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Remote eddy current testing
Posted Nov 9, 2010, 4:04 a.m. EST 4 Replies
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Hi,
I am making a simulation about remote eddy current testing. This is a 2D axisymmetric model. Two multi-turn coils are used. One is used for exciting and another for detecting. They are both located at the inside of a tube. The frequency is 3400. I found a strange phenomena. The induced voltage of coil for exciting is same as that of coil for detecting, but in fact they should be different from each other. Why are they same?
Looking forward to the explanation. Thank you very mach!
I am making a simulation about remote eddy current testing. This is a 2D axisymmetric model. Two multi-turn coils are used. One is used for exciting and another for detecting. They are both located at the inside of a tube. The frequency is 3400. I found a strange phenomena. The induced voltage of coil for exciting is same as that of coil for detecting, but in fact they should be different from each other. Why are they same?
Looking forward to the explanation. Thank you very mach!
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4 Replies Last Post Nov 29, 2010, 6:24 a.m. EST
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Posted:
1 decade ago
Hello Noritaka,
I loaded your model file and it seems to me you forgot to assign a domain to your second coil.
Multi-turn coil domain 1 corresponds to geometric domain 3.
Multi-turn coil domain 2 should correspond to geometric domain 2, I think, but doesn't.
Change that and check results.
Btw: You modeled air with an electrical conductivity of 100 S/m? That is waaay to much.
And in general I do not understand your model. Where is the object in which the eddy currents are expected?
Bye
MV
I loaded your model file and it seems to me you forgot to assign a domain to your second coil.
Multi-turn coil domain 1 corresponds to geometric domain 3.
Multi-turn coil domain 2 should correspond to geometric domain 2, I think, but doesn't.
Change that and check results.
Btw: You modeled air with an electrical conductivity of 100 S/m? That is waaay to much.
And in general I do not understand your model. Where is the object in which the eddy currents are expected?
Bye
MV
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Posted:
1 decade ago
Hi,
Sorry for the late reply. I have solved the problem. Now my model is correct. The induced eddy current occured on outer surface of tubes and it shows slower attenuation along axis direction than directly induced electromagnetic field at detecting coil. When a detecting coil keeps distance from exciting coil enough to neglect directly induced field, the detecting coil can catch "remote field", electromagnetic field induced by the eddy current on outer surface of tube.
Thank you for your help!
Sorry for the late reply. I have solved the problem. Now my model is correct. The induced eddy current occured on outer surface of tubes and it shows slower attenuation along axis direction than directly induced electromagnetic field at detecting coil. When a detecting coil keeps distance from exciting coil enough to neglect directly induced field, the detecting coil can catch "remote field", electromagnetic field induced by the eddy current on outer surface of tube.
Thank you for your help!
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Posted:
1 decade ago
Hi
if you are in "mef" you need to set the conductivity of air rather high (might go above 100S/m) to get a good numerical conversion, even if not "physical". But so long the conductivity of air is muchmuch lower than that of the conductors the results are still correct.
One exception if you run on a 256 bit, or more, floating processors, but I do not know about any handy ones out there ;)
do not forget the limited size of "eps", and even "sqrt(eps)" is mostly the limiting ratio factor for physical equations expressed in numerical form. The Binary number representation in limited bit format is far from ideal
--
Good luck
Ivar
if you are in "mef" you need to set the conductivity of air rather high (might go above 100S/m) to get a good numerical conversion, even if not "physical". But so long the conductivity of air is muchmuch lower than that of the conductors the results are still correct.
One exception if you run on a 256 bit, or more, floating processors, but I do not know about any handy ones out there ;)
do not forget the limited size of "eps", and even "sqrt(eps)" is mostly the limiting ratio factor for physical equations expressed in numerical form. The Binary number representation in limited bit format is far from ideal
--
Good luck
Ivar
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Posted:
1 decade ago
Hello,
this is interesting. When talking about "a good numerical conversion", do you mean numerical convergence? Or something that I do not yet have in mind?
Does that statement also apply if I model the conductivity of air as equal to zero? I can imagine that it is easier to find a solution, if there are materials air and copper, for example, with conductivities 10^7 and 10^2 S/m than in case of conductivities of 10^7 and 10^-10, respectively. But if one knows, that there is no current flow in one medium, i.e. conductivity equals zero, this should simplify the problem, shouldn't it?
In fact, I just gave it a go, changed on of my models and re-solved it. Result: computation time increased by factor 1.72 for the model with an air conductivity of 10^-2 compared to the model with air conductivity zero. So I wouldn't agree with you, Ivar. But maybe this applies only in my special case. Could you possibly discuss this issue a little more detailed?
Bye
MV
this is interesting. When talking about "a good numerical conversion", do you mean numerical convergence? Or something that I do not yet have in mind?
Does that statement also apply if I model the conductivity of air as equal to zero? I can imagine that it is easier to find a solution, if there are materials air and copper, for example, with conductivities 10^7 and 10^2 S/m than in case of conductivities of 10^7 and 10^-10, respectively. But if one knows, that there is no current flow in one medium, i.e. conductivity equals zero, this should simplify the problem, shouldn't it?
In fact, I just gave it a go, changed on of my models and re-solved it. Result: computation time increased by factor 1.72 for the model with an air conductivity of 10^-2 compared to the model with air conductivity zero. So I wouldn't agree with you, Ivar. But maybe this applies only in my special case. Could you possibly discuss this issue a little more detailed?
Bye
MV