Method and device for measuring target strength of underwater component based on near-field scanning mode

Abstract

The invention relates to an underwater component target strength measurement method and device based on a near-field scanning mode, and the method comprises the following steps: 1, placing an underwater component in a far field of a transducer, and guaranteeing that no other sound sources influence a sound field at the measurement device and near the underwater component; 2, dispersing the measurement surface of the underwater component into grid units, and determining the size and number of the grid units according to the measurement frequency wavelength and the irregularity degree of the shape of the underwater component; according to the invention, the problem that the far-field condition cannot be met in the target intensity measurement can be solved, the space required by the measurement is greatly reduced, and a new direction is provided for the target intensity measurement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of underwater acoustic measurement, and particularly relates to a target strength measurement method and device for underwater components based on a near-field scanning mode. BACKGROUND

[0002] Since underwater components are generally large in size, the far-field distance for testing is far, and thus, the target strength is generally measured in large open waters such as lakes or seas. However, there are too many uncontrollable factors in natural waters such as underwater positioning difficulties, water flow noise, ship-borne radiation noise and the like, which greatly affect the testing. Therefore, the underwater components are generally scaled down for testing in a laboratory, and then the full-scale underwater target is measured in a lake or sea, which are verified with each other to evaluate the acoustic stealth capability of the underwater components. In order to achieve the purpose of active acoustic stealth, the underwater components are usually covered with sound-absorbing materials or specially designed in structure and shape, which results in a low signal-to-noise ratio of the far-field acoustic scattering signal of the underwater target, greatly affecting the target strength measurement of the underwater components. Therefore, it is urgent to solve the problem of near-field testing of the acoustic scattering of the underwater target.

[0003] The target strength is a physical quantity for measuring the acoustic stealth capability of the underwater target against the active sonar, and is an important parameter for describing the echo characteristics of the underwater target. At present, the target strength measurement of the underwater target is generally performed in a far-field condition in a laboratory pool or a test lake. If the target size is large or the measurement site is limited, the measurement far-field condition requirements may be difficult to meet, and the effectiveness of the target strength measurement result cannot be guaranteed. SUMMARY

[0004] The technical problem to be solved by the application is to provide a target strength measurement method and device for underwater components based on a near-field scanning mode, which can solve the problem that the far-field condition cannot be met in the target strength measurement, greatly reduce the measurement space, and provide a new direction for the target strength measurement.

[0005] The technical solution of the application is to provide a target strength measurement device for underwater components based on a near-field scanning mode, which comprises

[0006] A signal source is configured to generate a sinusoidal pulse signal E1.

[0007] A power amplifier is configured to power amplify the signal E1.

[0008] A transducer is configured to generate a sinusoidal pulse acoustic signal under the excitation of the power amplified signal.

[0009] Vector hydrophone, used for receiving acoustic signal and vibration signal near the underwater structure and converting them into electric signals E2 and E3;

[0010] Pre-amplifier, used for amplifying E2 and E3, outputting electric signals E4 and E5;

[0011] Band-pass filter, used for band-pass filtering E4 and E5, outputting electric signals E6 and E7;

[0012] Signal collector, used for converting electric signals E6 and E7 into digital signals D1 and D2;

[0013] Underwater total station, used for measuring the spatial position of the vector hydrophone and the underwater structure, wherein the underwater total station has two.

[0014] The application also provides a measuring method of the underwater structure target strength measuring device based on the near-field scanning mode, comprising the following steps,

[0015] Step 1, placing the underwater structure in the far field of the transducer, ensuring that there is no other sound source near the measuring device and the underwater structure to affect the sound field;

[0016] Step 2, discretizing the measuring surface of the underwater structure into grid units, determining the grid unit size and number according to the measuring frequency wavelength and the irregularity degree of the underwater structure shape;

[0017] Step 3, sequentially scanning the grid units by the vector hydrophone, picking up the complex sound pressure p(r s ) and vibration velocity u(r s ) at each grid unit;

[0018] Step 4, taking out the underwater structure, measuring the complex sound pressure p t (r s ) and vibration velocity u t (r s ) of each grid when there is no underwater structure according to step 3;

[0019] Step 5, calculating the scattering function p ∞ (r) of the underwater structure according to the Helmhlotz integral formula

[0020]

[0021] Wherein, p S (r S ) = p(r s ) - p t (r S ); u S (r S ) = u(r S ) - u t (rS ) ; G ∞ (r,r S ) is the Green function of the scattered sound wave; p is the density of water; w is the angular velocity of the sound wave; r S is the displacement vector from the origin to the grid element; r is the displacement vector from the origin to any point outside the curved surface;

[0022] Step 6, the target strength of the underwater structure is finally obtained, and the calculation formula is

[0023]

[0024] As preferred, in step 2, for the non-plate-shaped underwater structure, the discrete grid elements should form a closed curved surface, if the appearance of the underwater structure is elongated, a cylindrical surface is selected as the measuring surface, and other shapes select a spherical surface as the measuring surface; and the flat plate-shaped underwater structure selects a plane as the measuring surface; in addition, the spacing between adjacent grid centers should be less than one-tenth of the wavelength.

