A Low-Frequency Sound Tube Measurement Method for the Particle Velocity Transfer Coefficient of Underwater Acoustic Materials

Abstract

The present invention discloses a low-frequency acoustic tube measurement method for the vibration velocity transfer coefficient of underwater acoustic materials, which includes the following steps. Step 1: The low-frequency acoustic tube is placed vertically, and a transmitting transducer is installed at its bottom. Two hydrophones are embedded in the low-frequency acoustic tube wall at intervals, and the low-frequency acoustic tube is filled with degassed water medium. Step 2: The underwater acoustic material to be measured is placed in the low-frequency acoustic tube and located on the water surface. The gap between the underwater acoustic material to be measured and the low-frequency acoustic tube wall is filled with water medium, and the upper surface of the underwater acoustic material to be measured is a rigid backing. An accelerometer is installed on the rigid backing, and a cavity is provided between the rigid backing and the upper cover of the low-frequency acoustic tube. The present invention realizes the measurement of the vibration characteristic parameters of the underwater acoustic material sample in the low-frequency acoustic tube, can fully simulate the working conditions of the sample in actual work and the structure of the submarine acoustic covering layer, and the measurement frequency band is concentrated in the range of 100 Hz to 1 kHz where it is difficult to reduce vibration and noise in submarine shock absorption technology.

Description

Technical field:

[0001] The invention relates to the field of underwater acoustics, and in particular to a low-frequency sound tube measurement method for a vibration velocity transfer coefficient of an underwater acoustic material. Background technology:

[0002] According to the main functions, submarine acoustic covering can be divided into anechoic tiles, decoupling tiles and multifunctional tiles, which are used to absorb the detection sound waves of enemy active sonar and shield the noise radiation of the boat to the seawater respectively. Multifunctional tiles take into account both sound absorption and decoupling functions. In theoretical research, it is assumed that the submarine hull model with covering is a planar multilayer structure, simulating the double-hull submarine (double-layer steel plate with ribs in the middle, with water layer in the middle) and single-hull submarine (water layer-steel plate-air) structure. However, since submarine acoustic covering is mostly made of rubber material and adopts cavity structure inside, it is increasingly difficult to achieve low-frequency performance under a certain pressure, which has become a bottleneck for the breakthrough and development of underwater acoustic stealth of my country's naval quiet submarines. It can be seen that the research on hydroacoustic materials has great development potential and expansion space, especially the performance measurement of decoupling tiles used to shield low-frequency vibration and sound radiation is an important guarantee for the development of submarine acoustic covering.

[0003] At present, it is still difficult to measure the acoustic performance of hydroacoustic material samples in the frequency band below 1kHz in a free field under certain water temperature and water pressure conditions. Because the wavelength in water is much larger than the size of the material sample, the edge diffraction and diffraction interference of the sample are serious. An ideal plane wave sound field can be generated in the hydroacoustic sound tube, and the required sample size is small, the boundary conditions are simple, and it is easy to compare with the theoretical calculation results. The measurement of hydroacoustic materials in the low-frequency band generally uses standing wave tubes and traveling wave tubes. In theory, their lowest operating frequency is not limited by the length of the sound tube. As long as there is enough low-frequency signal-to-noise ratio in the tube, the measurement requirements can be met. The sample diameter is close to the inner diameter of the low-frequency sound tube. When the traveling wave tube measurement device measures the reflection and transmission coefficients of the sample, the front and rear boundaries of the sample are both water media, which is suitable for evaluating the acoustic performance of the sample itself and can simulate the working conditions of the double-hull submarine anechoic tile. However, it cannot simulate the stratification of a single-hull submarine such as "seawater-decoupling tile-hull-air".

