Evaluation method considering landing gear installation rigidity ground resonance

Abstract

The invention relates to the field of structural strength design of helicopters, in particular to a ground resonance evaluation method considering landing gear installation rigidity. The method comprises the following steps: considering the influence of landing gear mounting rigidity when calculating ground resonance, and obtaining a more real modal parameter of an airframe on a landing gear and a vibration mode of a propeller hub center, so that design can be effectively guided before a dynamic characteristic test of the propeller hub center.

Description

Technical Field

[0001] The invention relates to the field of helicopter structural strength design, and in particular to an evaluation method taking into account ground resonance of landing gear installation stiffness. Background Art

[0002] The ground resonance instability of helicopters depends on the mutual influence of the vibration characteristics of each rotor blade in the rotation plane and the vibration characteristics of the helicopter hub center in the rotation plane, and the nature and degree of mutual influence depend on their respective vibration characteristics. The vibration characteristics of the hub center depend on the overall parameters of the helicopter body and the configuration and stiffness, damping and other performance parameters of the landing gear. The landing gear performance parameters are tested with buffer struts and wheel stiffness and damping characteristics. If these parameters are not selected well, after the external interference, the vibrations of the two vibration systems will couple with each other, aggravate each other, and form a vicious cycle, causing the amplitude to increase rapidly. This phenomenon is the ground resonance of the helicopter; if the parameters are selected appropriately, after the external interference, the vibrations of the two vibration systems will cancel each other out, weaken each other, and the amplitude will gradually decrease, so that ground resonance will not occur. Summary of the invention

[0003] Purpose of the invention: The present invention proposes for the first time to consider the influence of the landing gear installation stiffness when calculating the ground resonance, so as to obtain more realistic modal parameters of the fuselage on the landing gear and the vibration mode of the hub center, thereby effectively guiding the design before the hub center dynamic characteristics test, forming a ground resonance analysis method, and more effectively avoiding the risk of ground resonance.

[0004] Technical solution:

[0005] Provides an evaluation method that takes into account the ground resonance of the landing gear mounting stiffness, including:

[0006] The influence of the landing gear installation stiffness is taken into account when calculating the ground resonance, so as to obtain more realistic modal parameters of the airframe on the landing gear and the vibration mode of the hub center, thereby effectively guiding the design before the hub center dynamic characteristics test.

[0007] Furthermore, the influence of the landing gear mounting stiffness is considered when calculating the ground resonance, so as to obtain more realistic modal parameters of the airframe on the landing gear and vibration mode of the hub center, thus effectively guiding the design before the hub center dynamic characteristics test, including:

[0008] By establishing a local finite element model of the installation stiffness of the landing gear system, the installation stiffness of the landing gear is calculated; through the equilibrium state calculation program, the equivalent wheel center and equivalent stiffness and damping of the landing gear system under different take-off weights and lift states are obtained, and the above parameters are used as input parameters of the landing gear system in the full-aircraft finite element model of the modal calculation of the airframe on the landing gear, and the modal parameters of the airframe on the landing gear are calculated. Then several groups of modal parameter combinations are selected, and the plane dynamic model is used to perform ground resonance calculation and analysis to obtain the calculation results and draw the stability curve.

[0009] Furthermore, the installation stiffness of the landing gear is calculated, including:

[0010] Establish a local finite element model of landing gear mounting stiffness, which includes a part of the fuselage structure, landing gear mounting joints and landing gear system;

[0011] The model is established according to the main force transmission route of the system and the actual structural dimensions of the system to truly simulate the stiffness and mass distribution of the system;

[0012] Determine the connection method between the landing gear system and the fuselage structure and the connection method between the internal structures of the landing gear system;

[0013] Unit loads in three directions are applied to the center of the wheel, and the installation stiffness in three directions is obtained respectively.

[0014] Furthermore, the rod body and frame flange are simulated using beam elements 1D_Beam, the web is simulated using shell elements 2D_Shell, and the landing gear system is simulated using solid elements Tet10.

[0015] Furthermore, the landing gear system and the stub wing are connected by bolts using the rigid body element RBE2 for simulation, and the connections between the various components of the landing gear system are simulated using the rigid body element RBE2 for simulation.

