Evaluation Of Active Control Of Vortex-induced Vibration Of Marine Risers

Vortex-induced vibration suppression methods are mainly divided into active control method and passive control method.The active eontrol method is to suppress the vortex-induced vibration by interfering with the mechanism of vortex shedding by actively input energy into the system.Compared with passive control device,the advantage of active control method is more intelligente and can be adjusted timely according to actual ocean current conditions.In this paper,two-dimensional and three-dimensional numerical simulation of CFD is used to study the effect of active rotating control rod on vortex-induced vibration.After validation of the numerical simulation method,the simulation is carried out by changing the angle between the auxiliary cylinder control rod and the main cylinder atα=30°、60°、90°、120°、150°,the diameter ratio(d/D=0.06,0.12,0.24,0.48),and the rotation direction of the auxiliary cylinder,the outward reverse rotation(OC),inward reverse rotation(IC),upward in-phase rotation(UC),downward in-phase rotation(DC).Finally,the active control effect of the attached cylinder on the vortex-induced vibration is evaluated comprehensively from the aspects of amplitude response,lift-drag coefficient,vortex shedding and wake streamline and so on.(1)The results of varying clearance ratios(g/D=0.03D,0.06D,0.15D,0.3D)under the condition of low Reynolds number Re=200 show that when Ur<5,the auxiliary cylinder restrains the main cylinder,and the restraining effect is the best when g/D=0.15;when Ur>5,the main cylinder appears "galloping" phenomenon under different clearance ratios,and when g/D=0.15,the amplitude increases most obviously with the increase of reduction speed.In the process of varying clearance ratio,the vortex shedding mode captures the 2P0 mode.(2)The vibration of riser is restrained when the auxiliary cylinders are installed at a=90°、1200、1500 on the backflow surface,and the restraining effect is the best when the auxiliary cylinders are installed at α=120°、150° on the backflow surface.After installing a cylindrical appendage of α=30°、600 unitary on the upstream surface,the vibration of the riser is enhanced,and when Ur=12,the increase percentage of the amplitude is more than 800%.The momentum injection from the riser to the surrounding area can be clearly observed in the momentum map.(3)When the auxiliary cylinders are installed at α=90°,d/D=0.06、0.12、0.24,the vibration of risers is suppressed.When d/D=0.12,the vibration amplitude fluctuates very little with the increase of reduction speed,and the overall amplitude range is 0 to 0.1.The suppression effect is very good.When d/D=0.48,the vibration of riser is suppressed first and then strengthened with the increase of reduction speed,and the critical reduction speed is 8.(4)The vibration of the main cylinder was restrained under four different rotation modes:OC,IC,UC and DC.When Ur<6,UC-V rotation mode had the best restraining effect;when Ur>6,IC-V rotation mode had the most obvious restraining effect.