Defining / Plotting variables

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James Gear

James Gear

October 1, 2013 2:05pm UTC

Defining / Plotting variables

Hi there,

I've recently started trying to use comsol 4.0a (I'm fairly familiar with 3.5a) and I'm finding it extremely confusing. What I'm trying to do is solve a system with an incident electric field (in a waveguide-like geometry), then use some integrated boundary values of said system to calculate some properties (eg. effective permittivity).

I can do this easily in 3.5a, but in 4.0a the process seems entirely different. In 3.5a I just defined all my variables in the global variables section, solved the system and then went to postprocessing->Global variables plot. I found no such process in 4.0a, I can declare variables, but not plot them and I can't find any way to link my global variables to a data set, infact I can't even see how to solve the system! I realise I'm asking a lot, but after several days of sifting through the COMSOL userguide and COMSOL itself I'm no closer to a solution and my enthusiasm for this (admittedly very powerful) software is beginning to wane. Any help would be much apreciated.

Thanks,
James Gear

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Edgar J. Kaiser

Edgar J. Kaiser
Certified Consultant
emPhys Physical Technology

October 1, 2013 7:30pm UTC in response to James Gear

Re: Defining / Plotting variables

James,

to some degree I can understand your frustration because it is a huge step from 3.5 to the 4.x versions. The concept is really very different and it took me a while to get familiar with it.
However, don't give up, because in the end you will love it. The new user interface is far more productive and powerful than the old one.
My recommendation would be to attend one of COMSOL's training courses for the 4.x versions. This will save you a lot of time for trial and error. And I would recommend to update to the latest version. The 4.0 versions had their problems.
Regarding variables you can also define variables under the Model > Definitions node and there you have all the model couplings available.
These variables and globally defined ones as well are then available for post processing after you solve the model.
It is a bit difficult to directly assist with your model because I don't have 4.0a available any more and probably few people will.
I hope this could help and motivate a little.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology

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James Gear

James Gear

October 2, 2013 10:18am UTC in response to Edgar J. Kaiser

Re: Defining / Plotting variables

Hi Edgar,

Thanks for the reply. I'm now starting to get to grips with the newer versions, using the studies and results sections and so forth. I apologise for my dramatic post yesterday, I was having a less than ideal day and learning how to use COMSOL all over again (after spending months learning how to use 3.5a) was a daunting prospect.

Actually, one of the main reasons I've started using the 4.x versions is that in 3.5a I kept having meshing problems. If I just initialised the mesh, the mesh on opposite boundaries of my waveguide were different, so when I tried to solve for the field I got these wierd effects due to the mesh not being alligned. The only way to get rid of it was to manually copy the boundary meshes one at a time (which was rather tedious). Do you know if this is something that was fixed in the later releases or am I likely to have a similar problems with the 4.x versions?

Many thanks,
James

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Edgar J. Kaiser

Edgar J. Kaiser
Certified Consultant
emPhys Physical Technology

October 2, 2013 11:02am UTC in response to James Gear

Re: Defining / Plotting variables


Hi James,

I would recommend to try structured and swept meshes in a waveguide. This gives you full control over the mesh structure and size.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

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James Gear

James Gear

October 3, 2013 9:12am UTC in response to Edgar J. Kaiser

Re: Defining / Plotting variables

Hi Edgar,

Using the swept mesh helps a lot, thank you! I'm still having a few problems with my fields but I very much appreciate the advice.

Thanks again,
James

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