Abstract
In the present study, the effects of the draft ratio of the floating body on the fluid oscillation in the gap are investigated by using the viscous fluid model. Numerical simulations are implemented by coupling wave2Foam and OpenFOAM. The Volume of Fluid (VOF) model is used to capture the free surface waves. It is verified that the numerical results agree well with the experimental and other results. It is firstly found that, within the water depth range investigated in the present study, the depth of the wave tank has a significant effect on the numerical results. As the depth of the wave tank increases, the oscillation amplitude of the narrow-gap fluid largely decreases and the resonant frequency of the fluid oscillation in the narrow gap increases. The results also reveal that the draft ratio of floating bodies has a significant nonlinear influence on the resonant frequency and on the oscillation amplitude of the fluid in the narrow gap. With an increase in the draft of either the floating body on the wave side or the one on the back wave side, the resonant frequency decreases. The increase in the draft of the floating body on the wave side causes an increase in the reflection wave coefficient and leads to a drop in the fluid oscillation amplitude, and the increase in the draft of the floating body on the back wave side triggers a decrease in the reflection wave coefficient and results in an increase in the fluid oscillation amplitude. Meanwhile, the viscous dissipation induced by the fluid viscosity synchronously increases with the oscillation amplitude of the fluid in the increasing gap. Moreover, it is found that the draft ratio mainly affects the horizontal force of the floating body on the back wave side and that the highest calculated force increases with the draft ratio.
Highlights
With the shift of oil and gas exploitation to the deep sea, Floating Production Storage and Offloading (FPSO) and Floating Liquefied Natural Gas (FLNG) marine platforms are developing rapidly
This study presented an investigation of the effect of the draft ratio of floating bodies on the fluid oscillation in a narrow gap using the viscous fluid theory and Volume of Fluid (VOF) model
Numerical simulations were constructed by the Waves2Foam package based on the OpenFOAM solver
Summary
With the shift of oil and gas exploitation to the deep sea, Floating Production Storage and Offloading (FPSO) and Floating Liquefied Natural Gas (FLNG) marine platforms are developing rapidly. In 2001, Molin used a linear potential flow theory model to find a solution formula for the narrow gap resonance frequency of multi floating body systems. He found that there are two oscillation modes of fluids trapped between simple bodies: piston mode and longitudinal sloshing mode. Linear potential flow models tend to overestimate the fluid oscillation response amplitudes in the narrow gap resonance according to comparisons with the results of experimental tests. The influence of the draft ratio of floating bodies in a multi floating body system on the response amplitudes and resonance frequencies of narrow gap oscillation problems as well as viscous dissipation are discussed.
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