Research On The Characteristics Of Four Columns Vortex-induced Motions Considering Multi-factors

With the development of petroleum production in worldwide, the Vortex-InducedMotion (VIM) problem of offshore platform’s columns has gained increasing concern. Thisthesis is concerned with the latest VIM research direction about the column, researchmethod and development are summarized and analyzed. Taking the four columns asstudying object, this research introduces the related theory, numerical simulation andexperimental methods about VIM. Four columns of VIM is simulated in uniform flow, theeffect of cross section, flow approaching angle and space ratio on VIM are investigated.This thesis mainly analyzes the amplitude response, frequency spectrum characteristics,trajectory and vortex shedding pattern. The main research work and conclusions are asfollows:1. A comprehensive review and analysis about the advance of VIM research at homeand abroad is performed. Correlation parameters of Fluid, structure and couplingmovement of fluid and structure involved in the study of VIM are systematicallyintroduced.2. Dynamic-mesh method is used to realize the movement of columns. A programwhich connects the FLUENT software with the analysis code for structural motioncharacteristic is developed, thus the interactive transfer of fluid and structuralinformation become reality, and the program is verified by simulating the VIM ofa single column.3. The vortex-induced motion characteristics of four square and circular columns arecomparably analyzed under different reduced velocities. The maximumstream-wise displacement of four circular columns is smaller than four squarecolumns’, but its maximum transverse displacement is three times lager than foursquare columns’. The lock in phenomenon has appeared in the circular columns’condition but not happen in the square columns case. Vortex shedding mode offour square columns show2P mode, but the vortex shedding mode of four circularcolumns show P+S mode at low reduced velocity. When the reduced velocity ishigh, vortex shedding mode become2S mode.4. Computational grid is built to simulate vortex induced motion of four squarecolumns from flow approaching angles of0degree,15degree,30degree and45 degree. The flow approaching angle has a great influence on VIM characteristics.Stream-wise and transverse amplitude of0degree flow approaching angle is theminimum among the flow approaching angle0degree,15degree,30degree and45degree. The maximum stream-wise amplitude is1.60D from15degree flowapproaching angle, and the maximum transverse amplitude is1.22D from30degree flow approaching angle. Due to the interference effect between the columns,the trajectory and vortex shedding pattern are messy.5. Computational grid is built to simulate vortex induced motion of four squarecolumns at space ratio of3.0,4.0and5.0. For the space ratio of3.0、4.0and5.0conditions, stream-wise and transverse amplitude increases to a certain valve withreduced velocity, and then oscillation around its value. The maximum stream-wiseamplitude is0.39D at the space ratio of5.0, and the maximum transverseamplitude is0.61D at the space ratio of3.0. The distance of equilibrium positionaway from the initial position and the main frequency of lift coefficient bothincreases with the reduced velocity.