Simple hydroelastic impact models for water-borne debris

Debris driven by tsunamis pose a significant threat to structures, and yet most building codes that include debris impact are based on rigid-body dynamics. However, the debris will most likely not be rigid compared to the structural components, such as walls and columns, that they impact. Impact by flexible, water-borne wood poles and shipping containers is considered in this paper. A relatively simple one-dimensional model for acoustic wave propagation, for which an analytical solution is obtained, is shown to provide a good estimate for the initial impact force and duration. This model is validated with small-scale, in-air tests. The simple model is also validated with two-dimensional fluid–structure interaction using a finite element code. The acoustic model works well for initial impact as long as the debris rebounds from the impact target. When the water prevents separation, then the acoustic model significantly overestimates the asymptotic force. The effect of the gravitational waves resulting from impact is to retard re-impacts, as compared to the acoustic model.