# Discussion Forum

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## Coordinate system and COMSOL solver

Hi
This may sound silly but I need to understand the basics.
I am bit confused about how COMSOL handles coordinates. I have a circular geometry in 3D, preferably in theory it is usual to use a cylindrical coordinate system (r,theta,z). When I use comsol, the equation is generally expressed in cartesian coordinates. Does it matter to convert it to cylindrical coordinate? I guess comsol solver would eventually convert it back to x,y,z system.

For example, an equation is dependent on the stresses in x,y,z direction but the geometry is a circular. All the equations are in cartesian coordinate. Can some one please explain how comsol handles the equation in this case? I am using SM and heat trasnfer in solids together.

2 Replies Last Post Sep 5, 2013, 6:59 PM EDT
Posted: 5 years ago
Hi

COMSOL calculates all in orthonormal carthesian, but you can define any other coordinate system and refer to the variables, i.e. a first cylindrical coordinate system would typically have its naming sys2.r .phi, .z ...

Note: postprocessing is also by default in carthesian normal system, so there too you need to remap to your given coordinates, depending on what you are looking for

--
Good luck
Ivar

Posted: 4 years ago
Hello Ivar,
This sounds close to what I am looking for..may be this is a fundamental co-ordinate transformation method, but need some help . I have a cylindrical shield geometry with a B field applied from outside in Cartesian co-ordinate system. But I need the Bphi component inside the shield. I have co-ordinates in cylindrical system but couldn't figure out how Bphi to be designated. something like sys2.mf.Bphi ? :(

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