Advanced vibro-acoustic condensed models for multi-layer structures

Uthayasuriyan, Arasan (2022) Advanced vibro-acoustic condensed models for multi-layer structures. PhD thesis, University of Nottingham.

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This thesis concerns the development of analytical condensed models to predict the vibroacoustic responses of planar multi-layer structures. Typical structural components in, e.g., aerospace applications involve multi-layer composite panels and evaluation of vibroacoustic indicators (for example, transmission loss) of these multi-layer structures through finite element analysis would result in expensive computational power and time. This is due to an increase in the total number of degrees of freedom which results from a complete description of each different layer in the multi-layer system. This challenge could be tackled by employing a condensed and equivalent single layer that simulates the vibroacoustic behaviour of the multi-layer system which would require lesser computational storage that effectively reduces the computation time. In addition, condensed models enable us to understand the physical behaviour of the multi-layers at different frequency regimes. The existing equivalent plate models describe the propagation of bending and shear waves in multilayers, giving a useful prediction for vibroacoustic indicators across the range of audible frequencies if the multilayer structure does not contain soft material in terms of longitudinal compression. As the compressional (or dilatational) wave propagation is not employed in current models, they are applicable only to relatively thin multilayer systems.

In this context, this doctoral thesis addresses the four major research advancements made to these models. The first advancement focuses on the limits of applicability of plate theories, which are commonly employed in many vibroacoustic applications. As there are no clear-cut analytical expressions available in the literature for the frequency limits of plate theories, these expressions are obtained for an elastic solid layer of isotropic nature, through wavenumber and admittance analysis. Refined expressions for exact coincidence and critical frequencies are also provided by comparing the propagative wavenumbers in the single-layer plates. The Transmission Loss (TL) computations using plate theories are compared to the TL computed using the Transfer Matrix Method (TMM) for a variety of thin/thick and soft/stiff materials, to validate these frequency limits.

A simple condensed (or equivalent) plate model is developed as a second advancement,for three-layer sandwich structures made of isotropic materials. Even though the existing condensed plate models provide matched response with that of the principles of elasticity, these models would consume considerable time for implementation processes. Therefore, to overcome this challenge, a simpler and easier version of the equivalent plate model is developed by observing the physical behaviours of a three-layer structure. The model requires only four key parameters that are sufficient to describe the natural behaviour of the three-layer structure at all frequencies. Validation of this simple model has been done by comparing its response with the existing equivalent plate model as well as the experimental data, which are observed to be well-matched.

In the third advancement, an advanced vibro-acoustic condensed model is developed for symmetric multi-layer structures including its dilatational effects. The novelty of this model lies in capturing both symmetric and anti symmetric motions of the multilayers while the existing condensed plate models could handle only the anti-symmetric motions. The condensed layer obtained through the presented model will have three dynamic mechanical properties by describing two decoupled admittances correspond to symmetric and anti-symmetric motions. The model is validated with the transmission loss responses obtained from the TMM for different multi-layer configurations.

As a final advancement of this thesis, a Finite Element (FE) scheme is proposed, to compute vibro-acoustic indicators from the novel condensed model that is developed as the third advancement of this thesis. The FE scheme consists of two decoupled condensed plates with corresponding dynamic intrinsic properties that are obtained from the new condensed model. Through multiple validation cases, the computational efficiency of the proposed condensed FE scheme has been shown, in comparison with the conventional three-dimensional FE approach.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Chronopoulos, Dimitrios
Tanner, Gregor
Keywords: Condensed models, Equivalent plate models, Plate theories, Multi-layer structures, Flexural rigidities, Wavenumbers, Finite element analysis, Dilatational motion
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 67482
Date Deposited: 31 Jul 2022 04:40
Last Modified: 31 Jul 2022 04:40

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