Estimation of Hydrodynamic Loading on an Oscillating Sphere

The design of flexible submerged structures presents issues related to e.g. hydrodynamics loads, induced hydrodynamic motion, effect due to the vortex-induced vibrations, re-sonance phenomena. In this complex scenario results form simple benchmark studies are valuable. Recently, the motion, due to hydrodynamic loading, of an oscillating sphere characterized by low values of mass and damping has been studied by the authors in an free surface flow channel at different values of relative submersion. Knowledge of the mechanical response and of the principal dynamic characteristics of the sphere retaining (mooring) system allows for the reconstruction of the hydrodynamic loading starting form measured displacements. This paper reports on the experimental work carried out to characterize the retaining system and the consequences coming from the estimated structural parameters on non-dimensional hydrodynamic force coefficients.