Multiphysics Simulation on Vibration and Noise of Variable-Speed Permanent Magnet Brushless DC Motor With Eccentricity

Multiphysics finite element modeling process is derived to predict vibration and noise due to magnetic forces within a permanent-magnet brushless DC motor over a variable speed range under healthy and eccentric faulty conditions. Transient analysis for magnetic force in two-dimensional electromagnetic model is carried out over a variable speed range. To keep cyclic symmetry mesh and avoid numerical source of noise, the method of effective air gap layer is applied and manipulated with relative permeability derived for static and dynamic eccentric rotating condition depending on rotation angle and eccentric shift. Using discrete Fourier transformation and electromagnetic-structural one-way coupling schemes, magnetic harmonic forces for a range of rotation angular speed are imported and applied on stator’s inner surfaces. Vibration characteristics are calculated for a three-dimensional full finite element model of the motor in harmonic response analysis. Finally, surface velocities are imported and applied on acoustic domain using fluid-structure interaction (FSI) one-way coupling. Noise radiated from motor housing including front and end caps is evaluated. The waterfall diagram of equivalent radiation pressure level (ERPL) and sound pressure level (SPL) contour plotting in function of rotation angular speed and frequency is obtained in multiple RPM harmonic structural and acoustic analyses. The vibro-acoustic feature pattern could be utilized in faulty detection.