Micro-perforated plate-like / cavity-like low-detection anechoic material for submarines and preparation method thereof

Abstract

The present invention discloses a micro-perforated plate-like / cavity-like low-detection silencing material for submarines, which belongs to the technical field of silencing materials. The silencing material of the present invention includes a polyurethane matrix, an aerogel matrix and a 3D spacer fabric; the aerogel matrix is ​​a double-network sodium alginate composite aerogel made of sodium alginate solution and agar solution, and the aerogel matrix is ​​compositely filled between the upper and lower layers of the 3D spacer fabric to form a cavity-like silencing structure between the aerogel matrix and the spacer wires of the 3D spacer fabric; the polyurethane matrix is ​​filled between the upper and lower layers of the 3D spacer fabric to form a micro-perforated plate-like silencing structure between the polyurethane matrix and the spacer wires of the 3D spacer fabric; the silencing material of the present invention improves the acoustic stealth performance of submarine materials and can effectively absorb low-frequency sound waves; in addition to having good mechanical properties, the strength of the material can withstand the hydrostatic pressure of the deep sea, and can achieve a good stealth effect.

Description

Technical Field

[0001] The present invention relates to the technical field of sound-absorbing materials, and in particular to a micro-perforated plate-like / cavity-like low-detection sound-absorbing material for submarines. Background Art

[0002] In modern warfare and national defense security, submarines hold a crucial strategic and deterrent role, serving as a key indicator of a nation's military prowess and industrialization. Sound waves are the only carrier capable of transmitting effective information over long distances in the ocean. Therefore, as a quintessential stealth vehicle, submarines' underwater acoustic stealth—or, their underwater sound absorption—is their lifeline. Currently, coating submarines' surfaces and interiors with various anechoic materials is the primary method for achieving underwater acoustic stealth.

[0003] At present, homogeneous high molecular polymer sound-absorbing materials are widely used in the field of underwater acoustics. Homogeneous high molecular polymer sound-absorbing materials generally use rubber and polyurethane, which have a density similar to that of water and can easily achieve specific underwater acoustic functional requirements. However, the attenuation coefficient of homogeneous high molecular polymer sound-absorbing materials is usually proportional to the square of the frequency, and the absorption of low-frequency sound waves requires a larger material size, so it often appears bulky. In addition, this type of material has low strength and is not resistant to hydrostatic pressure, making it difficult to meet the needs of the high hydrostatic pressure environment in the deep sea. Due to these limitations, homogeneous high molecular sound-absorbing materials have obvious deficiencies in mechanical properties and medium and low frequency sound absorption performance (2kHz to 5kHz), and the thickness of existing materials is usually more than 25mm. To this end, the present invention proposes a new sound-absorbing material and preparation method for submarines. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems in the prior art and provide a micro-perforated plate / cavity-like low-detection anechoic material for submarines, which achieves the improvement of mechanical properties and medium and low frequency sound absorption performance at low thickness.

[0005] The present invention discloses a micro-perforated plate-like / cavity-like low-detection anechoic material for submarines, comprising: a polyurethane matrix, an aerogel matrix, and a 3D spacer fabric;

[0006] The aerogel matrix is ​​a double-network sodium alginate composite aerogel made of a sodium alginate solution and an agar solution. The aerogel matrix is ​​compositely filled between the upper and lower layers of the 3D spacer fabric, so that a cavity-like sound-absorbing structure is formed between the aerogel matrix and the spacer yarns of the 3D spacer fabric.

[0007] The polyurethane matrix is ​​filled between the upper and lower layers of the 3D spacer fabric to form a micro-perforated plate-like sound-absorbing structure between the polyurethane matrix and the spacer yarns of the 3D spacer fabric; the polyurethane matrix is ​​located on the upper layer of the aerogel matrix.

[0008] As a preferred embodiment, the upper layer of the 3D spacer fabric is the sound wave incident surface, and the lower layer is the sound wave reflecting surface. The upper layer of the 3D spacer fabric is a knitted fabric formed by a diamond mesh structure, and the lower layer is a knitted fabric formed by a chain link structure and a weft insertion structure.

