Method for detecting radiation characteristics of target to be detected in shallow sea waveguide environment

Abstract

The invention discloses a method for detecting radiation characteristics of a to-be-detected target in a shallow sea waveguide environment, which comprises the following steps of: 1, extracting real normal wave modal parameters of a sound source radiation signal in the shallow sea waveguide environment through an orthogonal constraint modal search method according to data received by a vertical array; 2, according to the real normal wave modal parameters, through a normal wave expression in a waveguide environment, performing inversion to obtain a sound field of the whole shallow sea waveguide; and step 3, acquiring sound field information required in the sound field of the shallow sea waveguide, mapping the sound source information into the free space by using the reciprocity theorem, realizing sound field migration from the shallow sea waveguide to the free space, and further acquiring the radiation characteristics of the target to be measured in the free space. The method is used for obtaining the radiation characteristics of the to-be-measured target in the free space according to the data received by the vertical array.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater sound-generating structure radiation characteristic testing, and in particular to a method for detecting the radiation characteristics of a target to be tested in a shallow sea waveguide environment. Background Art

[0002] Using underwater carriers such as buoys and submerged buoys, the radiation characteristics of the target under test can be acquired. As a key parameter of the 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 target's radiation characteristics, 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] It's well-known that the ideal environment for underwater acoustic radiation characteristics measurement is an open lake or anechoic tank. However, lake testing presents challenges such as high measurement cost and poor repeatability. Anechoic tanks offer poor low-frequency sound attenuation, making it difficult to meet free-field conditions. In contrast, the reverberation tank measurement method offers advantages such as low cost and high efficiency. This method combines spatial averaging measurement technology with low-frequency extension testing based on precise sound field measurements, addressing the uncertainty and low-frequency sound field inhomogeneity issues inherent in reverberation tank measurements. However, this method is not suitable for radiation characteristics testing of large-scale targets.

[0004] The seas surrounding my country are all shallow, making the study of radiated noise measurement methods in shallow waters of crucial importance. Commonly used methods for measuring radiation characteristics in shallow waters include constant-width beamforming and the virtual time-reversal mirror (VTRM). The constant-width beamforming method requires high array design and a large array aperture, making it inconvenient for engineering applications. The VTRM method suffers from source position mismatch, significantly degrading test performance and making it difficult to capture all target radiation characteristics.

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

[0006] The purpose of the present invention is to address the shortcomings of the existing technology and propose a method for detecting the radiation characteristics of a target to be measured in a shallow sea waveguide environment, which is used to obtain the radiation characteristics of the target to be measured in free space based on the data received by the vertical array.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A method for detecting radiation characteristics of a target to be measured in a shallow water waveguide environment comprises the following steps: Step 1: Based on the data received by the vertical array, the true simple normal wave modal parameters of the sound source radiation signal in the shallow sea waveguide environment are extracted through the orthogonal constrained mode search method; Step 2: Based on the actual normal wave modal parameters, the acoustic field of the entire shallow sea waveguide is inverted through the normal wave expression in the waveguide environment; Step 3: Obtain the required sound field information in the sound field of the shallow sea waveguide, use the reciprocity theorem to map the sound source information to the free space, realize the sound field migration from the shallow sea waveguide to the free space, and then obtain the radiation characteristics of the target to be measured in the free space.

[0008] Furthermore, the step 1 includes the following steps: Step 1.1: Based on the sound speed profile in the environment , calculate the horizontal wave number of the simple normal wave in the sound field Upper limit of search range , and set the horizontal wave number of the simple normal wave Lower limit of the search range and search step size , the calculation formula is as follows: ; Step 1.2: Calculate the horizontal wavenumbers of each simple normal wave within the search range using the following modal difference equation The simple normal wave mode function : ; In the formula, f is the frequency of the target radiation signal, ω is the angular frequency, z is the water depth, is the vertical difference step size; Step 1.3: According to the orthogonality of the simple normal wave modal functions, the simple normal wave modal functions of each simple normal wave horizontal wave number are grouped. The simple normal wave modal functions of the simple normal wave horizontal wave number in each group are orthogonal to each other, and the number of simple normal wave modal functions in each group is equal.

[0009] Furthermore, the step 1 further comprises the following steps: Step 1.4: Obtain the sound pressure P received by the vertical array; Step 1.5: According to the grouping in step 1.3, when When the following conditions are met, the simple normal wave horizontal wave number k1 and its simple normal wave modal function are the true simple normal wave modal parameters: .

