The demand for silent rolling bearing applications, such as electric motors and gearboxes, has resulted in an investigation of viscoelastic bearing supports. By placing a thin viscoelastic layer between the bearing outer ring and the surrounding structure, vibrations of the shaft-bearing arrangement can be isolated and damped in such a way that the radiated sound power is reduced. The ultimate goal of this research was to develop a design strategy for viscoelastic bearing supports resulting in an effective noise reduction. This thesis describes the dynamic and acoustic behaviour of rolling bearing applications with viscoelastic bearing supports. Ultimately, the investigations cover a wide range of aspects in mechanical engineering: (1) the description of viscoelastic material behaviour; (2) development of a new Component Mode Synthesis method for viscoelastic components; (3) experimental investigations into the mechanical properties of viscoelastic materials; (4) development of advanced structural models of rotor dynamics applications; (5) numerical and experimental investigations of the dynamic and acoustic behaviour of an electric motor; (6) development of a design strategy for noise reduction by viscoelastic bearing supports In the present research, elastic components, like the shaft or the housing, and the viscoelastic support are modelled with the finite element method. In addition, the models are reduced by Component Mode Synthesis to save computation time. Viscoelasticity is described by a generalised Maxwell representation suitable for both time and frequency domain analyses. Viscoelastic materials are measured on a Dynamic Mechanical Analyzer to obtain the frequency dependent stiffness and damping characteristics. The viscoelastic modelling approach is succesfully validated at a component level with sandwich rings. The results showed that a significant amount of damping can be created by the viscoelastic layer. As a next step, numerical and experimental studies were performed on a rotor dynamics test rig. A clear vibration reduction was achieved with viscoelastic supports, especially for high running speeds. Subsequently, the dynamic and acoustic behaviour of a running electric motor was analysed. The acoustic analysis was based on the boundary element method using so-called radiation modes. The agreement between experimental and numerical results was satisfactory in the noisiest frequency range from 1000 to 2500 Hz. It was found that the sound power level of the electric motor can be reduced by 3 to 5 dB(A) with a viscoelastic bearing support. Finally, a strategy is proposed for designing noise reducing viscoelastic bearing supports. A set of qualitative design rules and a more quantitative design approach are presented.
|Award date||27 Feb 2003|
|Place of Publication||Enschede|
|Publication status||Published - 27 Feb 2003|