Design Of Subsea Flex-Lay System And Dynamic Characteristic Analysis Of Pipeline During Laying Process

With the development of the economy,the demand for energy is increasing for countries all over the world.Due to the depletion of terrestrial oil and natural gas,marine oil and gas energy has gradually become the target of exploitation.In the process of offshore oil and gas energy exploitation,pipelines are mainly used to transport oil and gas.Therefore,pipeline laying and installation equipment has become the research focus of marine equipment.The flexble pipe laying occupies an important position in various pipe laying methods due to its high laying speed and large laying depth.As a major energy demand country,it is necessary for China to strengthen the research and development of marine oil and gas resources.The main work of the thesis includes the overall design of the flex-lay system and the dynamic characteristic analysis of pipeline during laying process.According to the technical requirements and workflow of the flexble pipe laying system,an overall scheme of the flexible pipe laying system is proposed and an overall structure of the flex-lay system is confiemed.The structure design of angle adjustment mechanism,tensioner bracket,curvature adjustment wheel,tower pulley block and auxiliary equipment is completed,and the hydraulic control system is designed on the basis of the structure design.Based on the natural catenary method,the static mechanical model of the flexible pipe was established and solved iteratively by Matlab.The static shape of the pipeline and the static tension at the top of the pipeline under different laying parameters were obtained,which lays the foundation for dynamic analysis and determines the maximum working load of the flexible pipeline laying system.Based on the maximum working load,the structural design and strength check of the flexible pipeline laying system are carried out.The rationality and safety of the design are verified by finite element simulation software.The wind pressure coefficient and the flow drag coefficient of the pipelaying vessel are obtained by reading the spectrum.Based on the semi-empirical formula,the wind load and the flow load are numerically calculated.Then based on the 3-D potential theory,the hydrodynamic coefficient of the hull is obtained by analyzing the hydrodynamic performance of the pipelaying vessel with AQWA.Finally,the frequency domain motion of the pipelaying vessel under given sea conditions is analyzed,and the vertical displacement at the installation position of the flexible pipe laying system under different wave parameters is calculated.In order to obtain the dynamic stress change of the flexible pipe,based on the finite element method,a generalized dynamic analysis model of the laying system is established in Orcaflex software.The simulation proves that the flexible pipe works well and the dynamic tension of the top end is within the safe range under the specified laying condition.The effects of wave parameters and different paving conditions on the dynamic stress of the pipeline are studied.Through the overall design of the flex-lay system and the dynamic characteristic analysis of the flexible pipe during the laying process,the paper lays a good foundation for the follow-up research and engineering application of the flexible pipe laying system.