1 (edited by johnnyontheweb 12-02-2018 12:03:34)

Topic: Thermal analysis sample

Dear all,
I need to perform a thermal analysis in which conductivity, specific heat and mass density should vary with termperature (as required for example in European codes for fire-resisting structures).

I cannot find a suitable example, I'm wondering if it is possible with the current OOFEM code.
Can anyone give some hints? thanks

2

Re: Thermal analysis sample

Hi,
this is basically a nonlinear thermal transport problem.What you need is to define a new material model, nonlinear, that is capable of
-evaluating heat fluxes based on actual temperature gradient
-evaluating the [tangent] conductivity, capacity
the rest should work  using transienttransport engineering model.

3 (edited by johnnyontheweb 23-03-2018 00:23:03)

Re: Thermal analysis sample

Thanks Borek for the reply. So, actually with the already included material it is not possible.
Simply, the base conductivity and specific heat properties should be scaled by a piecewise function.

4 (edited by johnnyontheweb 08-12-2018 19:39:12)

Re: Thermal analysis sample

After a while, I'm again on this. I seems from the isoheatmat code that I could set conductivity.dvType to be DV_FunctionReferenceType, and conductivity.fReference to the function I need (Temperature vs. conductivity).

The same for capacity and mass. Is this approach correct? In any case, I need to set the function number from the IsoHeat line in input, or there's another way? I see from the code that fReference has never been used.

EDIT: I used another dvType enum entry, in order to use normalized functions.

5

Re: Thermal analysis sample

Hi,
yes, for isoheat material this is possible. The conductivity and capacity can be functions of temperature and time.
The input can have following form:
*   simple double (constant) value,
*   simple expression, that is evaluated by internal parser and that can depend on any number of variables, which are defined by calling context (in your case you can use 't' for time and 'te' for actual temperature).
*   reference to a function, defined in input file and maintained by corresponding Domain.

The scalar functions can replace constant variables in many places. The advantage is that they are naturally supported by
input readers (simple values are formatted as usual, simple expressions are enclosed in '$', references to external functions
are formatted as @i, where i is the number of corresponding external function).
For an example, refer to tmpatch46.in (uses external function)

Borek