RU2532143C1 - Method of determination of nonlinear ultrasonic parameter of liquids and device for its implementation - Google Patents

Abstract

FIELD: physics, acoustics.

SUBSTANCE: invention relates to the field of physical acoustics and is intended for study of ultrasonic properties of liquids, such as marine water and various process fluids. The method includes the generation and reception of signals of minimum two different frequencies, passed through the measuring section, by a single emitter operating in the mode "generation - reception". The time interval between impulses is selected so that the previous impulse has been damped. The measuring section is a distance between the emitter surface and the reflecting surface located axially with it in a parallel plane. The signals area filtered at the difference frequency with measurement of amplitudes of pressure of waves of difference frequency and then the parameter of nonlinearity is determined by the value of nonlinear ultrasonic parameter (ε) according to the formula ε=ε₀[P_Ω(r)/P_Ω0(r)], where ε - value of nonlinear ultrasonic parameter in the studied medium, P_Ω(r) - amplitude of pressure of the wave of difference frequency at the distance r in the studied medium, and ε₀ and P_Ω0(r) - are the values of nonlinear ultrasonic parameter and amplitude of pressure of the wave of difference frequency at the distance (r) in known medium, respectively, determined earlier by calibration.

EFFECT: improvement of resolving ability spatially, sensitivity to manifestation of weak nonlinear effects, and also improvement of reliability of measuring at a small measuring base due to a possibility to accumulate nonlinear effects at a great distance of run of pump waves, which is restricted only by attenuation distance of the sound impulse.

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Description

The invention relates to the field of physical acoustics and is intended to study the acoustic properties of microinhomogeneous liquids, such as sea water and various technical fluids.

The problem of measuring the acoustic nonlinearity of liquids arose in connection with the need to create experimental methods for the diagnosis of micro-heterogeneous liquids of natural and artificial origin. Sea water refers to micro-heterogeneous liquids of natural origin. Its acoustic non-linearity is largely associated with the presence of microinhomogeneities in it such as gas bubbles, plankton, suspensions and other inclusions and their concentration. In technology, the use of microinhomogeneous liquids has positive and negative sides. A positive example of the application of such liquids in industry can be gas-vapor liquid mixtures used in chemical technology. An example of the manifestation of the undesirable properties of microinhomogeneous liquids is the explosive formation of vapor-gas mixtures in the pipelines of reactors and liquid transport systems, which, due to their high nonlinear characteristics, contribute to the formation of shock waves leading to the destruction of pipelines. The acoustic nonlinearity of a liquid changes significantly at high temperatures and during the formation of vapor-gas liquid mixtures.

There are various methods for measuring the nonlinear acoustic parameter of liquid, gaseous, and solid media, which are mainly based on the principle of measuring the amplitude of the 2nd harmonic of the emitted signal (“quadratic nonlinearity”), or waves resulting from the interaction of several initial waves (more often, 2- x acoustic waves - biharmonic signal) in a nonlinear medium.

As a characteristic of deviations from linearity, the concept of an acoustic nonlinearity parameter (G) is introduced [Krasilnikov V.A., Krylov V.V. Introduction to physical acoustics. M .: Nauka, 1984, pp. 11-12]:

, $$G=2{\rho }_{0}c{\left(\frac{\partial c}{\partial P}\right)}_S={\rho }_0{\left(\frac{\partial c^2}{\partial P}\right)}_S$$

,

where P is pressure, ρ is density, c is the speed of sound, S is entropy, derivatives are taken at constant entropy S.

Thus, to determine the nonlinearity parameter, it is necessary to determine the dependence of the speed of sound on pressure.

In the Russian-language literature, another parameter is more popular - the nonlinear acoustic parameter ε (NAP), which is associated with the parameter of acoustic nonlinearity G by the ratio ε = 1 + G / 2. The NAP is directly related to the Riemann solution in the evolution of simple waves, according to which the propagation velocity of a simple wave is c = c ₀ + εν, where ν is the velocity of particles in the wave. The appearance of the dependence of the wave propagation velocity on its amplitude leads to distortions of the wave profile up to the formation of shock waves. The distance at which a plane harmonic wave degenerates into a shock wave is commonly called the discontinuity distance. NAP (ε) has a clear physical meaning - it determines the rupture distance in the wave r ^* according to the relation: r ^* = 1 / εkM, where k = 2πf / c is the wave number, f is the frequency, M = ν / c = P / ρc ² is the Mach number.

