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Title: A combined modal/finite element technique for the non-linear dynamic simulation of aerospace structures
Author: McEwan, Matthew Ian
ISNI:       0000 0004 2679 9738
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2001
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The surface panels of modern high-speed aircraft are subjected to high-intensity acoustic loading from sources such as jet efflux and turbulent fluid flow. The vibration induced by this loading may result in fatigue crack growth near stress concentrations, and may eventually cause in-service failure of the structure. Central to the acoustic fatigue design problem is knowledge of the dynamic response of the structure in questions, so that some fatigue damage model may be applied in order to determine the fatigue life of the structure. In this thesis, a combined normal mode /finite element technique is developed for modelling non-linear beams, plates and stiffened panels, undergoing large amplitude vibrations. The loads and displacements from a number of static non-linear finite element test cases are transformed into modal co-ordinates using the normal modes of the underlying linear system. Regression analysis is then used to find the unknown coupled non-linear modal stiffness coefficients. The inclusion of finite element derived modal mass, and an arbitrary damping model completes the governing non-linear equations of motion. Time domain numerical integration is then used to simulate the response to excitation with a wide variety of possible spatial and temporal components. The particular benefits of this approach are that a significant time-saving mnay be achieved in comparison to conventional finite element methods, and that almost am commercial finite element package may be employed without modification. The proposed method is applied to homogeneous isotropic beams. Fully simply supported and fully clamped boundary conditions are considered. For the free vibration case, results are compared to those of previous researchers. For the case of steady state harmonic, and random excitation, results are compared with the direct integration non-linear finite element method. For plates and stiffened panels, the stress response of the structure is determined by, identifying the non-linear relationship between stress and modal displacements, using a regression analysis. Also a formulation is proposed to allow the simulation of travelling planar pressure waves. These waves may impinge upon the structure at any angle. In order to demonstrate the proposed method, random excitation is applied to flat rectangular plates, and orthogonally stiffened panels. The Autopower Spectral Density estimates of the displacement and stress are obtained for a number of different excitation cases. In all of these problems, the proposed method demonstrates good agreement with the direct integration finite element method.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available