RU2521717C1 - Method of passive acoustic monitoring of demersal gas-liquid flows - Google Patents

Abstract

FIELD: ecology.SUBSTANCE: method is based on registration of acoustic emission signals from the sources of gas bubbles near the bottom with use of vertical receiving antennas with the fan-shaped directional pattern in the vertical plane, which are preliminary calibrated with use of noise source with the uniform spectrum in the range of operating frequencies, and for determining the distribution function of the bubbles on the sizes D(R) and total gas flow the acoustic emission spectra normalised based on the acoustic calibration are used. Areas of exit of gas from the sources of acoustic noise are determined from the maxima of the correlation function between the signals received from different directions of the vertical directive pattern of receiving antennas and a time shift between them, according to the formula d=S×?, where dis the distances from centres of the first and second antennas to the source, Sis the speed of sound in water, ?is the time shifts for the case of the maxima of correlation functions of each antenna.EFFECT: method takes into account the interaction of pulsing and emitting acoustic signals bubbles with the bottom or the working parts of the technical systems, which leads to the change in the own oscillating frequency of bubbles forming in the emission spectrum of the gas exit area and the structure of the pressure field in the far zone which in this case has a dipole character.2 dwg

Description

The invention relates to ecology, protection and environmental monitoring and can be used to detect gas leaks from gas pipelines and technical hydrocarbon production systems, for localization and research of natural gas sources under water, as well as for a quantitative assessment of the volumes of gases released into the bottom area.

Currently, there is an increased need for methods for detecting gas bubbles coming from areas of the seabed into the water column. The importance of detecting leaks from gas tanks, storages and underwater gas pipelines is that, while undetected and illiquid, such leaks can lead to huge financial losses and environmental disasters. This becomes relevant due to the fact that the gas production and transportation infrastructure is rapidly aging in marine conditions. Therefore, reliable and timely detection of faults in any part of the pipeline infrastructure is a critical point to guarantee the reliability of the use of natural gas. Gas leaks can jeopardize marine ecosystems and the carbon and methane gas exchange cycles in the ocean. Also, the determination of the presence of bubbles and their quantity in the bottom and in the ocean is necessary for estimating gas reserves as a fuel for humanity and estimating the methane flow from the seabed to the atmosphere (Judd AG The global importance and context of methane escape from the seabed. Geo-Mar. Lett. 2003, 23, 147-154, doi: 10.1007 / s00367-003-0136-z). The thermal greenhouse effect due to each methane gas molecule is 20 times greater than due to the carbon dioxide molecule, and any estimate of the gas reserves in the ocean should be taken into account multiplied by the coefficient of its potential impact on climate change associated with heating of the atmosphere. The OOH proposed in recent years, a large-scale program to reduce greenhouse gas emissions into the atmosphere gives impetus to the development of methods for long-term monitoring of gas flows from the bottom of the oceans.

In the industrial sectors of gas and gas-liquid media production and transportation, systems are being developed that can detect gas leaks at all stages from production to gas use by end users. The developed methods for monitoring gas flows in water can be used both for studies of natural methane vultures and for monitoring commercial gas pipelines laid in the bottom.

Acoustic methods for detecting and determining gas leaks from technical systems and natural gas outlets in the bottom can be active and passive.

In active methods, acoustic signals are emitted into the studied aqueous medium, acoustic signals propagate in the aqueous medium with reflection and refraction processes, and then the reflected and (or) refracted acoustic signals are received and recorded. A model of the propagation of acoustic signals in the medium is formulated, and within the framework of the formulated model, recorded acoustic signals are analyzed and processed. Based on the processing results, the parameters of gas-liquid flows are calculated and the coordinates of the bubble source are determined.

Passive acoustic methods include the registration of emission radiation of bubbles emerging from the places of destruction of technical systems or from sources of natural vultures at the bottom of the sea. Next, an acoustic emission model is formulated to describe gas outflows from areas of destruction of technical systems or from sources of natural vultures. Within the framework of the formulated model, analysis and processing of recorded acoustic signals is performed, and according to the processing results, the parameters of gas-liquid flows are localized and calculated.

