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Documentation

Why Do Geometry Operations Fail?

This article covers the top reasons why imprint, internal and external flow volume extraction CAD Mode 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 software have their individual features to detect the common CAD errors.

Following are some geometry operations you will find in SimScale CAD Mode.

1. Imprint

Always use the imprint operation if you have a model with multiple parts.

  • Imprint operation fails due to the interference between parts.
example of an interference in a cad model to show one of the reasons why geometry operations fail
Figure 1: Interference means an overlap between the solid parts.

To resolve interference faults, first, you need to perform an interference check on the CAD model. Our CAD mode has this facility to detect and automatically fix interferences. For manual fixing, once you detect an overlap, you can subtract the body from the other one to remove the overlapping region. Alternatively, you can merge the two parts into one if this is suitable for your case. Check our Boolean operations integrated for this purpose.

In conclusion, imprint operation will work on an interference-free CAD model.

  • Inprint operation fails, if there is a small face or a sliver face on one of the contact faces. Clean the small and sliver faces in the CAD Mode or in your CAD software, before uploading the model to SimScale platform. In the following picture, you see a PCB board (green), covered by a resin layer (semi-transparent blue). The cooling is performed by a cooling pipe (grey). Imprint operation is necessary to capture the contacts between each part and execute a CHT analysis.
cooling pipe has a small face at the contact
Figure 2: Example of a small face on the contact interface

2. Flow Volume Extraction

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

2.1 Internal Flow Volume

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

Boundary Faces

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

example of non-parallel surfaces  in a cad model to show one of the reasons why geometry operations fail
Figure 3: An example for parallel and not parallel boundary faces

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:

example of an open boundary face in a cad model to show one of the reasons why geometry operations fail
Figure 4: An example for closed and not closed boundary faces at the opening.

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.

Contact Boundaries

  • 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:

example of an open channel with an internal triangular component to show edge-to-face contact causing geometry operations to fail
Figure 5: An example for an open channel, in edge-to-face contact with an internal component.

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, under some exceptional cases, internal 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. To clarify, this operation needs to be done in CAD mode.

internal flow volume extraction feature is being used on a box model with two openings and several cavities
Figure 6: Isolating the boundary faces of the openings from the main face can prevent flow volume extraction failures in CAD mode

2.2 External Flow Volume

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
comparison of right and wrong way of generating an enclosure around a triangular component
Figure 7: Ensure face-to-face contact or no contact while generating an enclosure

Further Tips

The following points are essential:

  • Firstly, avoid sheet/surface elements. In other words, 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.
this picture shows the comparison of an original pcb cad model and a cleaned one
Figure 8: Common CAD cleaning measures on PCBs.

Note

If none of the above suggestions solved your problem, then please post the issue on our forum or contact us.

Last updated: September 17th, 2021

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