A broadband underwater sound absorption structure

Abstract

Provided is a water sound broadband sound absorption structure, comprising an upper layer, a base and a lower layer, a central gradient cavity and a plurality of gradient distributed peripheral cavities formed on the base, and air in the cavities. The combined structure has an average sound absorption coefficient of 0.93 in a sound frequency range of 300-10000 Hz, and an average sound absorption coefficient of 0.9 in a sound frequency range of 200-10000 Hz. The structure can improve the low-frequency sound absorption performance while taking into account the medium and high-frequency sound absorption, and has the performance of broadband (100-10000 Hz) high sound absorption.

Description

Technical Field

[0001] This invention belongs to the field of acoustics and materials, and specifically relates to a novel sound-absorbing structure in low-frequency underwater acoustic media. Background Technology

[0002] The broadband (100-10000Hz) sound absorption problem in water media urgently needs to be solved in practical engineering, and has significant research and engineering application value. Currently available literature indicates that structures and materials in this research field exhibit relatively good sound absorption performance in the mid-to-high frequency range (1000Hz-10000Hz) (sound absorption coefficient greater than 0.9), but the sound absorption coefficient is significantly lower in the low frequency range (below 1000Hz) (below 0.8), especially under the constraint of thin layers (thickness less than 50mm), where the sound absorption performance cannot meet the needs of practical engineering. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention provides a broadband underwater acoustic absorption structure, comprising an upper layer, a substrate, and a lower layer, with a central gradient cavity and multiple gradient-distributed peripheral cavities formed on the substrate, the cavities being filled with air;

[0004] The substrate is a thin sheet structure with axially symmetric upper and lower surfaces. The projections of the upper and lower surfaces onto the horizontal plane coincide. Its materials include sound-absorbing materials and elastic media.

[0005] The upper and lower layers are encapsulation layers, which completely cover the upper and lower surfaces of the substrate, respectively; among them,

[0006] The central cavity of the sound-absorbing layer comprises five coaxial frustums along the axial direction, including one upright frustum 10 and four stacked inverted frustums (201, 202, 203, 204). The axis is the central axis that runs through the upper and lower surfaces of the substrate. The four inverted frustums (201, 202, 203, 204) have the same top diameter and height, and their bottom diameters gradually increase from bottom to top. The four inverted frustums (201, 202, 203, 204) are arranged closely together without any gaps in between along the axial direction. The inverted frustum has a certain distance between its largest diameter base and the upper surface of the substrate; below the four inverted frustums (201, 202, 203, 204) is a vertical frustum 10. The top diameter of the vertical frustum 10 is the same as the top diameter of the four inverted frustums (201, 202, 203, 204), and the bottom diameter of the vertical frustum 10 is greater than the largest bottom diameter of the four inverted frustums (201, 202, 203, 204); the bottom of the vertical frustum 10 has a certain distance between it and the upper surface of the substrate.

[0007] Using the center point of the lower surface of the substrate as the center, draw five circles with radii that are five progressively larger than the base radius of the upright frustum of a cone. On each circle, evenly position 12 points, with a central angle of 30 degrees between adjacent points. Using these 12 points as centers, draw circles to form 12 smaller circles. The smaller the radius, the smaller the diameter of the smaller circle, but smaller circles with the same radius have the same diameter. From these five larger circles, draw a total of 60 smaller circles in 12 directions with the same central angle. Each central angle direction includes five smaller circles (501, 502, 503, 504, 505) with diameters gradually increasing from the inside out. Using each smaller circle as the upper surface of a circular cone, machine five circular cones from the lower surface of the substrate inwards. The height of the circular cones is less than the thickness of the substrate, and the cones are filled with air.

[0008] The central cavity of the sound-absorbing layer is surrounded by two rings of inverted cones (30, 40). The projection of the large circle of the frustum onto the lower surface of the substrate is called the projection circle. With the center point of the lower surface of the substrate as the center, 12 rays are evenly positioned on the projection circle, with a central angle of 30 degrees between adjacent rays. These 12 rays are offset by 15 degrees from the 12 points positioned on the previous 5 circles. On each ray, inside and outside the projection circle, inner and outer points are respectively set. The center of the circle formed by the 12 inner points and the circle formed by the 12 outer points is the center point of the lower surface of the substrate. With each inner and outer point as the vertex of a regular circular cone, regular circular cones are machined from the lower surface of the substrate inward, forming 12 identical inner cones 30 and 12 identical outer cones 40. The height of the inner cones 30 and the outer cones 40 is less than the thickness of the substrate, and the diameter of the bottom surface of the inner cone is less than the diameter of the bottom surface of the outer cone. The inner cones 30 and the outer cones 40 are filled with air.

