Deactivating TIE in first step, and then activating TIE in second step.

[Le_Mickster]

Hi everyone.

What I am trying to achieve is pre-tension of some supportive tubes. The reason is that the tubes support a pipe, which is experiencing thermal expansion. To level out the displacement due to heat-transfer, then the tubes are moved a given displacement as a pre-tension.

In first step I want to use *BOUNDARY to give the block below a displacement.
In the second step I want to activate the tie, such that the lower surface (which is the master-surface) is not displaced also.

This is not possible to do with TIED surfaces, as seen below.
Do any of you have any suggestions how to achieve this in some other way or am I missing something?

Step 0 - Pre-Tension of Stays
*STATIC
*MODEL CHANGE, REMOVE, TYPE=CONTACT PAIR
SCR_Stay_Bot_S, SCR_Stay_Bot_M
*BOUNDARY, OP=MOD
MOVE3,1, ,-17.0
MOVE3,2, ,0.0
MOVE3,3, ,0.0
MOVE4,1, ,-17.0
MOVE4,2, ,0.0
MOVE4,3, ,0.0


Step 1 - Pressure
*STATIC
*MODEL CHANGE, ADD, TYPE=CONTACT PAIR
SCR_Stay_Bot_S, SCR_Stay_Bot_M
*BOUNDARY, FIXED
MOVE3,1,3,0.0
MOVE4,1,3,0.0
*DLOAD, OP=NEW
,GRAV,9820,0,0,-1
SCRress_shell,P,0.386
ScavRec_Press_Shells,P,0.386
Exht_Pressure,P,0.386

***ERROR: CONTACT PAIR (SCR_STAY_BOT_S, SCR_STAY_BOT_M) IS A TIED CONTACT
PAIR. *MODEL CHANGE CANNOT BE USED FOR TIED CONTACT PAIRS

 

[FEA way]

Try with no separation (and rough friction) contact. It will only approximately replace tied contact but should let you achieve desired effect.

 

[Le_Mickster]

Hi FEA way, thanks for your reply. I have tried out the matter, that you have described and it seems to be running - but not converging as it is down in incredibly small time steps/increments.

 

[FEA way]

Analyses with contact often exhibit convergence issues. You may have to provide some additional stabilization to your model as rigid body motions might occur. Try enabling automatic stabilization in the step settings. If that doesn’t work there are also special options for contact that increase the chance of convergence. Also reduce initial and maximum increment size and increase maximum number of increments.