3D static and dynamic eccentricities


Manatee software allows to assess the effect of 3D static and dynamic eccentricities due to mechanical tolerances on the electromagnetic noise and vibrations levels. Parallel and inclined static and dynamic eccentricity levels can be specified at drive end and non drive end, as well as the position of the static eccentricity axis. The effect of the parallel eccentricity direction on e-NVH level can be studied when importing a 3D FEA mechanical model.

For a quick analysis, Manatee uses a perturbation technique of the airgap flux density to estimate parasitic magnetic forces induced by 3D static and dynamic eccentricities. This method can be applied when using a Magnetic Look Up Table, even when importing the airgap flux from a third party software.

This perturbation technique, also used for uneven airgap, is suitable for low airgap deformation values (max 15% of the magnetic airgap width). It can be used to estimate the effect of eccentricity on “high frequency” magnetic force harmonics that are not strongly related to the saturation level of the electrical machine. When applying dynamic eccentricity quick model, a component due to the Unbalanced Magnetic Pull at H1 may be introduced in vibration and noise results. This component level might be overestimated due to the missing saturation effect in the perturbation model, and might be underestimated as well compared to experiments due to the missing mechanical unbalance force. Finally, H1 excitation occurs at “low frequency” where acoustic noise might be overestimated using the Equivalent Radiated Power (ERP) model. Therefore, H1 vibro-acoustic results under dynamic eccentricity should be interpreted carefully using the quick perturbation model.


This feature allows mechanical engineers to calculate the effect of 3D eccentricities on electromagnetic noise and vibrations. This way, too conservative values of mechanical tolerances can be avoided.

It also allows electrical engineers to perform robust e-NVH ranking of different electrical machines. An electrical machine A may be louder than machine B without eccentricity, while it becomes the opposite with 15% dynamic eccentricity.

It is recommended to model eccentricity effects when introducing a 3D FEA mechanical model in Manatee, including rotor and stator structures. Eccentricity induces parasitic Unbalanced Magnetic Pull resulting in additional structure-borne and air-borne noise.