A metamaterial load alleviating structure and method suitable for high speed water entry impact

Abstract

The application discloses a metamaterial load-reducing structure and method suitable for high-speed water-impact, which comprises a fairwater cover and a negative Poisson's ratio honeycomb structure inside the fairwater cover; the negative Poisson's ratio honeycomb structure is composed of a plurality of star-tetragonal unit cells; each unit cell comprises a four-star structure in the middle and a tetragonal structure arranged at four corners of the four-star structure; the tetragonal structure is provided with only one right angle, and the corners of the four-star structure are connected with opposite corners of the right angle of the tetragonal structure; the recesses of the four-star structure are provided with skeletons; the unit cells are connected with the right angles through adjacent right angle edges, and the skeletons are connected with adjacent skeletons. The metamaterial load-reducing structure can reduce the impact load of a navigation body when entering water, and realizes safe water-entry of a vehicle at high speed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-speed cross-medium water entry load reduction, and particularly relates to a metamaterial load reduction structure and method suitable for high-speed water entry impact. BACKGROUND

[0002] Compared with traditional launch methods, air-dropping or rocket-assisted launching has obvious advantages. They can not only achieve long-distance launching, ensure the concealment of the launching process and the safety of the launching platform, but also increase the operating range and flexibility of the vehicle, making it can perform tasks more widely.

[0003] When underwater vehicles are launched by air-dropping or rocket-assisted launching, one of the main challenges they face is the high-speed water entry phase. During this process, the vehicle will encounter strong impact from the water surface and great pressure caused by rapid entry into the water. According to the Wagner classic theory, the impact force on the vehicle during water entry is proportional to the square of its speed. Therefore, high-speed water entry will greatly increase the impact force, which may cause dynamic response to the structure of the vehicle, resulting in elastic deformation of the shell, and even buckling, damage or breaking in extreme cases. This poses a severe test to the equipment inside the vehicle. In addition, the impact force may also affect the trajectory stability of the vehicle, which may lead to rapid sinking, unstable underwater movement or even loss of control. Therefore, when designing and launching underwater vehicles, it is a key technical challenge to reduce the impact force caused by high-speed water entry.

[0004] In recent years, negative Poisson's ratio materials have been widely developed and applied in the field of cross-medium load reduction due to their good energy absorption. Among them, the classic negative Poisson's ratio cell structure includes: concave triangular structure, chiral structure, star-shaped structure and many combined topological structures. However, most of these structures are only suitable for low-speed water entry of the vehicle, and they often fail quickly during high-speed water entry, making it difficult to achieve good energy absorption and load reduction effect. The present application aims to solve the problem of achieving good load reduction effect through the breaking and energy absorption of special negative Poisson's ratio materials under high-speed water entry environment. SUMMARY

[0005] The purpose of the present application is to provide a metamaterial load reduction structure and method suitable for high-speed water entry impact, which can reduce the impact load on the vehicle during water entry and achieve safe high-speed water entry of the vehicle.

[0006] The technical solution to achieve the purpose of the present application is as follows:

[0007] A metamaterial load reduction structure suitable for high-speed water entry impact, comprising a fairwater cover and a negative Poisson's ratio honeycomb structure inside the fairwater cover.

[0008] The negative Poisson's ratio honeycomb structure is composed of a plurality of star-tetragonal unit cells; each unit cell comprises a central star-shaped structure and a tetragonal structure arranged at four corners of the star-shaped structure; wherein the tetragonal structure is provided with only one right angle, and the corners of the star-shaped structure are connected with opposite corners of the right angle of the tetragonal structure; the recesses of the star-shaped structure are provided with skeletons; and each unit cell is connected with an adjacent right angle edge through a straight edge.

[0009] A metamaterial load reduction structure suitable for high-speed water entry impact, and a load reduction method thereof, are provided.

[0010] Compared with the prior art, the present application has the following advantages:

[0011] (1) A star-tetragonal negative Poisson's ratio honeycomb metamaterial is used in the load reduction head cover, which can still play a good energy absorption and load reduction effect during the high-speed water entry of the vehicle, and the structure and assembly process are simple, the structure only contains the load reduction head cover and the internal star-tetragonal negative Poisson's ratio honeycomb metamaterial, and the internal star-tetragonal negative Poisson's ratio honeycomb metamaterial can be manually filled and pressed into the load reduction head cover.

