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Dynamic relaxation

    • Fady Elshazly
      Subscriber

      Hello

      Anyone knows how to definde spc in lsdyna during dynamic relaxation and to be released after that. I will prescribe in the transient step earthquake motion as boundaries using rigid part motion

       

      thanks

    • Ram Gopisetti
      Ansys Employee

      Hi Fady, 

      The spc constraints are honored in the DR phase when BOUNDARY_SPC  with the BIRTH_DEATH option and DEATH eq 0.0 is used, but they disappear as soon as LS-DYNA enters the TRANSIENT phase.

      cheers, Ram 

      • Fady Elshazly
        Subscriber

        I am trying to do this but it seems not to be working properly. Is this because i am trying to use a set of nodes in a rigid body? is there another way to constrain the rigid body instead of spc set?

    • Andreas Koutras
      Ansys Employee

      Hello,

      To add to the previous response, on*BOUNDARY_SPC_NODE_BIRTH_DEATH you will need to set the DEATH equal to a tiny number, such as DEATH=1e-12.

      • Fady Elshazly
        Subscriber

        I am trying to do this but it gives error as it cannot be assigned to a rigid body nodes. Is this because i am trying to use a set of nodes in a rigid body? is there another way to constrain the rigid body instead of spc set?

    • Andreas Koutras
      Ansys Employee

      For rigid bodies, please impose the constraints by prescribing a zero displacement through *BOUNDARY_PRESCRIBED_MOTION_RIGID (with VAD=2) at each of the dof you need to fix. As in the previous case, use a small DEATH time to release the constraints at the beginning of the transient phase. 

    • Andreas Koutras
      Ansys Employee

      Hello Fady,

      A correction for my previous response. In *BOUNDARY_PRESCRIBED_MOTION_RIGID, please do not define a DEATH time. Instead, in the *DEFINE_CURVE referenced by the LCID of *BOUNDARY_PRESCRIBED_MOTION_RIGID, set SIDR=1. This should work.

      • Fady Elshazly
        Subscriber

        I will try it and let you know what is going on. 

        Thank you so much.

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