In [Wendelboe G., Barchard S.M., Maillard E., Bjorno L. "High-resolution multibeam sonar for subsea leakage detection". Proceedings of the 11th European Conference on Underwater Acoustics (ECUA 2012: Edinburgh UK, 2nd - 6th July, 2012), p.894-901] proposed a combined active-passive acoustic method based on measurements of backscattering and acoustic emission using reversible multipath sonar with high spatial resolution SEABAT 7128. The compact sonar antenna consists of 256 hydrophones and has a directivity pattern of 1280 horizontal and 280 vertical with a resolution of 0.5 °. The method and equipment made it possible to visualize small gas leaks in the active mode at a frequency of 400 kHz at distances up to 200 meters. In the mixed active-passive acoustic mode, identification, localization and determination of gas exit points were carried out under controlled conditions at distances up to 70 meters. The disadvantage of the proposed method is the use of one (high) frequency when emitting and receiving acoustic signals, which limits the detection range of gas leaks due to the high attenuation of sound in the medium. Also, the method does not provide for the determination of the volume of outgoing gas according to the measurement data.

In [Leigthon TG and White PR Quantification of undersea gas leaks from carbon capture and storage facilities, from pipelines and from methane seeps, by their acoustic emissions. J. Proc. R. Soc. A id: RSPA20110221. doi: 10.1098 / rspa.2011.0221] a method is proposed for continuous monitoring of hydrocarbon emissions, tightness of gas pipelines and the study of underwater areas with many natural vultures. The known method is based on the use of passive acoustic emission signals of gas bubbles recorded by single hydrophones to calculate the size distribution function of gas bubbles for sources in the bottom. The registration of the signal of acoustic emission radiation generated during leakage of technical systems or as a result of the release of natural gases (sipes) of bubbles is carried out in the bottom area. Then, the spectral power of the received signal S (ω) is calculated, the inversion of the data of the spectral analysis of emission radiation is performed (within the framework of the method for solving the inverse problem), and the size distribution function of the bubbles D (R ₀ ) is calculated, according to

which determines the amount of gas released by summing the volumes of all gas bubbles. It is assumed that the emission signal is generated as a result of a linear superposition of signals from single gas bubbles that make free monopole oscillations and do not interact with each other, with the bottom or technical structures.

The system of practical application of the method of passive remote detection and control of natural gas outlets and gas leaks from technical systems under water requires a single receiver or horizontal acoustic receiving system located near controlled underwater technical objects or in the area of natural sip exits. The method is performed by receiving a signal of emission radiation from the exit region of the bubbles using hydrophones, transmitting the received signals to the spectral calculation unit, from where they are transferred to the calculation unit for the distribution function of the bubbles in terms of size and volume of the gas stream. Separate blocks or the entire system can be placed on underwater or surface media.

However, the use of single hydrophones localized in a horizontal plane near the bottom and not having directivity characteristics in space makes it difficult to determine the exact position of the areas of bubble sources in cases of real depth profiles. The dipole nature of the emission of bubbles near the bottom or of technical systems during leaks is not taken into account. The emission spectrum in the exit region of the bubbles is theoretical and is calculated in accordance with the parameters of the selected model and the distance between hydrophones and sources, an algorithm for determining which is not given in the work. The drawbacks noted above lead to errors in determining the shape of the emission spectrum and its specific values and, as a result, to a decrease in the reliability of determining the bubble function by size in the process of solving the inverse problem. To calculate the bubble size distribution function, we use the emission radiation model for the case of a small bulk density of bubbles at the moment of their exit from the source, which limits the application of the method in situations of technogenic gas leaks and for many natural gas sources at the bottom where large bulk densities of bubbles are observed. In addition, the used model of bubble emission radiation does not take into account their mutual correlation in the sound field, which leads to errors in calculating the spectral power density of acoustic noise S (ω) in the far field from the cloud of bubbles and does not allow the inversion of the obtained emission spectra to be correctly performed.

