Investigation of vertical slamming on point absorbers

This paper focuses on the impact of vertical slamming on floating point absorber systems and the associated pressures that might be expected when these phenomena occur. In a first part it will be shown how the occurrence probability of slamming can be reduced by implementing a slamming restriction, i.e. by controlling the motion of the point absorber. The impact of these slamming restrictions on power absorption will be discussed. Secondly an investigation is made of the pressures that occur when the buoys are subject to vertical bottom slamming. Analytical results are presented, which give a pressure prediction of an impacting body with conical and hemispherical shape, using Wagner theory. Laboratory experiments have been carried out at Ghent University. Impact pressures were measured during drop tests with both hemispherical and conical buoy shapes. These pressures were measured by ICP pressure sensors with a range up to 345 kPa with small membrane and very high resonance frequency (> 250 kHz). Analytical and physical results are compared and conclusions are drawn.Copyright © 2008 by ASME