Acoustic tube testing method for decoupling performance of acoustic covering layer

Abstract

The invention discloses a sound tube testing method for decoupling performance of an acoustic covering layer. The method comprises the following steps: S1, preparing a sample piece to be tested; the to-be-tested sample piece comprises a test sample piece and an acoustic covering layer sample piece, and the outer diameter of the test sample piece is the same as that of the acoustic covering layer sample piece and is matched with the inner diameter of the water sound pipe; s2, laying the acoustic covering layer sample piece on the surface of one side of the test sample piece to form a new sample piece to be tested, respectively arranging the test sample piece and the new sample piece to be tested in a water sound tube, and respectively testing to obtain complex reflection coefficients and complex transmission coefficients of the test sample piece and the new test sample piece under incident sound waves with different frequencies; s3, radiation sound pressure transfer coefficients of the test sample and the new to-be-tested sample are obtained respectively; and S4, calculating radiation sound pressure insertion loss according to the ratio of the radiation sound pressure transfer coefficients of the new sample piece to be tested to the test sample piece, and representing the decoupling performance of the acoustic covering layer through the radiation sound pressure insertion loss.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic testing, and in particular to a method for testing a sound tube for decoupling performance of an acoustic covering layer. Background Art

[0002] Acoustic coating refers to a special underwater acoustic material or component laid or installed on the surface of a submarine hull to reduce the submarine's radiated noise and target intensity. It is usually a type of polymer viscoelastic material with an internal acoustic structure. It has the functions of sound absorption, vibration suppression, sound insulation, and decoupling. It is a key component on a submarine that can effectively counter the enemy's active and passive sonar at the same time. Conducting experimental testing and evaluation of the decoupling performance of acoustic coatings is the most direct means to verify the accuracy of relevant design theoretical methods and test the effectiveness of design solutions.

[0003] The decoupling performance of the acoustic covering layer describes the ability of the acoustic covering layer laid on the surface of the structure to suppress the structural radiation noise by effectively "removing" the "coupling effect" between the surface of the structure and the external fluid medium. In the theoretical analysis process, the decoupling characteristics of the acoustic covering layer are usually characterized by the insertion loss of the radiation sound pressure (or radiation sound power) of an infinite plate excited by a simple harmonic point force before and after the acoustic covering layer is laid. Therefore, in order to match the conditions of the theoretical analysis as much as possible, the experimental test process also mainly uses the exciter excitation to simulate the point force excitation method, and the decoupling performance of the measured acoustic covering layer is characterized by comparing the insertion loss of the radiation sound pressure (or radiation sound power) of the excited structure before and after the acoustic covering layer is laid. However, this "formally" consistent excitation method brings difficulties to the test of the decoupling performance of the acoustic covering layer. In order to get as close to the infinite plate hypothesis as possible, it is usually necessary to manufacture a flat plate with a large enough lateral size (length and width), install a vibrator with sufficient power at the center of the plate, and place the device to be tested in an anechoic water tank to carry out relevant testing work. If the test results under pressurized conditions are required, the structure to be excited needs to be designed as a pressure-resistant container, the exciter needs to be placed inside the container, and the relevant experimental tests can only be carried out in an anechoic pressure water tank. The entire test process includes the design of the pressure-resistant container, the laying of the acoustic cover, the installation of the sensor, and the hoisting of the experimental samples. This not only places high demands on the design of the pressure-resistant container, but also requires a large amount of manpower, material resources and time costs. At this time, the boundary conditions have also deviated from the original theoretical model, which seriously restricts the rapid iterative design of the decoupling performance of the acoustic cover.

[0004] In order to solve the problems of difficulty in preparing test samples, complex test environment construction process, long test cycle and high cost in the above-mentioned large sample model test method, there are also small sample sound tube test methods in the prior art, including sound insulation test and sound tube exciter excitation test. The former is to directly measure the sound insulation of the acoustic coating layer in the underwater acoustic tube as an indicator for evaluating its decoupling performance. The measurement of sound insulation refers to the national standard GB / T 14369-2011 "Measurement method for insertion loss, echo reduction and sound absorption coefficient of acoustic underwater acoustic material samples"; the latter is to use an exciter to excite a cylindrical steel plate at the end of the sound tube, and measure the radiation sound pressure before and after the acoustic coating layer is attached to the steel plate surface. The radiation sound pressure insertion loss measured before and after the coating layer is attached is used to measure the decoupling performance of the acoustic coating layer. In these two methods, the sound insulation index used in the former is not equivalent to the decoupling performance of the acoustic coating layer, and the latter requires a more complicated exciter installation at the end of the sound tube, and it is difficult to measure under pressurized conditions. Summary of the invention

