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Can we remove the limitaion of largest geometry to smallest geometry ratio in comsol with matlab coding

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Dear All,

I have to work with nano size geometries. To get accurate results I do need to enclose them in a large geometry. But this coudnot be done in comsol as it giving an error in recognizing boundary condition. The reason was explained by Mr Ivar early to me. I would like know whether it is possible to do such a thing with matlab help. ( I am working with comsol 3.5a. But I have 4.0 also). The other trouble is that I could not use a fine mesh with these small geometries. In order to move my work I need a solution for these. So I am greatly appreciating if one could give me a support. Please be kind enough to help me.

Thank You.
Manjula

1 Reply Last Post Dec 2, 2010, 12:18 PM EST
Ivar Kjelberg CSEM SA (CH)

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Posted: 1 decade ago Dec 2, 2010, 12:18 PM EST
Hi
There is NO true limitations in the absolute size so long the size ratio remains reasonnable (I seldom set up models with size ratios greater than 1:10'000) but 1 could be 1[nm] as it can be 1[km]

For the geometry you must check your geometry relative and absolute tolerances, depending on the version they appear at different places, in the geometry, repair or import section, as well in the defeaturing section.

In v4 (I strongly suggest that you rapidly get hands on the latest v4.1) you can also change the scaling of the geometry (not the calculations) from the default 1[m] to 1[nm] to ease the model set-up.

Thereafter for the solver, normally it takes into account most scaling issues automatically for you such that all variables arrive close to 1, depending on what you are doing, you might need to scale by hand, but this is normally only for exotic cases, mostly you do not encounter such cases as a beginner (or shold not, it's better to learn the essentials first, there are anough buttons to tweak like that ;)
--
Good luck
Ivar
Hi There is NO true limitations in the absolute size so long the size ratio remains reasonnable (I seldom set up models with size ratios greater than 1:10'000) but 1 could be 1[nm] as it can be 1[km] For the geometry you must check your geometry relative and absolute tolerances, depending on the version they appear at different places, in the geometry, repair or import section, as well in the defeaturing section. In v4 (I strongly suggest that you rapidly get hands on the latest v4.1) you can also change the scaling of the geometry (not the calculations) from the default 1[m] to 1[nm] to ease the model set-up. Thereafter for the solver, normally it takes into account most scaling issues automatically for you such that all variables arrive close to 1, depending on what you are doing, you might need to scale by hand, but this is normally only for exotic cases, mostly you do not encounter such cases as a beginner (or shold not, it's better to learn the essentials first, there are anough buttons to tweak like that ;) -- Good luck Ivar

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