[0012] (2) Through the fairing shell structure, the fairing shell is flat, and an axisymmetric supercavity is formed during water entry, so that the fluid-solid separation of the vehicle head and water during the water entry of the vehicle is realized.

[0013] (3) The internal star-tetragonal negative Poisson's ratio honeycomb metamaterial is axially extruded under water entry stress, and continuously absorbs energy through compression and crushing, thereby reducing the water entry impact load reduction of the vehicle. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a schematic diagram of a star Poisson's ratio unit cell structure.

[0015] Figure 2 It is a simulation scene diagram of the star-tetragonal negative Poisson's ratio metamaterial at different speeds.

[0016] Figure 3 It is a specific energy absorption diagram of the star-tetragonal negative Poisson's ratio metamaterial at different speeds.

[0017] Figure 4 It is a schematic diagram of the star-tetragonal negative Poisson's ratio metamaterial filled and pressed into the fairing head cover.

[0018] Figure 5 It is Figure 4 an oblique view, which shows the connection of the star-tetragonal negative Poisson's ratio metamaterial in the thickness direction.

[0019] Figure 6It is a schematic diagram of the fairwater cover.

[0020] Figure 7 It is a schematic diagram of the fairwater cover of the star-shaped Poisson's ratio metamaterial and the vehicle.

[0021] Figure 8 It is Figure 4 It is an enlarged view of the head along AA1 after being cut.

[0022] Figure 9 It is the specific physical parameters of the aluminum alloy.

[0023] Figure 10 It is a comparison between the initial state and the dense form of the star-shaped-quadrilateral negative Poisson's ratio metamaterial. DETAILED DESCRIPTION

[0024] The application will be further described below in combination with the drawings and specific embodiments.

[0025] In combination with Figures 1-10 The application relates to a negative Poisson's ratio metamaterial load-reducing structure suitable for high-speed water entry impact, which comprises a fairwater cover and a negative Poisson's ratio metamaterial inside the fairwater cover. Figure 9 As shown in the figure.

[0026] The fairwater cover structure is connected to the head of the vehicle, so that the fluid-solid isolation between the head of the vehicle and water during the water entry process of the vehicle is realized.

[0027] The internal star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial is subjected to axial extrusion during water entry, and continuously absorbs energy through compression and crushing, thereby reducing the load of the vehicle water entry impact.

[0028] The negative Poisson's ratio metamaterial is an improved structure based on the existing star-shaped-quadrilateral negative Poisson's ratio structure. The improved star-shaped-quadrilateral negative Poisson's ratio structure is a square cell structure: the side length is H, the middle is a four-corner star structure, the top of the four acute angles alpha is connected with four quadrilaterals each containing only a right angle and being symmetrical along the straight angle bisector, the right angle side length of the quadrilateral is L1, the non-right angle side length is L2, the included angle between the two right angle sides and the adjacent non-right angle side is theta, the included angle between the four-corner star edges and the vertical direction is (pi / 4-alpha / 2) or the remaining angle, the four-corner star edge length is L3, the included angle between the four-corner star edges and the horizontal direction is (pi / 4+alpha / 2) or the remaining angle, the skeleton length of the four-corner star recess is L4, the edge width on the cell plane is T, and the extrusion thickness perpendicular to the plane is b. Each cell is a whole during processing. Each cell is connected through adjacent right angle edges and right angle edges in the plane structure, and the skeleton is connected with the skeleton. The connection form in the vertical plane direction (i.e. the thickness) is shown in the figure. Figure 4As shown: the processing technology to be adopted by the application is pouring mold, the thickness direction is the length of the mold, and the metal liquid is solidified and connected together during pouring.

[0029] Generally, θ is in the range of 0.35*π to 0.42*π, α is in the range of 0.2*π to 0.3*π, and L2 is in the range of L3 is in the range of

[0030] The rectifier head cover structure: the rectifier head cover is a rotary body, the whole is a flat head side inclined wrapping type, the rectifier head cover is in contact with the navigation body, the head diameter is D1, the axial matching length of the rectifier head cover and the navigation body is D2, the chamfer between the inclined surface of the navigation body matched in the rectifier head cover and the outer side surface of the head cover is β, the side surface transitions to the flat head with a round corner radius R, the flat head part of the rectifier head cover is filled and pressed with a thickness of D3, the side edge wrapping is filled and pressed with a thickness of D4, and the shell thickness is t.

