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No. 46 (1993/09) >

Title :ステップ型リーフ先端部での反射境界条件および砕波限界
Title alternative :Reflective Boundary Condition and Breaking Criteria on the Top of Step-Type Reef
Authors :筒井, 茂明
座間味, 健
Authors alternative :Tsutsui, Shigeaki
Zamami, Ken
Issue Date :Sep-1993
Abstract :According to the computational results of wave height distribution near the step-type reef by adopting the mild-slope equation with the conservation law of energy flux across the bathymetric discontinuity, reflection and transmission coefficients give suitable values for long period waves, but the reflection coefficient is underestimated for moderately shorter period waves. The reason comes from the fact that wave reflection from vertical wall on the top of the reef is not counted in the calculation above, that is, the mild-slope equation is derived on the assumption of weak horizontal variation of water depth, but the submerged vertical wall is a sudden change in water depth and is not considered in the equation. If we intend to take account of the wave reflection accurately, the three dimensional finite element method and/or the boundary element method are available. However, it is hopeful to deal with the problem above in a two-dimensional one. Therefore, the present paper, firstly, offers an approximate reflective boundary condition on the top of the reef and the corresponding functional, for application to the finite element method based on the mild-slope equation. The boundary condition is verified by predicting wave height around a submerged breakwater. The most important property of the boundary condition is independence on the direction of incident waves, that is, whether waves incident from deeper to shallower regions or shallower to deeper ones. Secondly, the present paper discusses wave breaking. Wave breaking have been taken into consideration in calculation of wave field based on the mild-slope equation, but the dissipation coefficient after breaking is available only for sloping beach and then any formulae suitable for numerical simulation in reef coasts have not been presented. A breaking criterion and the dissipation coefficient on the step-type reef are proposed based on the results of hydraulic experiments.
Type Local :紀要論文
ISSN :0389-102X
Publisher :琉球大学工学部
URI :http://hdl.handle.net/20.500.12000/2213
Citation :琉球大学工学部紀要 no.46 p.63 -74
Appears in Collections:No. 46 (1993/09)

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