Underwater bubble group scale distribution acoustic inversion device based on forward and backward scattering

Abstract

An underwater bubble group scale distribution acoustic inversion device based on forward and backward scattering belongs to the field of underwater acoustics, and comprises the following steps: with a transmitting transducer as an original point x = 0, laying a 1 # hydrophone at a position x = d1 in the axial direction, and laying a 2 # hydrophone at a position x = d1 + d2 in the axial direction; the transmitting transducer transmits a single-frequency pulse sound signal to the bubble-containing water medium to be detected at the position where x is equal to 0, and the hydrophone collects the signal; measuring an incident sound pressure amplitude, a forward scattering sound pressure amplitude and a backward scattering sound pressure amplitude; the emission frequency is changed for frequency sweeping, and an inversion equation in a matrix form is obtained according to an inversion equation discretized by a forward and backward scattering combined theory; the inversion equation is under positive constraint and finite constraint; tikhonov regularization is introduced into the inversion equation, and bubble group scale distribution parameters of the bubble-containing water medium to be measured are calculated. The method is suitable for a complex environment, can quickly measure the scale distribution of the underwater bubble group, corrects the error of an ideal inversion model, and solves the problem of accurate measurement of off-resonance bubbles.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater acoustics, and relates to a device for measuring the size distribution of a bubble group, and specifically to a device and method for acoustic inversion of the size distribution of an underwater bubble group based on forward and backscattering. Background Art

[0002] The presence of bubbles in the ocean water medium, on the one hand, affects the process of nonlinear interaction of sound waves, greatly increasing the difficulty of studying nonlinear wave theory, and on the other hand, causes complex changes in sound propagation behavior and sound field evolution, providing more possibilities for the use of sound fields. Therefore, the study of measuring the distribution of bubbles on the sea surface is of great significance to ocean exploration. When actually using or avoiding the influence of bubbles, it is also necessary to obtain the scale distribution parameters of bubbles in liquids.

[0003] In 1991, KW Commander proposed to discretize the first-order Fredholm integral equation for solving the bubble inversion problem, transform it into a matrix equation, and use regularization to obtain a stable solution to the equation, which realized the inversion of the attenuation coefficient at multiple frequencies to obtain the bubble distribution, and solved the problem that the ill-conditioned integral equation may not converge under small disturbances (Commander, Kerry W., and Robert J. McDonald. "Finite-element solution of the inverse problem in bubble swarm acoustics." The journal of the acoustic alsociety of America 89.2 (1991): 592-597.). In 2021, Hou Sen proposed to use an iterative method to invert the bubble distribution through the modified phase velocity and bubble vibration parameters, and gave a simplified inversion method for the problems encountered when the data is sparse. The results show that the simplified method can more accurately give the main parameters of the bubble group distribution (Hou Sen, Hu Changqing, Zhao Mei. Research on the method of inverting the distribution of bubble groups using acoustic attenuation [J]. Acta Physica Sinica, 2021.). In 2021, Jianghui Li proposed an adaptive single-bubble passive acoustic identification technology, which combines the acoustic characteristics of bubbles, including pulsation time interval, frequency bandwidth and radiation intensity, and uses cross-spectrum to improve the signal-to-noise ratio, thereby reducing the false alarm rate of bubble identification (Jianghui Li, et al. Acoustic and optical determination of bubble size distributions–Quantification of seabed gas emissions[J]. International Journal of Greenhouse Gas Control, 108[2024-02-20].).Acoustic measurements of bubbles have wide application significance. Several studies have focused on the acoustic scattering properties of ocean bubbles and evaluated the acoustic properties of seawater media containing bubble clouds based on experimental data obtained from acoustic scattering of bubbles in the upper layer of seawater (Liu, Ruoyun. The effects of bubble scattering on sound propagation in shallow water. Journal of Marine Science and Engineering 2021, 9(12), 1441.)(5Bulanov, Vladimir A. On sound scattering and acoustic properties of the upper layer of the sea with bubble clouds. Journal of Marine Science and Engineering 2022, 10(7), 872.).

