Analysis And Mitigation Of Steel Catenary Riser Considering Pipe-soil Interaction

With the continuous development of marine oilfields and marine natural gas resources,the center of gravity of oil and gas exploitation in the world has gradually shifted from land to sea.Marine risers are commonly used equipment in the process of offshore oil and gas production and exploitation.The study of their dynamic characteristics and response characteristics in complex marine environments can better guide the installation and maintenance of the risers,and serve the oil and gas exploitation work more efficiently..The steel catenary riser is a widely used riser system in marine risers.It is characterized by a long pipe-soil action section,which is prone to coupling with the soil during the contact process.The part that hangs in the marine environment is Vortex-induced vibration will occur under certain conditions under the action of ocean currents.To sum up,in the complex marine environment,different parts of the steel catenary riser are subjected to external loads,which are prone to local high stress,resulting in damage or even destruction of the riser.Therefore,it is necessary to consider the influence of the grounding part to systematically study the dynamic characteristics of the steel catenary,and on this basis,study the vibration reduction method of the steel catenary riser,so as to increase the service life of the riser.The thesis takes the steel catenary riser system as the research object,a large-scale threedimensional numerical calculation model is established through the APDL module in the ANASYS software,considering the comprehensive effect of the wave force and the vortex force,the P-y curve model is used to simulate the ground contact,and the fluid and structure are simulated.Coupling solution,modal analysis and transient analysis are carried out,and the factors affecting the natural vibration frequency and dynamic response of the riser are studied.On this basis,PTMD(Pounding Tuned Mass Damper)is applied to the riser system,and the amplitude and frequency of the riser node before and after the vibration reduction under different conditions of ocean current velocity,riser wall thickness and damper mass ratio are analyzed.Compared.The research shows that after applying the PTMD,the vibration reduction rate of the riser system reaches more than 50% under different wave force conditions,indicating that the PTMD can meet the vibration reduction requirements under various sea conditions and has stability.The thesis based on the Miner fatigue damage accumulation theory and the S-N curve theory describing fatigue damage,the stress time history data of the riser joints are sorted and analyzed,the fatigue damage of the riser is studied,and the factors affecting the structural fatigue damage are explored.On this basis,PTMD was applied to conduct the vibration reduction test,and the change of the fatigue life of the riser before and after the vibration reduction was analyzed and compared,and the stability of PTMD on the fatigue life enhancement was explored under the conditions of different ocean current velocity,riser wall thickness and damper mass ratio.The research shows that with the increase of ocean current velocity,the riser amplitude and frequency increase,and the fatigue life shortens.As the pipe wall thickness increases,the riser amplitude decreases and the fatigue life increases.After applying PTMD,the fatigue life of the riser increased significantly.Under different external loads and riser parameters,PTMD has excellent enhancement effect on riser fatigue life and is stable.The thesis takes Ontology as a platform,the Onto RE(Ontology for Risk Evaluation)risk evaluation system for marine risers is built,which realizes the quantitative analysis and comprehensive evaluation of the safety level of marine risers.Onto RE includes 5 first-level events,13 second-level events,and 31 third-level events,and uses SWRL language to define the logic rules between events,which can quantitatively analyze,evaluate,and predict the safety of offshore platforms from all aspects.To a certain extent,it fills the gap of the information-based marine platform evaluation system,and has certain practicability and scientificity.