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Bottom Boundary Layer Beneath Long Waves

Author(s): Hitoshi Tanaka

Linked Author(s): Hitoshi Tanaka

Keywords: Wave run up; Simulation; Boundary layer; Bed stress

Abstract: Long wave study is very important in coastal area. One of the phenomena in nature which fall in to this kind of wave is tsunami wave. The wave length of tsunami wave is usually very long as compared with the water depth, thus, it can be considered as long wave. Therefore, tsunami study is often conducted under this condition. One of the most common equations that can be used to study and simulate the long wave is shallow water equation (SWE). SWE equation is efficient in calculation with relatively good results. The momentum equation in SWE often refers to Manning method for bed stress calculation. This method assumes that the bed stress is proportional to the square of velocity. However, past studies and experiments have shown that boundary layer is important related to bed stress. Detail studies using turbulent model in the wave boundary layer have shown that bed stress is highly influenced by this layer. Nevertheless, the governing equation is more complex and therefore, a turbulent model covering from bed to surface, is considered to be time consuming and inefficient for practical application. This study objective is to develop a new method for long wave run up simulation which can improve the accuracy of existing SWE model by considering the simplicity of the model for practical application in coastal area. A combination of SWE and turbulent model is used. In order to achieve higher accuracy of the SWE, the bottom boundary layer is used to assess the bed stress. Thus, allowing a more accurate estimation of bed stress which increases the accuracy of long wave simulation using SWE. This method is more efficient than using the turbulent model in the whole domain from bed to surface.

DOI:

Year: 2010

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