Metamaterial load reduction structure and method suitable for high-speed water entry impact

Abstract

The invention discloses a metamaterial load reduction structure and method suitable for high-speed water entry impact. The metamaterial load reduction structure comprises a rectification head cover and a negative Poisson's ratio honeycomb structure in the rectification head cover. The negative Poisson's ratio honeycomb structure is composed of a plurality of star-quadrilateral unit cell elements; each unit cell element comprises a quadrangular star-shaped structure located in the middle and quadrilateral structures arranged at the four vertex angles of the quadrangular star-shaped structure; the quadrangular structure is provided with a unique right angle, and the vertex angle of the quadrangular star-shaped structure is connected with the opposite angle of the right angle of the quadrangular structure. A framework is arranged at the concave part of the quadrangular star-shaped structure; the cell elements are connected with the right-angle sides through the adjacent right-angle sides, and the skeletons are connected with the adjacent skeletons. According to the metamaterial load reduction structure, the impact load borne by the navigation body when the navigation body enters water can be reduced, and the high-speed safe entry of the navigation body into water is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed cross-medium water entry load reduction, and in particular relates to a metamaterial load reduction structure and method suitable for high-speed water entry impact. Background Art

[0002] Compared with traditional launch methods, airdrop or rocket-assisted launch have obvious advantages. They can not only achieve long-distance launch, ensure the concealment of the launch process and ensure the safety of the launch platform, but also increase the operating range and flexibility of the spacecraft, so that it can perform a wider range of tasks.

[0003] When underwater vehicles are launched by airdrop or rocket-assisted launch, one of the main challenges they face is the high-speed water entry phase. During this process, the vehicle will encounter strong impacts from the water surface and the huge pressure caused by rapid entry into the water. According to Wagner's classical theory, the impact force on the vehicle when entering the water is proportional to the square of its speed. Therefore, high-speed entry into the water will greatly increase the impact force, which may cause a dynamic response to the structure of the vehicle, resulting in elastic deformation of the shell, and even buckling, breakage or breakage in extreme cases. This poses a severe test for the equipment inside the vehicle. In addition, the impact force may also affect the trajectory stability of the vehicle, which may cause rapid sinking, unstable underwater movement or even loss of control. Therefore, when designing and launching underwater vehicles, reducing the impact force caused by high-speed entry into the water is a very critical technical challenge.

[0004] In recent years, negative Poisson's ratio materials have been widely developed, studied and applied in the field of cross-medium load reduction due to their good energy absorption. Among them, the more classic negative Poisson's ratio unit cell structures include: concave triangle structure, chiral structure, star structure and many combined topological structures. However, most of these structures are only suitable for low-speed entry of the navigation body into the water. They often fail quickly during high-speed entry into the water and are difficult to achieve good energy absorption and load reduction effects. The present invention aims to solve the problem that the navigation body can still achieve good load reduction effects through the crushing energy absorption of special negative Poisson's ratio materials in the high-speed water entry environment. Summary of the invention

[0005] The purpose of the present invention is to provide a metamaterial load reduction structure and method suitable for high-speed water entry impact, so as to reduce the impact load on the vehicle when entering the water and realize high-speed and safe entry of the vehicle into the water.

[0006] The technical solution to achieve the purpose of the present invention is:

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

[0008] The negative Poisson's ratio honeycomb structure is composed of a plurality of star-shaped and quadrilateral unit cells; each unit cell includes a four-pointed star structure located in the middle, and quadrilateral structures arranged at the four vertices of the four-pointed star structure; wherein the quadrilateral structure is provided with a single right angle, and the vertices of the four-pointed star structure are connected to the diagonals of the right angles of the quadrilateral structure; a skeleton is provided in the concave part of the four-pointed star structure; each unit cell is connected to the right angles through adjacent right angle sides, and the skeleton is connected to the adjacent skeleton.

[0009] A metamaterial load reduction structure suitable for high-speed water entry impact, wherein the load reduction method is as follows: the structure is arranged at the head of a navigation body and is used for fluid-solid isolation between the head of the navigation body and water during the navigation body entering the water.

