Three-dimensional numerical simulation of vortex-induced vibration of a free spanning submarine cable in uniform currents

Abstract

The free spanning submarine cable, a slender and flexible structure with a certain sag, exhibits unique vortex-induced vibration (VIV) characteristics in currents compared to offshore risers and submarine pipelines. To study the VIV of the cable, a three-dimensional numerical model based on the finite difference method (FDM) and the finite element method (FEM) is established. The large eddy simulation method is employed to close the turbulent motion equations in the hydrodynamic model, while the beam element method is used to solve the structural motion equations in the structural dynamic model. An analytical mapping method is adopted for the reconstruction of the structure surface in the fixed Cartesian fluid grids, and the immersed boundary method is used to deal with boundary conditions at fluid-solid interfaces. Since simulating VIV of a submarine cable with sag requires extensive local grid refinement near the cable's surface, a partition parallel algorithm with multi-GPU nodes is developed to enhance the computational efficiency, where the parallel efficiency of a single GPU can reach 80-90%. The numerical model is validated by a laboratory experiment on the VIV of a submarine cable, where the transverse response amplitudes and frequencies obtained by numerical simulation agree well with the experimental results. The streamwise vibration responses that are not measured in the experiment are analyzed by the numerical simulation. It is found that when the cable's equilibrium profile is deflected in the streamwise direction by the drag force, the streamwise vibration with the same frequency as the transverse vibration occurs, and the streamwise vibration amplitude increases with sag. The detailed flow field information provided by numerical simulation indicates that the size of the vortex structures gradually increases with the velocity, and the shape of the vortex structure has a strong correlation with the transverse vibration mode of the cable.