What is a spatiogram?


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 V1 Sound Power Level spatiograms
Manatee V1 Sound Power Level spatiograms

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

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