[0009] Four rays are drawn outward from the center of the lower surface of the substrate, each at 90 degrees. A large circle is drawn with the center of the lower surface of the substrate as its center and the radius greater than the largest of the five circles as its radius. Four sets of frustum-cone hybrid bodies 60 are set as centers of the intersection of the large circle and the four rays. Each set of frustum-cone hybrid bodies 60 is identical, containing two upright frustums and one right circular cone. Specifically, the first upright frustum 601, the second upright frustum 602, and the third right circular cone 603 are arranged from the lower surface of the substrate to the upper surface, coaxial, and closely arranged in sequence, without gaps in the middle along their respective axes. The four sets of frustum-cone hybrid bodies form... All four sub-axises are parallel to the sound-absorbing structure axis; the base diameters of the first upright frustum 601, the second upright frustum 602, and the third circular cone 603 decrease sequentially; the top diameters of the first upright frustum 601 and the second upright frustum 602 are the same, and this top diameter is smaller than the base diameter of the third circular cone 603; the base diameter of the first upright frustum 601 is larger than the diameter of the largest of the five small circles 505 in each central angle direction; the base of the first upright frustum 601 maintains a certain distance from the lower surface of the substrate, and the vertex of the third circular cone 603 maintains a certain distance from the upper surface of the substrate; the frustum-cone hybrid 60 contains air;

[0010] With the plane formed by the axis of each frustum-cone hybrid 60 and the central axis of the base as the plane of symmetry, a pair of circular cones (701, 702) are symmetrically arranged on the left and right sides of each frustum-cone hybrid 60 near the interior of the base. The base of the circular cones (701, 702) is kept at a certain distance from the upper and lower surfaces of the base, and the vertex of the circular cones (701, 702) is kept at a certain distance from the upper surface of the base. The diameter of the base of the circular cones (701, 702) is smaller than the diameter of the largest of the five small circles 505 in each central angle direction. The height of the circular cones (701, 702) is smaller than the thickness of the base. The circular cones are filled with air.

[0011] A rectangular elastomer is applied to both the upper and lower surfaces of the substrate, with the elastomers covering the upper and lower surfaces of the substrate exactly.

[0012] In one embodiment of the present invention,

[0013] The underwater acoustic broadband sound absorption structure is a thin rectangular structure with overall dimensions of 800-1200mm in length, 800-1200mm in width, and 30-100mm in thickness.

[0014] The four inverted frustums (201, 202, 203, 204) at the center have diameters of 120-130mm, 100-110mm, 80-90mm, and 60-70mm respectively, a top diameter of 20-30mm, and a height of 6-10mm; the upright frustum 10 has a base diameter of 200-230mm, a top diameter of 20-30mm, and a height of 5-7mm.

[0015] The diameter of the bottom surface of the two rings of inverted cones (30, 40) distributed around the central cavity varies uniformly from 5 to 25 mm.

[0016] Among the four sets of frustum-cone hybrid bodies 60, the base diameters of the first upright frustum 601, the second upright frustum 602, and the third circular cone 603 are 10-15, 25-35, and 45-55 mm, respectively.

[0017] In one specific embodiment of the present invention,

[0018] The overall dimensions of the underwater acoustic broadband sound absorption structure are: length 1000mm, width 1000mm, and thickness 50mm.

[0019] The matrix material is selected as a rubber body;

[0020] The four inverted frustums (201, 202, 203, 204) at the center have diameters of 120mm, 100mm, 80mm, and 60mm respectively, a top diameter of 25mm, and a height of 8mm.

[0021] The central cavity is surrounded by two rings of inverted cones (30, 40) with a base diameter of 230 mm, a top diameter of 25 mm, and a height of 6 mm.

[0022] Among the four sets of frustum-cone hybrid bodies 60, the base diameters of the first upright frustum 601, the second upright frustum 602, and the third circular cone 603 are 15, 35, and 55 mm, respectively.

[0023] In another specific embodiment of the present invention, the upper surface of the base is a square; four sets of frustum-cone hybrid bodies 60 are located at the four corners of the square.

[0024] In another specific embodiment of the present invention, the upper and lower layers are encapsulation layers, both of which are made of a solid rubber body.

