Study On The Mechanical Behavior Of Cluster Riser System For Tension Leg Platform

The dissertation is supported by China National Offshore Oil Corporation project named “Operation and technology research on drilling and completion of tension leg platform top tension riser”.Specific to the oil and gas exploratory development in the South China Sea,a research on the key technology of drilling and production riser system for tension leg platform and the mechanical behavior of cluster riser system are carried out for the first time.Major progress are acquired,including static analysis method,dynamic analysis method,local mechanical properties analysis method and wave-induced fatigue analysis method,which can provide technical support and operational guidance for the safety management of riser system for tension leg platform in the South China Sea and has important theoretical value and good engineering application prospect.The main achievements are as follows.(1)Study on static analysis on tension leg platform riser systemStatic analysis method and procedure of TLP risers in tandem are established.The current velocity at the downstream riser is calculated based on DNV-RP-F203 and Huse semi-empirical wake model.Considering the riser wake shielding effect,the finite element analysis model of risers in tandem is established by ABAQUS.The comparison of riser conventional model and riser-conductor model is studied.Static analysis of riser system is performed systematically and the effects of riser initial gap,current,top offset and top tension of risers are investigated.(2)Study on dynamic analysis on tension leg platform riser systemThe analysis model of tension leg platform is established by ANSYS.The dynamic response of tension leg platform is studied under wind,wave and current,and the platform motion response amplitude factor and motion time history are obtained.Considering the surge and heave motion of TLP,dynamic analysis of production riser and drilling riser in normal conditions are performed systematically.The variation characteristics of the bending moment,stress and gap of riser are investigated.The mechanical properties of production riser in extreme conditions are studied when impact occurs,and the impact position of the risers in tandem and the impact force at the impact point are determined.(3)Study on the local mechanical properties of riser system for tension leg platformThe local mechanical property of riser collision is studied based on the analysis results of production risers in tandem in extreme conditions.The stress variation characteristics of BOP spool and Christmas tree riser are studied on the basis of BOP and Christmas tree shaking.A finite element analysis model of taper stress joint is established and dangerous positions of taper stress joint are identified.The temperature-stress coupling analysis of thread joint is carried out based on analysis of production riser system.Then influence of temperature field on the mechanical properties of thread joint is studied.(4)Study on wave-induced fatigue of tension leg platform riser systemWave-induced fatigue analysis method of tension leg platform risers is established in time-domain.Nonlinear dynamic analysis of risers is conducted under platform motion,wave and current.The fatigue life of production and drilling riser are calculated based on Miner rule.The effects of platform motion and wave loads on the wave-induced fatigue damage are compared.The sensitivities of the riser wave-induced fatigue damage is carried out.A local fatigue analysis method and procedure of taper stress joint are proposed.,including dynamic analysis of riser system,equivalent fatigue stress calculation,finite element analysis and multi-scale fatigue analysis of taper stress joint.