Hydrodynamics interaction is a factor in the performance of fish schooling or underwater vessels in close formation. In this work, we visualized the wake structure of pitching hydrofoils using an inclined soap film. We considered one-, two-, three- and nine-foil configurations with different spacing and actuation parameters: amplitude (A), frequency (f), phase difference (), and flow speed (U). The wake structures were recorded with a high-speed camera and analyzed to measure the vortex angle created. The wake structure of two- and three-foil configurations were compared with the Strouhal number, St = fA/U, of a single foil. For the nine-foil configuration, the wake velocity and the standard deviation of the velocity were used to interpret the hydrodynamic interaction. It was found that both spacing and phase difference between foils are relevant in the hydrodynamic interaction. Qualitative observations are also made, and vortex street behavior characteristics are identified. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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Geometric modification as the most effective passive flow control method has recently received wide attention due to its enormous potential in enhancing performance characteristics of airfoils or hydrofoils without expensive manufacturing and maintenance cost. Two primary passive flow control modifications, known as leading-edge tubercles and internal slots and their applications in airfoils/hydrofoils have been investigated in this dissertation. For the hydrofoil, since free surface effects cannot be neglected, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil has been studied as well. In the theoretical approach aspect, an empirically-based model based on an iteration scheme has been proposed for predicting the lift coefficients of twisted airfoils with leading-edge tubercles by using experimental data for untwisted airfoils. With both numerical and experimental investigations, this dissertation has discussed the application of a custom optimized-design internal slot on a NACA 634-021 airfoil blade to allow ventilation of flow through the slot from the pressure side to the suction side of the blade, in support of delaying flow separation, and stall. The combined effect of an internal slot in an airfoil and transverse leading-edge tubercles on its performance has been further studied both numerically and experimentally. Moreover, performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of AoAs has been studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high AoAs close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. A similarly submerged hydrofoil with a custom-designed internal slot has further been studied. The performance characteristics of the slotted hydrofoil in the presence of the free surface are investigated both numerically and experimentally. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

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Thesis (M.S. in Mechanical Engineering)--University of Michigan, 2001. / Includes bibliographical references (p. 49). Also available online.

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Cette thèse présente un framework d’optimisation pour la conception hydrodynamique de forme d’hydrofoils. L’optimisation d’hydrofoil par simulation implique des objectifs d’optimisation divergents et impose des compromis contraignants en raison du coût des simulations numériques et des budgets limités généralement alloués à la conception des navires. Le framework fait appel à l’échantillonnage séquentiel et aux modèles de substitution. Un modèle prédictif est construit en utilisant la Régression par Processus Gaussien (RPG) à partir des données issues de simulations fluides effectuées sur différentes géométries d’hydrofoils. Le modèle est ensuite combiné à d’autres critères dans une fonction d’acquisition qui est évaluée sur l’espace de conception afin de définir une nouvelle géométrie qui est testée et dont les paramètres et la réponse sont ajoutés au jeu de données, améliorant ainsi le modèle. Une nouvelle fonction d’acquisition a été développée, basée sur la variance RPG et la validation croisée des données. Un modeleur géométrique a également été développé afin de créer automatiquement les géométries d’hydrofoil a partir des paramètres déterminés par l’optimiseur. Pour compléter la boucle d’optimisation,FINE/Marine, un solveur fluide RANS, a été intégré dans le framework pour exécuter les simulations fluides. Les capacités d’optimisation ont été testées sur des cas tests analytiques montrant que la nouvelle fonction d’acquisition offre plus de robustesse que d’autres fonctions d’acquisition existantes. L’ensemble du framework a ensuite été testé sur des