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In most of the current conventional tsunami numerical models, the steady flow friction law has been widely used to access the tsunami-induced bottom shear stress. However, according to our previous theoretical investigation showed that in almost the entire model domain from the tsunami source to the nearshore area, the tsunami-induced bottom boundary layer behaves like a wave boundary layer, rather than a quasi-steady flow boundary layer. The present study aims to develop a numerical method for tsunami simulation that elaborates a wave friction factor by implementing a correction method proposed by authors' previous work into the conventional 1D shallow water equation. As a result, the new method provides similar results to the original Manning method regarding the water level and the tsunami-induced velocity. However, the bottom shear stress estimated by the new method is higher than that from the Manning method over the entire computational domain. The transition locations from the wave friction zone to the steady friction zone are found at the water depth around 5 m under the present computational condition. [ABSTRACT FROM AUTHOR]

This paper presents a detailed investigation on unsteady effects in bottom boundary layer beneath a tsunami. In numerical simulation of tsunami, bottom shear stress has commonly been evaluated by using steady flow friction laws such as Manning equation, simply assuming that long-period wave motion satisfies quasi-steady flow conditions. However, the present study found that the behavior of tsunami-induced bottom boundary layer has an unsteady characteristics and acts similar to that induced by wind-generated waves even under long-period wave motion. As a result, bottom shear stress under tsunami is much larger than the estimation using steady friction coefficient due to a steep velocity gradient in the bottom boundary layer. Surprisingly, the steady flow friction law is not valid in almost the entire computational domain, from the source area to shallow region. This result highly coincides with the field measurement data obtained by Lacy group during the 2010 Chilean Tsunami at the Monterey Bay mouth in U.S. A correction coefficient is proposed to take into account unsteady effects in the conventional estimation method using a steady friction factor; this approach is validated by comparing with numerical simulation results using k-ω turbulence model. [ABSTRACT FROM AUTHOR]

An experimental study is carried out to investigate the transformation of oscillatory boundary layer from ordinary to depth-limited one by using an oscillating tunnel with triangular roughness pasted on the top and bottom surfaces. The velocity is measured by one-component LDV. It is proved that only longer period of oscillation is not sufficient to induce depth-limited properties. Instead, the ratio of boundary layer thickness to the distance from the bottom to the free surface must be used in order to distinguish a depthlimited oscillatory boundary layer from an ordinary one. The experimental data for mean velocity, phase difference, fluctuating velocity, friction coefficient and boundary layer thickness are presented in order to elaborate the structure of depth-limited oscillatory boundary layers on a rough bottom. On the basis of the present experiments, a modification has been made in an existing criterion to distinguish between ordinary and depth-limited wave boundary layers. A typical field situation is discussed to show the usefulness of the proposed criterion. [ABSTRACT FROM AUTHOR]