Vibroacoustic power flow in infinite compliant pipes excited by mechanical forces and internal acoustic sources

Abstract

The present thesis is concerned with the theoretical and experimental description of vibroacoustic power flow in infinite fluid-filled pipes excited by hydroacoustic noise sources, such as flow control valves. The walls of the pipes are assumed to be compliant, so that vibrations of the shell wall induce pressure fluctuations in the fluid, and vice versa. The coupling between the pipe wall and the contained fluid is provided by the fluid loading of the pipe; the methods presented are valid for both light and heavy fluid loading.

Two distinct and complementary approaches are investigated for quantifying the vibroacoustic power flow: numerical simulations and controlled experiments.

The core of the numerical simulation approach is a vibroacoustic analogy that transforms the excitation of the fluid-filled pipe by internal turbulent flow into an equivalent vibroacoustical problem where the excitation is provided by a distribution of vibroacoustic sources applied to a pipe containing stationary fluid. When the excitation is formulated as an equivalent distribution of vibroacoustic sources (structural and acoustical), the resulting vibroacoustic power flow can be calculated via an extension of existing theory.

The necessary analytical and numerical tools for the prediction of the vibroacoustic power flow are assembled for point force excitation of the pipe wall, and for point monopole, point dipole, and point quadrupole excitation of the fluid.

The relative Mach number scaling of far-field fluid pressure radiated inside the pipe, for point monopole, point dipole, and point quadrupole, is investigated and the in-pipe results are compared to the corresponding free field results.

The proposed experimental approach involves mounting the noise source in an instrumented pipe system under controlled conditions. If one-directional wave propagation can be established (e.g. through anechoic terminations of the pipe), then the power input by the source can be inferred from modal measurements of the pipe wall response.

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