[0025] In another specific embodiment of the present invention, among the five coaxial frustums in the central cavity of the sound-absorbing layer, the distance between the bottom surface of the inverted frustum with the largest diameter and the upper surface of the substrate is 10 mm; the distance between the bottom surface of the upright frustum 10 and the upper surface of the substrate is 10 mm.

[0026] In another specific embodiment of the present invention, among the two annularly distributed inverted cones (30, 40) around the central cavity of the sound-absorbing layer, the distances from the center of the inner cone 30 and the outer cone 40 to the axis are 210 mm and 250 mm, respectively; the top diameters of the inner cone and the outer cone are 15 mm and 20 mm, respectively; and the heights of the inner cone 30 and the outer cone 40 are both 40 mm.

[0027] In another embodiment of the present invention, the axis of each group of frustum-cone hybrid bodies 60, and the axis of each of the five small cones from the inside out in the direction of each central angle, are coplanar with the central axis of the base.

[0028] In another embodiment of the present invention, the underwater acoustic broadband sound-absorbing structure is a circular thin sheet structure.

[0029] Furthermore, in one embodiment of the present invention, the working mechanism of the underwater acoustic broadband sound absorption structure is as follows, which can achieve the effect of coupling multiple sound absorption and insulation mechanisms;

[0030] First, the vibration mechanism of the variable cross-section cantilever beam: there are four variable cross-section annular wedges in the central part of the structure. These variable cross-section annular wedges can be analytically calculated to have multiple resonant frequencies. The vibration energy of the corresponding frequencies is dissipated locally at different resonant frequencies. Therefore, a broadband sound absorption effect is generated.

[0031] Second, the coupling resonance between the matrix material above the cavity and the annular wedge; resonance is an important reason for the high sound absorption coefficient. The large cover plate of the cavity and each wedge have multiple natural frequencies, and the natural frequencies are low, corresponding to multiple different resonant frequencies, thus producing a broadband sound absorption effect.

[0032] Third, the wedge is perpendicular to the axis of the frustum, which means the wedge is perpendicular to the direction of the incident longitudinal wave. Therefore, when the incident longitudinal wave interacts with the wedge, each cross section of the wedge will undergo shear deformation to varying degrees, causing the waveform of the incident longitudinal wave to be transformed into a shear transverse wave. This results in a significant loss of energy in the incident longitudinal wave, leading to a wider overall sound absorption peak of the structure.

[0033] Fourth, the gradient wedge structure with scattering, reflection, and sound absorption functions will produce multiple reflections and scattering effects on the incident sound waves. As a result of multiple reflections, the energy is gradually lost and turned into heat energy, which can improve the sound absorption coefficient.

[0034] The underwater acoustic broadband sound absorption structure of this invention has an average sound absorption coefficient of 0.93 in the 300-10000Hz sound frequency range and an average sound absorption coefficient of 0.9 in the 200-10000Hz sound frequency range. This structure can improve low-frequency sound absorption performance while also taking into account mid- and high-frequency sound absorption, thus possessing broadband (100-10000Hz) high sound absorption performance. Attached Figure Description

[0035] Figure 1 shows a schematic diagram of the low-frequency sound-absorbing structure of the present invention, wherein Figure 1(a) shows a top view, Figure 1(b) shows a side view, Figure 1(c) shows an enlarged side view, and Figure 1(d) shows a perspective view.

[0036] Figure 2 A schematic diagram of a circular sample with a central multi-layered cavity and multiple circumferentially conical sound-absorbing structures is shown. Figure 2 (a) shows a top view. Figure 2 (b) Shows a side view (the left and right views are the same). Figure 2 (c) A three-dimensional view is shown;

[0037] Figure 3 A photograph of the test specimen is shown, in which... Figure 2 (a) shows the front view, where Figure 2 (b) shows a side view;

[0038] Figure 4 A schematic diagram of a wedge-shaped variable cross-section cantilever beam is shown.

[0039] Figure 5 The diagram shows the broadband sound absorption coefficient. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings.

[0041] As shown in Figure 1(a), the low-frequency sound-absorbing structure of the present invention includes an upper layer, a substrate and a lower layer, a centrally gradient cavity and multiple peripheral cavities with gradient distribution formed on the substrate, and the cavities are filled with air.

[0042] The substrate is a thin cuboid structure made of sound-absorbing material and an elastic medium. In one specific embodiment of the invention, the upper surface of the structure is square.

[0043] The upper and lower layers are encapsulation layers, each made of solid rubber, used to encapsulate the substrate. The upper and lower layers completely cover the upper and lower surfaces of the substrate, respectively.

