High-speed craft are in high demand in the maritime industry, for example, in maintenance operations for offshore structures, for search and rescue, for patrolling operations, or as leisure craft to deliver speed and excitement. Design and operation of high-speed craft are often governed by the hydrodynamic phenomena of slamming, which occur when the craft impact the wave surface. Slamming loads affect the high-speed craft system; the crew, the structure and various sub-systems and limit the operation. To meet the ever-increasing demands on safety, economy and reduced environmental impact, there is a need to develop more efficient high-speed craft. This progression is however limited by the prevailing semi-empirical design methods for high-speed planing craft structures. These methods provide only a basic description of the involved physics, and their validity has been questioned. This thesis contributes to improving the conditions for designing efficient highspeed craft by focusing on two key topics: evaluation and development of the prevailing design methods for high-speed craft structures, and development towards structural design based on first principles modeling of the slamming process. In particular a methodological framework that enables detailed studies of the slamming phenomena using numerical simulations and experimental measurements is synthesized and evaluated. The methodological framework involves modeling of the wave environment, the craft hydromechanics and structural mechanics, and statistical characterization of the response processes. The framework forms the foundation for an extensive evaluation and development of the prevailing semi-empirical design methods for high-speed planing craft. Through the work presented in this thesis the framework is also shown to be a viable approach in the introduction of simulation-based design methods based on first principles modeling of the involved physics. Summarizing, the presented methods and results provide important steppingstones towards designing more efficient high-speed planing craft. / <p>QC 20160907</p>

The concept of using aluminum as the primary construction material for high speed ships and the hydroelastic behavior of the structure is widely gaining importance as a significant research topic in naval architecture. Aluminum is lighter than steel and hence can be predominantly used in high speed crafts which experiences significant slamming. This thesis work is focused on wedge shaped models. Free fall wedge impact is studied and a FORTRAN 90 computer program is developed to estimate the structural response of the wedge experiencing slamming by the use of matrix methods, finite element techniques and Newmark-Beta numerical time integration methods. The numerical solution is validated by comparison with the static solution. The theoretical hydrodynamic pressures which are used as input for this work was originally developed by using a flat cylinder theory [26]. The wedge drop at 0.6096 m (24 inch) drop height with an impact veloc- ity of v=3.05 m/s is based as the premise and the experimental pressure distributions measured by the pressure-transducers and the theoretical pressure predictions are used as inputs and the structural response is derived. Additionally, the response is compared for three different plate thicknesses and the results are compared against each other. The maximum deflection is comparable to the deflection evaluated from the experiment and tends to attain convergence as well. As the plate thickness reduces there tends to be a significant rise in the deflection values for the wedge plate, in the manner that when the plate thickness is halved there is a deviation of more than 75% in the deflection values as such.

<p>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.</p>

The development in structural design and construction of high-speed craft has been extensive during the last decades. Environmental and economical issues have increased the need to develop more optimized structures, using new material concepts, to reduce weight and increase performance efficiency. However, both lack of, and limitations in design methodology, makes this a difficult task. In this thesis a methodological framework which enables detailed studies of the slamming loads and associated responses for high-speed planing craft in irregular waves is established. The slamming loads can either be formulated based on numerical simulations, or on experimental measurements and pressure distribution reconstruction. Structure responses are derived in the time-domain using finite element analysis. Statistical methods are used to determine design loads and lifetime extreme responses. The framework is applied to perform phenomenological studies of the slamming loading conditions for high-speed craft, and used to highlight and quantify the limitations in the prevailing semi-empirical method for design load determination with respect to slamming. A number of clarifications regarding the original derivation and the applicability of the prevailing semi-empirical method are presented. Finally, several potential improvements to the method are presented and the associated implications discussed. The long-term goal of the research project is to establish a method for direct calculation of loads and response for high-speed planing craft, which can enable design of truly efficient craft structures. The methodology and the results presented in this thesis are concluded to be important stepping-stones towards this goal. / <p>In page VII, Paper B is wrong title. The correct title is "Experiental Evaluation of Slamming Pressure Models Used in Structural Design of High-Speed Craft". QC 20130228</p>

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. / QC 20101126

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.

