Desen Yang

Statistically Optimized Cylindrical Near-Field Acoustic Holography Study Based on Measurement of Vector Hydrophone Array

Statistically optimized near-field acoustic holography (SONAH) is a new technique which is a variant of near-field acoustic holography (NAH). In SONAH, the reconstructed acoustic field is obtained from a weighted sum of the measured data on the holographic surface. Therefore, it could overcome the truncation errors posed by the spatial Fourier transform used in traditional NAH. Applying this method to identify the noise sources in underwater cylinder, the principle of the statistically optimized cylindrical near-field acoustic holography based on measurement of particle velocity was presented. A numerical simulation study has been carried out. Then an experiment has been conducted using vector hydrophone array. The experimental results show the great advantage of the SONAH in the reconstruction of sound field, as well as the identification and localization of noise sources. Keywords-statistically optimized; near-field acoustic holography; particle velocity; vector hydrophone array

Parameter Analysis and Experimental Investigations on Cylindrical Broadband Acoustic Holography

Broadband acoustic holography based on intensity measurement (BAHIM) is a new technique for the reconstruction of sources. In BAHIM method, the acoustic intensity vector and potential energy density, which are both quadratic quantities, on the measurement surface are used to obtain the pressure phase. The principle of the cylindrical BAHIM theory is presented. In addition, the numerical simulations have been conducted. The influences of the change of parameters are discussed in detail. At last, the validity of BAHIM method and the correctness of parameter analysis are assessed by underwater near-field acoustic holography experiments. The experimental results show the merits of the underwater cylindrical BAHIM in the reconstruction of sound field, identification and localization of the noise sources. Keywordscylindrical BAHIM; parameter analysis; intensity measurement

The evolution of the power spectral density for finite amplitude sound wave

A method to predict the effect of nonlinearity on the power spectral density of a plane sound wave traveling in fluid is presented. The Burgers equation is employed for the mathematical description of the combined effects of nonlinearity and dissipation. The effect of the random noise field on its power spectrum after the addition of the strong single frequency wave is discussed. The Burgers equation is numerically solved through the finite difference method. Numerical results have shown that the frequency of the high frequency wave extends the original noise within the noise frequency band and the transformation efficiency of the noise energy in the finite amplitude will increase after the addition of the high frequency wave.A method to predict the effect of nonlinearity on the power spectral density of a plane sound wave traveling in fluid is presented. The Burgers equation is employed for the mathematical description of the combined effects of nonlinearity and dissipation. The effect of the random noise field on its power spectrum after the addition of the strong single frequency wave is discussed. The Burgers equation is numerically solved through the finite difference method. Numerical results have shown that the frequency of the high frequency wave extends the original noise within the noise frequency band and the transformation efficiency of the noise energy in the finite amplitude will increase after the addition of the high frequency wave.

Research on the influence of dispersion in the shallow water waveguide on the parametric array

In practice, the application of parametric array is limited due to the effect of dispersion in the shallow water waveguide which has a significant impact on the propagation of the difference frequency wave. This paper attempts to provide better understanding of the difference frequency field in the shallow water waveguide by discussing the virtue source of parametric array in such circumstance. In the paper, the Green’s function of the shallow water waveguide is employed for calculating the difference frequency field with the help of virtue source in waveguide. It shows that the wavenumber mismatch caused by waveguide dispersion will restrain the accumulation of difference frequency wave and bring about fluctuations during the process of accumulation. Furthermore, this paper discusses the nonlinear interaction with different modes of pump wave based on the former conclusion and reveals pictures to describe the complicated mode structure of the difference frequency field.

Beam characteristics of the truncated parametric array generated by a panel piston radiator

A theoretical model is presented to describe the difference frequency beam characteristics of the truncated parametric array generated by a panel piston radiator. In this model, a low-pass acoustic filter is used to truncate the virtual-source. The truncated virtual-source can be viewed as a volume distributed cylindrical source and conic source within and beyond the Rayleigh distance, respectively. The difference frequency beam characteristics near the truncated position are significantly changed. Numerical simulation results show that the difference frequency beams near the truncated position are substantially sharpened with the distance between the observation point and the truncated position decreasing. Besides, the difference frequency beamwidth near the truncated position can be used to predict the farfield beamwidth of the truncated parametric array.

