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

本研究旨在研制一种新型超高速摄像机，通过实验室实验和数值计算，尽可能准确地测量气液界面上气泡的破碎起始和气泡的形成与破裂，并对破碎波引起的湍流进行研究。取得的主要成果如下：(1)研制了一种基于线阵电荷耦合器件的1000000fps现场存储图像传感器(ISIS)，并在国际上首次研制成功了1000000fps的高灵敏度超高速摄像机。(2)卡尔曼滤波和卡方方法(KC方法)已有很大的改进，用于跟踪破碎后的水颗粒运动。利用新型超高速摄像机(L，百万帧/秒)和改进的KC方法，在世界上首次以很高的精度拍摄了气泡的形成和崩塌过程。研究了粘度和表面张力对气泡形成和破裂的影响。(3)表面张力波在波的前表面形成并长大。(4)FFT方法和离散小波分析表明，在气泡形成后，水压力的高频分量迅速增加，声波是由水中气泡的运动产生的。(5)声波的衰减与气泡形成点的距离成反比，并用球面波传播理论很好地估计了声压的大小。(6)三维数值计算方法Dolfin，通过扩展CIP和SMAC方法，对固体-水-空气联合流动进行评价。

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.