[0016] Furthermore, the equivalent wheel center and equivalent stiffness and damping of the landing gear system under different takeoff weights and lift conditions are obtained through the equilibrium state calculation program, including:

[0017] The compression of the main and tail buffer struts is calculated by the equilibrium state calculation program at different take-off weights and lift states, and the equivalent center of the main and tail wheels is calculated by the compression of the main and tail buffer struts;

[0018] Through the equilibrium state calculation program, the equivalent stiffness and damping of the landing gear system in three directions at the equivalent center of the equivalent main and tail wheels are also obtained.

[0019] Furthermore, the above parameters are used as input parameters of the landing gear system in the full aircraft finite element model for modal calculation of the airframe on the landing gear, and the modal parameters of the airframe on the landing gear are calculated, including:

[0020] The finite element model of the whole aircraft in the landing gear mode is calculated, and the cross-sectional dimensions of the beam unit simulating the landing gear are obtained through the equivalent installation stiffness;

[0021] The finite element model of the whole aircraft in the landing gear mode is calculated, and the equivalent stiffness and damping of the landing gear system are simulated and calculated in the form of spring-damper units;

[0022] The finite element model of the computer body dynamics is used to obtain the six-order modal parameters of the body on the landing gear, where each modal parameter includes frequency, modal mass, modal stiffness, damping and vibration shapes in three directions.

[0023] Beneficial effects:

[0024] The present invention can obtain real landing gear performance parameters, ensure the needs of ground resonance calculation simulation, provide accurate and reliable landing gear performance data for ground resonance strength design, and can carry out ground resonance strength design more accurately, which has high universality and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of a method for evaluating the ground resonance of landing gear mounting stiffness;

[0026] Figure 2 is a schematic diagram of a local finite element model of the installation stiffness of a landing gear according to the present invention;

[0027] Figure 3 It is a schematic diagram of the airframe dynamics finite element model considering the landing gear mounting stiffness;

[0028] Figure 4 It is a graph of ground resonance stability. DETAILED DESCRIPTION

[0029] The present invention uses a local finite element simulation method to simulate the installation stiffness of the landing gear. The local finite element model includes an airframe, a landing gear system installation joint and a landing gear system. The landing gear parameters and airframe parameters are used as input to obtain the landing gear stiffness, which is then equivalent to the full-aircraft finite element calculation model of the airframe at the modal frequency of the landing gear. The ground resonance calculation uses a real simulation of the installation stiffness of the landing gear for the first time, which can more realistically simulate the performance parameters of the landing gear.

[0030] The equivalent wheel center and equivalent stiffness and damping of the landing gear under different takeoff weights and lift conditions are calculated through the equilibrium state calculation program. In the full-aircraft finite element model of the modal calculation of the fuselage on the landing gear, the equivalent installation stiffness of the landing gear is simulated by beam units, and the equivalent stiffness and damping of the landing gear system are simulated by spring-damper units. The modal parameters of the fuselage on the landing gear, including modal mass, modal frequency, damping ratio and vibration mode at the center of the hub, are calculated, and the modal parameters are selected for ground resonance calculation.

[0031] The present invention calculates the installation stiffness of the landing gear by establishing a local finite element model of the installation stiffness of the landing gear system, and proposes for the first time a real simulation of the installation stiffness of the landing gear, thereby being able to more realistically simulate the performance parameters of the landing gear. Through the equilibrium state calculation program, the equivalent wheel center and equivalent stiffness and damping of the landing gear system under different take-off weights and lift states are obtained, and the above parameters are used as input parameters of the landing gear system in the full aircraft finite element model of the modal calculation of the fuselage on the landing gear, and the modal parameters of the fuselage on the landing gear are calculated, and then several groups of modal parameter combinations are selected, and a plane dynamic model is used to perform ground resonance calculation and analysis to obtain calculation results, draw stability curves, and give ground resonance calculation conclusions.

