Noise reduction of rotating machinery by viscoelastic bearing supports


Tillema, Hetzer Gido (2003) Noise reduction of rotating machinery by viscoelastic bearing supports. thesis.

open access
Abstract: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
(3) experimental investigations into the mechanical properties of viscoelastic
(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
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.
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