Multi-unit combined underwater sound absorption structure for realizing underwater low-frequency broadband sound absorption

Abstract

The invention provides a multi-unit combined type underwater sound absorption structure for realizing underwater low-frequency broadband sound absorption. The underwater sound absorption structure comprises a combined body formed by connecting a plurality of units with different sizes and a rubber matrix material, each unit is wrapped by a layer of aluminum alloy frame (4), the units are filled with rubber parts (3), cylindrical cavities (2) with different sizes are formed in the rubber parts, each unit is fixed to a steel backing (1) at the bottom of the underwater sound absorption structure in a bonding mode, and the top of the underwater sound absorption structure is connected with an external water area (5). Gaps among the units are filled with rubber parts to form separation structures for separating the units, and the underwater low-frequency and broadband sound absorption performance of the multi-unit combined underwater sound absorption structure is adjusted by adjusting the size of an inner cavity of each unit; according to the invention, the underwater sound absorption performance at a low frequency of less than 1kHz and at a medium-high frequency band of 1kHz-10kHz can be realized.

Description

Technical Field

[0001] The invention relates to the field of acoustic technology, in particular to a multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption. Background Art

[0002] Because seawater has a strong absorption capacity for electromagnetic waves, and sound has a better ability to resist attenuation underwater, underwater acoustic technology is often used for underwater detection. For submarines, a series of vibration reduction and noise reduction measures are often used to avoid sonar detection. One of the methods is to add a layer of acoustic structure on the surface of the submarine to absorb the detection sound waves emitted by the sonar and reduce the probability of being discovered. This layer of acoustic structure is called an acoustic cover.

[0003] Acoustic covering layers were first used on German submarines during World War II. At that time, the acoustic covering layer was to add some periodic cavities of different sizes inside viscoelastic materials such as rubber, which was called an "Alberich" type structure. Later, people also conducted many studies and experimental verifications on the "Alberich" type cavity structure, but the previous sonar operating frequency was mostly between 1kHz and 10kHz, because many underwater sound absorption structure studies were also conducted for 1kHz-10kHz. With the development of modern sonar technology, the US Navy has begun to use low-frequency sonar of 100-500Hz for detection, which has led to many previous studies that can no longer meet practical requirements. In recent years, many low-frequency underwater sound absorption structures below 1kHz have emerged, but the effective sound absorption (sound absorption coefficient>0.8) frequency band of many structures is relatively narrow, only tens or hundreds of Hz, and it is impossible to achieve effective sound absorption in the full frequency band of 1kHz-10kHz. Therefore, it is of great significance to study an underwater sound absorption structure that can achieve low frequencies below 1kHz and take into account the mid- and high-frequency bands of 1kHz-10kHz. Summary of the invention

[0004] The present invention proposes a multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption, which can realize underwater sound absorption performance in low frequencies below 1 kHz as well as in medium and high frequency bands of 1 kHz-10 kHz.

[0005] The present invention adopts the following technical solutions.

[0006] A multi-unit combined underwater sound absorbing structure for achieving underwater low-frequency broadband sound absorption, the underwater sound absorbing structure comprising a combination of multiple units of different sizes and a rubber matrix material; each unit is wrapped by a layer of aluminum alloy frame (4), the interior of the unit is filled with rubber parts (3), the interior of the rubber parts contains cylindrical cavities (2) of different sizes, each unit is fixed on a steel backing (1) at the bottom of the underwater sound absorbing structure by bonding, and the top of the underwater sound absorbing structure is connected to an external water area (5); the gaps between the units are filled with rubber parts to form a separation structure that separates the units, and the underwater low-frequency and broadband sound absorption performance of the multi-unit combined underwater sound absorbing structure is adjusted by adjusting the size of the cavity inside each unit.

[0007] The combination is an absorption layer for sound absorption; the aluminum alloy frame is used to enhance the vibration and power consumption of the cavity of each unit, thereby improving the structural sound absorption coefficient.

[0008] When the underwater sound absorption calculation model of the underwater sound absorption structure is constructed using COMSOL Multiphysics; the pressure acoustics module is used in the air domain of the cavity and the external water area; the solid mechanics module is used in the rubber parts, aluminum alloy frames and backing steel plates.

