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How to implement definite integral on Boundary integration variables

Posted Oct 5, 2012, 3:17 p.m. EDT Version 3.5a 3 Replies

Selcuk Atalay
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Dear All,

I am trying to integrate the nr unit vector along a sphere on 2D axial symmetric model. My aim is to find force acting on the sphere and when I type to the boundary integration variable, nr*2*pi*r, it gives me wrong number in r-direction.

nr is changing wrt pi. I need to define a definite integral which change from 0 to pi and pi to two pi. How can I do that?

Thank you,

Best Regards,

SA
3 Replies Last Post Oct 11, 2012, 1:23 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 6, 2012, 5:20 p.m. EDT
Hi

I'm not sue I fully catch you, normally if you have a sphere in 2D-axi, its represented by a half circle in the projection plane, and by selecting this half circle nd integrating "nr" along it you get 2*r as expected, if you want the "sphere component" you check the integration Compute surface integral that basically adds an implicit "2*pi*r" component to your integral to count for the 2D-axis "loop length"

Now I have only 4.3 active but it ws there in v3.5 too

--
Good luck
Ivar
Hi I'm not sue I fully catch you, normally if you have a sphere in 2D-axi, its represented by a half circle in the projection plane, and by selecting this half circle nd integrating "nr" along it you get 2*r as expected, if you want the "sphere component" you check the integration Compute surface integral that basically adds an implicit "2*pi*r" component to your integral to count for the 2D-axis "loop length" Now I have only 4.3 active but it ws there in v3.5 too -- Good luck Ivar

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Selcuk Atalay
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Posted: 1 decade ago Oct 10, 2012, 11:38 a.m. EDT
Hi,

Thank you for your emai.

Could you please explain me how can I define a definite integral on the Boundary integration variables?

For example from 0 to pi the "nr " is "nr " and from pi to 2*pi "nr " is "-nr" around z-axis of the sphere 2D axial.

This is the point I could not implement on Comsol.

Thank you,

Regards,

ODU
Hi, Thank you for your emai. Could you please explain me how can I define a definite integral on the Boundary integration variables? For example from 0 to pi the "nr " is "nr " and from pi to 2*pi "nr " is "-nr" around z-axis of the sphere 2D axial. This is the point I could not implement on Comsol. Thank you, Regards, ODU
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 11, 2012, 1:23 a.m. EDT
Hi

I'm not sure I follow you, in a cylindrical coordinate system (r,phi,z) w.r.t. (x,y,z) the normal to acylindrical surface aligne on the coordinate axis has a nr scalar value of 1 all around the loop it points outwards (in the (r,phi,z) reference, the "-1" comes from the phi variation and the sin(phi) relation when you project it onto the (x,y,z) reference, but then nz has also three (x,y,z) componets that vary over any edge.

If you integrate in 2D-axi "nr" (2*pi*r*nr if you turn on the feature to integrate surfaces as edges, where 2*pi*nr is the loop length) you should get your result no ?

--
Good luck
Ivar
Hi I'm not sure I follow you, in a cylindrical coordinate system (r,phi,z) w.r.t. (x,y,z) the normal to acylindrical surface aligne on the coordinate axis has a nr scalar value of 1 all around the loop it points outwards (in the (r,phi,z) reference, the "-1" comes from the phi variation and the sin(phi) relation when you project it onto the (x,y,z) reference, but then nz has also three (x,y,z) componets that vary over any edge. If you integrate in 2D-axi "nr" (2*pi*r*nr if you turn on the feature to integrate surfaces as edges, where 2*pi*nr is the loop length) you should get your result no ? -- Good luck Ivar

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