RU2374744C1 - Underwater vibration source with controlled resonance frequency - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: radiating pistons (1) in a vibration source are fitted around an electric motor parallel its axis on connecting rods (2), which are connected to flanges (3) and (4), attached to faces of the inner (5) and outer (6) components of the electric motor. Component (5) is fitted on an axle (7) which joins rigid covers (8). The inside (9) of the source is sealed with elastic packing (10). One of the covers (6) is fitted with a connecting pipe (11) for letting compressed air into the cavity (9). Components of the electric motor are made in form of flywheels with equal moment of inertia, fitted with possibility of opposite rotational oscillatory motion. The length of connecting rods (2) is equal to the radius of the circle, along which connecting rods are movable attached to flanges (3, 4).

EFFECT: proposed device has regulated amplitude of the emitted signal at operating frequency, with elimination of circumferential loads in the arm of the piston and reduction of linear distortions of the emitted signal.

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Description

The invention relates to marine seismic and can be used as a generator of vibrations when performing a vibration effect on an oil sea deposit from a layer of water in order to increase its oil recovery.

The possibility of accelerating the process of restoring oil deposits on land using the vibrational effect on them from the surface of the earth is proved. (S.M. Gadiev. Using vibration in oil production. M.: Nauka, 1977, 160 p.). However, if we proceed from the arsenal of vibration sources developed for land (mainly unbalanced vibrators) to act on the deposits on the sea shelf, you will have to place them in airtight containers and firmly fix them on the ground, or use multi-ton inert mass overlays.

When using an underwater source of vibration, which includes the elastic volume of the gas and the power system for its buildup, the surrounding water can play the role of an inert mass. For this, the frequency of the emitted signal must be chosen from the condition that the depth of the sea is equal to an odd number of quarters of the compression wavelengths in water. This condition also determines the depth of the source, which may be less than the depth of the sea (Kovalevsky V.V. Creation of powerful seismic sources based on the use of elastic volume oscillations in a liquid. - In Sat: Problems of vibroseismic research methods. Novosibirsk, VTs, 1979, p. 25-31). Thus, the operating frequency of the source is determined by the depth of the sea.

Known broadband hydraulic underwater sources of vibration (for example, according to US patent No. 3978940, G01V 1/04, publ. 09/07/1976). An achievement in this area is the product of Geophysical Co. Inc. (USA). This is a non-resonant source with a 1.55 m diameter piston, weighing 1,530 kg, consuming hydraulic power of 50 kW and having an efficiency of 1.5% (Graham R. Jonson, Ian Thompson, Leon J. Walker The GECO Marine Vibrator System. - SEG Conference, Abstracts, Los Angeles, 1988, pp 71-73). It is clear that such a low efficiency of practitioners will not satisfy.

The difficulties in creating a highly efficient underwater source of vibration are associated with the smallness of its wave dimensions, as a result of which its emitting surfaces are loaded with radiation resistance, in which the reactive component predominates. This component has a mass character and can be compensated by adjusting the elasticity of the mechanical oscillatory system of the source to obtain resonance at the radiation frequency. An effective solution to this problem is to attach an underwater vibration source to the emitting piston of the air bubble chamber with a flexible sheath, which is tuned to resonance at the radiation frequency by changing its volume (Sims C. Bubble transducer for radiating high power low-frequency Sound in Water // J Acoust. Soc. Amer. 1960, V.32, No. 10, p. 1305-1308). However, if, for example, the sea depth is 150 m, then it turns out that to work at a frequency of 7.5 Hz, a vibration source immersed to a depth of 50 m needs a resonant spherical bubble with a volume of more than 5 cubic meters (M. Isakovich, General Acoustics. M: Science, 1973, 493 p.). Changes in the volume of air in such a bubble and compensation for its buoyancy is a serious technical problem.

The closest in technical essence and the set of essential features is an underwater source of vibration and low-frequency sound, containing a hard emitting piston, the oscillations of which are excited by a crank drive, which converts rotational motion into oscillatory (Rimsky-Korsakov A.V., Yamshchikov BC, Zhulin V. I., Rekhtman V.I. Acoustic underwater low-frequency radiators (Leningrad: Sudostroenie, 1984, 184 pp.). In such a source, the amplitude of the vibrational displacements of the piston does not depend on the crank speed, therefore, the mechanical load of the piston is proportional to the square of the radiation frequency (i.e., acceleration of the piston). As a result, the amplitude-frequency characteristic of the source is substantially non-linear, and the operating frequency range is small. If an air chamber-bubble, tuned in resonance with the radiation frequency, is not used, then its efficiency is extremely small in this range, except for the frequency at which the air elasticity in the inner cavity of the source compensates for the inertia of the piston and the vibrating mass of water. Angular vibrations of the connecting rod with respect to the piston surface cause harmful tangential loads in its suspension. For the same reason, the reciprocating component of the oscillations of the end of the connecting rod associated with the piston (with uniform rotation of the engine) is not harmonic, i.e. The source signal contains non-linear distortion.