High speed in waves, necessary in for instance rescue or military operations, often result in severe loading on both the craft and the crew. To maximize the performance of the high-speed craft (HSC) system that the craft and crew constitute, balance between these loads is essential. There should be no overload or underuse of crew, craft or equipment. For small high-speed craft systems, man is often the weakest link. The human exposure to vibration and shock results in injuries and other adverse health effects, which increase the risks for non-safe operations and performance degradation of the crew and craft system. To achieve a system in balance, the human acceleration exposure must be considered early in ship design. It must also be considered in duty planning and in design and selection of vibration mitigation systems. The thesis presents a simulation-based method for prediction and evaluation of the acceleration exposure of the crew on small HSC. A numerical seat model, validated with experimental full-scale data, is used to determine the crew's acceleration exposure. The input to the model is the boat acceleration expressed in the time domain (simulated or measured), the total mass of the seated human, and seat specific parameters such as mass, spring stiffness and damping coefficients and the seat's longitudinal position in the craft. The model generates seat response time series that are evaluated using available methods for evaluation of whole-body vibration (ISO 2631-1 \&amp; ISO 2631-5) and statistical methods for calculation of extreme values. The presented simulation scheme enables evaluation of human exposure to vibration and shock at an early stage in the design process. It can also be used as a tool in duty planning, requirements specification or for design of appropriate vibration mitigation systems. Further studies is proposed within three areas: investigation of the actual operational profiles of HSC, further development of seat models and investigation of the prevailing injuries and health problems among the crew of HSC. / <p>QC 20150126</p>

L'interaction fluide-structure vise à étudier le contact entre un fluide et un solide. Ce phénomène est très présent lors de l’impact d’une vague sur une structure ou l’inverse. La réponse de la structure peut être fortement affectée par l'action du fluide. L'étude de ce type d'interaction est motivée par le fait que les phénomènes résultants sont parfois catastrophiques pour les structures composites ou constituent dans la majorité des cas un facteur dimensionnant important. Le fluide est caractérisé par son champ de vitesse et de pression. Il exerce des forces aérodynamiques ou hydrodynamiques sur l'interface de la structure qui subit des déformations sous leurs actions. Ces déformations peuvent affecter localement le champ de l'écoulement et donc les charges appliquées. Ce cycle des interactions entre le fluide et le solide est caractéristique du phénomène de slamming. Pour une conception optimale des structures marines, la vitesse du navire est devenue un paramètre important. Par conséquent, les exigences de conception ont été optimisées par rapport au poids structurel. D'autre part, l'apparition des structures composites au cours des dernières décennies a favorisé l'exploitation de ces matériaux dans les grands projets de construction pour les applications marines et aérospatiales. Ceci est dû à la nature de leurs propriétés mécaniques, car elles présentent un rapport rigidité / poids élevé. En revanche, l'interaction entre les structures déformables et la surface libre de l'eau peut affecter le flux du fluide en contact avec la structure ainsi que et les charges hydrodynamiques estimées par rapport au corps rigide, en raison de l'apparition des effets hydro-élastiques. En outre, ces structures sont toujours soumises à des mécanismes de dommages différents et complexes sous un chargement dynamique. Pour ces raisons, la flexibilité et les modes de défaillance dans les matériaux composites présentent une complexité supplémentaire pour prédire les charges hydrodynamiques lorsqu'il y a une interaction avec un fluide (l'eau). Ceci a présenté un défi majeur pour utiliser ces matériaux dans les applications maritimes. Par conséquent, une attention particulière doit être accordée dans la phase de conception et l'analyse des performances pendant l'utilisation à vie. Les principales contributions de ce travail sont l’étude expérimentale et numérique du comportement dynamique des panneaux composites et la quantification de l'effet de la flexibilité de ces panneaux composites sur les charges hydrodynamiques et les déformations résultantes. Pour étudier ces effets, des panneaux composites stratifiés et sandwichs avec deux rigidités différentes sont soumis à diverses vitesses d'impact à l'aide d'une machine de choc équipée d'un système de contrôle de la vitesse. La résistance dynamique a été analysée en termes de charges hydrodynamiques, de déformations dynamiques et de mécanismes de défaillance pour différentes vitesses d'impact. L'analyse des résultats expérimentaux a montré que l’effort maximal augmente avec l’augmentation de la flexibilité des panneaux. D'autre part, le modèle numérique de tossage a été implémenté dans le logiciel Abaqus / Explicit basé sur l'approche du modèle Couplé Euler Lagrange (CEL). En outre, différents modes de défaillance des matériaux composites ont été développés et implémentés à l'aide d'une subroutine « VUMAT » définie par l'utilisateur et mis en œuvre dans le code de calcul éléments finis. Pour couvrir tous les modes de défaillance possibles dans les structures composites, l’implémentation de l’endommagement comprend : la rupture intralaminar, la décohésion de l'interface peau / âme et le cisaillement de l’âme. La confrontation des résultats expérimentaux avec les modèles numériques sur la prédiction de la force hydrodynamique et de la déformation du panneau valide l’approche adoptée. / Generally, when marine vessels encounter the water surface on entry and subsequently re-enter the water at high speed (slamming), this can subject the bottom section of the vessels to both local and global effects and generate unwanted vibrations in the structure, especially over very short durations. In marine design, the vessel speed has become an important aspect for optimal structure. Therefore, design requirements have been optimized in relation to the structural weight. In other hand, the appearance of the composite structures in the last decades has encouraged the exploitation of these structures in major construction projects for lightweight marine and aerospace applications. This is due to the nature of their mechanical properties which shows a high stiffness-to-weight ratio. In contrast, the interaction between deformable structures and free water surface can be modified the fluid flow and changed the estimated hydrodynamic loads comparing with rigid body, due to appearance of hydroelastic effects. Moreover, these structures are always subject to different and complex damage mechanisms under dynamic loading. For these reasons, the flexibility and the damage failure modes in composite materials introduce additional complexity for predicting hydrodynamic loads when interactive with water. This considered a key challenge to use these materials in marine applications. Therefore, special attention must be taken in the design phase and the analysis of performances during lifetime use. The main contributions of this work are the experimental and numerical study of the dynamic behavior of composite panels and the quantification of the effect of the flexibility of these structures on the hydrodynamic loads and the resulting deformations. To study these effects, laminate composite and sandwich panels with two different rigidities and subjected to various impact velocities have been investigated experimentally using high speed shock machine with velocity control system. The dynamic resistance was analysed in terms of hydrodynamic loads, dynamic deformation and failure mechanisms for different impact velocities. The general analysis of experiment results were indicated that more flexible panel has a higher peak force as velocity increases compared with higher stiffness panels. On the other hand, the slamming model was implemented in Abaqus/Explicit software based on Coupled Eulerian Lagrangian model approach (CEL). In addition, different damage modes are developed and constructed using a user-defined material subroutine VUMAT and implemented in Finite element method, including the intralaminar damage, debonding in skin/core interface, and core shear to cover all possible damage modes throughout structures. The numerical model gave a good agreement results in judging with experimental data for prediction of the hydrodynamic force and panel deformation. Additionally, this study gives qualitative and quantitative data which provides clear guidance in design phase and the evolution of performances during lifetime of composite structures, for marine structure designers.

