What is a spatiogram?

Definition

A spatiogram is a visualization tool aiming at filtering acceleration spectrograms per vibration wavenumber. The idea was first presented by EOMYS in the article Analysis of electromagnetically-induced vibrations of electrical machines based on spatiogram technique (ISEF 2015). It consists in performing a spatial FFT around e-motor to discriminate the vibration level due to specific vibration wavenumber, which can then be linked to a particular electromagnetic stress wave.

During NVH tests, it requires putting several accelerometers around lamination circumference (at least N accelerometers to capture vibration wavenumber N/2). Spatiogram technique can be carried both on radial and tangential acceleration, but it could also be applied to sound pressure waves around e-motor using several microphones.

Application to e-NVH

The principle of spatiogram is presented in the following pictures:

Principle of spatiogram derivation from spectrogram
Principle of spatiogram derivation from spectrogram

An example of its implementation in EV/HEV NVH module of OROS, developed with EOMYS support, is given here:

Example of spatiogram obtained with OROS EV/HV module
Example of spatiogram obtained with OROS EV/HV module

e-NVH issues can be more quickly diagnosed using spatiograms post processing:

  • quicker overview of the system vibration behaviour on whole speed and frequency range compared to an Operation Delfection Shape: in an ODS, vibration waves cannot be quantitatively ranked, and the analysis must be carried at a given speed and a given frequency.
  • quick identification of excitation force wavenumbers to identify the root cause of magnetic force
  • identification of static eccentricities (wavenumber modulation) and UMP effects (r=1)
  • quicker identification of natural frequencies

As an example, EV HEV NVH behaviour is driven by pulsating forces (r=0) in healthy conditions. Magnetic and geometrical asymmetries create additional harmonics coming from the modulation of pulsating forces. An ovalization of the stator bore radius therefore produce r=+/-2 magnetic force wavenumbers while keeping excitation frequencies unchanged. In a standard spectrogram, uneven airgap cannot be seen, but using spatiogram, additional harmonics at r=+/-2 would be observed.

Application to MANATEE

In MANATEE software, spatiograms are a natural post processing as the vibroacoustic effect of each Maxwell stress waves can be separated, especially when using Electromagnetic Vibration Synthesis algorithm.

MANATEE Sound Power Level spatiograms (plot_ASWL_spatiogram command)
MANATEE Sound Power Level spatiograms (plot_ASWL_spatiogram command)

The contribution of some specific structural modes to vibration and noise can also be quantified in MANATEE.

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