CN113686966B - Standing wave tube measuring method for decoupling characteristic parameters of underwater acoustic material - Google Patents

Abstract

The invention discloses a standing wave tube measurement method for decoupling characteristic parameters of underwater acoustic materials. The method realizes the measurement of decoupling characteristic parameters of underwater acoustic materials in low-frequency standing wave tubes. The integration of sound sources and sensors, and the configuration of electronic instruments have established a sample decoupling characteristic parameter measurement system, proposed a measurement method for the decoupling characteristic parameters of underwater acoustic materials in the frequency range of 100Hz to 1000Hz, and compiled automatic measurement software, which has solved the problems in the application. Difficult measurement in low frequency bands under environmental conditions.

Description

A Standing Wave Tube Measurement Method for Decoupling Characteristic Parameters of Underwater Acoustic Materials

technical field

The invention relates to the technical field of metrology and testing, in particular to a standing wave tube measuring method for decoupling characteristic parameters of underwater acoustic materials.

Background technique

The main purpose of realizing ship acoustic stealth is to reduce the reflection of the enemy's active sonar detection sound waves, reduce the target strength of the ship; reduce the radiation noise level of the ship, and reduce the probability of being detected by the enemy's passive sonar monitoring. Pasting sound-absorbing tiles on the hull of a ship is an effective means of acoustic stealth. According to foreign reports, anechoic tiles can be divided into anechoic tiles (Anechoic Tiles), decoupling tiles (Decoupling Tiles) and multifunctional tiles according to different main functions, which are used to absorb the detection sound waves of the enemy's active sonar and shield them respectively. The noise of the ship is radiated to the seawater, and the multifunctional tile takes into account both functions of sound absorption and decoupling.

In addition, with the development of underwater acoustic countermeasure technology, the research of new hull sonar technology such as submarine side array has been further promoted. The hull sonar is installed on the submarine hull platform, and the self-noise of the sonar mainly comes from the submarine platform and equipment. Structural vibration and reducing sonar self-noise are the primary conditions for increasing sonar detection distance and detection accuracy. For example, the side array sonar hydrophone module and the installation platform have strict requirements on vibration isolation. If there are no vibration isolation measures or the vibration isolation performance is not good, the vibration of the hull will have a serious impact on the performance of the receiving array. The technical indicators of the sonar will be greatly reduced. A certain type of side array sonar base array uses an air/rubber baffle and has a decoupling module inside.

In summary, it is very important to study the decoupling and vibration isolation performance of sonar array acoustic baffles, hydrophone modules and their mounting components. But our research in this area was not deep enough in the past. Because the acoustic and mechanical properties of hydroacoustic materials are very sensitive to frequency and hydrostatic pressure, their importance becomes more prominent as the working frequency of sonar decreases and the working depth increases. It is almost impossible to measure the acoustic performance of underwater acoustic materials or component samples in the free field at frequencies above 100 Hz. Because the wavelength in water is much larger than that of a material sample, the edge diffraction and diffraction of the sample seriously interfere with the measurement. Standing wave tubes and traveling wave tubes are generally used for testing low-frequency underwater acoustic materials. Their minimum operating frequency is theoretically not limited by the length of the acoustic tube. As long as there is sufficient low-frequency signal-to-noise ratio in the tube, the measurement requirements can be met. Samples The diameter is close to the inner diameter of the 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 all water media, which is suitable for evaluating the acoustic performance of the sample itself, but it cannot simulate the stratification of "seawater-tile-metal shell-air" . For the application of multi-functional tiles or sound-insulating decoupling tiles on submarine hulls, domestic research on the measurement of decoupling characteristic parameters is still relatively small, and there are no mature measurement methods. Due to the demand pull of the model project, it is necessary to establish a nitrogen-pressurized low-frequency standing wave acoustic tube to simulate the stratification of "seawater-tile-metal shell-air" and measure the decoupling characteristic parameters of the sample under the gas backing.

