水下针-板放电气泡脉动及冲击特性

为明确水中脉冲放电能量释放过程所产生气泡的脉动和压力波冲击特性，依据能量等效原则，在LS-DYNA软件中建立针-板电极结构的水下爆轰模型，模拟气泡形态。通过与获取的物理图像比对，发现气泡形态和时间演化尺度高度一致。在此基础上，对气泡的冲击特性进一步分析，结果表明:冲击波峰值、气泡脉动周期和半径大小随放电能量增加而加大，随静水压力的增加而减小；当放电电压由14 kV增至20 kV，二次压力波峰值由2.89 MPa升至4.09 MPa，提高41.5%；当静水压力由202.65 kPa增至506.63 kPa，二次压力波峰值从5.15 MPa升至6.36 MPa，提高23.5%，放电能量和水压的增加对二次压力波提升明显；随着距离增加，二次压力波所占冲击波的峰值压力比重，由12.6%增加至35.3%，远场放电位置二次压力波不可忽视。

Underwater needle-plate electrical bubble pulsation and impact characteristics

In order to clarify the bubble pulsation process and pressure wave shock characteristics produced in the process of pulse discharge energy release in water, based on the principle of energy equivalence, the liquid-phase pulse energy was transformed into an explosion source with the same energy, and the fluid-structure coupling model of underwater explosion with needle-plate electrode structure was established in LS-DYNA software to simulate the bubble pulsation process on the upper surface of steel substrate. By comparing with the experimental physical images obtained by high-speed photography, it was found that the numerical simulation was highly consistent with the experimental results in terms of bubble morphology and time evolution scales. On this basis, the impact characteristics of the bubbles was further analyzed, and the results show that the maximum impact pressure of the shock wave on the steel base can reach 94.9 MPa when the discharge is carried out with a 4-mm gap at a voltage of 20 kV and a capacitance of 0.8 μF. Besides, the bubble radius, expansion, jet velocity, pulsation period and peak shock wave pressure enhance with the increase of the discharge energy and decrease with the rise of the hydrostatic pressure. Among them, the increase of water pressure has little effect on the bubble expansion rate. The peak value of secondary pressure wave rises from 2.89 MPa to 4.09 MPa with the increase of voltage (14?20 kV), which reaches 41.5%; and up from 5.15 MPa to 6.36 MPa with the rise of hydrostatic pressure (202.65?506.63 kPa), which reaches 23.5%. And the enhancement of discharge energy and water pressure improves the secondary pressure wave significantly. Meanwhile, with the improvement of transmission distance, the proportion of secondary pressure wave in the peak pressure of shock wave rises from 12.6% to 35.3%, and the secondary pressure wave at the far-field discharge location cannot be ignored.