[0005] In view of this, the present invention provides a sound tube testing method for the decoupling performance of the acoustic covering layer, which is used to at least solve the problems in the prior art of insufficient accuracy of the decoupling performance test of the acoustic covering layer, difficulty in testing under pressurized conditions and complex process of setting up the testing environment.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A method for testing the decoupling performance of an acoustic cover layer of an acoustic tube comprises the following steps: S1. Prepare the sample to be tested; the sample to be tested includes: a test sample and an acoustic cover layer sample, wherein the outer diameter of the test sample is the same as that of the acoustic cover layer sample and is compatible with the inner diameter of the hydroacoustic tube; S2. Lay the acoustic covering layer sample on one side of the test sample to form a new test sample, respectively place the test sample and the new test sample in the underwater acoustic tube, and respectively test and obtain the complex reflection coefficient and complex transmission coefficient of the test sample and the new test sample under different frequency incident sound waves; S3. Obtain the radiation sound pressure transfer coefficient of the test sample and the new sample to be tested respectively, wherein the specific calculation method of the radiation sound pressure transfer coefficient is: , In the formula, is the radiation sound pressure transfer coefficient, and are the complex transmission coefficient and complex reflection coefficient respectively; S4. Calculate the radiation sound pressure insertion loss based on the ratio of the radiation sound pressure transfer coefficient of the new sample to be tested and the radiation sound pressure insertion loss to characterize the decoupling performance of the acoustic covering layer.

[0007] Preferably, the specific contents of the complex reflection coefficient and the complex transmission coefficient of the test sample under different frequency incident sound waves obtained by testing in S2 include: The test sample is placed in the hydroacoustic tube, and the axial direction of the test sample is consistent with the hydroacoustic tube, so that both ends of the test sample are water, and the complex reflection coefficient of the test sample under different frequency incident sound waves is obtained. and the complex transmission coefficient .

[0008] Preferably, the specific contents of the complex reflection coefficient and the complex transmission coefficient of the new test sample under different frequency incident sound waves obtained by testing in S2 include: The acoustic covering layer sample is laid on one side of the test sample to form a new test sample. The new test sample is placed in the hydroacoustic sound tube, and the axial direction of the test sample is consistent with the hydroacoustic sound tube, so that both ends of the test sample are water. The complex reflection coefficient of the new test sample under different frequency incident sound waves is obtained by testing. and the complex transmission coefficient .

[0009] Preferably, the specific calculation method of the radiated sound pressure insertion loss in S4 is: , In the formula, Radiated sound pressure insertion loss, and are the radiation sound pressure transfer coefficients of the new sample to be tested and the test sample respectively.

[0010] Preferably, a transmitting transducer is arranged at the opening of the hydroacoustic tube, and hydrophones are respectively arranged on the walls of the hydroacoustic tube. In S2, when the test sample is tested, two hydrophones are respectively evenly arranged on both sides of the test sample. When a new sample to be tested is tested, two hydrophones are also respectively evenly arranged on both sides of the new sample to be tested. The end of the hydroacoustic tube is a sound absorbing end.

[0011] Preferably, an internal acoustic structure is provided inside the acoustic cover layer.

