Large-amplitude free vibration test device for simulating bending-torsion coupling nonlinear stiffness

Abstract

The invention belongs to the technical field of bridge wind tunnel test devices, and provides a large-amplitude free vibration test device for simulating bending-torsion coupling nonlinear rigidity, which comprises a rigid model, a rigid rod, a rigid suspension arm, a bearing fixed pulley, a linear extension spring and a light high-strength thin rope. By adjusting the original length, the rigidity and the initial strain of the spring and the spatial positions of the suspension point of the rigid suspension arm and the bearing fixed pulley, the vertical and torsional target nonlinear rigidity can be realized, so that a large-amplitude bending-torsional coupling flutter vibration measurement test under the nonlinear rigidity of a bridge structure can be conveniently carried out. In the large-amplitude vibration process of the model, the spring can be kept in a vertical state all the time, and unstable damping and rigidity caused by local vibration of the spring are avoided. Compared with a traditional device, the large-amplitude free vibration testing device is additionally provided with the bearing fixed pulley and the light high-strength thin rope, and is simple in design, low in cost, easy to machine, efficient and feasible.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge wind tunnel test devices, and in particular relates to a wind tunnel test device capable of simulating large-amplitude free vibration of a bridge rigid model under vertical bending and torsional coupled nonlinear stiffness. Background Art

[0002] Long-span bridges are lightweight, low-damping structures with high wind sensitivity, making them susceptible to large-amplitude, coupled bending-torsion nonlinear flutter. The geometric stiffness of bridge structures experiencing large flutter varies with displacement, with greater displacement leading to greater changes in geometric stiffness. This is the inherent presence of geometric nonlinearity. Ignoring this geometric nonlinearity can significantly impact the accuracy of long-span bridge flutter performance tests.

[0003] Traditional bridge girder segment model coupled free vibration tests utilize a horizontal boom suspended by vertical upper and lower springs. When the model and boom experience torsional displacement, the springs tilt, resulting in geometrically nonlinear stiffness in the device. Torsional stiffness decreases nonlinearly with increasing torsional displacement and is only weakly affected by vertical displacement. Changes in vertical stiffness with torsional and vertical displacements are essentially negligible.

[0004] However, traditional test equipment is not suitable for conducting large-amplitude tests where the stiffness changes with displacement. The main reasons are: (1) The nonlinear stiffness characteristics of traditional equipment do not match those of actual bridges. For example, for the first-order positive symmetric vertical bending mode of a cable-supported bridge, the vertical stiffness of an actual bridge generally increases with the increase of vertical downward displacement and decreases with the increase of vertical upward displacement, while the vertical stiffness of traditional test equipment remains basically unchanged. (2) The torsion of the boom will cause the spring to tilt, and the tilted spring will vibrate locally during the vibration of the model, causing uncontrollable nonlinear stiffness, unstable damping, and inconstant mass and mass moment in the device.

[0005] Sébastien Maheux et al. have developed a test device that takes into account the geometric nonlinear stiffness of the structure by arranging springs with an initial tilt (Nonlinear Wind Tunnel Tests of Cable-Supported Bridges. Journal of Structural Engineering, 2023, 149(10): 04023137). However, the tilted springs are inevitably affected by the sag, which can cause local vibrations during the vibration of the model, leading to uncontrollable stiffness nonlinearity, unstable damping, and inconstant mass and mass moment, affecting the test accuracy. Therefore, it is urgent to develop a large-amplitude and stable low-damping free vibration wind tunnel test device that can achieve vertical and torsional stiffness changes with displacement. Summary of the Invention

[0006] The technical problem addressed by this invention is that conventional free-vibration wind tunnel test equipment cannot accurately simulate the geometric stiffness that varies with displacement in rigid segment models of bridge girders and other structural components. This improved approach allows accurate simulation of the vertical and torsional stiffness variations of actual bridges, while ensuring that the spring remains vertical and the device maintains stable low damping under large-amplitude coupled vibrations. The device comprises a rigid model, a rigid rod, a rigid boom, a bearing fixed pulley, a linear tension spring, and a lightweight, high-strength string.

