Energy transfer optimum in subaerial landslide impulse waves

Subaerial landslides can generate impulsive waves which, in turn, may cause significant damages to the facilities and people on the surrounding coasts. In spite of the numerous studies related to this complex phenomenon in the last decades, there is still a lot to understand, especially physically speaking.

The present work aims at better understanding the energy transformation process from the slide initial potential energy to the final wave train energy. In particular, we would like to emphasize the existence of an optimum energy rate of transformation and investigate the reason for this existence.

To do so, we rely on a Navier-Stokes two or three phases model (OpenFoam) and perform numerical experiments, fixing a few parameters (slope, density, rheology) and studying the effect of the others. The physics of the phenomenon is highly complex, involving liquid phases interaction, transient wave formation, nonlinear wave processes, dispersion, wave breaking, etc. Such a numerical model, despite its inherent uncertainty, is anyway able to provide a rich information, which may be later completed with experimental results. In particular, the model gives access to all the flow variables which allows to characterize in depth the energy processes. The free surface signal analysis is also valuable for wave celerity, and hence generation zone extent and dispersion analysis.

In terms of research strategy, in order to restrict the complexity and allow a better understanding of the phenomenon, the idea is to start with a very simple rheology, the inviscid case, and progressively increase the numbers of rheological parameters (i.e., viscous flows, Bingham and finally Herschell Bulkley).

During the conference, we will first illustrate the existence of an optimum in the rate of energy transformation for the inviscid slide by progressively increasing the slide volume. We will try to relate this optimum with the physical processes at stake (liquid mass interaction, wave breaking types, dispersion, etc.). Next, we will show the influence of the slide rheology in the process of energy transfer and in particular how the energy optimum varies with respect to the rheological parameters.