Field experiments on wind-wave forces acting on rough horizontal cylinders

Abstract

The present thesis deals with field experiments conducted to study the influence of barnacles on the evaluation of the windwaves forces at a horizontal submerged cylinder. Field tests were performed in the reserved portion of sea at the Marine Energy Laboratory (MEL) of the University of Reggio Calabria. The laboratory set-up was composed by three iron frames, carefully anchored on the sea bed at a water depth of 1.9 m, supporting a smooth cylinder treated to avoid the formation of marine fouling and a rough one. The latter was simulated by an external roughness printed artificially and characterized by the presence of barnacles. A battery of eight pressure transducers was placed in the middle of each cylinder to evaluate the wave forces, while two ultrasonic probes were used to detect the free surface and to deduce the wave direction and the undisturbed kinematic field at the cylinder centre. For practical purposes, the hydrodynamic force coefficients in the Morison and transverse equations were deduced from the experimental kinematics and forces at the cylinder. The effect of the involved roughness around the cylinder in comparison with the smooth one was analyzed in terms of force history, force peaks, force spectra and probability of exceedance of the force peaks. Deep learning techniques were applied to help in extracting the influences of barnacles on wind-waves loads on the studied horizontal cylinder. The main results highlight an overall increase of the wave forces on the rough cylinder if compared to the smooth one as well as of the hydrodynamic force coefficients. Furthermore, it has been observed an overall feasibility of Morison and transverse schemes in assessing the hydrodynamic loads, particularly for the case of smooth cylinder.