RU2376696C1 - Deepwater low-frequency hydroacoustic emitter for acoustic tomography systems - Google Patents

Abstract

FIELD: physics; acoustics.

SUBSTANCE: invention relates to hydroacoustics and allows for efficient emission of directional signals at frequencies in the range of first hundreds of hertz at large immersion depths. The deepwater low-frequency emitter for acoustic tomography systems comprises pipe sections 1, attached to a magnetic conductor 2, in which there is a row of radial through-holes 6 and longitudinal grooves 7. In the gaps between flanges 4 and the magnetic conductor 2, coils 9 are movably mounted on elastic suspensions 8 such that, directions of their vibrational displacements are opposite. When the emitter is working, axial distribution of the velocity of the sound wave, approximately corresponding to half-wave resonance, is established in the water filling the pipe. Main emitting surfaces are the open ends of the pipes.

EFFECT: simpler design, increased efficiency, reduced mass and size of the emitter.

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Description

The invention relates to hydroacoustic technology and can be used as a deep-sea directional emitter of low-frequency signals for sensing ocean waters in order to monitor and predict its state.

The sounding of the ocean with the subsequent solution of the inverse problem of hydroacoustics provides ample opportunities for remote, operational and continuous monitoring of mesoscale inhomogeneities of water masses. Effective use of this method, called "acoustic tomography", is possible only if systems are used that include a significant number of autonomous low-frequency sonar emitters installed in the ocean at various depths. At the same time, the requirements for emitters are:

- suitability for generating amplitude-modulated acoustic signals at frequencies in the range of 100-300 Hz;

- independence of acoustic parameters from immersion depth;

- axisymmetric radiation directivity characteristic, the maximum plane of which is horizontal (it is supposed to use signals propagating in different directions along trajectories close to horizontal);

- high efficiency and specific (per unit mass) acoustic power (equivalent to the requirement of low cost of operating autonomous emitters).

At present, many types of sonar emitters have been developed and are used. Some of them are suitable for generating low-frequency amplitude-modulated signals. The parameters of others do not depend on the depth of immersion. Both of these qualities combine emitters with liquid filled resonators made in the form of a half-wave tube segment with open ends. They have an axisymmetric radiation directivity characteristic, the maximum plane of which is perpendicular to the axis of the pipe.

A known emitter, for example, according to US patent No. 4855964, BV 1/06, H04R 17/00, publ. August 8, 1989, containing a transducer in the form of a piezoceramic ring mounted between the flanges of two identical pipe sections at the maximum alternating pressure of a standing sound wave. In the frequency range from 4600 to 2200 Hz, its efficiency is from 72% to 20%. If the main resonance frequency of such an emitter is in the range from 500 to 300 Hz, then at frequencies near the resonance the efficiency is from 30 to 10% (Lee B. Low-frequency sound projector for underwater sound. - IEEE International conference on engineering in the ocean environment. Halifax, 1974, v. 2, p. 10-15). With a decrease in the operating frequency of such emitters, maintaining the efficiency and acoustic power at the same level requires a sharp increase in their size and mass, which raises the cost of manufacturing and operating the emitters to unacceptable values. The main reason for this is the low specific power of piezoelectric transducers when used in the low sound frequency range.

The magnetic field energy densities easily attainable by conventional means are many times greater than the achievable electric field densities in piezoelectric transducers. Therefore, to increase the specific acoustic power and ensure high efficiency of deep-sea low-frequency emitters with half-wave resonant tubes operating at relatively low frequencies in the range of 100-300 Hz, it is necessary to use well-matched converters containing magnets in them.

