A multi-channel composite test method for low-frequency target characteristic test

Abstract

The application discloses a kind of multi-channel composite test methods for low-frequency target characteristic test, comprising the following steps: step 1: according to the theory of multi-stage development, the target to be tested is described as the linear superposition of multiple poles, and a multipole moment matrix equation of the target to be tested is constructed; the Green function matrix containing each order pole is constructed in combination with the test environment information;Step 2: according to the data received by different receivers in the water channel, the interface channel and the seabed channel, the received signal vector containing the overall low-frequency information of the target is obtained through multi-channel signal decoupling and information fusion technology;Step 3: in the process of solving multiple moments, the unique solution of each order multiple moment is obtained by introducing regularization technique, and then the low-frequency target radiation characteristics represented by the linear superposition of multiple poles are obtained.The method of the application is used to obtain the radiation characteristics of the low-frequency target to be tested in free space according to the data of the receivers in different channels.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic structure radiation characteristic testing technology, and in particular to a multi-channel composite testing method for testing the characteristics of low-frequency targets. Background Technology

[0002] The radiation characteristics of a target can be obtained using underwater instruments such as buoys and submersibles. As a crucial parameter of a sound source, obtaining radiation characteristics is of great significance in fields such as sound source level calibration and radiated sound field prediction. By accurately measuring the radiation characteristics of a target, key parameters such as its sound source level and directivity can be determined, providing support for target sound source level calibration and radiated sound field prediction.

[0003] Among various testing environments, the free-field environment is the most ideal for testing the acoustic radiation characteristics of underwater targets, such as open natural water bodies and anechoic pools. In practical engineering testing, test sites are typically established in deep-sea environments. However, deep-sea testing projects are difficult to implement, easily affected by environmental factors, and involve high workload and cost. Furthermore, for very low frequency signals, even deep-sea environments are difficult to approximate as free-field environments. The advantages of anechoic pool testing are fewer interfering factors and better stability and accuracy. However, anechoic pools are usually much smaller than natural water bodies and cannot be used to test radiation characteristics below the anechoic frequency band.

[0004] The seas surrounding my country are all shallow, making the study of low-frequency radiated noise measurement methods in shallow sea environments of great significance. Currently, commonly used methods for measuring radiation characteristics in shallow sea environments include propagation loss compensation, constant beamwidth beamforming, and sound field separation. Propagation loss compensation is simple to test, but requires high-precision seabed parameter information to ensure accuracy and cannot obtain vertical pointing characteristics. Constant beamwidth beamforming can obtain broadband spectral characteristics without distortion, but its algorithm is complex and highly sensitive to array manifold errors. Sound field separation methods can obtain complete target radiation characteristics, but each method has its own advantages and limitations. For example, sound field separation technology based on spatial Fourier transform has high computational speed and simple practical application; however, both the measurement surface and the shape of the sound source must be regular planes, and convolution errors and truncation effects exist during the calculation process. Sound field separation technology based on the equivalent source method is applicable to sound sources of arbitrary geometry and has high computational accuracy, but rationally arranging the position of the equivalent source is a very difficult problem.

[0005] In view of this, this invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a multi-channel composite testing method for testing the characteristics of low-frequency targets. This method is used to obtain the radiation characteristics of the low-frequency target under test in free space based on data from receivers in different channels.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A multi-channel composite testing method for testing the characteristics of low-frequency targets includes the following steps: Step 1: Based on the multi-level expansion theory, the target to be tested is described as a linear superposition of multiple order poles. The multi-pole moment matrix equation of the target to be tested is constructed, and the Green's function matrix containing each order pole is constructed in combination with the test environment information. Step 2: Based on the data received by different receivers in the water body channel, interface channel, and seabed channel, obtain the received signal vector containing comprehensive low-frequency information of the target through multi-channel signal decoupling and information fusion technology; Step 3: In the process of solving the multipole moments, a regularization technique is introduced to obtain the unique solution of each order of multipole moments, and then the low-frequency target radiation characteristics represented by the linear superposition of multipole moments are obtained.

[0008] Furthermore, step 1 includes the following steps: Step 1.1: Arbitrarily distributed sound sources Through the distribution of sound sources and the Green's function in the environment The convolution calculation produces the sound pressure field. The calculation formula is as follows: ; Where R is the receiver coordinate, R s The coordinates of the sound source region, The sound source region; Step 1.2: At the center of the sound source Green's function about The multivariate Taylor series expansion is as follows: ; in, For The derivative; Step 1.3: Using Green's function The symmetry of the source coordinates transforms the derivative with respect to the source center coordinates, thereby transforming the sound pressure field... Rewritten as follows: ; in, It is the highest order of a multilevel sub.

