I. Sh. Fiks

The use of receiving arrays for measuring underwater noise levels of moving sources

A method of measuring underwater noise levels of moving ships with the use of a vertical receiving array is considered. An algorithm is proposed for synthesizing the weight vector that provides a given measurement accuracy with maximal noise suppression for the cases of an interference with a known structure and an a priori unknown interference (the adaptive synthesis). Results of both numerical simulation of the method and its experimental testing under actual sea conditions are presented.

Reconstruction of the Beam Pattern of a Line Source from Near-Field Measurements

We study the error of reconstruction of the beam pattern of a line source, which is based on measuring its near field on an infinite cylindrical surface in the presence of uncorrelated noise. It is shown that the supremum error is proportional to the number of arbitrary orthogonal functions describing the source.

Experimental studies of sound field suppression at discrete frequencies

Practical implementation of an active sound control system ensuring sound suppression in outer space is described as applied to sound insulation problems for equipment whose total noise level is mainly due to low-frequency discrete spectral components. The operational principle of the proposed system is based on inverse field generation with respect to the field of the initial source of quasi-monochromatic signals. The inverse field is formed by a set of radiators, which are controlled by the signals of pressure receivers positioned in the near field of the source. Experimental studies carried out with the proposed sound control system demonstrate its efficiency and testify to the stability of its operation.

Remote sensing of moving wide-band sources

We consider the methods of covariance matrix reconstruction for sensing an extended noise-like emitter which moves near the receiving antenna array and is modelled as a random longitudinal distribution of external elementary sources. Linearized maximum-likelihood equations for the desired covariance matrix are obtained in the cases of a priori known and unknown covariance matrix of the noise background. The variance of estimates for the elements of the covariance matrix characterizing the emitter is studied.

Limiting Capabilities of the Active Suppression of Sound Harmonic Signals

A system for the active suppression of sound with an open-loop feedback is described in relation to problems of the sound insulation of devices that radiate at discrete frequencies. Its principle of operation is based on creating a compensating field inverse to that of the primary source. The compensating field is formed at a monochromatic frequency that coincides with or is close to the frequency of the compensated signal. The efficiency and limiting capabilities of such a system are investigated.

Near-field measurement of radiation levels of extended spatially uncorrelated sound sources

A method is considered for measuring the radiation levels of extended spatially uncorrelated sound sources in the near field in the case of their imprecise positioning with respect to the measurement system—a linear antenna array. An algorithm is proposed for synthesizing the vector of weight coefficients ensuring the given value of methodological measurement error under maximum suppression of external noise. Examples are given of numerical modeling and experimental testing of the method in natural conditions.

The parametric method of reconstructing the field of a radiator from pressure measurements in its near zone

A method of determining the field of a radiator from pressure measurements in its near zone is proposed. The method is based on parametrization of the field by a set of complex spherical sources. The field of the radiator is calculated using the spherical harmonic amplitudes, which are determined by solving the inverse problem. Results of numerical simulation are presented.