[0007] The technical solution of the present invention:

[0008] A large-amplitude free vibration test device for simulating bending-torsion coupling nonlinear stiffness includes a rigid model 1, a rigid rod 2, a rigid suspension arm 3, a first bearing fixed pulley 4, a first linear tension spring 5, a first lightweight high-strength thin rope 6, a second bearing fixed pulley 7, a second linear tension spring 8, and a second lightweight high-strength thin rope 9.

[0009] The rigid rods 2 are fixed at both ends of the rigid model 1, and the torsional center line of the rigid model 1 is ensured to be colinear with the axis of the rigid rod 2. The free end of the rigid rod 2 passes vertically through the center of the rigid boom 3 and is fixed thereto; there are two first bearing fixed pulleys 4, first linear tension springs 5 ​​and first lightweight high-strength thin ropes 6 on one side of the rigid model 1, which are arranged in a symmetrical structure to ensure that the first bearing fixed pulley 4 is directly below the first linear tension spring 5; the upper end of the first linear tension spring 5 is fixed, and its lower end is fixedly connected to the upper end of the first lightweight high-strength thin rope 6; the first lightweight high-strength thin rope 6 passes vertically downward through the first bearing fixed pulley 4, and the lower end of the inclined or vertical first lightweight high-strength thin rope 6 is connected to the upper hanging point of the rigid boom 3; there are two second bearing fixed pulleys 7, second linear tension springs 8 and second lightweight high-strength thin ropes 9 on one side of the rigid model 1, which are arranged in a symmetrical structure to ensure that the second bearing fixed pulley 7 is directly above the second linear tension spring 8; the lower end of the second linear tension spring 8 is fixed, and its The upper end is fixedly connected to the lower end of the second lightweight high-strength string 9; the second lightweight high-strength string 9 passes vertically upward through the second bearing fixed pulley 7, and the upper end of the inclined or vertical second lightweight high-strength string 9 is connected to the lower hanging point of the rigid boom 3; thereby ensuring that during the vertical and torsional coupled free vibration of the rigid model 1 and the rigid boom 3, the first lightweight high-strength string 6 above the first bearing fixed pulley 4 and the second lightweight high-strength string 9 below the second bearing fixed pulley 7 remain in a vertical state, so that the first linear tension spring 5 and the second linear tension spring 8 only undergo vertical telescopic deformation; the inclination angle of the first lightweight high-strength string 6 below the first bearing fixed pulley 4 and / or the second lightweight high-strength string 9 above the second bearing fixed pulley 7 changes nonlinearly with the vertical and torsional displacement of the rigid model 1, so that the deformation of the first linear tension spring 5 and the second linear tension spring 8 has a nonlinear relationship with the vertical and torsional displacement of the rigid model 1, thereby realizing the geometric nonlinear stiffness of vertical and torsional coupling.

[0010] The geometric nonlinear stiffness of the large-amplitude free vibration test device is related to the following parameters: the vertical displacement and torsional displacement of the rigid model 1, the original length, initial strain and stiffness coefficient of the first linear tension spring 5 and the second linear tension spring 8, the distance between the two upper hanging points of the rigid boom 3, the distance between the two lower hanging points and the height difference between the upper and lower hanging points, the distance between the two first bearing fixed pulleys 4 and the height difference between them and the upper hanging point of the rigid boom 3, the distance between the two second bearing fixed pulleys 7 and the height difference between them and the lower hanging point of the rigid boom 3; the initial inclination angle of the first lightweight high-strength rope 6 is determined by the spatial position of the upper hanging point of the first bearing fixed pulley 4 and the rigid boom 3, and the initial inclination angle of the second lightweight high-strength rope 9 is determined by the spatial position of the second bearing fixed pulley 7 and the lower hanging point of the rigid boom 3; the degree of stiffness nonlinearity is improved by increasing the initial inclination angle of the first lightweight high-strength rope 6 and the second lightweight high-strength rope 9 and reducing the initial strain of the first linear tension spring 5 and the second linear tension spring 8.

