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How to analyze lightning effect (warning 53512) in FEKO?

While simulating a model which includes lightning effect on aircraft, a warning appears ;

WARNING 53512: The sum of all inflowing/outgoing currents at an impressed current end point is not zero. Point charges at these terminations are not considered.

Please shed some light on this warning. what is its significance in the simulation and how it affects the results? How can we solve it.

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English

Feko

HyperMesh

v2021.1

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Mel

Often the impressed current source is used in a non-physical way: a constant impressed current of 1 A which does not go to zero at the ends. The constant current is not possible in reality, resulting in point charges on either side. Feko does not take these point charges into account.

Feko does a continuity check to ensure Kirchoff's law is satisfied at the impressed current end points. If the impressed current terminates against a ground plane, the current is assumed to be continuous.

If the impressed current is "floating" in the air, you can use two impressed current sources connected to each other. The first source start magnitude 0 A and end magnitude 1 A, and the 2nd source connected to the end of the first source with start magnitude 1 A and end magnitude 0 A. Or you could use 3 sources, two small ones at both ends plus then the actual (original) source.

If the source connects to an aircraft, you may need an "exit" source as well. The "exit" source still has its endpoint connected to the aircraft, but you set the phase to 180 degrees, assuming the first source is 0 degrees.

Sanjali Sharma

Often the impressed current source is used in a non-physical way: a constant impressed current of 1 A which does not go to zero at the ends. The constant current is not possible in reality, resulting in point charges on either side. Feko does not take these point charges into account.

Feko does a continuity check to ensure Kirchoff's law is satisfied at the impressed current end points. If the impressed current terminates against a ground plane, the current is assumed to be continuous.

If the impressed current is "floating" in the air, you can use two impressed current sources connected to each other. The first source start magnitude 0 A and end magnitude 1 A, and the 2nd source connected to the end of the first source with start magnitude 1 A and end magnitude 0 A. Or you could use 3 sources, two small ones at both ends plus then the actual (original) source.

If the source connects to an aircraft, you may need an "exit" source as well. The "exit" source still has its endpoint connected to the aircraft, but you set the phase to 180 degrees, assuming the first source is 0 degrees.

So, you mean, I can ignore this warning if it still appears? I am attaching CADFEKO file for your reference.

helicopter2.cfx

Mel

Thanks for attaching the model.

The source needs a start magnitude of 0. In addition, to ensure it connects to the mesh, use the check box "Connect the endpoint to the closest mesh vertex"

Your model unit is set to mm. I suppose this is a mistake? I changed this to meters.

Attached is a modified version and it should no longer give a warning.

helicopter2__alt.cfx

Sanjali Sharma

Thanks for attaching the model.

The source needs a start magnitude of 0. In addition, to ensure it connects to the mesh, use the check box "Connect the endpoint to the closest mesh vertex"

Your model unit is set to mm. I suppose this is a mistake? I changed this to meters.

Attached is a modified version and it should no longer give a warning.

Thank you so much for you replies. I have few more doubts about this. As I am connecting the endpoint to the closest mesh vertex either on triangle or on segment, the impressed current sources turn into spheres in space which I find difficult to visualize. I even brought those spheres in contact with the aircraft. In both the cases, during simulation two more warnings appear.

WARNING 3536: Possibly inaccurate radiated power for multiple impressed current elements

WARNING 3660: No accurate power computation possible for an excitation with an impressed current connected to a surface/wire segment

Kindly help me in learning about these warnings and how can I avoid them? If you could suggest me some papers or tutorials, that will also be great.

How do I know, the results I am getting are accurate or not?

Again, I am grateful to you.

Mel

Connecting to closest vertex changes the rendering unfortunately to a sphere, which is the start point of the source. The user interface does not "know" which vertex the end point will connect to, it will only be determined once you run Feko.

You can confirm the length and connection point by looking in the *.out file:

The above shows the element length, where the source connects to, etc. Triangles can be viewed in POSTFEKO by going to the Mesh tab, clicking Find elements and entering the triangle numbers.

This is the recommended way to do it, else you will get unexpected results.

Sanjali Sharma

Connecting to closest vertex changes the rendering unfortunately to a sphere, which is the start point of the source. The user interface does not "know" which vertex the end point will connect to, it will only be determined once you run Feko.

You can confirm the length and connection point by looking in the *.out file:

The above shows the element length, where the source connects to, etc. Triangles can be viewed in POSTFEKO by going to the Mesh tab, clicking Find elements and entering the triangle numbers.

This is the recommended way to do it, else you will get unexpected results.

Thank you. This is very helpful.