[0004] Therefore, how to solve the problem of measuring the acoustic vibration characteristic parameters of underwater acoustic material samples such as anechoic tiles and decoupling tiles is a technical problem that needs to be solved urgently. Summary of the invention:

[0005] The technical problem to be solved by the present invention is to provide a low-frequency acoustic tube measurement method for the vibration velocity transfer coefficient of underwater acoustic materials, so as to measure the decoupling characteristic parameters of underwater acoustic material samples such as decoupling tiles of submarine acoustic coatings, evaluate the vibration reduction and noise reduction effects of the samples, and study the relationship between the decoupling characteristics of the samples and factors such as water temperature, water pressure, and working frequency.

[0006] The technical solution of the present invention is to provide a low-frequency acoustic tube measurement method for the vibration velocity transfer coefficient of underwater acoustic materials, including the following steps:

[0007] Step 1: Vertically place the low-frequency acoustic tube, install a transmitting transducer at the bottom thereof, embed two hydrophones in the tube wall of the low-frequency acoustic tube at a certain distance interval, and fill the low-frequency acoustic tube with degassed water medium.

[0008] Step 2: Place the underwater acoustic material to be measured (with an outer diameter close to the inner diameter of the low-frequency acoustic tube) in the low-frequency acoustic tube and above the water surface. The gap between the underwater acoustic material to be measured and the tube wall of the low-frequency acoustic tube is filled with water medium, and the upper surface of the underwater acoustic material to be measured is a rigid backing. An accelerometer is installed on the rigid backing, and a cavity is provided between the rigid backing and the upper cover of the low-frequency acoustic tube.

[0009] Step 3: Set specific water temperature and hydrostatic pressure conditions.

[0010] Step 4: Under specific water temperature and hydrostatic pressure conditions, the transmitting transducer at the bottom of the low-frequency acoustic tube emits a sinusoidal continuous signal at each frequency point. The two hydrophones embedded in the tube wall of the low-frequency acoustic tube measure the sound pressure signal in the standing wave field in the low-frequency acoustic tube. The accelerometer installed on the rigid backing on the upper surface of the underwater acoustic material to be measured measures the vibration signal, and the vibration velocity transfer coefficient of the underwater acoustic material to be measured is calculated.

[0011] Preferably, the outer diameter of the underwater acoustic material to be measured is close to the inner diameter of the low-frequency acoustic tube.

[0012] Preferably, in Step 4, the incident sound pressure and the reflected sound pressure of the underwater acoustic material to be measured are separated by using the sound pressure measured by the two hydrophones in the standing wave field, the vibration velocity of the lower surface is calculated, the vibration velocity of the upper surface of the underwater acoustic material to be measured is measured, and the vibration velocity transfer coefficient of the underwater acoustic material to be measured is calculated by comparison.

[0013] Furthermore, in Step 3, when measurement is required under a certain hydrostatic pressure, it is realized by connecting a nitrogen pressurization control system through the air pipe on the upper cover; and when measurement is required under a certain water temperature condition, it is realized by precisely adjusting the water temperature in the low-frequency acoustic tube through the water jacket temperature control system outside the low-frequency acoustic tube.

[0014] Compared with the traditional vibration table measurement method in air, this method solves the measurement problem under simulated deep water environment conditions, and also simulates the overall structure of the submarine hull and the decoupling tile of the acoustic coating, making the measurement data more valuable for application and more meaningful for implementation.

[0015] Specifically, the implementation method of the low-frequency sound tube measurement method for the vibration velocity transfer coefficient of the underwater acoustic material of the present invention is as follows:

[0016] Establish a low-frequency sound tube measurement experimental system for the vibration velocity transfer coefficient of the underwater acoustic material to measure the sound absorption coefficient and vibration velocity transfer coefficient of the underwater acoustic material sample under variable temperature and variable pressure conditions.