[0009] As a preferred embodiment, the diameter of the spacer wires of the 3D spacer fabric is less than 0.25 mm.

[0010] As a preferred method, the thickness of the sound-absorbing material is 5-10 mm and the density is maintained at 0.5-0.9 g / cm 3 The compression creep thickness retention rate of 95h is more than 73%. In water, within the low frequency range of 1500Hz, the peak value of the sound absorption coefficient reaches 0.82.

[0011] As a preferred embodiment, the method for preparing the above-mentioned submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material of the present invention comprises the following steps:

[0012] Weave 3D spacer fabric, apply release agent in the mold, and lay the cut 3D spacer fabric into the mold;

[0013] An agar / sodium alginate blend was prepared, poured into a mold containing a spacer silk fabric, and allowed to stand at room temperature to allow cross-linking. The mixture was then immersed in a calcium chloride solution to allow cross-linking. A frozen sample was obtained after washing and pre-freezing, and freeze-dried under a vacuum environment of less than 1 Pa to prepare a structurally stable double-network sodium alginate composite aerogel.

[0014] The double-network sodium alginate composite aerogel is subjected to hydrophobic finishing to obtain a low-density hydrophobic double-network sodium alginate composite aerogel, and the low-density hydrophobic double-network sodium alginate composite aerogel is filled between the upper and lower layers of the 3D spacer fabric to form a cavity-like sound-absorbing structure;

[0015] Polyol and isocyanate are evenly mixed in a volume ratio of 1:1, spread on the cavity-like sound-absorbing structure and then foamed to form polyurethane foam; the polyurethane foam and the embedded spacer wire together form a filling micro-perforated plate structure, which is demoulded after standing to obtain a micro-perforated plate-like / cavity-like low-detection sound-absorbing material for submarines.

[0016] As a preferred method, octadecyltrichlorosilane (OTS) is added to a xylene solution under light-shielding conditions to form an OTS / xylene solution with a volume fraction of 1% to 5%; the double-network sodium alginate composite aerogel is immersed in the OTS / xylene solution, and then washed with xylene to remove excess modifier and by-products;

[0017] The double-network sodium alginate composite aerogel washed with xylene was placed in a ventilated place to volatilize excess xylene in the aerogel, and finally dried under vacuum conditions to obtain a cavity-like sound-absorbing structure composed of low-density hydrophobic sodium alginate composite aerogel.

[0018] As a preferred embodiment, the pre-freezing is performed in a refrigerator at -18°C for 48 hours.

[0019] As a preferred embodiment, the freeze drying is performed in a vacuum environment (<1 Pa) at -58°C for 48 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention uses low-density aerogel to create a cavity-like structure. A specially formulated 3D spacer fabric is then "transplanted" into the cavity-like underwater acoustic stealth material, resulting in a novel "microperforated plate / cavity-like" structure with a pore diameter equal to the diameter of the spacer wire and filled with the spacer wire. This leads to the design of a microperforated plate / cavity-like low-detection anechoic material for submarines. The cavity-like structure and the microperforated plate-like filling form a Helmholtz resonator, providing sufficient acoustic resistance and low mass resistance. More importantly, the porous nature of the aerogel increases the transmission path for incident sound waves, transforming the traditional cavity's simple reflection of sound waves into a combination of refraction and reflection. This significantly increases the sound wave transmission path and achieves the sound wave dissipation effect achieved only by conventional, thicker cavities, while maintaining a low thickness.

[0022] The new type of sound-absorbing material prepared by the present invention has achieved an outstanding low-frequency sound absorption coefficient (the peak value of the sound absorption coefficient reaches above 0.82 and occurs within 1500Hz), which can shorten the sonar detection distance by more than 60%. At the same time, on the basis of meeting the acoustic stealth performance of submarines, the material thickness is 5-10mm and the density can be maintained at 0.5g / cm 3 to 0.9g / cm 3 , with a long-term compression creep thickness retention rate of over 73%. After 12 months of seawater aging, the compressive strength of the silencing material decreased by 34.29%, and the average sound absorption coefficient decreased by 13.6%. In a 5°C seawater environment, the compressive strength retention rate of the silencing material was still 60% after 20 months, which provides a guarantee for its long-term operation in the sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the preparation process of the sound-absorbing material of the present invention.

