1,721,025 research outputs found
A technique for the measurement of the plane wave reflection coefficient of shallow water seabeds (paper presented at Acoustical Oceanography 2001)
No full textAirfoil gust interaction: historical survey. (In, collected presentations from a workshop on the acoustics of fan-gust interaction)
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Phase calibration of in-duct axial microphone arrays
No full textIn-duct microphone arrays are used in experimental test facilities to understand the generation of noise by aeroengine componants such as fan-blades. A typical microphone array used to perform modal analysis, for example, is a linear array of wall-mounted microphones. Accurate results can only be obtained if the microphone array is well calibrated for both magnitude and phase. As in-situ calibration is often impossible the microphones must therefore be calibrated outside of the duct. This is unsatisfactory as changes in the phase response that result from mounting the microphones in the duct wall after calibration, where they are exposed to flow and temperature effects, and the effects of the microphone mounting are not accounted for. This paper presents a method to calibrate the microphones in-situ using properties of the broadband noise generated, for example, by rotating fan blades. The technique allows the relative phase difference between individual microphones to be determined. The technique is validated using experimental data obtained from a laboratory scale no-flow rig
Modal dispersion curve measurement for the robust inversion of shallow water seabed parameters
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A numerical method for the calculation of dynamic response and acoustic radiation from an underwater structure
No full textAn approach combining finite element with boundary element methods is proposed to calculate the elastic vibration and acoustic field radiated from an underwater structure. The FEM software NASTRAN is employed for computation of the structural vibration. An uncoupled boundary element method, based on the potential decomposition technique, is described to determine the acoustic added mass and damping coefficients that result due to fluid loading effects. The acoustic matrices of added mass and damping coefficients are then added to the structural mass and damping matrices, respectively, by the DMAP modules of NASTRAN. Numerical results are shown to be in good agreement with experimental data. The complex eigenvalue analyses of underwater structure are obtained by NASTRAN solution sequence SOL107. Results obtained from this study suggest that the natural frequencies of underwater structures are only weakly dependent on the acoustic frequency if the acoustic wavelength is roughly twice as large as the maximum structural dimension
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