Flutter suppression device based on nonlinear superstructure and design method thereof

Abstract

The invention provides a flutter suppression device based on a nonlinear superstructure and a design method thereof.The flutter suppression device comprises a plurality of nonlinear oscillator unit cells arranged in an array mode, each nonlinear oscillator unit cell comprises four springs and a mass block assembly with the adjustable mass, the four springs are symmetrically arranged, and the mass block assembly is arranged between the four springs; the two ends of the spring are detachably connected with the side wall of the mass block assembly and the controlled stiffened wall plate respectively. The springs have pre-pressure or pre-tension force, so that the nonlinear oscillator unit cells can generate adjustable nonlinear band gap characteristics. According to the method, the unit cell parameters are designed and adjusted according to the actual situation of the controlled stiffened wall plate, flutter suppression of the controlled stiffened wall plate is achieved while the main structure is not damaged, the suppression effect is high, and the method is suitable for engineering application.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft aeroelastic design and flutter suppression, and in particular relates to a flutter suppression device based on a nonlinear superstructure and a design method thereof. Background Art

[0002] In the field of aerospace, when an aircraft flies at high speed in the atmosphere, the mutual coupling between aerodynamic force, elastic force and inertial force, as well as the aerodynamic heating effect caused by the viscosity of air during high Mach number flight, cause complex aeroelastic problems in the aircraft structure, which have a very serious impact on the normal flight and safety of the aircraft. Among them, flutter is one of the most prominent problems in aeroelastic problems. Once the aircraft is instability due to flutter, it will lead to serious accidents. Especially in hypersonic flight, the temperature effect caused by aerodynamic heating will seriously affect the aeroelastic characteristics of the aircraft wing, wall panel and other structures. At this time, under the joint action of inertial force, elastic force, aerodynamic force and aerodynamic heat, aerodynamic force, structure and material may show nonlinear characteristics, thereby reducing the flutter stability boundary of the aircraft, and even when the linear critical flutter speed is not reached, the wing and other structures will have limit cycle motion, resulting in structural fatigue failure. Therefore, the research on the improvement of the flutter boundary and dynamic response suppression of the aircraft structure has important academic research value and engineering application background, and is of great significance to the design of future hypersonic aircraft.

[0003] The research on suppressing the flutter of aircraft structures and adverse aeroelastic behavior has become one of the important issues that many researchers and aviation engineers are currently concerned about. Among them, active flutter suppression technology has received widespread attention because it is suitable for vibration control under variable conditions. However, the application of active control technology has problems such as high cost and poor reliability of intelligent material performance. It is difficult to apply to high temperature environments and faces many challenges in actual engineering applications. Existing passive suppression technology is mainly implemented by mass balance or increasing structural stiffness. Although the technology is safe and reliable, it changes the structural characteristics of the system and usually has a more complex and bulky structure, which violates the design principle of lightweight structure. In order to ensure that the aircraft can fly safely and stably under complex flight conditions, have good static / dynamic stability, and avoid catastrophic accidents such as flutter, it is necessary to conduct in-depth research on the flutter stability of aircraft structures and obtain a flutter suppression design method that is simple in structure and easy to apply.

[0004] Most of the newly proposed nonlinear energy sink (NES) devices for flutter suppression of wings and panels are designed to achieve their nonlinear characteristics by designing nonlinear spring oscillators with zero linear stiffness. However, the nonlinear energy sink device usually needs to be installed at the maximum modal strain energy of the controlled structure, and the maximum strain energy position of the aeroelastic mode under the action of airflow will change, resulting in the strong sensitivity of the nonlinear energy sink device to the installation position, resulting in limited suppression effect of the aeroelastic performance generated by the nonlinear energy sink device. In summary, the traditional nonlinear energy sink has the following shortcomings: 1. The structural design and installation are relatively complex, and there are high requirements for the installation space; 2. The installation position needs to be optimized and designed. If the installation position design is unreasonable, it will affect the flutter suppression effect; 3. The geometric parameters, stiffness characteristics, etc. cannot be changed once the design and processing are completed, and they are not adjustable and adaptive. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing aircraft structure flutter suppression devices, such as complex structure and poor flutter suppression reliability, and to provide a flutter suppression device based on a nonlinear superstructure and a design method thereof. The present invention is based on mechanical metamaterials / superstructures, combines nonlinear mechanical superstructures with aeroelastic systems, and realizes low-bandwidth vibration reduction of the structure by reasonably designing the oscillator parameters of the superstructure and utilizing its bandgap characteristics, thereby effectively suppressing the flutter of the aircraft structure.