[0009] Furthermore, step 1 includes the following steps: Step 1.4: For a vertically deployed receiver array in a shallow sea environment, the relationship between the target radiated signal and the received signal is established as follows: ; in: ; ; ; ; in, For the received signal vector, The matrix represents the Green's function. Let the target be the multipole moment vector. For noise vectors, R1~R M for The signal received by the receiver.

[0010] Furthermore, step 2 includes the following steps: Step 2.1: The data received at the location is represented as follows: ; in, It is a constant. The first in the water body m Modal depth function of the normal modes, For the depth of the sound source, It is a modal depth function for physical quantities such as longitudinal and lateral stress or displacement in water bodies and seabed channels. It is a zero-order Hankel function of the first kind. For the first m The horizontal wavenumber of the first normal mode; Step 2.2: For the elastic seabed condition, the relationship between displacement, velocity, acceleration, and stress is established as follows: ; in, Angular frequency, For density, Let i be the displacement vector, and i be the imaginary unit. Represents the velocity vector. Represents the acceleration vector. Represents the external force vector. Represents the stress tensor; Step 2.3: Using normal mode theory, calculate the position of a single-pole source in the water body on the seabed. The formulas for the horizontal and vertical stresses induced at the location are as follows: ; in, For a point source in a body of water, the effective stress tensor under cylindrical symmetry conditions. It is normal stress. This is the shear stress.

[0011] Furthermore, step 2 also includes the following steps: Step 2.4: Calculate the received signal vector The formula is as follows: ; in, This indicates the sound pressure received by the water body receiver. This indicates the acceleration received by the interface receiver. This represents the stress tensor received by the seabed receiver. , , These represent the number of hydrophones, accelerometers, and stress sensors in the receiving array, respectively.

[0012] Furthermore, step 3 includes the following steps: Step 3.1: Equivalently convert the target radiation characteristics acquisition process to using the received signal vector Solving for the multipole moment vector of the target under test The process, which uses least squares to solve, is shown in the following formula: ; in, Representing the Green's function matrix The generalized inverse; Step 3.2: Using Tikhonov regularization, solve for the multipole moments by minimizing the following function: ; in, For the received signal vector, For regularization parameters; Step 3.3: Calculate the radiated sound field of the target in free space. The formula is as follows: ; in, For the first n The multipole moment of a +1st order multipole For the highest order of a multilevel sub-sub, For The nth derivative.

[0013] Furthermore, step 3 also includes the following steps: Step 3.4: Calculate the sound source level using the following formula: ; in, For a point in the far field of free space, For reference sound pressure level.

[0014] Furthermore, step 3 also includes the following steps: Step 3.5: Calculate the directivity of the sound source, using the following formula: ; in, for Sound pressure in the direction, This refers to the sound pressure on the acoustic axis.

[0015] Compared with the prior art, the beneficial effects of this invention are as follows: 1. First, in step 1, the target to be tested is described as a linear superposition of multiple poles, and the multipole moment matrix equation of the target to be tested is constructed. Combined with the test environment information, a Green's function matrix containing each order of poles is constructed. Then, in step 2, based on the data received by different receivers in the water channel, interface channel and seabed channel, the received signal vector containing comprehensive low-frequency information of the target is obtained through multi-channel signal decoupling and information fusion technology. Finally, in step 3, the unique solution of each order of multipole moment is obtained by introducing regularization technology, thereby obtaining the low-frequency target radiation characteristics represented by the linear superposition of multiple poles.

[0016] 2. The measurement results are stable and reliable, and are suitable for underwater platforms such as vertical array buoys and submersibles; it effectively solves the problems of high cost and large workload in the existing free field environment target acoustic radiation characteristic test, as well as the frequency limitation problem in the shallow sea waveguide environment target acoustic radiation characteristic test; it can be used to test the target characteristics such as acoustic radiation intensity and directivity of underwater low frequency sound-emitting structures. Attached Figure Description

[0017] Figure 1 A flowchart of a multi-channel composite test method for testing the characteristics of low-frequency targets; Figure 2 This is a schematic diagram of the simulation environment in this embodiment; Figure 3 This is a schematic diagram showing the deployment of various receivers in different channels during radiation characteristic detection in this embodiment; Figure 4 This graph shows the variation of sound intensity from the same sound source with distance under different environments. Figure 5 This is a comparison diagram of the actual directivity of the sound source and the directivity obtained in this embodiment. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example

[0019] A multi-channel composite testing method for low-frequency target characteristic testing, such as Figure 1 As shown, it includes the following steps: Step 1: Based on the multi-level expansion theory, the target to be tested is described as a linear superposition of multiple order poles. The multi-pole moment matrix equation of the target to be tested is constructed, and the Green's function matrix containing each order pole is constructed in combination with the test environment information.

