The Effect Of Rough Surface On The Vortex-induced Vibration Of Circular Cylinder

When current flows over slender riser,it shall excite shedding vortexes within certain range of velocity.In turn,the riser shall be vibrated by vortices with tremendous periodical lift force and amplitude,especially in transverse direction.In range of certain velocity performance,the frequency of shedding vortex is closely related and approaches to that of submarine riser self-vibration.The vortex-induced vibration shall lock in the frequency of shedding vortexes,or in the vicinity,that of structure self-vibration.This frequency lock-in phenomena excites dramatic riser vibration,thus deteriorates the structural instability and fatigue breakdown.This article intended to study the shearing layer and wake that flows over rough surface riser and carry out numerical simulation with current-structure coupling model.Take another word,the article explores the response character of vortex-induced vibration of roughness surface submarine riser.By selecting the superior type of surface roughness parameters assemble,this article provides reference to engineering practice and guidance.This article concludes research and results as follows:(1)Based on Reynolds Navier-Stokes equation and SST k-? turbulent algorithm,this article unfolds fluid and structure coupling simulation for bare cylinder with two degrees of freedom.In comparison to Jauvtis-Williamson's experimental results,the validity of algorithm is confirmed.(2)By uniformly arrange 3?4?5?6?8?9?12 bumps,in shape of half-sine-wave,on cylinder surface,while putting one bump center in-line,this article has several conclusions.1)vortex shedding modes are changed and non-dimensional cross-flow amplitude is lower than bare cylinder with reduction of 50%.2)In comparion with bare cylinder,3 and 9 bumps catched sufficient amplitude suppression.Vortex shedding modes remain 2S.3)The 5,12 bumps reach higher non-dimensional cross-flow amplitude at higher velocity,Ur?6.5,but fluid forces remain high.4)The 4?8?9 bumps get to non-dimensional cross-flow amplitude peak at Ur?5.5)6 bumps effectively reduces vibrating amplitude 75%and controls fluid forces.It reached non-dimensional cross-flow amplitude at higher velocity,Ur=9,and keep its vibrating frequency and vortex shedding frequency away from structural nature frequency.Within Ur?8 the vortex shedding modes remain P+S.6)When bumps distributed in CF direction and others asymmetrically located IL,4?8?12 bumps amplify the phase angle between lift force and transvers amplitude(110°?179°).Vortex shedding modes changed from P+S,appeared in initial or upper branch,and stay 2S mode in desynchronization range.Sensitivity in trajectory is diminished.(3)This article brings bump scale into vortex-induced vibration research.With riser L1?L5 and H1?H6 frequency changing within 14.30%,the alteration of bump length comes to better effect of suppression of amplitude and forces in CF direction.The CF and IL directional non-dimensional amplitude in forms of mean square root for riser L1?L5 reduces 93.13%?0.74%,separately.Drag coefficient reduces 4.84%.The effect of changing bump height is more prominent.The CF and IL directional non-dimensional amplitude in forms of mean square root for riser H1?H6 reduces 93.24%?16.68%separately.Drag coefficient reduces 16.81%.The results proved that,when bump length is 0.32D and bump height changes within 0.0132D?0.0287D,the vibrating and vortex shedding characteristics make very slim difference.The same effect falls on situations as bump heigh is 0.0625D and bump length shifts through 0.49D-0.73D,which helps to select scale parameters.(4)Under the reciprocal influence of angle between bump(60°?45°?30°)and flow attack angle(0°?90°),the main results follows:1)revised cylinder with angle between bump 60%shall efficiently avoid synchronization,delay VIV fatigue damage,and abate attack angle sensitivity to fluid forces.2)As angle between bump diminishes:1)cross-flow and in-line amplitude approaches but constantly beneath cylinder;2)types and frequency of vortex shedding modes transition keeps rising,leading to flipper transition of amplitude,which the same cylinder's vortex structure includes P+S and 2P time-change phenomenon;3)structure vibrating frequency in CF and IL directions attains more obvious sensitivity,along with more complex trajectory types;4)the difference between structure frequency and vortex shedding frequency advances,and phase angle reaches higher sensitivity of attack angle.This article presents suggestions to dig in research of phase angle problem.(5)Simulation result proved that,the optimized design of cylinder meets the requirement of high velocity sensitivity and various attack angle.1)Cylinder entered into synchronization vibration when it reached reduced higher velocity(Ur=14),avoiding fluctuating transver amplitude in lower velocity.Strouhal remain 0.21?0.24.2)Before lock-in,the velocity sensitivity to fluid forces stay low.Pase angle between lift-transverse amplitude got sharply reduced,shifting from 1800 to 1°.3)When reduced velocity reached 8,16,19,structure vibrating frequency in CF and IL direction overlapped,so along as fluid forces frequency.4)The vortex shedding experienced modes transition P+S?2S?P+S and so forth,with fluid force frequency ratio from CF to IL changed multiple times.5)Moreover,optimized design of cylinder keeps low sensitivity to attack angle,as proved by Chap6.