A known method of measuring NAP (USSR AS No. 1233032, MKI G01N 29/00), in which the first and second high-frequency converters are installed at a distance from each other equal to less than two wavelengths emitted by a low-frequency converter installed at an angle to the radiation direction high frequency signal. In a non-linear environment, a low-frequency wave modulates a high-frequency wave. The high-frequency signal is emitted by the first converter and the maximum phase shift between the signals emitted by the first and the second converters respectively received is measured. The high-frequency signal is emitted by the second converter and the maximum phase shift between the signals emitted by the second and the first converters is measured. The measured values of the maximum phase shifts, taking into account the angle between the directions of propagation of the emitted low-frequency and high-frequency waves and the distance between the high-frequency converters, determine the desired parameter by the formula

, $$\epsilon =\frac{\left(\mathrm{one}+\cos {\theta }_0\right)\Delta {\varphi }_{\mathrm{one}}/\Delta {\varphi }_2-K\left(\mathrm{one}-\cos {\theta }_0\right)}{\Delta {\varphi }_{\mathrm{one}}/\Delta {\varphi }_2-K}$$

,

where ε is the nonlinear acoustic parameter of the medium; θ ₀ is the angle between the directions of propagation of low-frequency and high-frequency waves in the case when the emitter is the first and the receiver is the second high-frequency converters; Δφ ₁ and Δφ ₂ are the measured maximum phase shifts in the high-frequency wave, when, respectively, the first transducer is the emitter of the high-frequency wave and the second is the receiver, and vice versa, the second is the emitter and the first is the receiver.

A device that implements a method for measuring a nonlinear acoustic parameter comprises a first and second high-frequency transducers, a low-frequency transducer and a high-frequency wave generator, first and second synchronous keys, the inputs of which are connected to the output of the high-frequency wave generator, as well as a series-connected amplifier, phase detector, low-frequency amplifier, and indicator.

The disadvantages of this method are the low accuracy and reliability of determining the nonlinear acoustic parameter of the medium, due to the smallness of the measured phase modulation indices. It is known that the phase modulation Δφ≈εM = εν ₀ / c ₀ , where M is the acoustic Mach number; ν ₀ is the amplitude of the vibrational velocity in the low-frequency wave; c ₀ - speed of sound, ε - NAP (Zverev V.A., Kalachev A.I. Sound modulation by sound at the intersection of acoustic waves. // Acoustic Journal. 1970, v.16, issue 2. S.245-252) . In acoustics, as a rule, M≈10 ^-5 -10 ^-4 [Ultrasound. Little Encyclopedia. Chap. ed. Golyamina I.P. M .: Soviet Encyclopedia, 1979. P.209], therefore, the value Δφ lies in the range 3.5 · 10 ^-5 -3.5 · 10 ^-4 . Such Δφ values are comparable in order of magnitude with the phase noise of the electronic paths, possible phase fluctuations due to small mechanical vibrations of the measuring transducers relative to each other, etc.

Improving the reliability and accuracy of measuring a non-linear acoustic parameter is achieved in the method for determining the non-linear acoustic parameter of liquid media, described in RF patent No. 2168721, G01N 29/00. The method includes emitting a biharmonic wave into a controlled medium, consisting of harmonics with initial amplitudes ν ₀₁ (0), ν ₀₂ (0) of vibrational velocity and frequencies ω, 2ω, receiving a wave transmitted through the medium under study and isolating the second harmonic. The phase invariant of the emitted signal is set equal to π, the amplitudes of the components of the emitted signal are changed, keeping the parameter A constant, equal to the ratio of the initial amplitude of the second harmonic ν ₀₂ (0) to the initial amplitude of the first harmonic ν ₀₁ (0). The value of A is selected from the range from 0 to 0.61 until the amplitude of the received second harmonic at the location of the receiver becomes equal to zero. The initial amplitude of the first harmonic ν ₀₁ (0) of the emitted wave corresponding to this condition is determined, and the nonlinear acoustic parameter is calculated by the formula

, $$\epsilon =\frac{z_0{c}_0^2}{x\omega {\nu }_{01}\left(0\right)}$$

,

where z ₀ , x, ν are related to the coordinates of the receiver and the magnitude of the signals of the fundamental frequency and second harmonic.

