vtk file question

How to use openEMS. Discussion on examples, tutorials etc

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agmj117
Posts: 2
Joined: Tue 27 Mar 2012, 09:28

vtk file question

Post by agmj117 » Tue 27 Mar 2012, 10:10

Hi,

I am a beginner of the Electromagnetic simulation and I'm just began to learn FDTD.So there are some silly questions to ask you. :D
I saw the vtk file(Tutorials / horn antenna) use the Parawell,But I don't understand why It can get the shape like this:
Image
Why not extensions to Infinity? Is this because the absorbing boundary conditions?
Best regards
Liu

Youry
Posts: 51
Joined: Wed 22 Feb 2012, 12:50

Re: vtk file question

Post by Youry » Tue 27 Mar 2012, 10:41

Hello,

I am also new in openEMS and paraview, so my help is probably useless and maybe wrong...

Here what we see is the far field emission pattern of an horn antenna... So I don't understand why you speak/think about an infinite extension... ?
The figure simply show for example, that in the axis of antenna the fields is maximal, no infinite value can be obtain on antenna diagram. We see secondary maximum for particular theta/phi value and so one...

If I understand, the near field is compute thanks fdtd calculation, (from the guide to the 'output') then a function is call to find the far field (propagating field term) from the near fields (I am not sure that FDTD is needed at this step, I don't think so).
It probably allow use to have a small box calculation surrounding the antenna, and then the near2farfield give the useful result... It is good to save many cell (because we don't need very large calculation area in order to remove the non-propagating term of the field)...

I Hope I help little bit, moreover I think it is already to much difficult to deal with this example if you start.
I decide to download openEMS thank to this image, because I want to simulate an Horn-antenna also, but calculation failed at the end because of my limited memory (I think)...

agmj117
Posts: 2
Joined: Tue 27 Mar 2012, 09:28

Re: vtk file question

Post by agmj117 » Tue 27 Mar 2012, 11:24

Youry wrote:Hello,
……
I Hope I help little bit, moreover I think it is already to much difficult to deal with this example if you start.
I decide to download openEMS thank to this image, because I want to simulate an Horn-antenna also, but calculation failed at the end because of my limited memory (I think)...
Thank you very much!
Your answer is Very useful to me.

thorsten
Posts: 1438
Joined: Mon 27 Jun 2011, 12:26

Re: vtk file question

Post by thorsten » Tue 27 Mar 2012, 11:26

Hi,

you explained it correctly @Youry. Thanks

But why did it fail for you at the end? How much memory do you have?
The windows version of openEMS is currently only 32bit so it cannot use more than 4GB Ram anyway and I am pretty sure I tested this example using the Windows Version (I think :D )

I need to try compiling the 64bit version for windows, but it is such a pain working with Windows... :(

regards
Thorsten

Youry
Posts: 51
Joined: Wed 22 Feb 2012, 12:50

Re: vtk file question

Post by Youry » Tue 27 Mar 2012, 11:59

Hello,

I am really scare about what you say, because my windows is 64 bit...
But anyway it seems working...

About the bug on large size calculation, in fact I modify the horn antenna files to fit my frequency range and my antenna geometry... But the calculation becomes big and failed.
I notice latter on easy example that changing calculation box size, or increase the time iteration, make a bug at the end.
What happen is this :
Everything is fine, I see the information lines of the calculation states : (1 million cell in 4 s for example), and the time iteration increase.
It goes till the end, without troubles...
But it bug at the dumping time (I think).
I get no files in the tmp folder...
And octave close by itself...
Before closing strange line appear in command windows... I will try to catch them with print screen...

I would like to ask this question latter, with clear example, in fact I would like to know how much x*y*z*t I can handle with computer skills...
I will ask soon... (I don't want ask 100 questions in 1 day :D )
Maybe it comes form 64 bit, or other things...

thorsten
Posts: 1438
Joined: Mon 27 Jun 2011, 12:26

Re: vtk file question

Post by thorsten » Tue 27 Mar 2012, 16:36

Hi,

running 32bit software on 64bit Windows is not a problem at all...

But it's just that while a 64bit Windows can handle more than 4GB Ram. A 32bit Software cannot...

1 million cells should be no problem, just have a look into your Task-Manager how much memory is used by openEMS. It should use the most shortly before the simulation starts...

Keep in mind that you cannot just change the mesh-resolution that easily. You cannot have a mesh that is coarser than lets say 10% of the shortest wavelength... And furthermore. if you make it to coarse the metal of the horn antenna may not be resolved correctly.

It is a good idea, to just scale everything to your desired frequency... This means, exact the same number of lines and so on... just everything is scaled by a specific factor...

regards
Thorsten

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