Research On Collision Avoidance Control Method Of DP Vessels

With the development of deep offshore technology and propulsion, dynamic positioning systems are increasingly widely used in some works on the ship and oceanographic survey ship. So far, there have been more than 1000 vessels with capability of dynamic positioning,most of them using in areas related to mining exploration for oil and gas reserves. Ships frequently encounter with others during the voyage, whether they are in the narrow waterway,near the port, anchorage, or waters of the route cross point, still in the wide waters, ships might have the probability to occur collisions. For dynamic positioning ships, because of high cost, as well as the particulars of the job, once they collide, they lose more and the result is worse. Therefore, researching on DP ship collision avoidance has become more urgent and in need.First of all, this paper establishes the mathematical model of ship motion and the marine environment. We use the appropriate coordinate system to establish the kinematics model of ship; DP ships usually operate at low speed, based on this assumption we obtain ship dynamics model without Coriolis matrix. Then the environment disturbance models of ship such as wind, waves and currents environment are established.Second, we introduce the knowledge of related ship avoidance area, including ship avoidance mechanism, calculation of related ship movement parameter, establishing the cdegree of micro collision risk function baded on the measure indicators of the distance closest point of approach DCPA and the time to closest point of approach TCPA. We establish ship avoidance function, respectively defining detection domain, security domain and avoidance touch domain related of avoidance function, determining the regional shape and radius.Finally, based on the optimal control theory, we combine with collision avoidance functions, proposing the concept of coordinated collision avoidance control. We establish the dynamic model of DP vessels at low-speed, approximated as a linear time-invariant system,and choose an objective function. Based on the siuations such as whether collision exists between the DP ship, and whether ther are affected by the interference of the sea environment separately, we design the controller. through the solution of ordinary matrix riccati equation,working out the cooperative avoidance control laws. Thereafter, by constructing Lyapunov function, analysis of control algorithms stability, and carrying on MATLAB simulation,validating the control method is effective. The avoidance laws are effective only inside the boundary of sensing regions of every DP ship and outside of these regions they have no effeet on the DP ships' individual optimal control laws, which is the most attractive feature of the proposed optimization algorithm.