Tree-branch-like multilayer fractal superstructure with sound absorption and load bearing

Abstract

The application discloses a tree-branch-imitating multi-layer fractal superstructure with sound absorption and load bearing, and belongs to the technical field of acoustic supermaterials and multifunctional load bearing structures. The superstructure is composed of a plurality of unit cell arrays, and each unit cell comprises an upper micro-perforated panel, a middle micro-perforated panel, a lower panel and an internal tree-branch-imitating fractal partition. The middle micro-perforated panel divides the inner cavity of the unit cell into an upper back cavity and a lower back cavity. The tree-branch-imitating fractal partition is arranged in a hierarchical bifurcation and is centrally symmetrical, and divides the upper back cavity and / or the lower back cavity into a plurality of sub-cavities. Micro-holes are formed in the upper micro-perforated panel and the middle micro-perforated panel, so that each sub-cavity is in communication with an external sound field. The hierarchical bifurcation of the tree-branch-imitating fractal and the multi-layer series cavity coupling form a multi-order fractal Helmholtz resonance and micro-perforated panel thermal viscous loss composite sound absorption system, and wideband high-efficiency sound absorption is realized in a frequency range of 375 Hz to 1600 Hz. Meanwhile, the tree-branch-imitating fractal partition and each panel form a continuous force transmission skeleton, and the structural stiffness, load bearing capacity and buckling resistance are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of acoustic metamaterials and multifunctional load-bearing structures. Specifically, it relates to a dendritic multilayer fractal metastructure that combines low-frequency broadband sound absorption with high-efficiency mechanical load-bearing capacity. It is mainly applicable to engineering scenarios with clear requirements for lightweight structure, noise reduction and load-bearing integration, such as rail transit, aerospace, building interiors and equipment cabins. Background Technology

[0002] With the development of lightweight and integrated modern equipment, the integration of noise control and structural load-bearing function has become a key technological direction. The traditional separate design of "load-bearing main body + additional sound-absorbing components" generally suffers from problems such as redundant thickness, complex assembly, poor interface stability, and high maintenance costs, making it difficult to meet the high-performance requirements of high-end equipment and buildings.

[0003] Acoustic metamaterials have shown significant advantages in low-frequency noise reduction due to their ability to flexibly control sound waves through subwavelength structures. However, most existing acoustic metamaterials are designed with optimal acoustic performance as the sole objective, and generally employ high porosity, thin walls, and weakly connected resonant units. This results in low structural stiffness, easy buckling, and poor load-bearing capacity, making them unable to withstand the mechanical loads in actual service and severely limiting their engineering applications.

[0004] There is an inherent contradiction between sound absorption and load-bearing capacity: sound absorption relies on cavities, micropores, and resonant channels to dissipate sound energy, while load-bearing capacity depends on continuous force transmission paths, effective load-bearing cross sections, and buckling-resistant topologies. How to achieve synergistic optimization of sound absorption and mechanical properties within the same structure is the core technological bottleneck currently hindering the practical application of acoustic metamaterials.