[0006] To achieve the above purpose, the technical solution provided by the present invention is:

[0007] A nonlinear oscillator unit cell comprises four springs and a mass block assembly, wherein the mass of the mass block assembly is adjustable;

[0008] The four springs are symmetrically arranged, and the two ends of the springs are detachably connected to the side wall of the mass block assembly and the controlled stiffened wall plate respectively; the springs have pre-pressure or pre-tension, which can make the nonlinear oscillator unit cell produce adjustable nonlinear band gap characteristics.

[0009] Further, it is characterized in that the mass block assembly includes a mass block and a support plate;

[0010] The mass block is attached to the center of the support plate;

[0011] The support plate is evenly distributed with four through holes for engaging with the ends of the springs.

[0012] A flutter suppression device based on a nonlinear superstructure, the nonlinear oscillator unit cell; a controlled stiffened wall panel has a plurality of grids composed of stiffening ribs; a plurality of the nonlinear oscillator unit cells are arranged in a periodic array on the grid of the controlled stiffened wall panel; the nonlinear oscillator unit cells are respectively connected to the stiffening ribs through detachable connectors.

[0013] Furthermore, the detachable connecting member includes a base and a connecting boss assembly located on the top of the base;

[0014] A clamping groove is provided at the bottom of the base for clamping and cooperating with the cross-intersection position of the two reinforcing ribs;

[0015] The connecting boss assembly includes a first limiting boss, a connecting column and a second limiting boss which are coaxially connected from top to bottom; and the end of the spring is clamped on the connecting column.

[0016] The design method of a flutter suppression device based on a nonlinear superstructure comprises the following steps:

[0017] Step 1: Establish a mechanical model including a controlled stiffened panel and a flutter suppression device based on a nonlinear superstructure;

[0018] Step 2: According to the natural frequency of the controlled stiffened wall panel, the unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell are preset, and the fundamental frequency of the nonlinear oscillator unit cell is less than the first-order natural frequency of the controlled stiffened wall panel;

[0019] Step 3: Adjust the unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell, solve the flutter characteristics of the pure controlled stiffened wall panel and the controlled stiffened wall panel with additional flutter suppression device under different parameters, judge the influence of the nonlinear oscillator unit cell on the flutter stability of the controlled stiffened wall panel under different parameters, and take the unit cell mass, spring stiffness and fundamental frequency when the flutter characteristics are maximum as the optimal linear parameters of the nonlinear oscillator unit cell;

[0020] Step 4: Adjust the spring pretension ratio γ to change the nonlinear stiffness k of the nonlinear unit cell NL The post-flutter responses of the pure controlled stiffened panel and the controlled stiffened panel with additional flutter suppression device are calculated respectively, and the suppression effect of the nonlinear oscillator unit cell on the flutter characteristics of the controlled stiffened panel under different pre-tension ratios γ is compared and analyzed, and the pre-tension ratio with the highest suppression effect is taken as the optimal pre-tension ratio of the nonlinear oscillator unit cell;

[0021] Step 5: Design and determine the initial length of the spring based on the optimal pre-tension ratio and the mesh size on the controlled reinforcement edge;

[0022] Step 6: Arrange the nonlinear oscillator unit cells in an array according to the number and layout of grids on the controlled stiffened wall panel.

[0023] Furthermore, in the step 1, a mechanical model including a controlled stiffened wall panel and a flutter suppression device based on a nonlinear superstructure is established based on the Galerkin method.

