Three-dimensional (3D) semi-analytical solution of wave-induced fluid resonance in narrow gaps of caisson-type breakwaters

This study presents a 3D semi-analytical solution for wave-induced fluid resonance in narrow gaps of caisson type breakwaters. The energy dissipation near the breakwater is modelled by introducing a quadratic pressure loss condition on the gap entrance and exit. By introducing this treatment of nonlinear boundary, the pressure loss due to flow separation induced by the sudden contraction and expansion of a fluid domain can be accounted. The present semi-analytical solution is validated by previous analytical results. The dimensionless energy loss coefficient is calibrated with available experimental data and is found to be insensitive to the incident wave angle theta(0) (theta(0) <= pi/12) and wave frequency. The analytical predictions are in good agreement with experimental data. With calibrated coefficient, the effects of wave and geometrical parameters on hydrodynamic quantities are investigated. The results show that the gap resonance leads to large wave energy dissipation and wave force, and the wave resonant frequencies are insensitive with dimensionless gap width l/alpha ranging from 26.6 to 56.6. The abrupt changes of wave reflection and transmission coefficients at high wave frequency are mainly due to the occurrence of multiple reflection and transmission waves and the wave frequency at the occurrence of multiple waves is always larger than resonant wave frequency.