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Cylindrical coordinate system in boundary conditions

Posted Feb 20, 2012, 9:01 a.m. EST Version 4.2a 3 Replies

Francesca Messina
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Hi all,

I am using the laminar flow module in COMSOL 4.2a.
I included a cylindrical coordinate system and now I would like to use it in the boundary conditions of the laminar flow module (for example the inlet fluid components alond sys2.r and sys2.rho) but I can't.
I read on the user guide that "If the frame type does not match the one used by the physics interface, the coordinate system does not appear in the physics interface’s Coordinate system lists".
But what does it mean? What I must do?

Thanks

Francesca

3 Replies Last Post Feb 21, 2012, 4:45 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 20, 2012, 11:16 a.m. EST
Hi

COMSOL has mainly 4 coordinate systems: Spatial, Marterial, Mesh and Geometric. For many physics these are the same, for some, such as solid or CFD the spatial and material split up, for CFD and ALE the materail and Mesh might split up, and for DG physics (deformed geoemtry) the Geoemtric Frame takes it s only life ...

If you open a fresh new COMSOL in 2D or 3D and add e.g. HT physics and hit Finish + Definitions + Coordinate Systesm cylindrical Systems and you there look at the frames proposed, you see all four, but all with lower case x,y,z letter in the coordinate names (indicating they are all the same)

If you now delete the HT physics and add "solid" an hit Finish. Now you see that the spatial frame is in lower case, but both material and the two others are in upper case, the spatial frame is differentiated (normally it's (x=X+u) but from what I understand, since v4.2a, the numerical output x=X+u is only given to us if we turn on the Solver Include geoemtric non-linearity (for that you need to adda solver node that I havnt proposed so far)

I have added a few exercices I have done for myself herby

Now when you define BCs you must decide on which frame you apply them, if you apply to the spatial frame you should normally include the solution and you get a non linear problem, therefore e.g. in Solid you have uX and not ux as the forst derivative of the displacement field along X

So you might need to define your coordinate frame as MAterial, rather than spatial, or the inverse, depening on what you want to do

--
Good luck
Ivar
Hi COMSOL has mainly 4 coordinate systems: Spatial, Marterial, Mesh and Geometric. For many physics these are the same, for some, such as solid or CFD the spatial and material split up, for CFD and ALE the materail and Mesh might split up, and for DG physics (deformed geoemtry) the Geoemtric Frame takes it s only life ... If you open a fresh new COMSOL in 2D or 3D and add e.g. HT physics and hit Finish + Definitions + Coordinate Systesm cylindrical Systems and you there look at the frames proposed, you see all four, but all with lower case x,y,z letter in the coordinate names (indicating they are all the same) If you now delete the HT physics and add "solid" an hit Finish. Now you see that the spatial frame is in lower case, but both material and the two others are in upper case, the spatial frame is differentiated (normally it's (x=X+u) but from what I understand, since v4.2a, the numerical output x=X+u is only given to us if we turn on the Solver Include geoemtric non-linearity (for that you need to adda solver node that I havnt proposed so far) I have added a few exercices I have done for myself herby Now when you define BCs you must decide on which frame you apply them, if you apply to the spatial frame you should normally include the solution and you get a non linear problem, therefore e.g. in Solid you have uX and not ux as the forst derivative of the displacement field along X So you might need to define your coordinate frame as MAterial, rather than spatial, or the inverse, depening on what you want to do -- Good luck Ivar

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 20, 2012, 11:19 a.m. EST
Hi
Here is the other one

By the way I can only recommend the excellent, brand new, book of E.B. Tadmor, R.E. miller and R.S. Elliot " Continuum Mechanics and Thermodynamics" CUP, 2012, ISBN978-1-107-00826-7.
Among other chapter 3.3 "Material and Spatial field description"

The book by itself, even if not referring to COMSOL directly, is excellent and has a clear mathamatical notation, idem for the physics, all explained in details and that is from what I reead so far the best and closest book to COMSOL notation I have found so far.
I have just ordered the other book in the series on "Modelling Materials" CUP 2011, hoping its of the same caliber ;)

--
Good luck
Ivar
Hi Here is the other one By the way I can only recommend the excellent, brand new, book of E.B. Tadmor, R.E. miller and R.S. Elliot " Continuum Mechanics and Thermodynamics" CUP, 2012, ISBN978-1-107-00826-7. Among other chapter 3.3 "Material and Spatial field description" The book by itself, even if not referring to COMSOL directly, is excellent and has a clear mathamatical notation, idem for the physics, all explained in details and that is from what I reead so far the best and closest book to COMSOL notation I have found so far. I have just ordered the other book in the series on "Modelling Materials" CUP 2011, hoping its of the same caliber ;) -- Good luck Ivar

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Francesca Messina
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Posted: 1 decade ago Feb 21, 2012, 4:45 a.m. EST
Thank you so much for your response and your helpfulness!

Francesca
Thank you so much for your response and your helpfulness! Francesca

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