[0017] Among them, attached Figure 1 As the measurement system for implementing the measurement method of this patent, it can be divided into the following two parts:

[0018] (1) Low-frequency sound tube. The inner diameter is Φ300mm / outer diameter is 600mm, and the length is 3m. It is composed of two sections with lengths of 2m and 1m, placed vertically, and the opening and closing seals are controlled mechanically. The transmitting transducer is installed at the bottom of the sound tube, and a vibration isolation and decoupling design is adopted between the transducer and the flange. The inner part of the 2m section of the lower sound tube is filled with pure water. The sample is installed at the upper end of the lower sound tube, and the water surface is flush with the upper surface of the sample. The hydrophone array is embedded in the tube wall, and the sensitive element at the end of the hydrophone can measure the sound pressure in the tube. The upper part of the sound tube above the sample is a cavity, and pressurized nitrogen can be injected.

[0019] (2) Electronic measurement instrument. The signal transmitting part includes a signal generator and a power amplifier; the receiving part includes a multi-channel preamplifier and a filter, corresponding to the two-way hydrophones of the low-frequency sound tube, and conditioning the weak electrical signals output by the hydrophones; the signal processing part includes a multi-channel signal acquisition and analyzer, synchronously collecting and processing the signals received by the multi-channel hydrophones. The computer and peripherals are used to install measurement software, control the electronic instrument, perform acoustic calculations, and output the measurement results.

[0020] When the low-frequency sound tube is performing measurement work, a stable plane wave standing wave sound field must be established in the tube first. As Figure 2 shown, the coordinates in the tube and the positions of the hydrophone, sample, and transmitter are given, that is, the bottom surface of the sample is at x = 0. The position coordinates of the hydrophone array, the distance between hydrophones, and the distance between the hydrophone and the sample are given respectively. When measuring, the transmitting transducer at the bottom of the low-frequency sound tube emits a sinusoidal continuous sound wave, which is vertically incident on the surface of the sample. Let the sound pressure be p in , a part of the sound energy is reflected back, and the sound pressure is p re , a standing wave field is formed in the water medium, and at the same time, the sample is excited to vibrate. The sound pressures received by hydrophone 1 and hydrophone 2 on the tube wall are p1 and p2 respectively, and the vibration velocity measured by the accelerometer on the rigid back of the sample is v2.

[0021] The transmitting transducer at the bottom of the low-frequency sound tube emits a sinusoidal continuous wave with a frequency of f and an amplitude of A, forming a plane standing wave sound field in the waveguide in the tube. The plane wave sound pressure incident on the sample from the water medium is:

[0022] p inψ(x) = A·exp[j(ωt + kx)] (1)

[0023] The sound pressure of the reflected wave of the sample is:[[]]

[0024] p re ψ(x) = B·exp[j(ωt - kx)] (2)

[0025] The vibration velocity of the water medium in the pipe is:[[]]

[0026]

[0027] In the above formula, k = ω / c, ω = 2πf, ρ and c are the density and sound velocity of the water medium respectively. Therefore, the sound pressure at hydrophone 1 in the pipe can be written as:[[]]

[0028] p w1 ψ(l) = A·exp[j(ωt + kl)] + B·exp[j(ωt - kl)] (5)

[0029] The sound pressure at hydrophone 2 in the pipe is:[[]]

[0030] p w2 ψ(l + d) = A·exp[j(ωt + kl + kd)] + B·exp[j(ωt - kl - kd)] (6)

[0031] In the above formula, l is the distance from hydrophone 1 to the lower surface of the sample, and d is the distance between hydrophone 1 and 2. By measuring the sound pressures at hydrophone 1 and hydrophone 2, the incident wave sound pressure A and the reflected wave sound pressure B of the sample can be calculated:[[]]

[0032]

[0033] It can be seen from Equation (4) that the vibration velocity at the interface between the sample and the water medium is:[[]]

[0034]

[0035] The vibration velocity is directly measured by the accelerometer on the rigid backing of the sample:[[]]

[0036]

[0037] In the above formula, a1 is the measured acceleration, and finally the vibration velocity transfer coefficient between the water interface and the air interface of the sample can be calculated:[[]]

[0038]

[0039] After adopting the above scheme, compared with the existing technology, the present invention has the following advantages:[[]]

