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For the typical underwater acoustic channels with time-frequency double extension characteristics, the channel estimation performance can be improved by introducing a norm constraint into the channel estimation algorithm based on the sparse distribution feature of the channels. However, at the presence of varying multipath structure caused by change of depth or velocity gradient, the classic l0 or lx norm constraint methods are subject to performance degradation due to lack of adaptability to sparsity. A previously derived non-uniform norm constraint LMS (NNCLMS) algorithm is introduced, and then a convergence analysis is made on it. In the form of non-uniform norm, the NNCLMS algorithm is used to accommodate the different sparsities caused by different multipath structures. Numerical simulation and sea experimental results show that the estimation performance of the proposed method is superior to that of the classic l0 or lx norm constraint algorithm. [ABSTRACT FROM AUTHOR]

The sound positioning system is designed on the basis of two MCU configurations. The source of 1 kHz sound is from the buzzer controlled by MCU with PWM. The sound receive module consists of four electret microphone. The feature of our system is based on TDOA (Time DUference of Arrival). And the mainstream CHAN Algorithm algorithm could is used to improve the precision of sound positioning. [ABSTRACT FROM AUTHOR]

A blind space spectrum subtraction( BSSS) method based on hyper beam forming for interference cancellation is proposed for two typical near-field strong interference sources (towed-ship self noise and friendly neighbor ship noise) which affect the target detection performance of towed array sonar. The hyper beam technology is used to form multi-beams to cover a strong interference area. The amplitude spectrum of interfering beams is computed, and the multi-beam amplitude spectrum is subtracted from the basic element field amplitude spectrum by using an appropriate spectrum subtraction strategy. The frequency signal of basic element field is get from the cancelled amplitude spectrum signal, and the target azimuth is estimated using the frequency field block adaptive filtering algorithm. The simulation and sea test results show that BSSS method can improve the array gain by about 10 dB compared to the minimal variance distortionless response (MVDR) method under the conditions of high interference-to-noise ratio and low signal-to-noise ratio. BSSS method can be used simultaneously to cancel the towed-ship self noise and the friendly neighbor ship noise, and effectively reduce the fluctuation of detected background. [ABSTRACT FROM AUTHOR]

The volume changing characteristics of the bubble produced by the pyrotechnic composition combustion underwater are the research foundation of the underwater combustive sound source. In order to analyze the characteristic of the acoustic radiation and phenomenon of the pyrotechnic composition combustion underwater, the high speed photography was used to study the behavior of the bubble at exit, which was generated by the pyrotechnic composition combustion underwater. A new calculative method about volume of the bubble which was based on AutoCAD was put forward, then, their velocity and changing acceleration were obtained. Results showed that the maximum changing speed and changing acceleration of the volume for bubble is respectively 1. 62 X 10-4 m³/s and 1. 93 x 10-2 m³/s², respectively. And these results could be considered as solid references for mathematic model and composition design in near future. [ABSTRACT FROM AUTHOR]

To reduce vehicle inner noise caused by road excitation, the road surface is built, Acoustic Transfer Vector (ATV) method and 1/3 octave filter method are used to get A-level sound pressure of the center frequency and total sound pressure felt by drivers for the sound between 20 and 250 Hz beside driver's ears, and so the sound response of human ears to sound loudness can be reflected truly. The excitation forces between suspension and body under asphalt road excitation are simulated by using dynamics software; the body vibration velocity response is calculated by response analysis function of finite element method; taken body vibration velocity response as boundary constrains, the acoustic response in body cabin is calculated by acoustic transfer vector method which is based on boundary element. The obtained relationship between road excitation and vehicle inner noise can provide references for vehicle inner noise control and suspension system optimization. [ABSTRACT FROM AUTHOR]

To study the properties of sound absorption characteristics of porous metallic materials at high temperature conditions, the sound absorption properties of porous materials with temperature changes was studied firstly in theory. And then, a temperature-controlled high-temperature impedance tube measurement device was designed. Different results of different acoustic properties porous metal material were measured at different high temperatures, and the relationships between absorption properties and temperatures were studied. The predicted and measured results are in good agreement basically, and the theoretical analysis and design of measuring device are reasonable. [ABSTRACT FROM AUTHOR]

The time-domain blind deconvolution algorithm based on contrast function and deflation has recently become the focus of intensive research work due to its potential in many applications. However, it has a disadvantage that the separation results are easily influenced by the length of deconvolution filters when the signals come from machine sound. In this paper, an improved blind deconvolution algorithm based on hierarchical cluster is proposed. Hierarchical cluster is applied to analysis the results which are obtained by using a group of deconvolution filters of various lengths. Therefore, the improved algorithm can be employed to receive more reliable and better estimated signals. Computer simulation and acoustical transient impulse signal extraction of faulty bearing in a real-world situation are used to verify the validity of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Most mechanical vibration of machines is a random process with stochastic characteristics. The traditional wave superposition method can not solve acoustic radiation problem with random boundary condition. In this paper, the statistical wave superposition method is proposed, which combines the wave superposition method with the statistical one. By using the vibration velocity self-spectrum of the structure surface the random field is calculated. According to the simulations of the vibrating cubic box, it is proved that the method proposed in this paper can give good results of acoustic radiation caused by the random vibration in wide analytical frequencies. Its maximum calculation errors is 1. 3%. [ABSTRACT FROM AUTHOR]