CN112710733B - Method for measuring oblique incidence emission characteristics of underwater acoustic material by pulse tube - Google Patents
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- G—PHYSICS
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Abstract
The invention provides a method for measuring the oblique incidence reflection characteristic of an underwater sound material by using a pulse sound tube, which is used for measuring the oblique incidence reflection coefficient of a small sample underwater sound material within the frequency range of 1 kHz-20 kHz. On the basis of measuring the reflection coefficient of the underwater sound material by a pulse method, the purpose of measuring the oblique incidence reflection coefficient of the underwater sound material by using a small sample is achieved by changing the shape of the sample, introducing a correction value and a derivation formula thereof. The method provides measurement service for the research and development of the underwater acoustic material, improves the research efficiency of the related technology, promotes the development of the industry and provides guarantee for the construction of the underwater acoustic engineering in China.
Description
Technical Field
The invention belongs to the field of acoustics (underwater sound), and mainly relates to a method for measuring oblique incidence emission characteristics of an underwater sound material by using a pulse tube.
Background
The underwater acoustic material has very important application in both civil and military fields. The underwater sound components such as the silencing wedge, the silencing tile, the sound-transmitting window and the like which take the underwater sound material as the raw material are mainly applied in the fields of silencing pool construction, submarine sound stealth technical research, sonar equipment development and the like. The performance of the underwater acoustic material can directly influence the performance index of the underwater acoustic member, so that the accurate and comprehensive evaluation of the underwater acoustic material is beneficial to the development of the underwater acoustic technology. The reflection characteristic is one of the main factors for evaluating the performance of the underwater acoustic material, and the expansion of the evaluation index of the reflection characteristic of the underwater acoustic material has important significance for guiding the research related to the underwater acoustic material.
In the evaluation system of the performance of the underwater acoustic material, the research on the reflection characteristics of the underwater acoustic material has been carried out on the premise that the sound wave is incident from the normal direction of the surface of the material (hereinafter, simply referred to as "normal incidence", and the non-normal direction is referred to as "oblique incidence"). The initial underwater sound material sample is mainly made of simple-structure materials such as simple flat plates, wood plates, rubber plates and the like, and the reflection characteristics of normal incidence and oblique incidence of the initial underwater sound material sample have clear correlation. The reflection characteristic of the underwater acoustic material under normal incidence is known, and the oblique incidence reflection characteristic can be calculated by a dielectric layer reflection formula. The requirement on the method for measuring the oblique incidence reflection characteristic of the underwater acoustic material is not high, so that no relevant research is carried out in China.
However, with the development of underwater acoustic technology, in order to meet the higher and higher performance requirements of the current civil and military fields on the underwater acoustic material, a complex internal structure begins to appear in the design of the underwater acoustic material. Under the condition, the relation between the reflection characteristics of normal incidence and oblique incidence of the underwater sound material no longer follows a general rule, the reflection characteristics of oblique incidence cannot be calculated according to the normal incidence reflection characteristics, and the measurement requirement on the reflection characteristics of oblique incidence of the underwater sound material is generated.
In order to measure the oblique incidence reflection characteristic of the underwater acoustic material, Yiyan and the like of Hangzhou applied acoustics research institute provide an oblique incidence reflection characteristic measuring method of the underwater acoustic material based on an acoustic holography technology, and the method is applied to practice and successfully develops the evaluation index of the reflection characteristic of the underwater acoustic material. However, when the method is used for measurement, a hydrophone array is required to be used, and the measurement device is complex; the size of the sample to be measured limits the lower limit of the operating frequency of the measuring device, and if the reflection characteristic of 2kHz is to be measured, the minimum geometric size of the sample is not less than 2 m.
Large sample measurements are not conducive to controlling the development cost of materials; the longer time to prepare a large-sized sample will extend the research period for new materials. In order to improve the research efficiency of the underwater acoustic material and expand the measurement frequency, a method for measuring the oblique incidence reflection characteristic of the underwater acoustic material through a small sample in a corresponding low-frequency range is required.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for measuring the oblique incidence emission characteristic of an underwater acoustic material by using a pulse tube.
