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vector form variables in PDE

Posted 31 mar 2013, 09:19 GMT-4 Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3a 3 Replies

Waranatha Abeygunasekara
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What is the procedure to specify a dependent variable in PDE interface to be a vector rather than a scalar? In more specific terms, I'm trying to implement the vector wave equation in 3D using the coefficient form PDE. I need to define the dependent variable (u) to be the vector form electric field.
I'm new to the comsol environment and still haven't found this method in the user guide.

Thanks,
Waranatha.
3 Replies Last Post 1 apr 2013, 14:37 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 31 mar 2013, 13:17 GMT-4
Hi

COMSOl calcualtes with scalars, for vectores ou need to define triplets, so when using PDE math nodes, you must add 3 local scalar variables and not just one (vector)

--
Good luck
Ivar
Hi COMSOl calcualtes with scalars, for vectores ou need to define triplets, so when using PDE math nodes, you must add 3 local scalar variables and not just one (vector) -- Good luck Ivar
Waranatha Abeygunasekara
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Posted: 1 decade ago 1 apr 2013, 04:07 GMT-4
Hi Ivar,

Thanks for the information. You have saved me a lot of time, as I was so sure that vector form should be available with comsol, and was trying hard to locate it in the documentation. I have few more questions on the same lines. consider an example where the vector is defined using the Cartesian coordinates and the 3 local scalars represent x,y,z components of the vector.
1. Does the orthogonality between each component need to be enforced manually?
2. What is the procedure for implementing boundary conditions?(can this be done collectively for the group of variables or need to be specified individually? I'm asking this because it is more convenient to define boundary conditions in terms of normal and tangential components at the boundary, rather than the absolute values of x,y,z components at the boundary)
3. Also, do you know of an example where this have been implemented? ( I could not locate anything on these lines in model library)

Thank you.
Waranatha.

Hi Ivar, Thanks for the information. You have saved me a lot of time, as I was so sure that vector form should be available with comsol, and was trying hard to locate it in the documentation. I have few more questions on the same lines. consider an example where the vector is defined using the Cartesian coordinates and the 3 local scalars represent x,y,z components of the vector. 1. Does the orthogonality between each component need to be enforced manually? 2. What is the procedure for implementing boundary conditions?(can this be done collectively for the group of variables or need to be specified individually? I'm asking this because it is more convenient to define boundary conditions in terms of normal and tangential components at the boundary, rather than the absolute values of x,y,z components at the boundary) 3. Also, do you know of an example where this have been implemented? ( I could not locate anything on these lines in model library) Thank you. Waranatha.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 1 apr 2013, 14:37 GMT-4
Hi

by default COMSOL uses a carthesian (orthogonal) coordiante system as its base (only exception 1D and 2D axi)

COMSOL defines the default boundary coordinate system (tag = sys1...) at least in all physics, so why not also in "math" PDE nodes (I'm not by my WS so I cannot check just now)

Normally BC apply to all dependent variables, if you choose 3 PDE's under "_u_" (bold vector "u") you wil lget 3 elements in the BC definitions, make it a try, or just load in a PDE example and open up the Options Properties Equation view ad peek into the equation nodes (lowest level, by default hidden)

--
Good luck
Ivar
Hi by default COMSOL uses a carthesian (orthogonal) coordiante system as its base (only exception 1D and 2D axi) COMSOL defines the default boundary coordinate system (tag = sys1...) at least in all physics, so why not also in "math" PDE nodes (I'm not by my WS so I cannot check just now) Normally BC apply to all dependent variables, if you choose 3 PDE's under "_u_" (bold vector "u") you wil lget 3 elements in the BC definitions, make it a try, or just load in a PDE example and open up the Options Properties Equation view ad peek into the equation nodes (lowest level, by default hidden) -- Good luck Ivar

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