Apply inertia relief to only some of the subcases

Alfonso_20743
Alfonso_20743 Altair Community Member
edited May 8 in Community Q&A

Hi All,

I have a model with several load step subcases. Some of them are fully constrained while others are not. Is it possible to apply inertia relief to only some of the cases (the not fully cosntrained ones)? I assumed that inertia relief would be applied to only the subcases that need it, but it does change the result of the constrained subcases also.

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Answers

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee
    edited May 8

    Hi Alfonso,

    You can try out the Inertia relief case to the required loadsteps by defining SUPPORT1 card and PARAM,INREL,-1. 

    Follow the below tutorial for this set up.

    OS-T: 1030 3D Inertia Relief Analysis (altair.com)

    Thanks

    Rajashri

  • Alfonso_20743
    Alfonso_20743 Altair Community Member
    edited May 8

    Thanks for the reply Rajashri!

    I've seen that, however, my part is completely free floating and only forces are applied to it. Would it work properly if I add SUPPORT1 constraints, which allow all degrees of freedom? Or do I need to constrain at least some of the model's degrees of freedom with SUPPORT1 and it would not be possible to have only forces and no constraints acting on the model?

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee
    edited May 8
    Alfonso_20743 said:

    Thanks for the reply Rajashri!

    I've seen that, however, my part is completely free floating and only forces are applied to it. Would it work properly if I add SUPPORT1 constraints, which allow all degrees of freedom? Or do I need to constrain at least some of the model's degrees of freedom with SUPPORT1 and it would not be possible to have only forces and no constraints acting on the model?

    Hi Alfonso,

    With SUPPORT1, you are adding fictitious constrains to arrest the rigid body modes. The total number of degrees-of-freedom specified on SUPORT and SUPORT1 cards must be less than or equal to six.

    If you dont want to add SUPPORT1, then go for PARAM,INREL,-2. With this you only have to call the loading info in Loadstep. No need to define any SPC.

    Thanks

    Rajashri

     

  • Alfonso_20743
    Alfonso_20743 Altair Community Member
    edited May 8
    Rajashri Saha_20525 said:

    Hi Alfonso,

    With SUPPORT1, you are adding fictitious constrains to arrest the rigid body modes. The total number of degrees-of-freedom specified on SUPORT and SUPORT1 cards must be less than or equal to six.

    If you dont want to add SUPPORT1, then go for PARAM,INREL,-2. With this you only have to call the loading info in Loadstep. No need to define any SPC.

    Thanks

    Rajashri

     

    Hi Rajashri,

    yes, I'd like not to arrest any rigid body modes. I was using PARAM,INREL,-2, but it seems to be applied globally (to all subcases) and thus it seems to affect the result of a fully constrained subscase.

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee
    edited May 8
    Alfonso_20743 said:

    Hi Rajashri,

    yes, I'd like not to arrest any rigid body modes. I was using PARAM,INREL,-2, but it seems to be applied globally (to all subcases) and thus it seems to affect the result of a fully constrained subscase.

    In that case, you can separate out the loadsteps for which you want to Inertia relief. you can delete other load steps and then carryout with INREL,-2 option. Hope this works for you.

    Thanks

    Rajashri

  • Alfonso_20743
    Alfonso_20743 Altair Community Member
    edited May 8
    Rajashri Saha_20525 said:

    In that case, you can separate out the loadsteps for which you want to Inertia relief. you can delete other load steps and then carryout with INREL,-2 option. Hope this works for you.

    Thanks

    Rajashri

    I think this wouldn't do the job since I'd like to perform an optimization and for that I'd need the two load cases together

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