[0031] D2 is in the range of 2*D1 to 5*D1, D3 is in the range of 1.5*D4 to 3*D4, β is in the range of π / 3 to π / 2, t << D2, and t < D4.

[0032] In the formula, U m is the specific energy absorption, U is the total energy absorbed, M is the mass of the structure, v is the total volume of the honeycomb structure, which is obtained by assuming that the equivalent volume V is in a dense state and the void ratio Ψ is obtained, and the corresponding total volume of the honeycomb structure is obtained, wherein the void ratio of the unit cell is about 80%, and the equivalent volume V is N 长 *H 宽 *H 2 *b, N 长 is the number of unit cells arranged in the longer side of the unit cell matrix in the plane, N 宽 is the number of unit cells arranged in the shorter side of the unit cell matrix in the plane, H is still the edge length of the unit cell, b is still the extrusion thickness perpendicular to the plane, and for irregular shapes, SW modeling is generally used, and the specific volume can be obtained in mass analysis; U v is the energy absorbed per unit volume; σ is the internal stress of the star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial; ε d is the densification strain of the star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial, that is, the strain when the star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial begins to densify and the stress rapidly increases; ε is the strain deformation amount of the star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial; ρ r is the relative density of the negative Poisson's ratio honeycomb structure, and the relative density at this time is the ratio of the density of the negative Poisson's ratio honeycomb structure to the density of the negative Poisson's ratio honeycomb matrix material; ρ s is the density of the negative Poisson's ratio honeycomb matrix material.

[0033] A large part of the energy absorption depends on the ε mentioned above. d And σ. Both are related to the size of the unit cell, where ε d It is generally represented by the side length deformation of a single cell under longitudinal strain, and its compact configuration is as follows: Figure 10 As shown, under a longitudinal strain of σ, the longitudinal deformation is H-H1 (the side length after deformation), and σ is... The parameters correspond to those of the unit cell parameters mentioned above, with σ0 generally being the initial unit cell value specific to this type of negative Poisson's ratio material. However, according to the corresponding structural mechanics theory, under high-speed impact, inertial forces dominate. When the upper cell is compressed, most of the lower cells remain in a state of minimal deformation. In this case, the overall σ0 can be equivalent to the plateau stress σ1 under low-speed conditions.

[0034] Where σ ys Let η be the yield stress of the honeycomb matrix material, and η be a proportionality coefficient between 0 and 1. For this structure, η can be roughly calculated as 0.3. According to the calculation by the program, it can be concluded that the above parameter values ​​have a relatively good high-speed energy absorption effect. The following is a specific simulation case to support this.

[0035] Within the dimensional range, the unit cell parameters are: α = 45°, thickness T = 0.5mm, L1 = 2.9mm, L2 = 2.2mm, θ = 70°, L3 = 3.45mm, L4 = 3.6mm, and b = 100mm, using a 4×4 cell matrix. Simulation is performed using the shell163 element in ANSYS, referencing... Energy absorption monitoring points were set up to compare the energy absorption ratio images under impacts of 30 m / s and 100 m / s. The simulation images are as follows: Figure 2 As shown, both the rigid impact plate and the fixed impact plate are made of structural steel, while the internal star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial is made of aluminum alloy with a Poisson's ratio of 0.3. Its simulated specific energy absorption results are as follows: Figure 3 As shown, it is evident that at high speed (100 m / s), its specific energy absorption is greater than that at low speed (30 m / s) until it is fully compressed into a compact state. Therefore, it can be concluded that its star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial still possesses relatively excellent energy absorption properties under high-speed impact loads.

[0036] according to Figure 3 The rectifier head cover has the following parameters: θ = 45°, D1 = 12mm, D2 = 20mm, D3 = 60mm, corner radius R = 10mm, D4 = 10mm, and shell thickness t = 1mm. Figure 4The star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial unit cell structure has L1 of 2.9 mm, L2 of 2.2 mm, L3 of 3.45 mm, L4 of 3.6 mm, H of 10.42 mm, θ of 70°, α of 45°, and a thickness T of 0.5 mm on each side of the unit cell. The outer rectifier head cover material can be a structural rigid material with high compressive strength, while the inner star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial can be an aluminum alloy material with a Poisson's ratio of 0.3. In actual production, the cuboid star-shaped negative Poisson's ratio metamaterial can be cast using a mold, based on the above... Figure 6 The material is cut to specific dimensions and burrs are removed. Because the negative Poisson's ratio metamaterial contracts laterally under axial compression and exhibits a certain degree of elastic deformation, the star-shaped negative Poisson's ratio metamaterial can be manually pressed into the fairing. Then, the nose of the aircraft can be manually fitted directly into the fairing. After fitting, as shown... Figure 7 As shown, the details are as follows Figure 8 As shown.

