FBD and Moments

Akshay Sharma
Akshay Sharma New Altair Community Member
edited October 2020 in Community Q&A

Hi Everyone,
I have a problem where i have applied the forces in the y direction on four sides of a beam and then i need to study the reaction forces and moments which are caused by these forces at the constraints points. I have used GPFORCE card in order to get the result but when i observe the result the values seem to be strange and unpredictably high. May i am not view the result in a correct way. Can someone suggest me how should i set the FBD pannel to get the forces & moment on the SPC base because of the applied forces. Also what is the different in the FBD plot for Free body force/moment and Resultant foces7moment and what does the ignore node set used for.
Thanks in advance.

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Answers

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited July 2020

    Hi,

     

    actually you need to request SPCFORCES (SPCF output in OptiStruct). This will show you the reaction forces directly on your constrained nodes.

    Then you can plot them as a vector plot in HV.

  • Akshay Sharma
    Akshay Sharma New Altair Community Member
    edited July 2020

    At the moment i am using the GPFORCE card and using the FBD method to observe the forces as shown below. Will i be able to see the SPC force just like this for all the four constraint points.
    @Adriano A. Koga

     

    <?xml version="1.0" encoding="UTF-8"?>3.png

  • Akshay Sharma
    Akshay Sharma New Altair Community Member
    edited July 2020

    So i did try the same thing with the SPCF card and the results are almost same. My concern is why are there forces induced in X and Y direction when i have only applied forces in Z axis .
     

    <?xml version="1.0" encoding="UTF-8"?>4.png

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited July 2020

    If your structure is perfectly symmetric and loads are perfectly aligned, this should be zero. There might be some tiny  misalignements in your model. Check the summation (applield and reacted) in the .out file.

  • Akshay Sharma
    Akshay Sharma New Altair Community Member
    edited July 2020

    Even after i make the structure symmetric and checking for misalignment i couldn't find any. I checked the Sum App. Forces and Sum SPC it doesnt match up.
    Is there a way to check for misalignment?
     

    Unable to find an attachment - read this blog

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited July 2020

    looking closely at your model, you won't have zero reactions at all, as there are moments being carried on along the structure.

    Your SPCs are constraining all the DOFs, and these moments are turning into XY reactions. 

  • Akshay Sharma
    Akshay Sharma New Altair Community Member
    edited July 2020

    Thanks @Adriano A. Koga But since the structure is symmetric and also the value and direction of forces are opposite wouldn't they get cancelled? Also to notice is the value of these forces are very high in comparison to the input force. Also could you please elaborate how can i check the moments which are being carried along in the structure.

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited July 2020

    as the structure is static and in equilibrium, yes, they will sum as zero. If you look at SPCF they have the same magnitude, but in opposite directions.

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