To implement the method, a device is used that includes a sinusoidal oscillation generator connected in series, a first adjustable amplifier, to the output of which a frequency doubler and a second adjustable amplifier and phase shifter are connected in series; the outputs of the frequency doubler and the phase shifter are connected to the first and second inputs of the emitter, as well as a receiver, a selective amplifier, and a zero indicator connected in series. The scales of the regulating elements of the first and second adjustable amplifiers 2 and 4 are pre-calibrated so that by direct reference it is possible to determine the amplitudes of the emitted waves ν ₀₁ (0) and ν ₀₂ (0).

However, the measurement method requires the adjustment of the equipment when performing the measurement procedure, which leads to an increase in the measurement time, as well as to a significant complication of the measurement of NAP in natural conditions in the sounding mode in real time.

The measurement of NAP in the sensing mode is given in EP patent No. 0128635 B1, G01K 11/00. This method is based on a non-linear relationship between the speed of sound and the value of acoustic pressure.

$$C=C_0+\frac{\mathrm{one}}{2{\rho }_0{C}_0}\left(\frac{B}{A}\right)P$$

$$\Delta C=\frac{\mathrm{one}}{2{\rho }_0{C}_0}\left(\frac{B}{A}\right)\left(z\right)P$$

where z is the coordinate along the radiation axis.

Acoustic waves of low and high frequencies are emitted into the medium under study, the phase modulation of high frequency waves by low frequency waves is measured taking into account the geometry of the relative positions of the emitters and the receiver, and the change in the speed of sound is determined by the phase shift.

To implement the method, a system consisting of four devices is used: the first - creates a probe wave propagating in the medium under study, the second - provides a pump wave propagating so as to provide interaction with the probe wave, and the third - serves to record the phase change of the probe wave under the influence of the wave pumping and the fourth - in order to determine the magnitude of the nonlinear acoustic parameter based on the detected changes in the phase of the pump wave.

Closest to the claimed is a method for determining the nonlinearity parameter and a device for implementing this method, are described in US patent No. 5521882, publ. 05/28/1996 and selected by us as a prototype. The essence of the method is that an acoustic borehole probe is immersed in the test medium, consisting of at least one acoustic source emitting waves of two different frequencies located along the cable and at least one acoustic receiver for measuring the amplitude of the waves of the difference frequency or the sum of two different frequencies, as well as a complex of measuring equipment connected to them.

Due to the nonlinearity of the structure, acoustic waves of combination frequencies (total and difference) arise in the fluid and in the adjacent walls of the well, and the speed of generation of these waves in space is directly proportional to the degree of nonlinearity of the medium. It is proposed to measure the amplitude of the difference frequency, which decays in the medium more slowly than other waves. The receivers receive the emitted signals along with the signals generated by the nonlinearity of the medium. Using filters or using the Fourier transform, the amplitude of the difference frequency is obtained, and the expression is used to calculate the nonlinear characteristics of the well structure:

D _Δf (z) = 1/4 (2πf _a D _{o, a} / V) (2πf _b D _{o, b} / V) Ω (λµ a βγ) z.

This expression relates the amplitude of the wave of the difference frequency D _Δf (z), taken at a distance z, with the amplitudes and frequencies of the emitted waves D _oa , D _ob , f _oa , f _ob , and the speed of sound V in a given medium. The expression includes the so-called functional indicator Ω, which is associated with the Lamé coefficients λ, μ, characterizing the elastic properties of the medium, and nonlinearity characteristics α, β, γ.

The task of measuring the nonlinearity parameter in a well filled with a fluid is technically very similar to the task of measuring the nonlinear parameter of sea water at various depths of the sea or technical fluids inside the pipeline. In both cases, a measurement system is required that can operate at different depths, is compact and allows measurements to be carried out in minimal time. If in an oil well the measurement conditions are not subject to sharp changes in time and space, then for measurements in unstable conditions of the sea, and even more so in rapidly changing process conditions, it is desirable to have the shortest possible measurement period. In addition, microinhomogeneous liquids such as sea water are characterized by a sharp change in spatial nonlinear properties associated with the vertical layering of water determined by the seasonal heating of the upper layers of the sea (seasonal thermocline), as well as spatial heterogeneity associated with the presence of microinhomogeneities like bubble clouds, bottom gas emissions ("gas flares") in the presence of gas hydrates and oil fields, etc.

