Modeling And Simulation Of The Position Mooring System And Optimization Of Tension Allocation

The semi-submersible platform does not have self-recovery capability for horizontal position and heading changes caused by uncertain environmental disturbances,and needs to be equipped with corresponding position maintaining systems to offset the influence of external disturbance power.The position mooring system has the advantages of mature equipment,simple structure,low initial installation,low operation and maintenance cost and convenient control.However,as offshore oil exploitation continues to develop into the deep sea,the length and total weight of the conventional mooring lines have increased sharply,which has led to difficulties in system layout,installation complexity and cost.In order to enhance the positioning ability of semi-submersible platform,this paper optimizes the composition of its mooring system and proposes a scheme for tension distribution of active position mooring system.The main research is as follows:(1)In order to improve the ability to resist external interference,a method of calculating the displacement of semi-submersible platform is proposed.The method can estimate the displacement when the external interference is known,so as to improve the control accuracy of the controller for feedforward compensation.Using this method,the difference between platform displacement,mooring line tension and the heading change under the same external interference of the intersect mooring system and non-intersect mooring system is compared.The results show that the mooring system can be simplified into the intersect system to improve the timeliness of controller.The research work can provide reference for the design of mooring-assistant dynamic positioning system controller.(2)Taking the platform static restoring force,the tension uniformity of the mooring line and the heading change as the objective function,the improved genetic algorithm is used to optimize the mooring angle.After that,the optimized result is fed back to the tension model of the mooring system,which reduces the requirements of the mooring line on the damage strength.(3)In order to improve the safety and economy of offshore drilling rigs under complex sea conditions,an optimization method for adaptively adjusting the weights of the K values in objective functions under different sea conditions is proposed.The method can ensure the fast and accurate positioning of the offshore platform under the premise of ensuring the even distribution of the force field of the mooring line.Considering the existence of equation constraints of the independent variables,a genetic algorithm based on dimensionality reduction is used to optimize the tension allocation of the mooring system,and the genetic algorithm is improved to enhanced the convergence speed and accuracy:One is to use the method of equidistant initial population generation for elite individuals inherited from the last moment;secondly,adaptive adjustment algorithm is used to dynamically adjust crossover and mutation operators.Simulation results show that the proposed method can improve the timeliness and accuracy of offshore platform positioning while satisfying strict equality constraints.The relevant conclusions can provide reference for the design of mooring-assisted dynamic positioning system controller.