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Iteration displacement limit

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  • Iteration displacement limit

    Hello,
    I'm performing a moving load analysis along a cable (length 100 m), i.e. with a lot of load cases.
    Results are OK, but the convergence speed is very slow: it seems that dlubal limits the displacement for iteration to 200 mm (see image attached), even if there is NO particular convergence problem.
    Is it possible to increase this iteration increment limit (in order to reduce the number of iterations)?
    Regards
    Andy
    Zuletzt geändert von andy; 10.07.2021, 10:52.

  • #2
    Hello Andy,

    have you tried if the precision settings have any influence?

    Precision Settings

    A tip would be to try the solver "Dynamic Relaxation". For cable structures it is sometimes very fast.

    Dynamic Relaxation

    Frank Faulstich
    Support Team der
    Dlubal Software GmbH
    info@dlubal.com
    https://www.dlubal.com

    Kommentar


    • #3
      Hello Frank,
      the convergence plot for a combination requires 27 iterations, moslty limited to 200 mm for each step.
      Klicke auf die Grafik für eine vergrößerte Ansicht

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      If I relax tolerances
      Klicke auf die Grafik für eine vergrößerte Ansicht

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      the benefit is just the reduction of one iteration, being convergence limits less stringent. But I'm not asking for less stringent limits: the problem I observe is that during convergence most iterations are limited to a displacement limit / per iteration (200 mm) that slows the solution. Is this limit "hardcoded" in the solver?
      Klicke auf die Grafik für eine vergrößerte Ansicht

Name: immagine_2021-07-12_094119.png
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ID: 3435

      Dynamic relaxation is much slower (and takes 15000 iterations)
      Klicke auf die Grafik für eine vergrößerte Ansicht

Name: immagine_2021-07-12_094929.png
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ID: 3436

      Thank you
      Andy

      Kommentar


      • #4
        Hello Andy,

        I am not aware of any settings to change the displacement per iteration. But maybe the value depends on other parameters. I would like to investigate this in more detail. Can you please attach the file for this purpose.

        Frank Faulstich
        Support Team der
        Dlubal Software GmbH
        info@dlubal.com
        https://www.dlubal.com

        Kommentar


        • #5
          Hello Frank,
          here ( cable0.zip ) is a minimal input file. Please change the filename to "cable0.rfx" in order to open directly with RFEM.
          Best,
          Andy

          Kommentar


          • #6
            Hello Andy,

            I have taken a closer look at the problem. The deformation limit is hard coded and there is no way to influence it. It also does not depend on the size of the model.

            The Dynamic Releaxation in attached example takes a time slightly twice as long as the Newton-Raphson solver.

            Frank Faulstich
            Support Team der
            Dlubal Software GmbH
            info@dlubal.com
            https://www.dlubal.com

            Kommentar


            • #7
              Thank you Frank,
              may I suggest to improve this "hardcoded" limit to be at least model-size dependent (200 mm for a small frame is a "huge displacement", whereas on a big cable structure is a little displacement) or better, to expose it, for instance in the menu "Change standard settings"?

              Yours sincerely
              Andy

              Kommentar

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