不規則波通過梯形系列潛堤之布拉格共振數值研究

Abstract

本文應用二維非線性數值水槽模擬不規則波通過梯形系列潛堤所造成的布拉格共振現象。數值模式基於勢能理論，採用線性元素(linear element method)求解邊界積分公式(Boundary Integral Equation, BIE)，不規則波造波方式是採用線性波理論搭配JONSWAP波譜，在時間領域下給定造波邊界上的速度分佈。結果顯示，不規則波之布拉格反射率雖小於規則波，但其布拉格共振頻率範圍則較規則波者爲寬，對實際海域有較大的適用性，且布拉格反射強度隨相對堤高比、堤頂與堤基比、潛堤列數及堤腳坡度增加而遞增。 A 2-D fully nonlinear numerical wave tank (NWT) is developed to investigate the Bragg resonance scattered by submerged multi-array breakwaters for random waves. This model is based on a boundary integral equation method with linear element scheme. The incident random waves are generated by JONSWAP spectrum at one end of the wave tank. Results indicate that the reflection coefficient of random waves at the first peak of resonance is smaller than that of the regular waves, but the band width of frequency of Bragg effect has become wider and this advantage may compensate the peak reduction. Moreover, it shows that the Bragg reflection phenomenon will increase as the increase of the following parameters such as the relative bar height, the ratio of width between top and bottom of the bar, the number of bars, and the toe angle of submerged breakwaters.