| Co-Investigator(Kenkyū-buntansha) |
KATAYAMA Hiroyuki Yokohama National University, Graduate School of Engineering, Research Associate, 工学研究科, 助手 (50303079)
OKAYASU Akio Yokohama National University, Graduate School of Engineering, Associate Professor, 工学研究科, 助教授 (20213994)
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| Research Abstract |
The present study aims on numerical simulation of various processes of wave-mud interaction on mud shore profiles, i.e., two-dimensional profiles covered with cohesive materials, including determination of fixed bed elevation and thickness of mobile mud layer, surface erosion, wave height attenuation, mud mass transport and profile deformation.
The location of fixed bed is determined by comparing the vertical profiles of wave-induced shear stress, calculated by an analytical elastic model, and yield strength. Erosion rate is calculated by an empirical formula, expressed as a function of maximum shear stress at bed surface and water content of mud.
Wave height transformation is computed from energy conservation equation, including the energy dissipation of the mud bed. Formulation of wave decay is also extended to the surf zone, combining both energy dissipation rates of mud bed and wave breaking. In this regard, the hydrodynamic model combines different effects of shoaling, wave attenuat
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ion and wave breaking.
The rheological constitutive equations of visco-elastic-plastic model (Shibayama et al., 1989) are selected for numerical modeling of wave-mud interaction and downward gravity-driven flow of mud layer. Multi-layered models are used to calculate mud mass transport velocities under the external forces, i.e., pressure gradients of the passing wave and gravity. Net transport rate is then determined by superimposition of the results. Finally, the deformation of the shore profile is determined from mass conservation equation, considering net mud mass transport and surface erosion.
A series of wave flume experiments have been performed to obtain the required data on sloping bed, such as wave height distribtution, mud mass transport velocity, and profile change of muddy bed. Although the offshore and onshore boundaries of the limited mud section are effective on the measured parameters, comparison of the numerical results and laboratory data reveals that the model is able to predict the observed phenomena. The numerical results are also compared with the laboratory data of Nakano (1994). The model well predicts the bottom deformation for all different combinations of wave height and water content of mud. Less
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