[0004] The traditional bubble parameter measurement method mainly uses the acoustic attenuation and sound velocity characteristics of bubbles to invert and obtain the distribution characteristics of bubbles. The limitation of the previous bubble parameter acoustic measurement method is that when the number of bubbles is small, it is greatly affected by the pure water attenuation coefficient, and the measurement error is too large without prior information on the pure water attenuation coefficient. In addition, since there is no effective means to measure the bubble scattered sound pressure, the bubble acoustic inversion device that can overcome the above problems to the greatest extent has not yet been applied. Summary of the invention

[0005] Based on the previous theories, the present invention proposes an acoustic inversion device and method for the scale distribution of underwater bubble groups based on forward and backscattering. The device transmits a single-frequency pulse in a frequency sweeping manner, places two hydrophones in the direction of the acoustic axis of the transmitting transducer, measures the incident sound pressure, the forward and backscattered sound pressure amplitudes, substitutes the inversion theory of the discretization of the forward and backscattering joint theory, obtains the inversion equation in matrix form, introduces Tikhonov regularization under positive constraints and finite constraints, and obtains the bubble group scale distribution parameters of the bubble-containing water medium to be measured. The device has simple measurement and strong applicability, and is suitable for use in complex environments. It can more quickly measure the scale distribution of underwater bubble groups, correct the errors of the ideal inversion model, and solve the problem of accurate measurement of non-resonant bubbles.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] The present invention provides an acoustic inversion device for underwater bubble group size distribution based on forward and backscattering, comprising:

[0008] A signal source, which emits the required known electrical signal;

[0009] High-frequency power amplifier, converts the electrical signal from the signal source into a high-power electrical signal output;

[0010] Oscilloscope, monitor the electrical signal output by the signal source and high-frequency amplifier;

[0011] The transmitting transducer converts the electrical signal output by the high-frequency power amplifier into an acoustic signal and outputs it underwater;

[0012] Hydrophones, which convert sound signals received in water into electrical signals;

[0013] A collector collects the electrical signals received by the hydrophone in real time;

[0014] On the PC side, the electrical signals collected by the collector are stored and displayed;

[0015] Mounting frame, used to fix the device in place.

[0016] Furthermore, taking the transmitting transducer as the origin x=0, a 1# hydrophone is deployed at x=d1 along the axial direction, and a 2# hydrophone is deployed at x=d1+d2 along the axial direction.

[0017] The method for acoustic inversion of underwater bubble group size distribution based on forward and backscattering provided by the present invention is implemented by the acoustic inversion device for underwater bubble group size distribution based on forward and backscattering according to claim 1 or 2, and comprises the following steps:

[0018] (a) The device is deployed and the transmitting transducer sends out a signal;

[0019] With the transmitting transducer as the origin x=0, a 1# hydrophone is placed at x=d1 in the axial direction, and a 2# hydrophone is placed at x=d1+d2 in the axial direction; the transmitting transducer transmits a single-frequency pulse sound signal with a frequency of ω1 into the bubble-containing water medium to be tested at x=0, and the 1# hydrophone and the 2# hydrophone simultaneously collect the single-frequency pulse sound signal;

[0020] (b) Measure the incident sound pressure amplitude P1(ω1);

[0021] (c) Measure the forward scattered sound pressure amplitude P2(ω1);

[0022] (d) Measure the backscattered sound pressure amplitude P b (ω1);

[0023] (e) Changing the transmission frequency to perform frequency sweeping, the frequency sweeping range is ω[ω1ω2…ω n ], repeat steps (b)-(d), and obtain the inversion equation in matrix form according to the inversion equation discretized by the joint theory of forward and backscattering;

[0024] (f) Inversion equations under positive and finite constraints;

[0025] (g) Tikhonov regularization is introduced into the inversion equation, and the bubble group size distribution parameters of the bubble-containing water medium to be tested are obtained by calculation.

[0026] Furthermore, in step (b), the waveform of the direct wave signal received by the 1# hydrophone is Fourier transformed to read the incident sound pressure amplitude P1(ω1) of the bubble-containing water medium to be tested at the corresponding frequency ω1.

[0027] Furthermore, in step (c), the waveform of the direct wave signal received by the 2# hydrophone is Fourier transformed to read the forward scattered sound pressure amplitude P2(ω1) of the bubble-containing water medium to be tested at the corresponding frequency ω1.

[0028] Furthermore, in step (d), the time delay τ of the single-frequency pulse echo signal emitted in the bubble-containing water medium to be tested is calculated, the backscattered signal waveform received by the 1# hydrophone within the time delay τ is Fourier transformed, and the backscattered sound pressure amplitude P of the bubble-containing water medium to be tested at the corresponding frequency ω1 is read. b (ω1).

