Underwater explosion bubbles

Experimental results of underwater explosion tests using an emulsion explo-sivecomposed of ammonium nitrate and hydrazine nitrate showed 0.85 MJ kg for the shock wave energy and 2.0 MJ kg for the bubble energy. The shock wave energy of underwater explosions is increased by the addition of aluminum powder to the explosives. The aluminum powder reacts with H2O molecules in the bubble. Large amounts of Hj molecules and heat are produced by the oxidahon of the A1 with H2O according to ... 

The growth and collapse of cavitation bubbles is commonly described by considering irrotational expansion of a spherical cavity in an incompressible liquid of infinite extent, subject to the unsteady form of Bernoulli s equation (B3, P5). Effects of compressibility and bubble migration must also be considered for oscillating bubbles produced by underwater explosions (B3, C5). 

Fig 1 Pressure Waves and Bubble Phenomena of Underwater Explosions. 

Underwater Shock Wave and Bubble Energy Equivalent Weight Ratios for Underwater Explosives... 

Bubble Period Measurements(Used for Bubble Energy Measurements). See under Underwater Explosions... 

As stated previously, the gas formed by the underwater explosion first enters the small cavity previously occupied by the explosive, thus creating a gas bubble under a high degree of pressure. The water surrounding the bubble gives away, and the gas bubble expands. This causes the water mass to move radially at great velocity away from the point of explosion. This movement is known as the thrust . 

From the observations it becomes clear that the most effective underwater explosives are those which can produce a high-pressure gas bubble for the formation of the thrust. 

Result and Discussion of Underwater Test Using VP—50 Pipe The samples used were similar to those used in the in—sand test and shown in Fig. 5.49. The test was carried out in a test pond of Taketoyo Works of Nippon Oils Fats. The pond is 36m in diameter, with the deepest part being 10m in diameter and 8m deep. The explosion was set at a depth of 4m. When VP—50 pipe was used for the sample container, the measurement of shock wave strength and the frequency of expansion/contraction of the explosion bubble was made at lm and 3.5m distances. The shock wave was measured with a tall marine gauge. The recording of the shock wave... 

The unique properties of underwater explosions are due to the high velocity of sound in water meaning that the pressure-wave travels approximately four times faster in water than it does in air. Furthermore, due to the high density and low compressibility of water, the destructive energy (from the explosion) can be efficiently transferred over relatively large distances. The most important effects caused by an underwater explosion are the corresponding shock-wave and the gas bubble pulsations. 

A.P. Sukhotln, Disruption of a Solid Medium by an Explosion and B.D. Khristoforov, Parameters of a Shock Wave and Gas Bubble in an Underwater Explosion of Charges of PETN and Lead Azide of Different Density , ZhPrikl-Mekhan i TekhnFiziki 1961, No 4, pp 99—101 118—27 [Joint Intelligence Bureau, Division of Scientific Intelligence Transln No 791, British Ministry of Defense (1962)] 75) M.E. Sereb-... 

In order to report the energetics of these tests in a format better suited for comparison against underwater explosions, the PAV work of the Reynolds Industries RP-1 detonator was used as a standard on an equal volume basis. This comparison, the relative potential bubble energy (RPBE), can be written in the form 5... 

The combustion of metals in water is of practical importance in underwater propulsion [1, 2], hydrogen gas generation [3, 4] underwater explosives with increased shock and bubble energy [5, 6]. The influence of Al/O stoichiometric ratio on both shock and bubble energy of an explosive is shown in Figure 14.1 taken from Ref. [6] and other applications [7]. 

Figure 10.25a presents a typical pressure record for the underwater explosion of a gas mixture 2H2 + O2 in overpressure- time coordinates at an initial pressure Pq = 0.13 MPa. The pulsation period of the blast products bubble between the first two... 

Mixtures of TNT, RDX, and/or AN are used as TNT-based explosives. Various additives such as aluminum powder, barium nitrate, and/or some other small amounts of materials are used. Densities are in the range 1450-1810 kg m"l Aluminum powder is added to obtain bubble energy when used in underwater conditions. 

A modification of the above underwater method studied by Cook (p 37) is the measurement of the spall-dome velocity at the surface , caused by explosion at a fixed distance beneath the surface. The method (which is not described in Cook s book) is best applied by use of calibration curves employing as suitable standard a selected explosive. It has been claimed that the method is reproducible within 5 to 10% and gives data generally in fair accord with expectations from theoretical calculations, provided the depth and extent of the pond are sufficient to avoid shock reflections. In many cases, however, there was a necessity of taking into consideration the rate of evaporation of water at the gas bubble-water interface (Ref 17, p 37)... 

The volume of gas does not change in the first two reactions, i.e. 3 moles - 3 moles. Consequently, the increase in the output of heat from the oxidation of aluminium prolongs the presence of high pressures. This effect is utilized in explosive compositions for airblasts, lifting and heaving, or large underwater bubbles. However, there is a limit to the amount of aluminium that can be added to an explosive composition as shown in Table 5.18. 

In addition to measuring shock wave and bubble energies, underwater tests also can measure the shock wave impulse, another indicator of explosive strength. The shock wave impulse is derived by measuring the area under the pressure-time curve for a selected integration time interval at a known distance from the explosion... 

The pressure field parameters, impulse and time characteristics of waves and gas bubble pulsation occurring at an underwater gas explosion were measured in [45,46]. The underwater gas detonations were triggered in a half-closed vessel and a spherical shell. The pressure field of the last case is symmetrical and all-directional. The experimental data obtained for C3H8 + 5O2 and 2H2 + O2 mixtures were in good agreement with the theoretical results. 

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