Hydrodynamics of transient gap resonance between a heaving box and a vertical wall excited by focused wave groups

In this article, a two-dimensional numerical model based on OpenFOAM® is developed to study transient gap resonance occurring in between a free-heaving box and a vertical wall suffered from focused wave groups with various wave amplitudes and spectral peak periods. The evolutions of free surface elevation within the gap, heave response of the box, and wave forces on the box under various incident wave parameters are systematically examined. Based on a four-phase combination technique, their first four order harmonic components are also extracted. Results show that compared to the case where the box is fixed, allowing heave motion of the box significantly shifts the spectral peak periods associated with the maximum values of the dimensionless amplitude-period curves for both the surface elevation within the gap and the wave loads to longer periods. The fixed-box system exhibits higher peak values for both the surface elevation within the gap and the vertical force compared to the heaving-box system. The influence of incident wave parameters on the first four order harmonic components displays distinct differences between the fixed and the heaving configurations. Additionally, the variations in reflection and energy dissipation coefficients with incident wave parameters are also analyzed and compared for both systems.