Full-scale CFD simulation of tsunamis. Part 1: Model validation and run-up

This paper presents numerical simulations of the propagation, shoaling and run-up of full-scale tsunami waves. The simulations are performed with a model solving Reynolds-averaged Navier-Stokes equations with k-ω turbulence closure, and is one of very few studies involving CFD simulations at full tsunami scale, involving full resolution of small scale dispersive effects as well as wave breaking. It is demonstrated that a combination of previous analytical and empirical expressions for run-up heights and inundation speeds match those simulated well. This indicates that these are reasonable first approximation even in cases where the underlying assumption of linearity of the incoming tsunami is violated, as well as in cases where breaking occurs, though they generally slightly underestimate both run-up height and inundation speed. It is shown that the run-up of tsunamis can manifest in different ways depending on the initial wave shape and slope of the coast, and three qualitative run-up types previously identified in the literature are described in detail. It is further shown that the shorter waves of an undular bore, which appear during lengthy propagation in shallow water, can either maintain their shape the entire distance to shore, or break far offshore creating a breaking bore. It is demonstrated the front of the breaking bore will not appear as steep for N-waves as single waves because these need to re-wet the drawn-down region before reaching the original shoreline. Finally, the importance of shorter waves riding on the front of the tsunami is discussed. It is shown that they have little impact on the run-up height and inundation speed, but are important in terms of local flow velocities. The results presented here are Part 1 of a larger study, where Part 2 involves details of the tsunami-induced boundary layer dynamics, bed shear stresses and implication for sediment transport.