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Abstract Within tests during the INNWIND.EU project, a model offshore wind turbine has been placed in the jet of a wind generator whose outlet size is similar to the rotor area. This paper deals with the CFD (Computational Fluid Dynamics) simulation of this turbine in a simplified experimental environment. As this is a preliminary study to evaluate the influence of the jet flow, no comparison to experimental results is done. The loads on the wind turbine are evaluated and compared to a uniform inflow case. The study is focused on the thrust which is the biggest acting force and most important for floating turbine motion. The results show that the thrust of the whole rotor is comparable to the unifonn inflow case although there are bigger differences in the spanwise distribution for a single blade. Hence, it can be concluded that the model turbine in the jet flow is suitable for the experiments as long as it is guaranteed that the turbine is placed in the center of the jet at the investigated distance to the wind generator. INTRODUCTION The INNWIND. EU Project is dealing with investigations on large offshore wind turbines of the 1O:MW class. Basis of the investigations is the three bladed horizontal axis 10 MW DIU reference turbine (Bak, Zahle, Bitsche, Kim, Yde, Henriksen, Andersen; Natarajan, Hansen). To install this large turbine at offshore sites, new platform concepts are investigated for bottom fixed as well as for floating installation. Different codes are used to simulate the turbine on the platform. To simulate the floating platform, codes for aerodynamics, hydrodynamics as well as structural analysis are combined. The only way to validate the numerical results experimentally within the project is wave tank testing using a scaled model of the platform. These tests have been performed at Ecole Centrale de Nantes, France (ECN). On the one hand platform only tests have been conducted to evaluate the suitability of the hydrodynamic simulations using a Froude scaled model of the platform. On the other hand tests of the entire system, including turbine and platform have been performed. The geometric scaling factor is 1/60 and the scaling factor for the velocity is 1/60. Therefore a model turbine has been developed by Politecnico di Milano, Italy (POLIMI). It operates at the same tip speed ration (TSR) as the DTU reference turbine and has been designed for similarity of the thrust coefficient using a low Reynolds number airfoil (RG 14) for all sections excluding the cylindrical root. As it is operating at very low Reynolds numbers (~45000 in the present case), it is not possible to match the power coefficient of the full size turbine which is much higher than for the model turbine. As the motion of the turbine is mostly influenced by forces, the mismatch in power and respectively torque is expected to be negligible and the thrust is representative. This is a common approach, also presented in other publications like Make, Vaz, Fernandes, Bunnester and Gueydon (2015), which deals with the need of blade redesign for scaled model offshore wind turbines using CFD and BEM (Blade Element Momentum). Gueydon, Venet and Fernandes (2015) are presenting an optimization process for the simulation of the aerodynamics of a floating offshore wind turbine with a BEM approach. To match the measured Cp and CT they adjusted the polars with different approaches. Additionally, they show that the thrust coefficient in the referenced measurements could be match best using 3D CFD simulations.
SUMMARY: The paper refers to the stability analysis for underground cavities of large cross section, which are to be constructed either without or with minimum lining. Since such cavities may only be constructed in favorable engineering-geologically conditions, i.e. in hard rock masses, their stability is influenced mostly by the number, configuration and characteristics, as well as by latent discontinuities of fissures. The proposed procedure makes it possible to identify the safety factor for each monolith, which is a fundamental condition for establishing of the number, magnitude and direction of the anchors in the underground cavity. The procedure enables us to choose the best location, orientation, size and shape of the underground cavity. RESUME: Cet ouvrage se refère à l'analyse de la stabilite des cavites souterraines de grande section transversale que l'on construit soit sans soit avec le revêtement minime. Ces cavites ne pouvant être construites que dans les conditions ingenieurs-geologiques favorables, c'est-à-dire dans les roches en place solides, leur stabilite est la plupart du temps influencee par le nombre, la configuration et les caracteristiques des fissures, ainsi que par les discontinuites latentes. Ce procede nous permet de determiner le facteur de stabilite des monolythes; tout ceci sert de base pour la determination du nombre et de la position des ancres dans une cavite souterraine. Ce procede rend possible de determiner la meilleure localization, orientation, forme et grandeur de la cavite souterraine. ZUSAMMENFASSUNG: Dieses Werk bezieht sich auf die Stabilitatsanalyse der grossen unterirdischen Hallen, die konstruiert mit oder ohne leichtberg Gesicherung sind. Nachdem diese Raume nur unter den guenstigen ingenieur-geologischen Bedingungen konstruiert sein können, das heisst in den soliden Felsenmassen, ihre Stabilitat ist am meistens bei der Zahle, der Forme und bei den karakteristischen Fugen der der Diskontinuitaten beeinflusst worden. Diese Methode macht uns möglich den Sicherheitssgrad der vershiedenen Monolythen festzustellen, unci dies könnte auch als die Unterlage fuer die Bestimmung der Zahle und der Verteilung der Anker in einer unterirdische Halle dienen. Dieses Verfahren ermöglichst die Feststellung der besten Orientierung. Ort, Form und Grösse der unterirdische Halle. The engineering-geological structure of sites in Yugoslavia often calls for the construction of undergroung works in hard rock masses With lithologically or tectonically predisposed fissures. The paper presents an attempt to find a simple procedure to get the prior information on the degree of monolith's stability in the zone around the opening of an artificial underground cavity. The work analyzes the stability of monoliths around circular underground cavity's section (Fig.1). The starting points of the analysis are the following: - Sliding commences when at each point on the sliding surface the shear stress τ, inducted by external forces, reaches the shear strength at that surface. - Stresses in the rock mass around the tunnel opening of circular cross section are determined in the same way as for a homogeneous, isotropic and elastic medium - The rock mass is in the plane strain state. The basic steps in the procedure are the following: - The first step is to define the state of stress around the underground cavity, what enables us to determine the forces acting on monoliths. - The second step is to analyse sliding stability of monoliths alongside the surfaces of discontinuities. Normal forces and tangential forces acting on monoliths are the resultants of the corresponding stresses б n, б n and бe /equations (7).... (11)/. Knowing normal forces and tangential forces, we examine the stability of monoliths alongside the surfaces of discontinuities. This procedure will be shown on a monolith M (Fig.5). As the result of the shear strength of surfaces A3 and A4, it comes to the increasing of the partial safety factors, i.e. we are getting the global safety factors. We obtain the condition that the global safety factors for sliding of monolith M, alongside the sliding surfaces Al and A2 are equal one to another, i.e. This procedure may be the basis for the analysing the stability of monoliths when in the rock mass there is the three dimensional state and in the case when the underground cavity has not only the circular cross section, but has different cross sections. In that case the most difficult problem is to determine the stresses, i.e. forces acting on monoliths. In those cases we may use the finite element method. This procedure put us in the way of obtaining information about the stability of the monoliths around a planned underground cavity, provided that the structure of the fissured medium and the shear strength characteristics at the relevant contact surfaces are known. In such a way we may obtain an advantageous location of the underground cavity connected to that geotechnical aspect. We may determinate the number, magnitude and direction of anchors, if they are necessary, and the best directions for pressure groundings, too.