[0029] Furthermore, in step (e), for the radius range of the bubble-containing water medium to be tested, R = [R1 R2 ... R m ], according to the joint theory of forward and backscattering:

[0030] λ(ω)=∫σ s (ω,R)N(R)dR (1)

[0031] in, is the backscattering cross section of a bubble with a radius of R under frequency ω excitation, N(R)=[N1(R1)N2(R2)…N m (R m )] is the number of bubbles with a radius of R, δ is the viscous damping coefficient, and ω0 is the resonance frequency of the bubble with a radius of R.

[0032] Furthermore, the inversion equation in matrix form is obtained by discretizing formula (1):

[0033] λ(ω)=σ s (ω,R)N(R) (2)

[0034] Furthermore, in step (f), the inversion equation under the positive constraint and the finite constraint is expressed as follows:

[0035]

[0036] Furthermore, in step (g), the inversion equation introduces Tikhonov regularization, and its specific calculation formula is:

[0037]

[0038] Where N is the exact solution of the inversion equation, N * is the initial estimate, ε is the regularization parameter, and L = tridiag (1, -2, 1) is a tridiagonal matrix. The regularized solution N of the bubble group size distribution parameter of the bubble-containing water medium to be measured is obtained by calculation. ε .

[0039] The beneficial effects of the present invention are:

[0040] (1) Compared with the traditional bubble measurement device, the present invention solves the problem of accurate measurement of non-resonant bubbles, broadens the radius coverage of the inversion bubble, and solves the problem that the resonance frequency of small bubbles is too high to be accurately measured.

[0041] (2) In the present invention, the theory combines forward scattering with back scattering, which is more realistic than the previous inversion model under ideal conditions and corrects the error of the ideal inversion model.

[0042] (3) In the present invention, inversion can be performed when prior information is scarce, and has high robustness, which can effectively avoid the situation where the physical parameters of the bubble-containing water medium to be measured cannot be obtained a priori and affect the measurement results.

[0043] (4) The present invention is simple to operate and has strong applicability. It is suitable for use in complex environments. The calculation results are accurate, the calculation steps are simple and fast, and it has high experimental value and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The present invention is a flow chart of an acoustic inversion method for underwater bubble group size distribution based on forward and backscattering.

[0045] Figure 2 This is a structural diagram of an acoustic inversion device for underwater bubble group size distribution based on forward and backscattering according to the present invention.

[0046] Figure 3 Schematic diagram of the hydrophone receiving signal in one cycle.

[0047] Figure 4 This is the frequency response curve of the receiving sound pressure level of the receiving hydrophone.

[0048] Figure 5 This is the bubble inversion result.

[0049] Figure 6This is a comparison chart of the scattering coefficient of the measured bubble group and the scattering coefficient corresponding to the measured results. DETAILED DESCRIPTION

[0050] The device is further described in detail below in conjunction with the accompanying drawings and specific implementations.

[0051] like Figure 2 As shown, the present invention provides an acoustic inversion device for underwater bubble group size distribution based on forward and backscattering, which specifically includes the following components:

[0052] A signal source, which emits the required known electrical signal;

[0053] High-frequency power amplifier, converts the electrical signal from the signal source into a high-power electrical signal output;

[0054] Oscilloscope, monitor the electrical signal output by the signal source and high-frequency amplifier;

[0055] The transmitting transducer converts the electrical signal output by the high-frequency power amplifier into an acoustic signal and outputs it underwater;

[0056] Hydrophones, which convert sound signals received in water into electrical signals;

[0057] A collector collects the electrical signals received by the hydrophone in real time;

[0058] On the PC side, the electrical signals collected by the collector are stored and displayed;

[0059] Mounting frame, used to fix the device in place.

[0060] like Figure 1 As shown, the present invention provides an acoustic inversion method for underwater bubble group scale distribution based on forward and backscattering, and its specific implementation process is as follows:

[0061] (a) The device is deployed and the transmitting transducer sends out a signal;

[0062] Taking the transmitting transducer as the origin x=0, the 1# hydrophone is deployed at x=d1 along the axial direction, and the 2# hydrophone is deployed at x=d1+d2 along the axial direction.

