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2011 ANSYS, Inc. March 28, 20121 Release 14.0
14. 0 Release
Introduction to ANSYS
Mechanical Part 2
Lecture 5
Virtual Topology
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Chapter Overview
Virtual topology was introduced in the Mechanical Introduction Part 1 course.
In this chapter we extend the coverage of that topic:A. Virtual Topology
B. Defining Virtual Topology
C. Virtual Split Entities
D. Virtual Hard Vertices
E. Editing Virtual Topology
F. Meshing Implications
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A. Virtual Topology
Virtual topology is a feature that can aid you in reducing the number of elements
in the model, simplifying small features out of the model, and simplifying load
abstraction.
For meshing certain CAD models you may want to group faces and/or edges togetherallowing you to form virtual cells in order to reduce or improve the elements.
You can split a face to create two virtual faces, or split an edge to create two virtual
edges for improved meshing. A virtual cell in Mechanical modifies the topology of the local copy in Mechanical.
Your original CAD model remains unchanged.
Several examples follow to illustrate virtual topology . . .
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. . . Virtual Topology
This example shows 3 surfaces
selected and combined into avirtual cell.
Here 3 edges are selected to
form a virtual edge.
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. . . Virtual Topology
In this example one edge of this multibody
part has a size control assigned whichcauses irregularities in the overall mesh.
Shown in the upper right, 3 edges are
virtually split to accommodate improved
elements shapes.
Initial Mesh
Final Mesh
Virtual Split Edges
Size Control
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. . . Virtual Topology
Consider the example below:
Virtual
Cell
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B. Defining Virtual Topology
Virtual Topology branch is added below the Model
branch:
Individual virtual entities do not appear in the tree.
Instead, a statistics section in the details lists virtual
entities.
An automatic virtual topology function will attempt tocreate virtual cells based on the details settings.
Automatic Virtual Topology: Low, Medium, High: Indicates how aggressively
virtual topology will be searched for.
Edges Only: Searches for adjacent edges to be
combined.
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. . . Defining Virtual Topology
Virtual Cells can be created manually:
Select the entities (faces shown here) to be included in the virtual cell. Choose Merge Cells in the context menu (or RMB > Insert > Virtual Cell).
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C. Virtual Split EntitiesIn some instances it may be desirable to split a face to allow a specific meshing
operation.
With the Virtual Topology branch
highlighted, select 2 vertices as the desired
split point.
Choose Split Face at Vertices to complete
the operation. Vertex selection may be comprised of
existing vertices or virtual hard vertices
can be created (see following slides).
Note, selected vertices must both beassociated with the face to be split.
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. . . Virtual Split EntitiesVirtual split faces can be accomplished by creating virtual split edges (note the split
faces utilize the vertices generated when the edges are split).
Virtual Split Edge at +: splits at
the selection point along the
edge.
Virtual Split Edge: requires a
fractional entry indicating the
position along the edge where
the split will be located (e.g. 0.5results in the line split in half).
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D. Virtual Hard VerticesA Virtual Hard Vertex feature allows the creation of hard points which can be
used to split faces where no natural vertex exists.
With the Virtual Topology branch highlighted
select the face where the hard vertex is to be
located.
Note, a +sign will appear at the cursorlocation.
Choose Hard Vertex at + (or RMB > Insert
> Virtual Hard Vertex at +).
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E. Editing Virtual Topology
Virtual entities can be reviewed, edited or deleted
from the context toolbar (highlight Virtual Topology
branch):
Use the arrow keys to cycle through next/previous
virtual entities.
The virtual entity is highlighted graphically and the
status bar (bottom of graphics window) indicates thecurrent selection.
The Edit icon allows access to an editor window
where modifications to the virtual entity definitioncan be made.
Use Delete to remove unwanted virtual entities.
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F. Meshing ImplicationsKeep in mind that the topology can change!
Example: a chamfer is added to the top surface in this virtual cell. The interior lines are
not recognized anymore.
Mesh using virtual
topology
Original mesh
Elements edge is shown as a solid
line and the original chamfer and top
surface is shown as a dotted blue line.
The chamfer representation is no
longer present.