In this study, the pulsation process and load characteristics of spark-generated bubbles near a double-layer cylindrical structure with a circular hole in the outer layer were investigated experimentally under different dimensionless aperture sizes (β) and standoff distances (γ). The results show that γ strongly governs bubble morphology and jet evolution, and the observed pulsation process can be classified into five representative types within the tested range. As β increases, the cavity suction effect gradually weakens, the confinement on the internal bubble is reduced, and the downward jet is progressively suppressed, whereas the upward jet remains observable. Load analysis indicates that both β and γ significantly influence the shock-wave pressure and the bubble-collapse impulse, demonstrating that these two parameters jointly control the load evolution of the system. Compared with a corresponding single-layer perforated boundary, the double-layer perforated cylindrical structure shows a stronger inhibitory effect on jet development and can reduce the direct bubble-collapse load transmitted to the inner wall under relatively small opening sizes. However, sustained multi-stage loading may still pose a risk to internal sensitive equipment. These findings provide experimental support for the protection design of underwater structures and for the assessment of explosion-induced bubble effects in complex confined geometries. The conclusions are supported within the successfully completed experimental parameter range.
Ma et al. (Wed,) studied this question.