缓坡沙坝海岸波生沿岸流不稳定性特征

Longshore current instability on barred beaches

为研究沙坝对沿岸流不稳定运动特征的影响,本文开展了缓坡沙坝海岸沿岸流不稳定运动特征实验和理论分析,通过对流速时间历程的谱特征和示踪图像2方面进行研究,并讨论沙坝对沿岸流不稳定运动的影响。结果表明:1∶100坡度缓坡沙坝海岸的沿岸流存在明显的周期摆动,波动周期为100 s~150 s,且规则波的波动周期略大于不规则波情况。沙坝对沿岸流不稳定运动的影响,是通过对沿岸流速度剖面的改变来实现的,沙坝控制着沿岸流速度剖面峰值位置,从而控制沿岸流不稳定增长率和运动周期,这使得沙坝海岸与斜坡海岸沿岸流不稳定运动波动周期存在差异。

The study of the characteristics of the longshore current instability in gentle barred beaches can aid in the comprehensive and in-depth study of coastal sediment transport and beach evolution.To examine the influence of sandbar on longshore current instability,we conducted an experimental and theoretical analysis on the characteristics of longshore current instability in a gentle-slope barred beach.The spectral characteristics of the time series of the longshore current and tracing image were examined,and the influence of sandbar on the longshore current instability was discussed.The results show that the longshore current on the barred beach for a slope of 1∶100 has an obvious periodic oscillation,the fluctuation period of which is 100 s~150 s.The fluctuation period of regular waves is slightly larger than that of irregular waves.The influence of sandbar on the longshore current instability is realized by changing the velocity profile of the longshore current.The sandbar controls the peak position of the velocity profile of the longshore current.Thus,it also controls the growth rate of the longshore current instability and fluctuation period of the longshore current.As a result,the fluctuation period of the unstable movement of the longshore current becomes different from that of the plane beach.