Abstract
The wave-induced fluid resonance between twin side-by-side rectangular barges coupled with the roll motion of the twin barges is investigated by both numerical simulation and physical model test. A 2D numerical wave flume, based on an open source computational fluid dynamics (CFD) package OpenFOAM, is applied for the numerical simulation. After numerical validations and convergent verifications, the characteristics of the fluid resonance in the gap between the twin rolling side-by-side barges are examined. The resonant frequency of the oscillating fluid in the gap between the twin rolling barges decreases compared with that between the twin fixed barges. Generally, the twin barges roll in the opposite directions, and their equilibrium positions lean oppositely with respect to the initial vertical direction. A physical model test is carried out for a further investigation, in which the twin barges are set oppositely leaning and fixed. From the present experimental results, a linear decrease of the resonant frequency with the increasing leaning angle is found. Combined with the numerical results, the deflection of the equilibrium positions of the twin barges is a relevant factor for the resonant frequency. Besides, the effects of the gap width and incident wave height on the fluid resonance coupled with roll motion are examined.
Highlights
Floating structures in proximity are often found in the ocean engineering, for example, the offloading of liquefied gas from a floating production storage and offloading (FPSO) to an oil tank or liquefied natural gas (LNG) ship
The results of the present model experiments agree well with those predicted by the potential model, and the resonant frequency has a linear relationship with the leaning angle while the resonant wave height does not
Based on the present numerical results, a model experiment is conducted for a further investigation of the resonant wave height and the resonant frequency in the narrow gap between twin oppositely leaning and fixed barges
Summary
Floating structures in proximity are often found in the ocean engineering, for example, the offloading of liquefied gas from a floating production storage and offloading (FPSO) to an oil tank or liquefied natural gas (LNG) ship. The large amplitude fluid resonance can be observed in the narrow gap formed by the closely spaced structures when the incident wave frequency is close to the natural frequency of the fluid confined by the gap. Miao et al (2001) studied the wave interaction of twin floating barges with a small gap between them theoretically. By further assuming that the floating structures are fixed, the wave-induced fluid resonance in the narrow gap has been extensively studied, including theoretical analyses, laboratory tests and numerical simulations. It proved that the resonance takes place around kLB = nπ (n=1, 2, 3, ..., ∞), where k is the incident wave number and LB is the length of the barge. Fluid resonance between two floating horizontal circle cylinders is investigated analytically (McIver, 2005), so is the fluid resonance between a floating horizontal circle cylinder and a vertical wall (McIver and Porter, 2016)
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