Research On The Key Technology Of Underwater Hydraulic System Utilizing Seawater Pressure

Underwater hydraulic system plays an important role in underwater equipments. High reliability, compact size and low weight are specifically required in the deep ocean. To make it adapt to full ocean depth, a pressure compensator is adopted to balance the pressure inside and outside of the tank, which makes system pressure be established on seawater pressure. In this way the influence of seawater pressure on underwater hydraulic system is avoided. However, the underwater hydraulic system with submersible motor and hydraulic pump is not suitable for those underwater equipments with lower power consumption or shorter operation time as its complex system structure and low power-weight ratio. Therefore, a new kind of underwater hydraulic system utilizing seawater pressure is proposed, in which underwater hydraulic actuators are directly driven under the pressure difference between seawater pressure and empty pressure container. In this way, the structure of underwater hydraulic system could be simplified and the reliability of the system could also be improved. Meanwhile, the power-weight ratio of the system could be improved by utilizing the frame of equipments as empty pressure container.The research targets the underwater hydraulic system using oil as working medium. Based on analysis of various underwater hydraulic systems, key technologies of pressure-compensated underwater hydraulic system and new underwater hydraulic system utilizing seawater pressure are studied by means of theoretical analysis, computational simulation and experiment respectively. As for pressure-compensated underwater hydraulic system, a design method for pressure compensator is carefully studied. As for new underwater hydraulic system utilizing seawater pressure, the feasibility of utilizing seawater pressure, the hydraulic energy recovery technique and the load driving technique are studied systematically. The idea of utilizing seawater pressure is considered to be creative. The research work could provide references for the application of various underwater hydraulic systems.The content of each chapter is concluded as follows:In the first chapter, underwater hydraulic systems are introduced and the underwater hydraulic system using oil as working medium is summarized. Based on these, the significance and the feasibility of utilizing seawater pressure to power underwater hydraulic system are demonstrated and the research work has also been addressed. In the second chapter, the classification of underwater hydraulic systems is defined. The principle, characteristic and application of various underwater hydraulic systems are analyzed. As for pressure-compensated underwater hydraulic system, a design method for pressure compensator based on variable hydraulic volume has been studied.In the third chapter, the principle, characteristic and the application method of underwater hydraulic system utilizing seawater pressure have been studied. To demonstrate the feasibility of utilizing seawater pressure, prototype of new underwater hydraulic system—underwater power generation system utilizing seawater pressure has been developed and tested in the deep ocean. Results have demonstrated the feasibility of utilizing seawater pressure.In the fourth chapter, a hydraulic energy recovery method based on high-speed on/off valves is proposed to improve the efficiency of new underwater hydraulic system. In the hydraulic energy recovery system, redundant hydraulic energy is stored through flywheel and released when needed. Meanwhile, the load flow is also recycled. Mathematical model of hydraulic energy recovery system is established and the steady-state characteristic, fluctuation characteristic and system efficiency are studied respectively. Results show that the hydraulic energy recovery method could improve system efficiency effectively.In the fifth chapter, a hydraulic pressure boost method based on high-speed on/off valves is proposed to improve the load capacity of new underwater hydraulic system. In the hydraulic pressure boost system, higher pressure is obtained by the sudden brake of hydraulic motor. Meanwhile, the higher pressure is stabilized through hydraulic capacitor. Mathematical model of hydraulic pressure boost system is established and the steady-state characteristic, fluctuation characteristic and dynamic characteristic are studied respectively. Results show the hydraulic pressure boost method could improve system load capacity effectively.Whole research work and achievements obtained are concluded and the further research work is also expected in the last chapter.