Element Birth and Initial Stress

  • 23 Views
  • Last Post 2 days ago
jarrett.wise posted this 3 days ago

Hello,

I have a follow up question to the element birth.  I have a multi step model in which the elements of one body are killed in the first load step and birthed later on.  Initially the body which is deactivated has initial stress defined as APDL code under the geometry section (/prep7 - inistate).  

From what I have read in the manual and seen in my simulations, the initial stress is re-set to zero when the killed elements are re-activated.  I have attemped to add the inistate code under the load step, but get the error that it can only be added in the first load step.  Does anyone have any suggestions for having killed elements have a stress when birthed?

I tried to attach the archived project, but it is too large.

Thank you,

Jarrett

Order By: Standard | Newest | Votes
SandeepMedikonda posted this 3 days ago

Jarrett,

  Can you please post some snapshots of what you are trying to do and the errors you are seeing?

  Changing material properties: MPCHG is a method you can try but it has been advised to proceed with caution. Also, using the ETABLE command has been used to store values but I am not sure if you use it to active the stresses as well.

P.S: Solution marked/long threads are likely to get less attention. So, I've moved your question to a new post.

 

Regards,

Sandeep

jarrett.wise posted this 2 days ago

Thank you Sandeep,

The simulation is a 6 step model that is replicating the process to drill a well in rock. 

In the first step, the initial far field stresses (in the rock) are defined and the casing and cement elements are removed leaving a open hole with surface pressures.

The casing is re-added in the second step.

Different surface pressures on the rock and casing are changed in the next steps.

In the fifth step, the cement elements are added.  (The sixth step is the final load/stress measuring step since birth and death elements are cannot change loads in the same load step they are added according to the manual).

Since the cement elements appear to zero out the initial stresses defined for them when birthed, I added the inistate command along with the ealive command in Step 5.  This is when the error comes.

The first picture is the initial stresses added for the cement in the geometry section (prep7).

The second picture is the ealive and inistate commands for step 5.

The third picture is the error message that comes up due to the step 5 commands.

 

Sincerely, 

Jarrett

SandeepMedikonda posted this 2 days ago

Hi Jarrett,

  One recommendation would be to add a thermal condition to model the shrinkage and residual stress/strain in the load step where elements are being activated.

~Sandeep

Close