[0011] The first bearing fixed pulley 4 and the second bearing fixed pulley 7 are arranged on the rigid frame outside the wind tunnel for suspending the rigid model 1, and the spatial position is adjusted according to the target geometric nonlinear stiffness, while ensuring that there is no collision with the rigid boom 3 within the design amplitude; for the working condition that the vertical stiffness increases with the increase of vertical downward displacement and decreases with the increase of vertical upward displacement, the two upper hanging points of the rigid boom 3 and the spatial positions of the two first bearing fixed pulleys 4 can be adjusted so that the first lightweight high-strength thin rope 6 at the lower part of the first bearing fixed pulley 4 has an appropriate inclination angle, and the spacing between the two lower hanging points of the rigid boom 3 and the spacing between the two second bearing fixed pulleys 7 are adjusted to be the same, so that the second lightweight high-strength thin rope 9 is all in a vertical state; for the working condition that the vertical stiffness decreases with the increase of vertical downward displacement and increases with the increase of vertical upward displacement, the spacing between the two upper hanging points of the rigid boom 3 and the spacing between the two first bearing fixed pulleys 4 can be adjusted to be the same, so that the first lightweight high-strength thin rope 6 is all in a vertical state, and the rigid boom 3 is adjusted to be the same. The spatial positions of the two lower hanging points of the arm 3 and the two second bearing fixed pulleys 7 make the second lightweight high-strength rope 9 above the second bearing fixed pulley 7 produce an appropriate inclination angle; for the working condition that the vertical stiffness increases with the increase of the absolute value of the vertical displacement, or decreases with the increase of the absolute value of the vertical displacement, the spatial positions of the upper hanging point and the lower hanging point of the rigid boom 3, the spatial positions of the first bearing fixed pulley 4 and the second bearing fixed pulley 7 are adjusted respectively, so that the first lightweight high-strength rope 6 and the second lightweight high-strength rope 9 both produce appropriate inclination angles; on the basis of basically meeting the target vertical geometric nonlinear stiffness, the original length, stiffness coefficient and initial strain of the first linear tension spring 5 and the second linear tension spring 8, the spatial positions of the upper hanging point and the lower hanging point of the rigid boom 3, the spatial positions of the first bearing fixed pulley 4 and the second bearing fixed pulley 7 are further adjusted to finally achieve the target vertical torsional coupling nonlinear stiffness characteristics; the first lightweight high-strength rope 6 and the second lightweight high-strength rope 9 can be tilted to the inside or outside of the model according to actual conditions.

[0012] The first and second fixed pulleys 4 and 7 are lightweight and high-strength, with minimal friction coefficients during bearing rotation. During system vibration, the first and second lightweight, high-strength cords 6 and 9 compress and rotate the first and second fixed pulleys 4 and 7, respectively. The use of small-diameter bearings and large-diameter pulleys reduces bearing rotation distance, lowers system energy consumption, and reduces vibration system damping, even when the first and / or second lightweight, high-strength cords 6 and 9 experience the same displacement.

[0013] The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 are lightweight, high-strength, have a high elastic modulus, and are free of bending and torsion resistance, and can be made of any material. The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 should be of sufficient length to ensure that the first linear tension spring 5 does not collide with the first bearing fixed pulley 4, and the second linear tension spring 8 does not collide with the second bearing fixed pulley 7, within the designed amplitude.

[0014] The beneficial effects of the present invention are as follows: (1) by adjusting the original length, stiffness and initial strain of the linear tension spring, the spatial position of the rigid boom suspension point and the bearing fixed pulley, the target vertical and torsional nonlinear stiffness can be achieved, so as to facilitate the large-amplitude bending-torsion coupling flutter measurement test under the nonlinear stiffness of the bridge structure; (2) during the large-amplitude vibration of the model, the spring can always remain in a vertical state, avoiding unstable damping and stiffness caused by its local vibration; (3) compared with the traditional device, the device only adds a bearing fixed pulley and a lightweight and high-strength thin rope, and has a simple design, low cost, easy processing, high efficiency and feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram of the test device structure when the lightweight, high-strength thin rope is tilted outward.

