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How is the "time" defined in Comsol?

Posted 12 oct. 2011, 04:49 UTC−4 Heat Transfer & Phase Change, Materials, Parameters, Variables, & Functions Version 4.2 3 Replies

Kai Feldhusen
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Hello.

I would like to create a heat transfer model in which the external temperature increases with time. In this case I defined the external temperature in "heat flux" as "TemperatureExt" and defined this in variable definition as follows:

993.15*(1-exp(-time/tau))[K]

with tau as an defined constant.

But Comsol throws the following exception:

Failed to evaluate variable Jacobian.
- Variable: time
- Geometry: 1
- Boundary: 6

I thought that the intern time in Comsol is called "time", but obviously it isnt. So how it is defined?

Greetings
3 Replies Last Post 12 oct. 2011, 05:42 UTC−4
Edgar Kaiser
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Posted: 1 decade ago 12 oct. 2011, 04:54 UTC−4
Hi,

the time variable is simply 't'.

Cheers
Edgar
Hi, the time variable is simply 't'. Cheers Edgar
Kai Feldhusen
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Posted: 1 decade ago 12 oct. 2011, 05:25 UTC−4
Thanks, but there is still one problem:

The expression "993.15*(1-exp(-t/tau))[K]" is still in yellow with the fault "unexpected unit of input". But I dont see there any fault.

Btw: tau = 57.6055973[1]
Thanks, but there is still one problem: The expression "993.15*(1-exp(-t/tau))[K]" is still in yellow with the fault "unexpected unit of input". But I dont see there any fault. Btw: tau = 57.6055973[1]
Edgar Kaiser
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Posted: 1 decade ago 12 oct. 2011, 05:42 UTC−4
I think t has the unit [s], so giving tau the same unit should make it work.
I think t has the unit [s], so giving tau the same unit should make it work.

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