Investigation Of Electro-hydraulic Servo Load Simulation Ystem For Towing Device With Variable Stiffness

The load simulation system for towing device is a significant hardware-in-the-loopsimulation equipment, used to simulate the towed load changes on the towing device ofmarine vessel. It is designed to detecting the performance of the heave compensation devicefor comprehensively and accurately. Compared with the sea trial, the experiment of thehardware-in-the-loop simulation has the advantage of shorter period and lower cost. Inorder to achieve the fast response and wide range change, the electro-hydraulic servosystem is adopted. In the dissertation, the main contents are as following:Firstly, according to the overall scheme and the hydraulic principle of theelectro-hydraulic load simulation system for towing device, the mathematical model of thesystem is established. It is concluded that the wire-rope Stiffness is important to designand control in the system from the analysis of the mathematical model. It could change thecorner frequency, the natural frequency and the damping ratio of the electro-hydraulic loadsimulation system.Secondly, the nonlinear relationship expression between the wire-rope stiffness and theloading force is derived from the results of the experiments of the displacement-tensionmethod. By observing the mathematical model and the bode diagram of the system, it isconcluded that the corner frequency and the natural frequency will increase with theincreasing wire-rope stiffness. On the contrast, the damping ratio will be decreasing. Then,PID controller is proposed.Thirdly, the frequency width of the system requirement is greater than1Hz and thephase-tracking lag angle of the system requirement is less than10degree in the active work.The PID controller is difficult to meet the challenge because of the low natural frequencyand the damping ratio of the system. In order to achieve the goals, the feed-forwardcompensation is proposed. It would increase the frequency bandwidth of the system on thepremise without affecting the stability of the system. However, the coefficient of thefeed-forward control should be changed with the wire-rope stiffness in real time.Fourthly, the surplus force is a key issue to control accuracy of the system in thepassive loading performance. The mechanism and characteristics of the surplus force are analyzed in the paper. It is concluded that the surplus force is concerned not only with thespeed, acceleration, acceleration differential of the towing device, but also with thewire-rope stiffness. Then, a velocity feed-forward compensator is proposed to suppress thesurplus force based on structure invariance principle.Finally, the experiment is conducted. The results of the active loading show that theresponse is improved by the feed-forward compensation. And the velocity feed-forwardcompensator is effective to suppress the surplus force in passive loading.