Refinement Commands and Menu Paths

Use the following xREFINE commands and menu paths to select entities for refinement and to set re-finement controls. (The rere-finement controls are described in detail below.)

• To refine around a selected set of nodes, use one of the following methods:

Command(s):NREFINE

GUI: Main Menu> Preprocessor> Meshing> Modify Mesh> Refine At> Nodes

• To refine around a selected set of elements, use one of the following methods:

Command(s):EREFINE

GUI: Main Menu> Preprocessor> Meshing> Modify Mesh> Refine At> Elements Main Menu> Preprocessor> Meshing> Modify Mesh> Refine At> All

• To refine around a selected set of keypoints, use one of the following methods:

Command(s):KREFINE

GUI: Main Menu> Preprocessor> Meshing> Modify Mesh> Refine At> Keypoints

• To refine around a selected set of lines, use one of the following methods:

Command(s):LREFINE

GUI: Main Menu> Preprocessor> Meshing> Modify Mesh> Refine At> Lines

• To refine around a selected set of areas, use one of the following methods:

Command(s):AREFINE

GUI: Main Menu> Preprocessor> Meshing> Modify Mesh> Refine At> Areas

Figure 8.1: Examples of Local Mesh Refinement (p. 173) shows examples of mesh refinement around a node [NREFINE], element [EREFINE], keypoint [KREFINE], and line [LREFINE].

Figure 8.1: Examples of Local Mesh Refinement

Figure 8.2: Tetrahedral Mesh Refinement Around an Area (p. 173) illustrates the use of the AREFINE command to perform tetrahedral mesh refinement around an area.

Figure 8.2: Tetrahedral Mesh Refinement Around an Area

8.1.2.1. Specifying the Level of Refinement

Use the LEVEL argument to specify how much refinement is to be done. The value of LEVEL must be an integer from 1 to 5, where a value of 1 provides minimal refinement, and a value of 5 provides maximum refinement. When LEVEL = 1, the resulting element edges in the refined region are approx-imately 1/2 the original edge lengths; when LEVEL = 5, the resulting element edges are approxapprox-imately 1/9 the original edge lengths. The table below lists all of the possible settings of LEVEL, along with the approximate resulting edge length for each setting.

Approximate Edge Length

Values of LEVEL from 1 to 5 attempt to provide gradually decreasing element edge lengths. However, be aware that when RETAIN = ON, different values of LEVEL may provide the same refinement. (For more information, see the explanation of the RETAIN argument below.) Elements in the layer just outside of the refinement region (that is, beyond the specified DEPTH) may also be split in order to transition to the refinement elements.

Note

All values of LEVEL result in smaller elements in the refinement region. The local mesh re-finement process does not provide mesh coarsening.

8.1.2.2. Specifying the Depth of Refinement

By default, the mesh is refined one element outward from the chosen entities (except for element re-finement, which uses DEPTH = 0 as the default), and the elements are split one time (that is, the element edges are divided in half, since LEVEL = 1 by default).

8.1.2.3. Specifying Postprocessing for the Refinement Region: Smoothing and Cleanup

As part of the refinement process, you can specify the type of postprocessing ANSYS does after the original elements are split. You can choose smoothing and cleaning (the default), smoothing only, or neither one.

• If you want ANSYS to do smoothing and cleaning, set POST = CLEAN (or choose Cleanup & Smooth in the GUI).

• If you want ANSYS to do only smoothing, set POST = SMOOTH (or choose Smooth in the GUI).

• If you do not want ANSYS to do either type of postprocessing, set POST = OFF (or choose Off in the GUI).

Smoothing: By default, nodes in the refinement region are smoothed (that is, their locations are adjusted) to improve the element shapes. Node locations will be adjusted subject to the following constraints:

• Nodes on lines will move only on the line.

• Nodes within areas will remain on the surface.

• If the mesh has been detached from the solid model (MODMSH,DETACH or menu path Main Menu>

Preprocessor> Checking Ctrls> Model Checking), smoothing will not be done.

You can turn node smoothing off for all nodes by setting POST = OFF for the refinement command being used. (Doing so turns cleanup off as well.)

Cleanup: When cleanup is turned on (POST = CLEAN), the ANSYS program performs cleanup operations (in 2-D models) on all of the elements that are associated with any affected geometric entities. In 3-D models, ANSYS performs cleanup only on those elements that are in or directly adjacent to the refinement region. Cleanup operations improve the quality of the elements. If the mesh has been detached from the solid model, (MODMSH,DETACH or menu path Main Menu> Preprocessor> Checking Ctrls>

Model Checking), cleanup will not be done on area meshes, but it will be done on tetrahedral volume meshes.

When you are refining a quadrilateral mesh, cleanup operations attempt to eliminate triangles from the refinement transition region. If poorly-shaped quadrilateral elements remain after the cleanup operations have optimized element quality, ANSYS splits the elements into triangles. You can prevent this splitting of quadrilateral elements by setting RETAIN = ON (the default).Figure 8.3: All-Quadrilateral Mesh (p. 175) illustrates the cleanup of an all-quadrilateral mesh.

Note

You can turn cleanup off by setting POST = OFF or POST = SMOOTH for the refinement command being used.

Figure 8.3: All-Quadrilateral Mesh

8.1.2.4. Specifying Whether Quadrilateral Elements Should Be Retained

Note

The ANSYS program ignores the RETAIN argument when you are refining anything other than a quadrilateral mesh.

By default,RETAIN = ON, which means that the refinement process will not introduce triangular elements into an otherwise all-quadrilateral mesh. When RETAIN = OFF and POST = SMOOTH or OFF, the resulting refinement region may contain triangles in order to maintain transitioning. When RETAIN = OFF and POST = CLEAN, triangles are minimized; however, they may not be completely eliminated - a minimal number of triangles may remain in the transition region in order to provide good element quality.

Note

If an area is meshed with a mixture of quadrilateral and triangular elements, the quadrilateral elements will not be maintained in the refinement region even when RETAIN = ON.

Since quadrilateral meshes are much more constrained than triangular meshes, increasing or decreasing the value of the LEVEL argument may not provide the desired increase or decrease in the level of re-finement when RETAIN = ON. In addition, even when quadrilateral elements can be maintained, the quality of some of them may be poor, especially with a higher value of LEVEL. By setting RETAIN = OFF, however, some triangles may be introduced into the mesh. This may not be desirable, especially if you are using lower-order elements. You can keep these triangles out of the point of interest by doing one of the following:

• Refine with a larger DEPTH; that is, at a larger radius from the point of interest.

• Refine with POST = CLEAN. This setting for the POST argument minimizes the number of triangles as much as possible.

• Refine using another method (for example, use local mesh controls and remesh).