[0010] Furthermore, in step 2, the acoustic field of the entire shallow sea waveguide obtained by inversion can be expressed as follows: ; In the formula, , is the density profile, z s is the water depth of the sound source, is the sound source spectrum, is the zero-order Hankel function of the first kind, .

[0011] Furthermore, step 3 includes the following steps: Step 3.1: Calculate the radiated sound field of the sound source S in free space according to the following formula: : ; in, ; ; ; In the formula, and is the component of the horizontal wave number of the simple normal wave along the x and y directions, is an imaginary number, D is the area where the sound source is located, n is the normal vector, is the sound pressure at the boundary of the region where the sound source is located, obtained according to step 2.

[0012] Furthermore, the step 3 further includes the following steps: Step 3.2: Calculate the sound source level of the sound source according to the following formula: ; In the formula, R1 is a point in the far field, is the reference sound pressure.

[0013] Furthermore, the step 3 further includes the following steps: Step 3.3: Calculate the directivity of the sound source according to the following formula: ; In the formula, for The sound pressure in the direction, is the sound pressure on the acoustic axis.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. In step 1, a vertical array is used to receive the target radiated acoustic signal. The true simple normal wave modal parameters of the sound source radiation signal in the shallow sea waveguide environment are obtained through the orthogonal constrained modal search method. Then, in step 2, the sound field in the entire shallow sea waveguide is inverted. Finally, in step 3, the reciprocity theorem is used to map the sound source information to free space, realizing the sound field migration from the shallow sea waveguide to the free space, and then obtaining the radiation characteristics of the target to be measured in free space.

[0015] 2. The measurement results are stable and reliable, and are suitable for scenarios such as vertical array buoys, submerged buoys and other underwater platforms. It effectively solves the problems of high cost and heavy workload in the existing free-field environment target sound radiation characteristic test, as well as the frequency and scale limitations in the reverberation tank environment target sound radiation characteristic test. It can be used to carry out target characteristic tests such as sound radiation intensity and directivity of underwater sound-emitting structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a flow chart of the radiation characteristics detection method of this embodiment; Figure 2 Schematic diagram of the simulation environment of this embodiment; Figure 3(a) is a comparison of the horizontal wave numbers of the first five modes; Figure 3(b) is a comparison of the vertical mode functions of the first five modes; Figure 4 This is the result diagram of shallow sea environment sound field inversion in the embodiment; Figure 5 This is a graph showing the change in sound intensity with distance when the same sound source is excited in different environments; Figure 6 3 is a comparison diagram of the actual directivity of the sound source and the directivity obtained in this embodiment. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0018] Example 1: A method for detecting radiation characteristics of a target to be measured in a shallow water waveguide environment, as shown in 1, comprises the following steps: Step 1: Based on the data received by the vertical array, the true simple normal wave modal parameters of the sound source radiation signal in the shallow sea waveguide environment are extracted through the orthogonal constrained mode search method; Step 2: Based on the actual normal wave modal parameters, the acoustic field of the entire shallow sea waveguide is inverted through the normal wave expression in the waveguide environment; Step 3: Obtain the required sound field information in the sound field of the shallow sea waveguide, use the reciprocity theorem to map the sound source information to the free space, realize the sound field migration from the shallow sea waveguide to the free space, and then obtain the radiation characteristics of the target to be measured in the free space.

[0019] The radiation characteristic detection method of the target to be measured in the shallow sea waveguide environment of this embodiment first uses a vertical array to receive the target radiation sound signal in step 1, and obtains the true simple normal wave modal parameters of the sound source radiation signal in the shallow sea waveguide environment through the orthogonal constrained modal search method. Then, in step 2, the sound field in the entire shallow sea waveguide is inverted and finally, in step 3, the reciprocity theorem is used to map the sound source information to free space, realizing the sound field migration from the shallow sea waveguide to the free space, and then obtaining the radiation characteristics of the target to be measured in the free space.

[0020] The radiation characteristic detection method of the target to be measured in a shallow-water waveguide environment of this embodiment has stable and reliable measurement results and is applicable to scenarios such as vertical array buoys, submerged buoys and other underwater platforms; it effectively solves the problems of high cost and large workload in the existing free-field environment target sound radiation characteristic testing, as well as the frequency and scale limitation problems in the reverberation tank environment target sound radiation characteristic testing; and can be used to carry out target characteristic tests such as sound radiation intensity and directionality of underwater sound-emitting structures.

