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National audience; Numerous studies demonstrate the high efficiency of cetacean swim. The present study is conducted to investigate the influence of spanwise flexibility on the thrust of rectangular foils in pure heave motion. Classical kinematics from the literature are compared to a kinematics bioinspired by the deflexion of the caudal fins of bottlenose dolphins. This kinematics consists in introducing a characteristic time during the change of curvature of the foil where the displacements of the tips stay almost nil. A non-linear 3D lifting-line method is implemented. The oscillation is represented by a succession of stationary calculations for which the geometry and the apparent angle of attack of the foil depend on the current step time. The deflexion during the oscillation is postulated from experimental data from the literature. The existence of an optimal flexibility maximizing the thrust is highlighted and determined for the reduced frequency kG = 1.82. The influence of the proposed characteristic time was found to be detrimental for the thrust of the system, as was the concentration of the deflection towards the tips of the foil.; De nombreuses études ont démontré l'efficacité du mode de propulsion des cétacés. Une étude est menée pour étudier l'influence de la flexibilité dans le sens de l'envergure sur la poussée des foils rectangulaires en pilonnement pur. Les cinématiques classiques issues de la littérature sont comparées à une cinématique bio-inspirée par la déformation des nageoires caudales des grands dauphins. Cette cinématique consiste à introduire un temps caractéristique lors du changement de courbure du foil où le déplacement de ses extrémités est quasi nul. Un paramètre permettant de localiser la déformation vers l'extrémité du foil est également introduit. Une méthode de ligne portante 3D non linéaire est mise en œuvre. L'oscillation est modélisée par une succession de calculs stationnaires pour lesquels la géométrie et les vitesses apparentes du foil dépendent de l'instant considéré. Dans un premier temps, la déformée au cours de l'oscillation est issue de données expérimentales issues de la littérature. L'existence d'une flexibilité optimale maximisant la poussée est mise en lumière et déterminée pour la fréquence réduite kG = 1.82. L'influence du temps caractéristique proposé, durant lequel le déplacement de l'extrémité du foil est quasi nul, s'est révélée défavorable pour la poussée, tout comme la localisation de la déformation vers les extrémités du foil.

International audience; This paper presents sea trials on a 6-m boat specifically designed for kite propulsion. The kite control was automatic or manual, dynamic or static, depending on the point of sailing. The measurement system recorded boat motion and load generated by the kite. A particular attention was paid to wind measurement with several fixed and mobile locations directly on the kiteboat or in the vicinity. A high resolution weather modelling showed that a classical power law, describing the wind gradient, was not satisfactory to get the wind at kite location. 5-min measurement phases were systematically recorded. In the end, 101 runs were carried out. Data were processed with the phase-averaging method in order to produce reliable and accurate results. © 1996-2020 MDPI (Basel, Switzerland) unless otherwise stated

International audience; This paper presents a series of dynamic simulations for a ship towed by kite. To ensure time efficient computations, seakeeping analysis with forward speed correction factors is carried out in the frequency domain and then transformed in the time domain by convolution. The seakeeping modeling is coupled with a zero-mass kite modeling assuming linear dependence of aerodynamic characteristics with respect to turning rate. Decoupled (segregated) and coupled (monolithic) approaches are assessed and compared in different environmental conditions. Results show that in regular beam waves, strong interactions between the kite and the ship motions are captured by the monolithic approach. Around the wave frequency, especially for the lower one tested (0.4 rad/s), a kite lock-in phenomenon is revealed. It is concluded that the mean kite towing force can be increased whereas the ship roll amplitude can even be decreased compared to a non-kite assisted ship propulsion configuration.

La réalisation du simulateur a été motivée par la perspective de son utilisation à des fins sportives. L'objectif est de disposer d'un outil d'analyse tactique et stratégique afin d'apporter des réponses quantifiées aux questions des coureurs. La dernière partie de cet article présente un exemple du type de réponse que peut apporter le simulateur pour l'évaluation de scenarii tactiques. Pour que ces réponses soient pertinentes, il faut que le simulateur soit validé par des essais en navigation accompagnés de la mesure du vent sur le plan d'eau. Ces validations ont commencé et nous exposerons nos premières expériences dans ce domaine. Une première campagne de mesure a eu lieu lors d'une compétition de match racing. Une deuxième campagne a été réalisée sur un seul bateau avec une chaîne de mesures plus complète fournissant une position plus précise, l'attitude du bateau et l'angle de barre. Cette campagne comportait des essais de manœuvrabilité (sans voiles) en vue d'une validation partielle du simulateur et des essais sous voiles pour une validation globale

A dynamic kite flight can affect ship motions. Ship equations of motion associated with the analytical zero-mass kite model are developed. Aiming a realistic amplitude modeling of the kite excitation, a linear modification of the aerodynamic kite specs with the turning rate of the kite velocity heading is proposed. A good agreement with experimental data is obtained. Equations of motion are solved on a reaching path alternatively with a weak and a strong coupling between the ship and the kite. Differences between the two coupling methods become significant when a harmonic of the kite excitation approaches the natural roll frequency of the ship. For the presented case of study, these critical conditions can be avoided with longer tethers or larger kite trajectories.

