Sympathetic hydrostatic implosions and fluid-structure interaction of metallic cylinders in a semi-confined environment

This work develops an experimentally validated multi-faceted fluid–structure interaction (FSI) model using LS-DYNA to investigate sequential sympathetic implosion of metallic cylinders in semi-confined underwater environments. The numerical model was first validated using experiments in which sequentially arranged aluminum cylinders underwent hydrostatic collapse in a semi-confined chamber, with transient pressure sensors capturing key response metrics. Numerical simulations replicated the observed collapse sequence. They matched the dynamic pressure–time response in both magnitude and timing, reinforcing confidence in the accuracy and predictive capability of the FSI framework. Following this successful validation, a series of parametric studies was conducted by varying the secondary cylinder’s length-to-diameter (L/D) ratio to investigate its influence on sympathetic implosion dynamics, energy absorption, and pressure wave evolution. Results show that increasing the L/D ratio of the secondary cylinder from 4 to 6 leads to earlier sympathetic collapse, greater than 14 % increase in kinetic energy absorption, and strain energy surpassing that of the primary cylinder. Pressure recordings and FSI profiles reveal peak overpressures escalating by 10–15 %, fluid jet velocities doubling (from ∼65 to ∼130 m s -1 ), and more coherent pressure rebound patterns as slenderness increases. These findings reveal key relationships, including that higher L/D ratios accelerate energy transfer, amplify collapse intensity, and produce stronger, more focused pressure waves. Conversely, shorter cylinders exhibit delayed, impulsive collapse with reduced energy uptake. Overall, this work establishes a predictive framework for designing resilient clustered subsea systems by linking structural geometry, fluid–structure interaction, and shock dynamics to informed mitigation of cascading failure risks.