Introduction To Research On Steep Wave Riser Collision Law And Vortex Induced Fatigue Characteristics

With the reduction of land oil and gas resource reserves,more and more deep-sea oil and gas resources have been discovered through surveys,leading to the shifting of oil and gas development to the ocean.At present,the development conditions and equipment of my country’s South China Sea oil and gas resources are gradually mature,as a connection between offshore floating platforms and underwater the flexible riser of oil and gas wellheads is widely used in deep-sea oil development.The steep wave riser formed on the basis of the flexible riser has become a common deep-sea flexible riser arrangement because of its low bending stiffness and strong compliance.This paper takes the non-bonded flexible riser under the steep wave arrangement as the research object.Aiming at the collision and vortex-induced fatigue damage of the deep-sea non-bonded flexible riser,the tandem non-bonded flexible riser collision and flexible riser are developed.Vortex-induced vibration simulation provides basis and reference for collision calculation and fatigue analysis of flexible risers.First of all,in view of the complex characteristics of the non-bonded flexible riser’s composite pipe layer structure,a large amount of contact friction,nonlinear materials,a simplified mechanical analysis model is established based on the ABAQUS software,and the non-bonded flexible riser is carried out on this basis.The mechanical performance analysis considers the section stiffness response of the non-bonded flexible riser under the combined load conditions of equivalent orthotropic materials and axisymmetric loads,as well as bending and internal pressure.Secondly,using ABAQUS to simulate the collision process of two unbonded flexible risers arranged in tandem,considering the collision response law under the influence of different collision speeds,friction coefficients between tubes,and internal pressure within the tubes,the downstream collision during the collision process was analyzed.The collision law of strain,stress and collision force in the collision area of the tube along the collision direction is compared and analyzed with the collision response law of a single-layer riser under the same conditions.Lay the foundation for the further improvement of the riser collision law.Finally,the vortex-induced vibration calculation model of the tandem flexible riser is established based on ANSYS software.The vortex-induced vibration response of the downstream riser is considered in the static and moving situations,and the downstream riser movement is analyzed mainly through two-way fluid-structure coupling The method calculates the transverse and downstream amplitudes of the vortex-induced vibration,and at the same time derives the fatigue loss rate formula of the flexible riser based on the Miner fatigue damage theory,etc.,and then calculates the fatigue damage rate of the flexible riser in the downstream and transverse directions under different reduced speeds.