[0040] The measurement of the vibration characteristic parameters of the underwater acoustic material sample is realized in the low-frequency acoustic tube, which can fully simulate the working conditions of the sample in actual operation and the structure of the submarine acoustic covering layer. The measurement frequency band is concentrated in the range of 100 Hz to 1 kHz, where the technical difficulty of submarine shock and noise reduction is relatively high. It solves the problem that traditional vibration measurement can only be carried out on a vibration table in an air environment, which is of great help to the research and development of products such as submarine decoupling tiles and provides measurement data closer to actual applications. Description of the Drawings:

[0041] Figure 1 It is a block diagram of the low-frequency acoustic tube measurement experimental system for the vibration velocity transfer coefficient of underwater acoustic materials;

[0042] Figure 2 It is a block diagram of the measurement principle of the vibration velocity transfer coefficient of underwater acoustic materials in a low-frequency acoustic tube. Detailed Embodiments:

[0043] The following further describes the present invention in detail in conjunction with the drawings:

[0044] The present invention is a method for measuring the vibration velocity transfer coefficient of underwater acoustic materials using a low-frequency acoustic tube. The measurement work is carried out in Figure 1 the system shown and a low-frequency acoustic tube that meets the standing wave field conditions, as Figure 1 shown. The system includes a vertically installed low-frequency acoustic tube, a transmitting transducer installed at the bottom of the low-frequency acoustic tube, and the sample to be measured, i.e., the underwater acoustic material to be tested, located in the center of the low-frequency acoustic tube; the lower part of the low-frequency acoustic tube is filled with degassed water, and the water surface is flush with the upper surface of the sample to be measured; a hydrophone array is embedded in the wall of the low-frequency acoustic tube, and an accelerometer is installed on the sample backing; it also includes electronic instruments and temperature-changing, pressure-changing, and mechanical auxiliary equipment. The detailed embodiments are as follows:

[0045] 1) The sample to be measured is made into a cylinder with a clearance fit with the inner wall of the low-frequency acoustic tube, a cylinder with a diameter meeting the requirements, and the clearance with the tube wall is not greater than 1 mm;

[0046] 2) Open the low-frequency acoustic tube, place the sample to be measured on the bracket inside the tube, ensure it is flat, and close the low-frequency acoustic tube;

[0047] 3) Install a kinematic sensor on the rigid backing of the sample to be measured, and the wire passes through the sealing connector and through the upper cover of the low-frequency acoustic tube;

[0048] 4) Start the pressure control system connected to the low-frequency acoustic tube, turn on the vacuum extraction equipment to create a negative pressure in the low-frequency acoustic tube, and use the external atmospheric pressure to inject pure water into the low-frequency acoustic tube to a certain height so that the sample to be measured is just immersed in the water column;

[0049] 5) Turn on the measurement system, select the required measurement frequency points through the computer, set the output amplitude of the signal source, adjust the power amplifier gain and impedance, so that a standing wave field has been formed between the low-frequency transmitting transducer and the sample to be measured;

[0050] 6) Use a measurement system to collect and process two hydrophone signals and one accelerometer signal, calculate the vibration velocities v0 and v1 of the front and back surfaces of the sample to be measured within the measurement frequency range, and finally obtain the vibration velocity transfer coefficient Bv of the sample to be measured.

[0051] 7) Adjust different hydrostatic pressures or water temperatures and repeat step 6).

[0052] 8) After the measurement is completed, open the pressure relief valve to release the pressure in the low-frequency tube.

[0053] 9) Open the low-frequency acoustic tube and take out the sample to be measured.

[0054] The present invention realizes the measurement of the vibration characteristic parameters of the underwater acoustic material sample in the low-frequency acoustic tube, can fully simulate the working conditions of the sample in actual work and the structure of the submarine acoustic covering layer, and the measurement frequency band is concentrated in the range of 100 Hz to 1 kHz where it is difficult to reduce vibration and noise for submarines. It solves the problem that traditional vibration measurement can only be carried out on a vibration table in an air environment, is of great help to the research and development of products such as submarine decoupling tiles, and provides measurement data closer to actual applications.

