Method of determining grid sizes of finite element method of water quality models for geometrically complex river course |
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Authors: | Yang Chunping Zhong Yuanyuan Zeng Guangming |
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Institution: | (1) Department of Environmental Engineering, Hunan University, 410082 Changsha, China |
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Abstract: | The method of determining grid sizes of finite element method of water quality models is presented on the basis of characteristics
of pollutant distributed in the just downstream grid of discharge. A given length of the grid is applied to calculate the
minimum distance for the pollutant to complete mixing in the lateral direction n the just downstream grid of the discharge,
and the minimum distance is regarded as the maximum width of the grid. Application of the maximum width of the grid and flow
rate per unit width of the river results in the number of flow zones in the lateral direction of the river. Consequently division
of grids and numerical calculation of water quality with finite clement method can be carried out on the basis of available
method and topographic map of the river course. Analysis of scnsitivity shows that the effect of the width of the river and
the effect of the length of the grids on the minimum number of flow zones in the lateral direction is relatively small, and
that the effect of the given lateral mixing degree of the pollutants on the minimum number of flow zones is acceptable, which
indicates that the method presented is relatively stable. The method can avoid thc blindness and randomness in determining
the number of flow zones, and can decrease the amount of computation under the condition that the accuracy requirement is
mct. The problem that determining the sizes of the grids must rely on empirical knowledge has bcen solved. |
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Keywords: | river water quality model finite element method numerical calculation grid |
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