Research On Sea Buoyancy Regulating System And Control Technology

With the decrease of resources on land, nations all over the world have turned their focus of attention to ocean area, especially deep ocean. As an important tool for exploring the ocean,the technology of underwater vehicle has been developing towards multiple directions of long-range, multi-functional, great-submergence and intelligent. In the complex deep sea environment, buoyancy regulating system can take the place of vertical propeller,and plays a vital role in power-free heaving motion and depth control of underwater vehicles. Compared with other ways of buoyancy regulating, the way using seawater as working medium to regulate has the advantage of wide adjusting range and recyclable, which at the same time has greatly improved the efficiency of underwater vehicles in buoyancy regulating. Therefore,many underwater vehicles with great submergence are all equipped with this type of buoyancy regulating system at home and abroad. On account that the water hydraulic components in the system, like high pressure pumps and valves, are scarce, and the research is greatly difficult in technique, like seawater resistance and dynamic sealing under high pressure, it is of great research significance and utility value to study the seawater-type buoyancy regulating device and the control technology of quantitatively filling and draining water based on the system. The following research work were carried out in this paper:(1) The current achievement of research on buoyancy regulating system and water hydraulic components were analyzed at home and abroad. By taking the fundamental principle as reference and to avoid the problem of unavailability of high pressure seawater pumps and valves, a plan of seawater-type buoyancy regulating system which can work in deep sea environment was proposed after analysis and improvement. In the meantime, the working principle and process of the plan were analyzed and studied. The experimental prototype and platform of the design were developed.(2) According to the working characteristics and operating environment of the seawater-type buoyancy regulating system, three key technological difficulties were studied,which were seawater-type switching valve, power source and dynamic sealing under high pressure. In view of the problem of seawater switching valve in the system, the conventional way of applying solenoid switching valve was abandoned due to the high friction resulted from dynamic sealing of solenoid valve stem under high pressure, and a new method of a combination of three-port ball valve driven by electric actuator was developed to meet the demand of dynamic sealing under high pressure, which also broke the directional limit of inlet and outlet ports and achieved bi-directional function. As for the problem brought about by seawater pump with high pressure, concerning the scarce of products and due to the limitations of size and weight of buoyancy regulating system, the available ones are not suitable for directly use as power source of the system, a new way of seawater pressure-boosting pump driven by an oil gear pump as power source of the system was designed, which not only met the demand of the design target, but also provided a solution to the power source of buoyancy regulating system with greater submergence for reference.Concerning the dynamic sealing problem under high pressure in deep sea condition,two places need to be solved, which are the transmitting connection between motor and oil gear pump and the one between electric actuator and high-pressure ball valve. By studying the connecting structure of fitting surface, the dynamic sealing of transmitting connection was changed into the static end-face sealing of the pressure-resistant container, and the related experiments were performed to verify the sealing performance in the design.(3) To achieve the control accuracy of the seawater-type buoyancy regulating system,global mathematic model and transfer function were established after analyzing each part of the system. PID controller and fuzzy PID controller used for quantitatively filling and draining water were designed, and simulations of both controllers were built with MATLAB.The step response characteristic, the sine following feature and step anti-interference characteristic of the system under both controllers were compared and analyzed, which resulted in the control strategy of the system and the accurate control of quantitatively filling and draining water was achieved.(4) In order to verify the feasibility and effectiveness of some theories and methods in the process of studying seawater-type buoyancy regulating system, experiments relating to sealing performance under high pressure and calibration of the level gauge were carried out.With the load-simulating system, experiments were conducted with the developed seawater-type buoyancy regulating experimental platform and the ATmegal28 based control system of quantitatively filling and draining both on land and in pool.