Closest to the claimed method is a passive acoustic method for detecting leaks of gas-liquid flows from underwater pipelines (s.WO 02/025239 A1, IPC G01M 3/24).

The method includes receiving an acoustic signal from the area surrounding the underwater pipeline, transmitting said signal to a recording device, and then processing the received signal. The signal is received by a hydrophone with a radiation pattern determined by the internal pressure in the pipeline and which can be fan-shaped, conical or conical with an adjustable aperture. The received signal enters the signal transmission unit, from which it is transmitted via cable to the signal processing system installed on the vessel. The cable acts as a towing element for a sealed immersion unit, including a receiving and transmitting unit. In the case of inspections of pipelines using a towed underwater vehicle, the cable is not used, and signals are transmitted to the surface using the standard cable of the device. The stage of processing the registered signal includes eliminating frequencies below 30 kHz and above 70 kHz from the signal to obtain the working frequency band, then transferring the working band to the low-frequency region, obtaining two quadrature signals having half frequencies relatively relatively zero located in the audio (0- 20 kHz) frequencies, which allows you to use the low sampling frequency of the analog-to-digital signal conversion and perform audio monitoring by the operator. Within the limits of the audio frequency band, calculation and graphical display of the spectrogram and signal amplitude on the monitor are performed every second. At the same time, a calculated graph of the signal power as a function of frequency and time is displayed on the monitor. Using the signals from the sound device and graphics on the monitor, the operator detects leak signals. The disadvantages of this method are:

- low accuracy of localization of the source of acoustic emission due to the movement of the receiver and the need for positioning in the space of the underwater measuring unit,

- low sensitivity of the method, depending on the level of ambient noise due to both the movement of the receiver of acoustic signals and the operation of the mechanisms of the escort vessel,

- low efficiency and fundamental difficulties in the localization of pulsating and "sleeping" sources of emission signals due to the uncertainty of the duration, places and moments of the beginning of gas outflows at the bottom.

In addition, it should be noted that the known method does not allow monitoring over time and determining the amount of gas-liquid flow exiting the source.

The objective of the invention is the development of an effective method for the passive detection and monitoring of gas leaks from pipelines and technical systems for hydrocarbon production, localization of natural gas sources under water, as well as a quantitative assessment of gas flows emerging in the bottom area.

The technical result is an increase in the probability of identification and accuracy in determining the coordinates of the exit points of gas-liquid flows in the bottom area, as well as the determination of quantitative parameters of flows in a wide range of gas bubble concentrations, the ability to monitor the object under study.

, где S_norm(ω_k) - значения нормированного с учетом калибровки спектра эмиссионного сигнала в месте выхода газового потока, $${\left|X\left({\omega }_k;R_n^c\right)\right|}^2$$

- квадрат магнитуды преобразования Фурье дипольного излучения одиночного пузырька с учетом точного задания собственных частот и учетом взаимодействия пузырьков с дном в дальнем поле.The problem is solved by the proposed method of acoustic monitoring of bottom gas-liquid flows by receiving acoustic emission signals in the study area, recording and processing them, while calibrating signal reception systems in a specific area of work using a noise signal simulator with a uniform spectrum in the operating frequency range and recording of the calibration spectrum, at least two, placed stationary at a known distance, are used as signal reception systems and from each other, vertical antennas having circular radiation patterns in the horizontal plane and a fan radiation pattern in the vertical plane, the signals are recorded from all directions of the fan radiation pattern from each of the antennas, then, taking into account the calibration, the emission spectra of the investigated area are measured and normalized, conduct a cross-correlation analysis of the received signals in time, and determine the places of gas exit from sources of acoustic noise by function maxima correlations between the signals received from different directions of the vertical radiation pattern of the receiving antennas and the time shift between them according to the formula d _1,2 = C _sv × τ _1,2 , where d _1,2 are the distances from the centers of the first and second antennas to the source, C _sv is the speed of sound in water, τ _1,2 is the shear time (log) for the case of maxima of the correlation functions of each antenna, and the volume of the output stream by summing the volumes of all gas bubbles in the size distribution function of the bubbles ψ (n) obtained by solving the system equations $$S_{norm}\left({\omega }_k\right)\approx {\displaystyle \sum _{n=\mathrm{one}}^{N_b}\psi \left(n\right){|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2}$$