[0009] If multiple units need to be arranged periodically in the underwater sound-absorbing structure, radial constraints are added outside the solid domain of the underwater sound-absorbing structure to make its normal displacement zero.

[0010] Let h1 be the thickness of the backing; h2 be the thickness of the absorption layer; h k is the cavity height, d is the cavity diameter, D is the unit diameter, and t is the frame thickness;

[0011] When constructing the underwater sound absorption calculation model, the background pressure field is used to define the vertical incidence of the plane wave on the water area, and the sound pressure amplitude is p i =1Pa, plane wave radiation is used at the top of the water area to simulate infinite water area;

[0012] The reflected sound pressure at the top of water area 5 is calculated by integral calculation and is set as p r , then the reflection coefficient R and the sound absorption coefficient α are calculated as

[0013]

[0014] α=1-(R 2 ).

[0015] The underwater sound-absorbing structure improves the sound absorption coefficient by enhancing vibration loss and heat loss. In the range of 458Hz-10kHz, the sound absorption coefficient of the underwater sound-absorbing structure is greater than 0.8.

[0016] The underwater sound-absorbing structure increases the sound absorption coefficient of frequencies above 1000Hz by increasing the thickness of the aluminum alloy frame.

[0017] When the cavity height or radius of the underwater sound-absorbing structure increases, its low-frequency sound absorption performance improves.

[0018] When the unit diameter D of the absorption layer increases, the sound absorption coefficient of the underwater sound absorbing structure in the frequency range above 2000 Hz is improved.

[0019] The rubber parts are square rubber areas in the underwater sound absorbing structure, which form a multi-unit structure in the underwater sound absorbing structure and are arranged in an axisymmetric manner.

[0020] The present invention can achieve underwater sound absorption in low frequencies below 1 kHz and in the mid- and high-frequency bands of 1 kHz-10 kHz.

[0021] Compared with the traditional cavity structure, the structure of the solution of the present invention has the following advantages:

[0022] 1. The structure of the solution described in the present invention designs an aluminum alloy frame of a certain thickness outside the cavity, which can improve its vibration and power consumption compared with the traditional structure, thereby improving the structural sound absorption coefficient.

[0023] 2. The structure of the solution described in the present invention combines each unit into a cylinder with a diameter of 298 mm and a height of 40 mm by carefully setting the size of each unit. This increases the design variables and the adjustment range of the sound absorption coefficient. The final designed combined structure can achieve a sound absorption coefficient of more than 0.8 at 458Hz-10kHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0025] Attached Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0026] Attached Figure 2 It is a schematic diagram of a structural finite element model of a unit containing an aluminum alloy frame;

[0027] Attached Figure 3 1. It is a schematic diagram comparing the sound absorption coefficients of the structure containing the aluminum alloy frame of the present invention and the Alberich configuration of the conventional technology;

[0028] Attached Figure 4The structure of the aluminum alloy frame of the present invention and the Alberich configuration of the conventional technology show different frequency vibration displacements and power consumption densities (parts (a)-(f) show different frequency power consumption densities and vibration displacements of the Alberich configuration; parts (g)-(l) show different frequency power consumption densities and vibration displacements of the structure of the aluminum alloy frame of the present invention);

[0029] Attached Figure 5 It is a schematic diagram of the effect of the thickness of the aluminum alloy frame on the sound absorption coefficient in the present invention;

[0030] Attached Figure 6 Schematic diagram of the effect of cavity height on sound absorption coefficient of the present invention;

[0031] Attached Figure 7 Schematic diagram of the effect of cavity radius on sound absorption coefficient of the present invention;

[0032] Attached Figure 8 Schematic diagram of the effect of the absorption layer height on the sound absorption coefficient of the present invention;

[0033] Attached Fig. 9 Schematic diagram showing the effect of the diameter of the absorption layer on the sound absorption coefficient of the present invention;

[0034] Attached Fig.10 is a two-dimensional schematic diagram of a multi-unit structure of the present invention;

[0035] Attached Fig.11 Schematic diagram of the sound absorption coefficient of the multi-unit structure of the present invention;

[0036] Attached Fig.12 This is a schematic diagram showing the effect of adjusting the height of the rubber layer on the sound absorption coefficient;

