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General Mechanical

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Nonlinear convergence criteria in ANSYS APDL

    • ucess04


      I am doing a nonlinear analysis for the pretensioned concrete beam. The key focus is transfer length. After analyzing the beam, I checked several results. However, some parts were confirmed that were different from the predicted data.

      My teacher suggested I achieve a tighter convergence in the analysis.

      In addition to increasing the maximum number of iterations, I can use the CNVTOL command to set the convergence value for the nonlinear analysis. I have some questions:

      1. Convergence based issue: As far as the structure is concerned, which method has more convergence and better accuracy of the overall strain curve? Force or displacement?
      2. Is a lower tolerance value better?
      3. Minimum reference value. I don't understand what it is, Does this represent the best value of convergence achievable? 
      4. What is the difference between VALUE and minimum reference value?
      5. Should the convergence value be as low as possible (e.g. 10^(-10)) or as high as possible (e.g. (1,000,000,000)) in order to achieve higher accuracy of the results?

    • Surya
      Ansys Employee


      Convergence depends from problem to problem, but for majority of the nonlinear problems, force convergence serves as a first step, a displacement convergence acts as an additional verification step. All other convergence checks will also be done with their default settings. Please find this KM - 
      1) What is displacement convergence? 2) In some cases force or displacement convergence alone is sufficient while in some other cases both are activated. What is the reason for this? - Ansys Knowledge

      Also find this CNVTOL help documentation for more information - 
      CNVTOL (


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