The imported geometry is shown in Figure 2.
Figure 1. CAD model of a household tap
This CAD model consists of different types of CAD entities. Namely, geometric faces on conical and planar surfaces and B-splines. Individual entity types may be separately displayed by using the Show by Type func-tion, found under the VIEW menu. Figure 3 shows this in use, displaying only the B-splines and planes in the CAD model.
A quick way of extracting basic information and determining the type of entities is via the Entity Inspector.
By holding down the shift key the Entity Inspector window appears for any entity under the mouse cursor.
Figure 4 shows this in use where the underside face of the spout of the tap model is inspected. Here, the Figure 2. Imported geometry
Figure 3. Show by Type tool displaying only B-spline and plane face types
Entity Inspector gives information about Face 47 of the model, which is a B-spline surface. The length of the nearest edge, Edge 40, is also given.
As with any geometry that is successfully imported, this model can be immediately surface meshed using the Surface Automeshing tool. Using a relative Maximum Edge Length of 8%, the mesh of Figure 5 is produced.
In this example, however, this mesh is invalid if used for analysis. By clicking the Show Plate Free Edges but-ton, a number of free edges are shown, as seen in Figure 5. Figure 6 shows a zoomed view. The free edges that can be seen in Figure 5 imply that parts of the model are near, but topologically separated from one another. These free edges were not the result of the automeshing operation, but due to the lack of compat-ibility between faces of the imported geometry. The meshing operation can be undone by clicking the Undo button, or clicking EDIT, Undo. The free edges of the imported geometry can then be found by clicking the Show Geometry Free Edges tool, as shown in Figure 7.
Figure 4. Use of Entity Inspector
Figure 5. Meshed geometry with free edges
Figure 6. Mesh incompatibility
The free edges of Figure 7 must be removed by the Clean Geometry tool (Figure 8) if a resultant meshing operation is to produce a fully compatible mesh. An attempt to clean all the free edges may be performed by the clean tool with the default settings. For this example, however, the setting for the Maximum Edge Length is based on the information that can be obtained from the model. The default settings are usually sufficient for most models where unintended free edges due to ‘cuts’ in the surface are small and where in-tended features are not proportionally very small in comparison to the overall size. However, this is not al-ways the case. It is possible to import geometry where gaps are of a dimension that is greater than that specified by the default Minimum Edge Length. This would then mean that such gaps would not be seamed.
It is also possible to import a geometry containing features with edge lengths smaller than that specified by the default minimum. In such a case, these intended features can become distorted or removed by the Clean Geometry tool. If you are uncertain as to whether the default Minimum Edge Length setting is correct, you should manually inspect the edge length of a small feature in the geometry. The minimum edge length of all faces of a geometry can be obtained from the Statistics page. Figure 9 shows the Statistics page results for the tap model.
Figure 7. Geometry free edges
Figure 8. Clean Geometry tool dialog
From the results offered in the Statistics page as shown in Figure 9, the shortest edge length was found to be very small. If all features in the model are to be retained, then the whole model can be safely cleaned using an absolute Minimum Edge Length that is less than the shortest edge length. However, this edge length may be that of a small unnecessary feature. If this is the case, the Entity Inspector can be used to manually find the edge length of the smallest intended feature to succeed the cleaning operation. Figure 10 shows the Entity Inspector being used to inspect the edge length of a small face at the end of the spout of the tap.
If the intention is to preserve the small face shown in Figure 10, then based on the information obtained in the Entity Inspector, the whole model is cleaned with an absolute Minimum Edge Length of 0.01. Upon com-pletion of the clean however, two free edges remain about the tap orifice. This means that the gap between the two free edges is greater than the edge length of the smallest intended feature. Hence, to direct the Clean Geometry tool to seam the remaining edges, a larger Minimum Edge Length is required, but with the cleaning operation limited to selected faces only. This can be done by the following steps:
Figure 9. Statistics for the tap model
Figure 10. Using the Enity Inspector to find the edge length of a small feature
1
Select faces that neighbour existing free edges (as in Figure 11);2
Click TOOLS, Clean Geometry;3
Specify a Minimum Edge Length of 0.02 (ensure that the value is otherwise smaller than edge lengths in the selected faces);4
Select Act on ... selected only;5
Click Apply.After all free edges are removed, the geometry is ready to be meshed. Figure 12 shows the resulting surface mesh using a relative Maximum Edge Length of 4% and Quad4 elements as the target element type.
An alternative to selecting the faces to be acted upon would be to set the Free edges only check box. In this case, only the edges that are free would be seamed, without affecting other edges in the model that are already correctly seamed. The result would be the same as achieved above.
Figure 11. Selected faces around free edges
Figure 12. Meshed geometry