International audience; As a part of the design and operation of kites as auxiliary propulsion of vessels, it is necessary to be able to quickly estimate the aerodynamic efforts along various trajectories. A 3D non-linear model based on the lifting line of Prandtl has been developed for this purpose. It allows these rapid calculations for wings with any laws for the dihedral angle, the twist, and the sweep angle, along the span, and for a general flight kinematic taking into account translation velocities and rotation rates. This model has been verified by comparison with 3D simulations performed with a Navier-Stokes solver. It gives satisfactory results in incidence and sideslip, with gaps of about 4% for forecasts lift. Special attention has been paid to the estimation of the accuracy of the provided numerical results.; Dans le cadre de la conception et de l'exploitation de cerfs-volants pour la propulsion auxiliaire de navires, il est nécessaire de pouvoir simuler rapidement les efforts aérodynamiques le long de trajectoires quelconques. Un modèle 3D non linéaire basé sur une extension de la ligne portante de Prandtl a été mis au point à cet effet. Il permet des calculs rapides pour des ailes avec des angles de dièdre, de vrillage et de flèche, variables en envergure, pour des cinématiques de vol prenant en compte vitesses de translation et taux de rotation. Ce modèle a été vérifié grâce à des simulations 3D réalisées avec un solveur Navier-Stokes. Il donne des résultats satisfaisants en incidence et en dérapage, avec par exemple des écarts d'environ 4 % pour les prévisions en portance. Une attention particulière a été apportée à l'estimation de la précision des résultats numériques produits.

International audience; This paper describes an on board measurement campaign held in Grande-Rivière, Gaspésie, Province of Québec, Canada, in October 2015, involving a 13-meter trawler equipped with a 50-square-meter kite. The aim of the campaign was to access the boat performance when the kite is used for auxiliary propulsion. To achieve this purpose, in addition to the kite control system, a set of sensors was installed. During the trials, runs with kite in static flight were done, with around 12 knots of true wind speed. The data post processing is presented in this paper, and allows an estimate of the lift coefficient and the lift to drag ratio of the kite and the tethers. The collected data are consistent with other experimental data published.; Cet article décrit une campagne de mesure en mer réalisée sur un chalutier de 13 mètres équipé d'un kite de 50 mètres carrés. Cette campagne s'est déroulée à Grande Rivière, Gaspésie, Province de Québec, Canada, en octobre 2015. Le but était d'évaluer les performances du navire lorsque le kite est déployé. Pour cela, en plus des dispositifs de contrôle du kite, un ensemble de capteurs a été installé. Au cours de la campagne, des phases rectilignes avec le kite fonctionnant en vol statique ont été effectuées, avec environ 12 nœuds de vent réel. Le post-traitement des données qui est présenté permet d'estimer la finesse du kite en vol statique ainsi que son coefficient de portance. Les données obtenues sont cohérentes avec d'autres résultats expérimentaux publiés.

International audience; A tool dedicated to assess fuel economy induced by kite propulsion has been developed. To produce reliable results, computations must be performed on a period over several years, for several routes and for several ships. In order to accurately represent the impact of meteorological trends variations on the exploitability of the kite towing concept, a time domain approach of the problem has been used. This tool is based on the weather database provided by the ECMWF. Two sailing strategies can be selected for assessing the performance of the kite system. For a given kite area, the simulation can be run either at constant speed or at constant engine power. A validation has been made, showing that predicted consumption is close from in-situ measurement. It shows an underestimation of 11.9% of the mean fuel consumption mainly due to auxiliary consumption and added resistance in waves that were not taken into account. To conclude, a case study is performed on a 2200 TEU container ship equipped with an 800m² kite on a transatlantic route between Halifax and Le Havre. Round trip simulations, performed over 5 years of navigation, show that the total economy predicted is of around 12% at a speed of 16 knots and around 6.5% at a speed of 19 knots.

