Interaction sol-structure sous sollicitations cycliques dynamiques : Application aux éoliennes offshore fondées sur monopieu

Abstract : This PhD thesis deals with the main issue which is the evolution of the first natural frequency of an offshore wind turbine. These slender structures are submitted to cyclic and dynamic loads such as wind, waves, currents, and the blade rotations. The frequencies related to these loads are close to the first natural frequency of the turbine, which lay in a narrow interval between the frequencies of the rotor and the blades. In order to avoid any resonance phenomenon, one needs a precise evaluation of not only the natural frequency of the wind turbine after its installation but also its evolution during the operation of the turbine. These two issues are considered in this work.In this context, an experimental work was developed considering two 1g physical models of an offshore wind turbine with a monopile foundation installed in Fontainebleau sand. Based on the modelling of the foundation as a set of lateral and rotational springs, an experimental program was developed in order to evaluate the stiffness of these springs and the natural frequency of the scaled models. This method was first compared to the existing methods and has allowed to develop some original methods to evaluate the natural frequency of the considered scaled model. The tests, conducted on two physical models with different scales (1/60 and 1/120), also allowed us to adapt the obtained results to a real offshore wind turbine. As a part of the study of the turbine’s evolution during its operation, cyclic load tests were conducted. A parametric study is proposed with a focus on the influence of the load’s frequency and its amplitude. The obtained results allowed us to analyze the behavior of the scaled models submitted up to one million cycles considering, mainly, the evolution of the displacement, the rotation, and the natural frequency of the structures. These results were then compared to the limits imposed by the serviceability limit state of a real offshore wind turbine
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Laura Kerner. Interaction sol-structure sous sollicitations cycliques dynamiques : Application aux éoliennes offshore fondées sur monopieu. Géotechnique. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1118⟩. ⟨tel-01744313⟩

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