CircuitsAndDynamics

Numerical methods and mathematical models of Elmer
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MartinHoeijmakers
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CircuitsAndDynamics

Post by MartinHoeijmakers » 22 Oct 2017, 21:39

Hi all,
At this moment I use FEMM, but I miss the dynamics. Before doing a large investment into Elmer, I would like do do some experiments (2D). I have attached the first one.

It only consists of one square iron bar of 10x10 mm (cross-sectional area 100 mm^2) and a length of 1 m. This bar is connected to a voltage source of 1 V.
After running the file case.sif, you get the file transient_results.dat in the directory results, with the corresponding names in transient_results.dat.names.

The bar resistance found in transient_results.dat is 1.818 mOhm, which value I also found myself (sigma=5.5e6). The final current in transient_results.dat is 352 A, where I would expect 1/0.001818 A = 550 A. However, this is (accidentally?) the final value in the column "eddy current power".

As the voltage is 1 V, we expect in steady state a current density of 5.5e6 A/m^2. I found the same value by means of ParaView in the vtu files

Can anybody explain my results?

Kind regards,
Martin
Attachments
SimpleCircuit.zip
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mzenker
Posts: 1988
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: CircuitsAndDynamics

Post by mzenker » 23 Oct 2017, 11:36

Hi,

are you trying to calculate the current in your iron block at a potential difference of 1 V? Why don't you just use Static Current Conduction solver (see Models manual)?

Matthias

MartinHoeijmakers
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Re: CircuitsAndDynamics

Post by MartinHoeijmakers » 23 Oct 2017, 11:45

Hi,
Thank you for you suggestion
I am trying to understand Elmer and got the impression that the result in transient_results.dat is not right. However, I am new to Elmer.

Kind regards, Martin

mzenker
Posts: 1988
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: CircuitsAndDynamics

Post by mzenker » 23 Oct 2017, 12:19

Hi,

if you are new to Elmer, I would suggest you to start with something really simple, using ElmerGUI. If may be too involved to start with the circuits and dynamics solver in the first test case. Maybe you could take your iron block, open it with the GUI and model the current flow with static current solver. See ElmerGUI manual for more info on how to use the GUI. The GUI writes a sif file which you can examine and learn how it is built.
The problem is that ElmerGUI cannot handle the CircuitsAndDynamics Solver (yet). So to use that one, you have to write the sif file yourself, using the information from the Models Manual - which is apparently what you did. Unfortunately I don't know this solver and cannot help you here.
I would suggest that you first make sure that you really need to use exactly this solver. You might describe in more detail what you intend to do. If you need this solver, then the people who implemented it would have to take over...

HTH,
Matthias

MartinHoeijmakers
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Re: CircuitsAndDynamics

Post by MartinHoeijmakers » 23 Oct 2017, 12:35

Hi Matthias,
Thank you for your reply, but I already did those first simple steps. I am using FEMM for many years now, but I need dynamics. I already spend many days on Elmer with simple things and would like to know whether I can use Elmer for more serious dynamic problems. However, I get those strange (in my eyes) results. I was triggered for Elmer by "Elmer FEM - Induction Machine Tutorial" written by Pavel Ponomarev. I used this document for inspiration.
Kind regards, Martin

mzenker
Posts: 1988
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: CircuitsAndDynamics

Post by mzenker » 23 Oct 2017, 12:48

OK, I see. This is a very good tutorial indeed. If you already worked with it you are not that new to Elmer any more... ;)
Then let's hope Pavel who is also using this forum has the possibility to have a look at your problem.

Matthias

Takala
Posts: 183
Joined: 23 Aug 2009, 23:59

Re: CircuitsAndDynamics

Post by Takala » 24 Oct 2017, 16:59

MartinHoeijmakers wrote:Hi all,
At this moment I use FEMM, but I miss the dynamics. Before doing a large investment into Elmer, I would like do do some experiments (2D). I have attached the first one.

It only consists of one square iron bar of 10x10 mm (cross-sectional area 100 mm^2) and a length of 1 m. This bar is connected to a voltage source of 1 V.
After running the file case.sif, you get the file transient_results.dat in the directory results, with the corresponding names in transient_results.dat.names.

The bar resistance found in transient_results.dat is 1.818 mOhm, which value I also found myself (sigma=5.5e6). The final current in transient_results.dat is 352 A, where I would expect 1/0.001818 A = 550 A. However, this is (accidentally?) the final value in the column "eddy current power".

As the voltage is 1 V, we expect in steady state a current density of 5.5e6 A/m^2. I found the same value by means of ParaView in the vtu files

Can anybody explain my results?

Kind regards,
Martin
Hi Martin,

welcome to the community, I hope you will benefit from our great software!

I downloaded you case and tested it. By modifying it, I was able to get sensible results. There are few things that are wrong/missing.

I suggest that you start from one of the tests (https://github.com/ElmerCSC/elmerfem/tr ... /fem/tests). This is actually a general rule
that I recommend. That is what I always do when I start experimenting features that I have no experience with.

There are a bunch of circuits* cases but In your case I would start from circuits2D_transient_massive (this was a 2D axisymmetric case if I remember correctly).

Although, if you still want to make your own case working. It might be sufficient to just define "Variable = A" in solver 2 and "A = Real 0" in
Boundary Condition 1. However you were missing some keywords that could be handy in the future...

Best Regards,

Eelis

MartinHoeijmakers
Posts: 4
Joined: 22 Oct 2017, 21:03
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Re: CircuitsAndDynamics

Post by MartinHoeijmakers » 24 Oct 2017, 22:57

Hi Eelis,

Thank you for your help. I made the changes (also in solver 3) and the final value of the current is 550 A ( :D ) .
Now, I start studying circuits2D_transient_massive.

Kind regards, Martin

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