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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.

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.

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.
  • Boundary faces are not completely closing the openings of the cross-section.
  • An internal part has an edge-to-face or a point-to-face contact with the boundaries of the fluid volume

The following picture is an example for 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 2: 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.

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 3: 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.

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 4: 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.

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.
this picture shows the comparison of an original pcb cad model and a cleaned one
Figure 5: 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: August 28th, 2020

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