COMSOL 6.2 - Union

) to unite surface meshes in 3D. The operation introduces mesh edges if mesh elements intersect, thereby intersecting existing mesh elements. It also partitions geometric entities accordingly by, for example, introducing geometry edges where mesh faces intersect, as shown in Figure 8-111. If the surface meshes contain unmeshed domains, the domain information is updated to account for overlap domains.

Figure 8-111: Imported surface and edge meshes (left) that are united using the Union operation (right).


	This operation is available for 3D models only.

The operation often generates triangles of bad quality close to intersection edges. Use Free Triangular or Free Quad to remesh boundaries. See Remeshing Imported Meshes for more information.

The operation partitions existing faces in order to avoid self-intersecting faces. When this happens, an node is added with information about additional faces.

To add a (

) node, select entities to unite in the window, then choose one of the following:

•

Right-click in the window to open The Graphics Context Menu and select (

) from the menu.

•

Select (

) from the menu (

) on The Mesh Toolbar.

•

Right-click the node and select (

) from the menu.


	Note that uniting meshes can modify the number of geometric entities. Thus when you are adding this operation to a meshing sequence that is conforming with the component’s geometry, a new meshing sequence that is defining its own geometric model is automatically created, and the Union node is added to this new sequence. For more information, see The Mesh Node.

Enter the properties for (

) using the following sections:

Dimension

Define the geometric entities to intersect. From the list:

•

Choose (default) to unite all available entities.

•

Select to unite domains. Choose in the list to select the domains in the Graphics window, choose a named selection to refer to a previously defined selection, or choose to select all domains. Only unmeshed domains can be selected.

To remove domain elements while keeping the boundary mesh either

•

Clear the check box in the window of the node, or

•

Add a Delete Entities operation, add the domains to delete, and select the check box .

To later restore the domain mesh, add and build a Free Tetrahedral operation.

•

Select to unite boundaries. Choose in the list to select the boundaries in the Graphics window, choose a named selection to refer to a previously defined selection, or choose to select all boundaries.

•

Choose to unite isolated edges. Choose in the list to select the edge in the Graphics window, choose a named selection to refer to a previously defined selection, or choose to select all edges.

•

Select to specify a mixture of entities to unite.

Geometric Entity Selection

Click the

for the entity selections of interest to start adding entities. The selections support unmeshed domains, any boundary, isolated edges, and isolated points.

Cleanup

Intersection of boundary and edge elements can result in short mesh edges, relatively small elements, and elements of poor element quality. To improve the quality of the mesh, cleanup is done by snapping mesh vertices and collapsing short mesh edges. Lower the to decrease the amount of snapping performed.


	The Union operation can be used to clean up a mesh of very bad quality even if nothing needs to be united. It can, for example, be useful for a mesh imported from a Filter dataset.

Use the list to control the snapping distance when intersecting faces and for cleanup of the mesh. Choose to enter a value in the field. This value is relative to the length of the longest side of the mesh bounding box. Select (the default) to specify a value in the field. When the operation is built with either of the settings or , the values in the (for only) and fields are automatically updated to correspond to the actually used tolerance. The automatic tolerance is based both on the size of the bounding box and of the average size of mesh elements in the selection.

Use the setting to specify if the mesh vertices will be placed on the (default) or representation of intersection edges. See Figure 8-112.