The main objective of wave energy converters (WECs) is to ensure reliable electricity production at a competitive cost. Two challenges to achieving this are ensuring an efficient energy conversion and offshore survivability.         This thesis work is structured in three different sections: Control and maximum power optimization, forces and dynamics analysis in extreme wave conditions, and statistical modeling of extreme loads in reliability analysis.        The need for prediction and future knowledge of waves and wave forces is essential due to the non-causality of the optimal velocity relation for wave energy converters. Using generic concepts and modes of motion, the sensitivity of the prediction horizon to various parameters encountered in a real system is elaborated. The results show that through a realistic assumption of the dissipative losses, only a few seconds to about half a wave cycle is sufficient to predict the required future knowledge for the aim of maximizing the power absorption.          The results of a 1:30 scaled wave tank experiment are used to assess the line force and dynamic behaviour of a WEC during extreme wave events. Within the comparison of different wave type representations, i.e. irregular, regular and focused waves, of the same sea state, the results show that not all the wave types deliver the same maximum line forces. As a strategy of mitigating the line forces during extreme wave events, changing the power take-off (PTO) damping may be employed. With consideration of the whole PTO range, the results indicate an optimum damping value for each sea state in which the smallest maximum line force is obtained. Although wave breaking slamming and end-stop spring compression lead to high peak line forces, it is possible that they level out due to the overtopping effect. Waves with a long wavelength result in large surge motion and consequently higher and more damaging forces.         On the investigation of reliability assessment of the wave energy converter systems, computing the return period of the extreme forces is crucial. Using force measurement force data gathered at the west coast of Sweden, the extreme forces are statistically modelled with the peak-over-threshold method. Then, the return level of the extreme forces over 20 years for the calm season of the year is computed.