Experimental and numerical study on hydrodynamic characteristics of a bottom-hinged pitching flap breakwater under regular waves

A bottom-hinged flap breakwater is proposed for the wave attenuation and coastal protection. A series of laboratory experiments and a CFD numerical model were conducted to investigate the hydrodynamic characteristics in regular waves. The hydrodynamic coefficients, dimensionless maximum point pressure and average pitching amplitude of flap were examined with the parameters of incident waves and flap property. As the incident wave steepness increased, the wave reflection coefficient Kr, wave transmission coefficient Kt, dimensionless maximum point pressure pmax/pwgh, and average pitching amplitude of flap Oa increased for a given wave period; however, the wave dissipation coefficient Kd decreased. As the flap relative height increased, Kr and Oa increased for a given wave period; whereas, Kt decreased. Furthermore, as the flap density ratio increased, Kr, pmax/pwgh, and fitted Kd increased; however, Kt and Oa decreased. As the equivalent damping coefficient ratio increased, Kr and pmax/pwgh increased; however, Kt and Oa decreased. Additionally, a series of dimensionless parameters of incident waves and flap property were used to derive formulas for Kr, Kt and Kd, which were validated using the related data.