Breaking Mechanism of Water Surface and Detailed Structure of Wave Breaking-Caused Air-Entrained Turbulence

本研究的目的是研制一种新型的超高速摄像机，以尽可能精确地测量破波起始、气泡在气-水界面的形成和溃灭过程，并通过实验和数值计算研究破波引起的湍流，主要结果如下：（1）新开发了具有线性电荷耦合器件（CCD）的1，000，000 fps的原位存储图像传感器（ISIS）和1，000，000 fps的超高速摄像机，000，000 fps高灵敏度相机在世界上首次成功制造。(2)本文对卡尔曼滤波和卡方法（KC法）进行了改进，使之能跟踪波浪破碎后的水质点运动。利用新的超高速摄像机（每秒100万帧）和改进的KC法，在世界上首次以很高的精度拍摄了气泡的形成和破裂过程。研究了粘度和表面张力对气泡形成和溃灭的影响。(3)表面张力波是在波的前表面形成并长大的。临界表面张力波的空气包裹效应使前水面破裂，气泡进入水体。(4)FFT方法和离散小波分析揭示了气泡形成后水压的高频分量迅速增加，声波是由气泡在水中的运动产生的。(5)声波压力的衰减与气泡形成点的距离成反比，其大小可以用球面波传播理论很好地估计。(6)DOLFIN方法是对CIP方法和SMAC方法的扩展，发展起来的一种新的计算固体-水-空气混合流的三维数值计算方法。

This research aims to develop a new ultra-high speed video-camera to measure the wave breaking inception and formation and collapsing of air bubbles at the air-water interface as accurately as possible and to investigate the breaking wave-caused turbulence by means of laboratory experiments and numerical calculation.Main results obtained are as follows :(1) An In-situ Storage Image Sensor (ISIS) of 1,000,000 fps with linear Charge Coupled Device (CCD) has been newly developed and an ultra-high speed video-camera of 1,000,000 fps with high sensitivity has been successfully manufactured for the fist time in the world.(2) Kalman filtering and Chi-square Method (KC Method) has been much improved to trace the water particle motion after wave breaking. Using the new ultra-high speed video-camera (l,000,000 fps) and the improved KC Method, air bubble formation and collapsing process are filmed with very high accuracy for the first time in the world. The effect of viscosity and surface tension to the air bubble formation and collapsing are investigated.(3) Surface tension waves are formed on the front surface of wave and are grown up. The front water surface is broken by the air-wrapping effect of the grown critical surface tension wave and air bubbles are introduced in the water body.(4) FFT method and discrete wavelet analyses have revealed that high frequency components of water pressure rapidly increase after formation of air bubbles and that the sound wave is generated by the motion of air bubbles in water.(5) The sound wave pressure decays inverse proportional to the distance from air bubble formation point and its magnitude is well estimated theoretically with the theory of spherical wave propagation.(6) 3-dimensional numerical computation method DOLFIN has been newly developed, by extending CIP and SMAC methods, to evaluate the solid-water-air combined flow.