[0063] The transmitting transducer transmits a single-frequency pulse sound signal with a frequency of ω1 into the bubble-containing water medium to be tested at x=0, and the 1# hydrophone and the 2# hydrophone simultaneously collect the single-frequency pulse sound signal;

[0064] (b) Performing Fourier transform on the direct wave signal waveform received by hydrophone #1, and reading the incident sound pressure amplitude P1(ω1) of the bubble-containing water medium to be tested at the corresponding frequency ω1;

[0065] (c) Perform Fourier transform on the direct wave signal waveform received by hydrophone #2, and read the forward scattered sound pressure amplitude P2(ω1) of the bubble-containing water medium to be tested at the corresponding frequency ω1;

[0066] (d) Calculate the time delay τ of the single-frequency pulse echo signal emitted in the bubble-containing water medium to be tested, perform Fourier transform on the backscattered signal waveform received by hydrophone #1 within the time delay τ, and read the backscattered sound pressure amplitude P of the bubble-containing water medium to be tested at the corresponding frequency ω1. b (ω1);

[0067] (e) Changing the transmission frequency to perform frequency sweeping, the frequency sweeping range is ω[ω1ω2…ω n ], repeat steps (b)-(d), for the radius range of the bubble-containing water medium to be tested R = [R1 R2 ... R m ], according to the joint theory of forward and backscattering:

[0068] λ(ω)=∫σ s (ω,R)N(R)dR (1)

[0069] in, is the backscattering cross section of a bubble with a radius of R under frequency ω excitation, N(R)=[N1(R1)N2(R2)…N m (R m )] is the number of bubbles with a radius of R, δ is the viscous damping coefficient, and ω0 is the resonance frequency of the bubble with a radius of R.

[0070] Discretization gives the inverse equation in matrix form:

[0071] λ(ω)=σ s (ω,R)N(R) (2)

[0072] (f) Inversion equation under positive constraint and finite constraint:

[0073]

[0074] (g) Tikhonov regularization is introduced into the inversion equation:

[0075]

[0076] Where N is the exact solution of the inversion equation, N * is the initial estimate, ε is the regularization parameter, and L = tridiag (1, -2, 1) is a tridiagonal matrix. The regularized solution N of the bubble group size distribution parameter of the bubble-containing water medium to be measured is obtained by calculation. ε .

[0077] The present invention measures the incident sound pressure and the forward and backscattered sound pressure amplitudes, and utilizes the forward and backscattered joint theory to invert the bubble size distribution parameters. It has the advantages of simple operation and strong applicability, and is suitable for use in complex environments to more quickly invert the size distribution of underwater bubble groups.

[0078] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0079] The structure of the field experiment device is as follows Figure 2 As shown, the transmission signal type is CW pulse signal, the signal amplitude is 500mv, the pulse frequency is swept from 53kHz to 143kHz, a total of 91 frequency points, the frequency step is 1kHz, 1#2# two 8103 hydrophones are coaxial with the transmitting transducer, and the data are collected by B&KPULSE collector. The collection time is 60s, the sampling rate is 524288Hz, the pulse width is 20ms, the sound speed in water c0=1480m / s, and the water medium density ρ0=998kg / m 3 , the radius of the bubble to be measured R0 = (10, 10.5, 11, ..., 200) (μm), the gas density inside the bubble ρ g =1.29kg / m 3 , specific heat ratio γ = 1.4, the damping coefficient δ is set according to the Medwin model, and the regularization parameter is selected by the I-curve method.

[0080] The schematic diagram of the hydrophone receiving signal in one cycle is as follows Figure 3 As shown in the figure, the horizontal axis represents time and the vertical axis represents the received voltage response. Figure 3 The figure shows the original signal obtained by the device through step (a).

[0081] The frequency response curve of the receiving sound pressure level of the hydrophone is as follows: Figure 4 As shown in the figure, two acquisitions were carried out in total. The numbering example is: the first sound pressure level curve of the 1# hydrophone is represented by 1_1, the first sound pressure level curve of the 2# hydrophone is represented by 1_2, the second sound pressure level curve of the 1# hydrophone is represented by 2_1, and the second sound pressure level curve of the 2# hydrophone is represented by 2_2. Figure 4 The result shown is obtained by the device through steps (b)-(e).

[0082] The bubble inversion results are as follows Figure 5 The result shown is the result obtained by the device through steps (f)-(g), which is also the output result of the device.

[0083] The comparison of the scattering coefficient of the measured bubble group and the scattering coefficient corresponding to the measured result is shown in the figure below. Figure 6 As shown, Figure 6 The measured scattering coefficient in the experiment and the scattering coefficient corresponding to the measurement result have a good fit, which reflects that the measurement error of the device is small.

[0084] It can be seen from the above examples that the device of the present invention can be used to invert the bubble scale distribution parameters, reflect the influence of bubble group vibration and scattering on sound wave propagation, and realize the calculation of backscattered sound pressure of non-uniformly distributed bubbles, which is adaptable to the non-uniform distribution of bubbles, fits the reality, and is simple and fast to calculate.

