Electromagnetic Fields of Geophysics

How to use openEMS. Discussion on examples, tutorials etc

Moderator: thorsten

LEM
Posts: 15
Joined: Thu 10 Oct 2013, 09:17

Electromagnetic Fields of Geophysics

Post by LEM » Tue 26 Nov 2013, 16:46

Hi,
Is there anyone use openEMS to simulate the electromagnetic fields of geophysics? Like TEM(Transient Electromagnetic Methodhttp://en.wikipedia.org/wiki/Transient_ ... nd_sensors)?
For detail, how to simulate the loop source in reality?

thorsten
Posts: 1425
Joined: Mon 27 Jun 2011, 12:26

Re: Electromagnetic Fields of Geophysics

Post by thorsten » Tue 26 Nov 2013, 21:30

Hi,

I read a little bit about this TEM method and it sounds very challenging to simulate.
But maybe it is worth giving it a try.
What you can do is create a custom excite function see here.
The function would ramp up to a certain value and then after some constant time, decay quickly back to zero.
You may define a loop source e.g. as a curve port with a very low (maybe 0) Ohms impedance.
Additionally some additional curve (with port) to observe some induced currents.
I'm really not sure if this is going to work.
It depends on a good balance between mesh resolution, simulation domain size and highest expected frequency...
What you definitely need is something to benchmark against, e.g. some analytical result or maybe a simple measurement setup for comparison.

This may work or not at all. I don't know...

regards
Thorsten

LEM
Posts: 15
Joined: Thu 10 Oct 2013, 09:17

Re: Electromagnetic Fields of Geophysics

Post by LEM » Tue 26 Nov 2013, 22:22

Hi, Thorsten,

Thanks a lot for your quick reply. I will have a try and feed back the problem and result.

regards
LEM

LEM
Posts: 15
Joined: Thu 10 Oct 2013, 09:17

Re: Electromagnetic Fields of Geophysics

Post by LEM » Thu 28 Nov 2013, 08:47

Hi, Thorsten,

I got a problem. I can't understand how to relate the excitation to the curve port which I defined? I have read the tutorials. I can't really understood what the shape and location of excitation is?

LEM
Posts: 15
Joined: Thu 10 Oct 2013, 09:17

Re: Electromagnetic Fields of Geophysics

Post by LEM » Thu 28 Nov 2013, 09:26

Hi, Thorsten,

Another problem, :oops:. For example, I want to define a rectangular wire frame by using AddCurvePort(...), what's the meaning of the parameter 'start' and 'end '? How to assign them to form a rectangular wire frame?

regards
LEM

thorsten
Posts: 1425
Joined: Mon 27 Jun 2011, 12:26

Re: Electromagnetic Fields of Geophysics

Post by thorsten » Thu 28 Nov 2013, 14:32

Hi,
Another problem, :oops:. For example, I want to define a rectangular wire frame by using AddCurvePort(...), what's the meaning of the parameter 'start' and 'end '? How to assign them to form a rectangular wire frame?
Maybe calling it a line port would be more precise. This port is just a line, going from start to end with the port (resistance, voltage and current probe) in the middle.
To close your rectangle you should use a regular metal curve (AddCurve).
I got a problem. I can't understand how to relate the excitation to the curve port which I defined? I have read the tutorials. I can't really understood what the shape and location of excitation is?
I'm not sure I understand, you just define the excite vector (e.g. [1 0 0] for 1V/m in x-direction). But this value is only the amplitude which gets multiplied by the excitation time-signal you defined with "SetCustomExcite" or "SetGaussExcite". This time signal is global for all excitations. Your ports or AddExcitation can only define where (location) and with which amplitude and decay you can excite the time signal...

Maybe you can help improve the doc on the topic? http://openems.de/index.php/Excitation

regards
Thorsten

LEM
Posts: 15
Joined: Thu 10 Oct 2013, 09:17

Re: Electromagnetic Fields of Geophysics

Post by LEM » Fri 29 Nov 2013, 14:39

Hi,

I have read the code of ‘AddExcitation(...)’, I have a question. For example, I have AddCurve to form a rectangle source, how to AddExcitation on the rectangle? And the excitation is a E or H-field or plane wave excitation, what does a real-world loop which passed current generate? Just the H-field? Or plane wave?

I am sorry for my poor English.
regards
LEM

thorsten
Posts: 1425
Joined: Mon 27 Jun 2011, 12:26

Re: Electromagnetic Fields of Geophysics

Post by thorsten » Fri 29 Nov 2013, 15:44

Just create the curve and put e.g. a lumped port on top of it with a higher priority...

I would not create a simple excitation (with AddExcitation) yourself, because than you need additionally a voltage and especially a current probe.
A curve port or lumped port is doing that all in one...

a plane wave excite is something totally different...

regards
Thorsten

LEM
Posts: 15
Joined: Thu 10 Oct 2013, 09:17

Re: Electromagnetic Fields of Geophysics

Post by LEM » Mon 02 Dec 2013, 03:06

Hi,

I add the loop like this

Code: Select all

%define the source loop
Spoints(1,1)=350;Spoints(2,1)=350;Spoints(3,1)=250;
Spoints(1,2)=350;Spoints(2,2)=150;Spoints(3,2)=250;
Spoints(1,3)=150;Spoints(2,3)=150;Spoints(3,3)=250;
Spoints(1,4)=150;Spoints(2,4)=350;Spoints(3,4)=250;
Spoints(1,5)=350;Spoints(2,5)=350;Spoints(3,5)=250;
CSX=AddCurve(CSX,'loop',1,Spoints);

start=Spoints(:,1);
stop=Spoints(:,2);
[CSX,port{1}]=AddLumpedPort(CSX,2,1,0,start,stop,[0 1 0],true);

start=Spoints(:,2);
stop=Spoints(:,3);
[CSX,port{2}]=AddLumpedPort(CSX,2,2,0,start,stop,[1 0 0],true);

start=Spoints(:,3);
stop=Spoints(:,4);
[CSX,port{2}]=AddLumpedPort(CSX,2,3,0,start,stop,[0 1 0],true);

start=Spoints(:,4);
stop=Spoints(:,5);
[CSX,port{4}]=AddLumpedPort(CSX,2,4,0,start,stop,[1 0 0],true);
I have no idea whether it's right, I just had a try, but the calculation of 'RunOpenEMS(Sim_Path, Sim_CSX)' never stop. What's the basic argument control the calculating process(like 'when to start, when to end')?

thorsten
Posts: 1425
Joined: Mon 27 Jun 2011, 12:26

Re: Electromagnetic Fields of Geophysics

Post by thorsten » Mon 02 Dec 2013, 09:49

That the simulation does not stop, has most likely nothing to do with the curve, but the excitation signal.
After the excitation is done, the energy should start decaying...

Maybe you attach your entire script?

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