| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 89 === The purpose of this paper is to incorporate MODFLOW (McDonald and Harbaugh, 1988) finite difference method (FDM) with the technique of a numerical method to generate boundary-fitted orthogonal grids. It is intended to build a new numerical model MODFLOW/T to simulate a three dimensional groundwater problem with irregular boundaries in the horizontal plane.
The new model MODFLOW/T is to convert the horizontal irregular- boundary domain onto a transformed rectangle with four straight boundaries to generate orthogonal grids. By applying FDM to this domain, this new model is employed to simulate a 3-D groundwater system. It is intended to overcome the limitations of FDM irregular domains. By skillfully reformulating the governing equation, the original structure of MODFLOW has not been changed; only minor modifications based on the curvilinear orthogonal grids are added so that applications of original MODFLOW remain unchanged on input format.
This paper first describes the procedures of finite difference method used in MODFLOW, including formulation of the governing equations and finite difference approximation. A technique of region mapping using boundary integral element method is then followed. Finally, the technique to generate boundary-fitted orthogonal grids is incorporated into MODFLOW to solve 3-D groundwater problems in a region with horizontal irregular boundaries. Results of the modified MODFLOW are verified in two benchmark problems. The results of this analysis show integration of the MODFLOW with boundary-fitted orthogonal grids not only saves time to generate meshes but also diminishes the errors induced by irregular boundaries. Thus, the modified MODFLOW/T is more applicable to irregular regions in simulating groundwater flow problems.
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