[0044] As shown in Figure 1(b), the central cavity of the sound-absorbing layer includes five coaxial frustums along the axial direction, including one upright frustum 10 and four stacked inverted frustums (201, 202, 203, 204), with the axial direction being the central axis passing through the upper and lower surfaces of the substrate. The top surface (i.e., the diameter of the smaller circle of the frustum) of the four inverted frustums (201, 202, 203, 204) has the same diameter and height, while the diameter of the bottom surface (i.e., the diameter of the larger circle of the frustum) gradually increases from bottom to top (the smallest diameter is 201, and the largest is 204). The four inverted frustums (201, 202, 203, 204) are arranged closely together without any gaps in the middle along the axial direction. In addition, the bottom surface of the largest diameter of the inverted frustum is kept at a certain distance from the upper surface of the substrate. In a specific embodiment of the present invention, this distance is 10 mm. Below the four inverted frustums (201, 202, 203, 204) is a standing frustum 10. The top diameter of the standing frustum 10 is the same as the top diameter of the four inverted frustums (201, 202, 203, 204), and the bottom diameter of the standing frustum 10 is larger than the maximum bottom diameter of the four inverted frustums (201, 202, 203, 204). In addition, the bottom of the standing frustum 10 is kept at a certain distance from the upper surface of the substrate. In a specific embodiment of the present invention, this distance is 10 mm.

[0045] Using the center point of the lower surface of the substrate (which, along with the center of the upright frustum 10, is on the sound-absorbing structure axis) as the center, draw five circles with radii that are five progressively larger than the base radius of the upright frustum 10. On each circle, evenly position 12 points (with a 30-degree central angle between adjacent points). Using these 12 points as the center, draw circles to form 12 smaller circles. The smaller the radius, the smaller the diameter of the smaller circle, but the diameter of the smaller circle with the same radius is equal. From these 5 large circles, 60 small circles are drawn in 12 directions with the same central angle. Each central angle direction includes 5 small circles with gradually increasing diameters from the inside out (501, 502, 503, 504, 505, with the smallest diameter being 501 and the largest being 505). Using each small circle as the upper surface of a circular cone, 5 circular cones are machined from the lower surface of the base inwards. The height of the circular cone is less than the thickness of the base (that is, the cone starts from the lower surface of the base and does not reach the upper surface of the base). The circular cone is filled with air.

[0046] The central cavity of the sound-absorbing layer is surrounded by two concentric rings of inverted cones (30°, 40°). The projection of the large circle of the frustum onto the lower surface of the substrate is called the projection circle. With the center point of the lower surface of the substrate as the center, 12 rays are evenly positioned on the projection circle (with a 30-degree central angle between adjacent rays). These 12 rays are offset by 15 degrees from the 12 points positioned on the previous 5 circles. On each ray, inside and outside the projection circle, inner and outer points are respectively set. The center of both the circle formed by the 12 inner points and the circle formed by the 12 outer points is the center point of the lower surface of the substrate. Using each inner and outer point as the apex of a circular cone, circular cones are machined from the lower surface of the base inwards, forming 12 identical inner cones 30 and 12 identical outer cones 40. The height of both the inner cones 30 and outer cones 40 is less than the thickness of the base (i.e., the cones do not reach the upper surface of the base from the lower surface), and the diameter of the bottom surface of the inner cone is smaller than the diameter of the bottom surface of the outer cone. The inner cones 30 and outer cones 40 are filled with air. In a specific embodiment of the invention, the distances from the centers of the inner cones 30 and outer cones 40 to the axis are 210 mm and 250 mm, respectively; the top diameters of the inner and outer cones are 15 mm and 20 mm, respectively; and the height of both the inner cones 30 and outer cones 40 is 40 mm.

[0047] Draw four rays outward from the center of the lower surface of the substrate, one ray every 90 degrees. Using the center of the lower surface of the substrate as the center and the radius greater than the largest of the five circles, draw a large circle. Centered on the intersection of the large circle and the four rays, set four sets of frustum-cone hybrid bodies 60. Each set of frustum-cone hybrid bodies 60 is identical, containing two upright frustums and one right circular cone. Specifically, the first upright frustum 601, the second upright frustum 602, and the third circular cone 603 are arranged from the lower surface to the upper surface of the substrate, coaxial, and arranged closely together without gaps in between along their respective axes (the four sub-axes formed by the four sets of frustum-cone hybrids are all parallel to the sound-absorbing structure axis). The base diameters of the first upright frustum 601, the second upright frustum 602, and the third circular cone 603 decrease sequentially. The top diameters of the first upright frustum 601 and the second upright frustum 602 are the same, and this top diameter is smaller than the base diameter of the third circular cone 603. The base diameter of the first upright frustum 601 is larger than the diameter of the largest of the five small circles 505 in each central angle direction. The base of the first upright frustum 601 maintains a certain distance from the lower surface of the substrate, and the apex of the third circular cone 603 maintains a certain distance from the upper surface of the substrate. The frustum-cone hybrid 60 is filled with air. In one specific embodiment of the present invention, the axis of each group of frustum-cone hybrid bodies 60, and the axes of the five small cones from the inside out in each central angle direction, are coplanar with the central axis of the base.