[0020] In this embodiment, step 1 includes the following steps: Step 1.1: Arbitrarily distributed sound sources Through the distribution of sound sources and the Green's function in the environment The convolution calculation produces the sound pressure field. The calculation formula is as follows: ; Where R is the receiver coordinate, R s The coordinates of the sound source region, This is the sound source region.

[0021] Step 1.2: At the center of the sound source Green's function about The multivariate Taylor series expansion is as follows: ; in, For The derivative of .

[0022] In this embodiment, due to the Green's function In the sound source region Internal variables It is continuous and infinitely differentiable, therefore step 1.2 can be expanded.

[0023] Step 1.3: Using Green's function The symmetry of the source coordinates transforms the derivative with respect to the source center coordinates, thereby transforming the sound pressure field... Rewritten as follows: ; in, It is the highest order of a multilevel sub.

[0024] Therefore, the sound field It is decomposed into terms of different orders, each term consisting of... Space moments (i.e., the strength of each order of poles) and Green's function It consists of its spatial derivatives of various orders. Since the radiation efficiency of higher-order multipoles is very low, obtaining the spatial moments of the first few orders of multipoles allows for the reconstruction of the sound source. The far-field radiation characteristics.

[0025] Step 1.4: For a vertically deployed receiver array in a shallow sea environment, the relationship between the target radiated signal and the received signal is established as follows: ; in: ; ; ; ; in, For the received signal vector, The matrix represents the Green's function. Let the target be the multipole moment vector. For noise vectors, R1~R M for The signal received by the receiver.

[0026] Step 2: Based on the data received by different receivers in the water body channel, interface channel and seabed channel, obtain the received signal vector containing comprehensive low-frequency information of the target through multi-channel signal decoupling and information fusion technology.

[0027] In this embodiment, step 2 includes the following steps: Step 2.1: The data received at the location is represented as follows: ; in, As a constant, the first m Modal depth function of the normal modes, For the depth of the sound source, It is a modal depth function for physical quantities such as longitudinal and lateral stress or displacement in water bodies and seabed channels. It is a zero-order Hankel function of the first kind. For the first m The horizontal wavenumber of the normal mode.

[0028] Step 2.2: For the elastic seabed condition, the relationship between displacement, velocity, acceleration, and stress is established as follows: ; in, Angular frequency, For density, Let i be the displacement vector, and i be the imaginary unit. Represents the velocity vector. Represents the acceleration vector. Represents the external force vector. This represents the stress tensor.

[0029] Step 2.3: Using normal mode theory, calculate the position of a single-pole source in the water body on the seabed. The formulas for the horizontal and vertical stresses induced at the location are as follows: ; in, For a point source in a body of water, the effective stress tensor under cylindrical symmetry conditions. It is normal stress. This is the shear stress.

[0030] Furthermore, step 2 also includes the following steps: Step 2.4: Calculate the received signal vector The formula is as follows: ; in, This indicates the sound pressure received by the water body receiver. This indicates the acceleration received by the interface receiver. This represents the stress tensor received by the seabed receiver. , , These represent the number of hydrophones, accelerometers, and stress sensors in the receiving array, respectively.

[0031] Step 3: In the process of solving the multipole moments, a regularization technique is introduced to obtain the unique solution of each order of multipole moments, and then the low-frequency target radiation characteristics represented by the linear superposition of multipole moments are obtained.

[0032] In this embodiment, step 3 includes the following steps: Step 3.1: Equivalently convert the target radiation characteristics acquisition process to using the received signal vector Solving for the multipole moment vector of the target under test The process, which uses least squares to solve, is shown in the following formula: ; in, Representing the Green's function matrix The generalized inverse; Step 3.2: Using Tikhonov regularization, solve for the multipole moments by minimizing the following function: ; in, This is the regularization parameter.

[0033] In the low-frequency radiation model of a compact source, the Green's function matrix The large differences in amplitude between different columns cause the matrix equation to be severely ill-conditioned. Therefore, step 3.2 of this embodiment introduces Tikhonov regularization to solve the underdetermined equation problem.

[0034] Step 3.3: Calculate the radiated sound field of the target in free space. The formula is as follows: ; in, For the first n The multipole moment of a +1st order multipole For the highest order of a multilevel sub-sub, For The nth derivative.

[0035] Step 3.4: Calculate the sound source level using the following formula: ; in, For a point in the far field of free space, For reference sound pressure level.

