Assessment of Secondary Collision Hazards Induced by Tsunami Bores Using a Coupled NWT–LS-DYNA Framework

Although tsunami-driven drifting debris poses a critical secondary hazard to coastal infrastructure, quantifying the resulting impact forces is challenging because of the limited post-event observations and a lack of full-scale experimental data. This paper presents a coupled numerical framework integrating a numerical wave tank (NWT) with LS-DYNA to estimate the debris-induced impact forces under tsunami-like inundation conditions. The NWT was used to simulate wave generation, propagation, overtopping, and the resulting nearshore hydrodynamics. In contrast, the arbitrary Lagrangian–Eulerian (ALE) formulation in LS-DYNA was used to resolve debris transport and collision dynamics. Validation against existing hydraulic experiments showed that the proposed framework captures the overall sequence of debris drift and collision reasonably well. Nevertheless, some discrepancies remain in the drift initiation and collision velocity because of the simplified representations of friction and contact. The results further suggest that local contact conditions during collision and the momentum characteristics of the inundation flow strongly influence the maximum impact force. The proposed framework provides conservative estimates of debris-induced impact forces because the numerical model tends to produce surface-to-surface collisions owing to suppressed rotational motion. Overall, the coupled NWT–LS-DYNA framework provides a rational and conservative basis for assessing debris-collision hazards and supporting the structural design of tsunami-prone coastal infrastructure.