Numerical Simulation Study On Vortex-induced Vibration Response Of Marine Riser

With the oil and gas resources on land can be mined conventional less and less,the effective development of marine oil and gas resources has become a new way to ensure the stable supply of oil and gas resources.Ocean riser is one of the important equipment for offshore oil and gas exploration,along with the development of marine oil and gas resources to the deep waters,the operating depth of the ocean riser also increases,the ocean riser facing the marine environment is more complex.With the water depth increases,the flexibility of the riser structure itself is enhanced,in the complex and harsh conditions,the vortex-induced vibration response of the riser is more complicated and violent,the performance and service life of the riser there are serious hidden dangers.Therefore,in this paper,the produce mechanism and mechanical response for vortex-induced vibration of ocean riser are studied,the main contents of the research are as follows:According to the structural parameters of the riser and the parameters of the flow,the simulation model of fixed water pipe flow model is carried out,the flow field characteristics for the flow around the model of a riser under different Reynolds and the variation law of lift coefficient,drag coefficient,vortex shedding frequency and Strouhal number with Reynolds number are studied.revealed the vortex-induced vibration mechanism of the riser,the accuracy of the method and model in this paper is verified,these will lay the foundation for the next step in the research work..Based on the analysis of the flow model of the fixed riser,the vibration response characteristics of the vortex-induced vibration model of the riser are studied under two different constraints of single degree of freedom and two degrees of freedom.By varying the different damping ratios and different reduction rates,the influence of different damping ratio and degree of freedom on the lift coefficient,drag coefficient,response amplitude and vortex shedding frequency of vortex-induced vibration are compared and analyzed,which provides an analytical basis for the next study of vortex-induced vibration response by using the theoretical solution model.The theoretical solution model of vortex-induced vibration response of two different forms of risers with single degree of freedom is established and obtained,the equations are numerically solved by using the fourth order Runge-Kutta method,the numerical results are compared with the simulation results and the theoretical solution model is improved,using the improved theoretical solution model to study the vortex-induced vibration response under the periodic flow and the influence of the frequency of periodic flow on the vibration response is obtained,it is suggested that the natural frequency of the riser should be avoided near the frequency of the incoming flow in order to ensure the safety of the riser.The vortex-induced vibration of the riser under the action of tension is simulated,and the effect of different tension loading on the vortex-induced vibration response is studied,the variation law of vortex-induced vibration response under the condition of constant tension force loading and simple harmonic tension loading is obtained,which provides a reference for the vortex-induced vibration of the riser in practical application.In this paper,the understanding of the vortex-induced vibration of the riser and the variation of the vibration response in different flow modes and different tension loading modes are mainly completed,the conclusion of the study has a certain theoretical value and guiding significance for the research on the design of ocean septum pipe,the processing and the reclaiming compensation equipment of sea floating device,it is also has practical engineering significance in ensure the safety and economy of marine oil and gas resources exploitation.