To study the fine structure of a layered microinhomogeneous liquid, such as, for example, sea water, a high spatial resolution is required, for which it is necessary to measure NAP in a small volume of liquid. On the other hand, nonlinear effects, such as the generation of a difference frequency from two pump waves, do not appear immediately during the propagation of an acoustic wave; as the wave propagates in a nonlinear medium, they accumulate and become noticeable to sensitive equipment at some distance from the wave source. At short distances, these effects may be almost imperceptible. Thus, to obtain high spatial resolution when measuring NAP, small volume measurement is required, and for high accuracy of measuring NAP, an extended measuring base is required between the source and receiver of sound waves. These contradictory requirements are not realized in the given prototype, since with a large diversity of the source and receiver of sound in space, the NAP value is averaged over space, and at a small distance weak nonlinear effects are difficult to detect (a difference frequency wave has not yet formed).

Based on this, the objective of the present invention is to develop a method and device for measuring the acoustic nonlinearity of liquids, which allows to measure NAP with high spatial resolution, with high sensitivity, reliability by the value of NAP.

The problem is solved by determining the nonlinearity parameter of liquids, including the emission of pulses from at least two different frequencies, receiving signals transmitted through the measuring section, filtering the signals at the differential frequency, measuring the pressure amplitude of the waves of the differential frequency and then determining the nonlinearity parameter, while the measuring section is distance between the surface of the emitter and the reflecting surface located coaxially with it in a parallel plane, sending a pulse c and the reception of signals is carried out by a radiator operating in the radiation-reception mode, the time interval between pulses is chosen so that the previous pulse, having repeatedly passed the measuring section in the forward and reverse directions, has time to decay, and the nonlinearity parameter is determined by the value of the nonlinear acoustic parameter (ε) according to the formula

$$\epsilon ={\epsilon }_0\left[P_{\Omega }\left(r\right)/P_{\Omega 0}\left(r\right)\right],\left(\mathrm{one}\right)$$

where ε is the value of the nonlinear acoustic parameter in the studied medium, P _Ω (r) is the pressure amplitude of the differential frequency wave at a distance r in the studied medium, and ε ₀ is the value of the nonlinear acoustic parameter in the known medium and P _Ω0 (r) is the pressure amplitude waves of difference frequency at a distance r in a known medium, determined previously by calibration.

The problem is also solved by a device for implementing the proposed method, consisting of an acoustic probe, including a measuring base, a complex of measuring equipment connected to it with an acoustic signal processing and data storage system, while the measuring base is a rod, on one side of which an acoustic wave source is installed operating in the radiation-reception mode, on the other hand, a reflecting plate is mounted coaxially with it in a parallel plane, the radiation axis of the source is acoustically x waves is directed to the plate, and the complex of measuring equipment includes a radiation path and a reception path, while the radiation path consists of a clock generator connected to two sinusoidal signal generators whose outputs are connected to the inputs of a voltage adder connected to a power amplifier and a signal switch that switches radiation mode into the reception mode, the reception path includes a signal switch, a selective amplifier tuned to filter and amplify the difference frequency signals, and the ADC, sync ize a clock generator coupled to the system and processing acoustic signals, and data storage.

Figure 1 presents a diagram of the inventive device, where A is a radiation path, B is a reception path, 1 is a clock generator; 2 and 3 - sinusoidal voltage generators; 4 - signal adder; 5 - power amplifier; 6 - switch signal radiation-reception; 7 - emitter; 8 - measuring rod; 9 - reflective plate; 10 - receiving selective amplifier; 11 - ADC; 12 - computer processing and storage of data.

All structural elements of the device are standard and their technical characteristics are selected based on the research task. As a radiation source, it is possible to use, for example, a parametric emitter.

The pulse signal emitted by the acoustic wave source (7), which is generated in the radiation path (A) and transmitted through the cable through the switch (6) to the source (7), is the sum of the signals of at least two frequencies that are in the operating frequency range of the source acoustic waves. After the pulse signal is emitted to the side of the reflecting plate (9), the source (7) through the switch (6) switches to the mode of receiving the reflected signals. The pulse propagates in a space bounded by reflective surfaces (the surface of the emitter and plate (9), reflected and returning to the emitter (7) after each mileage cycle, is received by the emitter (7) and transmitted to the reception path (B). Using a selective amplifier (10 ) the reflected signals are extracted at the difference frequency and amplified, converted into a digital code in the ADC (11) and fed to the processing processor (12), which stores the value of the amplitude of the difference frequency, obtained earlier when calibrating the device by measuring Ia difference frequency signal amplitude in a medium with a known quantity of NAP.

