## Objectives

The accurate calculation of noise and vibrations induced by e-machine operation requires the assessment of **vibro-acoustics at variable speed, taking a high number of speed steps** to correctly catch structural resonances (the less damping, the more speed steps). This can represent a high computational load, as operational magnetic loads must be updated at each operating point as well as NVH calculations.

In Manatee software, two techniques allow to significantly reduce this computing time, making it possible to **quickly rank electric motor noise behaviour during early electromagnetic design phases**:

– Electromagnetic Vibration Synthesis (EVS)

– Load Extrapolation Algorithm (LEA)

This article presents the Load Extrapolation Algorithm.

## Principle

**Load Extrapolation Algorithm** is a method to speed up calculation of Maxwell force harmonics at variable speed using a limited number of single speed calculations (from 1 to 6 single speed calculation of harmonic forces).

A variable-speed vibroacoustic spectrum can be obtained based on a single speed vibroacoustic simulation when **the evolution of the magnetic excitation with speed can be predicted** in terms of magnitude and frequencies (including rotation direction).

As an example, the magnitude of the flux density and resulting Maxwell stress in an open circuit permanent magnet synchronous machine is independent of speed: the frequencies of the magnetic force harmonics change with speed but their magnitude is unchanged. This means that the** vibroacoustic behaviour of the electrical machines can be quickly calculated at variable speed without significant additional calculations**.

The Load Extrapolation Algorithm can also be used on synchronous machines at constant current angle, or at no-load on induction machine, accounting for field weakening control.

Load Extrapolation Algorithm is independent from both electromagnetic and structural models. It can therefore be used when importing the flux density calculated with another electromagnetic software, or when using Manatee coupling with external mechanical FEA software (e.g. during Electromagnetic Vibration Synthesis process).