Research On Thrust Allocation Optimization Problem For Dynamic Positioning System Of Marine Vessels

With the development of the deep-sea oil and gas exploration and exploitation,dynamic positioning(DP)technology has been widely concerned.As an important part of DP system,the primary objective of the thrust allocation is to map the generalized forces vector,computed by the controller,into individual thruster force and direction.The allocation result directly affects the precision of dynamic positioning,the continuous operation time of vessel and the service life of thrust device.Therefore,it is necessary to study the thrust allocation to improve the performance of dynamic positioning.This paper focuses on the thrust allocation optimization problem of dynamic positioning vessel equipped with the main propeller-rudders.Firstly,in order to deal with the non-convex of the attainable thrust regions,the boundary constraint conditions are linearized and decomposed into two parts,and four kinds of thrust allocation optimization sub-problems with convex attainable thrust region are obtained.In the meantime,considering the form of objective function and constraint conditions,the quadratic programming(QP)algorithm is implemented to solve the sub-problems,and the allocation result is obtained.Furthermore,considering the physical constraints of the rudder angle rate and the thruster rotational speed rate,the rudder angle and the rotational speed are taken as the variables.And four kinds of thrust allocation optimization sub-problems are obtained by decomposing the dynamic attainable region into two parts.In the meantime,considering the form of the objective function and constraint conditions,the particle swarm optimization(PSO)algorithm is implemented to solve the selected sub-problem,and the allocation result is obtained.Finally,in order to improve the computational efficiency,the constraint conditions of the mathematical models are modified and the switching technique is introduced based on the advantages of the two former methods combined together,and the hybrid thrust allocation optimization method that applies different optimization methods based on varying range of rotating speed is presented.At last,simulation studies on a scale model ship CyberShip ? are carried out,and the results illustrate the effectiveness of the proposed thrust allocation optimization methods.Meanwhile,the simulation results of the thrust allocation methods are compared with each other.