Error message

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VTiederle
Sherlock User
Posts: 39
Joined: 24 Jul 2013, 12:32

Error message

Post by VTiederle » 21 Sep 2016, 04:00

When running vibrational analysis some error messages like the following wording are coming up:
Mesh edge (-50.531,85.136) to (-48.8695,85.138) is not asociated with any faces

Results are generated for e.g. natural frequency or life curves of random vibration.

My questions:
- Are the results correct?
- What is the reason for that message?
- How to fix it?
Thank you for your support.

natalieh
Site Admin
Posts: 53
Joined: 01 Nov 2016, 08:43

Re: Error message

Post by natalieh » 17 Feb 2017, 18:22

Hi Viktor,

The results may not necessarily be correct.

At the very end of the vibration error, there is a message relating to one or more elements having a non-positive Jacobian determinant (complete message pasted below). The reason for this message is that the mesh size implemented might be too small or there are parts that are too close together. Another reason might be that there are too many nodes along the edge of the board, so you would have to eliminate some of the vertices along your board edges to alleviate the problem. Gil has a forum post titled "Non positive jacobian determinant" that has more recommendations on how to deal with this issue. Please let me know if you have any further questions.

"ERROR: One or more elements have a non-positive Jacobian determinant

This error is usually generated by Calculix when a component barely intersects a
mount point or hole, causing an extremely small element to be created in the
mesh. Sherlock attempts to identify and resolve such problem areas when the
mesh is generated, but in some cases Calculix determines that the elements are
too small for analysis anyway. In such cases, the issue can usually be resolved
by moving/resizing the component to eliminate the intersection or deleting the
mount point if it is not needed for the analysis.

This issue can also arise when modeling leads using the 'Bonded' mesh model. In
that case, the lead element that attaches to the PCB may not be tied properly in
Calculix because of the PCB mesh being used. The problem can usually be
resolved by tweaking the mesh size or using the 'Merged' mesh model.

This issue can also arise when generating trace layer meshes with fine details
using 2nd order elements in Calculix. In such cases, switching to 1st order
elements may eliminate the problem.”
Natalie Hernandez, PhD
Product Manager
DfR Solutions
nhernandez@dfrsolutions.com

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