Research On Modeling And Control Strategies For The Trawling System

Marine fishery is of great importance for the food and nutrition supply which human beings depend on for a living. Fish trawling has the advantages of good initiatives and wide production areas, and has become most important fishing method. With the recession of fisheries resources and the improvement of environment protection consciousness of the ocean, the catching efficiency and environmental influences of trawling has become a hot topic. As the distance between trawler and net can be thousands of meters, the trawl net movement is difficult to predict. Manual operation for the trawl system is often very slow and the control precision cannot be ensured. Therefore, increased control performance for the geometry and trajectory of trawl net would greatly improve trawling efficiency and catch quality.In this paper, a mathematic model of trawl system was developed including trawler, trawl winch and trawl net system, and the interface between subsystems was analyzed. The accuracy of trawl model was then testified through computer simulation and sea-trial. In order to improve the control performance, the tracking and geometry control within vertical plane and space were discussed, and robust control scheme was adopted for the purpose of disturbance attenuation. Simulation results illustrated the proposed control strategy was effective.The main contents of the dissertation are presented as follows:Chapter1give an overview of the trawl system, and the research background, significance and the main contents were also presented.Chapter2introduced the principle of the trawl winch, and the hydraulic system with pressure and flow control was designed according to the trawling conditions. Mathematical model of trawl winch hydraulic system was then established, and the tension and length compound control scheme was developed.Chapter3modeled the trawl net system with lumped mass method. The topological connections of trawl nets were first ensured with discrete method, and the cable tension, fluid hydrodynamic force and gravity in water were then derived. Finally, computer simulation and sea-trial were conducted to verify the modeling accuracy of the trawl net system.Chapter4first established the mathematical model for trawler, and the model was then integrated with trawl winch and trawl nets system model. The "kaifu" trawling system was then investigated for trawl system simulation and sea trial analysis.Chapter5discussed the trajectory tracking control problem of trawl system within the vertical plane. A simplified model within the vertical plane was first established, and a fuzzy robust trajectory tracking control strategy was proposed taking into account parameter perturbation and external disturbance. Simulation results verified the validity of the proposed fuzzy robust control algorithm.Chapter6further investigated the trajectory tracking control problem of trawl system in the space. An adaptive robust control strategy was proposed based on backstepping method, and a control allocation of trawl winch and trawler was developed for the consideration of the non-strict feedback characteristics of trawl system. Finally, simulation results illustrated the proposed adaptive robust controller was effective.Chapter7summarized the main results and conclusions, and the achievement and suggestion for the future work were also presented.