[0032] The specific steps are as follows:

[0033] [1] A local finite element model of the landing gear installation stiffness was established and the landing gear installation stiffness was calculated;

[0034] In order to evaluate the influence of fuselage installation stiffness on ground resonance, a local finite element model of landing gear installation stiffness is established, which includes a part of the fuselage structure, landing gear installation joints and landing gear system. The model is established according to the main force transmission route of the system and the actual structural dimensions of the system to truly simulate the stiffness and mass distribution of the system. Among them, the rod body and frame flange are simulated by beam elements (1D_Beam), the web is simulated by shell elements (2D_Shell), and the landing gear system is simulated by solid elements Tet10 (SOLID). The connection mode between the landing gear system and the fuselage structure and the connection mode between the internal structures of the landing gear system are determined. According to the corresponding force transmission form, the landing gear system and the short wing are connected by bolts and simulated by rigid body elements (RBE2), and the connection between the various components of the landing gear system is simulated by rigid body elements (RBE2). Unit loads in three directions are applied to the center of the wheel, and the installation stiffness in three directions is obtained respectively;

[0035] [2] The compression of the main and tail buffer struts is calculated at different takeoff weights and lift conditions through the equilibrium state calculation program. The equivalent centers of the main and tail wheels are calculated through the compression of the main and tail buffer struts.

[0036] [3] Through the equilibrium state calculation program, the equivalent stiffness and damping of the landing gear system in three directions at the equivalent center of the equivalent main and tail wheels are also obtained;

[0037] [4] Calculate the finite element model of the entire aircraft in the landing gear mode, and obtain the cross-sectional dimensions of the beam unit simulating the landing gear through the equivalent installation stiffness;

[0038] The beam unit of the landing gear system is simulated in the finite element model of the whole aircraft. The installation stiffness of the landing gear is obtained according to step [1], and the cross-sectional dimensions of the beam unit are obtained through equivalent calculation. The traditional approach is to assume that the fuselage installation stiffness is infinitely rigid, which cannot truly simulate the installation stiffness and affects the calculation results of the modal parameters of the fuselage on the landing gear in step [6].

[0039] [5] Calculate the finite element model of the whole aircraft in the landing gear mode, and simulate the equivalent stiffness and damping of the landing gear system calculated in step [3] in the form of spring-damper units;

[0040] In order to simulate the equivalent stiffness and damping of the landing gear system, the wheel center is taken as the base point, and the radius is 100mm around the wheel center. Three nodes are selected in the heading, longitudinal and vertical directions. Two beam elements (1D_Beam) are established between the base point and the heading node. One beam element simulates the heading equivalent stiffness, and the other beam element simulates the heading equivalent damping. The simulation methods of the longitudinal and vertical stiffness and damping are the same as those of the heading.

[0041] [6] The finite element model of the computer body dynamics was used to obtain the six-order modal parameters of the body on the landing gear, where each modal parameter includes frequency, modal mass, modal stiffness, damping, and vibration mode in three directions;

[0042] The six modes of the fuselage on the landing gear include the first and second order in heading, the first and second order in lateral direction, and the first and second order in vertical direction.

[0043] [7] Select any two sets of modal parameter combinations, perform ground resonance calculations, and obtain stability calculation results;

[0044] [8] Draw the ground resonance stability curve.

[0045] Application examples:

[0046] In order to prove the applicability and effectiveness of the present invention, the present invention is applied to a ground resonance calculation and analysis method of a certain type of aircraft taking into account the landing gear installation stiffness during the model development stage. The specific implementation method is as follows:

[0047] S1: Establish a local finite element model of the installation stiffness of the landing gear, and calculate the installation stiffness of the landing gear. The finite element model includes part of the fuselage structure, the landing gear installation joint, and the landing gear system. The installation stiffness of the landing gear is obtained by calculating the local finite element model. The local finite element model is shown in Figure 2 ;

[0048] S2: The equivalent wheel center and equivalent stiffness and damping of the landing gear under different takeoff weights and lift conditions are calculated through the equilibrium state calculation program, and the compression of the main and tail buffer struts is obtained. The equivalent main and tail wheel centers are calculated through the compression of the main and tail buffer struts; at the same time, the equivalent stiffness and damping of the landing gear system at the equivalent main and tail wheel centers are obtained, as shown in Table 1.