[0036] Step 3.5: Calculate the directivity of the sound source, using the following formula: ; in, for Sound pressure in the direction, This refers to the sound pressure on the acoustic axis.

[0037] This embodiment presents a multi-channel composite testing method for testing the characteristics of low-frequency targets. First, in step 1, the target under test is described as a linear superposition of multiple-order poles, and the multi-pole moment matrix equation of the target under test is constructed. Combined with the test environment information, a Green's function matrix containing each order of poles is constructed. Then, in step 2, based on the data received by different receivers in the water channel, interface channel, and seabed channel, the received signal vector containing comprehensive low-frequency information of the target is obtained through multi-channel signal decoupling and information fusion technology. Finally, in step 3, the unique solution of each order of multi-pole moment is obtained by introducing regularization technology, thereby obtaining the radiation characteristics of the low-frequency target represented by the linear superposition of multiple-order poles.

[0038] This embodiment presents a multi-channel composite testing method for testing the characteristics of low-frequency targets. The measurement results are stable and reliable, and it is applicable to scenarios such as underwater platforms such as vertical array buoys and underwater moorings. It effectively solves the problems of high cost and large workload in the existing free-field environment target acoustic radiation characteristic testing, as well as the frequency limitation problem in the shallow sea waveguide environment target acoustic radiation characteristic testing. It can be used to test the target characteristics such as acoustic radiation intensity and directivity of underwater low-frequency sound-emitting structures.

[0039] To verify and further illustrate the multi-channel composite test method for testing the characteristics of low-frequency targets in this embodiment, the following simulation was performed, with the simulation parameters as follows: Figure 2 As shown, the water depth is 75m, the sound velocity is 1500m / s, and the density is 1g / mL. The water-air interface is an absolutely soft boundary. The seabed consists of an elastic sedimentary layer and an elastic semi-infinite basement layer. The sedimentary layer has a longitudinal wave velocity of 2000m / s, a transverse wave velocity of 600m / s, and a density of 1.7g / mL; the basement layer has a longitudinal wave velocity of 4000m / s, a transverse wave velocity of 2200m / s, and a density of 2.6g / mL. The sound source to be measured is a combination of a monopole and a longitudinal dipole with an intensity of 1. The center depth of the sound source is 71m, and the radiated signal is a single-frequency signal of 20Hz.

[0040] The simulation deploys different types of receivers in different channels within a test environment to achieve multi-channel composite testing. For example... Figure 3 As shown, the sensors in the water channel are scalar hydrophones capable of measuring sound pressure. Hydrophones near the sea surface are located 2m underwater, while those near the seabed are located 2m above the water-sediment interface, with adjacent hydrophones spaced 1m apart. An accelerometer is placed at both the water-sediment interface and the sediment-basement interface. Stress sensors are placed within the sediment and basement layers. In the sediment layer, the first stress sensor is at a depth of 77m, the last at 93m, and the spacing between adjacent stress sensors is 2m. In the basement layer, the first stress sensor is at a depth of 97m, the last at 195m, and the spacing between adjacent stress sensors is 2m. The horizontal distance between all sensors and the sound source being measured is 100m.

[0041] The target sound source to be tested was selected as a combined sound source consisting of monopoles and dipoles. Figure 4The paper presents the variation of the sound pressure level of the sound source under test along the acoustic axis in free space with distance. The solid black line represents the theoretical value variation curve of the sound source under test, and the dashed red line represents the variation curve obtained by the formula in step 3.3 after measuring the multiple moment vector using this method. The results show that the theoretical sound source level of the combined sound source along the acoustic axis is 98.02 dB, the measured value is 97.87 dB, and the sound source level measurement error is 0.15 dB, indicating that this method can effectively achieve the testing of the sound source level of low-frequency targets. Existing target characteristic testing methods in shallow sea environments mainly include the equivalent source method and beamforming method; among them, the beamforming method can only obtain the sound source level of the target under test, and cannot obtain other target characteristics, and there is an environmental mismatch problem; the equivalent source method can simultaneously obtain the sound source level and directivity, but the measurement workload of this method in actual use is much greater than that of the method in this embodiment, and the maximum error can reach 40% at higher frequencies.

[0042] The target sound source to be tested was selected as a combined sound source consisting of monopoles and dipoles. Figure 5 The directivity of the sound source under test in free space is given. The solid black line represents the theoretical directivity of the sound source, and the dashed red line represents the directivity obtained by the formula in step 3.3 after measuring the multiple polar moment vector using this method. The results show that the relative error of the sound source directivity measured by the method in this embodiment is 1.07%, indicating that this method can effectively achieve the directivity testing of low-frequency targets.

