Modelling of multi-bodies in close proximity under water waves—Fluid resonance in narrow gaps

Abstract

f = −μV, μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon of fluid resonance in narrow gaps between multi-bodies in close proximity under water waves. The numerical results are compared with experimental data available in the literature. The comparison demonstrates that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well. However the conventional potential flow model (without artificial damping term) significantly over-predicts the wave height in narrow gaps around the resonant frequency. In order to calibrate the appropriate damping coefficient used for the potential model and make it work as well as the viscous fluid model in predicting the resonant wave height in narrow gaps but with little computational efforts, the dependence of damping coefficient μ on the body geometric dimensions is examined considering the parameters of gap width B g , body draft D, body breadth ratio B r and body number n (n = 2, 3), where B r = B B /B A for the case of two bodies (Body A and Body B) with different breadths of B A and B B , respectively. It was confirmed that the damping coefficient used for the potential flow model is not sensitive to the geometric dimensions and spatial arrangement. It was found that μ ∈ [0.4, 0.5] may guarantee the variation of H g /H 0 with kh to be generally in good agreement with the experimental data and the results of viscous fluid model, where H g is the excited wave height in narrow gaps under various dimensionless incident wave frequencies kh, H 0 is the incident wave height, k = 2π/L is the wave number and h is the water depth. narrow gap, fluid resonance, water wave, viscous fluid model, potential flow model, finite element method, boundary element method

Effect of inlet configuration on wave resonance in the narrow gap of two fixed bodies in close proximity

“…18a). It is also consistent with the results reported by Lu et al (2011) for sharp corner bodies. The resonance frequency decreases with the increase of body draft.…”

“…This is in accordance with the results obtained by Lu et al (2011) for the sharp corner geometries. However, it can be seen that the level of this reduction increases for highly curved corners, i.e.…”

“…(10) and (11), it is clear that the resonant frequency decreases with the increase of the body draft. It has been reported previously (Lu et al, 2011) that the fluid resonance occurs at a higher frequency as the draft decreases, which means that the corresponding fluid resonance will be excited by the short waves and strong wave reflection might be expected. Therefore the available wave energy accounted for the fluid resonance in the narrow gap decrease and the nondimensional wave height decrease accordingly.…”

“…Chen (2005) and Bunnik et al (2009) introduced a damping lid method while Lu et al (2010a) investigated the effect of adding an artificial damping to the momentum equations. Computational Fluid Dynamics (CFD) methods have also been utilized to investigate the fluid resonance in the narrow gap induced by the incident waves (Lu et al, 2008(Lu et al, , 2010a(Lu et al, , b, 2011Sauder et al, 2010). The numerical results agreed well with those obtained from experiments, indicating that the viscous fluid model performed well in predicting the violent free surface oscillation at the fluid resonance.…”

Modeling of fluid resonance in-between two floating structures in close proximity

“…It has been noted by other researchers that this problem is closely related to resonant phenomenon of the moonpool, which was comprehensively investigated by Molin (2001) and Molin et al (2002). Other works which pertain to this problem are those of Miao et al (2000), Zhu et al (2005;2008), Saitoh et al (2006), Iwata et al (2007), Wang and Wu (2008), and Lu et al (2011a;2011b).…”