International audience; Designing new large kite wings requires engineering tools that can account for flow-structure interaction. Although a fully coupled simulation of deformable membrane structures under aerodynamic load is already possible using Finite Element and Computational Fluid Dynamics methods this approach is computationally demanding. The core idea of the present study is to approximate a leading edge inflatable tube kite by an assembly of equivalent beam elements. In spanwise direction the wing is partitioned into several elementary cells, each consisting of a leading edge segment, two lateral inflatable battens, and the corresponding portion of canopy. The mechanical properties of an elementary cell—axial, transverse shear, bending, and torsion stiffness—and the chordwise centroid position are determined from the response to several imposed elementary displacements at its boundary, in the case of a cell under an uniform pressure loading. For this purpose the cells are supported at their four corners and different non-linear finite element analyses and linear perturbation computations are carried out. The complete kite is represented as an assembly of equivalent beams connected with rigid bodies. Coupled with a 3D non-linear lifting line method to determine the aerodynamics this structural model should allow predicting the flying shape and performance of new wing designs.

International audience; The use of traction kites as auxiliary propulsion systems for ships appears to be a high-potential alternative for fuel saving. To study such a system a tether model based on the catenary curve has been developed. This model allows calculating static flight positions of the kite on the edge of the wind window. The effect of the wind velocity gradient is taken into account for the evaluation of the aerodynamic forces acting on kite and tether. A closed-form expression is derived for the minimum wind velocity required for static flight of the kite. Results are presented for a kite with a surface area of 320 m2 and a mass of 300 kg attached to a tether with a diameter of 55 mm and a mass per unit length of 1:20 kgm−1. The minimum wind speed measured at 10 m altitude to launch the kite is found to be around 4:5 m/s. After the launching phase, we show that the optimal tether length for static flight is 128:4 m with a minimum wind speed of 4:06 m/s. The presented approach shows an error up to 9% for a zero-mass kite model with a straight massless tether regarding the maximal propulsion force estimation.

International audience; A performance prediction program dedicated to merchant ships was developed to assess fuel saving abilities of a kite. The solving of the parameterization presented led to kite velocities and tethers tensions prediction continuously along a flight path within the wind window, including especially wind gradient and ship velocity. Both static and dynamic flight cases were considered regarding optimization strategy for kite tow efficiency. For dynamic flight case azimuth, elevation and orientation of the trajectory are continuously optimized in the present algorithm. Magnitude orders of towing forces induced by the kite were compared to those obtained in the literature. Especially in upwind conditions, which are the most frequent point of sail for fast vessels, results are dramatically improved. Finally, using a 320 m2 kite on a 50,000 dwt tanker, the fuel saving predicted is about 10% for a wind velocity of 9.77 m s−1 (Beaufort 5) and reaches more than 50% for a wind velocity of 15.68 m s−1 (Beaufort 7).

This paper describes current progress made towards the realization of a match-racing simulator. The aim of the project is to be able to simulate and to modify typical situations while introducing quantifiable data for strategic and tactical analysis. The fundamental model consists of six fully coupled equations of the dynamics of two boats. The largest possible number of variables is taken into account, even though some are initially approximations. The influences of the three attitude angles on the hydrodynamic forces are taken into account using the ‘experiment planning method’ applied to towing-tank tests. For the aerodynamics, empirical models (for example IMS) are adopted. The interaction between the two boats is obtained by representing the sail perturbation by means of a single horseshoe vortex and a self-preserved viscous plane wake. The simulator has a modular structure, which allows the progressive improvement of each part as studies and knowledge advance. Comparisons with calculations of three-dimensional flows and with wind tunnel measurements validate the interaction model. The results presented show a satisfactory agreement with the polar velocity diagram available for the studied boat, even if more reliable trials at sea are needed, with measurements of boat behaviour, wind and sea state. Simulations allow us to quantify the relative influence of model coefficients on boat behaviour. Thus it is possible to identify which factors must be improved first. Tacking simulations are used to illustrate this possibility. To conclude, an example of the practical use of the simulator is presented by comparing two tactical scenarios for the final part of the upwind leg.

The use of kites for auxiliary propulsion reduces oil consumption for vessels. But the complexity of the kite numerical simulation induces the development of computationally efficient models based on lifting line theory to evaluate the aerodynamic characteristics of the kite. The presented 3D lifting line model takes into account the three-dimensional shape of the kite and the viscosity of the fluid. The proposed model was applied to a F-one Revolt Leading Edge Inflatable kite to predict its lift-to-drag ratio. Finally, this method is in very good agreement with CFD simulations in the case of a paragliding wing, but needs a much smaller computational effort.

