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September 3, 2010 3:29pm UTC

Definition of normal vector of the boundaries in COMSOL

Hello, everyone,

When I did powerflow integration on some boundary, the sign of the outflow is positive or negative which can not be explained by myself.
The outflow power defined (eg. in RF) : nPo_rfw=nx_rfw*Pox_rfw+ny_rfw*Poy_rfw+nz_rfw*Poz_rfw. It is defined as the scalar product of the power flow and the normal vector to the boundary.
However, I am totally confused about the definition of the normal vector of a plane boundary in COMSOL.
For example , an plane x=-0.1, the normal vector should be [1 0 0],right?
If it is like that, can you explain me eg. in the library model: waveguide_hbend_3d
The normal vector of boundary 1 is [1 0 0] or [-1 0 0], why the outflow power on boundary 1 is negative?
How can I plot normal vector nx_rfw, ny_rfw, nz_rfw inside GUI?
I want to check the sign of the normal vector. If I type this directly in the plot parameter, It does not show the value.

Can anyone explain me a little bit?

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September 4, 2010 7:14am UTC in response to Wei Tang

Re: Definition of normal vector of the boundaries in COMSOL

Hi

the normal direction are defined wrt the body/domain, it points normally "outward" from a closed volume ("up") and if you define a plane you need to say where is the geoemtrical entity of higher value (volume for a plane, surface for an edge, but a point has a singularity w.r.t normal ;) to define the outward ("up") direction ofthe normal.

Just a plane has two directions for a normal, they are opposite, you need to define a sign convention, in Comsol its normally + is outward away from the closed body

But indeed use the arrow plots to see, visualise nx,ny.nz or any other vector

Hope this helps
--
Good luck
Ivar

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