Harmonic analysis - Reaction forces -ANSYS APDL

Hi guys,

Is it possible to extract reaction force at a node of interest under a harmonic load (Harmonic analysis) . Preferably in complex form?.

Are there any available examples?.

Thank you very much!

Comments

  • BenjaminStarlingBenjaminStarling AustraliaMember

    Hi @Cpwtub

    ensure you have nodal forces enabled under output controls, or use the OUTRES command. Then inser a user defined result, select the nodes you are interested in, and put the expression, ENFOX, ENFOY, ENFOZ, or ENFOVECTORS.

  • CpwtubCpwtub BerlinMember

    Hi @BenjaminStarling @peteroznewman

    Thank you very much. I ll try it.

    But would that be possible to extract frequency response of the nodal reaction forces in harmonic analysis?

    Best regards

  • BenjaminStarlingBenjaminStarling AustraliaMember

    Hi @Cpwtub

    Now I understand what the issue is. Mechanical currently does not have the option to plot results over the frequency domain, other than the predefinded frequency response options.

    One option is to create a result at each frequency then export to excel and create your own frequency response curves. This is cumbersome but I may actually prefer this method as you will likely want the response in tabular form for your calculations, and creating results at all sets just takes two clicks. Unfortunately it is the export to excel which takes time, especially if you have many frequencies to extract results.

    The other option is to use MAPDL. /POST26 allows you to plot any result in the frequency domain. The downside of this is that ENFO results are element based. Therefore manually going through each element is cumbersome. This can be looped with APDL but I would need a bit of time to provide guidance on this loop.

    If the boundary you are looking to extract the frequency response on is restrained, you may be able use the F result. This is easier to loop, a rough example is shown below. This will plot the result but I am fairly sure you should also be able to output to a text file. This same example works for ENFO, but would require two extra loops to go through the elements, and then sum the ENFO result at nodes shared between elements.

    cmsel,s,surface,nodes    !component of nodes to get frequency response
    /post26
    n_next=ndnext(0)
    vari_n=1
    *DOWHILE,n_next
    RFORCE,vari_n,n_next,F,X
    XVAR,1
    PLVAR,vari_n
    vari_n=vari_n+1
    *ENDDO
    

    This example plots one node at a time without pausing in between. It should be adaptable to plot multiple nodes at a time, pause, export image, and to export multiple nodes to text file.

    I am not super familiar with this process, and the above code may not work straight away. Other commands to look at are in the POST26 family, namely NSOL, ESOL, PRCPLX and some others.

    https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/ans_cmd/Hlp_C_CH2_8.html

  • BenjaminStarlingBenjaminStarling AustraliaMember

    I forgot to actually loop the above example. Inside the loop you will need to remove the nodes incrementally. You can loop element selections in a similar manner using elnext(0)

    nsel,u,node,,n_next
    cm,s,surace,nodes
    n_next=ndnext(0)
    
    
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