[0043] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multi-channel composite testing method for testing the characteristics of low-frequency targets, characterized in that, Includes the following steps: Step 1: Based on the multi-level expansion theory, the target to be tested is described as a linear superposition of multiple order poles. The multi-pole moment matrix equation of the target to be tested is constructed, and the Green's function matrix containing each order pole is constructed in combination with the test environment information. Step 2: Based on the data received by different receivers in the water body channel, interface channel, and seabed channel, obtain the received signal vector containing comprehensive low-frequency information of the target through multi-channel signal decoupling and information fusion technology; Step 3: In the process of solving the multipole moments, a regularization technique is introduced to obtain the unique solution of each order of multipole moments, thereby obtaining the low-frequency target radiation characteristics represented by the linear superposition of multipole moments; Step 2 includes the following steps: Step 2.1: The data received at the location is represented as follows: ； in, It is a constant. The first in the water body m Modal depth function of the normal modes, For the depth of the sound source, It is a modal depth function for physical quantities such as longitudinal and lateral stress or displacement in water bodies and seabed channels. It is a zero-order Hankel function of the first kind. For the first m The horizontal wavenumber of the first normal mode; Step 2.2: For the elastic seabed condition, the relationship between displacement, velocity, acceleration, and stress is established as follows: ； in, Angular frequency, For density, Let i be the displacement vector, and i be the imaginary unit. Represents the velocity vector. Represents the acceleration vector. Represents the external force vector. Represents the stress tensor; Step 2.3: Using normal mode theory, calculate the position of a single-pole source on the seabed in the water body. The formulas for the horizontal and vertical stresses induced at the location are as follows: ； in, For a point source in a body of water, the effective stress tensor under cylindrical symmetry conditions. It is normal stress. Shear stress; Step 3 includes the following steps: Step 3.1: The process of obtaining the target radiation characteristics is equivalent to using the received signal vector. Solving for the multipole moment vector of the target under test The process, which uses least squares to solve, is shown in the following formula: ； in, Representing the Green's function matrix The generalized inverse; Step 3.2: Using Tikhonov regularization, solve for the multipole moments by minimizing the following function: ； in, For the received signal vector, For regularization parameters; Step 3.3: Calculate the radiated sound field of the target in free space. The formula is as follows: ； in, For the first n The multipole moment of a +1st order multipole For the highest order of a multilevel sub-sub, For The nth derivative.

2. The multi-channel composite testing method for testing the characteristics of low-frequency targets according to claim 1, characterized in that, Step 1 includes the following steps: Step 1.1: Arbitrarily distributed sound sources Through the distribution of sound sources and the Green's function in the environment The convolution calculation produces the sound pressure field. The calculation formula is as follows: ； in, For the receiver coordinates, The coordinates of the sound source region are: The sound source region; Step 1.2: At the center of the sound source Green's function about The multivariate Taylor series expansion is as follows: ； in, For The derivative; Step 1.3: Using Green's function The symmetry of the source coordinates transforms the derivative with respect to the source center coordinates, thereby transforming the sound pressure field... Rewritten as follows: ； in, It is the highest order of a multilevel sub.

3. The multi-channel composite testing method for low-frequency target characteristic testing according to claim 2, characterized in that, Step 1 includes the following steps: Step 1.4: For a vertically deployed receiver array in a shallow sea environment, the relationship between the target radiated signal and the received signal is established as follows: ； in: ； ； ； ； in, For the received signal vector, The matrix represents the Green's function. Let the target be the multipole moment vector. For noise vectors, R1~R M for The signal received by the receiver.

4. The multi-channel composite testing method for low-frequency target characteristic testing according to claim 1, characterized in that, Step 2 also includes the following steps: Step 2.4: Calculate the received signal vector The formula is as follows: ； in, This indicates the sound pressure received by the water body receiver. This indicates the acceleration received by the interface receiver. This represents the stress tensor received by the seabed receiver. These represent the number of hydrophones, accelerometers, and stress sensors in the receiving array, respectively.

5. The multi-channel composite testing method for testing the characteristics of low-frequency targets according to claim 1, characterized in that, Step 3 also includes the following steps: Step 3.4: Calculate the sound source level using the following formula: ； in, For a point in the far field of free space, For reference sound pressure level.

6. The multi-channel composite testing method for testing the characteristics of low-frequency targets according to claim 1, characterized in that, Step 3 also includes the following steps: Step 3.5: Calculate the directivity of the sound source, using the following formula: ； in, for Sound pressure in the direction, This refers to the sound pressure on the acoustic axis.

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