Numerical simulation of ringing responses of a vertical cylinder

Abstract

The pitch ringing vibrations of a vertical cylinder were investigated using a three-dimensional numerical model. The volume of fluid (VOF) method was used to simulate the wave surface, and the shear stress transport (SST) k-ω turbulence model was adopted to simulate the turbulence effect. The influence of the grid resolution was analyzed to verify the employed scheme, and the numerical simulation accuracy was validated by the experimental results. The previously reported experimental wave series was reproduced, and the inline forces acting on a fixed cylinder were calculated. The added mass moment of inertia induced by the water and its influence on the pitch vibration frequency were studied, and the spring stiffness of a cylinder system submerged in still water was determined. Under the action of focused and regular waves, the vibrations of the vertical cylinder model with three natural frequencies were numerically simulated. The ringing vibrations for focused wave cases are close to free vibrations, and under the regular waves, the dominant vibrations in higher natural frequencies cases are close to forced harmonic oscillations. The presence of Secondary Load Cycle (SLC) is not a prerequisite for the occurrence of ringing vibrations.