乱流モデルを用いた津波伝播の数値計算  [in Japanese] NUMERICAL STUDY OF TSUNAMI PROPAGATION USING A TURBULENCE MODEL  [in Japanese]

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Abstract

通常,津波の数値計算には浅水流方程式が用いられる.このため,津波に伴う流速場の鉛直方向の分布について議論することは出来ない.速度分布は底面せん断力と結びついており,精緻な地形変化予測のためにも,津波の下での底面境界層に関する検討が求められる.ここでは,東日本大震災津波を対象として,乱流モデルを用いた津波伝播の断面二次元計算を実施した.数値計算においては,通常の定常流抵抗則を用いた計算も行い,旧来の手法との比較も行った.その結果,流速分布の形状は定常開水路流れのものとは大きく異なっており,通常の波動境界層のそれに類似したものであった.そして底面せん断力の計算結果は,主に押し波時において境界層内の流速分布を加味した計算結果に比べ定常流抵抗則を用いた計算結果は小さい値を示した.

 The 2011 Great Earthquake and Tsunami has caused huge morphological changes along the coastal areas in the Tohoku region. One of the key parameters causing these dramatical damages is the tsunami bottom shear stress acting on the sea bottom. In general, the tsunami wave is a longwave and the steady flow resistance method have been practically used in many tsunami numerical models to estimate the bottom shear stress by mean of using the depth-averaged velocity and friction coefficient (Method 1). However, the actual tsunami waves are unsteady flow conditions, so the application of Method 1 may inappropriate. Therefore, the EFDC vertical turbulent model is applied to take into account the effect of complex boundary layer development under unsteady tsunami condition (Method 2). In this study, these both methods are applied to calculate the tsunami bottom shear stress and compare between them. The shape of vertical velocity distribution results from the Method 2 are similar to the wave friction method. And bottom shear stresses by Method 2 are overall larger compared to the Method 1 under tsunami wave impacts.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)

    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 74(2), I_163-I_168, 2018

    Japan Society of Civil Engineers

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