Strong shock waves can be generated by pulse discharge in water. Study of the pressure characteristics and attenuation law of these waves is highly significant to industrial production and national defense construction. In this research, the shock-wave pressures at several sites were measured by experiment under different conditions of hydrostatic pressure, discharge energy, and propagation distance. Moreover, the shock-wave pressure characteristics were analyzed by combining them with the discharge characteristics in water. An attenuation equation for a shock wave as a function of discharge energy, hydrostatic pressure, and propagation distance was fitted. The experimental results indicated that (1) an increase in hydrostatic pressure had an inhibiting effect on discharge breakdown; (2) the shock-wave peak pressure increased with increasing discharge voltage at 0.5 m from the electrode; it increased rapidly at first and then decreased slowly with increasing hydrostatic pressure; and (3) shock-wave attenuation slowed down with increasing breakdown energy and hydrostatic pressure during shock-wave transfer. These experimental results were discussed based on the mechanism described.

Engineering background of hydraulic fracturing is applied to improve the permeability of unconventional gas wells, such as coal seams and shale gas wells, by a pulsed discharge mechanism. We studied the general relations between water shock wave properties (the maximum pressure, wave velocity, and energy conversion efficiency), the discharge voltage, and hydrostatic pressure during high-voltage pulsed discharge experiments in pressurized liquid water. e following observations were made: (1) when the discharge voltage increased from 7 kV to 13 kV, the maximum pressure increased from 12.6 MPa (hydrostatic pressure P H � 12 MPa) to 40 MPa (P H � 6 MPa), wave velocity increased from 1418 m/s (P H � 12 MPa) to 1454 m/s (P H � 6 MPa), and energy conversion efficiency increased from 9% to 11%, and (2) when hydrostatic pressure increased from 0 MPa to 12 MPa, the maximum pressure and wave velocity augmented and then diminished slowly (the critical hydrostatic pressure occurs in the 3 to 6 MPa range), whereas the change of energy conversion efficiency was not obvious. eir properties are explained by the variation of electrical parameters during the pulsed discharge.

High voltage pulsed discharge in water (HVPD) is used throughout industry for fracturing both natural and man-made materials. Using HVPD, we modeled crack propagation of rocks under homenergic water shock waves (HWSW) with different characteristics and combination forms using a combination of experimental analysis and numerical simulation. The experimental results show that, under the same discharge energy (2 kJ), water shock waves (WSW) with different characteristics fractured the rock mass distinctly different. With a higher the peak pressure ( ) of WSW, more long cracks and microcracks were formed, creating a larger damage area. The numerical simulation results show that a single HWSWs impact with different characteristics will still only cause three long cracks to be well developed and almost no microcracks, when of HWSW was 3 MPa. With the increase of , the number of both long cracks and microcracks increased. This is consistent with the experimental results. When the peak pressure became greater than 15 MPa, crack propagation gradually became concentrated and the surrounding borehole wall became more severely broken. The rock model had optimal fracturing under the impact of the HWSW with a of 10 MPa. Also, the simulations showed that, under repeated-impacts of HWSWs with consistent characteristics, the fracturing characteristics were basically identical to those by a single-impact. While under the repeated-impact of HWSWs with variable characteristics, there was almost no relationship between the fracturing effect and the sequence of repeated-impacts. Finally, under a single-impact of HWSW with low and hydrostatic pressure ( ) acting within an initial crack (similar to hydraulic fracturing in a hydrocarbon well), the initial crack had excellent propagation with an increase in hydrostatic pressure. However, when of HWSW was too high, increasing had no effect on initial crack propagation.

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Bubble pulsation is known to occur as a result of high-voltage discharge in water. Due to advantages such as long duration and significant bubble pulsation production, this technique is widely used in industrial production. Bubble pulsation is directly reflected by the pulsation efficiency, which is mainly embodied in the transformation efficiency from the highvoltage discharge energy to the bubble expansion energy, as well as the residual rate of bubble pulsation energy. In this study, high-voltage discharge was used in water to form pulsating bubbles. The vertical displacement of water was restricted by the experimental equipment, so horizontal displacement was mainly generated. Therefore, any influence caused by the ascending motion of the bubbles could be effectively ignored. Consequently, the bubble pulsation process could be measured at stable hydraulic pressure. The pressure, bubble pulsation period and pulsation times generated by bubble expansion were measured in our experiments. The transient voltage and current were also measured. The relationship between bubble pulsation efficiency with discharge voltage and hydrostatic pressure was analyzed by combining the experimental results with results from simulations of bubble pulsation expansion.