans). Un modèle probabiliste est nécessaire pour extrapoler les maxima de pression. Le modèle usuel est une loi de Weibull. Comme ce sont les valeurs extrêmes des échantillons qui nous intéressent, les ajustements sont aussi effectués par les lois des valeurs extrêmes et de Pareto généralisées via les méthodes de maximum par bloc et d'excès au-dessus d'un seuil.L'originalité du travail repose sur l'emploi d'un système alternatif, plus pertinent pour la capture des maxima de pression et d'une quantité de 480 heures de mesures disponible pour les mêmes conditions d'essai. Cela fournit une distribution de référence pour les maxima de pression et nous permet d'évaluer la pertinence des modèles sélectionnés. Nous insistons sur l'importance d'évaluer la qualité des ajustements par des tests statistiques et de quantifier les incertitudes sur les estimations obtenues. La méthodologie fournie a été implémentée dans un logiciel nommé Stat_R qui facilite la manipulation et le traitement des résultats
This thesis focuses on statistical tools for the assessment of maxima sloshing loads in LNG tanks. According to ship features, tank cargo and sailing conditions, a sloshing phenomenon is observed inside LNG tanks. The determination of sloshing loads supported by the tank structure is derived from impact pressure measurements performed on a test rig. Pressure maxima per impact, extracted from test measurements, are investigated. Test duration is equivalent to 5 hours in full scale. This duration is not sufficient to determine pressure maxima associated with high return periods (40 years). It is necessary to use a probabilistic model in order to extrapolate pressure maxima. Usually, a Weibull model is used. As we focus on extreme values from samples, fittings are also performed with the generalized extreme value distribution and the generalized Pareto distribution using block maximum method and peaks over threshold method.The originality of this work is based on the use of an alternate measurement system which is more relevant than usual measurement system to get pressure maxima and a 480 hours measured data available for same test conditions. This provides a reference distribution for pressure maxima which is used to assess the relevance of the selected probabilistic models. Particular attention is paid to the assessment of fittings quality using statistical tests and to the quantification of uncertainties on estimated values.The provided methodology has been implemented in a software called Stat_R which makes the manipulation and the treatment of results easier

In the present world, Global Warming has been one of the biggest problems regarding environmental aspect and CO2 is held responsible for that. It is an inevitable necessity to mitigate the concentration of CO2 in the atmosphere. CO2 sequestration is one of the best methods to reduce its concentration by trapping it beneath the earth in different geological conditions. The unmined coal seams and thin bands of coal provide a potential storage for CO2 with suitable geological environment. These days it has become necessary to study the relationship between coal structure and flow of fluids inside. In this project, an effort has been made to study the behaviour of fluids i.e. carbon dioxide and methane inside of coal and the analysis has been carried out to study their velocity and pressure variations using COMSOL Multiphysics. Coal contains both cleat and porous structure. Cleats are the natural fractures in coal and pores are the important factors for migration of fluid inside coal. Two separate models are developed to understand the fluid flow behaviour in both cleat and porous structure of coal. A study on 3D model has also been carried out by developing a uniform coal block to analyze pressure and velocity variations inside it.