[0024] Figure 2 A physical picture of the sound-absorbing material of the present invention

[0025] Figure 3 Schematic diagram of the underwater sound absorption mechanism of the sound-absorbing material of the present invention.

[0026] Description of reference numerals:

[0027] 1. Polyurethane matrix, 2. Aerogel matrix, 3. 3D spacer fabric, 4. Spacer yarn. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0029] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons of ordinary skill in the field to which the present disclosure belongs. The words "first", "second" and similar terms used in the patent application specification and claims of the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. Words such as "connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0030] At present, homogeneous polymer sound-absorbing materials have strong designability. The acoustic properties of the material can be changed by changing the chain segment ratio, the number of branches or the intermolecular bonding force, and they are widely used in the field of underwater acoustics. However, the attenuation coefficient of homogeneous polymer sound-absorbing materials is usually proportional to the square of the frequency, and the absorption of low-frequency sound waves requires a larger material size, so it often appears bulky. In addition, this type of material has low strength and is not resistant to hydrostatic pressure, making it difficult to meet the needs of high hydrostatic pressure environments in the deep sea. Due to these limitations, homogeneous polymer sound-absorbing materials have obvious deficiencies in mechanical properties and medium and low-frequency sound absorption performance (2kHz to 5kHz), and the thickness of existing materials is usually more than 25mm.

[0031] While current filler-reinforced polymer-based anechoic materials have some advantages, they still require significant performance improvements to meet the stringent requirements of modern marine lightweight, high-strength anechoic materials. Based on a broadband resonant sound absorption system—a micro-perforated plate sound absorption structure—our company has developed a new underwater sound-absorbing anechoic material by combining a custom 3D spacer fabric with a polymer matrix. This material can withstand the hydrostatic pressure of the deep sea and effectively absorb low-frequency sound waves, addressing the shortcomings of existing products and potentially creating a broad market opportunity.

[0032] In addition, this embodiment also studies a new type of sound-absorbing material and the corresponding multi-physical field coupling life prediction model, which improves the acoustic stealth performance of submarine materials, has good mechanical properties, realizes the controllable preparation of the product, achieves comprehensive optimization of its performance, and promotes the assembly of actual boats.

[0033] This example first establishes a macroscopic composite sound absorption model. Using two equivalent fluid models, the JCA model and the DB-Miki model, as well as internal impedance translucent boundary conditions, the acoustic wave loss process of submarine-like microperforated plate / cavity-like low-detection anechoic materials is homogenized. Given that the transmission parameters involved in the above-mentioned equivalent fluid model and translucent boundary are all true geometric reflections of the material's microstructure and are difficult to obtain through experimental methods, we innovatively establish corresponding microscopic and mesoscopic structural models based on the true geometric structure of submarine-like microperforated plate / cavity-like low-detection anechoic materials. Using the multi-scale finite element method, we obtain the transmission parameters of the corresponding structures, thereby providing parameter support for the above-mentioned macroscopic composite sound absorption model. Finally, we conduct finite element simulations of the underwater sound absorption performance of submarine-like microperforated plate / cavity-like low-detection anechoic materials.

[0034] This example, based on a pure polymer sound-absorbing material and leveraging independently developed 3D fabric weaving technology, "transplanted" a custom-made, self-supporting, and diversely structurally-proper 3D spacer fabric into a quasi-filled underwater acoustic stealth material. This resulted in a novel "quasi-filled micro-perforated plate" structure within the quasi-filled underwater acoustic stealth material, with pores equal to the diameter of the spacer wires and filled with them. Subsequently, employing a variety of scientific methods, including structural manipulation, additive manufacturing, and finite element simulation, the optimized preparation of an ultra-thin (5-10 mm) sound-absorbing material with excellent low-frequency (1500 Hz) sound absorption capabilities was achieved.

