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Variance of Results Depending on the Types to Specify Current Direction

In the magnetic analysis, there is a case where the results of inductance calculation vary depending on the types to specify the current direction.

It happens if both of the two below are used in the analysis.

• 3D magnetostatic analysis

• Inductor that is not loop coil

 

In this case, the current direction is specified by either [Specify Inflow/Outflow Faces] or [Specify Inflow/Outflow Faces (In the Air Box)].
If the current direction is specified by [Specify Inflow/Outflow Faces (In the Air Box)], the inductance will be smaller.

Reasons of Inductance Difference

If the current direction is specified by [Specify Inflow/Outflow Faces], the assumption is that the both ends of coil contact the analysis domain peripheral (electric wall), and that the coil extends infinitely.
The analysis is performed assuming that a part of the coil is cut out for the simulation, which does not exist in the actuality.

 

If the model form is straight as in the below diagram, as the size of air domain becomes larger,
the inductance will be, theoretically, increased infinitely. The divergence from the reality takes place.

This phenomenon occurs distinctively in the inductor with a form as in the above diagram. This effect will be smaller in the spiral form like a helical coil.

It does not occur in the loop coil.

 

[Specify Inflow/Outflow Faces (In the Air Box)] can be applied to the inductor which has a finite length.

It is closer to the reality, but has drawbacks as follows.

• It can be applied to the static analysis only.

• The accuracy of magnetic field near the inflow/outflow faces is a bit low.
  

Which Specifying Types Shall Be Selected?

Please select the type considering the reasons explained above.

Generally, [Specify Inflow/Outflow Faces (In the Air Box)] is used for the static analysis. [Specify Inflow/Outflow Faces] is used for other analysis types.

 

For the Analyses Other than Static Analysis

[Specify Inflow/Outflow Faces (In the Air Box)] cannot be selected for the harmonic analysis and transient analysis.

It is because the finite element method cannot perform calculation properly in these two analysis types.