International audience; To meet the Microtransat challenge, ENSTA Bretagne chose to realize several sailing robots. The first, having served as a test platform, allowed us to develop two new boats, one for research and one for the Atlantic crossing. The different tests in the bay of Brest allowed us to improve the reliability of systems on our sailboat. Various studies have been conducted to improve reliability of sailboats both mechanically and electronically. This tests allowed us to test different concepts on the three Breizh Spirit boats. The results are very positive and we can now say that we have a boat able to resist to strong storms, to follow a predifined route, to supply its own energy and to navigate in sea waves. From the experience acquired from Breizh Spirit 1, we hope we will be able to cross the Atlantic Ocean.

SEA Design developed a fluid structure method (FSI) suitable for early design stage of appendage with complex shapes dedicated to the America’s Cup flying catamarans. The aerodynamic loading and the boat weight are counteracted by the appendages and mainly the dagger-board. Consequently, the appendage structural design is very critical. Based on a 3D lifting line and a modified beam element method, the GSEA Design FSI method takes less than one minute to compute. An illustrating example on a L-shape appendage shows that the FSI results compared to a non-FSI results can be particularly different at the elbow. Thanks to the short computational time of the method, multi-objective optimizations can be performed. For instance a second ilstrating example shows the optimization of the appendage weight and stiffness.

International audience

The present thesis is part of the beyond the sea® project which aims to develop tethered kite systems as auxiliary devices for ship propulsion. As a kite is a flexible structure, fluid-structure interaction has to be taken into account to calculate the flying shape and aerodynamic performances of the wing. A 3D Non-Linear Lifting Line model has been developed to deal with non-straight kite wings, with dihedral and sweep angles variable along the span and take into account the non-linearity of the section lift coefficient. The model has been checked with 3D RANSE simulations over various geometries and produces satisfactory results for range of incidence and sideslip up to 15°, with typical relative differences of few percent for the overall lift. The local results are also correctly estimated, the model is able to predict the position of the minimum and maximum loading along the span, even for a wing in sideslip. Simultaneously, a structure model has been developed. The core idea of the Kite as a Beam model is to approximate a Leading Edge Inflatable kite by an assembly of beam elements, equivalent each to a part of the kite composed of a portion of the inflatable leading edge, two inflatable battens and the corresponding canopy. The Kite as a Beam model has been compared to a complete kite Finite Element model over elementary comparison cases. The results show the behaviour differences of the two models, for example the torsion stiffness is globally overestimated by the Kite as a Beam model. Eventually, the Kite as a Beam model coupled with the 3D Non-Linear Lifting Line model is compared to the complete finite element model coupled with the 3D Non-Linear Lifting Line model. The gain in computation time is really significant but the results show the necessity of model calibration if the Kite as a Beam model should be used to predict the results of the complete finite element model., Cette thèse fait partie du projet beyond the sea® qui a pour but de développer la traction par cerf-volant à boudins gonflés (kite) comme système de propulsion auxiliaire des navires. Comme le kite est une structure souple, il est nécessaire de mettre en place une boucle d’interaction fluide-structure pour calculer la géométrie du kite en vol et ses performances aérodynamiques. Un modèle de Ligne Portante 3D Non-Linéaire a été développé pour pouvoir gérer ces ailes non planes, avec des angles de dièdre et de flèche qui varient le long de l’envergure, et également pour pouvoir prendre en compte la non-linéarité du coefficient de portance de la section aérodynamique. Le modèle a été vérifié par des simulations RANSE sur différentes géométries et donne des résultats satisfaisants pour des angles d’incidence et de dérapage variant jusqu’à 15°, avec des différences relatives de quelques pour cent pour l’estimation de la portance globale de l’aile. Les résultats locaux sont aussi correctement estimés, le modèle est capable d’estimer la position du minimum et du maximum de chargement local, selon l’envergure de l’aile, et cela même pour une aile en dérapage. En parallèle, un modèle structure a été développé. L’idée principale du modèle Kite as a Beam est de réduire le kite à un ensemble d’éléments poutre, chacun équivalent à une partie du kite composé d’une section du boudin d’attaque, de deux lattes gonflées et de la canopée correspondante. Le modèle Kite as a Beam a été comparé à un modèle éléments finis complet du kite sur des cas de déplacements élémentaires. Les résultats montrent certaines différences de comportement entre les deux modèles, avec notamment une surestimation de la raideur en torsion pour le modèle Kite as a Beam. Finalement, le modèle Kite as a Beam a été couplé avec la Ligne Portante 3D Non-Linéaire, puis comparé au modèle éléments finis, couplé également avec la Ligne Portante. La réduction du temps de calcul est réellement importante mais les résultats de la comparaison montrent la nécessité de calibrer le modèle Kite as a Beam pour pouvoir retrouver correctement les résultats du modèle éléments finis.

