Drift Behavior and Impact Risk of Tsunami-Driven Large Waterborne Debris Using Coupled FSI Analysis

• Nondimensional momentum flux effectively predicts debris drift behavior • Container weight significantly affects drift velocity and drift distance • Revetment type influences debris motion and associated impact potential • Lightweight containers pose higher collision risk at the early drift stage • Maximum drift distance delineates the spatial extent of potential damage Tsunamis pose significant threats to coastal infrastructure, causing severe economic losses and secondary damage from drifting debris. This study investigates the drift behavior and impact risks of large waterborne debris generated by tsunami inundations through a coupled fluid–structure interaction analysis. A numerical framework integrating the numerical wave tank and LS-DYNA was developed and validated against physical experiments involving container drift and impact. The analysis systematically evaluated the effects of tsunami scale, container weight, revetment type, and initial detached distance on maximum drift velocity and drift distance. The results demonstrated that nondimensional momentum flux is a more reliable predictor of debris motion than relative inundation depth, showing strong correlations with drift velocity (R² > 0.97) and distance (R² > 0.96). Lightweight containers exhibited drag-dominated behavior, drifting faster and farther under smaller tsunami events, whereas heavier containers required larger waves for buoyancy but, once afloat, caused greater impact potential. Wave-absorbing revetments promoted stronger momentum transfer than vertical ones, intensifying debris motion. Maximum drift velocity was directly related to collision force, while maximum drift distance delineated the spatial extent of potential damage. These findings highlight tsunami-driven debris as a secondary hazard that should be explicitly considered in coastal design and disaster risk reduction.