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l: Sound radiation patterns and prevailing sound intensity Sound radiation patterns and prevailing distribution sound pressure distribution

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l: Sound radiation patterns and prevailing sound intensity Sound radiation patterns and prevailing distribution sound pressure distribution

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This research study used a simple structure to describe the interaction between structure and fluid behavior. A better understanding of this interaction will help to improve the simulation of future vehicles during the early stages of development. This report was written in partial fulfillment of the requirements for the degree of bachelor of applied science at the HAN University, Automotive.
For a better understanding of the fluid behavior and the interaction between structure and fluid, first a defined structure was built. This rectangular enclosure behaved like a rigid body up to approximately 600 Hz. The box was first simulated, then built and verified using experimental modal analysis. It was possible to replace the rigid top of the enclosure with a more flexible in bending plate, mounted in a rigid aluminum frame. The project was first built up by obtaining defined fluid characteristics. The second step was obtaining defined structure characteristics of the plate on top. Both have analytical and experimental approaches. Finally, to reach the target of this research study, the radiation patterns were measured from the structure to the fluid.
Since the box and the contained fluid didn’t interact up to 600 Hz, boundary conditions for a rigid structure were used to calculate the fluid eigenmodes and frequencies. These calculations were compared to the experimental modal analysis of the fluid inside the box with all six rigid walls. The deviation of the measurement to the analytic solution was less than 0.5 %. This is considered accurate enough to obtain a defined fluid.
The same method was used for obtaining a defined flexible structure. First, calculated eigenfrequencies and eigenmodes were computed for both clamped and simply supported boundary conditions. Then, using these frequencies as target frequencies, the mounting was adapted in practice until this finally resulted in an accurate approach to the calculations of the simply supported structure. Note that the reproducibility of the plate is on 2 Hz difference, the deviation between calculation and measurement is less than 5 % up to 200 Hz and less than 1.5 % above 200 Hz.
The interaction of the structure to the fluid was only experimentally studied. The visualizations of the fluid were then later qualitatively analyzed to recognize characteristic behavior in the radiation patterns. The global fluid modes were hardly affected by the influence of the changed boundary condition of the top plate. The fluid modes appear at approximately the same frequency. They show the same pattern and show up in the same order. The results of the experiment showed four different radiation patterns depending on the wavenumbers of the plate’s modes as shown below:
1. When both modes are odd, the fluid is excited uniformly in every direction, resulting in a global radiation pattern in Z-direction.
2. When the X wavenumber is even, it results in a global radiation pattern in X-direction. 3. When the Y wavenumber is even, it results in a global radiation pattern in Y-direction. 4. When both wavenumbers are even, it results in a coupled radiation pattern both in X-
and Y-direction.
The results of this project can be used to validate an analytic model that describes the interaction between structure and fluid. However, it is recommended to perform an extra measurement of the fluids interaction with higher resolution. At higher frequencies, above 300 Hz, the fluid modes are hardly recognizable due to the lack of measurement points. In this study, the fluid modes up to 600 Hz were measured and these modes showed the same radiation patterns, though it is far less recognizable than the patterns up to 300 Hz.

Toon meer
OrganisatieHogeschool van Arnhem en Nijmegen
Opleiding
InstituutInstituut Automotive
Lectoraat
Gepubliceerd in
Datum2013-06-03
TypeBachelorscriptie
TaalEngels

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