[0035] This embodiment discloses a micro-perforated plate-like / cavity-like low-detection anechoic material for submarines, comprising: a polyurethane matrix 1, an aerogel matrix 2, and a 3D spacer fabric 3;

[0036] The aerogel matrix 2 is a double-network sodium alginate composite aerogel made of a sodium alginate solution and an agar solution. The aerogel matrix 2 is compositely filled between the upper and lower layers of the 3D spacer fabric 3, so that a cavity-like sound-absorbing structure is formed between the aerogel matrix 2 and the spacer yarns 4 of the 3D spacer fabric 3.

[0037] The polyurethane matrix 1 is filled between the upper and lower layers of the 3D spacer fabric 3, forming a micro-perforated plate-like sound-absorbing structure between the polyurethane matrix 1 and the spacer yarns 4 of the 3D spacer fabric 3. The polyurethane matrix 1 is located on the upper layer of the aerogel matrix 2. The filling height and filling ratio of the two can be adjusted according to needs. Different height ratios and contents can change the sound frequency corresponding to the sound absorption peak.

[0038] As a disclosure method of this embodiment, the upper layer of the 3D spacer fabric 3 is the sound wave incident surface, and the lower layer is the sound wave reflecting surface. The upper layer of the 3D spacer fabric 3 is a knitted fabric formed by a diamond mesh structure, so that the sound waves can better enter the interior of the sound-absorbing material. The lower layer is a knitted fabric formed by a chain link structure and a weft insertion structure. The lower layer uses a chain link plus weft insertion structure to improve the mechanical properties of the 3D spacer fabric 3, and can reflect the sound waves, so that the sound waves enter the interior of the sound-absorbing material again, and further dissipate the sound waves.

[0039] As a disclosed method of this embodiment, the diameter of the spacer yarns of the 3D spacer fabric 3 is less than 0.25 mm. The microperforated plate sound absorption structure of this embodiment is designed based on the perforated plate sound absorption structure, differing in that the aperture size of the perforated plate is reduced to less than 1 mm. In a microperforated plate, the acoustic impedance is increased by reducing the aperture of the resonant structure, thereby widening the sound absorption band. Furthermore, the size of the resonant cavity is used to control the resonant frequency of the absorption peak: a larger resonant cavity results in a lower resonant frequency.

[0040] However, microperforated plate sound absorption structures are primarily used for airborne sound absorption. Therefore, an attempt was made to expand their performance to accommodate underwater environments. However, the kinematic viscosity of water is smaller than that of air, at only 1 / 16th of the latter. Therefore, when a microperforated plate sound absorption structure of the same specifications is used underwater, its absorption bandwidth is significantly smaller than that in air. To achieve the same sound absorption effect as in air, this embodiment further reduces the aperture to 1 / 4 of the original size, to less than 0.25 mm.

[0041] Example 1

[0042] The preparation method of the submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material of this embodiment is as follows:

[0043] First, 2 g of sodium alginate was weighed on an electronic balance and added to a beaker containing 1000 mL of deionized water. The mixture was then rapidly stirred in a magnetic stirrer to form a 0.2% w / w sodium alginate solution. Agar was dissolved in distilled water and heated to 95°C in an oil bath with stirring for 2 h to prepare a 0.2% w / w agar solution. Subsequently, the sodium alginate solution was added to the agar solution at a volume ratio of 1:1 to form an agar / sodium alginate blend. The blend was poured into a mold containing a spacer silk fabric and allowed to stand at room temperature for 24 h to allow crosslinking. After completing these steps, the entire sample was immersed in a 5% w / w calcium chloride solution, crosslinked for 24 h, and washed three times with deionized water. The sample was then pre-chilled in a -18°C freezer for 48 h to obtain a frozen sample. The frozen sample was then freeze-dried in a freeze dryer at -58°C under a vacuum (<1 Pa) for 48 h. During the freeze-drying process, the solvent is frozen and sublimates through the triple point under vacuum, so that the aerogel achieves a porous structure. After the ice crystals are completely dried, a structurally stable double-network sodium alginate composite aerogel is prepared. Subsequently, the composite aerogel is hydrophobically finished, the xylene solution is measured, and octadecyltrichlorosilane (OTS) is added under light-proof conditions to form an OTS / xylene solution with a volume fraction of 3%. The double-network sodium alginate composite aerogel is immersed in the OTS / xylene solution to react for 2 hours, and then washed with xylene 2-3 times to remove excess modifiers and by-products. The sample is placed in a ventilated place for 12 hours to allow excess xylene in the aerogel to volatilize. Finally, the sample is placed in a vacuum drying oven and dried at 50°C for 12 hours, and finally a cavity-like layer composed of low-density hydrophobic sodium alginate composite aerogel is obtained.

[0044] Based on the preparation of the aforementioned cavity-like layer, polyol and isocyanate were preheated to 40°C to ensure fluidity. Then, polyol and isocyanate were measured separately and mixed evenly in a volume ratio of 1:1. After being spread on the cavity-like layer, they were foamed to form polyurethane foam. The polyurethane foam and the embedded spacer wires together formed a filled micro-perforated plate structure. The sample was placed at room temperature for 24 hours and demolded after stabilization to obtain a new underwater acoustic stealth material.

[0045] Example 2

[0046] The preparation method of the submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material of this embodiment is as follows:

[0047] First, 5 g of sodium alginate was weighed on an electronic balance and added to a beaker containing 1000 mL of deionized water. The mixture was then rapidly stirred in a magnetic stirrer to form a 0.5% w / w sodium alginate solution. Agar was dissolved in distilled water and heated to 95°C in an oil bath with stirring for 2 h to prepare a 0.5% w / w agar solution. Subsequently, the sodium alginate solution was added to the agar solution at a volume ratio of 1:1 to form an agar / sodium alginate blend. The blend was poured into a mold containing a spacer silk fabric and allowed to stand at room temperature for 24 h to allow crosslinking. After completing these steps, the entire sample was immersed in a 5% w / w calcium chloride solution, crosslinked for 24 h, and washed three times with deionized water. The sample was then pre-frozen in a -18°C refrigerator for 48 h to obtain a frozen sample. The frozen sample was then freeze-dried in a freeze dryer at -58°C under a vacuum (<1 Pa) for 48 h. During the freeze-drying process, the solvent is frozen and sublimates through the triple point under vacuum, so that the aerogel achieves a porous structure. After the ice crystals are completely dried, a structurally stable double-network sodium alginate composite aerogel is prepared. Subsequently, the composite aerogel is hydrophobically finished, the xylene solution is measured, and octadecyltrichlorosilane (OTS) is added under light-proof conditions to form an OTS / xylene solution with a volume fraction of 3%. The double-network sodium alginate composite aerogel is immersed in the OTS / xylene solution to react for 2 hours, and then washed with xylene 2-3 times to remove excess modifiers and by-products. The sample is placed in a ventilated place for 12 hours to allow excess xylene in the aerogel to volatilize. Finally, the sample is placed in a vacuum drying oven and dried at 50°C for 12 hours, and finally a cavity-like layer composed of low-density hydrophobic sodium alginate composite aerogel is obtained.

[0048] Based on the preparation of the aforementioned cavity-like layer, polyol and isocyanate were preheated to 40°C to ensure fluidity. Then, polyol and isocyanate were measured separately and mixed evenly in a volume ratio of 1:1. After being spread on the cavity-like layer, they were foamed to form polyurethane foam. The polyurethane foam and the embedded spacer wires together formed a filled micro-perforated plate structure. The sample was placed at room temperature for 24 hours and demolded after stabilization to obtain a new underwater acoustic stealth material.

