Abstract
This paper reports on experiments involving deep underwater explosion (UNDEX) that were conducted in a pressure container. The bubble pulsation behavior due to the deep UNDEX is recorded by a high-speed camera for equivalent depths up to 350 m. The bubble images show that although the shape of the explosive package affects the bubble shape at the initial moment, the bubble easily becomes spherical in shallow water which is 0.8m and 100m depth, but never becomes spherical during the whole first pulsation in deep water which is 200m, 300m and 350m in this paper. Solutions of the Rayleigh–Plesset equation fit well with the experimental data, and the value of the polytropic index γ of the gaseous detonation products changes from 1.25 to 1.3 as the depth is increased. Finally, empirical laws governing the pulsation of a deep-UNDEX bubble are established. The experimental pulsation period and that from the Rayleigh–Plesset equation agree with that obtained empirically, but the maximum radius is smaller than the empirical one. This phenomenon shows that the water depth not only creates a high hydrostatic pressure for the bubble but also changes the energy-release process of a deep UNDEX.
Highlights
The first studies of underwater explosion (UNDEX) were conducted to support naval combat.1 When an explosive is detonated in deep water, it generates an outward-propagating shock wave and high-pressure, high-temperature gaseous detonation products, the latter of which form an underwater bubble
The present paper reports on experiments conducted on deep UNDEX involving bubble pulsation behavior at depths up to 350 m
1) In the deepUNDEX experiments, the bubble pulsation motion is revealed by the high-speed camera for equivalent water depths up to 350m
Summary
The first studies of underwater explosion (UNDEX) were conducted to support naval combat. When an explosive is detonated in deep water, it generates an outward-propagating shock wave and high-pressure, high-temperature gaseous detonation products, the latter of which form an underwater bubble. The bubble expands quickly initially because of its high internal pressure and keeps expanding because of the inertia of the water until the internal pressure drops below the ambient pressure, whereupon the bubble begins to contract; in the same way, the bubble keeps contracting until the internal pressure exceeds the ambient pressure, whereupon the bubble has completed its first pulsation. Such bubble pulsations may take place dozens of times under suitable conditions, and if the bubble is near a rigid wall or shell they can even result in a high-speed water jet. The first theoretical work on bubble behavior was that published in 1917 by Rayleigh. Subsequently, Plesset derived an equation governing the dynamics of a spherical bubble in an infinite body of incompressible fluid, and through subsequent research that equation was improved to include factors such as surface tension and fluid viscosity. The governing equation is known as the Rayleigh–Plesset (RP) equation, and it has been used extensively to study of the behavior of various types of bubble
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