Meaning of entering a value in the DOF setup for MFRA

F. Beinhoff
F. Beinhoff Altair Community Member
edited February 28 in Community Q&A

Dear all, 

I am working with Modal Frequency Response Analyses (MFRA), to be used for subsequent acoustics analysis. I am using customized acceleration signals, that were converted from time domain to frequency domain, as an input signal. I have set up the boundary conditions at the load application point according to the HyperWorks tutorial.

In the direction of load (here: x), I have entered 1,0. The other DOFs are constrained, thus entered 0,0.

image

From static analysis, I know that entering a number value (>0) in the DOF-field means "displacement by a certain value in the respective direction" (here: 1 [mm] displacement in x-direction). 

However, when looking at the results, this definition seems not to apply to MFRA, as the model can move freely along the x-axis. 

My question is thus: What does entering a value (e.g. 1,0) in the DOF setup mean in the context of MFRA? Is it a scaling factor of the input signal ? And what is the difference between entering a number value (>0) and leaving the field completely empty ? 

I would be very happy if someone could answer my questions. 

I'm looking forward to your reactions and thanks a lot in advance. 

Best, Fabian 

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Best Answer

  • viniciusgomes
    viniciusgomes
    Altair Employee
    edited February 28 Answer ✓

    Hi Fabian, 

     

    You are correct. For MFRA this value will represent the scaling factor of the input signal, the most traditional way of using it it applying DOF = 1, but there are other use cases, e.g., if your signal is in terms of G's, you can set DOF = 9810 and use the curve in terms of G's instead of converting to mm/s^2.

    And there is no difference between setting DAREA to zero or leaving it empty. Just keep in mind that this does not apply for SPC load, where zero means fixed and empty means free. 

    Thanks,
    Vinicius 

     

Answers

  • viniciusgomes
    viniciusgomes
    Altair Employee
    edited February 28 Answer ✓

    Hi Fabian, 

     

    You are correct. For MFRA this value will represent the scaling factor of the input signal, the most traditional way of using it it applying DOF = 1, but there are other use cases, e.g., if your signal is in terms of G's, you can set DOF = 9810 and use the curve in terms of G's instead of converting to mm/s^2.

    And there is no difference between setting DAREA to zero or leaving it empty. Just keep in mind that this does not apply for SPC load, where zero means fixed and empty means free. 

    Thanks,
    Vinicius 

     

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