The split interactively function allows a boundary to be split based on the triangulation of the surface mesh region. Anywhere from one face to all the faces belonging to the boundary can be selected to belong to the new boundary. Only one boundary can be selected to be split at a time.
To split a boundary interactively, open the Regions node and then the region of interest. Right-click on the boundary name in the Boundaries node and then select Split Interactively... from the pop-up menu.
The Split Boundary Manually dialog will appear on the scene display:
The scene will also display the model with all boundaries other than the one selected set to be transparent. By default, the mouse can be used to select faces in the displayed boundary, with multiple selections possible by pressing the Ctrl key while selecting additional faces. Double clicking on the displayed boundary will select all continuous faces constrained by feature curves or sharp edges. To unselect entities, you can click on them again (while pressing the Ctrl key) or click anywhere off the model.
The Split Boundary Manually dialog provides access to five Selection Control buttons which can be used to further manipulate the face selections made by either growing from a face pre-selection or doing zone based selection/de-selections. These options are particularly useful when a large number of face selections need to be made which would otherwise be too time consuming to select individually. For more details on the buttons, refer to the selection control options for manual surface repair, which work in a similar way.
An example model with a part of a boundary selected is shown below:
When you have selected the face or faces of interest, enter in the new Boundary Name and then press the Create button to make a new boundary.
The new boundary name will appear in the simulation tree.
If you do not specify a new name then the original boundary name with a numerical increment will be used instead. The newly created boundary will be removed from the original displayed boundary.
The process can be repeated as many times as necessary for a given boundary and the Close button pressed when the operations are complete. If all faces for a given boundary are selected to become a new boundary then you will be left with an empty original boundary which should be then deleted.