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What is the difference between boundary and domain when assigning materials?

Posted Nov 7, 2012, 10:52 a.m. EST MEMS & Nanotechnology, MEMS & Piezoelectric Devices Version 4.3a 3 Replies

Mahatasin Azad
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Hi, I'm new to comsol and the answer maybe obvious to some of you, but here's my situation. I want to design a piezoresistive sensor. In the model library, there is a similar sensor example where the piezoresistive material is applied to a boundary. But I don't understand why. To my understanding, it should be assign to a domain.

I will also appreciate if anybody has a link to a site describing the differences.


Thanks,
Mahatasin
3 Replies Last Post Nov 8, 2012, 5:36 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 7, 2012, 1:16 p.m. EST
Hi

its important to understand the COMSOl notation of geoemtry (volume, surfaces, lignes and points) and processed "Entities" Domains, Boundaries, and if applicable edges and points. AAll for respective 3D,2D,1D,0D objects

Now when you deal with PDEs for physics, these are defined on domains (volumes in 3D, surfaces in 2D ...) surrounded by Boundaries (surfaces in 2D, edges in 2D, ...) and by defining the Physics on the DOMAINS, and the Boundary conditions (Dirichlet or neumann or mixed) on the Boundaries you get to link "physics to PDE math" and you can solve the model correspondingly.

It's worth to read carefully (a few times) the doc, in the beginning its tough withmany new concepts and notations, ut you will rapidly get used to these.

Starting wth models, pick the simple ones with one physics at the time, then later mix 2,3 etc physics, but one at the time.

Welcome to the "club" and have fun Comsoling

--
Good luck
Ivar
Hi its important to understand the COMSOl notation of geoemtry (volume, surfaces, lignes and points) and processed "Entities" Domains, Boundaries, and if applicable edges and points. AAll for respective 3D,2D,1D,0D objects Now when you deal with PDEs for physics, these are defined on domains (volumes in 3D, surfaces in 2D ...) surrounded by Boundaries (surfaces in 2D, edges in 2D, ...) and by defining the Physics on the DOMAINS, and the Boundary conditions (Dirichlet or neumann or mixed) on the Boundaries you get to link "physics to PDE math" and you can solve the model correspondingly. It's worth to read carefully (a few times) the doc, in the beginning its tough withmany new concepts and notations, ut you will rapidly get used to these. Starting wth models, pick the simple ones with one physics at the time, then later mix 2,3 etc physics, but one at the time. Welcome to the "club" and have fun Comsoling -- Good luck Ivar
Mahatasin Azad
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Posted: 1 decade ago Nov 8, 2012, 4:35 p.m. EST

It's worth to read carefully (a few times) the doc, in the beginning its tough withmany new concepts and notations, ut you will rapidly get used to these.

--
Good luck
Ivar


Hi, thanks for your reply. I was wondering which document you meant? is a document in help directory?


Thanks,
Mahatasin
[QUOTE] It's worth to read carefully (a few times) the doc, in the beginning its tough withmany new concepts and notations, ut you will rapidly get used to these. -- Good luck Ivar [/QUOTE] Hi, thanks for your reply. I was wondering which document you meant? is a document in help directory? Thanks, Mahatasin
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago Nov 8, 2012, 5:36 p.m. EST
Most of the time in 3D equations are solved on volumes, and in that case you only need to apply materials to the domains in question.
In some cases though you want to solving an equation on a boundary, in which case you may need to assign material properties to that boundary.

Think for instance of a situation where you have heat transfer between two solid objects separated by thin resistive layer. You would want to define a material on the domains (i.e. the solid objects) and another material on the boundary (for the thin layer). See the attached model: Teflon is assigned to the internal boundary, Titanium to the two cubes.

There are many similar situations with other physics where thin layers are modeled as surfaces that need to be assigned material properties independently of the material properties of the surrounding solids.

Similarly, you can also assign material properties to edges and points.
Most of the time in 3D equations are solved on volumes, and in that case you only need to apply materials to the domains in question. In some cases though you want to solving an equation on a boundary, in which case you may need to assign material properties to that boundary. Think for instance of a situation where you have heat transfer between two solid objects separated by thin resistive layer. You would want to define a material on the domains (i.e. the solid objects) and another material on the boundary (for the thin layer). See the attached model: Teflon is assigned to the internal boundary, Titanium to the two cubes. There are many similar situations with other physics where thin layers are modeled as surfaces that need to be assigned material properties independently of the material properties of the surrounding solids. Similarly, you can also assign material properties to edges and points.

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