[0025] As preferred, in step 3, the position and direction of the vector hydrophone are tracked and recorded by two underwater total stations.

[0026] As preferred, in step 5, the form of the Green function of the scattered sound wave is related to the boundary condition of the sound field, and for the free field condition, the expression of the Green function of the scattered sound wave is as follows

[0027]

[0028] Wherein, k is the wave number of the sound wave.

[0029] Further, the size of the vector hydrophone should be smaller than the size of the discrete grid element; the transducer should have a horizontal beam width of not less than 60° and a vertical beam width of not more than 30°.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] The present application innovatively applies the single curved surface scanning method to the sound scattering measurement of the underwater structure, uses the vector hydrophone to pick up the measured sound pressure and velocity information, completes the measurement of the curved surface sound pressure and velocity on the basis of the accurate ranging of the underwater total station, reconstructs the far-field scattered sound signal through the Helmhlotz integral formula, realizes the near-field measurement of the target strength of the underwater structure, solves the problem that the far-field condition cannot be met in the target strength measurement, greatly reduces the required space for measurement, and provides a new direction for the target strength measurement. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the composition block diagram of the underwater structure target strength device of the present application;

[0033] Figure 2 This invention relates to a surface for measuring acoustic signals. Detailed implementation method:

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0035] An underwater component target strength measurement device based on near-field scanning mainly consists of a signal source, power amplifier, transducer, vector hydrophone, preamplifier, bandpass filter, signal acquisition unit, and two underwater total stations. The size of the vector hydrophone should be much smaller than the size of the discrete grid cell; the transducer should have a horizontal beamwidth of not less than 60° and a vertical beamwidth of not more than 30°.

[0036] The measurement method based on a near-field scanning underwater component target strength measurement device includes the following steps.

[0037] Step 1: Place the underwater component in the far field of the transducer to ensure that there are no other sound sources near the measuring device and the underwater component that may affect the sound field.

[0038] Step 2: Discretize the measurement surface of the underwater component into grid cells, and determine the size and number of grid cells based on the measurement frequency wavelength and the irregularity of the shape of the underwater component.

[0039] Step 3: Scan the grid cells sequentially using a vector hydrophone and pick up the complex acoustic pressure p(r) at each grid cell. s ) and vibration velocity u(r) s );

[0040] Step 4: Remove the underwater components and measure the complex acoustic pressure p of each grid without the underwater components, as in Step 3. t (r s ) and vibration velocity u t (r s );

[0041] Step 5: Calculate the scattering function p of the underwater component according to the Helmhlotz integral formula. ∞ (r) is

[0042]

[0043] Where, p S (r S )=p(r s )-p t (r S );u S (r S )=u(r S )-u t (r S );G ∞ (r,rS ) is the Green's function for the scattered sound wave; ρ is the density of water; ω is the angular velocity of the sound wave; r S is the displacement vector from the origin to the mesh element; r is the displacement vector from the origin to any point outside the surface;

[0044] Step 6: Finally, the target strength of the underwater component is obtained, and its calculation formula is as follows:

[0045]

[0046] It is worth noting that for non-plate-shaped underwater components, the discrete mesh elements should form closed curved surfaces. If the underwater component is elongated, a cylindrical surface should be selected as the measurement surface; for other shapes, a spherical surface should be selected. For plate-shaped underwater components, a plane should be used as the measurement surface. In addition, the spacing between the centers of adjacent meshes should be less than one-tenth of the wavelength.

[0047] The following describes the measurement process of a 1m diameter spherical underwater component at a frequency of 500Hz. Figure 1 The instruments are connected in the following manner. The transducer is 20m away from the acoustic center of the underwater component, and the vector hydrophone scans at a distance of 0.1m from the acoustic center (i.e., the center of the sphere) of the underwater component. The scanning surface is a spherical curved surface, and the scanning is performed according to the following method: Figure 2 The spherical surface is discretized in a manner that the grid cells are evenly distributed on the latitude lines of the sphere, with a total of 72 latitude lines and 36 grid cells on each latitude line.

[0048] The scattered sound pressure at a given position r is related to the scattered sound field on the spherical surface S using the Helmhlotz integral formula. Outside the surface, the far-field scattering function is given by the following formula.

[0049]

[0050] In the formula, r S Let be the displacement vector pointing from the origin to a point on the sphere S. Let G(r,r) be the normal partial derivative on the sphere S. S ) is the Green's function, a solution to the Helmholtz equation, under free field conditions.

[0051]

[0052] Using Euler's equations of motion With the normal particle velocity u s (r s The scattering function at infinity is proportional to the scattering function at infinity.