[0016] Figure 2 This is the structural diagram of the first lightweight and high-strength thin rope tilt test device.

[0017] Figure 3 This is the structural diagram of the second lightweight and high-strength thin rope tilt test device.

[0018] Figure 4 This is a diagram of the test device structure when the lightweight, high-strength thin rope is tilted inward.

[0019] In the figure: 1 rigid model; 2 rigid rod; 3 rigid boom; 4 first bearing fixed pulley; 5 first linear tension spring; 6 first lightweight high-strength thin rope; 7 second bearing fixed pulley; 8 second linear tension spring; 9 second lightweight high-strength thin rope. DETAILED DESCRIPTION

[0020] The specific implementation of the present invention is described in detail below in conjunction with the technical solutions and drawings.

[0021] like Figure 1As shown, a large-amplitude free vibration test device simulating bending-torsion coupling nonlinear stiffness includes a rigid model 1, a rigid rod 2, a rigid suspension arm 3, a first bearing fixed pulley 4, a first linear tension spring 5, a first lightweight high-strength thin rope 6, a second bearing fixed pulley 7, a second linear tension spring 8, and a second lightweight high-strength thin rope 9. The rigid rods 2 are fixed at both ends of the rigid model 1, and the torsional center line of the rigid model 1 is ensured to be colinear with the axis of the rigid rod 2. The free end of the rigid rod 2 passes vertically through the center of the rigid boom 3 and is fixed thereto; there are two first bearing fixed pulleys 4, first linear tension springs 5 ​​and first lightweight high-strength thin ropes 6 on one side of the rigid model 1, which are arranged in a symmetrical structure to ensure that the first bearing fixed pulley 4 is directly below the first linear tension spring 5; the upper end of the first linear tension spring 5 is fixed, and its lower end is fixedly connected to the upper end of the first lightweight high-strength thin rope 6; the first lightweight high-strength thin rope 6 passes vertically downward through the first bearing fixed pulley 4, and the lower end of the inclined or vertical first lightweight high-strength thin rope 6 is connected to the upper hanging point of the rigid boom 3; there are two second bearing fixed pulleys 7, second linear tension springs 8 and second lightweight high-strength thin ropes 9 on one side of the rigid model 1, which are arranged in a symmetrical structure to ensure that the second bearing fixed pulley 7 is directly above the second linear tension spring 8; the lower end of the second linear tension spring 8 is fixed, and its The upper end is fixedly connected to the lower end of the second lightweight high-strength string 9; the second lightweight high-strength string 9 passes vertically upward through the second bearing fixed pulley 7, and the upper end of the inclined or vertical second lightweight high-strength string 9 is connected to the lower hanging point of the rigid boom 3; thereby ensuring that during the vertical and torsional coupled free vibration of the rigid model 1 and the rigid boom 3, the first lightweight high-strength string 6 above the first bearing fixed pulley 4 and the second lightweight high-strength string 9 below the second bearing fixed pulley 7 remain in a vertical state, so that the first linear tension spring 5 and the second linear tension spring 8 only undergo vertical telescopic deformation; the inclination angle of the first lightweight high-strength string 6 below the first bearing fixed pulley 4 and / or the second lightweight high-strength string 9 above the second bearing fixed pulley 7 changes nonlinearly with the vertical and torsional displacement of the rigid model 1, so that the deformation of the first linear tension spring 5 and the second linear tension spring 8 has a nonlinear relationship with the vertical and torsional displacement of the rigid model 1, thereby realizing the geometric nonlinear stiffness of vertical and torsional coupling.

