Theretical And Experimental Research On Passive Heave Compensator For Remotely Operated Vehicle System

With the expansion of marine activities and the deep-going exploitation of marine resources, as well as the rapid development of Seafloor Observatory Network in recent years, Remotely Operated Vehicle (ROV) is becoming more and more widely used in these areas. However, the roll, pitch and especially the heave motion of the mother ship might transmit through the umbilical tether to the Vehicle body, which might futhur cause operational failure to the vehicle or result in damage to the tether. Therefore, a heave compensation system is needed to reduce the induced vehicle motion, alleviate the dynamic tension and avoid slack of the tether which is a precause of snap load, so as to improve the vehicle control condition and prevent cable destruction, with an aim to enhance the operational safety.This paper is part of the National High Technology Research and Development Program project: 4500m Deep Ocean System, which is designed to develop a strong work class ROV and its operating tool system, including the Underwater Elevator, the Heave Compensator, the Operating and Rescuing Tools, as to complete such underwater tasks as seabed surveying and sampling, seafloor observatory network deploying, installing and repairing. This paper conducts the research of passive heave compensator for tethered ROV system through theoretical analysis, computer simulation and model experiment.Firstly, after studying the existing compensation technologies at home and abroad, and analyzing their pros and cons, the paper selects the flying sheave heave compensator as the compensation scheme for 4500m ROV system. At the same time, it figures out the compensator performance objective based on the designed ROV vehicle body and the umbilical tether parameters, thus designs the compensator parameters.Secondly, as the passive compensator is a nonlinear system, this paper builds the overall dynamic model of the whole in-line flying sheave heave compensation tethered ROV system, deduces and calculates the system characteristics like, the spring stiffness and natural period. Numerical simulations of system response in three typical kinds of sea state conditions, solved by the classic fourth-order Runge-Kutta scheme were done, so as to verify the compensator performance. Besides, it analyses the impact of tether's elasticity. To the question of low compensation efficiency and even the resonance situation in long seas, especially in deep water, the paper proposes a novel idea of adding a valve to regulate the system damping to solve that problem, and verifys this idea through numerical simulation later.Finally, this paper carries out the reduced scale model experimental research, simulates compensator response in different sea states and in various operating depths, to verify and improve the reliability of calculation analysis, while providing experiences for the real system.