Study on the dynamic characteristics of underwater explosion bubbles in a finite domain

To investigate internal underwater explosion bubble dynamics, load transmission, and structural response in finite open and closed domains, a transparent cylindrical tank was used as an oil-tank-like structure. High-voltage spark discharge, high-speed imaging, and acceleration measurements were combined with a boundary element method. Results show that bubbles exhibit multi-cycle “expansion–collapse–re-expansion” behavior. As water depth increases from 100 to 200 mm, bubble radius first rises from 17.37 to 22.76 mm, then drops to 20.3 mm. Under open conditions, shallower depths promote bubble penetration through the free surface and water jet formation, prolonging pulsation; greater depths enhance bubble expansion and collapse, increasing structural impact. Under closed conditions, the upper gas layer provides additional pressure feedback, leading to larger maximum bubble expansion (e.g., from 20.50 to 24.32 mm at H = 175 mm) but faster decay in subsequent cycles and easier formation of mixed clouds. Closed boundaries enhance positive pressure peaks mainly at shallower depths, while at larger depths they tend to induce persistent intensified negative pressure and cavitation. Notably, the absolute negative-pressure peak in closed cases increases continuously with depth, from 0.003 (H = 100 mm) to 0.107 MPa (H = 200 mm). These findings offer guidance for designing confined liquid-containing structures.