海岸裂流的浮子示踪法实验测量

Experimental measurement of rip currents with video-tracked drifters

研究模型实验中采用浮子示踪法测量沙坝海岸裂流的方法,讨论了该方法的具体技术实现和测量结果的精度。实验中裂流由波浪在垂直岸线的直墙上的反射所形成的两列交叉的波浪生成。通过处理CCD图像的浮子轨迹得到了流场的详细速度分布,如旋涡分布等,显示了该方法优于流速仪定点测量的一些特点。与ADV流速仪测量结果的对比表明,由浮子轨迹得到的表层平均流速具有可靠的精度,特别是也可以应用于波浪破碎产生的裂流这样复杂流场的测量。

This paper describes the technique of using video-tracked drifters to measure rip currents on a sandbar beach and discusses feathers of the measured rip currents.Rip currents result from the two intersecting wave trains produced by the reflection of obliquely incident waves on a vertical wall which stands perpendicular to the coastal line.Processed drifter tracks from CCD images are used to estimate dense surface velocity field,providing a major advantage over measurement of fixed flow meters.Comparison to results by ADV flow meters shows that mean surface velocities from drifter tracks have good accuracy.This shows that this method is applicable for complicated flow field in coastal zone,such as vortices and rip currents forced by breaking waves.