The object of the present invention is achieved by the following technical means. A method of measuring oblique incidence emission characteristics of an underwater acoustic material by a pulse tube, the method comprising the steps of:
1) the bottom of the pulse sound tube is provided with a receiving and transmitting combined transducer, the underwater acoustic material to be detected is processed into an underwater acoustic material sample according to requirements, the shape of the underwater acoustic material sample is a part of a cylinder, the diameter of the cylinder is the same as the inner diameter of the pulse sound tube, and the upper bottom surface and the lower bottom surface of the underwater acoustic material sample are in the same ellipse shape and are parallel to each other;
2) putting the underwater acoustic material sample into a pulse sound tube;
3) adjusting the position of the underwater acoustic material sample in the acoustic tube to separate direct waves, reflected waves and secondary transmitted waves;
4) measuring signal amplitudes of the direct wave and the reflected wave;
5) calculating a correction factor according to the following formula;
the expression for the correction factor that corrects for the energy decay phenomenon in the tube is:
wherein s represents the cross-section of the sound tube;
6) finally, calculating the oblique incidence reflection coefficient of the underwater acoustic material sample (2) according to the following formula;
wherein R (f)0θ) is a frequency of f0Sound pressure reflection coefficient of the sample, a, at an oblique incident angle of the sound wave θsIs the energy attenuation coefficient in the tube, where RmObtained by acoustic tube measurements, provided that a is knowns(f0The value of θ) yields a frequency f0And the sound pressure reflection coefficient of the sample when the oblique incident angle of the sound wave is theta.
The invention has the beneficial effects that: the method is used for measuring the oblique incidence reflection coefficient of the small sample underwater acoustic material within the frequency range of 1 kHz-20 kHz. On the basis of measuring the reflection coefficient of the underwater sound material by a pulse method, the purpose of measuring the oblique incidence reflection coefficient of the underwater sound material by using a small sample is achieved by changing the shape of the sample, introducing a correction value and a derivation formula thereof. The method provides measurement service for the research and development of the underwater acoustic material, improves the research efficiency of the related technology, promotes the development of the industry and provides guarantee for the construction of the underwater acoustic engineering in China.
Drawings
Fig. 1 is a schematic diagram of the acoustic performance of a sample measured in a pulse tube.
Fig. 2 is a preparation of oblique incidence underwater acoustic material.
Fig. 3 shows that when the incident plane wave encounters an obliquely incident sample, the reflected wave is slowly modified into a plane wave propagating along the axis of the sound tube.
Description of the reference numerals: the device comprises a transducer 1, an underwater acoustic material sample 2, a water-air interface 3 and a pulse sound tube 4.
Detailed Description
The invention will be described in detail below with reference to the following drawings:
in three-dimensional space, the general expression of the acoustic wave equation is:
△P-k2P＝0 (1)
in the formula, the constant k represents a wave number.
However, the current pipe measurement generally uses a round pipe, so for the convenience of calculation, we express the acoustic wave equation by cylindrical coordinates:
then we separate the variables in the form
By substituting (2) and then separating the variables, three equations can be obtained:
in which P is
The number of nodes distributed in the direction is 2 × m (m is 1,2,3 … …); k is a radical of formulazRepresenting the wavenumber of P propagating in the z-axis direction. If we consider the pipe wall as a rigid material, the radius in the pipe is ρ0And the sound wave only propagates along the positive direction of the z-axis without reflected wave in the direction of the z-axis. Then bringing the solutions of equations (4), (5) and (6) into expression (3) can yield the final expression of the acoustic wave propagation in the tube:
in the formula, JmRepresenting a Bessel function of order m; k is a radical ofmnIs the nth one satisfies
And the mode (m, n) of the acoustic wave propagating in the tube is expressed as
And k ismnAnd k iszmnThe relationship of (1) is:
here, kmnCan be seen as the projection of the wave number of the sound wave on any cross section of the sound tube perpendicular to the central axis of the sound tube, kzmnIt is the projection of the wave number of the sound wave on the central axis of the sound tube. If we use θmnTo express the angle formed by the wave number k and the positive direction of the central axis of the sound tube, the angle can be obtained
That is, each mode of sound wave has a unique pairThe angle of propagation of the response. Since m and n are positive integers, we can consider the propagation of an acoustic wave of any mode represented by expression (7) as if the wave numbers are the same, both k, and at a specific angle θmnSuperposition of plane waves propagating in the sound tube.
When k ρ0<1.83 (1.83 is the first to satisfy except 0)
Value of (c), which can be looked up in a Bezier function table), k is removed01Except that all kmnAre all greater than k value, corresponding to kzmnAre all pure imaginary numbers, -ikzmnIs a pure real number less than 0, and the amplitude of the corresponding modal sound wave is easy to obtain
Decreases with increasing propagation distance z. And k is01The corresponding sound wave mode is a plane wave.
