| In this paper, the nonlinear scattering of non-breaking and breaking waves by a submerged horizontal thin-plate are studied experimentally and theoretically.The linear waves are examined by the eigenfunction expansion method based on potential theory. The analytical results show that the maximum reflection coefficients (minimum transmission coefficients) occur at about B/L1=0.5, where B is the length of plate, L1, is the wave length over the plate.The scattering of non-breaking and breaking waves is investigated experimentally as the horizontal plate located at three submergences. By the fifth-order data fitting and the FFT method, the amplitude and phase angle of each wave component are obtained, from which we can calculate the reflection and transmission coefficients. The first order analyses show that the maximum reflection coefficients (minimum transmission coefficients) occur at about B/L1=0.5 for a larger submergence (no n-breaking waves). However, in the case of smaller submergence (breaking waves), two local extreme reflection coefficients can be indentified atB/L1=0.6,B/L1=1.0 respectively.The second order analyses show that the maximum second-harmonic transmission coefficients of free waves also occur at about B/L1= 0.5 for non-breaking waves. The second-harmonic transmission coefficients of locked waves are smaller than that of the second-harmonic transmission free waves. The second-harmonic transmission coefficients of free waves reduce with the decrease of submergence for breaking waves. In this case, there is a discrepancy between the result of data fitting and FFT.The energy analyses show that more than 70%of the incoming energy flux can be transferred to reflection, first-harmonic and second-harmonic transmission waves in the case of non-breaking waves. In the case of spilling breaking waves, more than 15%of the incoming energy flux is dissipated. In the case of plunging and colliding breaking waves, more than 40% of the incoming energy flux is dissipated.
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