[0055] The above is only an illustration of the preferred embodiments of the present invention, and it should not be construed as a limitation of the claims. Any equivalent structure or equivalent process transformation made using the specification of the present invention is included in the patent protection scope of the present invention.

Claims

1. A low-frequency acoustic tube measurement method for the vibration velocity transfer coefficient of an underwater acoustic material, characterized in that: It includes the following steps: Step 1: Place the low-frequency acoustic tube vertically and install a transmitting transducer at its bottom. Embed two hydrophones in the wall of the low-frequency acoustic tube at intervals. Fill the low-frequency acoustic tube with degassed water medium. Step 2: Place the underwater acoustic material to be measured in the low-frequency acoustic tube and on the water surface. The gap between the underwater acoustic material to be measured and the wall of the low-frequency acoustic tube is filled with water medium. The upper surface of the underwater acoustic material to be measured is a rigid backing, and an accelerometer is installed on the rigid backing. A cavity is provided between the rigid backing and the upper cover of the low-frequency acoustic tube. Step 3: Set specific water temperature and hydrostatic pressure conditions. Step 4: Under the specific water temperature and hydrostatic pressure conditions, the transmitting transducer at the bottom of the low-frequency acoustic tube emits a sinusoidal continuous signal at each frequency point. The two hydrophones embedded in the wall of the low-frequency acoustic tube measure the sound pressure signal of the standing wave field in the low-frequency acoustic tube. Measure the vibration signal through the accelerometer installed on the rigid backing on the upper surface of the underwater acoustic material to be measured, and calculate the vibration velocity transfer coefficient of the underwater acoustic material to be measured. The specific operation is as follows. Assume that the two hydrophones are hydrophone 1 and hydrophone 2, and measure the sound pressure at hydrophone 1 and hydrophone 2 in the standing wave field. The sound pressure at hydrophone 1 is: The sound pressure at hydrophone 2 is: wherein, k = ω / c , ω = 2 πf , f is the frequency emitted by the bottom-emitting transducer of the low-frequency acoustic tube, and c are the density and sound velocity of the water medium respectively, l is the distance from hydrophone 1 to the lower surface of the sample, d is the spacing between hydrophone 1 and hydrophone 2; Then calculate the incident wave sound pressure A and the reflected wave sound pressure B of the sample through the sound pressure at hydrophone 1 and hydrophone 2, and thus calculate the vibration velocity at the interface between the sample and the water medium. The vibration velocity at the interface between the sample and the water medium is: Then directly measure the vibration velocity of the rigid backing of the sample by the accelerometer on the rigid backing of the sample: wherein, is the measured acceleration; Finally, the vibration velocity transfer coefficient between the water interface and the air interface of the sample can be calculated: 。 2. The low-frequency acoustic tube measurement method for the vibration velocity transfer coefficient of the underwater acoustic material according to claim 1, wherein: The outer diameter of the underwater acoustic material to be measured is close to the inner diameter of the low-frequency acoustic tube.

3. The low-frequency sound tube measurement method for the vibration velocity transfer coefficient of the underwater acoustic material according to claim 1, characterized in that: The parameters of the low-frequency sound tube are as follows. The inner diameter is 300 mm, the outer diameter is 600 mm, and the length is 3 m. The low-frequency sound tube consists of two sections with lengths of 2 m and 1 m, and is opened and sealed by mechanical control.

4. The low-frequency sound tube measurement method for the vibration velocity transfer coefficient of the underwater acoustic material according to claim 1, characterized in that: In Step 3, when it is necessary to measure under the specific hydrostatic pressure, it is achieved by connecting the nitrogen pressurization control system through the air pipe on the upper cover; and when it is necessary to measure under the specific water temperature condition, it is achieved by precisely adjusting the water temperature inside the low-frequency acoustic tube through the water jacket temperature control system outside the low-frequency acoustic tube.

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