An experimental exploration of the properties of random frequency response functions

Clot, A ORCID: https://orcid.org/0000-0001-5805-2792, Meggitt, JWR ORCID: https://orcid.org/0000-0002-6665-2939, Langley, RS, Elliott, AS ORCID: https://orcid.org/0000-0003-4894-0053 and Moorhouse, AT ORCID: https://orcid.org/0000-0002-4034-1091 2021, 'An experimental exploration of the properties of random frequency response functions' , Journal of Sound and Vibration, 491 , p. 115773.

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Abstract

The vibro-acoustic analysis of complex structures over a broadband frequency range is an extremely challenging problem that may often require the use of a hybrid deterministic-statistical approach. Due to manufacturing imperfections, the frequency response functions (FRFs) of an ensemble of nominally identical systems can be considered to be random. These FRFs, however, have statistical properties that can be potentially used in vibro-acoustic models. This work explores some of these fundamental properties by using measured FRFs from an ensemble of nominally identical structures, obtained by randomising a thin rectangular plate using point masses. It is first shown that the measured ensemble of FRFs satisfies the analyticity-ergodicity condition, experimentally verifying this recently demonstrated fundamental property. Then, the ensemble is used to explore whether the direct field dynamic stiffness, a key parameter in a well-established hybrid deterministic-statistical formulation, can be obtained experimentally. The results are compared against those computed using numerical techniques, showing that measured data may be a suitable alternative provided that an ensemble of systems can be measured. Finally, an alternative method, based on the use of virtual point masses, opposed to physical ones, is proposed for those cases where experimental randomisation is particularly challenging. It has been found, however, that the method may be extremely sensitive to measurement imprecisions, specially when applied to lightly damped structures. It is concluded that the statistical properties of random causal FRFs are not only interesting in themselves, but can enhance and extend vibro-acoustic prediction models.

Item Type: Article
Additional Information: ** From Elsevier via Jisc Publications Router
Schools: Schools > School of Computing, Science and Engineering
Journal or Publication Title: Journal of Sound and Vibration
Publisher: Elsevier
ISSN: 0022-460X
Related URLs:
Funders: Engineering and Physical Sciences Research Council (EPSRC), Bentley Motors Ltd, Bruel Kjaer, Dyson Ltd, Wave six LLC
SWORD Depositor: Publications Router
Depositing User: Publications Router
Date Deposited: 24 Nov 2020 08:38
Last Modified: 17 Dec 2020 08:40
URI: http://usir.salford.ac.uk/id/eprint/58898

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