Research On Positioning And Path Following Control For A Deep-sea Remotely Operated Vehicle

The improvement of marine resources exploitation technology becomes the key to the development of marine industry.Design and development of new kinds of marine engineering equipment to enhance the technological level of ocean engineering industry in China is of great significance.Due to the complexity of the marine environment,the underwater vehicle has become an important tool for exploration and development of marine resources.With advantages like functional diversity,strong operation ability and high safety factor,ROVs(Remotely operated vehicle)have been widely used in ocean resource development and exploration,and become the important equipments in areas like marine resources development and underwater engineering.According to the essential characteristics of the tethered system's control,a positioning and path following control system for a tethered remotely operated vehicle is designed in this dissertation.The dissertation contains the following contents.(1)Tethered ROV systems are classified according to the deployment operation mode.The tethered ROV systems are divided into vertical suspension system and flexible umbilical cable system depending on the material type and underwater shape of the umbilical cable.Dynamic model of six degrees of freedom is set up under the condition of ocean current.(2)Dynamic model of the lateral oscillation for vertical suspension system consisting of underwater heavy equipment and armoured umbilical cable is set up under the conditions of external disturbance and current.And averaging method and linearization method are adopted to obtain approximate analytical solution of dynamic equation according to the different forms of damping terms.The approximate analytical solution is verified through simulation in the current environment.A double loop PID closed-loop control method is designed for the attitude adjustment and positioning control of the heavy equipment.(3)Static and dynamic analysis methods of flexible umbilical cable system are studied.The lumped mass method is adopted for dynamic simulation of flexible umbilical cable,and verified by comparison with the experimental data.The coupling dynamic model of ROV and umbilical cable is established.(4)Four degrees of freedom nonlinear sliding mode observer for the flexible tethered ROV system is set up.The current observer and flexible cable disturbance force simplified model are also established.The convergence and stability of the observer are proved,and the applicability and performance of the observer are verified by simulation in different working conditions.Unmeasured states like current velocity and cable disturbance can be observed with the designed observers.Effective methods to improve the observation precision are presented.Establishing a simplified disturbance model which can effectively estimate the actual disturbing force,and adopting disturbing force compensation method can effectively improve the observation precision.(5)A control system structure of flexible tethered ROV system is established.Combined with state observer and disturbance force simplified model of umbilical cable,two nonlinear controllers of four degrees of freedom are designed including the sliding mode controller with disturbance force compensation and sliding mode PID controller.The convergence and stability of the controllers are proved.The control strategies for positioning and path following of ROV are proposed.For complex situations with external disturbance,two kinds of effective methods to improve motion control precision of ROV are put forward: one is modelling the disturbance and adopting the disturbance force compensation for control model with observers.The other is a combination of various control methods,to improve the robustness and anti-disturbance ability of the controller.Finally,the control system performance is verified through positioning and path following simulation.Through this work,dynamic models and analysis methods for different tethered systems are established in this paper.The control system design for positioning and path following of a tethered ROV system is realized,and provides basis and reference for the design and application of other tethered ROV systems.