[0049] Example 3

[0050] The preparation method of the submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material of this embodiment is as follows:

[0051] First, 8 g of sodium alginate was weighed on an electronic balance and added to a beaker containing 1000 mL of deionized water. The mixture was then rapidly stirred in a magnetic stirrer to form a 0.8% w / w sodium alginate solution. Agar was dissolved in distilled water and heated to 95°C in an oil bath with stirring for 2 h to prepare a 0.8% w / w agar solution. Subsequently, the sodium alginate solution was added to the agar solution at a volume ratio of 1:1 to form an agar / sodium alginate blend. The blend was poured into a mold containing a spacer silk fabric and allowed to stand at room temperature for 24 h to allow crosslinking. After completing these steps, the entire sample was immersed in a 5% w / w calcium chloride solution, crosslinked for 24 h, and washed three times with deionized water. The sample was then pre-frozen in a -18°C refrigerator for 48 h to obtain a frozen sample. The frozen sample was then freeze-dried in a freeze dryer at -58°C under a vacuum (<1 Pa) for 48 h. During the freeze-drying process, the solvent is frozen and sublimates through the triple point under vacuum, so that the aerogel achieves a porous structure. After the ice crystals are completely dried, a structurally stable double-network sodium alginate composite aerogel is prepared. Subsequently, the composite aerogel is hydrophobically finished, the xylene solution is measured, and octadecyltrichlorosilane (OTS) is added under light-proof conditions to form an OTS / xylene solution with a volume fraction of 3%. The double-network sodium alginate composite aerogel is immersed in the OTS / xylene solution to react for 2 hours, and then washed with xylene 2-3 times to remove excess modifiers and by-products. The sample is placed in a ventilated place for 12 hours to allow excess xylene in the aerogel to volatilize. Finally, the sample is placed in a vacuum drying oven and dried at 50°C for 12 hours, and finally a cavity-like layer composed of low-density hydrophobic sodium alginate composite aerogel is obtained.

[0052] Based on the preparation of the aforementioned cavity-like layer, polyol and isocyanate were preheated to 40°C to ensure fluidity. Then, polyol and isocyanate were measured separately and mixed evenly in a volume ratio of 1:1. After being spread on the cavity-like layer, they were foamed to form polyurethane foam. The polyurethane foam and the embedded spacer wires together formed a filled micro-perforated plate structure. The sample was placed at room temperature for 24 hours and demolded after stabilization to obtain a new underwater acoustic stealth material.

[0053] The sample size is trimmed according to the test requirements. The forming principle diagram of the micro-perforated plate / cavity-like low-detection anechoic material for submarines in this embodiment is as follows Figure 1 shown.

[0054] The sound absorption mechanism of the sound-absorbing material of this embodiment is as follows Figure 2As shown, the sound-absorbing material attenuates sound waves through viscoelastic internal friction and elastic relaxation within the porous material. Its sound absorption mechanism is comprised of two aspects. First, a resonant sound absorption mechanism, similar to a filled microperforated plate structure, is formed between the polyurethane matrix and the spacer filaments. When the incident sound wave reaches a specific frequency, the spacer filaments resonate with the sound wave, converting the sound wave's energy into resonant mechanical energy. During this resonance, the spacer filaments and the polyurethane continuously rub against each other, converting the mechanical energy into heat, achieving the sound absorption purpose. Second, a cavity-like structure is formed between the aerogel matrix and the spacer filaments, containing various interfaces. When longitudinal waves encounter these interfaces, they are converted into shear waves, increasing sound energy loss. This is effectively absorbed by the viscoelastic sound-absorbing material. The combination of polyurethane and water-resistant aerogel allows sound waves to enter and be absorbed through the narrow pores of the polyurethane, where they are further dissipated within the cavities of the aerogel layer.

