A method for detecting radiation characteristics of a target to be measured in a shallow sea waveguide environment

Abstract

The application discloses a kind of radiation characteristics detection methods of target to be measured under shallow sea waveguide environment, comprising the following steps: step 1: according to the data received by vertical array, by orthogonal constraint mode search method, extract the real normal mode parameters of sound source radiation signal in shallow sea waveguide environment;Step 2: according to the real normal mode parameters, by normal mode expression in waveguide environment, the sound field of entire shallow sea waveguide is obtained by inversion;Step 3: obtain the sound field information required in the sound field of shallow sea waveguide, utilize reciprocity theorem to map sound source information to free space, realize the sound field migration from shallow sea waveguide to free space, and further obtain the radiation characteristics of target to be measured in free space.The method of the application is used to obtain the radiation characteristics of target to be measured in free space according to the data received by vertical array.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underwater sound radiating structure radiation characteristic testing, and particularly relates to a method for detecting radiation characteristics of a target to be tested in a shallow sea waveguide environment. BACKGROUND

[0002] The radiation characteristics of the target to be tested can be obtained by using a buoy, a submerged buoy and the like. As an important parameter of a sound source, the radiation characteristics are of great significance in the fields of sound source level calibration and radiation sound field prediction. By accurately measuring the radiation characteristics of the target, the sound source level, directivity and other key parameters of the target can be determined, thereby providing support for the target sound source level calibration and radiation sound field prediction.

[0003] It is known that an ideal environment for underwater sound radiation characteristic measurement is an open lake or an anechoic pool. However, lake testing has problems of high measurement cost and poor repeatability. The low-frequency anechoic effect of the anechoic pool is not good, and it is difficult to meet the free field condition. In contrast, the reverberation pool measurement method has the advantages of low cost and high efficiency. This method combines the spatial average measurement technology and the low-frequency extension test technology based on fine sound field measurement, and solves the problems of uncertainty and non-uniformity of the sound field in the low-frequency range in the reverberation pool measurement. However, this method is not suitable for radiation characteristic testing of large-scale targets.

[0004] The sea areas around China are all shallow seas, and it is of great significance to study the radiation noise measurement method in the shallow sea environment. The commonly used methods for measuring the radiation characteristics in the shallow sea environment include the constant beamwidth beamforming method and the virtual time reversal mirror method. The constant beamwidth beamforming method has high design requirements for the array, and the array aperture is large, which is inconvenient for engineering application. The virtual time reversal mirror method has the problem of mismatch of the sound source position, and the test performance decreases obviously when mismatched, and it is difficult to obtain all the target radiation characteristics.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The present application aims at solving the problems in the prior art, and provides a method for detecting the radiation characteristics of a target to be tested in a shallow sea waveguide environment, which is used for obtaining the radiation characteristics of the target to be tested in free space according to the data received by a vertical array.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] A method for detecting the radiation characteristics of a target to be tested in a shallow sea waveguide environment, comprising the following steps:

[0009] Step 1: According to the data received by a vertical array, the real normal mode parameters of the sound source radiation signal in the shallow sea waveguide environment are extracted by an orthogonal constraint modal search method.

[0010] Step 2: According to the real normal mode parameters, the sound field of the entire shallow water waveguide is obtained by the normal mode expression in the waveguide environment;

[0011] Step 3: Obtain the sound field information required in the sound field of the shallow water waveguide, map the sound source information to the free space by using the reciprocity theorem, realize the sound field migration from the shallow water waveguide to the free space, and further obtain the radiation characteristics of the target in the free space.

[0012] Further, the step 1 comprises the following steps:

[0013] Step 1.1: According to the sound speed profile in the environment , the horizontal wave number of the normal mode in the sound field is calculated , and the lower limit of the search range of the horizontal wave number of the normal mode is set and the search step , the calculation formula is as follows:

[0014] ;

[0015] Step 1.2: The normal mode function of each normal mode horizontal wave number in the search range is calculated by the following modal difference equation:

[0016] ;

[0017] 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;

[0018] Step 1.3: According to the orthogonality of the normal mode function, the normal mode functions of each normal mode horizontal wave number are grouped, the normal mode functions of the normal mode horizontal wave number in the group are mutually orthogonal, and the number of normal mode functions in each group is equal.

[0019] Further, the step 1 further comprises the following steps:

[0020] Step 1.4: Obtain the sound pressure P received by the vertical array;

[0021] Step 1.5: According to the grouping of step 1.3, when , the following conditions are satisfied, then the normal mode horizontal wave number k1 and its normal mode function are real normal mode parameters:

[0022] .