When k ρ0<1.83, all non-planar waves propagating in the tube attenuate in amplitude as the distance traveled increases and gradually self-modify the sound waves propagating in the sound tube to planar waves. The attenuated acoustic energy is dissipated in the process of changing the direction of particle vibration.
The proportion of consumed energy needs to pass through the correction factor asTo correct it. Then, according to the expression (7) for the propagation of the sound wave in the tube, when the distance traveled by the non-planar sound wave in the tube is long enough, the sound wave propagated in the tube can be approximated as leaving only the planar wave. The expression for the correction factor that corrects for the energy decay phenomenon in the tube is then:
where s represents the cross-section of the sound tube.
The principle of measuring the sound pressure reflection coefficient of a material in a pulse tube is shown in figure 1. A receiving and transmitting energy-exchanging device is arranged at the bottom of the pulse tube, and when the energy-exchanging device transmits a pulse signal s0After (t), the transducer will receive a signal formed by the superposition of multiple reflected, transmitted signals. When the initial signal pulse emitted by the transducer is sufficiently short, the acoustic signal s reflected by the primary sampler1(t) and the signal s totally reflected at the water-air interface 3 and transmitted through the sample twicet2(t) will be separated out. The latter three signals are Fourier transformed, i.e. S0(f)、Sr1(f)、St2(f) The corresponding frequency f can be obtained0Finally, the sound pressure reflection coefficient R (f) of the sample at the corresponding frequency is calculated0) As shown in equation (10).
This measurement is performed in a specific measurement environment, so that the sound wave must propagate in the form of a plane wave at any position of the pulse tube during the whole measurement process, namely:
wherein c represents the speed of sound propagation in water; rho0Is the inner radius of the pulse tube.
The method for measuring the angular spectrum of the sound pressure reflection coefficient of the material in the pulse tube changes the shape of a sample on the basis of the traditional test method and then carries out measurement. As shown in fig. 2. The two wedge surfaces of the upper and lower parts of the normal incidence sample shown in fig. 2(a) are cut off at an angle θ, and an oblique incidence sample is obtained, and a cross-sectional view and a plan view thereof are shown in fig. 2(b) and 2(c), respectively.
Wherein D represents the thickness of the sample, theta represents the angle between the normal vector of the test surface of the sample and the central axis of the pulse tube, and rho0Is the inner radius of the pulse tube. First, consider that the sound wave does not have a secondary reflection with the sample after it hits the tube wall, and θ takes less than π/6. In this case, when the plane wave excited by the transducer contacts the sample, the reflected wave of the acoustic wave propagates on the sample surface as shown in fig. 3.
It is clear that the propagation of the acoustic wave is not a plane wave propagating along the axis of the sound tube, when the incident wave has just been reflected by the sample. According to the calculation result of the formula (9), energy attenuation occurs due to the self-correction of the propagation direction of the acoustic wave. We default to the ratio R of the amplitude of the reflected signal to the amplitude of the incident signal at a particular frequency measured with a sufficiently long sound tubemComprises the following steps:
wherein R (f)0θ) is a frequency of f0Sound pressure reflection coefficient of the sample, a, at an oblique incident angle of the sound wave θsIs the energy attenuation coefficient in the tube. Wherein R ismCan be obtained by sound tube measurement as long as a is knowns(f0Theta) can be derived as a value of f0And when the oblique incident angle of the sound wave is theta, the sound pressure reflection coefficient of the sample is as follows:
since both the Bessel function and the trigonometric function have complete eigen function families and have orthogonality among the eigen functions, it can be seen that when the acoustic wave is a plane wave taking the positive direction of the z-axis as the propagation direction, that is, theta is 0, the energy attenuation coefficient a in the tube is the same as that of the plane wavesAnd (5) being 0, which meets the practical situation.
The method comprises the following specific steps:
the device comprises a transducer 1, an underwater acoustic material sample 2, a water-air interface 3 and a pulse sound tube 4.
