Numerical Simulation of Fluid Resonance in Narrow Gap of Two Bodies in Close Proximity

Abstract

The resonant behavior of the fluid trapped in the narrow gap between a floating LNG and an LNG carrier in a side-by-side offloading operation is investigated in this study employing a numerical wave flume. The wave flume is based on the finite volume solution of the Navier-Stokes equations to account for the viscous dissipation. The waveFoam toolbox, a modified version of the standard OpenFOAM multiphase flow solver interFoam developed by Jacobson et al (2011) has been used for the purpose of wave generation and relaxation inside the computational domain. This method has a quite high efficiency as it takes advantage of the potential flow theory for wave generation purpose and the viscous flow theory for inside the wave tank, respectively. The volume of fluid (VOF) method first introduced by Hirt and Nichols (1981) is used to capture the free surface oscillations at the air and water interface. Water waves are generated at a reasonable distance from the inlet boundary and two rectangular relaxation zones at the inlet and outlet boundaries of the domain have been implemented to suppress wave reflection at the outer boundaries as well as waves reflected internally in the computational domain. The influence of incident wave frequency on resonance wave height and frequency is examined. Numerical results of free surface evolution at different incident wave frequency seem to agree well with the experimental results of Saitoh et al (2006) and numerical results of Lu et al (2008). In order to justify the effect of bilge keels on flow separation at the bottom corner of the ship, four different corner configurations have been investigated and compared to the base sharp edged case. It is observed that the magnitude of the free surface elevation at the resonance frequency increases significantly by about 10 times the incoming wave height while the peak of resonant frequency curves shifts to higher frequencies in the higher curvature modes compared with the base case.