Research On The Configuration And Low-Power Holding Of The Electrically-Driven Subsea Gate Valve Actuator

The application of all-electric subsea production system is a growing trend of subsea oil and gas field development,which has become the consensus in the industry.As the core equipment of the system,the electrically-driven subsea gate valve actuator controls the opening and closing of the Christmas tree and manifold of the system.It is the final executive unit of the system and plays a vital role in the exploitation of oil and gas resources.At present,the electrically-driven subsea gate valve actuator has been in the trial stage in Europe and the United States,while it is still in the development phase in China.Acquiring the key technologies of the electrically-driven subsea gate valve actuator has important theoretical significance and practical application value for improving the offshore oil and gas exploitation technology in China.In this thesis,an overall scheme of electrically-driven subsea gate valve actuator is proposed according to the control requirements of all-electric subsea Christmas tree.The structure configuration of the actuator mechanical system is studied.Aiming at the performance requirements of actuator reliability,safety and energy saving,a spectrum of mechanisms are proposed,including redundancy drive mechanism with parallel arrangement of double motors and combining the gear and the nut-screw transmission,a failsafe closing mechanism with the closing spring,a damping self circulating buffering mechanism,a override and position indicating mechanism combined with nut-screw transmission and crank slider,as well as a low-power holding mechanism drived by electromagnet and combined the spiral transmission and the cam transmission,etc.Then realize the actuator functions of redundant drive,failsafe closing,auxiliary override,position indication and small power consumption remaining the gate valve open.The control and drive method of the actuator electrical system is studied.Design schemes of the control system and drive system are proposed to realize the monitoring,control and drive of actuator.The holding performance and unlocking performance of the low-power holding mechanism of the electrically-driven subsea gate valve actuator are studied.The mechanical and motional mathematical model in the holding process and the dynamic mathematical model in the unlocking process of the mechanism are established.The analytical relationship between the performance evaluation indexes such as the lockable maximum load of the closing spring,the driving torque in the unlocking process,the permissible stroke and the maximum stroke of the locking tab and the key design parameters of the mechanism is obtained.The numerical calculation method is used to analyze the effects of key design parameters on the performance of the mechanism.The optional parameter set of the mechanism is obtained based on the orthogonal test method,and the optimal design size of the low-power holding mechanism and the corresponding holding and unlocking performance,which satisfy constraint conditions and performance requirements,are obtained considering the constraint relationship between holding performance and unlocking performance.In order to realize the reasonable control of manufacturing errors to ensure the performance reliability and improve economy of the low-power holding mechanism of the electrically-driven subsea gate valve actuator,the effect of manufacturing errors on the performance of the low-power holding mechanism is analyzed.The error analytical model of holding performance and unlocking performance of the mechanism is established.The sampling formulas of various errors are deduced based on the probability distribution of error factors,and the performance error of the mechanism is simulated and statistically analyzed using statistical methods.The influence law of error factors on the performance of the mechanism and the performance distribution range of the mechanism under different machining accuracy are obtained,and the optimal accuracy design scheme of the low-power holding mechanism is determined.According to the characteristics that the error of contact surface changes dynamically and randomly in the unlocking process,the random sampling and cubic spline interpolation method are used to describe the random contour model of contact surfaces,and the dynamic modified model of the unlocking process considering the random surface error is established.The effect of random surface error on the unlocking process is is analyzed,and the dynamic characteristics range of the unlocking process under a given machining accuracy are obtained by the method of analysis of the random processes.Aiming at the loading-unloading cycle in the working process of the low-power holding mechanism of the electrically-driven subsea gate valve actuator,taking the contact form of two cylindrical surfaces in the low-power holding mechanism as the research object,the contact mechanical characteristics of the loading and unloading processes of contact surfaces are studied by fractal theory.According to the characteristics of two-dimensional fractal rough surface,the contact model of single asperity in loading and unloading processes considering friction is established.The size distribution function of asperities is revised by introducing the cylindrical contact coefficient and the load correction factor.The fractal analytical model for the loading-unloading process between two cylindrical surfaces with friction is presented,and the relation between the real contact area and the contact load in different deformation stages are deduced.The impacts of model characteristic parameters on the surface load-unload contact characteristics are analyzed by the numerical simulation method.The calculation results of the model are compared with the classical model to verify the correctness of the theoretical analysis,so as to provide a theoretical basis for improving the contact mechanical properties of the working surface of the low-power holding mechanism.An electrically-driven subsea gate valve actuator experimental prototype are developed,and a test system of the actuator is constructed including the test master control station,test electrical power and communication distribution unit,and signal generator.The various functions test of the electrical system and mechanical system of the electrically-driven subsea gate valve actuator are carried out to verify the validity of the electrical system design,as well as the correctness of configuration and theoretical analysis of the redundant drive mechanism,low-power holding mechanism,failsafe closing mechanism and valve position indicating mechanism of the mechanical system.