Long waves in a high-density, stratified fluid: Theoretical and numerical analyses of a suspended-flow tsunami
Year: 2026
Type: article
Abstract: High-density, suspended-flow tsunamis that entrain large amounts of sediment from the seabed, can trigger severe, cascading damage. However, the vertical distribution of fluid density in a transient tsunami is not well understood, so its influence on the tsunami dynamics is unclear. Here, we obtain insights into the basic properties of long surface waves in a density stratified, two-layer, inviscid fluid based on linear shallow-water wave theory, numerical solitary wave solutions of strongly nonlinear and strongly dispersive wave equations, and numerical simulations using smoothed-particle hydrodynamics. The linear analytical solution shows that, when the fluid beneath a shallow-water wave changes from one to two layers, the wave height may increase despite the increased depth-averaged density, and the flow velocity in the upper layer also increases. These changes are proportional to the density ratio between the upper and lower layers, and they are emphasized more in nonlinear wave fields; e.g., in solitary waves. Nevertheless, the relative phase velocity never exceeds that of the one-layer fluid, as in the linear analytical solution, regardless of the density stratification. The change in flow and phase velocities also play important roles in unsteady problems, accelerating the wave-breaking limit as the density ratio increases. Additionally, as the density ratio increases, both steady and unsteady long waves exhibit greater wave-height amplification upon collision with a vertical wall. These results indicate the importance of the density distribution in evaluating the effects of suspended-flow tsunamis.
Source: Coastal Engineering
Authors: Kei Yamashita, Takuya Toriyama, Nobuo Ishida
Institution: Nuclear Regulation Authority
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,250
OpenAlex ID: W7151249465