FFT2 contour plot of tangential magnetic force (plot_Ft_fft2)

Post-processing documentation
Matlab commandplot_Ft_fft2
Module EM.pp
Description PLOT_FT_FFT2 plots the 2D Fourier transform of airgap magnetic tangential force on outer structure (rotor or stator) per unit area with stator natural frequencies
Parameters
Restrictions
See also plot_Fr_fft2, plot_Ft_fft2_stem, plot_Ft_cfft2

Result

500. plot_Ft_fft2
plot_Ft_fft2

The top part of the FFT shows the magnitude of the harmonic force wave while the bottom part shows the phase angle of the harmonic force waves. The phase angle is useful to identify if a pulsating force occurs (e.g. two harmonics with opposite wavenumbers and same phase angle). Negative wavenumbers account for the different propagation direction of force waves.

The largest force harmonics should occur at r=2p (twice the number of pole pairs), f=2fs (twice the fundamental electrical frequency), and at r=0 f=0 (static force). Note that only the lowest force wavenumbers are important in magnetic noise and vibration process.

The reference level of the pressure dB scale can be tuned in

Input.Plot.PM0ref

For further plot options (e.g. change axis) see How to change plot options.

This type of graph is very useful to identify which are the main harmonic forces which can be responsible for magnetic noise and vibration of electrical machines. When a large force harmonic is close from a natural frequency, large vibration and noise can be expected.

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