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Error: MUMPS Residual Not Achieved

Error

The desired residual of the MUMPS solver could not be achieved. You may increase the residual in the settings to get results. To reach the desired residual, you should consider increasing the mesh quality (e.g. via refinements) though. For nonlinear calculations, you can ignore this by setting it to -1.

What Happened?

The residual defined under the Numerics settings was not achieved when using the MUMPS solver for structural simulations.

What Could Be the Possible Reason?

Possible reasons for this error are:

  • Bad mesh quality: The mesh was not sufficient to fully resolve your model which results in very high residuals.
  • The residual is too low: The residual was not achieved because the residual set under Numerics is too low. This can happen because high residuals were calculated or due to numerical round-offs.
  • Non-linear analysis: The non-linear analysis toggle is on in the global settings which results in the solver to take into account the non-linearity properties of the material.

What Can I Do Now?

Here are some steps you can follow to resolve this error:

  • Improve your mesh quality: The quality of your mesh will highly influence the results of the simulation. Therefore, you will need to check your mesh quality with the ‘Meshing log’ or with the ‘Mesh quality’ viewer. It is important to keep the nonOrthogonality under 70.
example of the meshing log in simscale showing mesh quality metrics
Figure 1: Mesh quality metrics highlighted to look out for after meshing is done.

You can improve your mesh by increasing the global fineness or by adding local refinements where it is necessary. Read more to find out how you can inspect and improve your mesh.

  • Increase the residual: You can find the calculated residual in the solver log and you can use this value as a guide to define a new residual.
computed mumps residual of a failed simulation in the solver log
Figure 2: Computed MUMPS residual inside solver log in SimScale.

To increase the residual, you can go to Numerics and define a different value under Linear system relative residual. For example, in Figure 2 the computed error is \(4.87569×10^{-5}\) which means you can set \(5×10^{-5}\) as the new residual.

location of residual settings under numerics
Figure 3: Residual settings under Numerics for solid analysis.
  • Set residual to a negative value: For a non-linear analysis, set the residual to some negative number (e.g. -1 ) so that the solver ignores the residual requirements.
setting the residual to -1 for linear analysis
Figure 4: Residual set to -1 for non-linear analysis.
  • Turn off non-linear analysis: However, if a non-linear analysis is not necessary, turn off the non-linear analysis in the global settings. This will turn the simulation into a linear analysis and you will be able to save computing resources.
the global settings toggle within the simscale platform
Figure 5: Global settings for static analysis with non-linear analysis toggled off.

You can find out which analysis you need in this article: When do I Need a Nonlinear Static Analysis?

Important Information

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

Last updated: September 11th, 2020

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