Winding coil-pitch vibro-acoustic effects with permeance / mmf model

Let’s try to remove the shorted-pitch winding by putting Input.Magnetics.coil_pitch1 = 0 in a new machine data file names machine_SCIM_B.m.
The tuto_test_SCIM_01 is copied-pasted (or loaded with the GUI), renamed in tuto_test_SCIM_03 with Input.Simu.machine_name = ’machine_SCIM_B’;

run_MANATEE(’tuto_test_SCIM_03')

One can check that the new winding is correctly modelled with plot_wind:

Winding with coil_pitch=0
Winding with coil_pitch=0

The SPL at variable speed is now given by plot_VS_ASPL_overall

New resonance at 702 rpm
New resonance at 702 rpm

This time, a new resonance appears at 702 rpm. One can see in the sonogram and in the modal contribution graph that the resonance is caused by the ovalization mode. To further understand the issue, one can re-run the calculation at the resonance speed which is 702 rpm, by changing Input.Simu.N0=702 in a separate new project named tuto_test_SCIM_04.m.

run_MANATEE(’tuto_test_SCIM_04')
plot_Fr_fft2_stem
Airgap radial pressure FFT2
Airgap radial pressure FFT2

One can see that the radial force responsible for this new resonance due to winding has the expression fs(2(1-s)Zr/p). The standard theoretical analysis given in MANATEE output does not consider spatial harmonics of stator mmf, but a more detailed analysis can be run by running the identification process of main exciting forces and their modal excitation through quality factor:

>> disp_theory_force_lines

This displays all the potential excitation forces and the quality factor at the simulation current speed. The highest is the quality factor Q, the largest is the resonance. One can notice the following large wavenumber 2 excitation (Q=100):

Potential excitation forces
Potential excitation forces
  • kr=2: second rotor slotting permeance harmonic
  • ks=1: first stator slotting harmonic
  • hs=1: first mmf stator harmonic at 7p
  • ka=0: no saturation harmonic involved

This analysis shows that the 7p=21 mmf space harmonic is responsible for the acoustic noise at 35 Hz. The removal of the short pitch has introduced a large mmf space harmonic responsible for a new resonance.

This analysis shows that the 7p=21 mmf space harmonic is responsible for the acoustic noise at 35 Hz. The removal of the short pitch has introduced a large mmf space harmonic responsible for a new resonance.

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