不规则波浪在陡坡上非线性传播变形的试验研究

Laboratory study of nonlinear transformation of irregular waves over a steep slope

通过试验研究了不规则波浪在一陡坡(1:10)上的传播过程中的非线性特征。为达到研究目的,在试验水槽中以JONSWAP谱为靶谱生成了两组随机波浪。试验结果显示,在坡前常水深区域和坡顶,两种波况下波高分布均符合瑞利分布;但是在变浅区域两种波况的波高分布却不尽相同。应用基于小波变换的二阶相位谱来分析波浪在传播过程中的非线性相位耦合特征,结果表明:随着水深的变浅,波浪的非线性逐渐增强并且参与非线性相互耦合的频率成份也越来越多。通过二阶相位谱发现:随着水深的减小,参与最强的非线性相位耦合频率向高频处移动。另外通过傅立叶频谱、二阶谱以及二阶频谱共同分析陡坡上两组波况下低频波浪的演化情况。

This paper considers the nonlinear transformation of irregular waves propagating over a steep slope（1：10）.Two experimental cases of random waves mechanically generated by JONSWAP spectra are used for this purpose.The results indicate that the wave heights in two cases obey the Rayleigh distribution both at the offshore location and on top of the slope,but,in the shoaling region,they behave different characteristic.The nonlinear phase coupling occurred within the irregular waves is investigated by the wavelet-based bicoherence.The bicoherence spectra reflect that,in the shoaling region,with the decrease of water depth,the number of frequency modes participated in the phase coupling increase,and the degree of the phase coupling enhances.In addition,the summed bicoherence shows that the frequency mode related to the local strongest nonlinear interactions shifts to higher harmonics with the decrease of water depth.This paper also investigates how the low frequency energy increases by the Fourier spectra,bicoherence spectra and summed bicoherence.