Fusing Boundaries

The fuse command can be used to combine a pair of boundaries from the same volume mesh region and replace them with interior faces.

The fuse boundaries action is not compatible with finite element solvers. Do not fuse boundaries that belong to regions that use finite element models, such as the Solid Stress, Finite Element Solid Energy, Viscous Flow, and Finite Element Magnetic Vector Potential models.

The fuse operation is illustrated schematically below.

For the fuse command to be successful, the boundaries must be coincident in space, but not necessarily composed of conformal discretizations. If the two boundaries are completely conformal or can be matched exactly via the interface computation, the selected boundaries will be deleted, and the matched faces will be added to the interior of the region. If the faces cannot be completely matched, any faces that do match will be added to the interior of the region while the remaining faces will be left in the original boundaries.

The advantage of removing boundaries by fusing is that there is no additional overhead involved in the calculation (as might be incurred at an interface).

To fuse boundaries, open the Regions node and the Boundaries node in the region of interest. Select the boundaries you want to fuse using a multiple selection technique and right-click on the selection. Select Fuse... from the pop-up menu.

This opens the Fuse Boundaries dialog.

The originally highlighted boundaries will be automatically selected in the dialog with a ticked checkbox. If you wish to match only conformal faces (faces which have vertices at the same coordinates), select the Fuse conformal faces only option. Otherwise, the full interface intersection computation is performed on the selected boundaries.

The boundaries must be geometrically adjacent and the Tolerance in the previous dialog is a measure of close the boundaries must be to be considered suitable candidates for fusing. The tolerance represents the amount that each vertex is allowed to move during the intersection process, and is the same as the Intersection tolerance specified on direct interfaces.

After entering the tolerance, click the OK button. This will begin the fusing process and display a progress bar at the bottom of the simulation window. Once the process is complete a message will be displayed in the Output window indicating the results of the fusing process.

Since an interface intersection is done when fusing boundaries (to convert the boundary faces into interior faces) you will see several messages about faces and vertices changing.

The simulation tree will be updated once the fuse is complete, and if all of the faces were matched with no remainders, neither of the boundaries that were selected will exist after fusing.

In some situations the Fuse... menu item is grayed even though you have selected more than one boundary.

There could be four reasons for this:

  • one or more of the boundaries are taking part in an interface;
  • one or more of the boundaries were created by an interface;
  • the selected boundaries belong to more than one region; or
  • you don’t have a volume mesh representation currently displayed