optimisations de sections 2Dd’hydrofoil ainsi que d’hydrofoil 3D avec surface libre. Dans les deux cas, le processus d’optimisation fonctionne, permettant d’optimiser les géométries d’hydrofoils et confirmant les performances obtenues sur les cas test analytiques. Les optima semblent cependant être assez sensibles aux conditions opérationnelles. / This thesis presents a practical hydrodynamic optimization framework for hydrofoil shape design. Automated simulation based optimization of hydrofoil is a challenging process. It may involve conflicting optimization objectives, but also impose a trade-off between the cost of numerical simulations and the limited budgets available for ship design. The optimization frameworkis based on sequential sampling and surrogate modeling. Gaussian Process Regression (GPR) is used to build a predictive model based on data issued from fluid simulations of selected hydrofoil geometries. The GPR model is then combined with other criteria into an acquisition function that isevaluated over the design space, to define new querypoints that are added to the data set in order to improve the model. A custom acquisition function is developed, based on GPR variance and cross validation of the data.A hydrofoil geometric modeler is also developed to automatically create the hydrofoil shapes based on the parameters determined by the optimizer. To complete the optimization loop, FINE/Marine, a RANS flow solver, is embedded into the framework to perform the fluid simulations. Optimization capabilities are tested on analytical test cases. The results show that the custom function is more robust than other existing acquisition functions when tested on difficult functions. The entire optimization framework is then tested on 2D hydrofoil sections and 3D hydrofoil optimization cases with free surface. In both cases, the optimization process performs well, resulting in optimized hydrofoil shapes and confirming the results obtained from the analytical test cases. However, the optimum is shown to be sensitive to operating conditions.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / The successful use of hydrofoil systems on catamarans, such as the Hysucat, led to the development of a similar foil system for a high speed trimaran. Firstly a mathematical model was developed to calculate the equilibrium planing conditions of a planing trimaran. This was then used in the hydrodynamic design of a fully planing trimaran with a design speed of 65 kn. The mathematical model was then modified to include the effects of added hydrofoils. This model was then used to design a hydrofoil support system for the planing trimaran. Towing tank tests were then performed on a scale model of the boat, with and without the supporting hydrofoil system. This was done to verify the theoretical design and to gather resistance data, which could then be compared to other boats. The results showed a notable improvement in efficiency of the boat with the addition of foils. The conclusion was made that with the addition of a well-designed foil system, hull efficiencies similar to that expected for the Hysucat, can be attained when the foil system is added to the trimaran. As this work was focused mainly on the high-speed performance of the boat, it is not certain how the boat will perform through the speed-range. It is therefore recommended that further testing be done, to determine the performance of the boat at lower speeds.

L'étude des instabilités aéro-élastiques, le flottement notamment, a été initiée au milieu du vingtième siècle, suite à de nombreux accidents de rupture d'aile d'avions ou de tabliers de ponts. L'un des accidents les plus connus est l'effondrement du pont de Tacoma, quelques mois après sa mise en service en 1940.Le flottement est une vibration synchronisée d'une structure souple se déplaçant dans un milieu fluide. Il se produit lorsque deux mouvements rythmiques réguliers coïncident de telle façon que l'un alimente l’autre, tirant l'énergie supplémentaire de l'écoulement environnant. Un cas classique de flottement d'aile d’avion consiste en la combinaison de mouvements de flexion et de torsion. Ce travail pose la problématique des instabilités par couplage fluide structure des surfaces portantes dans l’eau, les instabilités hydro-élastiques. Une différence importante par rapport aux instabilités aéroélastiques est le fait que la structure souple évolue dans un fluide lourd, ce qui implique en particulier des effets de masse ajoutée et d'amortissement fluide a priori importants. Le flottement est apparu pour la première fois sur les quilles composites des voiliers de compétition, donc dans l'eau, en 2004 :• Sur le voilier IMOCA 60 pieds POUJOULAT-ARMORLUX de Bernard Stamm, pendant la course transatlantique «The Transat» : il a perdu sa quille et chaviré.