[0005] Fractal structures possess multi-scale self-similarity characteristics, which can broaden the sound absorption frequency band through multi-level resonance; dendritic bionic bifurcation structures naturally possess mechanical advantages such as multi-path force transmission, stress dispersion, and suppression of overall buckling. Combining bionic fractal topology with the sound absorption mechanism of micro-perforated plates is expected to optimize the structural force transmission skeleton while constructing rich sound absorption resonance modes, thereby achieving an integrated design of sound absorption and load-bearing. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a biomimetic tree-like multi-layer fractal superstructure that combines sound absorption and load-bearing capacity. Through the biomimetic tree-like hierarchical branching structure, the coupling effect of multi-layer series cavities and micro-perforated plates, it achieves synergistic optimization of low-frequency broadband high-efficiency sound absorption with high stiffness, high load-bearing capacity, high specific energy absorption, and buckling resistance.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A multi-layered fractal superstructure with both sound absorption and load-bearing properties, the superstructure is composed of several unit cell arrays; each unit cell includes: an upper micro-perforated plate, a middle micro-perforated plate, a lower plate, and an internal fractal partition with tree-like structure; the middle micro-perforated plate is located below the upper micro-perforated plate and divides the inner cavity of the unit cell into an upper back cavity and a lower back cavity; the lower plate is located below the middle micro-perforated plate and serves as a bottom-closed support plate; the fractal partition with tree-like structure is located between the upper micro-perforated plate and the lower plate, arranged in a hierarchical and symmetrical manner, and divides the upper back cavity and / or the lower back cavity into multiple sub-cavities; micropores are formed on both the upper and middle micro-perforated plates to allow each sub-cavity to communicate with the external sound field; the fractal partition with tree-like structure, the upper micro-perforated plate, the middle micro-perforated plate, and the lower plate together constitute a continuous force-transmitting skeleton.

[0009] To optimize the above technical solution, the specific measures also include:

[0010] The aforementioned tree-like fractal partitions are classified into 0th, 1st, and 2nd order tree-like fractal structures (TFS) according to their branching order. After introducing a central micro-perforated plate for layering, corresponding 0th, 1st, and 2nd order tree-like multilayer fractal structures (MTFS) are formed.

[0011] The thickness of the aforementioned fractal partition resembling a tree branch is 0.5mm to 2mm, and its branch length gradually decreases as the number of branching stages increases.

[0012] The aperture of the upper micro-perforated plate is 0.4mm to 1mm, and the aperture of the middle micro-perforated plate is 0.7mm to 1mm.

[0013] The perforations of the upper micro-perforated plate are close to the fractal partitions of the simulated tree branch, and avoid the concave corners and edges of the unit cells; the perforations of the middle micro-perforated plate are arranged in concentric rings and angular positioning.

[0014] The outer diameter of the aforementioned unit cell is D = 80mm~120mm, and the total height is H = 42mm~102mm; the height of the upper back cavity and the height of the lower back cavity are distributed in a gradient ratio.

[0015] Working principle of the invention:

[0016] Sound absorption principle: Sound waves enter the interior of the structure through the upper micro-perforated plate and form Helmholtz resonance in the multi-layer fractal coupling cavity. Strong thermoviscous loss is generated in the microporous region. The multi-level fractal structure brings about the coupling and superposition of multiple resonance peaks, realizing broadband sound absorption.

[0017] Load-bearing principle: The branching partitions, resembling tree branches, form a multi-path continuous force transmission network, which can effectively disperse stress and suppress overall buckling; the middle layer plate provides local rigid constraints, enabling the structure to fail in a multi-lobe controlled folding mode under compression, achieving high stiffness, high stability load-bearing capacity and efficient energy absorption.

[0018] The present invention has the following beneficial effects:

[0019] 1. Excellent sound absorption performance: The second-order imitation dendritic multi-layer fractal structure has a sound absorption coefficient of no less than 0.8 in the frequency band of 375Hz to 1600Hz, and the half-power bandwidth is greatly improved.

[0020] 2. Outstanding mechanical properties: As the fractal order increases, the structural stiffness, strength, peak breaking force and specific energy absorption are significantly improved, which is superior to traditional honeycomb, fractal and biomimetic thin-walled structures.

[0021] 3. High parameter adjustability: fractal order, layering method, structural height, aperture, and wall thickness can all be customized according to the target sound absorption frequency band and load-bearing capacity.

[0022] 4. High degree of integration: It integrates sound absorption, load-bearing and lightweight, eliminating the need for additional sound-absorbing layers and significantly reducing system thickness, weight and assembly costs.

[0023] 5. Wide applicability: It can be directly used as cabin wall panels, ceilings, interior lining panels and sandwich structures, and is suitable for fields such as rail transportation, aerospace, architectural acoustics and engineering machinery. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the single cell of the tree-like multilayer fractal superstructure of the present invention;

[0025] Figure 2 This is a schematic diagram of different orders of the tree-like fractal partition of the present invention (order 0, order 1, and order 2 TFS).