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

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

[0012] (2) Through the fairing shell structure, the fairing shell is a flat head type, and an axisymmetric supercavitation is formed when entering the water, thereby achieving fluid-solid isolation between the head of the navigation body and the water during the entry of the navigation body into the water.

[0013] (3) The internal star-shaped quadrilateral negative Poisson's ratio honeycomb metamaterial is subjected to axial compression when entering water, and continuously absorbs energy through its compression and crushing process, thereby reducing the impact load of the navigation body entering water. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the star-shaped Poisson's ratio unit cell structure.

[0015] Figure 2 The simulation scene diagram of the star-quadric negative Poisson's ratio metamaterial at different speeds.

[0016] Figure 3 The specific energy absorption diagram of the star-quadric negative Poisson's ratio metamaterial at different speeds.

[0017] Figure 4 This is the overall schematic diagram of the star-shaped negative Poisson's ratio metamaterial filled into the fairing.

[0018] Figure 5 for Figure 4 The oblique view shows the connection of the star-quadric negative Poisson's ratio metamaterial in the thickness direction.

[0019] Figure 6This is a schematic diagram of the fairing.

[0020] Figure 7 Schematic diagram of the coordination between the star-shaped Poisson's ratio metamaterial fairing and the vehicle.

[0021] Figure 8 for Figure 4 Enlarged view of the head after sectioning along AA1.

[0022] Fig. 9 The specific physical parameters of aluminum alloy are adopted.

[0023] Fig.10 Comparison of the initial state and dense form of the star-shaped-quadrilateral negative Poisson's ratio metamaterial. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0025] Combination Figure 1-Figure 10 The present embodiment is a metamaterial load reduction structure suitable for high-speed water impact, and the structure includes a fairing and a negative Poisson's ratio metamaterial inside the fairing; the specific physical parameters of the material used are as follows: Fig. 9 As shown;

[0026] The fairing structure is connected to the head of the navigation body to achieve fluid-solid isolation between the head of the navigation body and water during the entry of the navigation body into the water;

[0027] The internal star-quadric negative Poisson's ratio honeycomb metamaterial is subjected to axial compression when entering water, and continuously absorbs energy through its compression and crushing process, thereby reducing the impact load of the vehicle entering water.

[0028] The negative Poisson's ratio metamaterial is an improved structure on the existing star-quadrilateral negative Poisson's ratio structure. The improved star-quadrilateral negative Poisson's ratio structure is a square unit cell structure: the side length is H, the middle is a four-pointed star structure, and the tops of the four acute angles α are connected with the diagonals of the right angles of four quadrilaterals each containing a unique right angle and symmetrical along the right angle bisector. The right angle lengths of the quadrilaterals are all L1, the non-right angle lengths are all L2, the angles between the two right angles and the adjacent non-right angles are all θ, the angles between each side of the four-pointed star and the vertical direction are (π / 4-α / 2) or the remaining angles, the lengths of each side of the four-pointed star are L3, the angles between each side of the four-pointed star and the horizontal direction are (π / 4+α / 2) or the remaining angles, the length of the skeleton extending from the concave part of the four-pointed star is L4, the width of each side on the unit cell plane is T, and the extrusion thickness perpendicular to the plane is b. Each unit cell is a whole during processing. Each cell is connected to the adjacent right angles on the plane structure, and the extended skeleton is connected to the extended skeleton. The connection form in the direction perpendicular to the plane (i.e., in thickness) is Figure 4As shown: the processing technology to be adopted in the present invention is a casting mold, and the draft length of the mold is in the thickness direction. During casting, the metal liquid solidifies and connects together.

[0029] Generally, the value range of θ is 0.35*π~0.42*π. The value range of α is 0.2*π~0.3*π. The value range of L2 is The value range of L3 is

[0030] The fairing cover structure: the fairing cover is a screwed body, and the whole is a flat head with obliquely wrapped sides. The inside of the fairing cover contacts the navigation body, the head diameter is D1, the axial matching length between the fairing cover and the navigation body is D2, the chamfer between the inclined surface of the navigation body inside the fairing cover and the external side of the cover is β, the radius of the transition fillet from the side to the flat head is R, the filling thickness of the flat head of the fairing cover is D3, the filling thickness of the side wrapping is D4, and the shell thickness is t.

