| Summary: | This thesis considers the problem of high-frequency wave energy scattering and propagation in composite structures.
In particular, structures made of the two-dimensional plate- or shell-like elements with composite laminate material are of interest. We propose an extension of the Dynamical Energy Analysis (DEA) method for such structures. For this purpose, we develop a semi-analytical and a hybrid Finite Element (FE) and Wave and Finite Element (WFE) methods to compute wave energy reflection/transmission at junctions of arbitrarily layered composite plates.
In the first part of the thesis, a brief review of high-frequency numerical methodologies is presented. Advantages and limitations of each method are discussed. Furthermore, a review of analytical and numerical methods for calculating wave propagation characteristics such as dispersion relations, group velocity and scattering coefficients is presented.
In the second part of the thesis, the main theoretical basics of the DEA method, Classical Laminated Plate theory and the WFE method are demonstrated.
In the third part of the thesis, semi-analytical method for computing the energy scattering coefficients of structural junctions made up of thin composite laminated plates is developed. Expressions quantifying transmission and reflection coefficients as a function of the frequency and the angle of incidence are derived. An effective scattering matrix for a plate with multiple finite stiffeners attached to it is obtained.
In the fourth part of the thesis, a hybrid FE/WFE model that predicts the scattering properties for different junctions of two-dimensional anisotropic composite plates is developed. The influence of the angle of incidence and the frequency on the distribution of the power flow of incident bending, shear and longitudinal type waves is investigated.
A detailed comparison with semi-analytical evaluations of scattering coefficients derived in the third part of the thesis is presented. The method gives for the first time a detailed recipe for computing scattering coefficients for the generic case of an arbitrary number of composite plates connected at a junction without restrictions on the angles at which the plate meet or the orientation of the principal axis of individual plates.
In the last part of the thesis, the theoretical base of the DEA method for composite structures is developed and discussed. The findings of the third and fourth parts of the thesis are used to derive the stationary wave energy density arising in the composite structure due to a harmonic point and edge sources. Numerical results for the cases of a polygonally shaped plate, an L-shaped composite plate and an electric vehicle gearbox are presented.
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