### Principle

The EVS (**Electromagnetic Vibration 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 consists in **decoupling the vibrational characterization of the electric motor structure from the operational electromagnetic excitation**, as one would do experimentally using an impact hammer or an electrodynamic shaker to measure Frequency Response Functions.

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 **artificially exciting the structure with some specific rotating force patterns** at variable frequency in radial and tangential directions. One obtains some normalized Frequency Response Functions (FRF) that can be stored for later use. This EVS method can be called the "rotating wave excitation method". Another EVS method consists in exciting each tooth of the stator with variable frequency radial, tangential and bending moment excitations. This method is called the "tooth excitation method".

Once the FRF are calculated, the electromagnetic loads are projected on the excitation basis and the vibration 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 EVS method is particularly computationally efficient at variable speed (when combined with Load Extrapolation Algorithm), or during electromagnetic optimization (current shaping, pole shaping, notching).

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

### Application to MANATEE software

MANATEE software v1.04.06 mechanical module can apply EVS algorithm to the following structural models:

- MANATEE built-in semi-analytical vibroacoustic models (rotating wave only)
- Altair Hypermesh/Optistruct structural FEA commercial software (tooth excitation or rotating wave)
- Ansys Mechanical structural FEA commercial software (rotating wave only)

Coupling with other FEA software are under study.

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

`Input.Simu.type_FRF `