[0022] The geometric nonlinear stiffness of the large-amplitude free vibration test device is related to the following parameters: the vertical displacement and torsional displacement of the rigid model 1, the original length, initial strain and stiffness coefficient of the first linear tension spring 5 and the second linear tension spring 8, the distance between the two upper hanging points of the rigid boom 3, the distance between the two lower hanging points and the height difference between the upper and lower hanging points, the distance between the two first bearing fixed pulleys 4 and the height difference between them and the upper hanging point of the rigid boom 3, the distance between the two second bearing fixed pulleys 7 and the height difference between them and the lower hanging point of the rigid boom 3; the initial inclination angle of the first lightweight high-strength rope 6 is determined by the spatial position of the first bearing fixed pulley 4 and the upper hanging point of the rigid boom 3, and the initial inclination angle of the second lightweight high-strength rope 9 is determined by the spatial position of the second bearing fixed pulley 7 and the lower hanging point of the rigid boom 3; the degree of stiffness nonlinearity is improved by increasing the initial inclination angle of the first lightweight high-strength rope 6 and the second lightweight high-strength rope 9 and reducing the initial strain of the first linear tension spring 5 and the second linear tension spring 8.

[0023] The first bearing fixed pulley 4 and the second bearing fixed pulley 7 can be arranged on a rigid frame outside the wind tunnel for suspending the rigid model 1. The vertical and horizontal positions can be adjusted according to the target nonlinear stiffness characteristics, while ensuring that they do not collide with the rigid boom 3 within the design amplitude.

[0024] like Figure 2 As shown, for the working condition where the vertical stiffness increases with the increase of vertical downward displacement and decreases with the increase of vertical upward displacement, the spatial positions of the two upper hanging points of the rigid boom 3 and the two first bearing fixed pulleys 4 can be adjusted so that the first lightweight high-strength thin rope 6 at the lower part of the first bearing fixed pulley 4 has an appropriate inclination angle, and the distance between the two lower hanging points of the rigid boom 3 and the distance between the two second bearing fixed pulleys 7 are adjusted to be the same so that all the second lightweight high-strength thin ropes 9 are in a vertical state.

[0025] like Figure 3 As shown, for the working condition where the vertical stiffness decreases with the increase of vertical downward displacement and increases with the increase of vertical upward displacement, the distance between the two upper hanging points of the rigid boom 3 and the distance between the two first bearing fixed pulleys 4 can be adjusted to be the same, so that all the first lightweight high-strength thin ropes 6 are in a vertical state, and the spatial positions of the two lower hanging points of the rigid boom 3 and the two second bearing fixed pulleys 7 are adjusted so that the second lightweight high-strength thin rope 9 above the second bearing fixed pulley 7 has an appropriate inclination angle.

[0026] like Figure 1 and Figure 4As shown, for the working condition where the vertical stiffness increases with the increase of the absolute value of the vertical displacement, or decreases with the increase of the absolute value of the vertical displacement, the spatial positions of the upper and lower hanging points of the rigid boom 3, the spatial positions of the first bearing fixed pulley 4 and the second bearing fixed pulley 7 are adjusted respectively, so that the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 both have appropriate inclination angles; on the basis of basically meeting the target vertical geometric nonlinear stiffness, the original length, stiffness coefficient and initial strain of the first linear tension spring 5 and the second linear tension spring 8, the spatial positions of the upper and lower hanging points of the rigid boom 3, and the spatial positions of the first bearing fixed pulley 4 and the second bearing fixed pulley 7 are further adjusted, and finally the target vertical torsional coupling nonlinear stiffness characteristics are achieved; the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 can be tilted to the inside or outside of the model according to actual conditions.

[0027] The first bearing fixed pulley 4 and the second bearing fixed pulley 7 are lightweight and high-strength, and the bearing rotational friction coefficient is minimized. The use of small-diameter bearings and large-diameter pulleys reduces the bearing rotation distance, lowering system energy consumption and reducing vibration system damping, even when the first lightweight, high-strength string 6 and / or the second lightweight, high-strength string 9 experience the same displacement.

