Sloshing-induced motions of a spar inside a cylindrical dock with baffles in waves

Abstract

The motions of a free floating offshore wind turbine’s (OWT) spar-type platform inside a bottom-less moored cylindrical dock are investigated for incident wave frequencies near the first lateral sloshing resonance, focusing on surge on pitch motions. The radiation and diffraction problems of the two-body system are first solved through a domain decomposition (DD) approach under linear potential flow assumptions. This semi-analytical model is extended to include the effects of solid and perforated baffles in the annular domain between the dock and the spar, adapting the method developed in our previous paper for the dock alone. Results are compared with those obtained with model tests, performed at scale 1:100 for both regular waves with low steepnesses and irregular sea states. The resonant peak amplitudes of the spar’s surge and pitch motions are reduced by almost half when a solid baffle is installed, with a strong dependency on the incident wave height due to viscous dissipation caused by the flow separation at the sharp edge of the baffle.