[0012] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a method for testing the acoustic tube decoupling performance of an acoustic covering layer, which has the following beneficial effects: 1. The present invention uses the radiation sound pressure insertion loss to measure the decoupling performance of the acoustic covering layer. Compared with the sound insulation test method that directly only examines the suppression of sound propagation by the acoustic covering layer without considering the vibration suppression effect of the structure itself after the covering layer is applied, the present invention further considers the suppression of structural surface vibration and sound propagation, which is more in line with the essence of the decoupling performance of the acoustic covering layer, and thus has better test accuracy; 2. The present invention can directly use the hydroacoustic sound tube to carry out relevant tests. Compared with the test method using the sound tube-exciter excitation, the complicated exciter installation operation can be omitted. At the same time, the existing hydroacoustic sound tube can be conveniently used to obtain the test results under pressurized conditions; 3. Compared with the large sample testing method, the present invention is simpler and easier to implement, has a short testing cycle and low cost, can significantly improve the testing efficiency, shorten the experimental cycle, and accelerate the iterative design of the acoustic cover decoupling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 A flow chart of a method for testing the acoustic tube decoupling performance of an acoustic cover provided by the present invention; Figure 2 A schematic diagram of vibration and sound radiation of an infinitely large plate with an acoustic covering layer under point force excitation in an existing test method provided by an embodiment of the present invention; Figure 3 A schematic diagram of the structure of a cylindrical sample to be tested provided by an embodiment of the present invention; Figure 4 The schematic diagram of the underwater acoustic tube test provided by the embodiment of the present invention; wherein, 1-transmitting transducer; 2-sound tube wall; 3-first hydrophone; 4-second hydrophone; 5-test piece; 6-third hydrophone; 7-fourth hydrophone; 8-sound absorbing end; Figure 5 A schematic diagram of the structure of a cylindrical acoustic cover layer and a steel block after bonding provided by an embodiment of the present invention; Among them, 9-cylindrical acoustic cover sample; 10-cylindrical steel block; Figure 6 This is a comparison diagram of the decoupling performance experimental test and theoretical prediction structure of a cavity-type acoustic cover layer measured in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The present invention provides a method for testing the acoustic tube decoupling performance of an acoustic coating layer, such as Figure 1 As shown, the following steps are included: S1. Prepare the sample to be tested; the sample to be tested includes: a test sample and an acoustic cover layer sample, wherein the outer diameter of the test sample is the same as that of the acoustic cover layer sample and is compatible with the inner diameter of the hydroacoustic tube; S2. Lay the acoustic covering layer sample on one side of the test sample to form a new test sample, respectively place the test sample and the new test sample in the underwater acoustic tube, and respectively test and obtain the complex reflection coefficient and complex transmission coefficient of the test sample and the new test sample under different frequency incident sound waves; S3. Obtain the radiation sound pressure transfer coefficient of the test sample and the new sample to be tested respectively, wherein the specific calculation method of the radiation sound pressure transfer coefficient is: , In the formula, is the radiation sound pressure transfer coefficient, and are the complex transmission coefficient and complex reflection coefficient respectively; S4. Calculate the radiation sound pressure insertion loss based on the ratio of the radiation sound pressure transfer coefficient of the new sample to be tested and the radiation sound pressure insertion loss to characterize the decoupling performance of the acoustic covering layer.

[0017] It should be noted that: Figure 2 This is a schematic diagram of the vibration and sound radiation of an infinitely large plate with an acoustic cover layer under point force excitation in the existing test method. Considering the cylindrical symmetry of the infinitely large plate, we take a cylindrical coordinate system and let The plane and thickness are The mid-surfaces of the plates coincide, and the harmonic point force acts at the origin of the coordinate system. .

[0018] Before laying the acoustic cover, the radiated sound pressure of the infinite plate under point excitation is: (1) in, is an imaginary unit, is the angular frequency, is the circumference of a circle, is the excitation frequency, is the density of water, is the amplitude of the excitation force, is a natural constant, is the wave number of sound waves in water, is the speed of sound in water, For observation point To the board excitation point distance; is the mechanical impedance of the plate, i.e. the impedance when there is no fluid load, and are the density and thickness of the sheet, respectively. , is the angle between the line from the observation point to the excitation point and the plate normal, is the bending wave number of the plate in vacuum, satisfying , is the bending stiffness of the plate, and are Young’s modulus and Poisson’s ratio of the flat plate material, respectively; is the radiation acoustic impedance of the plate.

[0019] The infinitely large plate with acoustic covering layer is called cladding plate, and the radiation sound pressure of cladding plate under point force excitation is obtained as: (2) in, and is the element of the sound pressure and vibration velocity transfer matrix of the front and rear interfaces of the acoustic cover layer. For observation point The distance to the point on the surface of the cover layer corresponding to the plate excitation point can be taken as the distance from the observation point to the plate excitation point under far field conditions, that is, .

[0020] From formulas (1) and (2), the ratio of the radiated sound pressure of the cladding plate and the bare plate in water when the excitation force is the same is obtained: (3) The decibel value of the above ratio is defined as the insertion loss of the acoustic cover layer to the radiated sound pressure of the infinite flat plate: (4) Since the radiated sound pressure has The directivity distribution varies, and the directivity is different at different frequencies. It is also a frequency-dependent The amount of change, usually expressed as , which is measured by the value in the vertical direction of the board.