[0026] Figure 3 This is a comparative schematic diagram of the non-layered structure of the present invention;

[0027] Figure 4 The sound absorption coefficient test curve of this invention (theoretical / simulation / experimental comparison);

[0028] Figure 5 This is the quasi-static compressive force-displacement curve of the present invention;

[0029] Figure 6 This is a comparison diagram of the mechanical properties of the present invention at different heights (a) and different orders (b).

[0030] List of reference numerals in the attached diagram: 1. Upper micro-perforated plate; 2. Middle micro-perforated plate; 3. Lower panel; 4. Fractal partition resembling a tree branch. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. For those skilled in the art, equivalent substitutions, simple modifications, improvements or combinations made to the technical solutions of the present invention without departing from the concept and essence of the present invention should all fall within the scope of protection of the present invention.

[0032] Example 1: Standard second-order dendritic multilayer fractal superstructure (2nd order -MTFS)

[0033] This embodiment provides a baseline configuration that achieves the optimal balance between broadband sound absorption and mechanical load-bearing capacity.

[0034] like Figure 1 As shown, the unit cell adopts a cylindrical structure with an outer diameter of 100 mm and a total height of 64.5 mm. The upper micro-perforated plate 1 is 0.5 mm thick with a hole diameter of 1 mm, and the perforations are evenly distributed along the partition area, avoiding corners and edges. The middle micro-perforated plate 2 is 2 mm thick with hole diameters of 0.85 mm, 0.7 mm, and 1 mm, and the perforations are arranged in a concentric ring and angular positioning manner. The tree-like fractal partition 4 is 1 mm thick and has a centrally symmetrical three-layer gradient distribution, with the branch length gradually decreasing as the order increases. The lower plate 3 is 2 mm thick and is a solid rigid panel.

[0035] The unit cell is divided into 24 independent sub-cavities by a fractal partition 4 resembling a tree branch. The central micro-perforated plate 2 divides the cavity into upper and lower layers, forming a four-level sound absorption structure consisting of an upper micro-perforated plate 1, an upper back cavity, a central micro-perforated plate 2, and a lower back cavity connected in series. Each sub-cavity is connected to the external sound field through micropores, forming a parallel coupling system of multiple Helmholtz resonators.

[0036] Impedance tube testing and finite element simulation verification show that the sound absorption coefficient of this structure is consistently no less than 0.8 in the 375Hz–1600Hz frequency range (see [link to relevant documentation]). Figure 4 The half-power bandwidth is 133% higher than that of a non-layered second-order fractal structure of the same size; the average sound absorption coefficient can reach 0.88 in the core frequency band of 500Hz to 1200Hz, covering the noise frequency band commonly used in engineering.

[0037] Quasi-static compression tests show that the initial stiffness of this structure is significantly higher than that of honeycomb and conventional fractal structures of the same mass. The peak breaking force is 312.42% higher than that of the 0th order structure, and the specific energy absorption is 55.34% higher than that of the 0th order structure. Under compression, it exhibits multi-lobe controlled buckling without sudden collapse, and has excellent load-bearing stability.

[0038] Example 2: Comparison of different fractal orders

[0039] This embodiment fixes the unit cell size, panel thickness, perforation parameters, and partition thickness, changing only the fractal order to compare the differences in sound absorption and mechanical properties. Figure 6 As shown in (b) of the diagram.

[0040] The 0th-order dendritic fractal structure has no hierarchical branching and consists only of a central column and an outer cavity. It has a narrow sound absorption frequency band and a distinct single resonant peak. The mechanical force transmission path is single, making it prone to overall buckling, and it has the lowest stiffness and strength.

