Research Of Ships Latitudinal Replenishment Forecast Based On Wave Compensation

When the ships underway or platforms offshore run out of the consume substance such as fuel,food and fresh water,they need replenishment at sea.In modern wars,replenishment at sea is also regarded as a very important part of naval logistics,and navy around the world have paid more and more attention to underway replenishment at sea.It is required that the replenishment ship and receiving ship must keep the same forward speed and the same direction,at the same time they also have to keep a certain distance,while under the complex ocean environment and the disturbance of replenishment equipment.The replenishment ship with dynamic positioning system is researched.Dynamic positioning system can make the vessel keep certain position and direction on the sea,have advantages that are not restricted by the depth of water and enter or retreat rapidly,and achieve the precise flexibility of ships.To many vessels which carry on the operation on the sea,it is necessary to use the dynamic positioning system.The movement of vessels on the sea is usually divided for low frequency movement that composes of wind,current,second-order wave drift and high frequency movement that composes of first-order wave drift force.As the performance of high frequency movement is periodic shocks and will not lead to the influence of average position,in order to avoid unnecessary energy waste and the thruster system wear,it usually isolates the low frequency signal to control from comprehensive position signal of vessels.So filter plays a very important role in the dynamic positioning system.In the traditional DP systems,the wave filtering and state estimation problems are solved by using Kalman filter.It must linearize the kinematic equations about a set of predefined constant yaw angles.Global exponential stability(GES)can not be guaranteed if Kalman filter is used.However,the numerous covariance tuning parameters may be difficult.In order to solve the problem when using the Kalman filter,a nonlinear observe is designed in this thesis.The observer is proven to be passive and GES.The number of tuning parameters is reduced to a minimum.The proposed observer includes features like estimation of both the low-frequency position and velocity of the ship from noisy position measurements and filter out the WF motion.Then,considering that the sea state is constantly changing,and the observer should be able to adjust the estimation of the LF motion.So a gain-scheduled observer is derived by measuring the wave model parameters.Also the gain-scheduled observer is proven to be GES.The performances of the observer are simulated on a computer model of a supply vessel.