General Mechanical

General Mechanical

APDL: Response of beam resting on nonlinear springs to acceleration

    • julius.langenhorst


      I would like to get the response of a beam resting on nonlinear springs (COMBIN39) to a constant acceleration in form of a acceleration vs. frequency plot.

      The acceleration load is constant in the range from 0 - 100 Hz.

      Due to the non-linearity I can't use modal analysis and harmonic analysis. Since a modal analysis is not possible, mode-superposition harmonic analysis, spectrum analysis and mode-superposition transient dynamic analysis are also not possible. Using a nonlinear static analysis doesn't seem right since frequency is involved. I also don't think that a nonlinear transient analysis is correct since I'm not interested in time dependece (on the other hand frequency is one over time maybe I should be?).

      Any help with this problem or a push in the right direction will be much appreciated.

    • peteroznewman

      You say the beam is “resting” on a nonlinear spring.  Is the beam fastened to the nonlinear spring or is there also nonlinear contact so that the beam can lift off the nonlinear spring?

      Is there a static preload such as gravity?

      If the beam is fastened to the nonlinear spring, you could linearize the spring and obtain preliminary results using a MSUP Harmonic Response analysis.  The results may be helpful in the next analysis.

      To accommodate all nonlinearities in the model, you will have to run Transient Structural multiple times. This will be tedious because you will have to edit the load to create a sinusoidal acceleration vs time input at the correct frequency and amplitude for each point on the frequency plot. Some rules are you need at least 20 values per cycle to represent the input and you will need hundreds of cycles to allow the transient response to die out so that all that you are left at the end time is the harmonic response. To ensure the transient response dies out, you must have damping defined in the model.

    • julius.langenhorst

      Thank you for your answer! Sorry for my late reply I forgot that I asked a question here.

      I want to analyse a beam embedded in a viscoelastic material (embedded meaning completely surrounded in radial direction). My goal is to find out how the eigenfrequencies change due to the surrounding viscoelastic material.

      When I asked my question I thought it would be a good idea to use nonlinear springs. By now, I switched to using COMBIN14 elements for the beam model. I also have a beam model made of volume elements where I enter the viscoelastic material properties as experimental data.

      I know that modal analysis in Ansys are linear but I can't help to think that there must be a way to conduct a nonlinear modal analysis. I would once more really appreciate it if someone could point me into the right direction with this problem.

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