[0037] Attached Fig.13 It is a schematic diagram showing the effect of adjusting the thickness of the metal frame on the sound absorption coefficient;

[0038] Attached Fig.14 It is a schematic diagram showing the effect of adjusting the frame material on the sound absorption coefficient;

[0039] In the figure: 1-backing; 2-cavity; 3-rubber part; 4-aluminum alloy frame; 5-water area. DETAILED DESCRIPTION

[0040] As shown in the figure, a multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption comprises a combination formed by connecting a plurality of units of different sizes and a rubber matrix material; each unit is wrapped by a layer of aluminum alloy frame 4, and the interior of the unit is filled with rubber parts 3, and the interior of the rubber parts contains cylindrical cavities 2 of different sizes, each unit is fixed on a steel backing 1 at the bottom of the underwater sound absorbing structure by bonding, and the top of the underwater sound absorbing structure is connected to the external water area 5; the gaps between the units are filled with rubber parts to form a partition structure separating the units, and the underwater low-frequency and broadband sound absorption performance of the multi-unit combined underwater sound absorbing structure is adjusted by adjusting the size of the cavity inside each unit.

[0041] The combination is an absorption layer for sound absorption; the aluminum alloy frame is used to enhance the vibration and power consumption of the cavity of each unit, thereby improving the structural sound absorption coefficient.

[0042] When the underwater sound absorption calculation model of the underwater sound absorption structure is constructed using COMSOL Multiphysics; the pressure acoustics module is used in the air domain of the cavity and the external water area; the solid mechanics module is used in the rubber parts, aluminum alloy frames and backing steel plates.

[0043] If multiple units need to be arranged periodically in the underwater sound-absorbing structure, radial constraints are added outside the solid domain of the underwater sound-absorbing structure to make its normal displacement zero.

[0044] Let h1 be the thickness of the backing; h2 be the thickness of the absorption layer; h k is the cavity height, d is the cavity diameter, D is the unit diameter, and t is the frame thickness;

[0045] When constructing the underwater sound absorption calculation model, the background pressure field is used to define the vertical incidence of the plane wave on the water area, and the sound pressure amplitude is p i =1Pa, plane wave radiation is used at the top of the water area to simulate infinite water area;

[0046] The reflected sound pressure at the top of water area 5 is calculated by integral calculation and is set as p r , then the reflection coefficient R and the sound absorption coefficient α are calculated as

[0047]

[0048] α=1-(R 2 ).

[0049] The underwater sound-absorbing structure improves the sound absorption coefficient by enhancing vibration loss and heat loss. In the range of 458Hz-10kHz, the sound absorption coefficient of the underwater sound-absorbing structure is greater than 0.8.

[0050] The underwater sound-absorbing structure increases the sound absorption coefficient of frequencies above 1000Hz by increasing the thickness of the aluminum alloy frame.

[0051] When the cavity height or radius of the underwater sound-absorbing structure increases, its low-frequency sound absorption performance improves.

[0052] When the unit diameter D of the absorption layer increases, the sound absorption coefficient of the underwater sound absorbing structure in the frequency range above 2000 Hz is improved.

[0053] The rubber parts are square rubber areas in the underwater sound absorbing structure, which form a multi-unit structure in the underwater sound absorbing structure and are arranged in an axisymmetric manner.

[0054] Embodiment 1:

[0055] This example proposes a combined structure with multiple units of different sizes. The square rubber area has an axisymmetric arrangement. Each unit in this example has a fixed position and cannot be changed. The final two-dimensional view of the structure of the multi-unit combination obtained after adjusting and optimizing the structural parameters is shown in the figure. Fig.10 Shown:

[0056] The specific structural parameters in the figure are as follows: H1 is the total height of the structure 70mm, H2 is the height of the absorption layer 40mm, the outer diameter of the structure D1 is 298mm, the inner diameter of the outer circle of the aluminum alloy D2 is 278mm, the width of W1 is 27mm, the width of W2 is 35mm, the remaining cube frames close to the edge have the same size as W1 or W2, the width of W3 is 65mm, the width of W4 is 55mm, the nine cube frame areas in the middle are located at four right angles and have the same size, and the remaining five have the same size, the thickness t of the aluminum alloy frame is 2.5mm, L1~L4 are positioning sizes, L1=64mm, L2=64mm, L3=36mm, L4=51mm.

