Number of Edges on Excavated Boundaries : What does it mean?

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1 As with all of Rocscience software, RS 3 is developed to be an easy-to-use, quick-to-learn 3D FEM software that takes care of tedious modeling tasks so the user may concentrate on simulating the geomechanical behavior of interest. In RS 3, a key feature is one-click meshing, where, if the user simply uses the suggested defaults, a quality graded tetrahedral mesh is automatically generated with just a click of a button. Number of Edges on Excavated Boundaries : What does it mean? In the Mesh Setup dialog, the user can easily select between a uniform or graded mesh and 4-noded or 10-noded elements. The third parameter labeled Number of Edges on Excavated Boundaries in the example above is a control for the density of elements near excavations. The larger the number, the denser the mesh is near the excavation(s).

2 This parameter is derived from the number of edges of any boundary that borders an excavation (as viewed in 2D). The default value is the sum of these edges over all slices and is a minimum or lower bound on the number of edges necessary for the current model. It is not possible to have fewer edges than the default value on the excavation(s) given the geometry. 20 vertices Material Boundary Stage Boundary Excavation Boundary Excavated Region In keeping with Phase 2, any geometry specified with an Excavation Boundary is considered an excavation, whether it contains an excavated material or not. Different from Phase 2, any excavated region is also considered an excavation, no matter if the bordering boundary is a material, stage, excavation or combination of these. An excavated region is any region that has excavated material in any stage. In graded meshes, mesh elements are always concentrated about the excavation(s). Using the mesh plane tool, the user can scroll through the mesh to visually inspect the distribution of elements. For models with excavations, the default behavior is to grade away from the excavation surfaces. In the Advanced settings in the Mesh Setup dialog, the three parameters Offset, Grading Factor and External Grading Factor control the gradation of element sizes in the mesh.

3 Offset Grading Factor External Grading Factor The Offset specifies a thickness about the excavated surfaces where the elements within this region are kept the same size. Grading will begin at the outer edge of this region. The offset is specified in terms of a number of element lengths, where, the element length is the edge length of the elements about the excavation (as viewed in 2D). The Grading Factor determines how quickly element sizes increase away from the offset. The larger the grading factor, the sparser the mesh. However, it is important to recognize that, depending on the geometry, large grading factors may also reduce the quality of the mesh elements. For models with irresolvable small features and/or constraint surfaces that create tight confined volumes, reducing the grading factor may improve the mesh.

4 Possible poor quality elements. The External Grading Factor controls the element sizes on the external boundary. A factor of 1 means the default RS 3 gradation behavior is used. A factor of 0.5 indicates the element sizes on the external boundary should be about half the sizes they were if the factor was 1. Similarly, a factor of 2.0 will try to double the element sizes on the external surface. It is important to note that changing this parameter affects the overall size of the mesh. For models without excavated regions (or mesh customization, discussed below), the third parameter in the Mesh Setup dialog will read Number of Edges on External Boundary. Analogously, this parameter controls the density of element faces on the external surface. Grading is performed from the external boundary into the volume.

5 For models that have regions that are excavated in all stages, the option Exclude boundaries of volumes that are always excavated. is available. Selecting this checkbox means that these regions are not treated as excavations and will not have elements concentrated about its boundary. This option may be useful for models where some of the excavated regions are not actually excavations and should not be treated as such. Always Excavated Always Excavated

6 After a graded mesh is generated, the user can customize the density of elements about a particular volume, surface, edge or point using the Customize Mesh tool. The RS 3 mesher will concentrate elements and grade about the customized volume, surface, edge or point as it would for an excavated region. It is easy to customize the mesh. Simply identify which piece of geometry you would like to adjust the density of elements of, enter a value in Multiply Element Density by field, select the appropriate Selection Mode, select the piece of geometry, and press Apply.

7 By default, excavated regions and volumes in the 3D view are not selectable. To enable selection, rightclick outside the model in the 3D view and select 3D Options > Draw Excavated Regions. You will see the excavated surfaces drawn. Now you can select the excavated surfaces and volumes.

8 Similarly, sometimes it can be difficult to select the extruded surfaces especially in cases where there is a lot of geometry. Deselecting Slice Faces in the Visibility Tree can make this selection in 3D view simple. Also, Show only excavated volumes in the Visibility Tree is helpful in isolating the excavation surfaces in the 3D view. Combined with Draw Excavated Regions, the user can easily inspect the surface mesh of excavations. All geometry where customization has been applied will have blue + symbols indicating that the element density as been modified from the initial mesh. Removing some or all of the mesh customization is just as easy. To remove some of the customization, in the Customize Mesh dialog, select Remove Customization from the drop-down menu, select the appropriate Selection Mode, select the piece of geometry, and press Apply. To remove all customization, simply select Remove All Mesh Customization from the Customize Mesh dialog or toolbar RS 3 mesher will automatically remesh and regrade the model with the updated settings.. The