Unit Load (Frequency Response)

Nancy Jewel Mcdonie
Nancy Jewel Mcdonie Altair Community Member
edited June 3 in Community Q&A

Hi all experts, 

I'm doing task about Frequency Response (Direct & Modal). I'm not really clear about unit load that we need to set up in our analysis. 

Can anyone explain for me about that? 

Thanks all.

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Answers

  • loistf
    loistf Altair Community Member
    edited May 28

    Hi Nancy. Frequency response is a linear analysis. Just like in linear static analysis, response is a linear function of the loads. When you run an analysis, you get the function (or the factor in the linear function). 

    If, say, after having done the analysis you realize that the load was not 1N, but 2N, you don't need to run the analysis again, you just multiply the response by 2. Using an unit load is just a typical thing to do out of convenience / simplicity and maybe consensus in the simulation community. But you can just use any other magnitude.

    Hope it helps. 

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee
    edited May 29

    Hi Nancy,

    Unit load is well explained in previous comment. I would like to add few more points.

    You can apply unit load in Optistuct for FRF analysis by creating DAREA (From constraint panel, load type DAREA). If you are applying frequency dependent loading then you need to create TABLED1 card to define the curve which will give you Load vs Frequency curve. The unit load will get multiplied with this curve during the course of analysis.

    You can follow the below tutorial for more information on FRF analysis in Optistruct.

    OS-T: 1305 Modal Frequency Response Analysis of a Flat Plate (altair.com)

    Thanks

    Rajashri

  • Nancy Jewel Mcdonie
    Nancy Jewel Mcdonie Altair Community Member
    edited June 3
    loistf said:

    Hi Nancy. Frequency response is a linear analysis. Just like in linear static analysis, response is a linear function of the loads. When you run an analysis, you get the function (or the factor in the linear function). 

    If, say, after having done the analysis you realize that the load was not 1N, but 2N, you don't need to run the analysis again, you just multiply the response by 2. Using an unit load is just a typical thing to do out of convenience / simplicity and maybe consensus in the simulation community. But you can just use any other magnitude.

    Hope it helps. 

    thank loistf. 

    But I wonder, in real-life problem, how do we know: how many units load need to apply to our part? 

    image

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