Simulation of energy transfers in waves generated by granular slides

Abstract

This paper presents a multi-fluid Navier-Stokes modelling of the waves generated by two granular slides (subaerial and submarine) which were previously studied experimentally and a pure synthetic submarine case used for results interpretation. In the numerical model, air and water are considered as Newtonian fluids. The slide is modelled as a Newtonian fluid whose viscosity is adjusted to fit the experimental results. Once the viscosity is adjusted, the first and the second waves are shown to be accurately reproduced by the model even though the computed slide is slower. For the subaerial case, the viscosity value found is shown to be consistent with the granular µ(I) rheological law. The second part of this work focuses on the energy transfers between a slide and its generated waves. Energy balance is computed in each phase. The wave energy is evaluated in the wave propagation zone. Energy dissipation, kinematic and potential energies are taken into account in the computation of energy transfer ratio allowing for a better understanding of the phenomena. In light of these results, the wave train generation process is discussed as well as the importance of the slide dynamics in the wave generation stage. The amount of energy transferred to wave is not constant with time and the transfer rate depends strongly on the definition of this rate as well as the case considered. For instance, in the subaerial case simulated, the energy transferred to surface waves is 30 % of the energy transferred to water at the time the transfer stops, but this conversion rate is only equal to 4 % of the overall available potential slide energy at the end of the process. For the two submarine cases simulated, the corresponding values, equal in both cases, are 2 % and 1 %, respectively. The simulation results also show that the slide energy is transferred to the water in a short period of time at the beginning whatever the case considered. This observation may be related to the initial nil slide velocity (subaerial case) and the relatively large slope values considered (both cases). Nevertheless, the results illustrate the importance of accurate simulation of the slide dynamics within the wave generation process.

Tsunamis Generated by Submerged Landslides: Numerical Analysis of the Near‐Field Wave Characteristics

“…3-D configurations (e.g., Abadie et al, 2010Abadie et al, , 2012Bellotti et al, 2008;Clous & Abadie, 2019;Grilli et al, 2017;Heidarzadeh et al, 2020;Heller et al, 2016;Kim et al, 2019;Liu et al, 2005;Løvholt et al, 2005;Lynett & Liu, 2005;Montagna et al, 2011;Ruffini et al, 2019;Shi et al, 2016Shi et al, , 2018Watts et al, 2003;Whittaker et al, 2017).…”

“…To date, the numerical reproduction of the landslide kinematics, although a simple geometry and a rigid and impermeable landslide is considered, is not an easy task. The physical phenomena governing both the triggering and the evolution mechanisms of a landslide (submerged or subaerial) are far from being included in most of the numerical hydrodynamics codes, although some remarkable progresses have recently been achieved (e.g., Clous & Abadie, 2019;Shi et al, 2016;Si et al, 2018).…”

La Palma landslide tsunami: calibrated wave source and assessment of impact on French territories

“…This type of work usually covers the most frequent sources, namely coseismic displacements and submarine landslides, but long-return period sources, like volcano tsunami sources, must also be investigated. Volcanic islands may indeed have the potential to generate tsunamis (see, for instance, the recent case of Anak Krakatau; Paris et al, 2020;Grilli et al, 2019), and even megatsunamis, through a flank collapse process (Tappin et al, 2019), are known to occur relatively regularly (Elsworth and Day, 1999). Footprints of such gigantic past events are large underwater landslide debris surrounding specific oceanic islands (Masson et al,3020 S. Abadie et al: La Palma landslide tsunami 2002) and marine conglomerates at high elevation on the flanks of other ones .…”

Review of the paper "An efficient two-layer landslide-tsunami numerical model: effects of momentum transfer validated with physical experiments of waves generated by granular landslides"

“…Printer-friendly version Discussion paper Minor Points: L20-42: please add some missing references (e.g. Lynett & Liu, 2005;Panizzo et al, 2005;Abadie et al, 2010;Løvholt et al, 2015;Clous & Abadie, 2019) L59: "wrong", please choose another word or rephrase the whole sentence.…”

“…-Point-0, L37-43 A more detailed discussion of more complex and time consuming numerical models (based on the RANS equations, e.g. Abadie et al, 2010;Clous & Abadie, 2019) is needed. This would help the Readers in comparing the approach proposed by the Authors with the ones available in the scientific literature (see also Point-1).…”