[0057] The heights of different cavities are different. The diameter of cavity d1 is 14mm and the height is 5mm. The diameter of cavity d2 is 20mm and the height is 5mm. The other cylindrical cavities located in the edge cube frame have the same diameter and height as d1 or d2. The diameter of cavity d3 is 36mm and the height is 10mm. The diameter of cavity d4 is 20mm and the height is 5mm. The diameter of cavity d5 is 36mm and the height is 5mm. The diameter of cavity d6 is 20mm and the height is 5mm. The diameter of cavity d7 is 5mm and the height is 15mm. The diameter of cavity d8 is 20mm and the height is 15mm. The diameter of cavity d9 is 50mm and the height is 15mm. The diameter of cavity d10 is 12mm and the height is 5mm. The diameter of cavity d11 is 35mm and the height is 10mm.

[0058] In this example, the material parameters used for each part are: rubber density 1100kg / m^3, Young's modulus 10MPa, Poisson's ratio 0.49, isotropic loss factor 0.3; structural steel density 7850kg / m^3, Young's modulus 210GPa, Poisson's ratio 0.3; aluminum alloy density 2700kg / m^3, Young's modulus 70GPa, Poisson's ratio 0.33; water density is 1000kg / m^3, sound speed is 1500m / s; plastic density 1190kg / m^3, Young's modulus 3.2GPa, Poisson's ratio 0.35.

[0059] Establish the basic unit structure finite element model such as Figure 2 As shown:

[0060] The simulation results of the sound absorption coefficient of the multi-unit structure are as follows: Fig.11 As shown, the final structure can achieve a low-frequency broadband sound absorption effect with a sound absorption coefficient of more than 0.8 from 458Hz to 10kHz.

[0061] Condition 1 of this example: Under the premise of keeping the cavity size unchanged, the height of the rubber layer is changed, and its influence on the sound absorption coefficient is as follows Fig.12 As shown in the figure, according to the calculation results, increasing the height of the rubber layer increases the sound absorption below 3000 Hz and decreases the sound absorption above 3000 Hz.

[0062] Condition 2 of this example: Changing the thickness C of the metal frame has the following effects on sound absorption: Fig.13 As shown in the figure, according to the calculation results, increasing the frame thickness is beneficial to improving the sound absorption coefficient in the frequency band above 2000 Hz, but it will cause the structural density to be too high.

[0063] Condition 3 of this example: Changing the frame material to plastic, aluminum alloy, and structural steel, respectively, and its effect on sound absorption is as follows: Fig.14 As shown, according to the calculation results, the sound absorption coefficients of aluminum alloy and structural steel are almost the same, and the overall sound absorption performance of plastic frame is reduced.

[0064] Embodiment 2:

[0065] First, the sound absorption coefficient of the unit structure with aluminum alloy frame is compared with that of the Alberich configuration with the same size. The basic parameters are h1 = 30 mm, h2 = 50 mm, h k =40mm, d=40mm, D=50mm, t=3mm, the calculation results of sound absorption coefficient are compared. Figure 3 As shown in the figure, it can be found that the sound absorption coefficient of this structure can be improved more than that of the Alberich structure in the full frequency band. The mechanism of improving the sound absorption coefficient can be explained by vibration loss and heat loss. Therefore, the power consumption cloud diagram and vibration displacement of the two structures at the same frequency are calculated and compared. Figure 4 shown.

[0066] By comparing the vibration displacement and power consumption density of the two structures at the same frequency, it can be found that the vibration displacement and power consumption density of the designed unit structure with an aluminum alloy frame are higher than those of the Alberich configuration at the same frequency. Therefore, the overall sound absorption coefficient of the unit with an aluminum alloy frame is improved.

[0067] Next, we test the effect of various unit structure parameters on the sound absorption coefficient. First, we examine the effect of the width t of the aluminum alloy frame on the sound absorption coefficient. Figure 5 As shown, it can be found that increasing the frame thickness has little effect on the first absorption peak, but increasing the thickness is beneficial to increasing the sound absorption coefficient at frequencies above 1000 Hz.

[0068] Test cavity height h k The influence of sound absorption coefficient on Figure 6 As shown, it can be found that the increase in cavity height is beneficial to the movement of the first absorption peak frequency toward low frequency, improving the low-frequency sound absorption performance, but the sound absorption coefficient after the first peak will decrease.