[0049] Table 1

[0050]

[0051]

[0052] S3: In the full aircraft finite element model of the modal calculation of the airframe on the landing gear, the equivalent installation stiffness of the landing gear calculated by S1 is simulated by the beam unit through the equivalent installation stiffness, and the equivalent stiffness and damping of the landing gear system calculated by S2 are simulated in the form of spring-damper units. The equivalent wheel center is represented by a node unit; the airframe dynamics finite element model considering the landing gear installation stiffness is shown in Figure 2 ;

[0053] S4: The modal parameters of the airframe on the landing gear are obtained by calculating the body dynamics finite element model. The calculation results are shown in Table 2.

[0054] Table 2

[0055]

[0056] S5: Select the second-order heading and the second-order lateral direction, and use the plane dynamic model to calculate the ground resonance;

[0057] S6: Plot the ground resonance stability curve.

Claims

1. A method for evaluating landing gear mounting stiffness ground resonance, characterized in that: include: The influence of the landing gear installation stiffness is taken into account when calculating the ground resonance, so as to obtain more realistic modal parameters of the airframe on the landing gear and the vibration mode of the hub center, thereby effectively guiding the design before the hub center dynamic characteristics test.

2. The method according to claim 1, characterized in that: The influence of the landing gear mounting stiffness is taken into account when calculating the ground resonance, so as to obtain more realistic modal parameters of the airframe on the landing gear and vibration mode of the hub center, thus effectively guiding the design before the hub center dynamic characteristics test, including: By establishing a local finite element model of the installation stiffness of the landing gear system, the installation stiffness of the landing gear is calculated; through the equilibrium state calculation program, the equivalent wheel center and equivalent stiffness and damping of the landing gear system under different take-off weights and lift states are obtained, and the above parameters are used as input parameters of the landing gear system in the full-aircraft finite element model of the modal calculation of the airframe on the landing gear, and the modal parameters of the airframe on the landing gear are calculated. Then several groups of modal parameter combinations are selected, and the plane dynamic model is used to perform ground resonance calculation and analysis to obtain the calculation results and draw the stability curve.

3. The method according to claim 2, characterized in that The installation stiffness of the landing gear is calculated, including: Establish a local finite element model of landing gear mounting stiffness, which includes a part of the fuselage structure, landing gear mounting joints and landing gear system; The model is established according to the main force transmission route of the system and the actual structural dimensions of the system to truly simulate the stiffness and mass distribution of the system; Determine the connection method between the landing gear system and the fuselage structure and the connection method between the internal structures of the landing gear system; Unit loads in three directions are applied to the center of the wheel, and the installation stiffness in three directions is obtained respectively.

4. The method according to claim 3, characterized in that The rod body and frame flange are simulated by beam element 1D_Beam, the web is simulated by shell element 2D_Shell, and the landing gear system is simulated by solid element Tet10.

5. The method according to claim 4, characterized in that The landing gear system is connected to the short wing by bolts and simulated by the rigid body element RBE2. The connection between the various components of the landing gear system is simulated by the rigid body element RBE2.

6. The method according to claim 5, characterized in that Through the equilibrium state calculation program, the equivalent wheel center and equivalent stiffness and damping of the landing gear system under different takeoff weights and lift conditions are obtained, including: The compression of the main and tail buffer struts is calculated by the equilibrium state calculation program at different takeoff weights and lift states, and the equivalent center of the main and tail wheels is calculated by the compression of the main and tail buffer struts; Through the equilibrium state calculation program, the equivalent stiffness and damping of the landing gear system in three directions at the equivalent center of the equivalent main and tail wheels are also obtained.

7. The method according to claim 6, characterized in that The above parameters are used as input parameters of the landing gear system in the full aircraft finite element model for modal calculation of the airframe on the landing gear, and the modal parameters of the airframe on the landing gear are calculated, including: The finite element model of the whole aircraft in the landing gear mode is calculated, and the cross-sectional dimensions of the beam unit simulating the landing gear are obtained through the equivalent installation stiffness; The finite element model of the whole aircraft in the landing gear mode is calculated, and the equivalent stiffness and damping of the landing gear system are simulated and calculated in the form of spring-damper units; The finite element model of the computer body dynamics is used to obtain the six-order modal parameters of the body on the landing gear, where each modal parameter includes frequency, modal mass, modal stiffness, damping and vibration shapes in three directions.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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