[0023] Further, the sound field of the whole shallow waveguide obtained by the inversion in step 2 can be expressed as follows:

[0024] ;

[0025] 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 first Hankel function, .

[0026] Further, the step 3 comprises the following steps:

[0027] Step 3.1: Calculate the radiated sound field of the sound source S in the free space according to the following formula :

[0028] ;

[0029] In the formula,

[0030] ;

[0031] ;

[0032] ;

[0033] In the formula, and are the components of the normal wave horizontal wave number along the x and y directions, is an imaginary number, D is the area where the sound source is located, and n is the normal vector, is the sound pressure on the boundary of the area where the sound source is located, which is obtained according to step 2.

[0034] Further, the step 3 further comprises the following steps:

[0035] Step 3.2: Calculate the sound source level of the sound source according to the following formula:

[0036] ;

[0037] In the formula, R1 is a point in the far field, is the reference sound pressure.

[0038] Further, the step 3 further comprises the following steps:

[0039] Step 3.3: Calculate the directivity of the sound source according to the following formula:

[0040] ;

[0041] In the formula, is sound pressure in the direction, is the sound pressure on the sound axis.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] 1. In step 1, a vertical array is used to receive the target radiation sound signal, the real normal mode parameters of the sound source radiation signal in the shallow sea waveguide environment are obtained through the orthogonal constraint mode search method, then in step 2, the sound field in the entire shallow sea waveguide is obtained by inversion, finally in step 3, the reciprocity theorem is used to map the sound source information to the free space, realizing the sound field migration from the shallow sea waveguide to the free space, and further obtaining the radiation characteristics of the target to be measured in the free space.

[0044] 2. The measurement result is stable and reliable, and is suitable for underwater platforms such as vertical array buoys, subsurface buoys and the like; effectively solves the problems of high cost and large workload existing in the current free field environment target sound radiation characteristic test, and the frequency and scale limitation problems existing in the reverberation pool environment target sound radiation characteristic test; can be used for target characteristic test such as sound radiation intensity and directivity of underwater sound emitting structure. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a flowchart of the radiation characteristic detection method of the embodiment;

[0046] Figure 2 is a simulation environment schematic diagram of the embodiment;

[0047] Fig. 3(a) is a comparison diagram of horizontal wave numbers of the first five modes;

[0048] Fig. 3(b) is a comparison diagram of vertical mode functions of the first five modes;

[0049] Figure 4 is a result diagram of the inversion of the shallow sea environment sound field of the embodiment;

[0050] Figure 5 is a diagram of the change of sound intensity with distance of the same sound source excited in different environments;

[0051] Figure 6 is a comparison diagram of the actual directivity of the sound source and the directivity obtained by the embodiment. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments.

[0053] Embodiment one:

[0054] A method for detecting radiation characteristics of a target to be measured in a shallow sea waveguide environment, as shown in FIG. 1, includes the following steps:

[0055] Step 1: According to the data received by the vertical array, the real normal mode parameters of the sound source radiation signal in the shallow sea waveguide environment are extracted by the orthogonal constrained mode search method;

[0056] Step 2: According to the real normal mode parameters, the sound field in the entire shallow sea waveguide is obtained by inversion through the normal wave expression in the waveguide environment;

[0057] Step 3: Obtain the required sound field information in the shallow sea waveguide sound field, map the sound source information to the free space using the reciprocity theorem, realize the sound field migration from the shallow sea waveguide to the free space, and further obtain the radiation characteristics of the target to be measured in the free space.

[0058] The method for detecting radiation characteristics of a target to be measured in a shallow sea waveguide environment of the embodiment first receives the target radiation sound signal by a vertical array in step 1, obtains the real normal mode parameters of the sound source radiation signal in the shallow sea waveguide environment by the orthogonal constrained mode search method, then obtains the sound field in the entire shallow sea waveguide in step 2, and finally maps the sound source information to the free space using the reciprocity theorem in step 3, realizes the sound field migration from the shallow sea waveguide to the free space, and further obtains the radiation characteristics of the target to be measured in the free space.

[0059] The method for detecting radiation characteristics of a target to be measured in a shallow sea waveguide environment of the embodiment has stable and reliable measurement results, is suitable for underwater platforms such as vertical array buoys and subsurface buoys, effectively solves the problems of high cost and large workload in the existing free field environment target sound radiation characteristic test, and the frequency and scale limitation problems in the reverberation tank environment target sound radiation characteristic test, and can be used for target characteristic test such as sound radiation intensity and directivity of underwater sound emitting structure.