[0021] when Sometimes, there is , , for the case of a flat plate covered with a single layer of acoustic covering, the vertical radiation sound pressure insertion loss is: (5) From the above formula, we can see that the insertion loss of the acoustic cover layer in the vertical direction is a relative quantity, and its value has nothing to do with the magnitude of the excitation force. As long as the four elements of the acoustic cover layer transfer matrix can be obtained, and The value of can be used to characterize the decoupling performance of the acoustic cover layer by formula (5). Further deduction will show that the radiation sound pressure insertion loss of the acoustic cover layer in the vertical direction can also be obtained by testing under uniform surface force excitation.

[0022] Under the excitation of uniformly distributed surface forces, only longitudinal waves can be excited in multi-layer homogeneous media. The one-dimensional transfer matrix can be used to describe the transfer relationship between particle velocity and stress between the front and rear interfaces of each layer of media: (6) in, and For the Normal stress and normal vibration velocity at the front interface of the layered medium, and For the Normal stress and normal vibration velocity at the interface behind the layer medium; For the Layer medium The transfer matrix, where , and Respectively The wave number, thickness and impedance of the layer medium, and Respectively Density and longitudinal wave speed of the layer medium. Full transfer matrix of the multilayer system It can be obtained by multiplying each sub-matrix and satisfies: (7) and is the normal stress and normal vibration velocity at the front interface of the first layer of medium, Respectively The transfer matrix of the layer medium, is the total number of layers in the multi-layer system, and Transfer matrix for multi-layer system The four elements of and For the Normal stress and normal vibration velocity at the interface behind the layered medium.

[0023] For the case of a single-layer acoustic cover layer laid behind an infinitely large flat plate, the two form a double-layer system, with: (8) in, and is the normal stress and normal vibration velocity of the front interface of the plate, and are the normal stress and normal vibration velocity of the interface behind the acoustic cover, and is the longitudinal wave number of the thin plate, and the longitudinal wave characteristic impedance, is the density of the plate and the longitudinal wave speed, and are the elements of the sound pressure and vibration velocity transfer matrix at the front and rear interfaces of the acoustic cover.

[0024] Assume that the flat plate structure is The direction is excited by uniformly distributed simple harmonic surface force, and the excitation amplitude is Considering that the medium on the back side of the plate is air and the medium on the front side is water, the forward radiated plane waves generated in the medium on both sides of the plate are and the reverse propagation wave , is the sound wave number in air, is the speed of sound waves in air, we have: (9) in, and are the densities of air and water respectively.

[0025] Combining equation group (9) and formula (7), the radiation wave sound pressure can be solved as: (10) in, and are the acoustic characteristic impedances of air and water respectively. Considering , the above formula can be further simplified as: (11) Substituting formula (11) into the total transfer matrix elements of the bare plate and the cladding plate, we can obtain the ratio of the radiated sound pressure of the plate with the cladding layer and the bare plate in water under the same excitation force conditions: (12) The decibel value that defines this ratio is the insertion loss of the cover to the sound pressure radiated by the panel: (13) It can be seen that formula (13) is consistent with the expression (5) of the radiation sound pressure insertion loss in the vertical direction of the same structure when subjected to point excitation, that is, the radiation sound pressure insertion loss under surface force excitation can be used as a brief representation of the insertion loss under point excitation conditions.

[0026] At this point, the acoustic cover layer radiation sound pressure insertion loss can be converted into the radiation sound pressure insertion loss of the small-sized sample before and after the acoustic cover layer is attached under the uniform surface force excitation condition for simple characterization. However, although the implementation of the uniform surface force excitation condition can be achieved by using an exciter to excite the small-sized sample, it still cannot solve the problem that the exciter needs to be pressure-resistant and sealed under pressure conditions. Observing formula (11), this problem can be further solved by the relationship between the complex reflection coefficient and the complex transmission coefficient and the transfer matrix of the sample to be tested during the pipe sound insulation test in the underwater acoustic tube.

[0027] The relationship between the complex reflection and complex transmission coefficients measured in the underwater sound insulation test and the total transfer matrix is: (14) It is not difficult to get: (15) By comparing formula (11) and formula (15), the radiation sound pressure transfer coefficient can be further obtained: satisfy: (16) This expression shows the radiation sound pressure transfer coefficient of the pressure hull under unit surface force excitation. The complex reflection obtained by the sound insulation test in water and the complex transmission coefficient Converted.

