Investigating the Mid-Frequency Range of Micro-Vibration Predictions in Spacecraft Structures

Abstract eng:
In the recent years, due to the higher-stability requirements imposed by the modern satellites’ payloads, an increasing amount of emphasis is being placed in understanding microvibrations. Current research aims to achieve a higher stability of the entire structure, including the control of these low level mechanical disturbances created by different sources in the spacecraft, e.g. reaction wheels and cryo-coolers. One of the main issues relating to micro-vibrations is their computational analysis. Satellite structures when in operation may behave differently than expected due to the low stress conditions (and zero gravity), vacuum and other characteristics of the space environment, and consequently a more adequate modeling approach is needed. Other concerns involve obtaining accurate predictions in the mid frequency range - i.e. above the first few modes of vibration. Finite Element Analysis (FEA) is at its most effective when analyzing the low frequency range that encompasses the first few modes of vibration in the structure. It allows for accurate estimates to be made of the low frequency response of a range of structures. At higher frequencies, Statistical Energy Analysis (SEA) is the method of choice, being proven to accurately assessing structural responses. When frequencies between these two ranges are involved, many methods have been developed, but all of them are subject to limitations. Here a new method is presented, created to meet the needs of three different necessities: (i) the requirement to implement a method which gives accurate estimates covering the entire frequency range; (ii) the common practice to transfer models between companies in a reduced form (often stiffness and mass matrices); (iii) the constant need to further increase the speed of analysis without adversely affecting the quality of the results. This method involves both the Craig-Bampton reduction and modal perturbations: in this paper a benchmark example and a practical application will be shown. All the work done in drawing the conclusions of the project behind this paper has been supported by an experimental campaign involving the spacecraft SSTL 300 (made available by Surrey Satellite Technology Limited), the use of which also being briefly described herein.

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