Abstract
The transitional flow regime of the bottom boundary layer under hypothetical shoaling tsunamis is investigated in the entire region from the tsunami source to the shallow sea area. In order to calculate the shoaling process of a tsunami, an analytical method based on Green’s law and the linear long wave theory are employed, and flow regime criteria for the wave boundary layer proposed by one of the authors are applied. It is found that the bottom boundary layer in a tsunami source area is located in the laminar regime. Subsequently, transition occurs to the smooth turbulence during the shoaling process, with a transition from the smooth to the rough turbulent region in the shallow area. For precise evaluation of bottom friction acting on the sea bed and the resulting energy dissipation beneath the tsunami, it is highly necessary to include such transitional behavior in sea bottom boundary layers.
Highlights
The nature of the flow pattern can be classified into laminar and turbulent regimes depending on the relevant Reynolds number
Since the frictional resistance on the wall surface and resulting energy dissipation are significantly dependent on the mode of flow motion, identification and understanding of the flow regime is of practical importance for various flow phenomena
Williams and Fuhrman [6] carried out numerical analysis of tsunami-like wave boundary layers using a transitional variant of the k-ω turbulence model
Summary
The nature of the flow pattern can be classified into laminar and turbulent regimes depending on the relevant Reynolds number. Williams and Fuhrman [6] carried out numerical analysis of tsunami-like wave boundary layers using a transitional variant of the k-ω turbulence model According to their numerical result, the critical Reynold numbers similar to Equations (1) and (2) are valid for the transition to turbulence in a tsunami boundary layer. With an increase in wave Reynolds number, another transition occurs in the wave boundary layer from a smooth to a rough turbulent regime. To recognize this type of transition under combined waves and current, both Myrhaug and Slaattelid [17] and Tanaka and Thu [18] applied Equations (4) and (5). Equations (4) and (5) or Equations (6) and (7) will be applied for recognition of transitional behavior in the present investigation on the tsunami boundary layer
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