[0021] In order to verify and further illustrate the radiation characteristic detection method of the target to be measured in the shallow sea waveguide environment of this embodiment, the following simulation is carried out, and the simulation parameters are as follows: Figure 2 As shown in the figure, the water depth is 50m, the sound velocity is 1500m / s, and the density is 1g / mL. The seabed is a semi-infinite liquid space with a sound velocity of 1600m / s and a density of 1.7g / mL. The point source sound source is at a depth of 20m, and the radiated signal is a single-frequency signal at 200Hz. The vertical array elements are distributed throughout the water, with a horizontal distance of 3750m from the sound source and an element spacing of 1m.

[0022] In an optional embodiment, step 1 includes the following steps: Step 1.1: Based on the sound speed profile in the environment , calculate the horizontal wave number of the simple normal wave in the sound field Upper limit of search range , and set the horizontal wave number of the simple normal wave Lower limit of the search range and search step size , the calculation formula is as follows: ; In this alternative embodiment, After the calculation is completed, the horizontal wave number of the simple normal wave is set according to experience. Lower limit of the search range and search step △ξ.

[0023] Step 1.2: Calculate the horizontal wavenumbers of each simple normal wave within the search range using the following modal difference equation The simple normal wave mode function : ; In the formula, f is the frequency of the target radiation signal, ω is the angular frequency, and z is the water depth. is the vertical difference step size.

[0024] Step 1.3: According to the orthogonality of the normal mode functions, group the normal mode functions of each normal mode horizontal wave number. The normal mode functions of the normal mode horizontal wave numbers within the group are orthogonal to each other, and the number of normal mode functions in each group is equal. In this optional embodiment, the condition of the orthogonality of the normal mode functions can be expressed as follows: ; In the formula, φ m (z, k m ) and φ <a000004>(z, k n ) are the normal mode functions of the normal mode horizontal wave numbers k n and k m respectively, and δ m is the Kronecker function.

[0025] Specifically, for a given normal mode horizontal wave number ξ m , find M (M is a preset value, M < N, and N is the number of elements of the vertical array) columns of normal mode functions orthogonal to it, as follows: ; And: .

[0026] Step 1.4: Obtain the sound pressure P received by the vertical array. In this optional embodiment, the sound pressure P received by the vertical array can be expressed as: ; ; Step 1.5: According to the grouping in Step 1.3, when , if the following conditions are met, then the normal mode horizontal wave number k1 and its normal mode function are the true normal mode parameters: .

[0027] In the above calculation process, ; ; ; In the formula, z sis the depth of the sound source, r0 is the distance between the array and the sound source, H0 (1) is the zero-order Hankel function of the first kind.

[0028] In this optional embodiment, after the grouping in step 1.3, the above formula is used for judgment to obtain the true simple normal wave modal parameters. The estimation results are shown in Figures 3(a) and 3(b), where Figure 3(a) is a comparison diagram of the horizontal wave numbers of the first five modes, the red asterisk in the figure represents the estimation result of this embodiment, and the blue circle represents the kraken calculation result; Figure 3(b) is a comparison diagram of the vertical modal function of the first five modes, the red dotted line in the figure represents the estimation result of this embodiment, and the blue circle represents the kraken calculation result.

[0029] In an optional embodiment, in step 2, the inverted acoustic field of the entire shallow sea waveguide can be expressed as follows: ; In the formula, , that is, the three-dimensional coordinates, is the density profile, z s is the water depth of the sound source, is the sound source spectrum, is the zero-order Hankel function of the first kind, , that is, two-dimensional coordinates.

[0030] The sound field in the shallow sea environment can be represented by the normal wave theory. The normal mode can be characterized by the horizontal wave number and the vertical mode function. The sound field is composed of the superposition of normal modes of different numbers, and the above formula is obtained. Combined with the real normal wave modal parameters obtained in step 1, the entire sound field can be inverted. The inverted sound field is as follows: Figure 4 shown.

[0031] In an optional embodiment, step 3 includes the following steps: Step 3.1: Calculate the radiated sound field of the sound source S in free space according to the following formula: : ; in, ; ; ; In the formula, and is the component of the horizontal wave number of the simple normal wave along the x and y directions, is an imaginary number, D is the area where the sound source is located, n is the normal vector, is the sound pressure at the boundary of the region where the sound source is located, obtained according to step 2.

[0032] Step 3.2: Calculate the sound source level of the sound source according to the following formula: ; In the formula, R1 is a point in the far field, As the reference sound pressure, it is usually taken in water =1μPa.

