Experimental investigation of the validity of linear theory to assess the behaviour of a heaving point absorber at the Belgian Continental Shelf

The results of an experimental investigation on a heaving point absorber are presented. The physical tests are used to validate numerical simulations of the behaviour of the point absorber based on linear theory in the frequency and time domain. Floater response and power absorption are evaluated in regular and irregular waves representing a mild wave climate. A good correspondence is found between the physical and numerical test results. In irregular waves the difference between numerical and experimental power absorption is generally smaller than 20 %. In regular waves the correspondence is good as well, except in the resonance zone; i.e. when the natural frequency of the buoy is tuned towards the resonance frequency of the incident wave. In this case, non-linear effects such as viscosity and a non-linear hydrostatic restoring force become important due to the high velocities and motion amplitudes of the point absorber. However, because of these large amplitudes, pure resonant cases are often not preferred in practical applications. In general it is concluded that the numerical results are in good accordance with the experimental results and can be used to predict the point absorber behaviour in mild energetic waves in non-resonance conditions