This paper presents a numerical station-keeping simulation in waves (regular and irregular waves) for a simplified FPSO with two DP systems. The main difference of the simulation with these two DP systems was that the first DP system (called MOT DP in this paper) was included in a seakeeping simulation code (MOTSIM) while another DP system (called IOT DP, developed by NRC/IOT) was an external system and installed on another computer (which was the same as the one used to control the vessel in physical model experiments). In order to exchange command messages between the simulation code (MOTSIM) and the IOT DP system, a communication code executed in the same time step was developed by using Windows™ socket functions.

By using these two DP systems a station-keeping simulation for a 1:40 scale model FPSO with six azimuthing thrusters was conducted in regular and irregular waves and wind. The seakeeping RAO results in regular waves were compared between these two DP systems, and also with physical model experiments with external IOT DP system and analysis using a commercial linear, 3-dimensional panel code, HydroStar. In irregular waves a mean station keeping force Fx, Fy in horizontal plane was calculated and its total mean force was compared with results from the physical model experiments. Finally, a discussion between these two DP systems was provided.

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