Contribution to the study of the electro-magneto-mechanic strong couplings for the acoustic and vibration of eletric motors of aeronautic ventilation systems
Résumé
The noise heard by passengers on airplanes can reach eighty decibels and become a real burden. This noise mainly comes from the ventilation system. The acoustic of such system has become, during the past years, an important requirement of the specifications, and is taken into consideration in the design phase. In particular, the importance of the coupling between the shaft vibrations and the electromagnetic phenomenon has been highlighted in recent experiments. Here this coupled problem is studied with a simple model able to predict the strong couplings that might produce high level of noise. This model is divided in 3 steps: 1) Modeling of the electromagnetic forces of an induction motor. A subdomain model is used to solve the Maxwell equation and calculate the Maxwell forces acting on the rotor. Here the forces depend on the airgap between the stator and the rotor which might change during rotation. This airgap is related to the flexural deflection of the shaft. 2) Modeling of the shaft dynamic behavior. A 1D rotating Timoshenko beam is considered to predict the deformed shape of the rotor excited with the Maxwell forces calculated in the previous step. 3) Strong coupling of these two models. A loop between the two models is used to couple the mechanical and the electromagnetic parts. The Maxwell forces are updated at each step in the mechanical model while the air gap angular distribution of the Maxwell forces is updated at each step in the electromagnetic model. After convergence, the vibratory signature of the shaft line is obtained and the excitations can be compared with the carter modal basis to prevent mechanical resonances. The industrial aim is to have a better control of the parameters that create a strong and unacceptable coupling, in order to tend towards quieter products.
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