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define heat capacity as a functin of temperature
Posted 2011/02/18 9:49 GMT-5 Heat Transfer & Phase Change 4 Replies
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Hi:
I'm trying to define my specific heat capacity as a function of temperature in V4.0, say
Cp = Cp1 for T < 400 K
Cp = Cp2 for T >= 400K
I've tried the Cp1*(T<400 ) and heaviside functions, but Comsol kept on failing to solve for the variable,
anyone can help ???
thanks
Spencer
I'm trying to define my specific heat capacity as a function of temperature in V4.0, say
Cp = Cp1 for T < 400 K
Cp = Cp2 for T >= 400K
I've tried the Cp1*(T<400 ) and heaviside functions, but Comsol kept on failing to solve for the variable,
anyone can help ???
thanks
Spencer
4 Replies Last Post 2011/02/21 18:06 GMT-5
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Posted:
1 decade ago
Hi
Have you tried to interpolate on a list of numerical data with a function ?
--
Good luck
Ivar
Have you tried to interpolate on a list of numerical data with a function ?
--
Good luck
Ivar
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Posted:
1 decade ago
Hi
Have you tried to interpolate on a list of numerical data with a function ?
--
Good luck
Ivar
dear Ivar,
thanks for your advice, i've done two interpolation functions and they seem to be working.
however there seems to be a problem, it used to take abt 10mins to run a simulation and now it's taking hours if not days, ( it's actually still running at this very moment ), is this normal ??
thanks so much !
Spencer
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Posted:
1 decade ago
Hi
could be, but it is really difficult to say like that. Normally if you replace a constant material parameter by a temperature or pressure dependent one, and that T and/or p are part of you simulation you are getting a non-linear probelem, that might need to iterate several times to find a valid solution.
So you must check the convergence of the solver, often following the results with a probe or a useful plot helps to identify if the system converges or are just running away.
It is clear that a few hours running, in blind, is not very encourraging. You might STOP the solver look at th results and RESTART from current location. This might also help the convergence, some times
--
Good luck
Ivar
could be, but it is really difficult to say like that. Normally if you replace a constant material parameter by a temperature or pressure dependent one, and that T and/or p are part of you simulation you are getting a non-linear probelem, that might need to iterate several times to find a valid solution.
So you must check the convergence of the solver, often following the results with a probe or a useful plot helps to identify if the system converges or are just running away.
It is clear that a few hours running, in blind, is not very encourraging. You might STOP the solver look at th results and RESTART from current location. This might also help the convergence, some times
--
Good luck
Ivar
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Posted:
1 decade ago
did you try the if operator?
you could define Cp as a variable:
Name: Cp
Expression: if(T<400,Cp1,Cp2)
you could define Cp as a variable:
Name: Cp
Expression: if(T<400,Cp1,Cp2)