The closest in technical essence and the set of essential features to the proposed technical solution is a converter, for example, according to US patent No. 7071584, Н02К 41/00, publ. July 4, 2006, FIGS. 4 and 19, comprising a hollow cylindrical inductor with a permanent magnet and two pole-flanges, a cylindrical magnetic circuit and two coils mounted on a common clip and movably mounted in the annular gaps between the cylindrical surfaces of the flanges and the magnetic circuit. The windings are turned on so that the directions of the alternating forces created by them coincide. Such a converter does not lose operability when filling its cavities with liquid and, therefore, can be used in deep-sea low-frequency emitters with half-wave resonant tubes. However, this requires matching devices: a rod, a piston and a cylinder whose axis is perpendicular to the axis of the pipe, complicating the emitter and increasing its mass, the converter will have to be located next to the pipe, which will increase the transverse dimensions of the emitter. If a single converter is used, then during its operation unbalanced transverse oscillations of the radiator reducing efficiency will occur. The use of two or more converters will additionally complicate the design and increase the transverse dimensions of the emitter.

The objective of the proposed technical solution is to simplify the design, reduce the size and weight of the deep-sea low-frequency sonar emitter with a half-wave resonant tube.

The problem is solved in that in a low-frequency sonar emitter containing a hollow cylindrical inductor with a permanent magnet and two pole-flanges, a cylindrical magnetic circuit and two coils, movably mounted in the annular gaps between the cylindrical surfaces of the flanges and the magnetic circuit, the coils are turned on so that their vibrational directions the displacements are opposite, at the ends of the magnetic circuit there are segments of quarter-wave resonance tubes, the inductor is mounted on rigid brackets, and in nitoprovode there are a number of through radial holes and longitudinal grooves intersecting holes.

The essence of the proposed technical solution is illustrated by drawings, where Fig. 1 shows a longitudinal axial section of the emitter, and Fig. 3 shows transverse sections of the transducer. The emitter contains a rigid casing in the form of two pipe sections 1, mounted on the ends of the magnetic circuit 2, as well as an inductor with a permanent magnet 3 and pole-flanges 4. The inductor is mounted on rigid brackets 5. In the magnetic circuit 2, opposite the magnet 3 there are a number of through radial holes 6 and longitudinal grooves 7 intersecting the openings 6. In the annular gaps between the flanges 4 and the magnetic circuit 2, on the elastic suspensions 8, coils 9 are movably mounted. The coils 9 are turned on so that the winding directions of the wire coincide in them, which provides positive directions of vibrational displacements of the coils 9.

Such a radiator works as follows. The emitter is immersed in water, ensuring the vertical position of the axis of the housing, while its cavities are freely filled with water. When applying alternating current to the coils 9 with a frequency equal to the main frequency of the longitudinal resonance, the axial distribution of the amplitudes of alternating pressure P and velocity V of the standing sound wave, approximately corresponding to the half-wave resonance, shown in Fig. 2, is established in the water column in the pipes. The surface area of the end face of the coil 9 is much smaller than the internal cross section of the pipe 1, and the wave value of the diameter of the pipe is small. Therefore, due to the effect of "hydraulic transformation", the mechanical impedance on which each coil is loaded is much less than the impedance of the cross section of the water column in the pipe, which provides a sufficiently high speed of oscillation of the coils and allows to achieve high efficiency. Moreover, the volumetric vibrational velocity of water in the holes 6 is much less than the volumetric vibrational velocities at the open ends of the pipe sections 1, the cross sections of which are the main radiating surfaces. The longitudinal grooves 7 eliminate the unused metal of the magnetic circuit, which facilitates the design, and reduce the speed of water oscillations near the radial holes 6, which reduces viscous and hydrodynamic losses.

Claims (1)

A deep-sea low-frequency sonar emitter containing segments of quarter-wave resonant tubes, a hollow cylindrical inductor with a permanent magnet and two pole-flanges, a cylindrical magnetic circuit and two coils movably mounted in the annular gaps between the cylindrical surfaces of the flanges and the magnetic circuit, characterized in that, in order to simplify the design , increase the efficiency, as well as reduce the dimensions and mass of the emitter, pipe sections are installed at the ends of the magnetic circuit yes, in the magnetic circuit there are a number of through radial holes and longitudinal grooves intersecting these holes, and the coils are turned on so that the directions of their vibrational displacements are opposite.

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