Study On The 5-dof Motion Theory And Control Of A Semi-submersible With Dynamic Positioning System

In dynamic positioning systems for vessels, a three degrees of freedom multivariable controller, which takes the angles and velocities of the horizontal plane motions, surge, sway and yaw into consideration, has always been regarded as adequate for motion control. However, the coupling influences between horizontal plane motions and vertical plane motions of some floating marine constructions may cause large roll and pitch motions, especially for some small-waterplane-area vessels.The research about the 5 degree of freedom motion of the semi-submersible are not very much and some control models have been presented but the detail of the motion theory has not been touched. In this paper, a new controller is proposed. The angles,angular velocities and angular accelerations of the roll and pitch motion are taken into consideration. Firstly, the basic theory of roll and pitch motion of a DP semi-submersible is analyzed. Secondly, the time-domain simulation which use the new controller is done. Thirdly, the positioning effect of the new control law is compared with the effect of the former control law in order to test and optimize the new law. According to the comparing result, it is found that the new control law can limit the maximum amplitude of angle, angular velocity and angular acceleration of the roll and pitch motions without decreasing the positioning accuracy obviously.