Bubble nonlinear dynamics and stimulated scattering process

A complete understanding of the bubble dynamics is deemed necessary in order to achieve their full potential applications in industry and medicine. For this purpose it is first needed to expand our knowledge of a single bubble behavior under different possible conditions including the frequency and pressure variations of the sound field. In addition, stimulated scattering of sound on a bubble is a special effect in sound field, and its characteristics are associated with bubble oscillation mode. A bubble in liquid can be considered as a representative example of nonlinear dynamical system theory with its resonance, and its dynamics characteristics can be described by the Keller–Miksis equation. The nonlinear dynamics of an acoustically excited gas bubble in water is investigated by using theoretical and numerical analysis methods. Our results show its strongly nonlinear behavior with respect to the pressure amplitude and excitation frequency as the control parameters, and give an intuitive insight into stimulated sound scattering on a bubble. It is seen that the stimulated sound scattering is different from common dynamical behaviors, such as bifurcation and chaos, which is the result of the nonlinear resonance of a bubble under the excitation of a high amplitude acoustic sound wave essentially. The numerical analysis results show that the threshold of stimulated sound scattering is smaller than those of bifurcation and chaos in the common condition.

Analogy between the one-dimensional acoustic waveguide and the electrical transmission line in the cases of nonlinearity and relaxation

The propagation of plane acoustic waves can be investigated by taking advantage of the electro-acoustical analogy between the one-dimensional acoustic waveguide and the electrical transmission line, because they share the same type of equation. This paper follow the previous studies and expand the analogy into the cases of quadratic nonlinearity and dispersion produced by relaxation process. From the basic equations relating acoustic pressure, density fluctuation and velocity, which are valid for the nonlinear and relaxing media, the equivalent travelling-wave circuits of one-dimensional acoustic waveguide with the consideration of nonlinearity and relaxation processes are obtained. Furthermore, we also discuss the analogy relationship of parameters which exist in the acoustical and electrical systems.

Acoustic characteristics of the medium with gradient change of impedance

The medium with gradient change of acoustic impedance is a new acoustic structure which developed from multiple layer structures. In this paper, the inclusion is introduced and a new set of equations is developed. It can obtain better acoustic properties based on the medium with gradient change of acoustic impedance. Theoretical formulation has been systematically addressed which demonstrates how the idea of utilizing this method. The sound reflection and absorption coefficients were obtained. At last, the validity and the correctness of this method are assessed by simulations. The results show that appropriate design of parameters of the medium can improve underwater acoustic properties.

Numerical investigation of bubble nonlinear dynamics characteristics

The complicated dynamical behaviors of bubble oscillation driven by acoustic wave can provide favorable conditions for many engineering applications. On the basis of Keller-Miksis model, the influences of control parameters, including acoustic frequency, acoustic pressure and radius of gas bubble, are discussed by utilizing various numerical analysis methods, Furthermore, the law of power spectral variation is studied. It is shown that the complicated dynamic behaviors of bubble oscillation driven by acoustic wave, such as bifurcation and chaos, further the stimulated scattering processes are revealed.

Nonlinear interaction of monochromatic wave with noise

The nonlinear interaction of monochromatic wave with noise is studied theoretically, and that is based on the theory of O. V. Rudenko about interactions of intense noise waves and the theory of G. H. Du about nonlinear interaction of finite amplitude irregular waves. The effect on shifting of noise energy by the intensity and frequency of monochromatic wave is discussed during the propagation of the monochromatic wave and noise. Some numerical simulations about this process are conducted under different initial conditions to investigate the changes of their spectrum. The agreement between theoretical analysis and numerical simulation demonstrates that under some conditions the noise can be modulated and the noise spectrum becomes flatter and broader with the increasing distance.