Numerical modelling of floating debris impact on structures during extreme hydrodynamic events

Extreme hydrodynamic events, such as tsunamis, can transport debris of a very wide range of dimensions, from cohesive sediments to debris such as trees and cars. Large sized floating debris are particularly hazardous for two main reasons: (i) they can accumulate in narrow passages, such as the case of log jams at bridges, and obstruct the flow, creating potential for further flooding; (ii) they can impact directly on structures transferring significant energy to them, due to their mass and velocity, which can lead to damage and even failure. The transport and the interactions of this type of debris is studied experimentally, often in the context of tsunamis and flash floods. However, numerical studies on large floating debris impact on structures are rare. Therefore, the present study aims to address this gap by numerically modelling of the flow-debris-structure interactions. First, the experiments of Stolle et al. (2018) are simulated numerically. These experiments involve a single positively buoyant container impact a structure as a result of being transported by a dam-break flow. The numerical simulations are carried using the open source DualSPHysics model based on the Smoothed Particle Hydrodynamics method. First, the hydrodynamics results were validated with data from Stolle et al. (2018). Subsequently, DualSPHysics was coupled with the Multiphysics engine CHRONO to simulate the container and its impact on the structure. The dam break event described in Stolle et al. (2018), was generated by modelling the movement of a swing gate using the experimental time series, with the container and the structure positioned at 3.2 m and 7.03 m, respectively, downstream of the reservoir consistently with Stolle et al. (2018). The trajectory as well as the velocity of the centroid of the container were tracked throughout the simulation. The agreement between the model and the experiment results is quantitatively assessed and it is shown that the model is accurate in reproducing the floating container trajectory, impact velocity and, in turn, force. In a second stage, numerical simulations beyond the conditions tested by Stolle et al. (2018) are used to investigate the role of the flow velocity, impact angle and location.