[0041] The first-order simulated tree-like fractal structure adopts first-order bifurcation, increases the number of cavities, and slightly increases the number of resonant modes; the sound absorption frequency band is slightly broadened; the mechanical properties are improved compared with the 0th-order structure, and stress concentration is alleviated.

[0042] The second-order dendritic fractal structure adopts a two-stage bifurcation, significantly increasing the number of cavities and exhibiting a significant multi-resonance peak coupling effect; the half-power bandwidth is increased by 68.9% compared to the first-order structure, and the sound absorption frequency band is significantly broadened; the specific energy absorption is increased by 78.39% compared to the first-order structure, and the buckling resistance is significantly enhanced.

[0043] The second-order simulated tree-like multi-layer fractal structure adds a middle layer plate to the second-order fractal structure, which increases the half-power bandwidth by 133% compared with the second-order non-layered structure, achieving ultra-wideband sound absorption; the peak breaking force is increased by 5.14% compared with the second-order non-layered structure, and only slightly decreases by 12.92% compared with the energy absorption, achieving a significant improvement in acoustic performance while basically maintaining mechanical performance.

[0044] The experimental results show that the higher the fractal order, the better the sound absorption bandwidth and load-bearing capacity; the layered design can achieve a breakthrough improvement in sound absorption performance without significantly sacrificing mechanical properties.

[0045] Example 3: Comparison of Examples with Different Structural Heights

[0046] In this embodiment, the fractal order is fixed at 2, and the layered structure and cross-sectional dimensions are kept constant. The total height is set to 42mm, 62mm, 82mm, and 102mm respectively to study the influence of height on performance. Figure 6 As shown in (a) of the diagram.

[0047] In terms of sound absorption performance: as the structural height increases, the peak sound absorption shifts to lower frequencies; as the height decreases, the peak sound absorption shifts to higher frequencies; when the total height is 64.5mm, the widest and most efficient sound absorption range is achieved in the 375Hz to 1600Hz range.

[0048] In terms of mechanical properties: the lower the height, the stronger the buckling resistance. Compared with the structure with a height of 102mm (MTFS-H102), the 42mm height structure (MTFS-H42) has a 130.49% increase in initial stiffness, a 17.98% increase in ultimate strength, a 17.69% increase in peak crushing force, and a 34.87% increase in specific energy absorption, resulting in better crushing efficiency and more stable energy absorption.

[0049] Therefore, the structural height can be used to adjust the peak frequency of sound absorption, and the low-profile configuration is more suitable for high load-bearing and impact-resistant scenarios.

[0050] Example 4: The Influence of Key Micropore Parameters on Example

[0051] In this embodiment, the topology and external dimensions of the structure are fixed, and only the aperture of the upper / middle micro-perforated plate 2 is changed to study its influence on the sound absorption performance.

[0052] When the diameter of the micro-perforated holes in the upper part varies within the range of 0.4mm to 1mm, the smaller the hole diameter, the lower the resonant frequency and the narrower the sound absorption peak; as the hole diameter increases, the half-power bandwidth widens accordingly; the sound absorption bandwidth is optimal when the hole diameter is 1mm.

[0053] The diameter of the micro-perforated aperture in the middle has a significant impact on low-frequency resonance. If the aperture is too small, it will lead to excessively high acoustic impedance and a decrease in the peak sound absorption. When the aperture is in the range of 0.7mm to 0.85mm, the coupling effect between the upper and lower cavities is optimal, and the broadband sound absorption performance is the best.

[0054] The perforations are distributed close to the center of the partition and away from the concave corners and edges, which can prevent airflow short-circuiting, enhance thermal viscosity loss, and increase the sound absorption coefficient by 10% to 15%.

[0055] Example 5: Comparison with Existing Technology

[0056] This embodiment compares the second-order MTFS of the present invention with a beetle-sheath thin-walled structure, a square honeycomb fractal structure, a multicellular hexagonal structure, and a triangular multicellular column under the same areal density and the same external dimensions.

