The mathematical modelling of a dynamic positioned vehicle is analysed. The basic equations for the slow vessel dynamics in the horizontal plane are presented, followed by a brief description of the models adopted to represent the hydrodynamic reaction and evvironmental forces. A more detailed analysis is dedicated to the forces imposed on the vehicle by the riser. The relative importance of the term is evaluation in a static forces balance. The thruster system force is evaluated based on the environmental forces and the thruster performance degradation due to interaction effects. The vessel dynamics is simulated, with a PID control for the thruster forces and moment in order to evaluation if thruster system was properly designed.
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