Fixed-point Control Research Of Dynamic Positioning Ship Based On The Event-driven Method

With the development of marine engineering operations, the ship dynamic positioning technology gets more and more people's attention. Due to continuous operation of ocean engineering,the dynamic positioning system needs to work for a long time in operation condition. And in traditional time-driven control method,output of is the controller is updated in fixed interval, which may inevitably cause frequent action of the propeller, even under good sea condition. These methods increase attrition of the propeller. But event-driven control can solve this problem well. In this paper, taking the surface dynamic positioning ship -"offshore oil 201" as the research object, we investigate the positioning control based on event driven control algorithm, which can not only effectively reduce the propeller attrition and prolong the service life of the propeller but also guarantee the effect of positioning control at the same time.The main work of this paper is organized as follows:1, Six degrees of freedom of the unified mathematical ship model is built, including mathematical model of environmental disturbances such as wind, wave and flow. First of all,a reference coordinate system for ship motion is established; Second, supersite all forces to build a unified ship model; Then, the establishment of wind, wave and current mathematical model is given; Finally, a simulation is carried out to validate the correctness of the mathematical model.2, The linear event-driven positioning controls algorithm is studied. First of all, the six degrees of freedom nonlinear ship model is simplified to a linear model with three degrees of freedom; Secondly, the composition of event driven positioning control system is introduced;Then, the stability analysis of continuous sampling event-driven positioning control system and the smallest sampling interval is discussed; In the next, the stability analysis of discrete sampling event-driven positioning control system is discussed; Finally, the designed controllers are verified through simulations.3, A state sensitive event driven positioning control algorithm for nonlinear ship is proposed. First, the ADRC (Active Disturbance Rejection Control) positioning control algorithm based on time trigger is designed; Secondly, combining with the ADRC positioning control algorithm, a state sensitive event trigger function is designed to solve the problem of discrete system. Thus, a new state sensitive event driven positioning control algorithms is developed; Finally,simulations are carried out to validate the control effect of the proposed algorithm.Through the above research, the ship dynamic positioning can be realized based on event-driven control positioning. The simulation results show that this method can reduce the calculating frequency of controller and action frequency of the propeller, which can improve the economic benefit of the ship behind ensuring the positioning precision. Therefore,research of this paper has great significance for dynamic positioning ship in application.