, where S _norm (ω _k ) are the values normalized taking into account the calibration of the spectrum of the emission signal at the exit of the gas stream, $${|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2$$

- the square of the magnitude of the Fourier transform of the dipole radiation of a single bubble, taking into account the exact setting of natural frequencies and taking into account the interaction of the bubbles with the bottom in the far field.

The inventive method by recording acoustic emission signals from the exit point of the bubbles and from the gas "flame" using two stationary mounted receiving antennas with a fan radiation pattern in the vertical plane, more accurately setting the natural frequencies of the emission of gas bubbles by taking into account the interaction of pulsating bubbles with each other and with the bottom, determining the spatial radiation pattern of the acoustic emission region, as well as preliminary calibration of the receiving systems allows ysit probability of identification of gas-liquid flow in the bottom area, increase the accuracy of determining the coordinates of output locations, and determine the quantitative parameters of gas flow in a wide range of concentrations by volume of bubbles in the flow.

In the inventive method for monitoring bottom gas-liquid flows, the interaction of the pulsating and emitting acoustic signals of the bubbles with the bottom is taken into account, which leads to a change in the natural frequency of the oscillations of the bubbles forming the emission spectrum at the gas outlet and the structure of the pressure field in the far zone, which in this case has a dipole character .

Indeed, the radius of the bubbles found in the vultures is R ₀ ~ 0.25 cm [Leifer I., Patro RK The bubble mechanism for methane transport from the shallow sea bed to the surface: A review and sensitive study // Cont. Shelf. Res. 2002. V. 22. P.2409-2428.], And their resonant frequency f ₀ = (0.326 / R ₀ ) (1 + 0.1 · H) ^1/2 kHz (H - depth in meters) is greater than 1 kHz. The Q factor of the bubbles generated in sipes is Q ~ 10 and the radiation time is τ = Q / f ₀ = 0.03 × R ₀ (1 + 0.1 · H) ^-1/2 . The velocity of the bubbles is 14 ÷ 20 cm / s. Thus, during the emission time, the bubbles float above the bottom by a distance of d = (4 ÷ 6) × R ₀ (1 + 0.1 · H) ^-1/2 , which is comparable to their size, and the length of the acoustic wave emitted by the bubble is orders of magnitude exceeds both the size of the bubble and the distance to the bottom. Accounting for the interaction of the bubble with the bottom is performed by introducing imaginary sources - Figure 1.

Taking into account the interaction of bubbles by the boundaries leads to the fact that, firstly, the eigenfrequency of the bubble oscillations will change, which will be described by the formula:

$$f_0^c=\frac{f_0}{{\left(\mathrm{one}-\frac{{\rho }_w-\beta }{{\rho }_w+\beta }\frac{R_0}{2d}\right)}^{\mathrm{one}/2}},(\mathrm{one})$$

. Во-вторых, структура поля давления в дальней зоне будет формироваться двумя источниками (дипольное излучение), совпадающими с расположением исходного и мнимого пузырька, и будет иметь вид:where f ₀ is the natural frequency of the free bubble, ρ _w is the density of water, β = ρ _s (ν / 1-ν), ρ _s is the density of precipitation, ν is the Poisson's ratio of precipitation. Expression (1) is used in the inventive method to invert the spectral density of the emission radiation of bubbles and to calculate the volumetric characteristics of the gas stream. The previously mentioned interaction of the bubbles was not taken into account and a simpler ratio was used $$f_0^c=f_0$$

