Numerical Study On Vortex-induced Vibration Of Fluid-conveying Pipeline Under External Current And Internal Flow

Due to the complex ocean current environment and the large aspect ratio,the vortex-induced vibration of the slender flexible ocean riser has become a key issue that needs to be resolved in the research of deepwater riser technology all over the world.Vortex-induced vibration is an extremely complex nonlinear fluid-structure coupling problem,and its internal mechanism has attracted extensive attention from academia and engineering fields.In this paper,the multi-physics software STAR-CCM+ is adopted.Based on the Navier-Stokes equations of the viscous flow field and the structural dynamics equations,the multi-modal response characteristics of the vortex-induced vibration about the slender pipeline model under high Reynolds number is revealed.The application of radial basis function interpolation technology enables the entire fluid-structure coupling numerical solution to meet the need of the large mesh deformation condition.First of all,a series of numerical simulations related to the model tests of the fiberglass-reinforced plastic pipe model and the bare brass pipe model respectively,are conducted to verify the effectiveness of the fluid-structure coupling numerical algorithm.Subsequently,the further numerical research and analysis on the vortex-induced vibration of the fiberglass-reinforced plastic pipe model are carried out:(1)First,the vortex-induced vibration characteristics of flexible pipe model under different shear velocities,such as multi-mode and spanwise waveforms,are numerically studied.The results show that: 1)The order of the vibration mode increases with the incoming flow velocity,and the coexistence of multiple modes is prominent.2)With the alternating appearance of standing waves and traveling waves,the phenomena such as modal transitions can be clearly observed along the pipe span,which is mainly due to the coupling effect of vortex-induced vibration and flow-induced vibration.3)Along the pipe span(from the low-velocity region to the high-velocity region),typical cylindrical vortex tubes,inclined twisted vortex tubes,and a large number of discrete small vortices appear in sequence.As the three-dimensional effect increases,inclined honeycomb vortices appear.(2)This paper further numerically studies the fluid-structure interaction characteristics of the vibration response of flexible pipe model under the coupling of uniform internal flow and shear external current.The following conclusions are obtained: 1)The whole structure response is a mixed mode of standing waves and traveling waves,which is characterized by the superposition and modulation of the dominant standing wave by the local traveling wave.2)When multiple modes start to compete in time and space,the dominant mode becomes indistinguishable.With the appearance of traveling waves,the dynamic response becomes very complicated.3)In the process of multi-mode coexistence and competition,there is a special phenomenon that vibration energy transfers in time and space.With the increase of the external current velocity,the multi-mode broadband vibration response gradually transforms into the coexistence of multi-mode and mono-mode.In addition,the internal vortex structure is generated and shed along the wall of pipe,finally spread across the entire cross section.