[0024] Furthermore, in step 2, when the unit cell mass is preset, the mass of the spring and the bottom support plate of the mass block are ignored.

[0025] Furthermore, in step 3, the flutter characteristics include flutter speed and flutter frequency.

[0026] The advantages of the present invention are:

[0027] 1. The flutter suppression device of the present invention comprises a plurality of nonlinear oscillator cells, each of which is composed of four springs and a mass block located at the center of the springs. The nonlinear oscillator cells are arranged in a periodic array on the controlled stiffened wall panel to form an adjustable nonlinear superstructure with nonlinear bandgap characteristics. The flutter instability and aeroelastic response of the controlled main structure are suppressed by adjusting the oscillator parameters of the nonlinear oscillator cells and utilizing the nonlinear bandgap characteristics. The design of the present invention breaks the mass constraints of traditional linear superstructures and provides a new design idea for flutter suppression in various engineering fields, especially in the field of aeroelastic response suppression of plate and shell structures, which has broad application prospects.

[0028] 2. The springs in the nonlinear oscillator unit cell of the present invention can be springs of different stiffness and length according to actual conditions, and can be installed on the ribs through the base connector, so as to suppress the aeroelastic response of the controlled main structure without destroying the main structure.

[0029] 3. The nonlinear oscillator unit cell designed in the present invention is adjustable, and its nonlinear stiffness coefficient k can be changed by adjusting the pre-compression length or pre-tension length of the spring. 1 , which makes the flutter suppression device of the present invention have strong adaptability.

[0030] 4. The flutter suppression device of the present invention has a simple structure, is easy to process and install, has a wide range of uses, has high reliability, and is more suitable for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0032] Figure 1 It is a schematic diagram of the cooperation between the flutter suppression device based on the nonlinear superstructure and the controlled stiffened wall panel of the present invention;

[0033] Figure 2 It is a schematic diagram of the structure of the nonlinear oscillator unit cell in the present invention;

[0034] Figure 3It is a schematic diagram of the connection between the detachable connecting member and the reinforcing ribs of the controlled reinforced wall panel in the present invention;

[0035] Figure 4 is the relationship between the nonlinear restoring force and displacement of the nonlinear oscillator unit cell in the present invention;

[0036] Figure 5 is a comparison diagram of the flutter characteristics of a controlled stiffened wall panel structure with the flutter suppression device of the present invention added thereto and a pure stiffened wall panel structure;

[0037] Figure 6 is a bifurcation diagram of the flutter response of the three-dimensional stiffened wall panel structure after the flutter suppression device of the present invention is added;

[0038] Figure 7 It is the bifurcation diagram of the flutter response of the three-dimensional stiffened panel structure under different stiffness parameters of the oscillator in the nonlinear oscillator unit cell.

[0039] Explanation of the reference numerals: 1-controlled stiffened wall panel, 2-nonlinear oscillator unit cell, 3-spring, 4-mass block, 5-strengthening ribs, 6-support plate, 7-detachable connector. DETAILED DESCRIPTION

[0040] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0041] Reference Figure 1 This embodiment proposes a nonlinear oscillator unit cell, including four springs 3 and a mass block assembly, wherein the four springs 4 are symmetrically arranged, and one end of the spring is detachably connected to the side wall of the mass block assembly. The other end of the spring is used to connect to the controlled stiffened wall plate. The mass of the mass block assembly is adjustable, and by adjusting the pre-compression or pre-tension length of the spring, the nonlinear oscillator unit cell can generate an adjustable nonlinear band gap characteristic.

[0042] Specifically, the mass block assembly includes a mass block 4 and a support plate 6, wherein the mass block 4 is pasted at the center of the support plate 6. The support plate 6 is evenly provided with four through holes for engaging with the ends of the springs.

[0043] The four springs in the nonlinear oscillator unit cell described in this embodiment have preload or prestress, and can generate nonlinear restoring force in the vertical direction, so they have nonlinear stiffness characteristics. The length and spring stiffness of the spring can be designed according to the nonlinear stiffness design requirements, and the preload or pretension length of the spring needs to be adjusted.

