On hydrodynamic behavior of fluid resonance in moonpool and its suppression by using various convex appendages

Abstract

Fluid resonance in moonpool formed by two identical hulls undergoing heave oscillation is investigated by using a viscous fluid flow solver with RNG turbulent model based on OpenFOAM® package. By comparison of experimental and numerical results, it is confirmed the present numerical model can simulate the gap resonance problem in a high level accuracy. Numerical simulations suggest that the resonant amplitude in moonpool decreases dramatically when installing the convex appendages, which is the reason of significant variation of velocity flow field in the vicinity of moonpool. The single convex appendages at the bottom or near the free surface can generate smaller resonant amplitude than that at the middle of moonpool wall. The vortex bubbles from the convex appendages at the moonpool bottom create more energy dissipation than those for the convex appendages in the middle of moonpool and near the free surface. As for the multiple convex appendages, the variation of resonant amplitude with appendages types follows the suppressing characteristics of single convex appendages when heave amplitude is small. However, the additional appendages at the middle of moonpool wall shrink the region of vortex bubbles from the bottom appendages when the heave amplitude is large, leading to the increased resonant amplitude in moonpool. All of these phenomena indicate the complex effect of vortex shedding in the moonpool region on resonant behavior. Finally, the vertical force on each appendage in multiple types is always smaller than that on the appendage in single types, implying the multiple appendages types can reduce the fluid force on the appendage.