Résumé de la publication
Submarine cables such as electrical umbilical power cables for floating wind turbines are subject to biofouling which can have an important effect on their dynamical behaviour under wave and current conditions by drastically increasing their size and mass. The impact of biofouling on the dynamic behaviour of an underwater power cable characterized by the hydrodynamic coefficients, such as drag and inertia coefficients, must therefore be quantified. Hence, experiments have been carried out in a flume tank to compare the dynamics of a cylinder colonized by several kinds of roughnesses. The studied roughnesses concern realistic marine growth shapes and patterns with larger and sharper edges than those classically studied, in order to be more representative of hard fouling, such as Mytilus Edulis encountered on the western and north coasts of France. Seven configurations are tested with relative roughness coefficient ranging from roughness to cylinder diameter ratio up to 0.136. A specificity of this work is the highly realistic representation of the marine growth colonization through 3D printing covers, defined by statistical analysis of in situ observations and measurements. Tests are carried out using current only, then in line horizontal oscillating motions only and finally the combination of both, with the intention of reproducing specific wave and current conditions suitable for offshore applications. Using current conditions, the calculated coefficients are quite similar between configurations. However, the addition of oscillating motions to simulate wave induced motions has a significant impact on calculated results. The presence of roughness leads to a particular increase of drag and inertia phenomena. The Morison method used to characterize hydrodynamic coefficients in wave conditions is discussed in this paper.