[0031] The value range of D2 is 2*D1~5*D1, the value range of D3 is 1.5*D4~3*D4, the value range of β is π / 3~π / 2, t< <D2,t<D4。

[0032] Where 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, and its value is obtained by assuming the equivalent volume V*void ratio Ψ in the dense state, where the void ratio of this single cell is about 80%, and the equivalent volume V is N for the cell matrix. 长 *N 宽 *H 2 *b,N 长 N is the number of cells arranged on the longer side of the cell matrix in the plane, 宽 is the number of cells arranged on the shorter side of the cell matrix in the plane, H is still the side length of the cell, b is still the extrusion thickness perpendicular to the plane. For irregular shapes, we generally use SW modeling, and its 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-quadrangular 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 increases rapidly; ε is the strain deformation 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 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 honeycomb matrix material with negative Poisson's ratio.

[0033] A large part of the specific energy absorption depends on the above ε d and σ. Both are related to the size of the unit cell, where ε d It is usually expressed by the side length deformation of the unit cell under longitudinal strain. Its dense configuration is as follows: Fig.10 As shown, under the longitudinal strain of σ, the longitudinal deformation is H-H1 (the length of the side after deformation), and σ is The parameters are consistent with the above-mentioned unit cell parameters. σ0 is generally the initial value of the unit cell that is unique to this type of negative Poisson's ratio material. However, according to the corresponding structural mechanics theory, under high-speed impact, the inertial force dominates. When the upper unit cell is compressed, most of the lower units are still in a state of small deformation. At this time, the overall σ0 can be equivalent to the platform stress σ1 under low-speed conditions.

[0034] where σ ys is the yield stress of the honeycomb matrix material, η is a proportional coefficient between 0 and 1, and the η of this structure can be roughly calculated as 0.3. According to the program calculation, it can be concluded that the above parameter value range has a better high-speed energy absorption effect. The following is a specific simulation case to support this.

[0035] The parameters of the unit cell in the size range are: α is 45°, thickness T is 0.5mm, L1 is 2.9mm, L2 is 2.2mm, θ is 70°, L3 is 3.45mm, L4 is 3.6mm, b is 100mm, and a 4×4 cell matrix is ​​used. The shell163 unit is used for simulation in ansys, refer to Set up energy absorption monitoring points and compare the energy absorption ratio images under 30m / s and 100m / s impact. The simulation images are as follows: Figure 2 As shown in the figure, the rigid impact plate and the fixed impact plate are both made of structural steel, and the internal star-shaped quadrilateral negative Poisson's ratio honeycomb metamaterial is made of aluminum alloy with a Poisson's ratio of 0.3. The simulation specific energy absorption results are shown in Figure 3 As shown: It can be clearly seen that at high speed (100m / s), its specific energy absorption is greater than that at low speed (30m / s) before it is completely compressed to a compact state. Therefore, it can be seen that the star-quadrangular negative Poisson's ratio honeycomb metamaterial still has relatively good energy absorption properties under high-speed impact loads.

[0036] according to Figure 3 For the fairing, θ is 45°, D1 is 12mm, D2 is 20mm, D3 is 60mm, fillet R is 10mm, D4 is 10mm, and shell thickness t is 1mm. Figure 4The star-shaped quadrilateral negative Poisson's ratio honeycomb metamaterial unit cell structure has L1 of 2.9mm, L2 of 2.2mm, L3 of 3.45mm, L4 of 3.6mm, H of 10.42mm, θ of 70°, α of 45°, and the thickness T of each side of the unit cell is 0.5mm; the external fairing head cover material can be made of structural steel with high compressive strength, and the internal star-shaped quadrilateral negative Poisson's ratio honeycomb metamaterial can be made of aluminum alloy material with a Poisson's ratio of 0.3. In actual production, a rectangular star-shaped negative Poisson's ratio metamaterial can be cast through a mold. Figure 6 The specific size is cut and the burrs are removed. Since the negative Poisson's ratio metamaterial shrinks laterally when axially squeezed and has a certain elastic deformation, the star-shaped negative Poisson's ratio metamaterial can be manually pressed into the fairing, and then the head of the vehicle can be directly matched with the fairing. Figure 7 As shown, the matching details are as follows Figure 8 shown.

