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Need help in writing a function.

Posted Dec 14, 2011, 9:41 a.m. EST Heat Transfer Version 4.1 3 Replies

Tim Tan
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Hi, i am very new to comsol and i need help in writing a funtion

I have a phase change model and i need variable dynamic viscosity.

The variable dynamic viscosity is input as a piecewise, continuous, second derivative function as follows:
V=10^8 for T<303K
V=0.008 for t > 306K

How do i input as a function?
I would be glad if there is other place where i can learn how to write a function.
Thanks

Tim
3 Replies Last Post Nov 5, 2015, 9:58 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 14, 2011, 10:21 a.m. EST
Hi

I would propose to use an analytical function with a step function and use the "transition zone to go from one level to the next.

But another issue I see is the step size 10^8 to 10-2 which is 10 orders of magnitude change over 3 K temperature difference, I'm afraid you are demanding too much for the binary representation of numbers there, a regular slope of 3E9 : 1 is very tough.

Nevertheless try it, but I suspect some solver issues in view

--
Good luck
Ivar
Hi I would propose to use an analytical function with a step function and use the "transition zone to go from one level to the next. But another issue I see is the step size 10^8 to 10-2 which is 10 orders of magnitude change over 3 K temperature difference, I'm afraid you are demanding too much for the binary representation of numbers there, a regular slope of 3E9 : 1 is very tough. Nevertheless try it, but I suspect some solver issues in view -- Good luck Ivar
Lechoslaw Krolikowski
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Posted: 1 decade ago Dec 14, 2011, 10:24 a.m. EST
Hi,

You can use step function. See documentation, for instance, Introduction to Comsol Multiphysics v.4.1, pp. 30-32.

BR
Andrzej
Hi, You can use step function. See documentation, for instance, Introduction to Comsol Multiphysics v.4.1, pp. 30-32. BR Andrzej
Howie He
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Posted: 9 years ago Nov 5, 2015, 9:58 p.m. EST
Hi, Tim
Have you solved the problem? I come with the same problem with you.
I am a newer in comsol, I don't know how to deal with it.
Could you give me some help?
Howie,
Thanks!
Hi, Tim Have you solved the problem? I come with the same problem with you. I am a newer in comsol, I don't know how to deal with it. Could you give me some help? Howie, Thanks!

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