feflow_user_manual_classic.pdf

Automatic zooming during the areal and grad ual

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Automatic zooming during the areal and grad- ual meshing process : Automatically zooms to the current supermesh element. The smallest super- element will be shown first. qêá~åÖäÉ The Triangle mesh generator, developed by J. R. Shewchuk, provides a fast triangulation algorithm for triangular meshes including a large number of add-ins. Several options are available to control the meshing process, which can be used individually or combined. Most important are the following options: The Quality Mesh ( q -switch) option constrains the minimum angle of the triangles. This angle can be directly prescribed. Furthermore, using the L -switch option the triangula- tion can be forced to be a Delaunay for all triangles, not just a constrained Delaunay. Commonly, the divide and conquer Delaunay meshing algorithm is pre- ferred. Alternatively, the i -switch option performs the incremental Delaunay meshing algorithm. dêáÇÄìáäÇÉê GridBuilder is an efficient meshing tool for com- plex superelement meshes including line and point add-ins. It has been developed by Rob McLaren at the University of Waterloo in Ontario, Canada. It is loosely based on the approach outlined by Sadek, 1980. (Sadek, E.A., A scheme for the automatic generation of Figure 4.2 Mesh generator options. qÜÉ qêá~åÖäÉ ãÉëÜ ÖÉåÉê~íçê ÉåÖáåÉ áë åçí éêçîáÇÉÇ ïáíÜ cbcilt> cçê ÇÉí~áäë ~Äçìí Üçï íç çÄí~áå íÜÉ qêá~åÖäÉ ãÉëÜ ÖÉåÉê~íçêI ëÉÉ íÜÉ ~äÉêí Äçñ çéÉåáåÖ ïÜÉå óçì íêó íç ìëÉ qêá~åÖäÉK
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PS ö rëÉêÛë j~åì~ä J m~êí f QK jÉëÜ dÉåÉê~íçê triangular finite elements. International Journal for Numerical Methods in Engineering, Vol. 15, 1813- 1822, 1980.) The GridBuilder source code is included in FEFLOW. Briefly, the steps GridBuilder follows are: • extend line-addins so that the domain is subdi- vided into a number of subregions which are defined by closed polygons • nodes, whose spacing satisfies user-specified cri- teria, are generated along the polygon edges • each subregion is filled with triangular elements • an automatic mesh relaxation scheme is applied to smooth the mesh The GridBuilder meshing option is activated by choosing it as the ‘Type of mesh generator’ from the Generator options menu dialogue box, shown here. A minimum of one superelement, which defines the outer boundary of the domain to be meshed must be present. The domain may optionally be further subdi- vided by defining more superelements. Line-addins Line-addins are an option that may be used with GridBuilder, but care must be exercised when consider- ing the order in which they are defined and in how they are terminated. This is because in step 1 above, we see that GridBuilder will automatically extend any line- addin as necessary. The figure below illustrates the var- ious possibilities that can arise. In this figure, an exist- ing superelement is defined with black lines and yellow nodes, and 3 line-addins are defined with red lines and black nodes. Potential line-addin extensions are shown
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