Vibroacoustic response of stiffened plates and cylinders for acoustic fatigue application

Abstract

Vibroacoustic response prediction is a key requirement when one considers acoustic fatigue and sound transmission. Whilst various methods have been developed for vibroacoustic predictions, their applicability and efficiency are limited when applying the methodologies to complex structures and conditions typically present in aerospace applications. The aims of this study are to improve a simplified prediction methodology, so that the effects of stiffeners, curvature, nonlinearity and elevated temperature can be incorporated into a general, efficient and accurate prediction. To achieve this a new framework with some of the existing formulated vibroacoustic quantities is proposed. A linear modal model was developed to predict the vibroacoustic response of stiffened thin plates to incident sound. The model was subsequently extended and applied to stiffened cylinders, where the rigid scattering of the incident sound was included. Subsequently, the surface pressure prediction from the model was experimentally validated for a scaled fuselage structure. Finally, a geometrically nonlinear reduced order model (NLROM) was developed for structures possessing deep stiffeners, high curvature and elevated temperatures. The effects of the nonlinear static characterisation and direct time integration on the predictions were investigated. The effects of vibroacoustic coupling, nonlinearity and elevated temperature for fatigue were quantified. The key finding was that stiffeners, curvature, nonlinearity and elevated temperature can have significant impacts on the vibroacoustic response and subsequent fatigue life. Firstly, the vibroacoustic coupling is enhanced by stiffeners. Secondly, the presence of curvature can weaken the coincidence and wavelength selectivity as seen in the Joint Acceptance Functions (JAFs). Thirdly, the onset of nonlinear behaviour is initiated at higher excitation levels when there is the presence of stiffeners and curvature. These features, together with a temperature rise, can be captured by the NLROM with appropriate improvement, development and implementation. Finally, the vibroacoustic coupling, nonlinearity and raised temperature are important factors in the estimation of the fatigue life. A significant computational reduction is also achieved and shown using the proposed model, whilst retaining good accuracy compared to existing methodology such as a fully coupled finite element – boundary element model or a fully dynamic nonlinear finite element model solution.

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Identifiers

ORCID for Dong Zhao: orcid.org/0000-0002-1380-9306

ORCID for Neil Ferguson: orcid.org/0000-0001-5955-7477

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