• Sur le voilier IMOCA 60 pieds SILL de Rolland Jourdain: la quille et le bateau ont été sauvés. Suite à ces problèmes - en particulier suite à la perte de la quille du voilier de Bernard Stamm, un accident qui aurait pu avoir des conséquences dramatiques pour le skipper – la société HDS, spécialisée dans la conception et le dimensionnement de structures composites, notamment dans le domaine du nautisme, s’est penchée sur le phénomène. Le flottement ne s'est produit que sur des quilles composites basculantes de voilier IMOCA 60 pieds et VOLVO 70 pieds. Les principales questions posées sont donc "Pourquoi les quilles composites sont-elles susceptibles de flotter, et est-il possible de prévoir et de prévenir ce comportement ?", puis "Une bonne estimation de la vitesse critique de flottement d'une quille peut-elle être calculée à moindre frais ?".Ce travail présente les méthodes analytiques, expérimentales et numériques mises en œuvre pour estimer la vitesse critique de flottement pour différents types d'appendices dans l'eau. Des modèles, basés sur une base modale tronquée pour les modes les plus énergétiques qui sont généralement, pour une quille à bulbe, le mode de flexion prépondérante et le mode de torsion prépondérante, sont développés et un outil de conception est proposé. Une des exigences de ce travail était, en effet, de réaliser un outil simple pour intégrer le calcul de la vitesse critique de flottement dans les premières boucles de conception d'une quille composite ou acier. Les modèles proposés, qui donnent de bons résultats pour les deux cas de flottement de quille présentés ci-dessus, sont confrontés à des résultats expérimentaux et à des simulations multiphysiques en couplage fluide structure réalisées en utilisant le logiciel ADINA. Enfin, une étude paramétrique est proposée présentant l'influence des principaux paramètres de conception sur l'apparition des instabilités. / The study of aeroelastic instabilities, including flutter, was initiated in the mid-twentieth century, following numerous accidents breaking wing aircraft or bridge decks. One of the most famous accidents is the collapse of the Tacoma Narrows Bridge, a few months after its commissioning in 1940.Flutter is a synchronized vibration which takes place in a flexible structure moving through a fluid medium. It occurs when two regular, rhythmic motions coincide in such a way that one feeds the other, drawing additional energy from surrounding flow. A classic case of wing flutter might combine wing bending with either wing twisting. This work raises the issue of instabilities in fluid-structure coupling for hydrofoils in water. An important difference from the flutter phenomenon in air is the fact that the flexible structure is evolving in heavy fluid; this implies in particular added mass effects and important fluid damping. Flutter appeared for the first time on racing yacht keels with composite fins, so in water, in 2004 :• On the IMOCA 60 feet boat POUJOULAT-ARMORLUX of Bernard Stamm during the transatlantic race 'TheTransat': he lost his keel and capsized.• On the IMOCA 60 feet boat SILL Rolland JOURDAIN: the keel and the boat were saved. Following these problems - particularly following the loss of the keel of Bernard Stamm sail-boat, accident that could have dramatic consequences for the skipper - HDS company, which is is a major player in the design of complex composite parts, especially for racing sailing yachts, focused on the phenomenon. Flutter has occurred only for canting keels with composite fins on IMOCA 60 feet and VOLVO 70 feet racing yacht. The main questions asked are “Why are composite keels susceptible to flutter, and is it possible to predict and prevent this behaviour?”, then “Can a fair indication of the flutter critical speed of the keel be given at low cost? ». This work presents the analytical, experimental and numerical methods implemented to estimate the critical speed for different types of appendages in water. Models, based on a truncated modal for most energetic modes which are generally, for a bulb keel, the lateral bending predominant mode and the torsion predominant mode, are developed and a design tool is proposed. One of the requirements of this work was to make a simple tool to integrate the calculation of the flutter critical speed in the first design loops of a composite or steel keel. The proposed models that give good results for both flutter cases on keels presented above, are confronted with experimental results and with fluid-structure multiphysic simulations performed using the software ADINA. Finally, a parametric study is proposed with the influence of the main design parameters on the occurrence of instabilities.