In order to quickly and correctly measure various performances of sound insulation and decoupling tiles, various test methods have been studied in underwater acoustic tubes. The sound field in the underwater acoustic tube is an ideal plane crossing sound field, the required sample is small, the boundary conditions are simple, and it is easy to compare with the theoretical calculation results. It is very suitable as an experimental method in the research process to calculate the its radiation sound pressure. We can simply summarize the conditions of the sound radiation test into two points: one is no reflection, and the other is plane wave. These two points are very easy to implement in the underwater acoustic tube. In the acoustic tube waveguide, the sample to be tested should have a plane vibrating surface, and the radiated sound waves generated by its excited vibration propagate in the form of plane waves in the acoustic tube. See accompanying drawing 3, if sound pipe end is equipped with sound-absorbing wedge with excellent performance, just can accomplish non-reflection. The incident and reflected waves can be separated by using the double hydrophone method. The sample to be tested is installed on the top of the sound tube. The sample is excited by a vibrator, and the sample is excited to vibrate and radiate sound waves into the sound tube. The force sensor and hydrophone are used to measure the force on the surface of the sample and the sound field in the sound tube respectively. When the exciter excites the sample in the underwater acoustic tube, the excitation frequency is controlled to be lower than the cut-off frequency of the acoustic tube, so that only plane waves appear in the acoustic tube. The test piece is attached to the steel backing of the same thickness, and the acoustic radiation sound pressure of the sample is measured under different frequency excitations, and normalized relative to the excitation force, the acoustic pressure of the sample under the same excitation force is obtained. Radiation intensity value, i.e. the force-acoustic transfer characteristic of the damping structure. However, since the wedge cannot completely absorb sound in the frequency band below kilohertz, this method has a higher low frequency limit.

Contents of the invention

The invention provides a standing wave tube measurement method for decoupling characteristic parameters of underwater acoustic materials, in order to solve the problem of difficulty in low-frequency measurement under application environment conditions in the prior art.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

A standing wave tube measurement method for decoupling characteristic parameters of underwater acoustic materials, comprising the steps of:

Step 1, the underwater acoustic decoupling material to be tested is made into a tested sample whose diameter conforms to the inner diameter of the standing wave tube;

Step 2, open the standing wave tube, put the sample to be tested on the central support in the standing wave tube to ensure it is flat; start the mechanical control system, close the standing wave tube; start the pressure control system, turn on the vacuum equipment to form a negative pressure in the standing wave tube Pressure, use external atmospheric pressure to inject pure water into the standing wave tube to a predetermined height, and pressurize to the pressure point to be measured;

Step 3, turn on the electronic instruments and software of the measuring device, select the required measurement frequency point according to the measurement needs, set the output amplitude of the exciter signal source on the measurement software interface, adjust the gain and impedance of the power amplifier, A standing wave field is formed between the tested sample;

Step 4, assuming that the sample to be tested is a two-terminal linear system, then:

Among them, 1 and 2 respectively represent the front and back of the surface of the tested sample, and the 4 impedance components can characterize the characteristics of the tested sample, allowing any response function to be calculated;

Let the impedance matrix of the water layer and the decoupling layer be Z:

Among them, the boundary condition of the terminal is p ₂ =Z _H ·v ₂ , measured p ₀ , v ₀ and v ₂ , and obtained Z:

Z＝Z ₀ Z ₁ (3)

Z ₀ is the transfer impedance of the water layer, for the equivalent uniform layer, there is

Z ₁₁ =Z ₂₂ (4)

Z ₁₁ · Z ₂₂ - Z ₁₂ · Z ₂₁ = 1 (5)

Formula (2) is written as:

p ₀ =z ₁₁ p ₂ +z ₁₂ v ₂ (6)

v ₀ =z ₂₁ p ₂ +z ₂₂ v ₂ (7)

From formula (6) get:

p ₂ =Z _H ·v ₂ (9)

It is derived from formulas (8) and (9):

It is derived from formulas (7) and (9):

It is derived from formulas (4), (5) (10) and (11):

From formula (3) get:

Z ₁ =Z ₀ ·Z ^-1 (15)

set up:

Decoupling factor:

Step 5, if necessary, adjust different hydrostatic pressures, repeat step 4;

Step 6: After the measurement is completed, start the pressure control system, open the pressure relief valve, and release the pressure in the standing wave tube; start the mechanical control system, open the standing wave tube, and take out the sample to be tested.