[0028] Therefore, after the above theoretical derivation process, the radiation sound pressure insertion loss of the acoustic cover layer can be calculated by measuring the complex reflection coefficient and complex transmission coefficient of the small-sized acoustic tube sample. The specific method is: first, through theoretical calculation or underwater acoustic tube test steel plate radiation sound pressure transmission coefficient ; Then, an acoustic covering layer of equal diameter was pasted on the surface of the steel plate, and the radiation sound pressure transfer coefficient of the covering plate was measured. Finally, the logarithm of the ratio of the radiation sound pressure transfer coefficients under the two working conditions is taken according to formula (17) to obtain the radiation sound pressure insertion loss value of the acoustic cover layer: (17) By obtaining the complex reflection and complex transmission coefficients under different pressure conditions through the in-tube test environment of the hydroacoustic tube, the radiation sound pressure insertion loss of the acoustic covering layer under different hydrostatic pressure conditions can be obtained, thereby characterizing its decoupling performance under different pressures.

[0029] In this embodiment, the material of the test sample can be selected according to actual needs, such as steel, titanium alloy, aluminum alloy and hard composite material plate, etc. The shape of the test sample is designed according to the shape of the hydroacoustic tube. For example, the current hydroacoustic tube is cylindrical, so in this embodiment, the test sample is set to be cylindrical.

[0030] In order to further implement the above technical solution, the specific contents of the complex reflection coefficient and complex transmission coefficient of the test sample under different frequency incident sound waves tested in S2 include: The test sample is placed in the hydroacoustic tube, and the axial direction of the test sample is consistent with the hydroacoustic tube, so that both ends of the test sample are water, and the complex reflection coefficient of the test sample under different frequency incident sound waves is obtained. and the complex transmission coefficient .

[0031] In order to further implement the above technical solution, the specific contents of the complex reflection coefficient and complex transmission coefficient of the new test sample under different frequency incident sound waves tested in S2 include: The acoustic covering layer sample is laid on one side of the test sample to form a new test sample. The new test sample is placed in the hydroacoustic sound tube, and the axial direction of the test sample is consistent with the hydroacoustic sound tube, so that both ends of the test sample are water. The complex reflection coefficient of the new test sample under different frequency incident sound waves is obtained by testing. and the complex transmission coefficient .

[0032] In order to further implement the above technical solution, the specific calculation method of the radiated sound pressure insertion loss in S4 is: , In the formula, Radiated sound pressure insertion loss, and are the radiation sound pressure transfer coefficients of the new sample to be tested and the test sample respectively.

[0033] In order to further implement the above technical scheme, a transmitting transducer is arranged at the opening of the hydroacoustic sound tube, and hydrophones are respectively arranged on the walls of the hydroacoustic sound tube. In S2, when the test sample is tested, two hydrophones are respectively evenly arranged on both sides of the test sample. When a new sample to be tested is tested, two hydrophones are also respectively evenly arranged on both sides of the new sample to be tested. The end of the hydroacoustic sound tube is the sound absorbing end.

[0034] In order to further implement the above technical solution, an internal acoustic structure is provided inside the acoustic covering layer.

[0035] It should be noted that: The internal acoustic structure can be a simple air cavity, a heavy material or other specially designed structure that performs a specific acoustic function. That is, the interior of the acoustic covering layer can be a cavity that can be provided with an acoustic structure, or can be other solid or porous structures. When the test method disclosed in the present invention is specifically implemented, specific settings can be made according to actual test requirements.

[0036] In this embodiment, if Figure 3The structural schematic diagram shown in the figure respectively prepares the test samples for underwater acoustic tube testing, wherein the test sample is a cylindrical steel block, and the new test sample is a cylindrical acoustic covering layer sample with a cylindrical acoustic covering layer, and the acoustic covering layer sample contains a uniformly distributed internal cavity structure. The 120mm cylindrical hydroacoustic tube was tested. The outer diameter of the selected cylindrical sample was for 118mm, the thickness of the cylindrical steel block is 30mm, the thickness of the cylindrical acoustic cover sample is 36.5mm, and it contains 13 16×12.5mm cylindrical cavity.

