A dimensionless metric for quantifying fluid–structure interaction in blast-loaded plates

In blast-loading scenarios, the interaction between the structural motion and the blast load (fluid–structure interaction, FSI) can dominate the response of lightweight or flexible structures. Prior studies have clarified key mechanisms and advanced semi-analytical models, but complex configurations still require numerical simulations. In practice, quantifying FSI typically relies on comparing results from two separate modelling strategies, which is often impractical. This work proposes a pragmatic procedure to obtain inexpensive estimates of FSI effects using uncoupled simulations only. The approach builds on one-dimensional theories that include non-linear gas compressibility and inertial effects, combined with saturation analysis, and it centres on a single nondimensional index. Two complementary options are provided: Option 1 uses the reflected gas state and plate properties; Option 2 identifies characteristic times from uncoupled structural simulations. The procedure yields dimensionless estimates of the reductions in peak midpoint velocity and deflection for clamped plates. Validation covers 28 cases representing a compressed-gas shock-tube configuration established in the literature, including steel and aluminium plates over multiple thicknesses and load levels. The estimates show good agreement with high-fidelity numerical benchmarks and are robust across cases. The proposed fast-running engineering method enables rapid, objective, and operator-independent assessment of FSI effects suitable for practical use, and it supports informed selection of the appropriate numerical strategy for subsequent detailed analyses.