[0037] After the buffer hood is combined with the vehicle body, it enters the water at high speed. When the flat-headed fairing enters the water, it first forms a supercavitation to achieve fluid-structure isolation between the head of the vehicle body and the water. Then, the star-shaped-quadrilateral negative Poisson's ratio honeycomb metamaterial inside the buffer hood is subjected to axial compression and undergoes deformation and breakage process to continuously absorb energy, thereby reducing the impact load on the vehicle body under high-speed water entry and achieving the goal of safe and high-speed water entry of the vehicle body.

[0038] This invention employs a flat-bottomed fairing to achieve fluid-structure isolation between the vehicle's nose and the water, making it suitable for high-speed water entry and improving entry stability. This invention utilizes a star-shaped to quadrilateral negative Poisson's ratio honeycomb metamaterial, which can absorb more impact kinetic energy compared to common energy-absorbing materials such as aluminum foam; compared to simple spring energy absorption, it can effectively reduce load oscillations and improve stability.

Claims

1. A metamaterial load alleviating structure suitable for high speed water entry impact, characterized in that, The rectifier head cover and the negative Poisson's ratio honeycomb structure inside the rectifier head cover are included. The negative Poisson's ratio honeycomb structure is composed of a plurality of star-tetragonal unit cells; each unit cell includes a central star-shaped structure and a tetragonal structure arranged at four corners of the star-shaped structure; the tetragonal structure is provided with only one right angle, and the corners of the star-shaped structure are connected to opposite corners of the right angle of the tetragonal structure; the recesses of the star-shaped structure are provided with skeletons; and each unit cell is connected to the right angle through adjacent straight edges. The angle between each edge of the star-shaped structure and the vertical direction is (π / 4-α / 2) or the remaining angle, and the angle between each edge of the star-shaped structure and the horizontal direction is (π / 4+α / 2) or the remaining angle; the angle θ between the right angle of the tetragonal structure and the adjacent non-right angle is in the range of 0.35*π to 0.42*π; and the angle α of the corner of the star-shaped structure is in the range of 0.2*π to 0.3*π. The super material load reduction structure is arranged on the rectifier head cover arranged on the head of the navigation body, is used for fluid isolation of the head of the navigation body and water during the navigation body entering the water, and continuously compresses and deforms through the negative Poisson's ratio star-tetragonal honeycomb super material filled inside, and continuously absorbs impact kinetic energy. The rectifier head cover is a spin body, and is a flat head side inclined wrapping type; the axial fitting length D2 of the rectifier head cover and the navigation body is in the range of 2*D1 to 5*D1, D1 is the head diameter; the flat head filling thickness D3 of the rectifier head cover is in the range of 1.5*D4 to 3*D4, D4 is the side wrapping filling thickness, the value range of the chamfer β between the inclined surface of the navigation body matched with the rectifier head cover and the outer side surface of the rectifier head cover is π / 3 to π / 2; the shell thickness t of the rectifier head cover is less than D2 and less than D4.

2. The metamaterial load alleviating structure suitable for high speed water entry impact according to claim 1, characterized in that, The specific energy absorption is realized by adjusting the internal stress value σ, wherein σ is: wherein σ0 is the initial stress value of each unit cell; b is the extrusion thickness; L1 is the length of the right angle side of the quadrilateral structure, L2 is the length of the non-right angle side of the quadrilateral structure, L3 is the length of each side of the quadrangular star structure, L4 is the skeleton length of the quadrangular star structure, θ is the included angle between the right angle side and the adjacent non-right angle side of the quadrilateral structure, α is the top angle of the quadrangular star structure, T is the width of each side in the horizontal plane of the unit cell, ρ s is the material density of the negative Poisson's ratio honeycomb structure, and v is the total volume of the negative Poisson's ratio honeycomb structure.

3. The metamaterial load alleviating structure suitable for high speed water entry impact according to claim 2, characterized in that, L2 has a value range of L3 has a value range of

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