The vibroacoustic behaviour of aluminium extrusions used in railway vehicles
The vibroacoustic behaviour of aluminium extrusions used in railway vehicles
The objective of this thesis is to establish a modelling approach for aluminium extrusions which enables an extruded panel to be represented in terms of a small number of subsystems and be incorporated into the overall SEA model for interior noise of vehicles.
To estimate the modal density of extruded panels, the effects of boundary conditions on the mode count and modal density of one- and two-dimensional structural systems, beams and plates respectively, are investigated by using the wavenumber integration method. It is demonstrated, for one-dimensional systems, that the average mode count is reduced by between 0 and 1 for each boundary constraint, depending on the type of boundary conditions. The effects of line constraints on the mode count of two-dimensional systems are similar to the equivalent one-dimensional constraints but they are always frequency-dependent. The modal density is largely independent of boundary conditions for one-dimensional systems, although there are exceptions, while it is dependent on boundary conditions for two-dimesional systems. The results are compared with those from previously published formulae for natural frequencies and with results from finite element (FE) analysis. Inclusion of the effect of the boundary conditions in SEA estimations will result in improved agreements with both analytical and numerical model results.
To model the sound radiation from extruded panels, the average radiation efficiency of point-excited rectangular plates, including those with a very large aspect ratio (‘strips’), is investigated by using a modal summation method based on the far-field sound intensity. By taking an average over all possible forcing positions on the plate, the cross-modal contributions average out to zero. The numerical results from the modal summation are compared with established formulae for rectangular plates. For wavenumbers where acoustic circulation takes place, it is shown that the previously published formulae are not applicable for predicting the average radiation efficiency for a strip. Approximate expressions for calculating the average efficiency of the strip are then derived. The maximum radiation efficiency of a rectangular plate around the critical frequency is found to vary less with Halmholtz number kca where kc is the wavenumber at the critical frequency and a is the width, than previously published models suggest.
The vibration behaviour of an extruded panel is dominated by global modes at low frequency while local modes of individual strips are dominant at high frequency. By taking account of the boundary effects, the approximate mode count and modal density are obtained for extruded panels. The result is compared with that from an FE model. The coupling between global and local modes is modelled in terms of the travelling global waves exciting the edges of each strip under the assumption that the local modes of each strip are uncorrelated. The coupling between the local modes is modelled using standard expressions for various structural joints. The average radiation efficiency of the extruded panel is developed using a modal summation approach. SEA models for extruded panels are finally assembled using these components.
University of Southampton
Xie, Gang
e0263fb8-0c53-4790-97ee-273424cfd0c0
2004
Xie, Gang
e0263fb8-0c53-4790-97ee-273424cfd0c0
Xie, Gang
(2004)
The vibroacoustic behaviour of aluminium extrusions used in railway vehicles.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The objective of this thesis is to establish a modelling approach for aluminium extrusions which enables an extruded panel to be represented in terms of a small number of subsystems and be incorporated into the overall SEA model for interior noise of vehicles.
To estimate the modal density of extruded panels, the effects of boundary conditions on the mode count and modal density of one- and two-dimensional structural systems, beams and plates respectively, are investigated by using the wavenumber integration method. It is demonstrated, for one-dimensional systems, that the average mode count is reduced by between 0 and 1 for each boundary constraint, depending on the type of boundary conditions. The effects of line constraints on the mode count of two-dimensional systems are similar to the equivalent one-dimensional constraints but they are always frequency-dependent. The modal density is largely independent of boundary conditions for one-dimensional systems, although there are exceptions, while it is dependent on boundary conditions for two-dimesional systems. The results are compared with those from previously published formulae for natural frequencies and with results from finite element (FE) analysis. Inclusion of the effect of the boundary conditions in SEA estimations will result in improved agreements with both analytical and numerical model results.
To model the sound radiation from extruded panels, the average radiation efficiency of point-excited rectangular plates, including those with a very large aspect ratio (‘strips’), is investigated by using a modal summation method based on the far-field sound intensity. By taking an average over all possible forcing positions on the plate, the cross-modal contributions average out to zero. The numerical results from the modal summation are compared with established formulae for rectangular plates. For wavenumbers where acoustic circulation takes place, it is shown that the previously published formulae are not applicable for predicting the average radiation efficiency for a strip. Approximate expressions for calculating the average efficiency of the strip are then derived. The maximum radiation efficiency of a rectangular plate around the critical frequency is found to vary less with Halmholtz number kca where kc is the wavenumber at the critical frequency and a is the width, than previously published models suggest.
The vibration behaviour of an extruded panel is dominated by global modes at low frequency while local modes of individual strips are dominant at high frequency. By taking account of the boundary effects, the approximate mode count and modal density are obtained for extruded panels. The result is compared with that from an FE model. The coupling between global and local modes is modelled in terms of the travelling global waves exciting the edges of each strip under the assumption that the local modes of each strip are uncorrelated. The coupling between the local modes is modelled using standard expressions for various structural joints. The average radiation efficiency of the extruded panel is developed using a modal summation approach. SEA models for extruded panels are finally assembled using these components.
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Published date: 2004
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Local EPrints ID: 465281
URI: http://eprints.soton.ac.uk/id/eprint/465281
PURE UUID: 77b6dfd1-c78d-45cd-a6c5-921ed47560e4
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Date deposited: 05 Jul 2022 00:34
Last modified: 16 Mar 2024 20:05
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Author:
Gang Xie
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