Color-VTR image analysis on catastrophic deformations of water waves

为研究破碎、过顶等灾难性波浪变形的流动机理，开发了高速彩色vtr图像空间相关分析技术。聚苯乙烯珠作为示踪剂用于流动可视化。反复试验和错误以确定图像分析中示踪剂混合、照明、视频记录和帧大小的最佳条件。像素级数据的统计意味着需要进一步改进可视化技术来获得具有广泛色调的图像。在本研究中，利用分级亮度数据的定量增加，即结合红、绿、蓝三种分量图像的三个相关系数，实现了高可靠性的流速检测。通过从流动连续性角度评价剩余误差，检验所得速度矢量场的准确性和可靠性。在实验盆地中再现了在固定斜坡上的孤立波倾覆，并提取了内部流速。通过对速度场的详细描述，可以推导出压力场和涡度场。因此，在波峰区域发现的极其温和的压力梯度可能在破裂现象中起重要作用。在波峰后侧水面以下观察到明显的涡度。建立了垂直防波堤模型，研究了漫顶孤立波中的流场。在防波堤的上前角附近出现了主要的剪切流，在那里检测到强烈的涡度。波峰下的过顶流速总体较高，最大流速出现在水面以下。

Technology of spatial correlation analysis of high-speed color-VTR imageries was developed for investigating flow mechanisms of catastrophic wave deformations such as breaking and overtopping. Polystirene beads were used as tracers for flow visualization. Trials and errors were repeated to determine the optimum conditions of tracer mixing, lighting, video recording, and frame sizes in image analysis.Statistics of pixelwise data implies that further improvement in visualization techniques are required to obtain imageries with widely ranged colortones. In this study, flow velocity detection with high reliability was realized by taking advantage of quantitative increase in graded brightness data, that is, by incorporating three correlation coeffcients for red, green, and blue component imageries. Accuracy and reliability of velocity vector fields thus obtained were examined through evaluation of residual error in terms of flow continuity.Solitary wave overturning over a fixed slope was reproduced in an experimental basin, and internal flow velocities were extracted. Thorough description of velocity fields allowed the deduction of pressure and vorticity fields. Extremely mild pressure gradient thus found in the wave crest region may play an essential role in the breaking phenomenon. Notable vorticity was observed below the water surface on the rear side of the crest.A vertical breakwater model was installed for investgation of the flow field in an overtopping solitary wave. A predominant shear-flow appeared near the upper-front corner of the breakwater, where strong vorticities were detected. The overtopping flow velocity is high in general under the wave crest, and its maximum appeared slightly below the surface.