[0053]

[0054] As ||r||→∞, the Green's function will be

[0055]

[0056] During measurement, a vector hydrophone sequentially scans the grid cells, picking up the complex sound pressure p(r) at each grid cell. s ) and vibration velocity u(r) s Then, the underwater components were removed, and the complex acoustic pressure p of each grid was measured without the underwater components. t (r s ) and vibration velocity u t (r s Furthermore, the scattered sound pressure and vibration velocity at each grid point on the sphere S are calculated.

[0057]

[0058] Substituting formula (5) into (3) and discretizing (3), the specific numerical calculation formula is as follows:

[0059]

[0060] Where ΔS represents the area of ​​the grid, r S_i Let |r|| represent the displacement vector of the i-th grid. For example, to calculate the scattered sound pressure at 1000m, ||r|| = 1000. Substitute the numerical calculation result of formula (6) into the following formula...

[0061]

[0062] The target strength of the underwater component was finally obtained.

[0063] This invention innovatively applies a single-curved surface scanning method to the sound scattering measurement of underwater components. It uses a vector hydrophone to pick up the measured sound pressure and vibration velocity information. Based on the accurate distance measurement of an underwater total station, it completes the measurement of surface sound pressure and vibration velocity. The far-field scattered sound signal is reconstructed by the Helmholtz integral formula, realizing the near-field measurement of the target strength of underwater components. This solves the problem of not being able to meet the far-field conditions in target strength measurement, significantly reduces the space required for measurement, and provides a new direction for target strength measurement.

[0064] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. Any equivalent procedural modifications made using this specification are included within the patent protection scope of this invention.

Claims

1. A device for measuring the strength of underwater structural components based on near-field scanning, characterized in that: include The signal source is used to generate a sinusoidal pulse signal E1; A power amplifier used to amplify the power of the sinusoidal pulse signal E1; The transducer, under the excitation of a power amplified signal, generates a sinusoidal pulse sound signal; Vector hydrophone is used to receive acoustic and vibration signals near underwater components and convert them into electrical signals E2 and E3. The preamplifier amplifies electrical signals E2 and E3, and outputs electrical signals E4 and E5. A bandpass filter is used for bandpass filtering of electrical signals E4 and E5, and outputs electrical signals E6 and E7. The signal acquisition unit is used to convert electrical signals E6 and E7 into digital signals D1 and D2. The underwater total station is used to measure the spatial position of vector hydrophones and underwater components. There are two underwater total stations.

2. The measurement method of the underwater component target strength measuring device based on near-field scanning according to claim 1, characterized in that: Includes the following steps, Step 1: Place the underwater component in the far field of the transducer to ensure that there are no other sound sources near the measuring device and the underwater component that may affect the sound field. Step 2: Discretize the measurement surface of the underwater component into grid cells, and determine the size and number of grid cells based on the measurement frequency wavelength and the irregularity of the shape of the underwater component. Step 3: Scan the grid cells sequentially using a vector hydrophone and pick up the complex acoustic pressure p(r) at each grid cell. s ) and vibration velocity u(r) s ); Step 4: Remove the underwater components and measure the complex acoustic pressure p of each grid without the underwater components, as in Step 3. t (r s ) and vibration velocity u t (r s ); Step 5: Calculate the scattering function p of the underwater component according to the Helmhlotz integral formula. ∞ (r) is Where, p S (r S )=p(r s )-p t (r S );u S (r S )=u(r S )-u t (r S );G ∞ (r,r S ) is the Green's function for the scattered sound wave; ρ is the density of water; ω is the angular velocity of the sound wave; r S is the displacement vector from the origin to the mesh element; r is the displacement vector from the origin to any point outside the surface; Step 6: Finally, the target strength of the underwater component is obtained, and its calculation formula is as follows:

3. The measurement method of the underwater component target strength measurement device based on near-field scanning according to claim 2, characterized in that: In step 2, for non-plate-shaped underwater components, the discrete grid cells should form a closed curved surface. If the underwater component is slender, a cylindrical surface is selected as the measurement surface, and for other shapes, a spherical surface is selected as the measurement surface. For plate-shaped underwater components, a plane is selected as the measurement surface. In addition, the distance between the centers of adjacent grids should be less than one-tenth of the wavelength.

4. The measurement method of the underwater component target strength measuring device based on near-field scanning according to claim 2, characterized in that: In step 3, the position and orientation of the vector hydrophone are tracked and recorded by two underwater total stations.

5. The measurement method of the underwater component target strength measuring device based on near-field scanning according to claim 2, characterized in that: In step 5, the form of the Green's function of the scattered sound wave is related to the boundary conditions of the sound field. For free field conditions, the expression for the Green's function of the scattered sound wave is as follows: Where k is the wave number of the sound wave.

6. The measurement method of the underwater component target strength measuring device based on near-field scanning according to claim 2, characterized in that: The size of the vector hydrophone should be smaller than the size of the discrete grid cell; the transducer should have a horizontal beamwidth of not less than 60° and a vertical beamwidth of not more than 30°.

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