. Secondly, the structure of the pressure field in the far zone will be formed by two sources (dipole radiation), which coincide with the location of the initial and imaginary bubbles, and will look like:

, $$P\approx {\rho }_w\left(R_0^2\ddot{R}\right)\left(\mathrm{one}-\frac{{\rho }_w-\beta }{{\rho }_w+\beta }\frac{R_0}{2d}\right)/r(2)$$

,

.instead of the field of a monopoly source coinciding with the center of the bubble, $$P\approx {\rho }_w\left(R_0^2\ddot{R}\right)/r$$

.

To implement the method, acoustic signals are received in the work area using at least two antennas. The maximum number of antennas is almost unlimited and is determined by the length of the monitored objects or the investigated area of a natural object, for example, at least two are required to control the linear sections of underwater gas pipelines, and at least three antennas are required to control the areas of natural gas outlets or technical objects having a distributed configuration at the bottom . Antennas are fixed stationary at the bottom and have a circular radiation pattern in the horizontal plane and a multi-beam fan radiation pattern in the vertical plane. Before starting work, receiving antennas are calibrated using an acoustic emitter - a noise signal simulator. In the process of calibrating and monitoring a given area, the received signals from all directions of the fan radiation pattern from each antenna are transmitted to a computing multiprocessor device (VMU), where a cross-correlation analysis of signals received from all beams of different antennas is performed. The coordinates of the places of exit of gas bubbles (sources of acoustic noise in the bottom area) are determined by the maxima and lags of the cross-correlation functions and the known angles of arrival of the signals. The real acoustic emission power spectra from the bubble exit region are also determined (two spectra from both antennas for the pipeline case and three spectra from three antennas for the natural vulture exit region). Determination of the real emission spectrum of pulsating gas bubbles in the region of their exit is performed by searching for the nearest calibration point and normalizing the obtained measured spectra using the spectrum of the simulator signal at this point. The criterion for the absence of measurement errors is the proximity of the values of the normalized spectra determined using each antenna. The size distribution function of the bubbles in the region where the gas stream enters the aqueous medium is also determined in the VMF based on the inversion algorithm (AI) of the normalized spectra. To increase the reliability of identification of the gas outlet, use is made of the spectrum averaged over all antennas from the emission region, as well as the results of analysis of the emission spectrum for the presence of low-frequency components due to the collective interaction of gas bubbles in the “plume”. A diagram and a set of devices for implementing the proposed method for a gas pipeline monitoring option are shown in FIG. 2, where 1 is a vertical antenna with 2 fan patterns, 3 is a block for generating directivity patterns, 4 is the space between antennas, 5 is a given control object, 6 is points of position of the simulator of acoustic noise during calibration, 7 - VMU, 8 - communication channel.

Before starting monitoring a given object 5, for example, a gas pipe or technical systems of a gas pipeline, an acoustic calibration of the area of work is performed. For this, the source of acoustic noise, the energy spectrum of the signal of which has a known constant value in the operating frequency range from 500 Hz to 100 kHz, is sequentially placed at equally spaced points of space 6 along the pipeline or at the nodal points of the three-dimensional lattice covering the region of possible gas exit. Receive and transmit to block 7 (VMU) white noise signals received from all angles of the fan radiation pattern from each of the antennas 1 when the simulator is at the calibration points. At the end of the calibration procedure, interpolation of the measured calibration spectra to intermediate points is performed taking into account the specified spatial accuracy of the measurements.

