Influence of the power take-off damping of a dual chamber floating oscillating water column on the mooring fatigue damage

A series of 1:50 model tests are conducted to study the mooring dynamics of a dual-chamber floating oscillating water column device. This device consists of two chambers, namely one traditional oscillating water column chamber and one Backward Bend Duct Buoy chamber. To discuss the power take-off damping on system dynamics, the cap of each chamber is designed with three orifices. During model tests, one orifice is open and the other two are closed so that nine power take-off damping cases are studied for each wave condition. The mooring tension response amplitude operators are measured in regular wave tests. The irregular wave model tests with four different wave peak periods are conducted to measure mooring tensions. Based on the measured mooring tension time series, the rainflow flow counting technique, a spectral method and a spectral method taking the non-Gaussian behaviour into account are applied to study mooring fatigue damage. Furthermore, the spectral method combined with mooring tension response operators for mooring fatigue damage analysis is also studied. It is found that the power take-off damping can affect mooring fatigue damage to some extent. Spectral methods show better performance in predicting chain fatigue damage than in the application for fatigue damage analysis of hawsers.