[0060] To verify and further illustrate the method for detecting radiation characteristics of a target to be measured in a shallow sea waveguide environment of the embodiment, the following simulation is performed, and the simulation parameters are as follows: Figure 2 as shown in the figure, wherein the water depth is 50 m, the sound speed is 1500 m / s, and the density is 1 g / mL. The seabed is a liquid semi-infinite space, the sound speed is 1600 m / s, and the density is 1.7 g / mL. The point source sound source depth is 20 m, and the radiation signal form is a single frequency signal of 200 Hz. The vertical array elements are distributed in the water body, the horizontal distance from the sound source is 3750 m, and the element interval is 1 m.

[0061] In an optional embodiment, the step 1 includes the following steps:

[0062] Step 1.1: According to the sound speed profile in the environment , the normal mode horizontal wave number upper limit of the search range , and set the normal mode horizontal wave number lower limit of the search range and search step The calculation formula is as follows:

[0063] ;

[0064] In this optional embodiment, After the calculation is completed, the normal mode horizontal wave number lower limit of the search range and search step

[0065] Step 1.2: Calculate the normal mode function of each normal mode horizontal wave number in the search range through the following modal differential equation :

[0066] ;

[0067] 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 differential step.

[0068] Step 1.3: According to the orthogonality of the normal mode function, group the normal mode functions of each normal mode horizontal wave number, the normal mode functions of the normal mode horizontal wave numbers in the group are mutually orthogonal, and the number of normal mode functions in each group is equal.

[0069] In this optional embodiment, the condition of the orthogonality of the normal mode function can be expressed as follows:

[0070] ;

[0071] In the formula, φ m (z, k m ) and φ n (z, k n ) are the normal mode functions of the normal mode horizontal wave numbers k n and k m , and δ m is the Kronecker function.

[0072] In specific implementation, for a given normal mode horizontal wave number ξ m , find M (M is a preset value, M < N, N is the number of elements of the vertical array) column normal mode functions orthogonal to it, as follows:

[0073] ;

[0074] and

[0075] .

[0076] Step 1.4: Obtain the vertically array received pressure P;

[0077] In this optional embodiment, the vertically array received pressure P can be expressed as:

[0078] ;

[0079] ;

[0080] Step 1.5: According to the grouping of step 1.3, when , the following conditions are met, then the normal wave horizontal wave number k1 and its normal wave mode function are real normal wave mode parameters:

[0081] .

[0082] In the above calculation process,

[0083] ;

[0084] ;

[0085] ;

[0086] In the formula, z s is the depth of the sound source, r0 is the distance between the array and the sound source, H0 (1) is the zero-order first Hankel function.

[0087] In this optional embodiment, after the grouping of step 1.3, the above formula is used to determine the real normal wave mode parameters, and the estimation results are shown in Figures 3(a) and 3(b). Figure 3(a) is a comparison diagram of the horizontal wave numbers of the first five modes, in which the red star represents the estimation results of this embodiment, and the blue circle represents the kraken calculation results; Figure 3(b) is a comparison diagram of the vertical mode functions of the first five modes, in which the red dashed line represents the estimation results of this embodiment, and the blue line represents the kraken calculation results.

[0088] In one optional embodiment, in step 2, the entire shallow sea waveguide sound field obtained by inversion can be expressed as:

[0089] ;

[0090] In the formula, x, y, and z are three-dimensional coordinates, z is the density profile, s z is the source depth, z is the source spectrum, z is the zeroth order Hankel function of the first kind, z is the two-dimensional coordinate.

[0091] The sound field in shallow water environment can be represented by the normal mode theory, the normal mode can be described by horizontal wave number and vertical mode function, the sound field is superimposed by different order normal modes, and then the above formula is obtained; the real normal mode parameters obtained by the step 1 are combined to obtain the entire sound field, and the sound field obtained by the inversion is as shown in Figure 4 .

[0092] In an optional embodiment, the step 3 comprises the following steps:

[0093] Step 3.1: calculating the radiated sound field of the sound source S in the free space according to the following formula :

[0094] ;

[0095] wherein,

[0096] ;

[0097] ;

[0098] ;

[0099] In the formula, and are the components of the normal wave horizontal wave number along the x and y directions, is an imaginary number, D is the area where the sound source is located, n is a normal vector, is the sound pressure on the boundary of the area where the sound source is located, which is obtained according to the step 2.

[0100] Step 3.2: calculating the sound source level of the sound source according to the following formula:

[0101] ;

[0102] In the formula, R1 is a point in the far field, is a reference sound pressure, which is usually taken as =1μPa in water.

