Post on 26-Nov-2015
As with all of Rocscience software, RS3 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 RS3, 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).
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.
In keeping with Phase2, any geometry specified with an Excavation Boundary is considered an
excavation, whether it contains an excavated material or not. Different from Phase2, 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.
20 vertices Material Boundary
Stage Boundary
Excavation Boundary
Excavated
Region
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.
Offset
Grading Factor
External Grading Factor
The External Grading Factor controls the element sizes on the external boundary. A factor of 1 means
the default RS3 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.
Possible poor quality elements.
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
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 RS3 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.
By default, excavated regions and volumes in the 3D view are not selectable. To enable selection, right-
click 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.
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 . The
RS3 mesher will automatically remesh and regrade the model with the updated settings.