Étude des interactions entre deux hydroliennes à axe horizontal alignées avec l'écoulement

Les fermes d'hydroliennes de seconde génération sont des fermes dans lesquelles les interactions négatives, c'est-à-dire susceptibles de détériorer les performances des hydroliennes en aval, sont inévitables. Ceci est dû au fait que de nouvelles rangées d'hydroliennes doivent être ajoutées à une ferme de première génération afin d'augmenter sa capacité. Ces nouvelles rangées se situent inéluctablement dans le sillage des rangées précédentes et leur performance peut alors être profondément modifiée. Afin de mettre ces interactions en évidence, des essais expérimentaux ont été réalisés dans le bassin de l'IFREMER de Boulogne-Sur-Mer, sur des prototypes d'hydroliennes à l'échelle 1/30ème. Dans cette étude, nous nous concentrons sur l'interaction élémentaire de deux hydroliennes à axe horizontal, alignées l'une derrière l'autre avec l'écoulement. L'évolution des coefficients de puissance et de traînée en fonction de la vitesse de rotation de l'hydrolienne aval sont présentés afin de déterminer son efficacité. Pour cela, nous comparons les performances de l'hydrolienne aval aux performances de référence obtenues sur une hydrolienne seule. Par ailleurs, nous exposons des cartes de vitesse axiale, d'intensité turbulente et de cisaillement dans le sillage des hydroliennes afin d'expliquer leur comportement. Nous considérons une large gamme de distances, allant de deux à douze diamètres, entre les deux hydroliennes. D'autre part, nous étudions deux conditions d'intensité turbulente ambiante, à savoir 5% et 25%. Nous mettons en évidence l'influence de ce paramètre sur le comportement des hydroliennes et ainsi sur les effets d'interaction. En particulier, il apparaît clairement que des taux d'intensité turbulente élevés dans l'écoulement amont favorisent la dissipation des effets de sillage et offrent alors un meilleur compromis entre l'espacement entre les hydroliennes et leur performance individuelle

Couche limite et sillage rencontrés sur un chalut de fond

Les écoulements autours des engins de pêche sont complexes et mals connus. Nous proposons de présenter les travaux réalisés pour améliorer la connaissance des phénomènes d'interactions fluide/structure rencontrés dans ce domaine. Les résultats d'essais expérimentaux seront présentés : caractérisation de l'écoulement autour d'un chalut de fond à partir de mesures PIV. Les analyses POD réalisées permettent de caractériser les couches limites se développant sur les parties planes de la structure, mais également les instabilités rencontrées sur les parties en incidence et poreuses de l'engin

Fast segmentation for texture-based cartography of whole slide images

In recent years, new optical microscopes have been developed, providing very high spatial resolution images called Whole Slide Images (WSI). The fast and accurate display of such images for visual analysis by pathologists and the conventional automated analysis remain challenging, mainly due to the image size (sometimes billions of pixels) and the need to analyze certain image features at high resolution. To propose a decision support tool to help the pathologist interpret the information contained by the WSI, we present a new approach to establish an automatic cartography of WSI in reasonable time. The method is based on an original segmentation algorithm and on a supervised multiclass classification using a textural characterization of the regions computed by the segmentation. Application to breast cancer WSI shows promising results in terms of speed and quality

Synthesizing Whole Slide Images

The increasing availability of digital whole slide images opens new perspectives for computer-assisted image analysis complementing modern histopathology, assuming we can implement reliable and efficient image analysis algorithms to extract the biologically relevant information. Both validation and supervised learning techniques typically rely on ground truths manually made by human experts. However, this task is difficult, subjective and usually not exhaustive. This is a well-known issue in the field of biomedical imaging, and a common solution is the use of artificial “phantoms”. Following this trend, we study the feasibility of synthesizing artificial histological images to create perfect ground truths. In this paper, we show that it is possible to generate a synthetic whole slide image with reasonable computing resources, and we propose a way to evaluate its quality

Design and manufacture of a bed supported tidal turbine model for blade and shaft load measurement in turbulent flow and waves

Laboratory testing of tidal turbine models is an essential tool to investigate hydrodynamic interactions between turbines and the flow. Such tests can be used to calibrate numerical models and to estimate rotor loading and wake development to inform the design of full scale machines and array layout. The details of the design and manufacturing techniques used to develop a highly instrumented turbine model are presented. The model has a 1.2 m diameter, three bladed horizontal axis rotor and is bottom mounted. Particular attention is given to the instrumentation which can measure streamwise root bending moment for each blade and torque and thrust for the overall rotor. The model is mainly designed to investigate blade and shaft loads due to both turbulence and waves. Initial results from tests in a 2 m deep by 4 m wide flume are also presented

VIV and WIO using wake oscillator. Comparison on 2D response with experiments.

AbstractExperimental results are used to validate a 2D phenomenological model of the near wake based on Van Der Pol wake oscillators, which is the first one which describes the 2D motion of a cylinder in its transversal plan. In the case of a single cylinder, experimental and numerical results are in relatively good agreement. Those first results show that the proposed model can be used as a simple computation tool in the prediction of 2D VIV effects

Wake effects characterization using wake oscillator model. Comparison on 2D response with experiments

A model using wake oscillators is developed to predict the 2D motion in a transverse plan of two rigid cylinders in tandem arrangement. This model of the wake dynamics is validated with experimental data from previous trials which took place at the Ifremer flume tank in Boulogne-sur-Mer, France. The agreement between the model and the experimental results allows using this model as a simple computational tool in the prediction of 2D Vortex-Induced Vibrations (VIV) and, after some futher developments, Wake-Induced Oscillations (WIO) effects

A self-regularising DVM–PSE method for the modelling of diffusion in particle methods

International audienceThe modelling of diffusive terms in particle methods is a delicate matter and several models have been proposed in the literature. The Diffusion Velocity Method (DVM) consists in rewriting these terms in an advective way, thus defining a so-called diffusion velocity. In addition to the actual velocity, it is used to compute the particles displacement. On the other hand, the well-known and commonly used Particle Strength Exchange method (PSE) uses an approximation of the Laplacian operator in order to model diffusion. This approximation is based on an exchange of particles strength. Although DVM is particularly well suited to particle methods since it preserves their Lagrangian aspect, its major drawback stems in the fact that it suffers from severe singular behaviours. This paper intends to give insights and ideas for coping with these issues, based on an exact decomposition of the diffusion coefficient allowing a hybrid DVM-PSE treatment of diffusive terms

Numerical simulation of the wake of marine current turbines with a particle method

International audienceThis paper presents numerical computations of three bladed horizontal axis marine current turbines in a uniform free upstream current. The unsteady evolution of the turbine wake is taken into account by some three-dimensional software, developed to assess the disturbances generated in the sea. An unsteady Lagrangian method is considered for these computations using "Vortex Method"; a velocityvorticity numerical implementation of the NaviereStokes equations. The vortex flow is discretised with particles carrying vorticity, which are advected in a Lagrangian frame. The present paper aims at presenting results on both power and thrust coefficient (C P and C T) predictions and wake characterisation, up to ten diameters downstream of the turbine. Moreover, two different marine current turbines configurations are considered: one is taken from literature [1] and the second one is an open-modified version of turbine inspired from previous works [2]