Why Do Geometry Operations Fail?

This article covers the top reasons why imprint, enclosure, open inner region, and closed inner region geometry operations fail.

Before we start, it is advised to visit the documentation page on CAD preparation and upload. In addition, please visit the following Knowledge Base article to find out how to find CAD faults.

Common CAD Faults

CAD faults, in general, will most likely cause geometry operations to fail. Therefore, you should make sure that before uploading the model to the platform, it does not have any CAD faults. The most common CAD faults are:

• Small features/faces
• Inexact edges
• Overlapping faces/solids
• Sliver faces
• Knife edges/vertices
• Discontinuous faces/edges
• Bad faces
• sheet/surface elements
• Overlapping solids (interference)

To check the CAD faults above, many CAD softwares have their individual features to detect the common CAD errors.

Following are the two main geometry operations supported by SimScale after uploading the geometry:

1. Imprint
2. Flow volume extraction

1. Imprint

Always use the imprint operation if you have a model with multiple parts. This operation fails due to the interference between parts.

You can resolve interference faults by checking for faces that are overlapping. Most CAD tools already have this included. After knowing which faces are intersecting, if one of the faces is unnecessary you can delete that face. However, if both are necessary, you can merge them into one face.

2. Flow Volume Extraction

To learn more about the flow volume extraction geometry operation, visit this Knowledge Base article.

2.1 Open Inner Region

If your model has openings and you would like to create a flow volume inside, use this geometry operation. This operation possibly fails because of the following CAD faults:

• Interference between surfaces

• Boundary faces are not parallel

The following picture is an example for the boundary faces not being parallel:

In this case, you will need to make sure that all the faces that are facing the environment outside of your model are parallel. The picture on the left shows that the two faces on the top are not parallel with the two faces on the side. The picture on the right shows an example of a parallel boundary face.

• Boundary faces are not completely closing the openings of the cross-section

The following example shows how the boundary faces at the opening should be created:

You will also need to ensure that the boundary faces do not have any openings. This can be seen in the picture on the right where the top and side faces do not meet on the four corners. You can solve this by changing the four faces into one face.

• An internal part has an edge-to-face or point-to-face contact with the boundaries of the fluid volume

You see an edge-to-face contact example in the following picture:

Avoid any point-to-face or edge-to-face contact between the internal parts and the boundaries of the fluid volume. One way to avoid this issue is to trim the sharp edges and/or corners, in contact with the walls.

• A boundary face is shared by multiple openings and cavities

If the boundary face is shared by multiple openings and cavities, open inner region flow volume extraction might fail. In this case, it is recommended to separate the boundary faces of the inlets.

In the following example (Figure 5), there are two openings and seven cavities on the highlighted face. The flow volume will be generated inside the box, not in the cavities. Therefore, we had to separate (isolate) the boundary faces of the openings from the main face. This operation needs to be done in CAD software.

2.2 Closed Inner Region

This operation possibly fails because of the following CAD faults:

• Interference between surfaces
• An internal part has an edge-to-face or a point-to-face contact with the boundaries of the fluid volume

2.3 Enclosure

This operation possibly fails because of the following CAD faults:

• Interference between surfaces
• An internal part has an edge-to-face or a point-to-face contact with the boundaries of the fluid volume

Further Tips

The following points are essential:

• Firstly, avoid sheet/surface elements. The CAD model should only consist of solid parts.
• Secondly, avoid overlapping solids (unless they represent cell zones).

The following points are not essential, but we strongly recommend to perform a cost-effective simulation experience:

• Model only the essential parts. In other words, remove unnecessary features or components, such as small nuts, bolts, pins, etc.
• Fill leftover holes and gaps.