[0044] Reference Figure 2This embodiment proposes a flutter suppression device based on a nonlinear superstructure, including a plurality of the above-mentioned nonlinear oscillator cells, which are arranged on the controlled stiffened wall panel in a periodic array. Specifically, the controlled stiffened wall panel has a plurality of grids composed of stiffening ribs 5, and the number and array mode of the nonlinear oscillator cells are the same as the number and layout mode of the grids. The four spring ends of the nonlinear oscillator cell are detachably connected to the cross-intersection positions of the stiffening ribs in the grid through a detachable connector 7. The dynamic characteristics of the nonlinear oscillator cell can be adjusted by adjusting the pre-tension or pre-compression state of the spring 3.

[0045] Reference Figure 3 The detachable connector includes a base and a connecting boss assembly arranged on the top of the base. A slot is provided at the bottom of the base for engaging with the cross position of the two reinforcing ribs. The connecting boss assembly includes a first limiting boss, a connecting column and a second limiting boss coaxially connected from top to bottom; the end of the spring is engaged with the connecting column.

[0046] The reinforcing ribs of the controlled reinforced wall panel 1 are rectangular, and the reinforcing ribs 5 are bidirectionally distributed. Multiple reinforcing ribs are evenly distributed on the wall panel to form a three-dimensional reinforced wall panel structure. The length, width and thickness of the three-dimensional reinforced wall panel are ap, bp and hp respectively. The specific size is determined according to the actual structure and load conditions. In this embodiment, the length, width and thickness of the controlled reinforced wall panel are ap=1.0m, bp=1.0m, hp=5mm respectively. The rectangular reinforcing ribs 5 are integrated with the wall panel, and the cross-sectional parameters of the reinforcing rib adjustment strips 5 are determined according to the load conditions. The wall panel and the reinforcing ribs are made of 7075 aluminum alloy, and its density, Young's modulus and Poisson's ratio are 2700kg / m3, 71.7GPa and 0.33 respectively. The material of the circular support and the base connector is ABS resin material, and its density, Young's modulus and Poisson's ratio are 1050kg / m3, 1.8Gpa, and 0.397 respectively. The mass block is made of lead material and its density is 11343.7kg / m3.

[0047] The dimensions of the nonlinear oscillator unit cells arranged in an array on the controlled stiffened wall plate of this embodiment are: spring stiffness k = 130 N / m, and the stretched length L of the spring after installation 0 =0.064m, the length of the spring after unloading is L = 0.06m. The size of the mass block is 0.01×0.01×0.003mm 3 The fundamental frequency of the nonlinear oscillator unit cell is set at a position lower than the first-order natural frequency of the controlled stiffened wall panel.

[0048] Based on the above-mentioned controlled stiffened wall panel parameters and controlled requirements, this embodiment proposes a design method for a flutter suppression device based on a nonlinear superstructure, including the following steps:

[0049] Step 1: Establish a mechanical model including a controlled stiffened panel and a flutter suppression device based on a nonlinear superstructure based on the Galerkin method;

[0050] Step 2: According to the natural frequency of the controlled stiffened wall panel, the unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell are preset, and the fundamental frequency of the nonlinear oscillator unit cell is less than the first-order natural frequency of the controlled stiffened wall panel;

[0051] The mass of the spring and the supporting plate at the bottom of the mass block are ignored during the design process. Therefore, the unit cell mass here is the mass of the mass block.

[0052] Step 3: Adjust the unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell, and solve the flutter characteristics (including flutter velocity and flutter frequency) of the pure controlled stiffened wall panel and the controlled stiffened wall panel with additional flutter suppression device under different parameters by using the state space eigenvalue method, and judge the influence of the nonlinear oscillator unit cell on the flutter stability of the controlled stiffened wall panel under different parameters. The unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell when the flutter velocity and flutter frequency are maximum are taken as the optimal linear parameters of the nonlinear oscillator unit cell.

