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.