Hydrodinamic forces acting on an oscillating structure

The submerged and not completely submerged structures (off-shore platforms, wind farms, floating buildings, marine turbines, oil conduits, buoys) in sea currents are often subjected at strong vibrations that condition the structural stability and give rise also to serious damages to the mechanical parts of the structures, with consequent efficiency loss of the system and above all repercussions in the environmental in which they are located. These vibrations increase when the structures are immersed in bounded flows (presence of the bed and/or the free surface). In order to attenuate and eliminate these problems, analytical and experimental means are used to describe the dynamic behaviour of structures for different flow field configurations and boundary conditions. Recent researches have demonstrated as the integrated numerical modelling (considering both structure and fluid characteristics) is the more suitable way to value the dynamic response of a system, also if the check on the reliability of the resolution methods needs to experimental controls that, for the complexity of structures, requires models with simplified geometries (spheres, cylinders, rectangles). In this context, the present work wants to provide some experimental results obtained analyzing both the oscillations and the forces acting on a structure to simple geometry (sphere) characterized by low values of mass and damping and invested by a free surface steady flow.