What is the ENS (Electromagnetic Noise Synthesis) method?

Principle

The ENS (Electromagnetic Noise Synthesis) is an algorithm designed to speed up electromagnetically-excited noise and vibration calculations and get more physical insights on the e-NVH behaviour of the machine.

It is equivalent to the EVS (Electromagnetic Vibration Synthesis) for acoustic noise. It consists in decoupling the acoustic characterization of the electric motor structure from the operational electromagnetic excitation.

As electromagnetic forces due to Maxwell stress can be decomposed in a discrete series of rotating force waves with specific wavenumbers which depends on slot / pole combination and winding pattern, this characterization can be carried by exciting the structure with unit-magnitude rotating force patterns at variable frequency in radial and tangential directions, on rotor and stator sides. One obtains some normalized acoustic Frequency Response Functions (FRF) that can be stored for later use. This ENS method can be called the "rotating wave excitation method".

Once the acoustic FRF are calculated, the electromagnetic loads are projected on the excitation basis and the acoustic response is synthesized without additional calculations. Besides, torque ripple, Unbalanced Magnetic Pull, and radial ripple excitations can be separated in the e-NVH response. Air-borne noise due to stator excitation can also be seperated from structure-borne noise due to rotor excitation, similarly to a numerical transfer path analysis.

The vibroacoustic FEA model must currently exist under Actran.

The ENS method is particularly useful when a high number of operational loads have to be calculated, for instance in variable speed calculations (e.g. NVH maps on torque speed plane) or in optimization mode (e.g. pole shaping).

An example of rotating wave Electromagnetic Noise Synthesis is illustrated here:

Rotating wave noise synthesis
Rotating wave noise synthesis

Application to MANATEE software

MANATEE software v1.04.09 mechanical module can apply ENS algorithm to the following structural models:

  • Patran structural FEA commercial software
  • Actran structural FEA commercial software

and to the following acoustical models:

  • Actran acoustical FEA commercial software

Coupling with other FEA software are under study.

In MANATEE software scripting mode the noise synthesis method is chosen using the input parameter

Input.Simu.type_FRF

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