<title>Pressure caused by underwater discharge near the surface of water</title>

Spark discharge in water generates a spherical shock wave and a bubble that contains water vapor, with each center at a gap between electrodes. The bubble repeats the movement of the expansion and contraction. An impulsive pressure wave also arises at each transition from the contraction to the expansion of the bubble. In case that a rigid wall exists near the bubble, the bubble moves toward it keeping the expansion and contraction and then a water jet is formed toward the wall. The jet exerts the impulsive pressure on the wall. In case that the bubble is near the surface of water, it moves as if a rigid wall existed just below it and then the downward water jet is also formed. We are interested in the relationship of the movement of the bubble to the effect of the pressure caused by the under-water discharge near the surface of water. We are also interested in whether there are some differences between the following two cases as to the effect of pressure; one case is that the bubble exists near the surface of water and its movement is affected by the surface, another case the movement of the bubble is not affected by the surface of water for the sake of enough large distance between the bubble and the surface. In this study, impulsive pressure waves caused by the under-water discharge in above two cases are observed by means of a transducer or their schlieren photographs are taken with an image converter camera, and observations are examined.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.