The objective of the proposed technical solution is to provide the ability to control the frequency of the resonance of the source (without changing its average volume) and control the amplitude of the emitted signal at the operating frequency, as well as eliminate tangential loads in the suspension of the pistons and reduce non-linear distortions of the emitted signal.

The problem is solved in that in an underwater vibration source containing a vibration exciter such as a rotation motor, connecting rods and radiating pistons, the electric motor elements are made in the form of flywheels with equal moments of inertia installed with the possibility of counter rotational vibrations, these elements are equipped with flanges associated with radiating pistons by means of connecting rods, and the length of the connecting rods is equal to the radius of the circle along which the connecting rods are movably mounted on the flanges.

Figure 1 shows an axial section of the proposed source of vibration, figure 2 - its transverse sections.

Radiating pistons 1 are mounted around the electric motor, parallel to its axis, on the connecting rods 2, connected with flanges 3 and 4, fixed at the ends of the internal (5) and external (6) elements of the electric motor. The element 5 is mounted on the axis 7 connecting the rigid covers 8. The inner cavity 9 of the source is sealed with elastic gaskets 10. One of the covers 6 is equipped with a fitting 11 for supplying compressed air to the cavity 9. A DC motor is used in the source (its collector is not shown in the figures) .

The source of vibration works as follows. Through the nozzle 11, compressed air is supplied into the cavity 9 to obtain the necessary excess (relative to the external environment) pressure. Its value is determined by the frequency of the emitted signal and does not depend on the depth of immersion. Under the action of excessive pressure, the pistons 1 move apart, occupying the extreme position, the connecting rods 2 are oriented radially. The mechanical system of the source becomes oscillatory. With the same angular deviation of the flanges 3 and 4 in mutually opposite directions, a returning moment of forces arises, determined by the magnitude of the overpressure. For one period of torsional vibrations of the flanges of the connecting rods 2 occupy a radial position twice. Thus, the pistons 1 in-phase oscillate in radial directions with a frequency twice the frequency of torsional vibrations of the flanges. An alternating current of a frequency close to the frequency of torsional vibrations is supplied to the motor armature (element 5). At the resonance, the reactive components of both the radiation resistance and the intrinsic mechanical resistance of the vibration source are compensated.

The amplitude of the linear velocity of the connecting points of the connecting rods 2 on the flanges 3, 4 during torsional vibrations exceeds the amplitude of the speed of the radial vibrations of the pistons 1. Therefore, the bulk of the kinetic energy of the vibrational system is stored in flywheels and its relatively small part in the pistons and the oscillating mass of the environment. For small oscillation amplitudes of the pistons, the resonant frequency of torsional vibrations F is mainly determined by the total moment of inertia of the flywheels I and the excess pressure P (but not the average volume of the emitter’s air cavity, and not the immersion depth) in the source cavity 10:

,

,

where S is the surface area of the pistons; R is the radius of the circles along which the connecting rods 2 are mounted on the flanges 3, 4. In this case, the emitting pistons 1 in-phase oscillate in radial directions with a frequency of 2F.

The amplitude control of the emitted signal at the operating frequency can be carried out both by changing the effective value of the alternating current of the armature (element 5), and due to the excess pressure R.

Calculations show that if the length of the connecting rods 2 is equal to the radius of the circle along which the connecting rods are movably fixed on the flanges 3, 4, then the radial component of the oscillations of the ends of the connecting rods connected with the pistons is close to harmonic and the nonlinear distortions of the emitted signal are practically absent.

Each piston is associated with an oscillation agent by two pairs of connecting rods, and the angular vibrations of the connecting rods with respect to the piston surface in each pair are out of phase, therefore there are no harmful tangential loads in the piston suspensions.

Claims (1)

An underwater vibration source with a controlled resonance frequency, comprising an oscillating agent in the form of radiating pistons that are mounted around the electric motor parallel to its axis, whose vibrations are excited by a crank drive, characterized in that the radiating pistons are mounted on rods connected to flanges fixed to the ends of the armature and the external element of the electric motor, the frequency of torsional vibrations of which is determined by the excess pressure of the internal sealed cavity of the vibrats source and the frequency of the current supplied to the anchor, while the length of the connecting rods is equal to the radius of the circle along which the connecting rods are movably mounted on the flanges, and each radiating piston is connected to the oscillator by two pairs of connecting rods, the angular oscillations of which are opposite to the surface of the piston in each pair.

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