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Set sin function in my heat flux boundary condition

Posted 18.03.2010, 14:27 GMT-4 Heat Transfer & Phase Change Version 3.5a 4 Replies

Ehsan
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Hello Guys,

I do not know how I can set a function in my boundary condition rather than a scalar. I need to define my wall's heat flux as a function of time which is almost like a sin function. I am sure the COMSOL should be able to handle that, but I do not know how!

Thank you

Ehsan
4 Replies Last Post 11.09.2011, 13:57 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 18.03.2010, 17:01 GMT-4
Hi

I would try to multiply the heat source value (amplitude) by a "*sin(2*pi*t)" factor.

But as "t" is only defined in "transient mode" you would get an error message if you switch to back to stationary, without supressing it again.

Good luck
Ivar
Hi I would try to multiply the heat source value (amplitude) by a "*sin(2*pi*t)" factor. But as "t" is only defined in "transient mode" you would get an error message if you switch to back to stationary, without supressing it again. Good luck Ivar
Rock Rockins
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Posted: 1 decade ago 09.09.2011, 16:32 GMT-4
I am trying to change the external temperature as a sinusoidal function of time. The model is in transient mode, yet i still get the unit error when i simply plug in ext. temp = 280*Sin(t).
I also tried to change it from global expression, but still i get the unit mismatch error. How else can i change the external temperature as a sine function?

Appreciate any help. Thanks
I am trying to change the external temperature as a sinusoidal function of time. The model is in transient mode, yet i still get the unit error when i simply plug in ext. temp = 280*Sin(t). I also tried to change it from global expression, but still i get the unit mismatch error. How else can i change the external temperature as a sine function? Appreciate any help. Thanks
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 10.09.2011, 05:32 GMT-4
Hi

the unit mishmthc is that "t" has units [s] and the operator sin() wants unitless values:

hence you shoud either write a[m]=a0[m]*sin(2*pi*f[Hz]*t[s]) without necessarily all units if already defined
or just sin(t[1/s]) to be unitless

--
Good luck
Ivar
Hi the unit mishmthc is that "t" has units [s] and the operator sin() wants unitless values: hence you shoud either write a[m]=a0[m]*sin(2*pi*f[Hz]*t[s]) without necessarily all units if already defined or just sin(t[1/s]) to be unitless -- Good luck Ivar
Rock Rockins
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Posted: 1 decade ago 11.09.2011, 13:57 GMT-4
Thanks. It worked.
Thanks. It worked.

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