[0053] Step 4: Adjust the pre-pull ratio γ of the nonlinear oscillator unit cell to change the nonlinear stiffness k of the nonlinear unit cell NL , and use the Runge-Kutta method or other numerical methods to calculate the post-flutter responses of the pure controlled stiffened wall panel and the controlled stiffened wall panel with additional flutter suppression device, respectively. Compare and analyze the suppression effect of the nonlinear oscillator unit cell on the flutter characteristics of the controlled stiffened wall panel under different pre-tension ratios γ, and take the pre-tension ratio with the highest suppression effect as the optimal nonlinear parameter of the nonlinear oscillator unit cell, that is, the spring pre-tension ratio.

[0054] Step 5: According to the optimal pre-tension ratio and the mesh size on the controlled reinforcement edge, the initial length of the spring is designed;

[0055] Step 6: Arrange the nonlinear oscillator unit cells in an array according to the grid layout and quantity on the controlled stiffened wall panel.

[0056] When the controlled stiffened wall panel is affected by external airflow, the flutter suppression device based on the nonlinear superstructure designed in this embodiment can generate nonlinear vibration, so that the vibration energy of the controlled stiffened wall panel is transmitted in large quantities to the flutter suppression device composed of a plurality of nonlinear oscillator unit cell arrays, and utilizes its nonlinear band gap characteristics to achieve the purpose of efficient flutter suppression.

[0057] Figure 4 The relationship between the nonlinear restoring force and displacement of the nonlinear oscillator unit cell is given. It can be seen from the figure that when the nonlinear oscillator unit cell moves in a direction perpendicular to the controlled stiffened wall panel, a nonlinear elastic restoring force will be generated, indicating that within the motion range of the nonlinear oscillator unit cell, the nonlinear oscillator unit cell exhibits a significant nonlinear effect.

[0058] In order to analyze the flutter characteristics of the controlled stiffened wall panel after the flutter suppression device of the present invention is added, this embodiment calculates the unsteady aerodynamic force of the controlled stiffened wall panel in supersonic airflow based on the first-order piston aerodynamic theory, and analyzes the flutter stability and aeroelastic response characteristics. The flight state is Mach number Ma=3.0, air density ρ ∞ =1.226kg / m 3 .

[0059] like Figure 5 As shown in FIG. 1 , it is a comparison diagram of the flutter characteristics of the controlled stiffened wall panel and the pure stiffened wall panel structure with the flutter suppression device of the present invention. It can be seen from the figure that the flutter boundary λ of the pure stiffened wall panel structure cr =369.91, and the flutter boundary of the controlled stiffened panel with the flutter suppression device of the present invention is λ cr =397.9, the flutter stability margin is improved by 7.6%.

[0060] like Figure 6 As shown in FIG. 1 , it is a bifurcation diagram of the flutter response of the three-dimensional stiffened wall panel structure with the controlled stiffened plate after the flutter suppression device of the present invention is added. It can be seen that at the flutter critical point λ cr =397.9, the original divergent aeroelastic response can be suppressed to a stable limit cycle response with a finite amplitude. When the dynamic pressure λ<422, the limit cycle response amplitude is stabilized within w / h=2, further widening the stability boundary to 14.1%, achieving effective suppression of the post-flutter response of the aeroelastic system.

[0061] like Figure 7 As shown, it is a bifurcation diagram of the post-flutter response of the three-dimensional stiffened wall panel structure under different stiffness parameters of the mesh nonlinear oscillator. It can be seen that with the increase of the spring stiffness system k and the decrease of the pre-tension parameter γ, the nonlinear stiffness of the mesh nonlinear oscillator gradually increases, its passive suppression performance is significantly improved, and the post-flutter response amplitude of the three-dimensional stiffened wall panel is significantly reduced. This shows that the mesh nonlinear superstructure of the present invention can improve the flutter stability boundary of the controlled three-dimensional wall panel structure by adjusting the oscillator spring stiffness and pre-tension length, and suppress the post-flutter response amplitude of the system, thereby realizing the adjustability of the flutter suppression performance.

