Research On Thruster Saturation Handling And Allocation Strategy Of Dynamic Positioning

The ocean,which accounts for 79% of the total area of the earth,is rich in minerals,oil,natural gas and fishery resources.Entering the 21 st century,many countries have make the ocean development as the national strategy,rational development and utilization of marine resources has become an important way to solve the problem of population growth,food security,land resources exhaustion etc..The mooring system and dynamic positioning system is important technical equipment for offshore operations which provide protection for the offshore engineering operation vessels and platforms.The traditional mooring system can meet the operation requirement of 200-300 meters depth.However,with the increase of water depth,the operation cost increased greatly.Dynamic positioning system(DPS)is free from the limitation of operating depth which is an essential key technology of deep sea development and research.The ship dynamic positioning system,which is composed of the measurement system,the control system,the propulsion system and the dynamic system,is an integration engineering of multiple systems.The basic working principle is to use the propeller thrust force generated by the thrusters which layout on the ship to resist wind,wave,current and other environment loads and make the ship maintain a predetermined position and heading.The control system is the core of the whole system,which includes three modules: state estimation,controller and thrust allocation.This paper mainly focuses on the research and simulation experiment of thrust allocation handling and distribution strategy of the thrust allocation module.The main contents include:(1)In order to solve the problem of thruster saturation solved by the pseudo inverse method,a weighted pseudo inverse distribution algorithm is proposed.In this paper,according to the suppression and enhancement of the weight matrix elements to the corresponding thruster,the method of updating the weight matrix in fixed angle mode and variable angle mode is studied separately.Finally,the effectiveness of the weighted pseudo inverse method is verified by simulation experiments.(2)In order to avoid the process of thruster saturation handling by using pseudo inverse method,this paper introduces the direct allocation algorithm to solve the thrust allocation problem which has been translate into a vector geometry problem.The effectiveness of the proposed algorithm is verified by designing a set of comparative experiments,and the advantages has been show by comparing with the pseudo inverse method.(3)Because of the diversity of operation conditions and the complexity of sea conditions endurance by the dynamic positioning ship,environment force-fixed mode,variable mode and fixed-reversible model and the standard of switching between several distribution modes has been study and set.Finally,the effectiveness of the switching strategy is verified by the simulation experiment.