Research On Valve-controlled Hydraulic Cylinder System Under Extremely High Ambient Pressure In Deep Sea

Valve-controlled hydraulic cylinder systems are widely used in deep-sea operating equipment to achieve linear telescopic motion and,on this basis,to realize the required complex operating movements.In the deep-sea environment with high ambient pressure,the prerequisite for a deep-sea valve-controlled hydraulic cylinder system to operate normally is the stability and reliability of pressure compensation technology.The high ambient pressure introduced by the pressure compensation technology will cause structural deformation of the parts,which will affect the sealing performance of the O-ring seal and the clearance-fit dynamic seal in the system.In addition,the high ambient pressure introduced by the pressure compensation technology will cause a significant increase in the viscosity of the hydraulic oil,which will affect the leakage of the clearance-fit dynamic seal and the pressure loss of the pipeline in the system.However,with the adoption of pressure compensation technology,the development and design of the deep sea valve-controlled hydraulic cylinder system and the selection of hydraulic components still follow the design standard and experience on land,so the structural deformation and hydraulic fluid viscosity change caused by high pressure in the deep sea environment are ignored,which greatly affects the reliability and working performance of the valve-controlled hydraulic cylinder system in the deep sea environment.Therefore,based on the data of deep sea conditions measured by the "Fendouzhe" manned submersible and the high pressure viscosity tests of hydraulic oil,in this thesis,research on sealing technology,pressure compensation technology,and pipeline pressure loss characteristics in deep-sea valve-controlled hydraulic cylinder systems was carried out.On this basis,a model of a deep-sea valve-controlled hydraulic cylinder system was formed,and research on the motion delay mechanism of deepsea valve-controlled hydraulic cylinder systems,together with energysaving and precise control,was carried out.The research results can provide a theoretical basis for the optimization and design of deep-sea hydraulic components and provide technical support for the reliable,energy-saving,and accurate operation of deep-sea valve-controlled hydraulic cylinder systems.The main research progress achieved in this thesis is summarized as follows:(1)With the actual measurement data of the "Fendouzhe" manned submersible,the change law of deep sea conditions at the 10,000 m level was analyzed,and the results showed that the ambient pressure increased by about 10 MPa for every 1000 m increase in depth,and the ambient temperature is kept in the low temperature range of 1～5℃ when the depth is greater than 1000 m.The two hydraulic fluids used in the "Kunlong 500" subsea mining vehicle and the "Fendouzhe" manned submersible were analyzed by high pressure viscosity tests,and the results showed that the viscosity of the hydraulic fluids increases exponentially with the ambient pressure in the deep sea,and the viscosity of the two fluids increases with each increase of 1000 m in depth by 25.26% and 21.62% respectively,which will seriously affect the working performance of hydraulic components and hydraulic systems under deep-sea conditions.(2)With the structural deformation and hydraulic oil viscosity change caused by the extremely high ambient pressure in the deep sea considered,the structural deformation mechanisms of O-ring seals and clearance-fit dynamic seals and the hydraulic oil leakage mechanisms of clearance-fit dynamic seals were studied.The finite element numerical analysis of the O-ring seal and clearance fit dynamic seal was carried out,and the deformation and leakage mechanisms were verified.On the basis of this,the design recommendations for the O-ring seal and the design guidelines for the clearance-fit dynamic seal were proposed.(3)With the characteristics of high pressure and low temperature in deep sea environments considered,the dynamic time response of the pressure compensator was solved,its working process was analyzed,the optimization design criteria were proposed,and the optimized design of pressure compensator parameters was completed.The numerical model of the pressure compensator was established,and numerical simulation analysis and validation were carried out.The manufacturing of the pressure compensator was completed,and deep-sea high-pressure simulation experiments were carried out to validate it.(4)With the high ambient pressure in the deep sea and the viscositypressure characteristics of hydraulic fluid considered,the flow process of hydraulic fluid in the deep sea hydraulic pipeline was studied,and the pressure loss calculation formula considering the change of hydraulic fluid viscosity during the pipeline flow was derived.The proposed formula is proven to be an extension of the classical Poiseuille’s law through Taylor series expansion.The influence of parameters on the pressure loss along the pipeline was analyzed,and design suggestions were made.The correctness of the proposed formula was verified by CFD numerical simulation and experimental tests.(5)On the basis of the aforementioned deep-sea high-pressure conditions,the viscosity-pressure characteristics of hydraulic oil,the numerical model of the pressure compensator,and the pressure loss characteristics of the pipeline,a mechanical-hydraulic numerical cosimulation model of a deep-sea valve-controlled hydraulic cylinder system was established.The analysis of its motion characteristics under extremely high ambient pressure conditions in the deep sea was carried out,and the mechanism of significant motion delay was investigated.And design suggestions to improve the delay phenomenon were proposed.(6)With the extremely high ambient pressure in the deep sea,the viscosity-pressure characteristics of hydraulic oil,and pipeline pressure loss characteristics considered,an energy-saving and precise control strategy for deep-sea valve-controlled hydraulic cylinder systems was proposed,which adopted the proportional relief valve to dynamically adjust the pump pressure and employed variable gain PID control.Through a mechanical-electric-hydraulic numerical co-simulation analysis,the performance of the proposed control strategy was investigated and its effectiveness was verified.The proposed control strategy provides a new solution for the low energy consumption and high precision operation of the valve-controlled hydraulic cylinder system under deep-sea conditions.