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Necessity of Using a Wave Friction Factor in Tsunami Numerical Simulation

Author(s): Hitoshi Tanaka; Nguyen Xuan Tinh

Linked Author(s): Hitoshi Tanaka

Keywords: Tsunami; Bottom boundary layer; Bottom shear stress; Current friction factor; Wave friction factor; Numerical simulation

Abstract: In most of the existing tsunam i numerical models, a steady flow friction factor such as Manning’s n or DarcyWeisbach's f has commonly been applied for accessing the tsunam i-induced bottom shear stress. However, it has theoretically been proved by the authors that a wave friction law is valid, rather than a steady flow friction law in almost the entire computational domain from tsunam i source to shallow area (Tinh and Tanaka, 2019). In this study, a k-ω model is used to calculate velocity profile, turbulent kinetic energy and resultant sea bottom shear stress under shoaling hypothetical tsunam i propagating over a uniform ly sloping bathymetry. Numerical solution is obtained by applying a finite difference method with finer grid spacing in the vicinity of the bottom to achieve accurate numerical analysis. It is found that the behavior of tsunam i-induced bottom boundary layer has an unsteady characteristic and acting sim ilar to that induced by wind-generated waves even under a long period tsunam i. Therefore, the conventional steady flow friction law gives underestimated value for tsunam iinduced bottom shear stress. In addition, a calculation method of tsunam i-induced bottom shear stress using a wave friction factor is proposed.


Year: 2020

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