In the monitoring mode, emission signals are received by the antennas 1 from the area of space 4 between them. The radiation pattern is formed using block 3 of the formation of the directivity pattern (PFN). In block 3, due to the joint digital processing of signals recorded by each hydrophone of both vertical antennas, spatial filtering of acoustic vibrations and the formation of the antenna directivity in the vertical plane along the angle α≤5 ° are performed for the frequency range of the received signals from 300 Hz to 100 kHz (spatial filtering - a general term for linear filtering of received signals in the time and frequency domains, with the aim of forming a radiation pattern). Also in block 3, the identification of emission signals obtained from different directions (angles) for each antenna is performed. The signals and the results of their spatio-temporal identification are transmitted to block 7 (VMU), where, based on the results of cross-correlation processing of signals in time, the moment of time and place of exit of gas bubbles is determined by searching for the maximum correlation function between signals received from different directions of the vertical radiation pattern receive antennas, the determination of time shifts for functions having peaks and determining the distance to the source of emission d _1,2 = C _ulcers × τ _1,2, where d _1,2 - distance from each ntenny to the source, _ulcers C - the speed of sound in water, τ _1,2 - time shift (lag) for the case of the maxima of the correlation functions of each antenna. The source position is defined as the intersection of two circles having radii d ₁ and d ₂ that extend from the centers of the first and second antennas, respectively. Since there are two intersection points, according to the number of roots corresponding to these circles of the equation, the natural choice is the position of the source point in the bottom region.

In parallel with the calculation of the cross-correlation functions of signals from two antennas in block 7 (VMU), the power spectra of the same signals are determined. The power spectra of the signals, the correlation functions of which were used to determine the exit location of the gas stream, after preliminary normalization are used to determine the size distribution function of the bubbles. The spectra of signals received by the antennas are normalized by multiplying the transmission coefficient over the spectrum in the gas outlet region by the measured spectrum of the acoustic emission signal. The transmission coefficient is defined as the reciprocal of the spectrum of the received calibration signal (measured or interpolated) from the gas outlet area. The determination of the bubble size distribution function is performed in block 7 based on the inversion algorithm (AI). Measurement data and processing results from all modules are transmitted via the communication and power supply channel 8 to the control center to assess the situation and make decisions. In this stationary measurement scheme, there are no problems associated with the positioning of movable measuring systems and time limits for measurements due to the external power supply of 8 used systems.

The inversion algorithm includes the representation of the normalized values taking into account the calibration of the spectrum of the emission signal at the gas stream exit point S _norm (ω) in the form

$$S{}_{norm}\left(\omega \right)={\displaystyle {\int }_0^{\infty }D\left(R_0\right){|\; |\; |X_b\left(\omega ;R_0\right)|\; |\; |}^{2}d{R}_0(3)}$$

является числом пузырьков, генерируемым за секунду в диапазоне радиусов (R₁, R₂). Резонансные радиусы связаны с резонансными частотами пузырьков ω₀ согласно выражениюwhere D (R ₀ ) is the size distribution of emission bubbles as a function of the radii of their resonance radii R ₀ , defined in such a way that $${\displaystyle {\int }_{R_{\mathrm{one}}}^{R_2}D\left(R_0\right)d{R}_0}$$

is the number of bubbles generated per second in the range of radii (R ₁ , R ₂ ). Resonance radii are associated with the resonant frequencies of the bubbles ω ₀ according to the expression

$${\omega }_0=\frac{\mathrm{one}}{R_0\sqrt{{\rho }_0}}\times \left(\sqrt{3k\left({\rho }_0-{\rho }_{\nu }+\frac{2\sigma }{R_0}\right)-\frac{2\sigma }{R_0}+{\rho }_{\nu }-\frac{\mathrm{four}\eta }{{\rho }_0{R}_0^2}}\right)\times {\left(\mathrm{one}-\frac{{\rho }_w-\beta }{{\rho }_w+\beta }\frac{R_0}{2d}\right)}^{-\frac{\mathrm{one}}{2}}(\mathrm{four})$$