[0048] Using the plane formed by the axis of each frustum-conical hybrid 60 and the central axis of the base as the plane of symmetry, a pair of right circular cones (701, 702) are symmetrically arranged on the left and right sides of each frustum-conical hybrid 60 near the interior of the base. The base of the right circular cones (701, 702) maintains a certain distance from the upper and lower surfaces of the base, and the apex of the right circular cones (701, 702) maintains a certain distance from the upper surface of the base. The diameter of the base of the right circular cones (701, 702) is smaller than the diameter of the largest of the five small circles 505 in each central angle direction. The height of the right circular cones (701, 702) is less than the thickness of the base. The right circular cones are filled with air.

[0049] A rectangular elastomer is applied to both the upper and lower surfaces of the substrate, with the elastomers covering the upper and lower surfaces of the substrate exactly.

[0050] The upper and lower layers are thin rectangular bodies, whose projections on the horizontal plane completely coincide with the projections of the substrate on the horizontal plane; the upper and lower layers are respectively tightly bonded to the upper and lower surfaces of the substrate, for example, by adhesive or other means. In a specific embodiment of the invention, the upper and lower layers are made of rubber.

[0051] The low-frequency sound-absorbing structure of this invention was modeled and calculated using COMSOL software. The sample dimensions were 800-1200 mm in length, 800-1200 mm in width, and 30-100 mm in thickness. The matrix material was selected as rubber (density 1000-1200 kg / m³). 3 (Poisson's ratio 0.4-0.5, Young's modulus 1.4e8Pa, loss factor 0.2-0.3), four inverted frustums (201, 202, 203, 204) with gradually changing base diameters are stacked at the center (the base diameters of the four frustums are 120-130mm, 100-110mm, 80-90mm, and 60-70mm respectively, the top diameter is 20-30mm, and the height is 6-10mm for each). Below this is an upright frustum 10 (base... The surface diameter is 200-230mm, the top surface diameter is 20-30mm, and the height is 5-7mm. The periphery of the rubber body is a ring of right circular cones (30, 40) with gradually changing bottom diameters. The bottom diameters change uniformly from 5-25mm. Among the four sets of frustum-cone hybrid bodies 60, the bottom diameters of the first upright frustum 601, the second upright frustum 602, and the third right circular cone 603 are 10-15, 25-35, and 45-55mm, respectively. All cavities are filled with air.

[0052] In one specific embodiment of the present invention, the sample dimensions are 1000mm in length, 1000mm in width, and 50mm in thickness, and the matrix material is selected as rubber (density 1100kg / m³). 3The rubber body has a Poisson's ratio of 0.49, Young's modulus of 1.4e8Pa, and loss factor of 0.23. At the center, there are four inverted frustums (201, 202, 203, 204) with gradually changing base diameters (the base diameters of the four frustums are 120mm, 100mm, 80mm, and 60mm respectively, the top diameter is 25mm, and the height is 8mm). Below is a right frustum 10 (base diameter 230mm, top diameter 25mm, height 6mm). The periphery of the rubber body is surrounded by right circular cones (30, 40) with gradually changing base diameters, with the base diameters varying uniformly from 5 to 25mm. Among the four sets of frustum-cone hybrid bodies 60, the base diameters of the first right frustum 601, the second right frustum 602, and the third right circular cone 603 are 15, 35, and 55mm respectively. All cavities are filled with air.

[0053] Furthermore, the matrix does not necessarily have to be a thin rectangular parallelepiped structure; a circular sheet structure can be chosen, such as... Figure 2 As shown.

