Prediction of Wave Loads on Tidal Turbine Blades

AbstractWave loads are one of the main contributors to fatigue loads of tidal turbine blades. Because of this, they are a determinant parameter for calculation of turbine blade life time. To avoid cost associated with oversizing blades or replacing a damaged blade, it is essential to evaluate the loads acting on the turbine, and especially wave loads on the blades, with the best possible accuracy.Experience from wind industry is valuable for horizontal axis tidal turbine design and loads acting on the blade can be estimated using the same methods, even if the loads are different. This article presents the main features of a code written with Matlab, able to predict thrust force and torque on each blade while the turbine is operating in a regular wave field. The quasi-static Blade Element Momentum theory is combined here with an added mass force modeling. The linear wave theory is employed to describe the water particle velocity due to waves. This velocity is, as a first approximation, simply added to a uniform stream velocity to account for wave-current interaction.The analytical results are validated by comparing them with experimental data obtained by testing a 1.475m-diameter rotor towed in a 260m-long wave tank, for different combinations of current speeds and wave characteristics. This emphasizes the importance of wave effects and dynamics in the design of tidal turbine blades

From A Medial Surface To A Mesh

International audienceMedial surfaces are well-known and interesting surface skeletons. As such, they can describe the topology and the geometry of a 3D closed object. Many applications in computer graphics can benefit from their properties, if we use them as Shape Representation Models (SRMs). However, visualizing the shape described by a medial surface remains a challenging problem. In this paper, we propose a method to build a mesh for any closed surface described by a medial surface. This method is based on the construction of an adaptive voxelisation from the geometry encoded with the medial surface. This discretization has the same topology as the described object, regardless its genus. Then, we mesh the boundary of this voxel-based representation to get a coarse approximation. Finally we refine this mesh using an original migration algorithm, in order to smooth the result and be as close as possible to the described object. An empirical study, on both CAO and laser scan models, shows the efficiency of our method in providing high quality surfaces with a reasonable computational complexity

Bords d'une surface médiane : Identifications et applications

National audienceUn squelette d'une forme fermée est une structure mince, centrée dans cette forme, décrivant sa topologie et sa géométrie. Les squelettes permettent de développer des applications interactives en synthèse d'images~: l'utilisateur peut manipuler intuitivement des formes en modifiant leurs squelettes. Parmi toutes les formulations de squelettes, nous nous intéressons en particulier à la surface médiane. Ses éléments, nommés atomes, sont les sphères maximales intérieures à la forme décrite. Les positions des atomes sont organisées en courbes et surfaces, qui composent la structure squelettale. Cette structure peut être d'une grande aide pour manipuler une forme. Cependant, en pratique, les liens entre atomes qui définissent la structure squelettale ne suivent aucune règle. Il est alors difficile d'en faire usage. Nous proposons ici une contribution à l'obtention d'une structure squelettale utile, en présentant nos deux méthodes d'identification des bords de la structure squelettale. La force de ces méthodes est qu'elles ne nécessitent que les sphères et la structure squelettale. Nous montrons enfin quels types d'applications tirent profit de cette identification des bords