The Key Technology Research On The Umbilical Fatigue Test System For The Subsea Production System

The umbilical is used as a “lifeline” which connects the offshore facilities with the submarine production control system.Researchers all over the world dedicate to guarantee and prolong the fatigue life of the umbilical.The umbilical stretching and bending fatigue test system can be used to emulate the loading environment of an umbilical under operating conditions and provide scientific foundation for the umbilical designing and fatigue life estimation.However,the nonlinear bending and stretching characteristics of the umbilical,probable vibration of the umbilical during the test and the time-varying parameters existing in the hydraulic system make it difficult to have enough constant stretching force control precision for the umbilical during the stretching and bending combination fatigue test.For solving this problem,a type of discrete-time model reference adaptive control system(MRACS)based on Diophantine equation and discrete model matching method is proposed to control the stretching force.An adaptive law,a combination of the adaptive linear neural network and the Normalized Least Mean Square(ADALINE-NLMS)algorithm,is proposed to improve the tracing ability of the control system.The main work of this paper is organized as follows:Firstly,the research background of the umbilical stretching and bending test system is introduced and the load characteristics of the umbilical is simplified and analyzed.Based on pertinent references inside and outside China,the key technical problems of the umbilical fatigue test system is discussed and the development of the umbilical stretching and bending test system and the electro-hydraulic force servo control system are summarized.Secondly,the structure type of the aforementioned fatigue test system is chosen as the horizontal type after the advantages and disadvantages of several structure types of the fatigue system are discussed.Subsequently,the mechanical structure of the test system including stretching mechanism,bending mechanism and the steel frame structure,is designed.Since the fatigue system is powered by the hydraulic system,main elements of the hydraulic system is selected and verified.Thirdly,the dynamic model of the electro-hydraulic force servo system is deduced and the transfer function of this system is established.Furthermore,the elongation rigidity variability of the umbilical and its influence on the electro-hydraulic force servo control system are analyzed.Finally,a type of discrete-time model reference adaptive control system(MRACS)based on Diophantine equation and model matching method is proposed to control the stretching force.An adaptive law,a combination of the adaptive linear neural network and the Normalized Least Mean Square(ADALINE-NLMS)algorithm,is used to improve the tracing ability to the reference model output of the control system.Afterwards,the simulation and experiment are performed to verify its validity.