[0037] The buffer hood cooperates with the vehicle to enter the water at high speed. When the flat-head fairing hood enters the water, supercavitation is first formed to achieve fluid-solid isolation between the head of the vehicle 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 a deformation and crushing process to continuously absorb energy, thereby reducing the impact load of the vehicle under high-speed entry into the water and achieving the goal of safe and high-speed entry of the vehicle into the water.

[0038] The present invention adopts a flat-bottom fairing to achieve fluid-solid isolation between the head of the navigation body and the water, which is suitable for high-speed water entry and improves water entry stability. The present invention adopts a star-quadrangular negative Poisson's ratio honeycomb metamaterial, which can absorb more impact kinetic energy than common energy-absorbing materials such as foam aluminum; compared with simple spring energy absorption, it can effectively reduce load vibration and improve stability.

Claims

1. A metamaterial load-reducing structure suitable for high-speed water impact, characterized in that: It includes a fairing and a negative Poisson's ratio honeycomb structure inside the fairing; The negative Poisson's ratio honeycomb structure is composed of a plurality of star-shaped and quadrilateral unit cells; each unit cell includes a four-pointed star structure located in the middle, and quadrilateral structures arranged at the four vertices of the four-pointed star structure; wherein the quadrilateral structure is provided with a unique right angle, and the vertices of the four-pointed star structure are connected to the diagonals of the right angle of the quadrilateral structure; a skeleton is provided in the concave part of the four-pointed star structure; each unit cell is connected to the right angle side by the adjacent right angle sides, and the skeleton is connected to the adjacent skeleton.

2. The metamaterial load reduction structure suitable for high-speed water impact according to claim 1, characterized in that: Its specific energy absorption is achieved by adjusting the internal stress value σ, where σ is: Where σ0 is the initial value of the internal stress of each unit cell; b is the extrusion thickness; L1 is the length of the right-angled side of the quadrilateral structure, L2 is the length of the non-right-angled side of the quadrilateral structure, L3 is the length of each side of the four-pointed star structure, L4 is the skeleton length of the four-pointed star structure, θ is the angle between the right-angled side of the quadrilateral structure and the adjacent non-right-angled side, α is the vertex angle of the four-pointed 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 honeycomb structure with negative Poisson’s ratio, and v is the total volume of the honeycomb structure with negative Poisson’s ratio.

3. The metamaterial load reduction structure suitable for high-speed water impact according to claim 1, characterized in that: The value range of θ is 0.35*π~0.42*π; the value range of α is 0.2π~0.3π; the value range of L2 is The value range of L3 is 4. The metamaterial load reduction structure suitable for high-speed water impact according to claim 1, characterized in that: The angle between each side of the four-pointed star structure and the vertical direction is (π / 4-α / 2) or other angles, and the angle between each side of the four-pointed star structure and the horizontal direction is (π / 4+α / 2) or other angles.

5. The metamaterial load reduction structure suitable for high-speed water impact according to claim 1, characterized in that: The fairing is a rotating body, and is in the form of a flat head with obliquely wrapped sides.

6. The metamaterial load reduction structure suitable for high-speed water impact according to claim 1, characterized in that: The axial matching length D2 of the fairing and the navigation body ranges from 2*D1 to 5*D1, where D1 is the head diameter; the filling thickness D3 of the flat head of the fairing ranges from 1.5*D4 to 3*D4, where D4 is the side wrapping thickness; the chamfer angle β between the inclined surface of the navigation body and the external side of the fairing ranges from π / 3 to π / 2; the shell thickness t <D2,t<D4。 7. The metamaterial load reduction structure suitable for high-speed water impact according to any one of claims 1 to 6, characterized in that: The load reduction method is as follows: it is set at the head of the navigation body to separate the fluid and solid between the head of the navigation body and the water during the process of the navigation body entering the water.

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