[0054] In fact, each large circle can have more than 12 small cones; multiple small cones can be set as needed. N points are evenly positioned on each large circle (with a central angle interval of (360 / N) degrees between adjacent points). Circles are drawn with these N points as centers, forming N small circles, and thus N small cones. Alternatively, it can be more than just 5 large circles; N large circles can be drawn as needed, each forming N small circles, as long as the dimensions allow. It is essential to ensure that the radial dimensions of the cones at each central angle gradually increase from the center of the base. After molding and vulcanization processes, a sample is prepared, such as... Figure 3 As shown. The working mechanism of the low-frequency sound-absorbing structure of the present invention is described below. The low-frequency sound-absorbing structure of the present invention can achieve the effect of coupling multiple sound absorption and insulation mechanisms based on the following mechanism.

[0055] First, the vibration mechanism of a variable cross-section cantilever beam. The test diagram shows four annular wedges in the central structure of the rubber body. From the perspective of analytical calculation of vibration dynamics, these annular wedges within the cavity can be simplified as a variable cross-section cantilever beam (see attached diagram). Figure 3 As shown in the figure, l is the length of the wedge and d is the thickness of the end. According to the Rayleigh-Ritz method (first proposed by Rayleigh in his book "Theory of Acoustics" in 1877 and later widely used in the field of acoustics), the variable cross-section wedge can be analytically calculated to have multiple resonant frequencies. The vibration energy of the corresponding frequencies is localized and dissipated at different resonant frequencies. Therefore, a broadband sound absorption effect occurs, corresponding to multiple different resonant frequencies.

[0056] Secondly, there is the coupled resonance between the matrix material above the cavity and the annular wedge. Resonance is an important reason for the high sound absorption coefficient. The large cover plate of the cavity and each wedge have multiple natural frequencies, and the natural frequencies are relatively low, corresponding to multiple different resonant frequencies, thus resulting in a broadband sound absorption effect.

[0057] Third, as can be seen from the shape in Figure 1, the wedge is perpendicular to the axis of the frustum, which means that the wedge is perpendicular to the direction of the incident longitudinal wave. Therefore, when the incident longitudinal wave interacts with the wedge, each cross section of the wedge (i.e., the annular cross section perpendicular to the upper and lower surfaces of the substrate) will undergo shear deformation to varying degrees, which will cause the waveform of the incident longitudinal wave to be transformed into a shear transverse wave, resulting in a greater energy loss of the incident longitudinal wave and a wider overall sound absorption peak of the structure.

[0058] Fourth, the functional gradient wedge structure for scattering and reflection sound absorption will produce multiple reflections and scattering effects on the incident sound waves. As a result of multiple reflections, the energy is gradually lost and turned into heat energy, which is beneficial to improving the sound absorption coefficient. The functional gradient wedge structure can integrate four typical sound absorption mechanisms into one, thus achieving a broadband sound absorption effect.

[0059] Based on the commercial software COMSOL, simulation calculations were performed on the combined structure of the rubber body and steel plate. Figure 4 This is a graph showing the sound absorption coefficient of the structure in the 100-10000Hz frequency range under underwater acoustic background. As can be seen from the graph, in the 300-10000Hz sound frequency range, the average sound absorption coefficient is 0.93, the maximum value is 0.97, and the minimum value is 0.84; in the 200-10000Hz sound frequency range, the maximum value is 0.97, the minimum value is 0.84, and the average sound absorption coefficient is 0.9, which shows a good high sound absorption coefficient over a wide frequency range.