[0028] The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 are lightweight, high-strength, have a high elastic modulus, and are free of bending and torsion resistance. The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 should be of sufficient length to prevent collision between the first linear tension spring 5 and the first bearing fixed pulley 4, and between the second linear tension spring 8 and the second bearing fixed pulley 7, within the designed amplitude.

[0029] The above description is merely an example of a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any equivalent changes, modifications, or variations made by a person skilled in the art using the technical solution of the present invention to the above examples shall still fall within the scope of the technical solution of the present invention.

Claims

1. A large-amplitude free vibration test device for simulating bending-torsion coupling nonlinear stiffness, characterized in that: The large-amplitude free vibration test device comprises a rigid model (1), a rigid rod (2), a rigid suspension arm (3), a first bearing fixed pulley (4), a first linear tension spring (5), a first light-weight high-strength thin rope (6), a second bearing fixed pulley (7), a second linear tension spring (8) and a second light-weight high-strength thin rope (9); The rigid model (1) has two rigid rods (2) fixed at both ends, and ensures that the torsion center line of the rigid model (1) is colinear with the axis of the rigid rod (2), and the free end of the rigid rod (2) vertically passes through the center of the rigid boom (3) and is fixed thereto; the first bearing fixed pulley (4), the first linear tension spring (5) and the first light high-strength thin rope (6) on one side of the rigid model (1) are both two and arranged in a symmetrical structure, ensuring that the first bearing fixed pulley (4) is directly below the first linear tension spring (5); the upper end of the first linear tension spring (5) is fixed, and its lower end is fixed to the first linear tension spring (5). The upper end of the first light high-strength string (6) is fixedly connected; the first light high-strength string (6) passes vertically downward through the first bearing fixed pulley (4), and the lower end of the inclined or vertical first light high-strength string (6) is connected to the upper hanging point of the rigid boom (3); the second bearing fixed pulley (7), the second linear tension spring (8) and the second light high-strength string (9) on one side of the rigid model (1) are both two and arranged in a symmetrical structure to ensure that the second bearing fixed pulley (7) is directly above the second linear tension spring (8); the lower end of the second linear tension spring (8) The upper end of the second lightweight high-strength string (9) is fixed, and the upper end thereof is fixedly connected to the lower end of the second lightweight high-strength string (9); the second lightweight high-strength string (9) passes vertically upward through the second bearing fixed pulley (7), and the upper end of the inclined or vertical second lightweight high-strength string (9) is connected to the lower suspension point of the rigid boom (3); thereby ensuring that during the vertical and torsional coupled free vibration process of the rigid model (1) and the rigid boom (3), the first lightweight high-strength string (6) above the first bearing fixed pulley (4) and the second lightweight high-strength string (9) below the second bearing fixed pulley (7) remain in a vertical state. The first linear tension spring (5) and the second linear tension spring (8) are caused to undergo only vertical telescopic deformation; the inclination angle of the first light-weight high-strength thin rope (6) below the first bearing fixed pulley (4) and / or the second light-weight high-strength thin rope (9) above the second bearing fixed pulley (7) is nonlinearly changed with the vertical and torsional displacement of the rigid model (1), so that the deformation of the first linear tension spring (5) and the second linear tension spring (8) is nonlinearly related with the vertical and torsional displacement of the rigid model (1), thereby realizing vertical and torsional coupled geometric nonlinear stiffness.

