Shengguo Shi

The High Resolution Orientation Research of under Water Composed Array Sources in near Field via the Most Likely Estimation

The high resolution orientation of under water composed array sources in near field via the most likely estimation is represented in this paper. In this method, the Most Likely Estimation algorithm is applied to a single vector hydrophone and composed array which is built up by sound-pressure hydrophones. The left or right fuzzy in the noise source orientation is decreased by using the unilateral directivity of vector hydrophone. With the advancement of the sound pressure array ML in high resolution orientation, heredity algorithm is used to gain the most optimized solution of ML. In this way, the high resolution orientation of the under water source in near field is achieved. The algorithm is proved to be effective in the computer simulation

Nearfield acoustical holography for cylindrical geometry: Resolution and accuracy in the two boundaries

With the development of the vector hydrophone, the underwater NAH (nearfield acoustic holography) technology based on the particle velocity measurement gradually become a research hotspot. Compared with the measurement of the sound pressure, the particle velocity amplitude decays more quickly which makes it have a better resolution for the complex sound sources situation. Particularly when reconstructed the sound field based on the STSF algorithm, it could get a better edge continuity. This paper applied NAH technology based on the particle velocity measurement to reconstruct the cylinder surface sound field based on STSF algorithm, analyzed the affection of the sample interval for the reconstructive resolution and accuracy. And compared advantages and disadvantages when reconstruct the sound field by the sound pressure and the radial particle vibration velocity in the two typical boundaries.

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.

Underwater asymmetric acoustic transmission structure using the medium with gradient change of impedance

We propose an underwater asymmetric acoustic transmission structure comprised of two media each with a gradient change of acoustic impedance. By gradually increasing the acoustic impedances of the media, the propagating direction of the acoustic wave can be continuously bent, resulting in allowing the acoustic wave to pass through along the positive direction and blocking acoustic waves from the negative one. The main advantages of this structure are that the asymmetric transmission effect of this structure can be realized and enhanced more easily in water. We investigate both numerically and experimentally the asymmetric transmission effect. The experimental results show that a highly efficient asymmetric acoustic transmission can be yielded within a remarkable broadband frequency range, which agrees well with the numerical prediction. It is of potential practical significance for various underwater applications such as reducing vibration and noise.

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.