Claims

1. A broadband underwater acoustic absorption structure, comprising an upper layer, a substrate, and a lower layer, wherein a centrally graded cavity and multiple gradedly distributed peripheral cavities are formed on the substrate, and the cavities are filled with air; The substrate is a thin sheet structure with axially symmetric upper and lower surfaces. The projections of the upper and lower surfaces onto the horizontal plane coincide. Its materials include sound-absorbing materials and elastic media. The upper and lower layers are encapsulation layers, which completely cover the upper and lower surfaces of the substrate, respectively. Its features are, The central cavity of the sound-absorbing layer includes five coaxial frustums along the axial direction, including one upright frustum (10) and four stacked inverted frustums (201, 202, 203, 204), with the axis being the central axis running through the upper and lower surfaces of the substrate; the top diameter and height of the four inverted frustums (201, 202, 203, 204) are the same, and the bottom diameter gradually increases from bottom to top. The four inverted frustums (201, 202, 203, 204) are arranged closely in sequence without any gaps in the middle along the axial direction; The base of the frustum with the largest diameter is kept at a certain distance from the upper surface of the substrate; below the four inverted frustums (201, 202, 203, 204) is a standing frustum (10), the top diameter of the standing frustum (10) is the same as the top diameter of the four inverted frustums (201, 202, 203, 204), and the bottom diameter of the standing frustum (10) is greater than the maximum bottom diameter of the four inverted frustums (201, 202, 203, 204); the bottom of the standing frustum (10) is kept at a certain distance from the upper surface of the substrate. Using the center point of the lower surface of the substrate as the center, draw 5 circles with 5 gradually increasing values ​​greater than the radius of the bottom surface of the upright frustum (10). On each circle, 12 points are evenly positioned, with a central angle of 30 degrees between adjacent points. Using these 12 points as the center, draw circles to form 12 small circles. The smaller the radius, the smaller the diameter of the small circle, but the diameter of the small circle with the same radius is equal. Thus, 60 small circles are drawn in 12 directions with the same central angle on the 5 large circles. Each central angle direction includes 5 small circles (501, 502, 503, 504, 505) with the diameter gradually increasing from the inside to the outside. Using each small circle as the upper surface of the circular cone, process 5 circular cones from the lower surface of the substrate inward. The height of the circular cone is less than the thickness of the substrate, and the inside of the circular cone is air. The central cavity of the sound-absorbing layer is surrounded by two rings of inverted cones (30, 40). The projection of the large circle of the frustum onto the lower surface of the substrate is called the projection circle. With the center point of the lower surface of the substrate as the center, 12 rays are evenly positioned on the projection circle, with a central angle of 30 degrees between adjacent rays. These 12 rays are offset by 15 degrees from the 12 points positioned on the previous 5 circles. Inner points and outer points are set on each ray, inside and outside the projection circle, respectively. The circle formed by the 12 inner points... The circles formed by the 12 outer points are all centered on the center point of the lower surface of the base. Using each inner and outer point as the vertex of a circular cone, circular cones are machined from the lower surface of the base inward to form 12 identical inner cones (30) and 12 identical outer cones (40). The height of both the inner cones (30) and the outer cones (40) is less than the thickness of the base, and the diameter of the bottom surface of the inner cone is less than the diameter of the bottom surface of the outer cone. The inner cones (30) and the outer cones (40) are filled with air. Draw four rays outward from the center of the lower surface of the substrate, one ray every 90 degrees. Draw a large circle with the center of the lower surface of the substrate as the center and the radius greater than the largest of the five circles as the radius. Set four sets of frustum-cone hybrid bodies (60) as the center, each set of frustum-cone hybrid bodies (60) is the same, each containing two upright frustums and one right circular cone. Specifically, the first upright frustum (601), the second upright frustum (602), and the third right circular cone (603) are arranged from the lower surface of the substrate to the upper surface, coaxial, and arranged closely in sequence, without gaps in the middle along their respective axes. The four sets of frustum-cone hybrid bodies form a total of four rays. The axes are all parallel to the sound-absorbing structure axis; the base diameters of the first upright truncated cone (601), the second upright truncated cone (602), and the third circular cone (603) decrease sequentially; the top diameters of the first upright truncated cone (601) and the second upright truncated cone (602) are the same, and the top diameter is smaller than the base diameter of the third circular cone (603); the base diameter of the first upright truncated cone (601) is larger than the diameter of the smallest of the five small circles (505) in each central angle direction; the base of the first upright truncated cone (601) maintains a certain distance from the lower surface of the substrate, and the vertex of the third circular cone (603) maintains a certain distance from the upper surface of the substrate; the truncated cone-cone mixture (60) contains air; Using the plane formed by the axis of each frustum-cone hybrid (60) and the central axis of the base as the plane of symmetry, a pair of circular cones (701, 702) are symmetrically arranged on the left and right sides of each frustum-cone hybrid (60) near the interior of the base. The base of the circular cones (701, 702) is kept at a certain distance from the upper and lower surfaces of the base, and the vertex of the circular cones (701, 702) is kept at a certain distance from the upper surface of the base. The diameter of the base of the circular cones (701, 702) is smaller than the diameter of the smallest of the five small circles (505) in each central angle direction. The height of the circular cones (701, 702) is smaller than the thickness of the base. The circular cones are filled with air. A rectangular elastomer is applied to both the upper and lower surfaces of the substrate, with the elastomers covering the upper and lower surfaces of the substrate exactly.