[0103] In this optional embodiment, the theoretical value of the point source sound source level is 105.4dB, the measured value is 106.7dB, the relative error is 1.23%, and the sound intensity changes with distance in different environments as shown in Figure 5As 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 by the embodiment, and the blue line represents the actual value of the sound source in the waveguide environment. The existing target characteristic test method in shallow water environment mainly includes equivalent source method, beam forming method, etc.; wherein, the beam forming method can only obtain the sound source level of the target to be measured, cannot obtain other target characteristics, and has environment mismatch problem; the equivalent source method can obtain the sound source level and directivity at the same time, but the measurement workload in the actual use of the method is much larger than that of the method of the embodiment, and the maximum error can reach 40% at higher frequency.

[0104] Step 3.3: Calculate the directivity of the sound source according to the following formula:

[0105] ;

[0106] In the formula, is the sound pressure in the direction, is the sound pressure on the sound axis.

[0107] In this optional embodiment, the target sound source to be measured is selected as a point source with the same directivity in each direction, and the directivity of the point source is represented by the blue solid line in Figure 6 , and the result measured according to the method of the embodiment is represented by the red dashed line in Figure 6 .

[0108] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.​

Claims

1. A method for detecting radiation characteristics of a target object in a shallow sea waveguide environment, characterized in that, The method comprises the following steps: Step 1: according to the data received by the vertical array, the real normal mode parameters of the sound source radiation signal in the shallow sea waveguide environment are extracted by the orthogonal constrained mode search method; Step 2: according to the real normal mode parameters, the sound field of the entire shallow sea waveguide is inverted by the normal wave expression in the waveguide environment; Step 3: the required sound field information in the sound field of the shallow sea waveguide is obtained, the reciprocity theorem is used to map the sound source information to the free space, the sound field migration from the shallow sea waveguide to the free space is realized, and then the radiation characteristics of the target to be measured in the free space are obtained; The step 1 comprises the following steps: Step 1.1: Calculate the normal mode horizontal wave number k in the acoustic field according to the sound speed profile c(z) in the environment m (f) the upper limit of the search range ξ max and set the normal mode horizontal wave number k m (f) the lower limit of the search range ξ min and the search step size Δξ, the calculation formula is as follows: Step 1.2: Calculate the horizontal wave numbers k of each normal mode within the search range by the following modal difference equation m Normal mode functions of (f) In the equation, f is the frequency of the target radiation signal, ω is the angular frequency, z is the water depth, Δz = z i+1 -z i is the vertical difference step size; Step 1.3: according to the orthogonality of the normal wave mode function, the normal wave mode functions of the horizontal wave number of each normal wave are grouped, the normal wave mode functions of the horizontal wave number of the group are orthogonal to each other, and the number of the normal wave mode functions of each group is equal; The step 1 further comprises the following steps: Step 1.4: the sound pressure P received by the vertical array is obtained; Step 1.5: according to the grouping of step 1.3, when k1=ξ1, the following conditions are met, then the normal wave horizontal wave number k1 and its normal wave mode function are real normal wave mode parameters: ||P-Φ(ξ1)a(ξ1)||2=0, Wherein, Φ(ξ1) is the mode function group corresponding to ξ1, and a(ξ1) is the mode function amplitude corresponding to ξ1.

2. The method according to claim 1, wherein, In the step 2, the sound field of the entire shallow sea waveguide inverted can be expressed as follows: In the equation, R = (x, y, z), p(z) is the density profile, z s is the source depth, S(f) is the source spectrum, H0 (1) is the zeroth-order Hankel function of the first kind, r = (x, y).

3. The method of claim 2, wherein, The step 3 comprises the following steps: Step 3.1: the radiation sound field p2(R) of the sound source S in the free space is calculated according to the following formula: Wherein, k r = (k x ,k y ) ; In the formula, k x and k y Let i be the horizontal wavenumber of the normal mode along the x and y directions, i be the imaginary number, D be the region where the sound source is located, n be the normal vector, and p1(R) be the sound pressure at the boundary of the region where the sound source is located, obtained according to step 2.

4. The method of claim 3, wherein, The step 3 further comprises the following steps: Step 3.2: the sound source level of the sound source is calculated according to the following formula: In the formula, R1 is a point in the far field, p0 is a reference sound pressure, p2 is the radiation sound field of the sound source S in the free space obtained in step 3.1, g is an amplitude coefficient, and g=1 is taken here.

5. The method of claim 4, wherein, The step 3 further comprises the following steps: Step 3.3: the directivity of the sound source is calculated according to the following formula: In the equation, (P a ) θ is the sound pressure in the θ direction, (P a ) θ＝0 is the sound pressure on the sound axis.

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