Hydrodynamic difference of rectangular-box systems with and without narrow gaps

To analyze the hydrodynamic difference between marine structures with and without narrow gaps, a two-dimensional fully nonlinear time-domain numerical wave flume is developed to investigate the hydrodynamics around multiple rectangular-box structures close to one another in waves. In the numerical model, the incident waves are generated by inner-domain sources such that re-reflection at the input boundary can be avoided. The fully nonlinear kinematic and dynamic boundary conditions are satisfied for the instantaneous free surface, and artificial damping is used for the free surface in the gaps to model the viscous effect. The proposed model is first validated against the experimental data for an isolated box and twin- and triple-box systems with narrow gaps. Then extensive numerical experiments are performed to compare the wave heights and wave loads on rectangular boxes with and without narrow gaps. The first comparison is made between the hydrodynamics of each individual box of a multiple-box system and those of an isolated box. The numerical investigation shows that the wave loads on each box in a multiple-box system are greater than those on an isolated box near the resonant wave frequency. Next the hydrodynamics for a multiple-box system are compared with those for a single-monolithic-box system with a total length equal to that of the entire multiple-box system. It is found that the wave height on the weather side of a multiple-box system at resonance is smaller than that of a single-monolithic-box system, and it decreases as the number of gaps increases. The opposite trend is found for the wave height on the lee side.