Compared with the prior art, the standing wave tube measurement method of the decoupling characteristic parameters of the underwater acoustic material according to the present invention has the following remarkable superior effects:

1. The present invention provides a standing wave tube measurement method for the decoupling characteristic parameters of the underwater acoustic material. This method realizes the measurement of the decoupling characteristic parameters of the underwater acoustic material in the low-frequency standing wave tube. The integration of low-frequency excitation sound sources and sensors, and the configuration of electronic instruments have established a sample decoupling characteristic parameter measurement system, proposed a measurement method for the decoupling characteristic parameters of underwater acoustic materials in the frequency range of 100Hz to 1000Hz, and compiled automatic measurement software, which solved the problem well. Difficult problems in low-frequency band measurement under application environment conditions.

Description of drawings

Fig. 1 is the schematic diagram of standing wave tube measuring device;

Figure 2 is a schematic diagram of a plane wave model for decoupling coefficient measurement;

Fig. 3 is a schematic diagram of an acoustic tube measurement system for force-acoustic transfer characteristics of underwater acoustic material samples.

Detailed ways

The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

An embodiment of the present invention provides a standing wave tube measurement method for decoupling characteristic parameters of underwater acoustic materials, including the following steps:

Step 1, the underwater acoustic decoupling material to be tested is made into a tested sample whose diameter conforms to the inner diameter of the standing wave tube;

Step 2, open the standing wave tube, put the sample to be tested on the central support in the standing wave tube to ensure it is flat; start the mechanical control system, close the standing wave tube; start the pressure control system, turn on the vacuum equipment to form a negative pressure in the standing wave tube Pressure, use external atmospheric pressure to inject pure water into the standing wave tube to a predetermined height, and pressurize to the pressure point to be measured;

Step 3, turn on the electronic instruments and software of the measuring device, select the required measurement frequency point according to the measurement needs, set the output amplitude of the exciter signal source on the measurement software interface, adjust the gain and impedance of the power amplifier, A standing wave field is formed between the tested sample;

Step 4, assuming that the sample to be tested is a two-terminal linear system, then:

Among them, 1 and 2 respectively represent the front and back of the surface of the tested sample, and the 4 impedance components can characterize the characteristics of the tested sample, allowing any response function to be calculated;

Let the impedance matrix of the water layer and the decoupling layer be Z:

Among them, the boundary condition of the terminal is p ₂ =Z _H ·v ₂ , measured p ₀ , v ₀ and v ₂ , and obtained Z:

Z＝Z ₀ Z ₁ (3)

Z ₀ is the transfer impedance of the water layer, for the equivalent uniform layer, there is

Z ₁₁ =Z ₂₂ (4)

Z ₁₁ · Z ₂₂ - Z ₁₂ · Z ₂₁ = 1 (5)

Formula (2) is written as:

p ₀ =z ₁₁ p ₂ +z ₁₂ v ₂ (6)

v ₀ =z ₂₁ p ₂ +z ₂₂ v ₂ (7)

From formula (6) get:

p ₂ =Z _H ·v ₂ (9)

It is derived from formulas (8) and (9):

It is derived from formulas (7) and (9):

It is derived from formulas (4), (5) (10) and (11):

From formula (3) get:

Z ₁ =Z ₀ ·Z ^-1 (15)

set up:

Decoupling factor:

Step 5, if necessary, adjust different hydrostatic pressures, repeat step 4;

Step 6: After the measurement is completed, start the pressure control system, open the pressure relief valve, and release the pressure in the standing wave tube; start the mechanical control system, open the standing wave tube, and take out the sample to be tested.