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An acoustic inversion device for underwater bubble group size distribution based on forward and backscattering, characterized in that: include: A signal source, which emits the required known electrical signal; High-frequency power amplifier, converts the electrical signal from the signal source into a high-power electrical signal output; Oscilloscope, monitor the electrical signal output by the signal source and high-frequency amplifier; The transmitting transducer converts the electrical signal output by the high-frequency power amplifier into an acoustic signal and outputs it underwater; Hydrophones, which convert sound signals received in water into electrical signals; A collector collects the electrical signals received by the hydrophone in real time; On the PC side, the electrical signals collected by the collector are stored and displayed; Mounting frame, used to fix the device in place.

2. The acoustic inversion device for underwater bubble group size distribution based on forward and backscattering according to claim 1 is characterized in that: Taking the transmitting transducer as the origin x=0, the 1# hydrophone is deployed at x=d1 along the axial direction, and the 2# hydrophone is deployed at x=d1+d2 along the axial direction.

3. The acoustic inversion method of underwater bubble group size distribution based on forward and backscattering is characterized by: The method is implemented by using the acoustic inversion device for underwater bubble group size distribution based on forward and backscattering as described in claim 1 or 2, and comprises the following steps: (a) The device is deployed and the transmitting transducer sends out a signal; With the transmitting transducer as the origin x=0, a 1# hydrophone is placed at x=d1 in the axial direction, and a 2# hydrophone is placed at x=d1+d2 in the axial direction; the transmitting transducer transmits a single-frequency pulse sound signal with a frequency of ω1 into the bubble-containing water medium to be tested at x=0, and the 1# hydrophone and the 2# hydrophone simultaneously collect the single-frequency pulse sound signal; (b) Measure the incident sound pressure amplitude P1(ω1); (c) Measure the forward scattered sound pressure amplitude P2(ω1); (d) Measure the backscattered sound pressure amplitude P b (ω1); (e) Changing the transmission frequency to perform frequency sweeping, the frequency sweeping range is ω[ω1ω2…ω n ], repeat steps (b)-(d), and obtain the inversion equation in matrix form according to the inversion equation discretized by the joint theory of forward and backscattering; (f) Inversion equations under positive and finite constraints; (g) Tikhonov regularization is introduced into the inversion equation, and the bubble group size distribution parameters of the bubble-containing water medium to be tested are obtained by calculation.

4. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 3 is characterized in that: In step (b), the waveform of the direct wave signal received by the 1# hydrophone is Fourier transformed to read the incident sound pressure amplitude P1(ω1) of the bubble-containing water medium to be tested at the corresponding frequency ω1.

5. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 3 is characterized in that: In step (c), the waveform of the direct wave signal received by the 2# hydrophone is Fourier transformed to read the forward scattered sound pressure amplitude P2(ω1) of the bubble-containing water medium to be tested at the corresponding frequency ω1.

6. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 3 is characterized in that: In step (d), the time delay τ of the single-frequency pulse echo signal emitted in the bubble-containing water medium to be tested is calculated, the backscattered signal waveform received by the 1# hydrophone within the time delay τ is Fourier transformed, and the backscattered sound pressure amplitude P of the bubble-containing water medium to be tested at the corresponding frequency ω1 is read. b (ω1).

7. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 3 is characterized in that: In step (e), for the radius range of the bubble-containing water medium to be tested, R = [R1 R2 ... R m ], according to the joint theory of forward and backscattering: λ(ω)=∫σ s (ω,R)N(R)dR (1) in, is the backscattering cross section of a bubble with a radius of R under frequency ω excitation, N(R)=[N1(R1)N2(R2)…N m (R m )] is the number of bubbles with a radius of R, δ is the viscous damping coefficient, and ω0 is the resonance frequency of the bubble with a radius of R.

8. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 7 is characterized in that: Discretizing formula (1) yields the inversion equation in matrix form: λ(ω)=σ s (ω,R)N(R) (2).

9. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 3 is characterized in that: In step (f), the inversion equation is expressed mathematically under positive constraints and finite constraints:

10. The acoustic inversion method for underwater bubble group size distribution based on forward and backscattering according to claim 3 is characterized in that: In step (g), Tikhonov regularization is introduced into the inversion equation, and its specific calculation formula is: Where N is the exact solution of the inversion equation, N * is the initial estimate, ε is the regularization parameter, and L = tridiag (1, -2, 1) is a tridiagonal matrix. The regularized solution N of the bubble group size distribution parameter of the bubble-containing water medium to be measured is obtained by calculation. ε .

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