Research On Dynamic Response Of Top Tension Riser

There are many reservoirs in the deep sea,but it is difficult to drill offshore.We need high-tech drilling equipment.Riser is the key equipment to connect the wellhead to the platform.Due to the complex offshore environment and riser's large slenderness ratio,riser may occur vortex induced vibration and parametric resonance and the resonance will accelerate the speed of fatigue failure of riser.Once the riser is destroyed,it will bring severe pollution to the ocean and lead to a big economic loss.So it is very meaningful to analyze the dynamic response of top tension riser.This thesis focuses on the dynamic characteristics of the top tension riser under complex environmental loads and internal loads,such as the waves,streams and floating platform sports.Not only the factors of impacting the VIV of riser system,but also dynamic response of the top tension riser are studied,which can provide a theoretical basis for engineering design.Firstly,control equations of the riser's motion are derived and solved.The ocean load on the riser and the calculation methods of load are introduced,besides,a simplified model of the riser is built on the base of some reasonable assumptions and the appropriate boundary conditions of the riser.Based on the D'Alembert principle,the equations of motion of the riser are derived by vortex-induced lift and fluid-solid coupling;then the equations are solved by use of Newmark-? method after Hermit discrete.Secondly,the factors that influence the natural frequency of riser and their sensitivity are studied.The characteristics of riser model are studied according to the control equations of motion.Using ANSYS,the factors that affect the natural frequency of riser such as constraint,riser length and tension ratio are studied by using control variable method,while the sensitivity of the factors is studied.Finally,the dynamic response of risers is studied with ANSYS software.The dynamic response of an extreme rare sea condition is studied based on the stokes wave theory.After analyzing the pure parametrically excited vibration of riser which is suffered from platform heave excitation,the resonance excitation mechanism of riser is revealed.Also,the vibration characteristics of the riser under the action of platform heave,wave and current are analyzed.