[0033] In this optional embodiment, the theoretical value of the point source sound source level is 105.4dB, the measured value is 106.7dB, and the relative error is 1.23%. The sound intensity changes with distance in different environments as shown in the figure below. Figure 5 As shown in the figure, the red line represents the theoretical value of the sound source in free space, the black line represents the measured value of the sound source in free space obtained in this embodiment, and the blue line represents the actual value of the sound source in a waveguide environment. Existing target characteristic testing methods in shallow water environments mainly include the equivalent source method and beamforming. Among them, the beamforming method can only obtain the sound source level of the target to be measured, but cannot obtain other target characteristics, and it suffers from environmental mismatch issues. The equivalent source method can simultaneously obtain the sound source level and directivity, but the actual measurement workload of this method is much greater than that of the method in this embodiment, and the maximum error can reach 40% at higher frequencies.

[0034] Step 3.3: Calculate the directivity of the sound source according to the following formula: ; In the formula, for The sound pressure in the direction, is the sound pressure on the acoustic axis.

[0035] In this optional embodiment, the target sound source to be measured is selected as a point source with the same directivity in all directions. Figure 6 The blue solid line indicates that the results obtained by the method of this embodiment are as follows: Figure 6 Indicated by the red dotted line.

[0036] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for detecting radiation characteristics of a target under test in a shallow sea waveguide environment, characterized in that: The steps include: Step 1: Based on the data received by the vertical array, the true simple normal wave modal parameters of the sound source radiation signal in the shallow sea waveguide environment are extracted through the orthogonal constrained mode search method; Step 2: Based on the actual normal wave modal parameters, the acoustic field of the entire shallow sea waveguide is inverted through the normal wave expression in the waveguide environment; Step 3: Obtain the required sound field information in the sound field of the shallow sea waveguide, use the reciprocity theorem to map the sound source information to the free space, realize the sound field migration from the shallow sea waveguide to the free space, and then obtain the radiation characteristics of the target to be measured in the free space.

2. The method for detecting radiation characteristics of a target under shallow water waveguide environment according to claim 1, characterized in that: The step 1 comprises the following steps: Step 1.1: Based on the sound speed profile in the environment , calculate the horizontal wave number of the simple normal wave in the sound field Upper limit of search range , and set the horizontal wave number of the simple normal wave Lower limit of the search range and search step size , the calculation formula is as follows: ； Step 1.2: Calculate the horizontal wavenumbers of each simple normal wave within the search range using the following modal difference equation The simple normal wave mode function : ； In the formula, f is the frequency of the target radiation signal, ω is the angular frequency, z is the water depth, is the vertical difference step size; Step 1.3: According to the orthogonality of the simple normal wave modal functions, the simple normal wave modal functions of each simple normal wave horizontal wave number are grouped. The simple normal wave modal functions of the simple normal wave horizontal wave number in each group are orthogonal to each other, and the number of simple normal wave modal functions in each group is equal.

3. The method for detecting radiation characteristics of a target under a shallow sea waveguide environment according to claim 2, characterized in that: The step 1 further comprises the following steps: Step 1.4: Obtain the sound pressure P received by the vertical array; Step 1.5: According to the grouping in step 1.3, when When the following conditions are met, the simple normal wave horizontal wave number k1 and its simple normal wave modal function are the true simple normal wave modal parameters: 。 4. The method for detecting radiation characteristics of a target under a shallow sea waveguide environment according to claim 1, characterized in that: In step 2, the inverted acoustic field of the entire shallow sea waveguide can be expressed as follows: ； In the formula, , is the density profile, z s is the water depth of the sound source, is the sound source spectrum, is the zero-order Hankel function of the first kind, .

5. The method for detecting radiation characteristics of a target under shallow water waveguide environment according to claim 4, characterized in that: The step 3 comprises the following steps: Step 3.1: Calculate the radiated sound field of the sound source S in free space according to the following formula: : ； in, ； ； ； In the formula, and is the component of the horizontal wave number of the simple normal wave along the x and y directions, is an imaginary number, D is the area where the sound source is located, n is the normal vector, is the sound pressure at the boundary of the region where the sound source is located, obtained according to step 2.

6. The method for detecting radiation characteristics of a target under shallow water waveguide environment according to claim 5, characterized in that: The step 3 further comprises the following steps: Step 3.2: Calculate the sound source level of the sound source according to the following formula: ； In the formula, R1 is a point in the far field, is the reference sound pressure.

7. The method for detecting radiation characteristics of a target under shallow water waveguide environment according to claim 5, characterized in that: The step 3 further comprises the following steps: Step 3.3: Calculate the directivity of the sound source according to the following formula: ； In the formula, for The sound pressure in the direction, is the sound pressure on the acoustic axis.

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