, ν - коэффициент Пуассона в осадках. Выражение |X_b(ω;R₀)|² представляет собой квадрат магнитуды преобразования Фурье дипольного излучения одиночного пузырька, обнаруживаемое в дальнем поле, равного $$X\left(\omega ;R_0\right)=\left({\left({\omega }_0{R}_0\right)}^2\frac{{\rho }_0}{r}{R}_{\epsilon oi}\right)\frac{{\omega }_0{\delta }_{tot}/2+j\omega }{\left[{\omega }_0{\delta }_{tot}/2+j\left(\omega -{\omega }_0\right)\right]\left[{\omega }_0{\delta }_{tot}/2+j\left(\omega +{\omega }_0\right)\right]}\times \left(1-\frac{{\rho }_w-\beta }{{\rho }_w+\beta }\frac{R_0}{2d}\right)(5)$$

where ρ _ν is the vapor pressure, σ is the surface tension of the liquid, η is the shear viscosity, k is the polytropic index varies between γ (the ratio of the specific heat of the gas at constant pressure to the value in a constant volume) and unity depending on whether the gas behaves adiabatically, isothermally or in some intermediate way, $$\beta ={\rho }_0\left(\frac{\nu }{\mathrm{one}-\nu }\right)$$

, ν - Poisson's ratio in sediments. The expression | X _b (ω; R ₀ ) | ² represents the square of the magnitude of the Fourier transform of the dipole radiation of a single bubble, detected in the far field, equal to $$X\left(\omega ;R_0\right)=\left({\left({\omega }_0{R}_0\right)}^2\frac{{\rho }_0}{r}{R}_{\epsilon oi}\right)\frac{{\omega }_0{\delta }_{tot}/2+j\omega }{\left[{\omega }_0{\delta }_{tot}/2+j\left(\omega -{\omega }_0\right)\right]\left[{\omega }_0{\delta }_{tot}/2+j\left(\omega +{\omega }_0\right)\right]}\times \left(\mathrm{one}-\frac{{\rho }_w-\beta }{{\rho }_w+\beta }\frac{R_0}{2d}\right)(5)$$

, а отрезки радиуса находятся в диапазоне R_l,n<R₀≤R_u,n, где R_l,n и R_u,n - нижний и верхний пределы распределения, соответственно. Кроме того, предполагается, что отрезки непрерывны, так что R_u,n-1=R_l,n для n=2, 3…, N_b. B этом случае:where r is the distance to the point of measurement of emission radiation, R _ε0 is the amplitude of the oscillation of the wall of the bubble of the ith bubble. The exponential attenuation for a bubble that oscillates at the natural frequency ω ₀ , having an initial amplitude R _ε0i , is described by the general dimensionless attenuation coefficient, δ _tot . To estimate the number of bubbles from measurements of the power spectrum in the far field, equation (3) is solved for D (R ₀ ) and normalized S _norm (ω). To do this, discretize (3) on N _b finite segments of radius such that the nth segment of radius having a center at $$R_n^c$$

, and the radius segments are in the range R _{l, n} <R ₀ ≤R _{u, n} , where R _{l, n} and R _{u, n} are the lower and upper limits of the distribution, respectively. In addition, it is assumed that the segments are continuous, so that R _{u, n-1} = R _{l, n} for n = 2, 3 ..., N _b. In this case:

$$S_{norm}\left({\omega }_k\right)\approx {\displaystyle \sum _{n=\mathrm{one}}^{N_b}\psi \left(n\right){|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2}(6)$$

The function Ψ (n) reflects the generation of bubbles in the range of discretization of radii (i.e., the number of bubbles produced per second within the nth segment of the radius) and can be represented as

$${\Psi }_{\left(n\right)}={\displaystyle {\int }_{R_{l,n}}^{R_{u,n}}D\left(R_0\right)d{R}_0(7)}$$