[0057] The results show that the initial stiffness of the present invention is comparable to that of the existing optimal structure, and the peak breaking force is significantly higher than that of all the comparative structures, with an improvement of more than 20%. The comparative structures can only achieve narrowband sound absorption, while the present invention can achieve ultra-wideband high-efficiency sound absorption from 375Hz to 1600Hz. The comprehensive performance is characterized by the product of the peak breaking force and the average sound absorption coefficient divided by the mass. The present invention is far superior to the existing traditional structure.

[0058] The comparative results demonstrate that the present invention has outstanding novelty and significant technological progress in the synergistic optimization of sound absorption and load-bearing capacity.

[0059] Industrial applicability:

[0060] The tree-like multi-layer fractal superstructure disclosed in this invention integrates sound absorption and noise reduction with mechanical load-bearing capacity. It can be directly used as structural components such as wall panels, linings, sandwich panels, and ceilings. It is formed in one piece and simultaneously undertakes load-bearing and noise reduction functions, significantly reducing system weight, thickness, and assembly costs. It has broad industrial application prospects in fields such as rail transportation, aerospace, architectural acoustics, and engineering machinery.

[0061] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A multi-layered fractal superstructure mimicking a tree branch, combining sound absorption and load-bearing properties, characterized in that: The superstructure is composed of several unit cell arrays; each unit cell includes: an upper micro-perforated plate (1), a middle micro-perforated plate (2), a lower plate (3), and a tree-like fractal partition (4); the middle micro-perforated plate (2) is located below the upper micro-perforated plate (1) and divides the inner cavity of the unit cell into an upper back cavity and a lower back cavity; the lower plate (3) is located below the middle micro-perforated plate (2) and serves as a bottom-closed support plate; the tree-like fractal partition (4) is located below the upper micro-perforated plate (1). The micro-perforated plate (1) and the lower panel (3) are arranged in a hierarchical and symmetrical manner, dividing the upper back cavity and / or the lower back cavity into multiple sub-cavities; micro-holes are provided on both the upper micro-perforated plate (1) and the middle micro-perforated plate (2) so that each sub-cavity can be connected to the external sound field; the tree-like fractal partition (4), the upper micro-perforated plate (1), the middle micro-perforated plate (2) and the lower panel (3) together constitute a continuous force transmission skeleton.

2. The multi-layered fractal superstructure with both sound absorption and load-bearing properties as described in claim 1, characterized in that, The simulated tree fractal partition (4) is divided into 0th, 1st and 2nd order simulated tree fractal structures TFS according to the number of branches; after introducing the middle micro-perforated plate (2) layer, 0th, 1st and 2nd order simulated tree multilayer fractal structures MTFS are formed accordingly.

3. The multi-layered fractal superstructure with both sound absorption and load-bearing properties as described in claim 1, characterized in that, The thickness of the simulated tree branch fractal partition (4) is 0.5mm to 2mm, and its branch length decreases step by step as the number of branching stages increases.

4. The multi-layered fractal superstructure with both sound absorption and load-bearing properties as described in claim 1, characterized in that, The upper micro-perforated plate (1) has a hole diameter of 0.4 mm to 1 mm, and the middle micro-perforated plate (2) has a hole diameter of 0.7 mm to 1 mm.

5. A multi-layered fractal superstructure with both sound absorption and load-bearing properties, as described in claim 4, is characterized in that... The perforations of the upper micro-perforated plate (1) are distributed close to the fractal partition (4) of the simulated tree branch, and avoid the concave corners and edges of the unit cell; the perforations of the middle micro-perforated plate (2) are arranged in concentric rings and angular positioning.

6. The multi-layered fractal superstructure with both sound absorption and load-bearing properties as described in claim 1, characterized in that, The outer diameter of the unit cell is D = 80mm to 120mm, and the total height is H = 42mm to 102mm; the height of the upper back cavity and the height of the lower back cavity are distributed in a gradient ratio.

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