GB1168947A - Method of and Apparatus for Reducing the Bubble Pulse from Underwater Explosions and Pressure Impulses - Google Patents

Abstract

1,168,947. Seismic exploration charges. BOLT BERANEK & NEWMAN Inc. 22 March, 1968 [22 March, 1967], No. 14039/68. Heading F3A. [Also in Division H4] To eliminate secondary pulses due to the bubble generated by actuating a seismic source in a liquid, collapse of the bubble is prevented by introducing within the bubble during its expansion gas at a rate insufficient to generate a shock wave and in a sufficient quantity to produce within the bubble at its maximum size a pressure substantially equal to the hydrostatic pressure outside the bubble. The source may be of the pneumatic, hydraulic, electromagnetic, spark, exploding wire or exploding gas type. In the Fig. 1 embodiment the source comprises a charge 4 of fast propellant or high explosive in a thin-walled plastic tube 3 which will not attenuate the primary pulse, and electrically detonatable initiating charge 1. A deflagrating slow charge 6 in plastic tube 5 is initiated with or after charge 4 and provides the gas to prevent bubble collapse. The weight ratio of charges 4 and 6 is selected according to charge composition and hydrostatic pressure. For use 35 feet underwater, charge 1 may be five grains of PETN, charges 4 and 6 may be respectively a smokeless pistol powder propellant and black powder in pellet form (in 1:1 weight ratio). Alternatively charges 4 and 6 may be TNT and smokeless powder in a 1: 2 weight ratio. In a second embodiment a volatilizable solid or liquid material (e.g. CCl 3 F) in a black polyethylene tube surrounds a number six detonator and transmits the detonator shock wave substantially unattenuated. The tube ensures heat transfer from the detonation to volatilize the material and so provide gas to prevent bubble collapse. In a third embodiment the primary shock wave is generated by a detonator and ruptures a pressurized condensible-gas cartridge (e.g. containing CO 2 ).