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about the "down()" in comsol 3.5a and 4.0

Posted 2011/01/30 0:08 GMT-5 Version 4.0 5 Replies

Xiaoyi Yu
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When I read the example "freeze-drying", I saw such kind of expression (the physic is heat conduction)
Q_s=down(fluxz_ht)*dnz+down(fluxy_ht)*dny+down(fluxx_ht)*dnzx
I think it is used to calculate the heat flux

However, this example is solved in comsol 3.5a
When I input the same expression above in comsol 4, the error happened, as follows

Failed to evaluate operator dependencies.
- Operator: down
- Geometry: 1
- Domain: 1

Why?
comsol4 doesn't know "down"? then what's the corresponding one?
5 Replies Last Post 2011/02/03 13:08 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011/01/30 3:25 GMT-5
Hi

I believe the down() operator is as before its the variable naming that has changed. Check the operators in the 4.1 COMSOL user guide p77 under "Special Operators"

its probably something like (if you have rebuild from scratch in v4)

fluxz_ht => ht.fluxz

Turn on the "equations view", see under Preferences to help to identify the new namings



--
Good luck
Ivar
Hi I believe the down() operator is as before its the variable naming that has changed. Check the operators in the 4.1 COMSOL user guide p77 under "Special Operators" its probably something like (if you have rebuild from scratch in v4) fluxz_ht => ht.fluxz Turn on the "equations view", see under Preferences to help to identify the new namings -- Good luck Ivar
Xiaoyi Yu
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Posted: 1 decade ago 2011/02/02 16:14 GMT-5

Hi

I believe the down() operator is as before its the variable naming that has changed. Check the operators in the 4.1 COMSOL user guide p77 under "Special Operators"

its probably something like (if you have rebuild from scratch in v4)

fluxz_ht => ht.fluxz

Turn on the "equations view", see under Preferences to help to identify the new namings



--
Good luck
Ivar


Thank you, Ivar!
in v4, it is ht.dfluxz (I don't know why there is a "d" before fluxz)
What are these? built-in variables? Are there introductions about them in doc?
Thank you!
[QUOTE] Hi I believe the down() operator is as before its the variable naming that has changed. Check the operators in the 4.1 COMSOL user guide p77 under "Special Operators" its probably something like (if you have rebuild from scratch in v4) fluxz_ht => ht.fluxz Turn on the "equations view", see under Preferences to help to identify the new namings -- Good luck Ivar [/QUOTE] Thank you, Ivar! in v4, it is ht.dfluxz (I don't know why there is a "d" before fluxz) What are these? built-in variables? Are there introductions about them in doc? Thank you!
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011/02/03 6:24 GMT-5
Hi

I'm not by my Comsol station (waiting for flight) so I cannot tell exactly, but if I rememer right you have the d&u flux terms. Index your pdf doc and try a serch, but I'm not sure that all variables have been written out yet in the doc, as they were in the 3.5a doc. Note 4.1 doc is far more precise than 4.0

--
Good luck
Ivar
Hi I'm not by my Comsol station (waiting for flight) so I cannot tell exactly, but if I rememer right you have the d&u flux terms. Index your pdf doc and try a serch, but I'm not sure that all variables have been written out yet in the doc, as they were in the 3.5a doc. Note 4.1 doc is far more precise than 4.0 -- Good luck Ivar
Magnus Ringh COMSOL Employee

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Posted: 1 decade ago 2011/02/03 6:49 GMT-5
Hi,

To get a description and definition of a variable, check the Variables list in the Settings window for the Equation View node under the main Heat Transfer node (requires that the Equation View is activated from the View menu, which is the downward-pointing triangle in the upper-right corner of the Model Builder window):

ht.dfluxz is the "Conductive heat flux, z component".

In general, the "d" prefix is for conductive heat flux, the "a" prefix is for the convective (advective) heat flux, and the "t" prefix is for the total heat flux (essentially the sum of the convective and conductive heat fluxes).

Best regards,
Magnus Ringh, COMSOL
Hi, To get a description and definition of a variable, check the Variables list in the Settings window for the Equation View node under the main Heat Transfer node (requires that the Equation View is activated from the View menu, which is the downward-pointing triangle in the upper-right corner of the Model Builder window): ht.dfluxz is the "Conductive heat flux, z component". In general, the "d" prefix is for conductive heat flux, the "a" prefix is for the convective (advective) heat flux, and the "t" prefix is for the total heat flux (essentially the sum of the convective and conductive heat fluxes). Best regards, Magnus Ringh, COMSOL
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011/02/03 13:08 GMT-5
Hi

Thanks Magnus, indeed the equations description is very usefull, could even be better if we could sort the variables alphabetically and copy the names to the clipboard to paste them further down in the postprocessing nodes

--
Good luck
Ivar
Hi Thanks Magnus, indeed the equations description is very usefull, could even be better if we could sort the variables alphabetically and copy the names to the clipboard to paste them further down in the postprocessing nodes -- Good luck Ivar

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