Vibration analysis of built-up structures by combining finite element analysis and analytical impedances
Vibration analysis of built-up structures by combining finite element analysis and analytical impedances
Most of today's structures such as a ship machinery foundation or a car body are built up from beams and plates. In many cases, the vibration sources are supported by either the large stiffness of beams or the large in-plane stiffness of thin plates. The thesis argues that under this condition, the power injected into, and the power transmitted around the structure is controlled by long wavelength waves. As these long waves propagate they generate short wavelength flexural waves at the numerous structural joints. The long waves transmit some of their energy to the short waves which therefore damp the long waves. The difference in the wavelengths of the long and short waves is often very large. Additionally, the impedance of the long waves may be much larger than that of the short waves. The difference in the wavelengths means that the short waves present a locally-reacting impedance to the long waves at the structural joints. These conditions allow the vibration to be predicted using a 'hybrid method' which comprises 3 steps as follows: First, the long wave response is analysed in isolation of the short wave response using finite element analysis; second, the short wave response is analysed in isolation of the long wave response using analytical impedances; third, the two separate responses are coupled using a standard sub-structuring procedure to yield the complete response due to both waves.
The hybrid method is applied to 2 structures. The first is a plate-stiffened beam consisting of a directly-excited beam attached to a large plate which is representative of the machinery foundation of a ship. The second is a 6-sided thin plate box which when excited at its edges is representative of a car body. The hybrid method predicts the frequency response of these structures which compare very well with laboratory measurements, thereby confirming the thesis.
The method is particularly adept in predicting structural response in cases where the long waves are modally sparse and the short waves are modally dense. In these cases, current methods for the analysis of built-up structures are generally either theoretically inapplicable or practically inefficient. The hybrid method is therefore considered a useful extension to current methods.
University of Southampton
1998
Grice, Richard Michael
(1998)
Vibration analysis of built-up structures by combining finite element analysis and analytical impedances.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Most of today's structures such as a ship machinery foundation or a car body are built up from beams and plates. In many cases, the vibration sources are supported by either the large stiffness of beams or the large in-plane stiffness of thin plates. The thesis argues that under this condition, the power injected into, and the power transmitted around the structure is controlled by long wavelength waves. As these long waves propagate they generate short wavelength flexural waves at the numerous structural joints. The long waves transmit some of their energy to the short waves which therefore damp the long waves. The difference in the wavelengths of the long and short waves is often very large. Additionally, the impedance of the long waves may be much larger than that of the short waves. The difference in the wavelengths means that the short waves present a locally-reacting impedance to the long waves at the structural joints. These conditions allow the vibration to be predicted using a 'hybrid method' which comprises 3 steps as follows: First, the long wave response is analysed in isolation of the short wave response using finite element analysis; second, the short wave response is analysed in isolation of the long wave response using analytical impedances; third, the two separate responses are coupled using a standard sub-structuring procedure to yield the complete response due to both waves.
The hybrid method is applied to 2 structures. The first is a plate-stiffened beam consisting of a directly-excited beam attached to a large plate which is representative of the machinery foundation of a ship. The second is a 6-sided thin plate box which when excited at its edges is representative of a car body. The hybrid method predicts the frequency response of these structures which compare very well with laboratory measurements, thereby confirming the thesis.
The method is particularly adept in predicting structural response in cases where the long waves are modally sparse and the short waves are modally dense. In these cases, current methods for the analysis of built-up structures are generally either theoretically inapplicable or practically inefficient. The hybrid method is therefore considered a useful extension to current methods.
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Published date: 1998
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Local EPrints ID: 463354
URI: http://eprints.soton.ac.uk/id/eprint/463354
PURE UUID: 48901ba0-8b31-41db-ba8b-8903bde0dd51
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Date deposited: 04 Jul 2022 20:50
Last modified: 04 Jul 2022 20:50
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Author:
Richard Michael Grice
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