[0055] Performance Verification

[0056] In the sound absorption coefficient test within the frequency range of 800 to 4000Hz, the average sound absorption coefficient of the submarine-type micro-perforated plate / cavity-type low-detection anechoic material reached 0.32, showing a certain sound absorption effect. In particular, the average sound absorption coefficient in the 1500Hz range can reach above 0.76, which is worse than other frequency ranges, with the highest sound absorption coefficient reaching 0.82. However, the sound absorption coefficient of polyurethane increases with the increase of sound wave frequency, and its sound absorption performance in the medium and low frequencies is not as good as that of the submarine-type micro-perforated plate / cavity-type low-detection anechoic material. Some data are shown in Table 1:

[0057] Table 1

[0058]

[0059] This embodiment proposes the world's first micro-perforated plate / cavity-like resonance silencer structure. The silencer material with this type of micro-perforated plate / cavity-like resonance silencer structure is based on pure polymer silencer material and based on the independently developed three-dimensional fabric weaving technology. The special 3D spacer fabric with self-support and multiple structural properties is "transplanted" into the filled underwater acoustic stealth material, thereby realizing a new "filled micro-perforated plate" structure with an aperture equal to the diameter of the spacer wire and filled with spacer wire inside the filled underwater acoustic stealth material, and thus a new type of silencer material is designed.

[0060] This embodiment utilizes a unique three-dimensional knitting technology independently developed by the inventors' team. This unique technology, designed and woven, features self-supporting 3D spacer fabrics with diverse structural properties. This technology has been expanded to include pressure ulcer protection pads and Janus dressings. Furthermore, multi-scale methods and genetic algorithm optimization have been expanded to non-destructive testing of textiles, demonstrating significant application value.

[0061] This embodiment proposes and uses a life prediction model for the sound absorption performance of sound-absorbing materials. To achieve the controllable preparation of the novel sound-absorbing material of the present invention, the present invention accurately extracts the nonlinear expansion information of the micro-perforated three-dimensional pore structure after seawater aging through multi-plane and multi-source point expansion based on linear degradation and Fick's law. The project's technical route and multi-scale simulation life prediction system, based on the compression strength attenuation dataset and the three-dimensional pore structure dataset after aging and expansion, combines macroscopic, mesoscopic, and microscopic multi-physics field coupling models to establish a highly accurate underwater sound absorption performance life prediction model. The model then predicts the sound absorption performance retention rate of the material under any aging conditions, predicts its service life and performance attenuation law, and ultimately achieves controllable product preparation.

[0062] The present invention uses an original preparation process to give conventional materials new life. It adopts a variety of scientific methods such as structural control, additive manufacturing, and finite element simulation to achieve the optimized preparation of ultra-thin (5-10mm) sound-absorbing materials with excellent low-frequency (within 1500Hz) sound absorption capabilities. The Comsol finite element sound absorption model is established to accurately predict the sound absorption performance of the sound-absorbing material. This achieves comprehensive optimization of the acoustic and mechanical properties of this new underwater stealth material that meets the low-thickness and strong low-frequency sound absorption requirements of modern submarines, thereby promoting their actual submarine configuration.

[0063] A new type of sound-absorbing material in this embodiment improves the acoustic stealth performance of submarine materials and can effectively absorb low-frequency sound waves; at the same time, it has good mechanical properties, and the strength of the material can withstand the hydrostatic pressure of the deep sea, which improves the comprehensive combat capability of my country's submarines. It has broad market prospects and contributes to the country's economic and military construction. In addition, the product also has excellent air sound absorption performance. In the future, the product range can be expanded and promoted to the field of air sound materials, with obvious economic benefits.

[0064] Innovations in raw materials and technology in this embodiment reduce the raw material cost of the product. The addition of a specialized 3D spacer fabric improves the product's mechanical properties by 20%-70%. The polyurethane-aerogel matrix forms a two-part sound absorption mechanism. These materials work together to achieve excellent sound absorption while simultaneously reducing the product's weight, meeting the requirements for marine noise reduction materials. This embodiment's production process is streamlined, production speeds are high, and product quality is stable, ensuring timely delivery.