[0037] Reference Figure 4 The test principle shown is to place the cylindrical steel block sample in the hydroacoustic tube. When placing it, the axis direction of the steel block is consistent with the hydroacoustic tube. Both ends of the sample are water. The four-hydrophone transfer function method is used to test and obtain the complex reflection coefficient of the sample under different frequency incident sound waves. and the complex transmission coefficient , and calculate its radiation sound pressure transfer coefficient , wherein the four hydrophones are respectively a first hydrophone, a second hydrophone, a third hydrophone, and a fourth hydrophone; Reference Figure 4 The test principle shown is to apply the cylindrical acoustic covering layer on the surface of one side of the cylindrical steel block by pasting. Figure 5 The pasting direction shown is consistent with the actual application of the acoustic cover layer). The pasted sample is placed in the hydroacoustic tube so that the surface in contact with the external seawater in actual application faces the transmitting transducer in the hydroacoustic tube. Both ends of the sample are water. The four-hydrophone transfer function method is used to test and obtain the complex reflection coefficient of the sample under different frequency incident sound waves. and the complex transmission coefficient , and further calculate its radiation sound pressure transfer coefficient .exist Figure 4 middle, is the incident wave, For reflected waves, each and The length of the distances shown is not shown in the figures.

[0038] According to the test and , the radiation sound pressure insertion loss of the cylindrical steel block before and after the acoustic cover is applied is calculated .

[0039] Figure 6A comparison diagram of the decoupling performance experimental test and theoretical prediction structure of a cavity-type acoustic cover layer measured in this embodiment is given. The theoretical prediction results are in good agreement with the experimental test results, proving the effectiveness of the method of the present invention.

[0040] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for testing the acoustic tube decoupling performance of an acoustic cover layer, characterized in that: The following steps are involved: S1. Prepare the sample to be tested; the sample to be tested includes: a test sample and an acoustic cover layer sample, wherein the outer diameter of the test sample is the same as that of the acoustic cover layer sample and is compatible with the inner diameter of the hydroacoustic tube; S2. Lay the acoustic covering layer sample on one side of the test sample to form a new test sample, respectively place the test sample and the new test sample in the underwater acoustic tube, and respectively test and obtain the complex reflection coefficient and complex transmission coefficient of the test sample and the new test sample under different frequency incident sound waves; S3. Obtain the radiation sound pressure transfer coefficient of the test sample and the new sample to be tested respectively, wherein the specific calculation method of the radiation sound pressure transfer coefficient is: ， In the formula, is the radiation sound pressure transfer coefficient, and are the complex transmission coefficient and complex reflection coefficient respectively; S4. Calculate the radiation sound pressure insertion loss based on the ratio of the radiation sound pressure transfer coefficient of the new sample to be tested and the radiation sound pressure insertion loss to characterize the decoupling performance of the acoustic covering layer.

2. The acoustic tube testing method for acoustic cover decoupling performance according to claim 1, characterized in that: The specific contents of the complex reflection coefficient and complex transmission coefficient of the test sample under different frequency incident sound waves tested in S2 include: The test sample is placed in the hydroacoustic tube and between two groups of hydrophones. The axis direction of the test sample is consistent with the hydroacoustic tube. Both ends of the test sample are filled with water. The complex reflection coefficient of the test sample under different frequency incident sound waves is obtained. and the complex transmission coefficient .

3. The acoustic tube testing method for acoustic cover decoupling performance according to claim 1, characterized in that: The specific contents of the complex reflection coefficient and complex transmission coefficient of the new test sample under different frequency incident sound waves tested in S2 include: The acoustic coating layer sample is laid on the surface of one side of the test sample to form a new test sample. The new test sample is placed in the hydroacoustic sound tube and located between two groups of hydrophones. The axial direction of the test sample is consistent with the hydroacoustic sound tube. The side where the acoustic coating layer sample is laid faces the position of the transducer in the hydroacoustic sound tube and contacts the external seawater. The complex reflection coefficient of the new test sample under different frequency incident sound waves is tested. and the complex transmission coefficient .

4. The acoustic tube testing method for acoustic cover decoupling performance according to claim 1, characterized in that: The specific calculation method of the radiation sound pressure insertion loss in S4 is: ， In the formula, Radiated sound pressure insertion loss, and are the radiation sound pressure transfer coefficients of the new sample to be tested and the test sample respectively.

5. The acoustic tube testing method for acoustic cover decoupling performance according to claim 1, characterized in that: A transmitting transducer is arranged at the opening of the hydroacoustic sound tube, and hydrophones are respectively arranged on the walls of the hydroacoustic sound tube. In S2, when the test sample is tested, two hydrophones are respectively evenly arranged on both sides of the test sample. When a new sample to be tested is tested, two hydrophones are also respectively evenly arranged on both sides of the new sample to be tested. The end of the hydroacoustic sound tube is a sound absorbing end.

6. The acoustic tube testing method for acoustic cover decoupling performance according to claim 1, characterized in that: An internal acoustic structure is provided inside the acoustic cover.

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