Investigation into the Parameters Affecting the Microvibration Response of Reaction Wheel Assembly Bearings
Creators: name: HODGE, CAMERON CHARLES
Publisher: name: University of Surrey
Year: 2021

description: Reaction wheel assemblies (RWA) are well-known major sources of microvibrations, whilst they have been studied thoroughly and many disturbance types can be reasonably modelled, bearing disturbances and how their amplitude evolves with the RWA rotational speed are not at the same level of confidence. Whilst studies have been carried out, many of the test rigs used do not truly show the bearing harmonic development, either due to interference from other disturbances such as structural modes or are not representative of an RWA. This study aims to investigate the parameters that affect the bearing harmonic amplitudes using a novel test rig. The work covered in this thesis can be split into two sections focusing on the design and application of a novel test rig.
description: The first piece of work discussed in this thesis is the design and validation process of the novel test rig named the Kistler bearing test rig (KBTR). The focus of this mechanism was to simulate the motion of a reaction wheel assembly, whilst creating a structurally dynamic free region so that the fundamental bearing disturbances determined using a series of analytically determined equations could be observed without interference. This test rig is considered novel as it bridges the gap between a full RWA and bearing specific test. By taking an industry standard RWA, the objectives of the novel test rig was achieved by raising the natural frequencies using a small inertia disk and relocating the motor away from the other components. The microvibration signature of the KBTR was then recorded using a dynamometric table and then plotted on a series of disturbance maps. After isolating the bearing harmonics, it showed that the majority followed a parabolic function with no distinct interference from any other disturbance. To complete this section, two empirical models taken from the literature, were used to fit curves to the results which confirmed that fundamental harmonics followed a parabolic function.
description: The remaining work carried out for this study aimed at investigating how a range of parameters and external influences affect the microvibration response. The parameters and external influences discussed in this study predominantly involves those introduced during the manufacture, and launch. Including the effect of assembly, static unbalance, and the effects of the launch environment. Whilst the static unbalance had almost no distinct changes on the bearing harmonics large variability was observed when the KBTR was disassembled and reassembled. A detailed investigation was carried at analysis levels ranging from a macroscopic down to harmonic and included creating statistical distributions. Comparing the results to those seen in flight ready RWA pre flight tests, it was thought that this variability is likely caused by manufacturing tolerances and as result slight movement or non-exact assembly is occurring. To further investigate this, finite element analysis was carried out simulating many different localised defects scenarios.