[0069] The effect of the test cavity diameter d on the sound absorption coefficient is as follows Figure 7 As shown, it can be found that the increase in the cavity radius is also beneficial to the first absorption peak frequency moving toward low frequency, improving the low-frequency sound absorption performance, but the sound absorption coefficient after the first peak will also decrease.

[0070] The influence of the test absorption layer height h2 on the sound absorption coefficient is as follows Figure 8 As shown, it can be found that as the height of the absorption layer increases, the first absorption peak decreases and moves toward high frequency, but the sound absorption coefficient after the first absorption peak increases.

[0071] The influence of the diameter D of the test absorption layer on the sound absorption coefficient is as follows Fig. 9 As shown, increasing or decreasing the diameter D of the absorption layer has little effect on the first absorption peak, and increasing the diameter D of the absorption layer is beneficial to improving the sound absorption coefficient in the frequency band above 2000 Hz.

Claims

1. A multi-unit combined underwater sound absorbing structure for achieving underwater low-frequency broadband sound absorption, characterized in that: The underwater sound absorbing structure comprises a combination formed by connecting a plurality of units of different sizes and a rubber matrix material; each unit is wrapped by a layer of aluminum alloy frame (4), the interior of the unit is filled with rubber parts (3), the interior of the rubber parts contains cylindrical cavities (2) of different sizes, each unit is fixed on a steel backing (1) at the bottom of the underwater sound absorbing structure by bonding, and the top of the underwater sound absorbing structure is connected to the external water area (5); the gaps between the units are filled with rubber parts to form a separation structure separating the units, and the underwater low-frequency and broadband sound absorption performance of the multi-unit combined underwater sound absorbing structure is adjusted by adjusting the size of the cavity inside each unit.

2. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 1, characterized in that: The combination is an absorption layer for sound absorption; the aluminum alloy frame is used to enhance the vibration and power consumption of the cavity of each unit, thereby improving the structural sound absorption coefficient.

3. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 2, characterized in that: When the underwater sound absorption calculation model of the underwater sound absorption structure is constructed using COMSOL Multiphysics; the pressure acoustics module is used in the air domain of the cavity and the external water area; the solid mechanics module is used in the rubber parts, aluminum alloy frames and backing steel plates.

4. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 3, characterized in that: If multiple units need to be arranged periodically in the underwater sound-absorbing structure, radial constraints are added outside the solid domain of the underwater sound-absorbing structure to make its normal displacement zero.

5. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 4, characterized in that: Let h1 be the thickness of the backing; h2 be the thickness of the absorption layer; h k is the cavity height, d is the cavity diameter, D is the unit diameter, and t is the frame thickness; When constructing the underwater sound absorption calculation model, the background pressure field is used to define the vertical incidence of the plane wave on the water area, and the sound pressure amplitude is p i =1Pa, plane wave radiation is used at the top of the water area to simulate infinite water area; The reflected sound pressure at the top of water area 5 is calculated by integral calculation and is set as p r , then the reflection coefficient R and the sound absorption coefficient α are calculated as α＝1-(R 2 )。 6. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 5, characterized in that: The underwater sound-absorbing structure improves the sound absorption coefficient by enhancing vibration loss and heat loss. In the range of 458Hz-10kHz, the sound absorption coefficient of the underwater sound-absorbing structure is greater than 0.

8.

7. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 7, characterized in that: The underwater sound-absorbing structure increases the sound absorption coefficient of frequencies above 1000Hz by increasing the thickness of the aluminum alloy frame.

8. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 7, characterized in that: When the cavity height or radius of the underwater sound-absorbing structure increases, its low-frequency sound absorption performance improves.

9. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 7, characterized in that: When the unit diameter D of the absorption layer increases, the sound absorption coefficient of the underwater sound absorbing structure in the frequency range above 2000 Hz is improved.

10. The multi-unit combined underwater sound absorbing structure for realizing underwater low-frequency broadband sound absorption according to claim 5, characterized in that: The rubber parts are square rubber areas in the underwater sound absorbing structure, which form a multi-unit structure in the underwater sound absorbing structure and are arranged in an axisymmetric manner.

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