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Research On Wave Compensation Control Of Offshore Gangway

Posted on:2021-02-26Degree:MasterType:Thesis
Country:ChinaCandidate:M ZhangFull Text:PDF
GTID:2392330602997964Subject:Engineering
Abstract/Summary:PDF Full Text Request
The offshore gangway is a new type of offshore transfer equipment,which is equivalent to an offshore passage.It is convenient for people to transfer between a ship and an offshore structure.Due to the disturbances of the marine environment,ships experience motion in 6 degrees of freedom.The yaw,sway and surge of ships can be suppressed by dynamic positioning systems.Fixing the offshore gangway's pedestal on the center of one side of the ship can reduce the impact of the ship's pitch motion on the offshore gangway.The offshore gangway actively compensates the roll and heave motion of the ship through the coordinated movement of three mechanisms,so that the gangway is always stable and the end of the gangway is relatively stationary with the offshore structure.In addition,the marine environment and the offshore gangway's load often change.Each mechanism of the offshore gangway is driven by a hydraulic system.Since the friction between the hydraulic oil and the inner wall of the cylinder would change the temperature of the system,which would change the viscosity and the elastic modulus of hydraulic oil,there 'exist uncertainties of each mechanism's mathematical model parameters.Therefore,it is of great theoretical significance and practical application value to research wave compensation control of offshore gangway.In this paper,firstly,the ship's roll and heave motion are predicted.To compensate them,the amount of mo'tion required for the heave mechanism,the pitch mechanism and the telescopic mechanism of the offshore gangway are calculated using the distance formula between two points,sine theorem and cosine theorem.Besides,three mechanisms'mathematical models of the offshore gangway are established.Then,considering the mathematical model parameters uncertainties and the unknown time-varying external load of the gangway,an extended state observer is constructed to estimate the total disturbance due to the mathematical model parameter uncertainties and the unknown time-varying load,which is compensated in the feed-forward path.The error feedback control law is designed to achieve the wave compensation control of offshore gangway.Further,a finite-time extended state observer is constructed,and based on the non-singular fast terminal sliding mode control technology,the wave compensation finite-time control law is designed,so that the wave compensation control of offshore gangway is achieved and the error converges in finite-time.However,there exists the chattering problem of control input.To overcome this problem,the super-twisting sliding mode control technology is used to weaken the chattering of control input caused by non-singular fast terminal sliding mode technology.A finite-time super-twisting extended state observer is constructed,and based on the super-twisting sliding mode control technology,the wave compensation finite-time control law is designed,so that the wave compensation control of offshore gangway is achieved and the error converges in finite-time.Taking an offshore gangway as an example,the simulations of the designed wave compensation control laws are carried out using MATLAB/Simulink.The simulations results show that the designed control laws can effectively achieve the wave compensation control of offshore gangway,so that the gangway is always stable and the end of the gangway is relatively stationary with the offshore structure.
Keywords/Search Tags:Offshore Gangway, Extended State Observer, Non-singular Fast Terminal Sliding Mode Control, Super-twisting Sliding Mode Control, Finite-time Control
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