связаны с угловой резонансной частотой пузырьков ω_k, и когда число частот равно числу пузырьков с соответствующими радиусами, можно записатьIn practice, the spectrum of S _norm (ω) is considered in a discrete form in terms of frequencies, ω _k , with ranges of radii, $$R_k^c$$

are related to the angular resonant frequency of the bubbles ω _k , and when the number of frequencies is equal to the number of bubbles with corresponding radii, we can write

$$S_{norm}\left({\omega }_k\right)\approx {\displaystyle \sum _{n=\mathrm{one}}^{N_b}\Psi \left(n\right){|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2}(8)$$

or in matrix form

$$S_{norm}=\Sigma \Psi (9)$$

и S - вектор-столбец, содержащий измеренные и нормированные спектры S_norm(ω_k). Функция Ψ(n) определяется путем решения уравнения (8) или (9) стандартными методами решения систем линейных уравнений.Here Σ is a spectral matrix with elements $${\displaystyle {\sum }_{k,n}{|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2}$$

and S is a column vector containing the measured and normalized spectra of S _norm (ω _k ). The function Ψ (n) is determined by solving equation (8) or (9) by standard methods for solving systems of linear equations.

In contrast to the known algorithms that use the inversion of the emission spectrum to determine the size distribution function of the bubbles, the proposed method uses acoustic emission signals from sources of gas bubbles near the bottom, obtained using vertical receiving antennas with a fan radiation pattern in the vertical plane, which are pre-calibrated, using a noise source with a uniform spectrum in the operating frequency region, and to determine the size distribution function of the bubbles D (R ₀₎ and full gas flow is used with the normalized acoustic calibration of acoustic emission spectra.

Thus, the use of the proposed method of passive acoustic monitoring of bottom gas-liquid flows can improve the accuracy of identification and determination of the position of acoustic emission sources (gasps and gas leaks from technical systems) in the bottom area due to the proposed method for recording acoustic emission signals using directional vertical antennas with circular horizontal radiation patterns and a vertical fan pattern, an lysis of emission spectra and the shape of the directivity of the radiation region, to determine the quantitative characteristics of gas flows from the bottom through the use of normalized spectra obtained taking into account preliminary acoustic calibration of the work area, and also allows for long-term monitoring of the bottom areas in order to detect new gas flows and control operating gas-liquid sources at the bottom.

Claims (1)

The method of acoustic monitoring of bottom gas-liquid flows by receiving acoustic emission signals in the studied area, their registration and processing, characterized in that at least two vertical antennas having circular radiation patterns placed stationary at a known distance from each other are used as signal reception systems in the horizontal plane and the fan radiation pattern in the vertical plane, the registration of signals is carried out from all directions of the fan diagram, for example signal from each of the antennas, while preliminary calibrating the signal reception systems in a particular area of work using a noise signal simulator with a uniform spectrum in the operating frequency region and recording the calibration spectrum, and then taking into account the calibration, measure and normalize the emission spectra of the studied area, cross-correlation analysis of the received signals in time and determine the places of gas exit from the sources of acoustic noise by the maxima of the correlation function between the signal lamellas obtained from different directions of the vertical radiation pattern of the receiving antennas and the time shift between them, according to the formula d _1,2 = C _sv × τ _1,2 , where d _1,2 are the distances from the centers of the first and second antennas to the source, C _sv is the speed of sound in water, τ _1,2 is the shear time for the case of maxima of the correlation functions of each antenna, and the volume of the output stream by summing the volumes of all gas bubbles in the size distribution function of the bubbles Ψ (n) obtained by solving the system of equations $$S_{norm}\left({\omega }_k\right)\approx {\displaystyle \sum _{n=\mathrm{one}}^{N_b}\Psi \left(n\right){|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2}$$

, where S _norm (ω _k ) are the values normalized taking into account the calibration of the spectrum of the emission signal at the exit of the gas stream, $${|\; |\; |X\left({\omega }_k;R_n^c\right)|\; |\; |}^2$$

- the square of the magnitude of the Fourier transform of the dipole radiation of a single bubble, taking into account the exact setting of natural frequencies and taking into account the interaction of the bubbles with the bottom in the far field.

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