2. The large amplitude free vibration test device according to claim 1, characterized in that: The geometric nonlinear stiffness of the large amplitude free vibration test device is related to the following parameters: the vertical displacement and torsional displacement of the rigid model (1), the original length, initial strain and stiffness coefficient of the first linear tension spring (5) and the second linear tension spring (8), the distance between the two upper hanging points of the rigid suspension arm (3), the distance between the two lower hanging points, the height difference between the upper and lower hanging points, the distance between the two first bearing fixed pulleys (4) and the height difference between the two first bearing fixed pulleys (4) and the upper hanging point of the rigid suspension arm (3), the distance between the two second bearing fixed pulleys (7) and the lower hanging point of the rigid suspension arm (3), and the vertical displacement between the two second bearing fixed pulleys (7) ... The height difference of the hanging points; the initial tilt angle of the first light high-strength thin rope (6) is determined by the spatial position of the upper hanging point of the first bearing fixed pulley (4) and the rigid suspension arm (3), and the initial tilt angle of the second light high-strength thin rope (9) is determined by the spatial position of the lower hanging point of the second bearing fixed pulley (7) and the rigid suspension arm (3); by increasing the initial tilt angles of the first light high-strength thin rope (6) and the second light high-strength thin rope (9) and reducing the initial strains of the first linear tension spring (5) and the second linear tension spring (8), the nonlinear degree of stiffness is improved.

3. The large amplitude free vibration test device according to claim 1 or 2, characterized in that: The first bearing fixed pulley (4) and the second bearing fixed pulley (7) are arranged on a rigid frame outside the wind tunnel for suspending the rigid model (1), and their spatial positions are adjusted according to the target geometric nonlinear stiffness, while ensuring that they do not collide with the rigid boom (3) within the design amplitude; for the working condition in which the vertical stiffness increases with the increase of the vertical downward displacement and decreases with the increase of the vertical upward displacement, the spatial positions of the two upper hanging points of the rigid boom (3) and the two first bearing fixed pulleys (4) can be adjusted so that the first light high-strength thin rope (6) at the lower part of the first bearing fixed pulley (4) has an inclination angle, and the spacing between the two lower hanging points of the rigid boom (3) and the spacing between the two second bearing fixed pulleys (7) are adjusted to be the same so that all the second light high-strength thin ropes (9) are in a vertical state; for the working condition in which the vertical stiffness increases with the increase of the vertical downward displacement and decreases with the increase of the vertical upward displacement, the spatial positions of the two upper hanging points of the rigid boom (3) and the two first bearing fixed pulleys (4) can be adjusted so that the first light high-strength thin rope (6) at the lower part of the first bearing fixed pulley (4) has an inclination angle, and the spacing between the two lower hanging points of the rigid boom (3) and the spacing between the two second bearing fixed pulleys (7) are adjusted to be the same so that all the second light high-strength thin ropes (9) are in a vertical state; For the working condition where the vertical stiffness decreases or increases with the increase of the vertical upward displacement, the distance between the two upper hanging points of the rigid boom (3) and the distance between the two first bearing fixed pulleys (4) can be adjusted to be the same, so that all the first light high-strength thin ropes (6) are in a vertical state, and the spatial positions of the two lower hanging points of the rigid boom (3) and the two second bearing fixed pulleys (7) are adjusted so that the second light high-strength thin rope (9) above the second bearing fixed pulley (7) generates an inclination angle; for the working condition where the vertical stiffness increases with the increase of the absolute value of the vertical displacement or decreases with the increase of the absolute value of the vertical displacement, the spatial positions of the upper hanging point and the lower hanging point of the rigid boom (3), the spatial positions of the first bearing fixed pulley (4) and the second bearing fixed pulley (7) are adjusted respectively, so that both the first light high-strength thin rope (6) and the second light high-strength thin rope (9) generate an inclination angle.

4. The large amplitude free vibration test device according to claim 3, characterized in that: On the basis of satisfying the target vertical geometric nonlinear stiffness, the original length, stiffness coefficient and initial strain of the first linear tension spring (5) and the second linear tension spring (8), the spatial positions of the upper hanging point and the lower hanging point of the rigid suspension arm (3), and the spatial positions of the first bearing fixed pulley (4) and the second bearing fixed pulley (7) are further adjusted to ultimately achieve the target vertical torsional coupling nonlinear stiffness characteristics.

5. The large amplitude free vibration test device according to claim 4, characterized in that: The first light-weight high-strength string (6) and the second light-weight high-strength string (9) are tilted toward the inside or outside of the model according to actual conditions.

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