[0065] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A micro-perforated plate / cavity-like low-detection anechoic material for submarines, characterized in that: include: Polyurethane matrix, aerogel matrix and 3D spacer fabric; The aerogel matrix is ​​a low-density hydrophobic double-network sodium alginate composite aerogel made of a sodium alginate solution and an agar solution. The aerogel matrix is ​​compositely filled between the upper and lower layers of the 3D spacer fabric to form a cavity-like sound-absorbing structure between the aerogel matrix and the spacer yarns of the 3D spacer fabric. The polyurethane matrix is ​​filled between the upper and lower layers of the 3D spacer fabric to form a micro-perforated plate-like sound-absorbing structure between the polyurethane matrix and the spacer yarns of the 3D spacer fabric; the polyurethane matrix is ​​located on the upper layer of the aerogel matrix.

2. The submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material according to claim 1, characterized in that: The upper layer of the 3D spacer fabric is the sound wave incident surface, and the lower layer is the sound wave reflecting surface. The upper layer of the 3D spacer fabric is a knitted fabric formed by a diamond mesh structure, and the lower layer is a knitted fabric formed by a chain link structure and a weft insertion structure.

3. The submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material according to claim 1, characterized in that: The diameter of the spacer wires of the 3D spacer fabric is less than 0.25 mm.

4. The submarine-use micro-perforated plate-like / cavity-like low-detection anechoic material according to claim 1, characterized in that: The thickness of the sound-absorbing material is 5-10 mm, and the density is maintained at 0.5-0.9 g / cm 3 The compression creep thickness retention rate after 95h is more than 73%. In water, the peak value of the sound absorption coefficient reaches 0.82 in the low frequency range of 1500 Hz.

5. The method for preparing the micro-perforated plate-like / cavity-like low-detection anechoic material for submarines according to claim 1, characterized in that: The following steps are involved: Weaving 3D spacer fabric, applying release agent in the mold, and laying the 3D spacer fabric into the mold; An agar / sodium alginate blend was prepared, poured into a mold containing spacer silk fabric, left to stand at room temperature for cross-linking, and then immersed in a calcium chloride solution for cross-linking. After washing and pre-freezing, a frozen sample was obtained, and freeze-dried under a vacuum environment of less than 1 Pa to prepare a structurally stable double-network sodium alginate composite aerogel. The double-network sodium alginate composite aerogel is subjected to hydrophobic finishing to obtain a low-density hydrophobic double-network sodium alginate composite aerogel, and the low-density hydrophobic double-network sodium alginate composite aerogel is filled between the upper and lower layers of the 3D spacer fabric to form a cavity-like sound-absorbing structure; Polyol and isocyanate are evenly mixed in a volume ratio of 1:1, spread on the cavity-like sound-absorbing structure and then foamed to form polyurethane foam; the polyurethane foam and the embedded spacer wire together form a filling micro-perforated plate structure, which is demoulded after standing to obtain a micro-perforated plate-like / cavity-like low-detection sound-absorbing material for submarines.

6. The method for preparing the micro-perforated plate-like / cavity-like low-detection anechoic material for submarines according to claim 5, characterized in that: The method for hydrophobic finishing of the double-network sodium alginate composite aerogel is as follows: Octadecyltrichlorosilane (OTS) is added to a xylene solution in the dark to form an OTS / xylene solution with a volume fraction of 1% to 5%. The double-network sodium alginate composite aerogel is immersed in the OTS / xylene solution and then washed with xylene to remove excess modifier and by-products. The double-network sodium alginate composite aerogel washed with xylene was placed in a ventilated place to volatilize excess xylene in the aerogel, and finally dried under vacuum conditions to obtain a cavity-like sound-absorbing structure composed of low-density hydrophobic sodium alginate composite aerogel.

7. The method for preparing the micro-perforated plate-like / cavity-like low-detection anechoic material for submarines according to claim 5, characterized in that: The pre-freezing step is to pre-freeze the sample in a -18°C refrigerator for 48 h.

8. The method for preparing the micro-perforated plate-like / cavity-like low-detection anechoic material for submarines according to claim 5, characterized in that: The freeze drying step is freeze drying at -58°C in a vacuum environment for 48 hours.

Images