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about "the direction of the normal component on interior boundaries"

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I see such kind of introduction about the direction of the normal component on interior boundaries:

In ID:
- unx, the outward unit normal seen from the upper domain
- dnx, the out ward unit normal seen from the lower domain

1) What's the meaning of upper/ lower domain? For example, if I draw two domains, domain 1 and domain 2, the upper domain is domain 1 and the lower is domain 2 (judged according to the domain number)?

2) If (1) is correct, what's the meaning of "seen from the upper / lower domain"? For example, "the outward unit normal seen from the upper domain (domain 1)" refers to the outward unit normal pointing out from the lower domain (domain 2) ?

2 Replies Last Post 31.01.2011, 10:22 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 31.01.2011, 01:18 GMT-5
Hi

I understand it as :

see from current domain: "up" is "outward" of current domain, "down" is "inward",

hence up for one of two ajacent domains is down for the other

--
Good luck
Ivar
Hi I understand it as : see from current domain: "up" is "outward" of current domain, "down" is "inward", hence up for one of two ajacent domains is down for the other -- Good luck Ivar

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Posted: 1 decade ago 31.01.2011, 10:22 GMT-5

Hi

I understand it as :

see from current domain: "up" is "outward" of current domain, "down" is "inward",

hence up for one of two ajacent domains is down for the other

--
Good luck
Ivar


Hi, thank you!
I see, in the example of freeze-drying of comsol 3.5a, a variable, named Q_s, defined as down(fluxz_ht)*dnz+down(fluxy_ht)*dny+down(fluxx_ht)*dnx
so, if "down" is "inward" of current domain, how did comsol know which domain is current domain?

by the way, it is quite difficult to understand this part just reading the user's guide.
[QUOTE] Hi I understand it as : see from current domain: "up" is "outward" of current domain, "down" is "inward", hence up for one of two ajacent domains is down for the other -- Good luck Ivar [/QUOTE] Hi, thank you! I see, in the example of freeze-drying of comsol 3.5a, a variable, named Q_s, defined as down(fluxz_ht)*dnz+down(fluxy_ht)*dny+down(fluxx_ht)*dnx so, if "down" is "inward" of current domain, how did comsol know which domain is current domain? by the way, it is quite difficult to understand this part just reading the user's guide.

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