2. The underwater acoustic broadband sound absorption structure as described in claim 1, characterized in that, The underwater acoustic broadband sound absorption structure is a thin rectangular structure with overall dimensions of 800-1200mm in length, 800-1200mm in width, and 30-100mm in thickness. The four inverted frustums (201, 202, 203, 204) at the center have diameters of 120-130mm, 100-110mm, 80-90mm, and 60-70mm respectively, a top diameter of 20-30mm, and a height of 6-10mm; the upright frustum (10) has a bottom diameter of 200-230mm, a top diameter of 20-30mm, and a height of 5-7mm. The diameter of the bottom surface of the two rings of inverted cones (30, 40) distributed around the central cavity varies uniformly from 5 to 25 mm. Among the four sets of frustum-cone hybrid bodies (60), the base diameters of the first upright frustum (601), the second upright frustum (602), and the third circular cone (603) are 10-15, 25-35, and 45-55 mm, respectively.

3. The underwater acoustic broadband sound absorption structure as described in claim 2, characterized in that, The overall dimensions of the underwater acoustic broadband sound absorption structure are: length 1000mm, width 1000mm, and thickness 50mm. The matrix material is selected as a rubber body; The four inverted frustums (201, 202, 203, 204) at the center have diameters of 120mm, 100mm, 80mm, and 60mm respectively, a top diameter of 25mm, and a height of 8mm. The central cavity is surrounded by two rings of inverted cones (30, 40) with a base diameter of 230 mm, a top diameter of 25 mm, and a height of 6 mm. Among the four sets of frustum-cone hybrid bodies (60), the diameters of the base surfaces of the first upright frustum (601), the second upright frustum (602), and the third upright cone (603) are 15, 35, and 55 mm, respectively.

4. The underwater broadband sound absorbing structure of claim 2, wherein, The upper surface of the substrate is a square; four sets of frustum-cone hybrid bodies (60) are located at the four corners of the square.

5. The underwater acoustic broadband sound absorption structure as described in claim 1, characterized in that, The upper and lower layers are encapsulation layers, both made of a solid rubber body.

6. The underwater acoustic broadband sound absorption structure as described in claim 1, characterized in that, Among the five coaxial frustums in the central cavity of the sound-absorbing layer, the inverted frustum has a bottom surface with the largest diameter that is 10 mm away from the upper surface of the substrate; the upright frustum (10) has a bottom surface that is 10 mm away from the upper surface of the substrate.

7. The underwater acoustic broadband sound-absorbing structure as described in claim 1, characterized in that, The two rings of inverted cones (30, 40) surrounding the central cavity of the sound-absorbing layer have the following distances from the center of the inner cone (30) to the axis: 210 mm and 250 mm, respectively; the top diameters of the inner cone (30) and the outer cone (40) are 15 mm and 20 mm, respectively; and the heights of the inner cone (30) and the outer cone (40) are both 40 mm.

8. The underwater acoustic broadband sound absorption structure as described in claim 1, characterized in that, The axis of each group of frustum-cone hybrid bodies (60), and the axis of the five small cones from the inside out in the direction of each central angle, are coplanar with the central axis of the base.

9. The underwater acoustic broadband sound absorption structure as described in claim 1, characterized in that, The underwater acoustic broadband sound-absorbing structure is a circular thin sheet structure.

10. The underwater acoustic broadband sound-absorbing structure as described in claim 1, characterized in that, The working mechanism of this structure is as follows, which can achieve the effect of coupling multiple sound absorption and insulation mechanisms; First, the vibration mechanism of the variable cross-section cantilever beam: there are four variable cross-section annular wedges in the central part of the structure. These variable cross-section annular wedges can be analytically calculated to have multiple resonant frequencies. The vibration energy of the corresponding frequencies is dissipated locally at different resonant frequencies. Therefore, a broadband sound absorption effect is generated. Second, the coupling resonance between the matrix material above the cavity and the annular wedge; resonance is an important reason for the high sound absorption coefficient. The large cover plate of the cavity and each wedge have multiple natural frequencies, and the natural frequencies are low, corresponding to multiple different resonant frequencies, thus producing a broadband sound absorption effect. Third, the wedge is perpendicular to the axis of the frustum, which means the wedge is perpendicular to the direction of the incident longitudinal wave. Therefore, when the incident longitudinal wave interacts with the wedge, each cross section of the wedge will undergo shear deformation to varying degrees, causing the waveform of the incident longitudinal wave to be transformed into a shear transverse wave. This results in a significant loss of energy in the incident longitudinal wave, leading to a wider overall sound absorption peak of the structure. Fourth, the gradient wedge structure with scattering, reflection, and sound absorption functions will produce multiple reflections and scattering effects on the incident sound waves. As a result of multiple reflections, the energy is gradually lost and turned into heat energy, which can improve the sound absorption coefficient.

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