Thruster-wave Interaction during DP Stationkeeping - Model Tests in Open Water and under a Ship Hull

Wave orbital motions may cause variations in the inflow conditions of thrusters, resulting in variations in thrust and torque. Physical scale model tests were carried out to investigate these thruster-wave interaction effects, with an azimuthing thruster running at constant RPMs. The observed effects include a change in mean thrust and torque values, as well as wave frequency variations. The test conditions were systematically varied to investigate the effects of the incoming waves, the presence of the hull and the vessel motions.
First, measurements were carried out on an azimuthing thruster in open water conditions. The thrust and torque in regular waves were compared with bollard pull conditions.
Second, measurements were carried out on the azimuthing thruster under the hull of a vessel, which was rigidly connected to the basin carriage. Again, regular wave tests were performed, showing the effect of the presence of the hull.
Third, measurements were carried out on the same azimuthing thruster under the hull of the vessel in a softmooring system. This kept the vessel in position and at the required heading, while allowing unrestricted wave frequency motions. Again, regular wave tests were performed, now showing the combined effects of the passing waves, the presence of the vessel hull and the vessel motions.