Specifically, the sample in the acoustic tube is pasted on the backing, and the medium in the tube has a multi-layer structure. The plane wave model composed of the tested sample, its front surface water layer, and the back surface backing layer is shown in Figure 2. The height of the water layer is H _W , the sound velocity and density in water are ρ _w , c _w , the sound pressure and vibration velocity of the water layer on the piston surface are p ₀ and v ₀ respectively; the height of the material sample layer is H _L , and the sound velocity in the material and density are ρ _L , c _L , the sound pressure and vibration velocity of the sample layer on the water surface are p ₁ and v ₁ respectively; the height of the backing layer is H _M , the sound velocity and density in the layer are ρ _M , c _M , The sound pressure and vibration velocity on the backing layer are p ₂ and v ₂ , respectively. The vibration of the exciter is coupled to the sample through the water medium. The measured sound pressure and acceleration sensor signals are conditioned and amplified and then collected by the dynamic signal analysis system under the control of the computer. After processing, the sound pressure p ₀ and vibration velocity of the piston surface can be obtained v ₀ and the vibration velocity v ₂ of the rigid backing surface can further obtain the transfer matrix elements of the layered sample, and finally obtain the decoupling coefficient B _V =v ₂ /v ₁ of the tested sample.

Applying this patent to the standing wave tube measuring device for acoustic and vibration characteristic parameters of underwater acoustic materials (see Figure 1), it is possible to measure the decoupling coefficient of underwater acoustic material samples such as sound insulation decoupling tiles under the actual hydrostatic pressure condition, which is A brand-new measurement method and application of underwater acoustic materials, which have not been reported in domestic and foreign journals. Compared with the traditional pulse sound tube measurement method, this method solves the problem of difficulty in low-frequency measurement under application environmental conditions.

In the description of this specification, specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in an appropriate manner.

Certainly, the present invention can also have other multiple embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these changes and modifications All should belong to the protection scope of the claims of the present invention.

Claims (1)

1. The standing wave tube measuring method of the decoupling characteristic parameter of the underwater acoustic material is characterized by comprising the following steps of:

step 1, preparing a to-be-measured underwater acoustic decoupling material into a to-be-measured sample with the diameter conforming to the inner diameter of a standing wave tube;

step 2, opening the standing wave tube, and placing the sample to be tested on a central support in the standing wave tube to ensure flatness; starting a mechanical control system and closing the standing wave tube; starting a pressure control system, starting a vacuum pumping device to form negative pressure in the standing wave tube, injecting purified water into the standing wave tube to a preset height by using external atmospheric pressure, and pressurizing to a pressure point to be measured;

step 3, starting an electronic instrument and software of the measuring device, selecting a required measuring frequency point according to the measuring requirement, setting an exciter signal source output amplitude on a measuring software interface, adjusting power amplifier gain and impedance, and forming a standing wave field between an exciter piston surface and a measured sample;

step 4, setting the tested sample as a two-end linear system, and then:

wherein 1 and 2 represent the front and back, respectively, of the surface of the sample being measured, 4 impedance components being able to characterize the sample being measured, allowing any response function to be calculated;

let the impedance matrix of the water layer and decoupling layer be Z:

wherein the boundary condition of the terminal is p ₂ ＝Z _H ·v ₂ P is measured ₀ ，v ₀ And v ₂ Obtaining Z:

Z＝Z ₀ ·Z ₁ (3)

Z ₀ for the transfer resistance of the water layer, for an equivalent uniform layer, there is

Z ₁₁ ＝Z ₂₂ (4)

Z ₁₁ ·Z ₂₂ -Z ₁₂ ·Z ₂₁ ＝1 (5)

Formula (2) is written as:

p ₀ ＝z ₁₁ p ₂ +z ₁₂ v ₂ (6)

v ₀ ＝z ₂₁ p ₂ +z ₂₂ v ₂ (7)

obtained from the formula (6):

p ₂ ＝Z _H ·v ₂ (9)

derived from formulas (8) and (9):

derived from formulas (7) and (9):

derived from formulas (4), (5) (10) and (11):

obtained from the formula (3):

Z ₁ ＝Z ₀ ·Z ^-1 (15)

setting:

decoupling coefficient:

step 5, if necessary, adjusting different hydrostatic pressures, and repeating step 4;

step 6, after the measurement is finished, starting a pressure control system, opening a pressure release valve, and releasing the pressure in the standing wave tube; and starting the mechanical control system, opening the standing wave tube, and taking out the tested sample.