Search

International audience; Over the past decade, interest in autonomous vessels significantly increased as the technology improved, especially in the automotive industry. Unlike cars, ships travel in a wild environment and maritime lanes are not limited by white lines. This makes the design of fully autonomous vessels even more challenging. Additionally, the need to reduce greenhouse gas emissions led to a renewed interest in wind propulsion. Sailboats have several advantages, such as full energy autonomy and a limited environmental impact. The Microtransat Challenge, which consists of crossing the Atlantic Ocean, is a tremendous test field. This paper describes, within that frame, a design procedure for the development of a robust fully autonomous sailboat to be deployed for long-term missions. In this paper, the mechanical and electronic design strategies are presented. A focus is on reliability and power management. Moreover, a test procedure for validating each design increment is described as well as a path plan that considers the risk of collision and weather routing with wind and currents. The Microtransat remains a challenge that no autonomous ship has ever succeeded (and has been completed by a single unmanned vessel, SB Met in 2018). However, the results by Breizh Tigresse and Sealeon in 2015 and 2018 made a step forward in terms of time and distance. They are presented and analyzed in this work

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.

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).

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.