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Magnetization constitutive relation in Ampere's Law in Magnetic Field interface

Posted 26 feb 2019, 22:53 GMT-5 Low-Frequency Electromagnetics Version 5.4 1 Reply

Serhat
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There are several options in magnetic field constitutive relations in Ampere's law domain of Magnetic Fields interface on Comsol 5.4.

One of the options is Magnetization, where you can enter manually a fixed Magnetization field for the material.

My question is whether the value entered here will be treated as AC, or as a DC field.

I am using the Frequency Domain solution.

1 Reply Last Post 27 feb 2019, 05:02 GMT-5
Magnus Olsson COMSOL Employee

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Posted: 6 years ago 27 feb 2019, 05:02 GMT-5

Dear Serhat,

In the frequency domain study step, the solution is assumed to oscillate at a single frequency around a linerization point of zero. All explicit excitations like magnetization, remanent flux density, domain, surface and edge currents as well as coils are to be interpreted as AC sources. There is really only one type of excitation that should be interpreted as a DC quantity and that is the velocity in the Velocity (Lorentz Term) feature that, in the magnetic fields interface, is available in 2D only (in the MEF interface, it is available in 3D too). The effect of the Lorentz term is equivalent to adding an electric field vxB and a corresponding current density of sigma*(vxB). As B is an AC quantity, v must be DC as otherwise the source term would oscillate at twice the fundamental frequency which violates the assumption of a single frequency.

For nonlinear cases, for example when magnetic saturation is considered, it makes more sense to use the small-signal analysis or frequency domain, perturbation study that allows you to solve in two steps. The first step typically solves for the (large) DC bias excitation (DC current, permanent magnets etc) and in a second step you solve for a (small) AC perturbation type excitation (typically an AC coil current). Here is an example on that approach: ACDC_Module/Inductive_Devices_and_Coils/small_signal_analysis_of_inductor

For cases, where either the dynamic excitation is not sinusoidal or when it is not small compared to the DC sources, you will need to solve the nonlinear problem in the time domain with a stationary initialization (getting the consistent initial fields from DC currents and permanent magnets). Here is an example on that approach: ACDC_Module/Motors_and_Actuators/generator_2d

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Magnus
Dear Serhat, In the frequency domain study step, the solution is assumed to oscillate at a single frequency around a linerization point of zero. All explicit excitations like magnetization, remanent flux density, domain, surface and edge currents as well as coils are to be interpreted as AC sources. There is really only one type of excitation that should be interpreted as a DC quantity and that is the velocity in the Velocity (Lorentz Term) feature that, in the magnetic fields interface, is available in 2D only (in the MEF interface, it is available in 3D too). The effect of the Lorentz term is equivalent to adding an electric field vxB and a corresponding current density of sigma*(vxB). As B is an AC quantity, v must be DC as otherwise the source term would oscillate at twice the fundamental frequency which violates the assumption of a single frequency. For nonlinear cases, for example when magnetic saturation is considered, it makes more sense to use the small-signal analysis or frequency domain, perturbation study that allows you to solve in two steps. The first step typically solves for the (large) DC bias excitation (DC current, permanent magnets etc) and in a second step you solve for a (small) AC perturbation type excitation (typically an AC coil current). Here is an example on that approach: ACDC_Module/Inductive_Devices_and_Coils/small_signal_analysis_of_inductor For cases, where either the dynamic excitation is not sinusoidal or when it is not small compared to the DC sources, you will need to solve the nonlinear problem in the time domain with a stationary initialization (getting the consistent initial fields from DC currents and permanent magnets). Here is an example on that approach: ACDC_Module/Motors_and_Actuators/generator_2d

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