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Error: Newton Convergence Could Not Be Reached

Error

Newton convergence could not be reached. Possible options to prevent that behavior: Update the tangent matrix more often, increase the maximum number of iterations, use automatic timestepping or decrease the timestep.

What Happened?

The solution diverged since no convergence could be reached with the defined number of nonlinear Newton iterations.

What Could Be the Possible Reason?

This error occurs when a non-linear simulation fails to converge the solution with the specified number of nonlinear Newton iterations while solving a nonlinear problem. Possible reasons are:

  • Unphysical simulation setup.
  • Bad mesh quality.
  • Physical contacts are too stiff.
  • The convergence criteria are too strict.
  • The Maximum Newton iterations are too low.

What Can I Do Now?

To resolve this error, you can follow these steps:

  • Check the setup of your simulation. The Newton convergence will not be reached when the setup of your simulation is not realistic. For example, if the load is applied as static, not ramped with a table or a formula.
  • Increase your mesh quality. Firstly, you will need to check your mesh quality with the ‘Meshing log’ or ‘Mesh quality’ viewer. After observing your mesh metrics, you can improve your mesh quality by increasing the global fineness of your mesh or by adding refinements where it is necessary.
steps on how to increase global mesh fineness in the mesh settings
Figure 1: Increasing global mesh fineness under Mesh settings.
  • Increase the ‘Tolerance’ of the convergence criteria under Numerics so that the solver will allow higher errors. For example, rather than 1e-5 give 1e-3. You should also keep in mind that this may result in an imprecise solution.
  • Increase ‘Maximum Newton iterations‘ under Numerics to allow for more iterations in each time increment.
  • Update the tangent or elastic matrix more often. For example, set Reactualisation every nth increment or Reactualisation every nth iteration to 1 rather than 3.
tolerance, newton iterations and iteration update settings under numerics in simscale to resolve newton convergence error
Figure 2: Tolerance (1), newton iterations (2), iteration update (3), and convergence criteria (4) settings under Numerics in SimScale.
  • Change ‘Convergence criteria’ to ‘Absolute’. If you intend to not apply any load in your simulation, firstly you will get a warning saying “No load was defined for the analysis. This might lead to a non-convergent analysis. Please review your boundary conditions” when starting the simulation. Secondly, when you run into this warning, you can resolve this by changing the Convergence criteria under the Numerics settings to ‘Absolute’. This will calculate the residual as a difference between the internal and external forces. For more information regarding the difference between ‘Absolute’ and ‘Relative’ residual in structural analysis, proceed here.
  • Use ‘Automatic’ in ‘Time step definition‘ rather than manual under Simulation control.
time step settings under simulation control to solve newton convergence could not be reached error
Figure 3: Time step settings under Simulation control.

Important Information

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

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Last updated: October 15th, 2020

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