Experimental study on the wave-induced fluid resonance and suppression scheme in the narrow gap of two floating rectangular structures

An experimental study on the wave-induced gap resonance and resonant suppression scheme for two floating rectangular structures (TFRSs) is systematically presented. The instantaneous velocity fields for the present problem are measured using an enhanced underwater particle image velocimetry measurement system. Detailed experimental results have been presented to study the influences of the wave and structural parameters on the gap resonant characteristics. The resonant wave height and wave frequency were sensitive to the variation of the gap width but not very sensitive to the variation of the surface roughness on the rounded corner of TFRSs. The nonlinear effects of harmonic components on resonant free surface elevation are estimated. To analyze the vortex structures, different vortex identification methods in literature are analyzed and their merits and demerits are summarized based on a comparative analysis of the measured velocity data. The Ω-criterion vortex identification approach is then selected to evaluate the vortex intensity and capture the main vortex cores. Thanks to the adopted technique, the subsequent separation of the two quasi-symmetric vortex structures is considered to be a significant contribution to energy dissipation. The vortex shedding and dissipation modes of different TFRSs are very similar and exhibit slight variations in resonant responses. A formula of the modified Reynolds number for the gap resonance problem of TFRSs is proposed. The non-dimensional vortex strengths are nonlinearly dependent on the newly modified Reynolds number and linearly dependent on the Keulegan–Carpenter (KC) number. Finally, an optimal suppression scheme for the gap resonance problem of TFRSs is suggested.