Cylindrical vessel - non positive jacobian error

General Questions
1

Hi i have problems simulating this cylindrical vessel, am having a non positive jacobian error and i could not find the solution to my problem in the forum

Am using the axisymmetric for this simulation, sorry if the solution is obvious :frowning:

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2

In axisymmetric models, all faces must lie to the right of the Y axis. That’s most likely why the left part of your geometry has this error.

If you want to simulate a complete vessel, rotate it so that Y axis is the axis of symmetry - that’s what CalculiX expects.

Also, you should refine the mesh significantly.

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3

Thanks so muchhhhh i will try!!

4

Not sure if this is the same issue @FEAnalyst , but I’m trying to create a simple axisymmetric cylinder.
When I generate the mesh, I get a warning message.

At first, I ignored it and the simulation ran with results.
Then I tried flipping the face normals on my CAD model and ran the simulation again, but this time I got a non-positive Jacobian error.

Is it safe to ignore the initial warning, or could it affect the results? IS there a better way to process ? I joined you my geometry normaly I take care to make it right with the axes setup.

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5

If you are running an axisymmetric analysis, you have to make sure that:

  1. All surfaces lie entirely on the XY plane.
  2. All surfaces lie on the right of the Y axis.
  3. Surface normals point in the positive Z direction. You can fix it in CAD software (FreeCAD has the Reverse shape tool for that) or in PrePoMax (Geometry → CAD Part → Flip Face Normal),

This has to be corrected in order to avoid such errors. Negative jacobians in 2D models are a typical sign that the normals are pointing in the wrong direction.

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