[0062] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be included in the protection scope of the present invention.

Claims

1. A nonlinear oscillator unit cell, characterized in that: It includes four springs and a mass block assembly, and the mass of the mass block assembly is adjustable; The four springs are symmetrically arranged, and the two ends of the springs are detachably connected to the side wall of the mass block assembly and the controlled stiffened wall plate respectively; the springs have pre-pressure or pre-tension, which can make the nonlinear oscillator unit cell produce adjustable nonlinear band gap characteristics.

2. The nonlinear oscillator unit cell according to claim 1, characterized in that: The mass block assembly comprises a mass block and a support plate; The mass block is attached to the center of the support plate; The support plate is evenly distributed with four through holes for engaging with the ends of the springs.

3. A flutter suppression device based on a nonlinear superstructure, characterized in that: A nonlinear oscillator unit cell comprising the nonlinear oscillator unit cell according to claim 1 or 2; The controlled stiffened wall panel has a plurality of grids formed by stiffening ribs; A plurality of the nonlinear oscillator unit cells are arranged in a periodic array on the grid of the controlled stiffened wall panel; The nonlinear oscillator unit cells are connected to the reinforcing ribs through detachable connecting parts respectively.

4. The flutter suppression device based on nonlinear superstructure according to claim 3, characterized in that: The detachable connecting member includes a base and a connecting boss assembly located on the top of the base; A card slot is provided at the bottom of the base for carding with the cross-intersection position of the two reinforcing ribs; The connecting boss assembly includes a first limiting boss, a connecting column and a second limiting boss which are coaxially connected from top to bottom; and the end of the spring is clamped on the connecting column.

5. A design method for a flutter suppression device based on a nonlinear superstructure, characterized in that: The following steps are involved: Step 1: Establish a mechanical model including a controlled stiffened panel and a flutter suppression device based on a nonlinear superstructure; Step 2: According to the natural frequency of the controlled stiffened wall panel, the unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell are preset, and the fundamental frequency of the nonlinear oscillator unit cell is less than the first-order natural frequency of the controlled stiffened wall panel; Step 3: Adjust the unit cell mass, spring stiffness and fundamental frequency of the nonlinear oscillator unit cell, solve the flutter characteristics of the pure controlled stiffened wall panel and the controlled stiffened wall panel with additional flutter suppression device under different parameters, judge the influence of the nonlinear oscillator unit cell on the flutter stability of the controlled stiffened wall panel under different parameters, and take the unit cell mass, spring stiffness and fundamental frequency when the flutter characteristics are maximum as the optimal linear parameters of the nonlinear oscillator unit cell; Step 4: Adjust the spring pretension ratio γ to change the nonlinear stiffness k of the nonlinear unit cell NL The post-flutter responses of the pure controlled stiffened panel and the controlled stiffened panel with additional flutter suppression device are calculated respectively, and the suppression effect of the nonlinear oscillator unit cell on the flutter characteristics of the controlled stiffened panel under different pre-tension ratios γ is compared and analyzed, and the pre-tension ratio with the highest suppression effect is taken as the optimal pre-tension ratio of the nonlinear oscillator unit cell; Step 5: Design and determine the initial length of the spring based on the optimal pre-tension ratio and the mesh size on the controlled reinforcement edge; Step 6: Arrange the nonlinear oscillator unit cells in an array according to the number and layout of the grids on the controlled stiffened wall panel.

6. The design method of a flutter suppression device based on a nonlinear superstructure according to claim 5, characterized in that: In the step 1, a mechanical model including a controlled stiffened wall panel and a flutter suppression device based on a nonlinear superstructure is established based on the Galerkin method.

7. The design method of a flutter suppression device based on a nonlinear superstructure according to claim 5, characterized in that: In step 2, when the unit cell mass is preset, the mass of the spring and the support plate at the bottom of the mass block is ignored.

8. The design method of a flutter suppression device based on a nonlinear superstructure according to claim 5, characterized in that: In step 3, the flutter characteristics include flutter speed and flutter frequency.

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