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Using analytical functions

Posted 4 feb 2011, 18:48 GMT-5 Version 4.1 3 Replies

Henry Wong
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Hello,

I have a simple question. I am trying to use analytical functions in COMSOL. However, after I define my function in the model, I can't seem to access it if I put in a variable as the argument.

For instance, suppose that I define a function Cb = t. When I try to input Cb(t) as a term in the boundary conditions, it doesn't seem to work. However, if I say Cb(100), it seems to work, but it's not what I want. I want to be able to use Cb as a function of time.

Thanks,
Henry
3 Replies Last Post 6 feb 2011, 02:52 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 5 feb 2011, 03:26 GMT-5
Hi

how is your variable "t" defined ? Normally for COMSOL "t" is time and if you have no transient solver then t=0 by default.

Try to avoid single lettr variable names for private variables, most of these are already used internally by COMSOL

Unfortunately there is no build-in "variable name conflict help or "detector" " today

--
Good luck
Ivar
Hi how is your variable "t" defined ? Normally for COMSOL "t" is time and if you have no transient solver then t=0 by default. Try to avoid single lettr variable names for private variables, most of these are already used internally by COMSOL Unfortunately there is no build-in "variable name conflict help or "detector" " today -- Good luck Ivar
Henry Wong
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Posted: 1 decade ago 5 feb 2011, 16:55 GMT-5
Hi Ivar,

Yes, I'm trying to run a transient analysis, so "t" is referring to time in my problem. It's just that if I define a function and then try to to evaulate that function at time "t", it doesn't work.

For instance, suppose my function is Cb = t. If I try to access that function as "Cb(t)" in the boundary settings, it doesn't work. If I type in "Cb(100)" or something like that, it works. It I directly put in "t" in the boundary setting, it also works.

Do you have any idea why this is the case?

Thanks,
Henry
Hi Ivar, Yes, I'm trying to run a transient analysis, so "t" is referring to time in my problem. It's just that if I define a function and then try to to evaulate that function at time "t", it doesn't work. For instance, suppose my function is Cb = t. If I try to access that function as "Cb(t)" in the boundary settings, it doesn't work. If I type in "Cb(100)" or something like that, it works. It I directly put in "t" in the boundary setting, it also works. Do you have any idea why this is the case? Thanks, Henry
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 6 feb 2011, 02:52 GMT-5
Hi

what do you mean by not working ?

normally you should write Cb(t[1/s]) to avoid the "orange" unit errors, as operands are to be "unitless", but if "t" is defined = you are running a transient analysis it should work. Strange

--
Good luck
Ivar
Hi what do you mean by not working ? normally you should write Cb(t[1/s]) to avoid the "orange" unit errors, as operands are to be "unitless", but if "t" is defined = you are running a transient analysis it should work. Strange -- Good luck Ivar

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