沿岸流不稳定性的实验研究及理论分析

Laboratory study and analysis of the instability of alongshore currents

在坡度为1∶40的平面斜坡上进行了单向不规则波的沿岸流不稳定运动实验,观测到了沿岸流的周期性波动(波动周期约为100 s)。利用最大熵方法和三角函数回归法求得这种波动的主频率以及幅值,分析了波动幅值在垂直岸线方向的变化,结果表明该变化与沿岸流变化类似,即在沿岸流最大值附近这种波动强度最大。为了分析波动的机理,利用线性沿岸流不稳定模型对模型实验结果进行了分析,求得了不稳定运动增长模式和波动周期,并与对应实测结果进行了比较,结果表明,计算结果与实测值符合,从而说明实验中观测到的这种周期性波动为沿岸流不稳定引起的剪切波。

Laboratory experiments on the instability of alongshore currents were performed on a plane beach with slope 1 ： 40. Low-frequency fluctuations of alongshore currents with the period of approximately 100 s were observed. The dominant frequency and amplitude of the oscillations of alongshore currents were determined using maximum entropy method and the regression method of trigonometric function, and the results showed that the variations of the amplitude of the alongshore current oscillations were similar to the variations of the mean alongshore currents in the cross-shore direction. The linear shear instability theory was used to analyze the mechanism of the oscillation, and the calculated results agreed with measurements. This confirms that the observed fluctuations of alongshore currents are due to the shear instability of alongshore currents.