Learning Forum

[Alex1EDP]

Dear all, 

I have done a transient thermal analysis and the results are being used as body forces on a static structural analysis.

However I need to use the thermal loads as a temperature variation from timestep(i) - timestep(i-1), for instance in timestep 10 i want the thermal load to be equal to the [temperature in timestep(10) - the temperature in timestep (9)]

I have been using the following APDL code:

*Do, iCalc, 1, 50, 2

     AllSel, All, All
     BfCum, Temp, Repl
     LdRead, Temp, iCalc, , , , C:\xxxxxx 

    Solve
*Enddo

Does anyone know how to do this?

Thank you

 

[dlooman]

It seems the need for the structural temperatures to be the delta between load steps is only due to the use of the bfcum command.  Without this command the transient temperatures should become the structural temperatures in the static analysis as usual.  Is there some reason bfcum is being set or for structural temperatures not being equal to the transient thermal temperatures?

[Alex1EDP]

I was using the BFCUM because according to the Ansys help it allows to replace the load between load steps. I also tried to use the Add operator and applied a Factor = -1 but it did not work.

I used the BF, All, Temp command but obtained the same results. 

BFCUM,Lab,Oper,FACT,TBASE

Oper
Accumulation key:
REPL
Subsequent values replace the previous values (default).
ADD
Subsequent values are added to the previous values.
IGNO
Subsequent values are ignored.
FACT
Scale factor for the nodal body load values. Zero (or blank) defaults to 1.0. Use a small number for
a zero scale factor. The scale factor is not applied to body load phase angles.
TBASE
Used (only with Lab = TEMP) to calculate the temperature used in the add or replace operation
(see Oper) as:
Temperature = TBASE + FACT* (T - TBASE)

[dlooman]

I'd like to compare what you are doing to the normal workflow below.

1. Transient thermal analysis produces an rth file with model temperature at many time steps.
2. Static structural analysis solves for temperatures on the rth file at various times.  The solutions are independent of each other.  Unlike a transient there is no carryover from one solution to the next:   /SOLU LDREAD,temp,,,time_1,,file,rth SOLVE LDREAD,temp,,,time_2,,file,rth SOLVE etc...  There is no reason to issue bfcum in this work flow.

[Alex1EDP]

Thank you for your help, Dave! I was forced to interrupt my analysis but i am back on track now.

I have successfully implemented the workflow you suggested.

However, the problem of the thermal load remains, what I would like to apply as a thermal load is the delta temperature between step (i) and step (i-1), and obtain the corresponding structural response.

I can obtain these results in the linear elastic problem using the above workflow and subtracting the displacements between load steps, but when I in the nonlinear analysis this will be an issue.

Thank you for your help.

[dlooman]

What's does applying the deltaT between load steps as a structural temperature load represent?  I've never heard of doing that.

[Alex1EDP]

I am analysing the structural response of a dam when the applied action is the air temperature. 

I want to obtain the displacements that occur in the dam body through time and compare them to the actual displacements measured in real life.

In order to do this i must apply the variation of the temperature between two dates (load steps).

[dlooman]

I think that would be better done with postprocessing.  It's easy to subtract the displacement at one load step from another.