Reaction Wheel Ball Bearings Microvibration Source Characterisation
The microvibration disturbances originating from high speed rotating devices such as Reaction Wheel Assemblies (RWA) have been a satellite stability issue since the beginning of the human space exploration. The potential RW rotor unbalances, assembly misalignments and imperfections affecting the ball bearing components, are some of the main causes that generate microvibrations disturbances onboard, affecting the pointing stability of the satellite line-of-sight. The work presented in this thesis aims to characterize the RW disturbance microvibration amplitude generated by a group of localized geometry imperfections in the ball bearing rolling components. The mathematical and finite element (FE) models developed are combined considering variations of the main bearing structural parameters such as preload, number of balls and the respective diameter size. Several combinations of these parameters are implemented in the various ball bearing nonlinear transient simulations to identify the trends in overall microvibration noise emitted by the bearing during rotation. Consequently, the bearing disturbance trend evaluated is used to show the combination of bearing structural parameters (preload, balls count and balls dimensions) that reduce as much as possible the RW disturbances produced by the bearing imperfections. Furthermore, relative angular displacements between the localized positions of the indentations are introduced in the model to analytically combine each single defect train of impulses and therefore generate the final generalized bearing disturbance model. Moreover, an arbitrary combination of a pair of these bearing models are introduced in the general equations of motions of an imbalanced rotor to analytically evaluate the final microvibration disturbances emitted at the RW base mounting points. Finally, the resulting rotor disturbances analytically estimated are compared against the waterfall plots from a physical rotor test measurement to validate the microvibration amplitude predictions from the proposed numerical-analytical model.
microvibrations, ball bearing, reaction wheels, finite element model
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