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Random Data Analysis And Measurement Procedures

An analytical solution is presented for the problem of radiation of sound waves from a semi-infinite circular cylindrical coated pipe which is partially lined from inside. By stating the total fiel...

Radiation analysis of sound waves from semi-infinite coated pipe

The thesis investigates possibilities of air-borne sound characterisation of arbitrary sound sources. To this end a particular approach is studied where the source characterisation is done via an interface surface which fully or partially envelopes the physical source. Two frequency dependent descriptors are defined across such a surface: the blocked sound pressure and the source impedance. The former represents the sound pressure created by the operating source which acts on the enveloping surface when this is made immobile. The latter represents the ratio of pressure response amplitudes and normal velocity excitation amplitudes across the surface. The enveloping surface defines an air volume containing the physical source, called the source space. The two source descriptors defined on the source space, the blocked pressure and the source impedance, are shown to be intrinsic to the source, i.e. independent of the surrounding acoustical space. Once defined, these descriptors allow one to find the sound pressure and normal particle velocity at the interface surface when the source space is coupled to an arbitrary receiver space, i.e. a room. This in turn allows for sound prediction in the receiver space. The coupling conditions require that the receiver space is characterised using the same enveloping surface as the source space. Bearing the measurement simplicity in mind, the enveloping surface has been conceived as consisting of one or several rectangular plane surfaces. The research challenge was then to obtain meaningful surface impedance across a (continuous) rectangular plane surface as well as the blocked pressure compatible with impedance formulation. This has led to a spatial decomposition of sound pressure and particle velocity into finite number of components, each defined by a complex amplitude and a particular spatial distribution. In this way the blocked pressure reduces to a vector of complex pressure amplitudes while the impedance becomes a matrix of pressure and velocity complex amplitude ratios. Two decomposition methods have been investigated in detail: the surface harmonic method and the patch method. The former approximates the surface pressure and normal velocity by combinations of 2D trigonometric surface functions while the latter splits the surface into small patches and treats each patch in a discrete way, using patch-averaged values.

https://tel.archives-ouvertes.fr/tel-01777809/document

Characterisation of air-borne sound sources using surface coupling techniques

This paper describes the use of a single hydrophone to estimate the motion parameters of an autonomous underwater vehicle (AUV) from the underwater acoustic signal excited by its propulsion motor. First, the frequency range of the hydroacoustic signal radiated by the AUV motor is determined, and a detection and recognition model is designed. In the case of uniform linear motion of the AUV, the geometric relationship between the Doppler frequency shift curve of the sound source is derived and the motion model of the sound source and sound line propagation is established. An estimation algorithm for the motion parameters of multiple AUVs based on data from a single hydrophone is derived. Then, for Doppler underwater acoustic signals disturbed by independent identically distributed noise with an arbitrary probability distribution, a cumulative phase difference power amplification instantaneous frequency estimation method is proposed. This method is based on the sum of multiple logarithmic functions. Finally, the effectiveness and accuracy of the algorithm in estimating the motion parameters of multiple AUVs are verified through simulations and experiments.

/pdf/motion-parameter-estimation-of-auv-based-on-underwater-3q8h5qtf.pdf

Motion parameter estimation of AUV based on underwater acoustic Doppler frequency measured by single hydrophone

Airborne sound characterisation by a dummy source approach

Measurement of volume velocity of a small sound source

A proper characterisation of noise of a vibrating source has to take into account both radiation from the source and diffraction by its body in order to enable prediction of sound pressure of the source when inserted into a given acoustical space. A particular technique, named the dummy source approach, has been developed with the aim of characterising real noise sources. Here the original source is replaced by a closed rigid cabinet of similar size and shape-the dummy-equipped with several small flush-mounted drivers. The noise of the original source is measured first in a number of control points and the source strengths of the drivers are then identified by inversion. Once a source is experimentally characterised by its dummy, further noise prediction steps can be carried out in a fairly straightforward manner since the source is represented by a simple shape and its excitation is of monopole type. The paper introduces the concept of the dummy source and discusses criteria of its acoustical layout. A characterisation procedure is then carried out via a virtual experiment aimed at validating the approach. The approach is finally validated by experimental results.

https://hal.archives-ouvertes.fr/hal-01279945/document

Characterisation of air-borne noise by a dummy-source approach

This paper investigates least squares spectral analysis as a tool to analyze non-stationary signals from pass-by noise measurements in water. The spectral analysis involves successive least squares fitting of a finite Fourier series to approximate the observation in a piecewise manner. The least squares spectral analysis is used to search the signals for first- and second-order periodicity as well as the presence of fundamental periodicity. A first-order analysis reveals line components in the signals, whereas a second-order analysis reveals periodic amplitude modulations. Analysis with a higher-order finite Fourier series reveals harmonic structures in the signals. The main contribution of this paper is the model of a magnitude-squared cosine wave which can be used to analyze second-order periodicity. The developed short-time least squares spectral analysis is illustrated on noise radiated from a rigid inflatable boat in shallow water.

Short-time least squares spectral analysis of pass-by noise in water from a rigid inflatable boat.

Sound radiation by a driver set in a rigid closed cabinet is modeled analytically using the principle of wave superposition. The driver-cabinet assembly is replaced by an array of volumeless substitute sources—monopoles—confined within its surface. The role of substitute sources is to reproduce the sound field exterior to the surface as close to the original field as possible. The frequency dependent positions and strengths of substitute monopoles are optimized by an iterative search procedure aimed at matching the prescribed surface boundary conditions of the original source. The time-consuming optimization of monopole positions is carried out at narrowband center frequencies reducing the computational cost without significant loss of accuracy. The consistency of computed results is verified by checking the power output through the cabinet surface. Modeling is done for anechoic and semi-anechoic conditions. The model has been validated experimentally in a semi-anechoic room with satisfactory results using a mid-range driver set in a closed-box baffle.

Computation of sound radiation by a driver in a cabinet using a substitute source approach

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Papers

Measurement of volume velocity of a small sound source

Characterisation of air-borne noise by a dummy-source approach

Short-time least squares spectral analysis of pass-by noise in water from a rigid inflatable boat.

Computation of sound radiation by a driver in a cabinet using a substitute source approach