Research On Nonlinear Dynamic Response Of Vortex-induced Vibration Of Risers Conveying Pulsating Flow

Marine risers are significant components of subsea production system.They are set erectly in the sea and contacted directly with seawater.Marine risers will be caused vortex-induced vibration(VIV)while suffering from the complicated load of wind,wave and current.This kind of VIV phenomenon will ruin the whole subsea production system,fatigue the riser and reduce its life.Therefore,it is highly necessary and significant to do research on VIV phenomenon.Primarily,the research status of riser vibration induced by internal flow,VIV and VIV dynamic response influenced by internal flow is introduced.The main innovations and contents are also summarized,then the theoryies and parameters of VIV are introduced,the basic theory of wake oscillator model is also presented.And afterwards the vibration of the riser conveying internal flow in the still water is analyzed.The Generalized Integral Transform Technique(GITT)is applied for predicting the dynamic response of vibration of the riser.The differential equations are solved by using the Adams-Moulton and Gear method(DIVPAG)which is developed by the International Mathematics and Statistics Library(IMSL).We draw some conclusions including: Firstly,the vibrational frequency will decrease as the velocity of the internal flow increases;the vibrational amplitude will increase as the velocity of the internal flow increases.The dynamic response of the riser conveying pulsating flow is also predicted.The conclusion that the vibrational amplitude will reach the maximum when the frequency of pulsating internal flow comes close the natural frequency of the riser is obtained.Secondly,the dynamic response of VIV of the riser model we use is analyzed.The results indicated the relation between vibration frequency and vortex shedding frequency.They have referential value for the next-step analysis.Finally,the nonlinear dynamic response of VIV of the riser conveying internal flow is studied.Firstly the riser conveying steady flow is analyzed.Results show that the frequency will decrease and amplitude will increase when riser conveying internal flow,but the frequency is still very close to the vortex shedding frequency.As the velocity of internal flow increases,vibrational frequency decreases and amplitude increases.When the riser conveys pulsating flow,the vibrational amplitude will reach the maximum when the frequency of pulsating flow and the natural frequency are close to each other.