Results and analysis of a microsecond time scale underwater electrical wire explosion are presented. Experiments were carried out with a Cu wire exploded by a current pulse ⩽100kA with microsecond time duration. The analysis is based on shadow and spectrally resolved streak photography which were used to monitor the evolution of the discharge channel and the shock wave. The obtained data were used for hydrodynamic calculation of the generated water flow parameters, such as pressure and flow velocity distribution between the discharge channel and the shock wave. In particular, the pressure at the discharge channel boundary and the energy transferred to the water were estimated. The results of the calculation have been verified by comparing the measured and calculated trajectories of the shock wave. Based on the results of the calculation the energy transferred to the water was estimated. In addition, the analysis shows that the energy initially deposited in the discharge channel continues to produce mechanical work after the deposition of the electrical energy has ended.
A brief review of the results obtained in recent research of underwater electrical wire explosions using microsecond and nanosecond generators is presented. It was shown that the increase in the rate of energy input into the exploding wire allows one to increase the wire temperature and amplitude of shock waves (SWs). Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. In microsecond time scale wire explosion, a good agreement was attained between the wire resistance calculated using the equation of state (EOS) and that obtained experimentally. Conversely, in nanosecond time scale wire explosion, the wire resistance of EOS was modified in order to fit experimental data. Analysis of the emitted radiation showed that black body approximation cannot be used to characterize exploding wire radiation. It was found that 24% of the deposited energy is transferred into the water flow's mechanical energy. Also, it was shown that converging SWs formed by the explosion of cylindrical wire arrays can be used to achieve a pressure up to 250 kbar at the axis of implosion. Hydrodynamic simulations showed that with the use of relatively moderate pulsed power generators with stored energy of several hundred kilojoules, a pressure of several megabar can be achieved at the axis of implosion.
Investigation of underwater electrical wire explosions occurring in the time scale of few microseconds requires a measurement of pressure waves with nanosecond rise time and microsecond fall time. Various types of pressure gauges are used for this purpose, however, none of them seems to be suitable for the task since the frequency range of the pressure waves lies between 107 and 109 Hz, whereas all types of mechanical gauges have a bandwidth below 107 Hz. Therefore, a mathematical processing of measurements is required for reconstruction of the actual pressure wave forms. In this article, a signal processing algorithm, based on energy conservation requirements and Fourier analysis, for reconstruction of the wave form of the pressure wave generated under water by electrical explosion of wires is proposed. The gauge used in the experiments is a PCB 119A12 type pressure gauge with a bandwidth below 1 MHz produced by Piezo-Electronics, Inc. Pressure waves were produced by underwater electrical explosion of a thin wire made of Cu by a current pulse with an amplitude of 30–60 kA having a rise time of a 3 μs. It is shown that the error of the gauge in the measurement of the peak pressure is more than 100%, which leads to an error in the estimation of the energy of almost 300%.
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