Learning Forum

[Fady Elshazly]

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]

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]

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]

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]

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]

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]

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]

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

Thank you so much.