Experimental study on the hydrodynamic characteristics of a Bragg breakwater with triple vertical plates

Abstract

Abstract The hydrodynamic characteristics of a Bragg breakwater with triple vertical plates in monochromatic regular waves are experimentally studied. The two spacings between the every two adjacent plates are denoted by S 1 and S 2 respectively which are both wide enough for the necessary of Bragg reflection, and S 2 is equal or unequal to S 1. A series of experiments are carried out in the wave flume equipped with a piston-type wave generator, and the hydrodynamic performance are analysed with the variation of the spacing S 2, the plate draft d 1 and freeboard d 2, the wavelength L and the wave steepness H/L (H is the wave height). Special attention is paid to the effects of nonuniform spacings on the hydrodynamic performance and the characteristics of Bragg reflection. In addition, the comparisons between the fixed and the unrestrained positioning are also presented. The results show that the transmission coefficients of the two unequal spacings mostly are smaller than the two equal spacings, and the intensity and bandwidth of Bragg reflection are increased by the non-uniform spacings. Under the unrestrained positioning, the movements have no serious effects on the wave attenuation performances of the breakwater. Moreover, the trough of transmission coefficient occurs at the left of the primary Bragg reflection condition due to both of Bragg resonance and wave energy dissipation not just Bragg resonance.