1) Arranging a receiving and transmitting combined transducer 1 at the bottom of a pulse sound tube 4, processing a tested underwater sound material into an underwater sound material sample 2 according to requirements, wherein the shape of the underwater sound material sample is a part of a cylinder, the diameter of the cylinder is the same as the inner diameter of the pulse sound tube, and the upper bottom surface and the lower bottom surface of the underwater sound material sample are in the same ellipse shape and are parallel to each other;
2) putting the underwater sound material sample into a pulse sound tube;
3) adjusting the position of the underwater acoustic material sample in the acoustic tube to separate direct waves, reflected waves and secondary transmitted waves;
4) measuring the signal amplitudes of the direct wave and the reflected wave;
5) calculating a correction factor according to the following formula;
the expression for the correction factor that corrects for the energy decay phenomenon in the tube is:
wherein s represents the cross-section of the sound tube;
6) finally, calculating the oblique incidence reflection coefficient of the underwater acoustic material sample (2) according to the following formula;
wherein R (f)0θ) is a frequency of f0Sound pressure reflection coefficient of the sample at oblique incident angle of sound wave θ, asIs the energy attenuation coefficient in the tube, where RmObtained by acoustic tube measurements, provided that a is knowns(f0The value of θ) yields a frequency of f0And the sound pressure reflection coefficient of the sample when the oblique incident angle of the sound wave is theta.
In the research process of the underwater acoustic material decoupling characteristic parameter measurement method, the measurement result is stable after a plurality of experimental measurements are carried out in the pulse acoustic tube of the measuring station 715 under the environment of normal temperature and normal pressure.
In summary, in the pulsed acoustic tube, when the acoustic wave is obliquely incident, the measurement of the acoustic pressure reflection coefficient of the underwater acoustic material is summarized as the measurement of the echo pulse signal and the direct pulse signal of the sample with different frequencies and different incident angles, and the calculation of the energy attenuation coefficient in the tube.
It should be understood that the technical solutions and the inventive concepts of the present invention should be replaced or changed by equivalents and modifications to the technical solutions and the inventive concepts of the present invention by those skilled in the art.
Claims (1)
1. A method for measuring the oblique incidence emission characteristic of an underwater acoustic material by a pulse tube is characterized in that: the method comprises the following steps:
1) the underwater acoustic material testing device is characterized in that a receiving and transmitting combined transducer (1) is arranged at the bottom of a pulse sound tube (4), a tested underwater acoustic material is processed into an underwater acoustic material sample (2) according to requirements, the shape of the underwater acoustic material sample (2) is a part of a cylinder, the diameter of the cylinder is the same as the inner diameter of the pulse sound tube (4), and the upper bottom surface and the lower bottom surface of the underwater acoustic material sample (2) are in the same oval shape and are parallel to each other;
2) putting the underwater acoustic material sample (2) into a pulse acoustic tube (4);
3) adjusting the position of the underwater sound material sample (2) in the sound tube to separate direct waves, reflected waves and secondary transmitted waves;
4) measuring the signal amplitudes of the direct wave and the reflected wave;
5) calculating a correction factor according to the following formula;
the expression for the correction factor that corrects for the energy decay phenomenon in the tube is:
wherein s represents the cross-section of the sound tube;
6) finally, calculating the oblique incidence reflection coefficient of the underwater acoustic material sample (2) according to the following formula;
wherein R (f)0θ) is a frequency of f0Sound pressure reflection coefficient of the sample, a, at an oblique incident angle of the sound wave θsCorrection factor for energy decay phenomena, in which RmObtained by acoustic tube measurements, provided that a is knowns(f0The value of θ) yields a frequency f0And the sound pressure reflection coefficient of the sample when the oblique incident angle of the sound wave is theta.
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| CN102243213A (en) * | 2011-04-15 | 2011-11-16 | 中国船舶重工集团公司第七一五研究所 | Separated underwater sound pipe system |
| CN103675100A (en) * | 2013-12-20 | 2014-03-26 | 中国船舶重工集团公司第七一五研究所 | Method for measuring angular spectrum of sound transmission performance of underwater acoustic material |
| CN109001297A (en) * | 2018-06-05 | 2018-12-14 | 哈尔滨工程大学 | Large sample underwater acoustic materials acoustical reflection factor measurement method based on single vector hydrophone |
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Patent Citations (4)
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| WO2005026716A1 (en) * | 2003-09-16 | 2005-03-24 | Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno | An acoustic testing apparatus for testing a laminate material and an acoustic testing method for testing a laminate material |
| CN102243213A (en) * | 2011-04-15 | 2011-11-16 | 中国船舶重工集团公司第七一五研究所 | Separated underwater sound pipe system |
| CN103675100A (en) * | 2013-12-20 | 2014-03-26 | 中国船舶重工集团公司第七一五研究所 | Method for measuring angular spectrum of sound transmission performance of underwater acoustic material |
| CN109001297A (en) * | 2018-06-05 | 2018-12-14 | 哈尔滨工程大学 | Large sample underwater acoustic materials acoustical reflection factor measurement method based on single vector hydrophone |
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