The work in this thesis examines the structural-acoustic interaction problem within
enclosures using both analytical and numerical solutions. The analytical solutions for
the noise generated within a uniform linear duct and a three-dimensional rectangular
cavity are given. It is shown how the acoustic field inside the linear duct could be
controlled by altering the boundary conditions. This gives a basic understanding of the
interaction problem and of the measures available in the much more complex case of
vehicle noise control to reduce or avoid boom problems.
An analytical solution for the acoustic pressure within a closed rectangular cavity with
one flexible simply supported panel is given. The results of this analysis are used to
find the effect, in terms of acoustic stiffness, of such a backing cavity on panel
vibration. Both the acoustic field and the structure are analysed. It is shown that using
mobility measurement as input data to the acoustic analysis gives better results than
using structural analysis.
Numerical modelling of interior noise problems, with application to the interior of
vehicles, is presented. An efficient and accurate computer program has been developed
and tested on a variety of enclosures. The code is written in FORTRAN and uses the
Boundary Element Method as the analysis tool to calculate the interior sound level in
a volume surrounded by boundaries of arbitrary shape. The input data required for the
numerical model are a surface mesh of boundary elements and the vibrational data on
the surface. The vibrational data in this thesis are obtained from mobility
measurements. The acoustic field is then modelled by the Boundary Element Method.
The numerical technique is applied initially to simple geometries, such as a uniform
linear duct and a three-dimensional rectangular cavity, and later the technique is applied
to a scale-model of a vehicle. Predicted results are compared with the measured
pressure response in the interior of these cavities.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.