field dependent material data

Hello Team,

I'm trying to model a time dependent thermal conductivity material by specifying thermal conductivity using TBFIELD command. The model has 3 link elements and I solved transient run for 6 sub-steps.

After looking the output of the stiffness matrix for every substep, I see that they are not changing.

I'm not sure if my input for TBFIELD is correct, although the output echo of the command didn't give any errors.

I have attached the input to reproduce the issue. Could you please take a look into this issue and let me know if time dependent KXX is correctly accounted.


Thanks

Vinod


Best Answer

  • akhemkaakhemka Forum Coordinator
    Accepted Answer

    Hi @vinod ,


    Based on a response to a similar question - Material properties can only be temperature-dependent. They cannot be dependent on any other variables. We do not have any examples of time-dependent thermal conductivity but there may be two possible approaches that you could try. They are not simple but they might work.

    1. If the temperature is time-dependent you could trick the solver by defining a temperature-dependent conductivity that was equivalent to a time-dependent conductivity.

    2.In MAPDL set-up a table that relates conductivity to time. Within the /SOLU module define the thermal conductivity for each solution time using the table. You will not be able to use automatic time stepping and the solver will probably issue a warning message about defining material properties within the solution module but it should let you do it. In Mechanical you would need to use MAPL commands within a Command Object.


    Regards,

    Ashish Khemka

Answers

  • akhemkaakhemka Forum Coordinator
    Accepted Answer

    Hi @vinod ,


    Based on a response to a similar question - Material properties can only be temperature-dependent. They cannot be dependent on any other variables. We do not have any examples of time-dependent thermal conductivity but there may be two possible approaches that you could try. They are not simple but they might work.

    1. If the temperature is time-dependent you could trick the solver by defining a temperature-dependent conductivity that was equivalent to a time-dependent conductivity.

    2.In MAPDL set-up a table that relates conductivity to time. Within the /SOLU module define the thermal conductivity for each solution time using the table. You will not be able to use automatic time stepping and the solver will probably issue a warning message about defining material properties within the solution module but it should let you do it. In Mechanical you would need to use MAPL commands within a Command Object.


    Regards,

    Ashish Khemka

  • Hello Ashish,

    I was presuming that TB based commands apply for all the field types defined under TBFIELD. Also I was seeing the examples of TB,ELASTIC and TB,SDAMP, along with this below example in the help where in they leverage the field type. Additionally I could also see few examples where they define frequency as the field

    TB,ELASTIC,1
     
    TBFIELD,XCOR,0.0
    TBFIELD,YCOR,1.0
    

    So I was wondering why TIME is not accounted although its valid field under TBFIELD

    For the step-2 which you suggested, how is the table setup? Are you referring to the custom table using *DIM?

    Thanks

    Vinod

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