In order to reduce greenhouse gas emissions and shipping costs, the use of kites as an auxiliary propulsion device for ships is promising. In order to estimate the performance and the operability of a kite-towed vessel, a dynamic modeling of the system is implemented. A classical kite modeling is used. This model neglects the mass of the kite and assumes straight and inelastic tethers. These assumptions lead to a kinematic model depending on the lift coefficient and the aerodynamic lift to drag ration angle. A linear evolution of these aerodynamic coefficients as a function of the curvature of the flight path is proposed. In addition, by developing a quasi-analytical line model, it is shown that from 2 m.s-1 of relative wind the straight tether assumption is reasonable. Based on the tether model, an analytical criterion assessing the minimum wind speed to enable a quasi-static kite flight is developed. To solve all the interaction terms between the kite and the ship, a time domain seakeeping model based on the linearized ship equation of motion assuming a potential flow is developed. The convolution product of the impulse response of the ship is computed with state-space systems. However, since horizontal ship motions are not well represented by such theories, a coupling with a maneuvering model is presented.Comparisons to experimental data tests show good agreements. To study the interactions between the kite and the ship, a monolithic coupling and a dissociated coupling are compared. The dissociated coupling neglects the influence of ship motions on the kite flight. In a calm water case, results obtained by the two types of coupling are very close. In regular waves, ship motions are dominated by the wave influence. Thus, with the monolithic coupling, a network of low frequency subharmonic appears in the kite excitation spectrum. The fundamental frequency of the subharmonic is given by the difference between the wave frequency and the frequency of the nearest kite excitation harmonic. When this difference is small enough, a lock-in phenomenon appears. This phenomenon is a benefit for the kite and the ship when the shift of the excitation harmonics corresponds to an increase. Furthermore, a course keeping stability study shows that the rudder needs to be actively controlled., Afin de réduire les émissions de gaz à effet de serre et le coût du transport maritime, l'utilisation des cerfs-volants comme système de propulsion auxiliaire des navires est prometteuse. Pour estimer les performances et l’opérabilité d’un navire tracté par cerf-volant, une modélisation dynamique du système est alors mise en oeuvre. Une modélisation analytique de cerf-volant est utilisée. Ce modèle néglige la masse du cerf-volant et suppose que les lignes sont droites et indéformables. Ces hypothèses conduisent à un modèle cinématique dépendant du coefficient de portance et de la finesse aérodynamique. Une évolution linéaire des coefficients aérodynamiques en fonction de la courbure de la trajectoire de vol est proposée. Par ailleurs, en développant un modèle quasi analytique de ligne, il est montré qu’à partir de 2 m.s-1 de vent relatif que l’hypothèse de ligne droite est raisonnable. En se basant sur un modèle de ligne, un critère analytique de vitesse de vent minimum permettant un vol quasi-statique est présenté. Dans le but de résoudre l’ensemble des termes d’interaction entre le cerf-volant et le navire, un modèle linéarisé de tenue à la mer temporelle est développé. Le produit de convolution de la réponse impulsionnelle du navire est calculé avec des systèmes d’états. Cependant comme celle-ci représente mal les mouvements horizontaux des navires, le modèle développé est alors couplé à un modèle de manoeuvrabilité. Pour étudier les interactions entre le cerf-volant et le navire un couplage monolithique et un couplage dissocié sont comparés. Le couplage dissocié néglige l’influence des mouvements du navire sur le vol du cerf-volant. En cas de mer calme, les résultats obtenus par les deux types de couplage sont très proches. En cas de houle régulière les mouvements du navire sont principalement causés par la houle. Le couplage monolithique montre qu’un réseau de sous-harmoniques basse fréquence apparait alors dans le spectre d’excitation du navire. La fréquence fondamentale des sous-harmoniques est donnée par la différence entre la fréquence de vague et la fréquence de l’harmonique la plus proche de l’excitation du kite. Quand cette différence est suffisamment petite, un phénomène d’accrochage apparait. Ce phénomène est bénéfique pour le cerf-volant et le navire quand le décalage des harmoniques d'excitation correspond à une augmentation. Par ailleurs, une étude de la stabilité de route montre qu'il est nécessaire de contrôler activement le safran.