Underwater patch near-field acoustical holography based on particle velocity and vector hydrophone array

One-step patch near-field acoustical holography(PNAH) is a powerful tool for identifying noise sources from the partially known sound pressure field.The acoustical property to be reconstructed on the surface of interest is related to the partially measured pressure on the hologram surface in terms of sampling and bandlimiting matrices,which cost more in computation.A one-step procedure based on measuring of the normal component of the particle velocity is described,including the mathematical formulation.The numerical simulation shows that one-step PNAH based on particle velocity can obtain more accurately reconstructed results and it is also less sensitive to noise than the method based on pressure.These findings are confirmed by an underwater near-field acoustical holography experiment conducted with a vector hydrophone array.The experimental results have illustrated the high performance of one-step PNAH based on particle velocity in the reconstruction of sound field and the advantages of a vector hydrophone array in an underwater near-field measurement.

Research on fiber-optic interferometric hydrophone array using frequency division multiplying technique

From the point of view of system design, a configuration of fiber-optic interferomet- ric hydrophone array and its modulation and demodulation approach using frequncy division multiplexing technique based on Phase Generated Carrier (PGC) is introduced. And the em- phasis on demonstrating the relationship among the number of units N, the detectable signal amplitude D and the detectable frequency ws through analyzing the frequency spectrum of the output signal of the J × K array and the key factor which restricts N, D, Ws for increasing are presented. The maximum phare shift and the law of its variation according to frequency are specially analyzed. The results induced from some relative theory were verified by experiments.

High-resolution azimuth estimation algorithm based on data fusion method for the vector hydrophone vertical array

To aim at the problem that the horizontal directivity index of the vector hy- drophone vertical array is not higher than that of a vector hydrophone, the high-resolution azimuth estimation algorithm based on the data fusion method was presented. The proposed algorithnl first employs MUSIC algorithm to estimate the azimuth of each divided sub-band signal, and then the estimated azimuths of multiple hydrophones are processed by using the data fusion technique. The high-resolution estimated result is achieved finally by adopting the weighted histogram statistics method. The results of the simulation and sea trials indicated that the proposed algorithm has better azimuth estimation performance than MUSIC algorithm of a single vector hydrophone and the data fusion technique based on the acoustic energy flux method. The better performance is reflected in the aspects of the estimation precision, the probability of correct estimation, the capability to distinguish multi-objects and the inhibition of the noise sub-bands.

Interior noise field of a viscoelastic cylindrical shell excited by TBL pressure fluctuations:Ⅱ. finite hydrophone and array

Finite hydrophone and hydrophone array are the wave vector filter and can re-duce the flow noise. In this paper the responses of the cylindrical area hydrophone and two-circular area hydrophone within viscoelastic cylindrical shell to the TBL (turbulent boundary layer) pressure fluctuations are investigated. Applying the method based on the wavenumber frequency spectrum analysis, the expressions of 1) the noise power spectrum of a single hy-drophone; 2) the space correlation of two hydrophones; 3) the noise power spectrum of array are derived. The dependencies of the noise reduction on hydrophone shape, dimension, element amount and separation of hydrophones of array are calculated by numerical integration. The wide-band and narrow-band correlation for two hydrophones is also calculated. The numerical results show that hydrophone array can effectively reduce the interior noise.