Research On The Electro-hydraulic System Of Heave Compensation In Marine Operations

Deep-sea towing system is widely used in a variety of fields such as seabed resource exploration,and high-power sonar drag.During offshore installations or towing in harsh sea conditions,the involved towing system must satisfy rigorous requirements in terms of safety and efficiency.The force resulting from the vertical motion of the vessel have an extensive effect on the overall towing structure and its lifetime.During the process of drag,towed body produce huge heave movement with vessel irregular movement due to wave action.Moreover,vessel motion is handicaps the operator during fine positioning of the payload.Heave compensator can effectively buffer and compensate towed body's heave movement,preventing the load from the influence of vessel out of wave's effect,which is necessary to ensure the normal operation of the deep towed system.Passive heave compensation system can have a certain compensation effect on the towed body's displacement and the cable's tension without external energy consumption.Therefore,it is widely used.However,the passive compentor is always with low compensation accuracy and large hysteresis.What's more,the mismatch parameter may cause the system unstable.Active heave compensation system(AHC)can effectively compensate for the load's displacement or strain,but it is not suitable for heavy towing system because of the large energy consumption.Therefore,active and passive composited heave compensator is becoming a mainstream.However,at present in China,the technology of heave compensation is still in an initial stage,the research and development on design parameters of heave compensator and compensation control method of electro-hydraulic system is relative hysteresis,but the researches of heave compensator are listed as a key security technology in foreign monopoly.In this study,according to the load characteristics and functional requirements of heavy duty deep-sea towing system in marine equipment,the electrohydraulic system of a composited heave compensation was designed.In which,we carried out research based on combination of methods including principles of design,theoretical modeling,simulation analysis and experimental research.The main contents of the study are as follows:In chapter 1,the research background and significance of heave compensator was described,and working principle,classification and development overview was reviewed.We summarized the national and international research status in relative fields including displacement control of electro-hydraulic servo system,pressure control strategy,and wave prediction.Furthermore,we proposed the main research topics after the analysis of the necessity and innovation of research.In chapter 2,the motion characteristics of marine equipment in the waves were researched.A heave motion simulator for the ship was built based on Matlab/Simulink to simulate the ship's motion in different sea conditions from level 3 to 6.A Motion Reference Unit(MRU)was employed in the South China Sea to capture and analyze the ship's real-time heave motion in different sea conditions.Through the analysis of the time lag from the heave compensator and the sensors,and the research on the motion characteristics of the deep sea towed equipment in the ocean waves,a new wave model prediction algorithm was proposed which based on Fast Fourier transform,active disturbance rejection state observer and parameter adaptive law.Simulation and experimental research were carried out on the proposed prediction algorithm based on the simulation of the heave motion condition and the measured heave datum of the ship's motion in different sea area of the South China Sea.The experimental results show that the proposed prediction algorithm can achieve very good prediction and real-time dynamic compensation effect in different sea conditions and different time delays.Therefore,it can be used for the compensation of time lag in in heave compensation control.In chapter 3,taking a 100T level deep sea towed system as the research object,we carried out the experimental researches on the characteristics of deep sea heavy towed body and the cable's load.Based on the analysis of the experimental data,the mathematical model of the load was established,which provided a theoretical and experimental basis for the design of the following control algorithm.A 100T level passive heave compensator was designed.And the mathematical model of passive heave compensation system was established.Simulation research and parameter optimization of the passive heave compensator were carried out based on a joint simulation platform by AMESim and Matlab/Simulink,and the design theory and design parameters were simulated and analyzed.The effects of the passive heave compensation which caused by the accumulator's volume,the the accumulator's average load pressure and the frequency of the heave motion were especially discussed.The displacement compensation and the tension inhibition effect of the passive heave system in different sea conditions were simulated.Based on the analysis of the load and the characteristics of the passive heave compensator for the deep sea towed system,a hybrid heave compensation system(HAHC)for the 100T level heavy towed system was designed.The mathematical of the HAHC is established,which will be used in the following research on the controller's design.In chapter 4,a nonlinear dynamics model of the hybrid heave tension compensating system was built.Considering the time-varying irregular heave disturbance in deep-sea towing system,and taking the cylinder's load pressure or cable's tension as control target,a hybrid heave tension compensating electro hydraulic control system was designed.A nonlinear adaptive robust integral sliding control(ARISMC)method for constant tension compensation of deep-sea towed system was designed,which combined with adaptive robust control and integral sliding mode control and other modern control theories.Among this method:(1)Using high order differential tracker,the average value of load pressure or tension within a period of time was considered as the system control command(the expected pressure),and the displacement of cylinder is introduced and solved by high order differential filter,whose different order derivatives were regarded as the internal model feed forward or state limit variables of the pressure compensation controller;(2)The equivalent elastic modulus of hydraulic oil,the flow coefficient of the servo valve and the leakage coefficient of the hydraulic cylinder are updated online through parameter adaptive law,and the integral sliding mode term is introduced to suppress the parameter estimation error;(3)The system's modeled part was taken as the controller's feedforward,and the nonlinear robust feedback was added to improve the controller's dynamic accuracy and to ensure the stabilization of the whole system;(4)Based on backstepping method,the system is divided into two subsystems.The Lyapunov function and virtual control variables of each subsystem were designed so as to keep the system stable and to complete the design of the whole system's control law.The proposed controller solved the problems such as model nonlinearity,parameter uncertainty and nonlinear disturbance in the tension compensation of the heavy deep-sea towed system.The parameters design of the actual bybrid heave compensator was carried out and an experimental prototype was built.The data of the heave motion of the ship mearsured in the South China Sea was introduced,and the heave motion of the mother ship in 3?6 sea conditions was simulated,according to which,simulation and experimental study on the pressure compensation with the proposed algorithm under different conditions was carried out.The simulation and experimental results showed that the ARISMC controller performed a good inhibitory effect on the model nonlinearity,parameter uncertainty and nonlinear disturbance characteristics,showing good tension compensation accuracy and strong robustness.In chapter 5,an extended adaptive disturbance observer(EADOB)is designed,which is based on the load characteristics and functional requirements of the HAHC system.Introducing nonlinear cascade control(NCC)and robust control(RC),a nonlinear robust cascade controller based on an extended adaptive disturbance observer(EADOB-NCRC)was proposed.Integrated the prediction algorithm,a nonlinear robust cascade predictive control algorithm based on extended adaptive disturbance observer(EADOB-NCRPC)was constructed,which was designed for the displacement control of hybrid active heave compensator.In the proposed algorithm,EADOB was designed to estimate the HAHC's time-varying parameters and unknown disturbance.NCRC divided the control system into two parts,the outer loop displacement controller and the inner loop pressure controller,which were independent of each other.Predictive controller(PC)was used to compensate the negative effects by the time lag from MRU and the actuator.The virtual pressure control input and the actual control output were designed based on back-stepping.The stability of the HAHC was verified based on Lyapunov stability theory.In order to eliminate the measurement noise,a fourth order linear tracking differentiator(HTDF)is designed before the observer.The data of the ships's heave motion which measured in the South China Sea and the simulated heave data in' 3-6 grade sea conditions were used for simulation and experiment.The parameters design and the verification of the proposed controller were carried out in an experimental prototype.Simulation and experimental results showed that the EADOB-NCRPC algorithm has a good displacement compensation effect,and superiority in the control accuracy and robustness.In chapter 6,the major research work of the study was summarized.The conclusions and innovations of the study were elaborated and suggestions for further study on the subjected were presented.