Calibration is a standard procedure, carried out before the start of measurements and consists in the fact that a probe is immersed in a medium with a known NAP value and the amplitude of the difference signal is measured at a distance where the amplitude of the difference frequency signals has grown to acceptable values for measurement. The obtained amplitude values are then used to calculate the NAP in the test medium according to the claimed expression (1).

For example, it is known that the value of NAP in fresh water at a temperature of 20 ° C is ε = 3.7 (Nugolnykh K.A., Ostrovsky L.A., Sutin AM Parametric sound emitters. // Nonlinear acoustics. Theoretical and experimental studies. Gorky: IAP Academy of Sciences of the USSR, 1980. S.143-160). To calculate the NAP of the studied liquid according to the given formula (1), the value (PΩ0 (r)) measured in water with the above-described properties (ε = 3.7) can be used as a calibration value, while the pressure amplitudes of the pump frequency waves during measurements in the studied liquid and gauge should be equal.

Thus, the proposed method has an increased spatial resolution, since the studied liquid region is limited by the space between two parallel planes, the minimum distance between which is limited only by the spatial extent of the emitted pulse signal, as well as by increased sensitivity to the manifestation of weak nonlinear effects, and, as a result, and reliability of measurements due to the ability to accumulate nonlinear effects at a large distance The pump wave, which is limited only by the attenuation length of the sound pulse.

The use of the inventive device measuring base, implemented in the form of a rod with a radiation source operating in the mode of emission and reception of acoustic signals, and two reflective surfaces - the surface of the emitter and reflective plate, where the increase in nonlinear effects (generation of combination frequencies) occurs due to multiple reflection of the pulse inside the base, allows to reduce the dimensions of the device compared to the prototype. The design of the device expands the possibilities of its use in a limited space, since a short measuring base can be moved on a cable inside cavities of complex configuration, which is impossible when using a long cable with a transmitter and receivers located on it.

The device layout was used to study the nonlinear acoustic parameter of water containing bubbles at different equilibrium contents of gas and steam, depending on the temperature when heated to a temperature close to the boiling point.

Figure 2 shows graphs of the temperature dependence at the difference frequencies of 30, 50 and 70 kHz in water with vapor-gas bubbles. Studies were also conducted of the dependence of the nonlinear acoustic parameter of real sea water with various microinhomogeneities contained in it on depth under oceanic conditions.

Figure 3 presents a typical graph of the dependence of the nonlinear acoustic parameter of sea water on depth in the Indian Ocean.

Claims (2)

1. A method for determining the nonlinearity parameter of liquids, which includes emitting pulses of at least two different frequencies, receiving signals transmitted through the measuring section, filtering the signals at the differential frequency, measuring the pressure amplitude of the waves of the differential frequency and then determining the nonlinearity parameter, characterized in that the measuring section represents the distance between the surface of the emitter and the reflecting surface located coaxially with it in a parallel plane, sending pulses and receiving a signal carried emitter operating in emission-reception mode, the time interval between the pulses is selected such that decayed by the preceding pulse, and the nonlinearity parameter is determined by the magnitude of the nonlinear acoustic parameter (ε) by the formula
ε = ε ₀ [P _Ω (r) / P _Ω0 (r)],
where ε is the value of the nonlinear acoustic parameter in the medium under study, P _Ω (r) are the pressure amplitudes of the differential frequency wave at a distance r in the medium under study, and ε ₀ and P _Ω0 (r) are the values of the nonlinear acoustic parameter and the pressure amplitude of the differential frequency wave at distance (r) in a known medium determined previously by calibration. 2. A device for determining the nonlinear acoustic parameter of microinhomogeneous liquids, consisting of an acoustic probe including a measuring base and a complex of measuring equipment connected to it with an acoustic signal processing and data storage system, the measuring base being a rod with an acoustic source installed on one side of it waves operating in the radiation-reception mode, on the other hand, a reflecting plate is installed coaxially with it in a parallel plane, the radiation axis of the source acoustic waves is directed to the plate, and the complex of measuring equipment includes a radiation path and a reception path, while the radiation path includes a clock generator connected to two sinusoidal signal generators, the outputs of which are connected to the inputs of a voltage adder connected to a power amplifier and a signal switch that switches the mode radiation in the reception mode, the reception path includes a signal switch, a selective amplifier tuned to filter and amplify the difference frequency signals, and the ADC synchronized with a clock generator and connected to an acoustic signal processing and data storage system.

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