EXPERIMENTAL SETUP FOR THREE-DEGREE-OF-FREEDOM LARGE-AMPLITUDE FREE VIBRATION IN WIND TUNNEL TEST

Abstract

An experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test. The setup includes a rigid test model, rigid circular rods, rigid lifting arms, arc blocks with grooves, lightweight high-strength thin strings, linear tensile springs, fixed pulleys, and bearings. Large-amplitude three-degree-of-freedom free vibrations of test models can be adapted by the vertical deformation of the springs without any tilt. The possible nonlinear mechanical stiffness due to vertical spring tilt and lateral spring deflection in the traditional setup are excluded. It is convenient to install the test model and adjust the initial angle of attack in the new experimental setup. The linear stiffness property and hence constant vibration frequency can be ensured for very large-amplitude vibrations due to the eliminations of spring deflection and tilt.

Claims

1. An experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test, wherein the setup includes a rigid test model, rigid circular rods, rigid lifting arms, arc blocks with grooves, first lightweight high-strength thin strings, first linear tensile springs), a first fixed pulley, second thin strings, second linear tensile springs, a second fixed pulley, and bearings; the rigid test model is connected with rigid circular rods at each end; the rigid circular rods are perpendicularly passed through the center of the rigid lifting arms to ensure that the torsional center of the rigid test model is on the same line with those of the rigid circular rods and the rigid lifting arms; the arc blocks with grooves are fixed at the both ends of rigid lifting arms, and the center of arc blocks is coincide with that of the rigid lifting arms; the first lightweight high-strength thin strings wraps around the arc block, the upper end of the first lightweight high-strength thin strings is connected with the lower end of the vertical spring, and the lower end of the first lightweight high-strength thin strings is fixed at the bottom of the arc blocks; during the large-amplitude three-degree-of-freedom free vibration process, the arc blocks rotate along the first lightweight high-strength thin string, and the security of the setup can be ensured; the first lightweight high-strength thin strings are vertically passed through the first fixed pulleys to prevent any lateral tilt of the springs during the lateral vibration of the rigid test model; the top ends of the second thin strings is connected with bottom of the second linear springs; the second thin strings curved around the second fixed pulleys, and their lower ends are connected with the bearings that supported on the rigid circular rods; the bearings can freely rotate around the rigid circular rods, and the friction should be as small as possible; during the lateral vibration of the rigid test model, the second linear tensile springs only vertically deform, and hence the linear lateral stiffness requirement can be satisfied.

2. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test according to claim 1, wherein the length of rigid lifting arms and the diameter of arc blocks) are determined according to several parameters including the rigid test model mass, inertia of moment, and the frequency ratio between torsional and vertical modes; generally, they are within 0.21.5 m.

3. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test according to claim 1, wherein the friction coefficients between the first fixed pulleys and the first lightweight high-strength thin strings, and between the second fixed pulleys and the second thin strings should be as small as possible; during the three-degree-of-freedom free vibrations, the damping ratio of the system should be as small as possible; in order to restrain the lateral motion of the first lightweight high-strength thin strings, the distance between the first two fixed pulleys should be as small as possible under the condition that the rotation of first fixed pulleys cannot be affected; in other words, the lateral motion space of the first lightweight high-strength thin strings should be very small to ensure the vertical state of the first lightweight high-strength thin strings and the first linear tensile springs; thus, the first linear tensile springs only generate vertical deformation.

4. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test according to claim 1, wherein the second thin strings should be kept in a tensioning state to ensure the second linear tensile springs always keep linear elastic state.

5. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test according to claim 3, wherein the second thin strings should be kept in a tensioning state to ensure the second linear tensile springs always keep linear elastic state.

6. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel according to claim 1, wherein the vertical distance between the first fixed pulleys and the rigid lifting arms, and the horizontal distance between the second fixed pulleys and the bearings should be sufficiently long; then, the effect of the vertical motion on the lateral stiffness, and the effect of the lateral motion on the vertical stiffness can be reduced.

7. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test according to claim 3, wherein the vertical distance between the first fixed pulleys; and the rigid lifting arms, and the horizontal distance between the second fixed pulleys and the bearings should be sufficiently long; then, the effect of the vertical motion on the lateral stiffness, and the effect of the lateral motion on the vertical stiffness can be reduced.

8. The experimental setup for three-degree-of-freedom large-amplitude free vibration in wind tunnel test according to claim 4, wherein the vertical distance between the first fixed pulleys and the rigid lifting arms, and the horizontal distance between the second fixed pulleys and the bearings should be sufficiently long; then, the effect of the vertical motion on the lateral stiffness, and the effect of the lateral motion on the vertical stiffness can be reduced.

Description

DESCRIPTION OF THE DRAWINGS

[0011] The sole FIGURE is a structural diagram of proposed experimental setup for three-degree-of freedom large-amplitude free vibration device for deck rigid model in wind tunnel test.

[0012] Rigid test model; 2 rigid circular rod; 3 rigid lifting arm; 4 arc blocks with grooves; 5 the first lightweight high-strength thin string; 6 the first linear tensile spring; 7 the first fixed pulley; 8 the second thin string; 9 the second linear tensile spring; 10 the second fixed pulley; 11 the bearings.

DETAILED DESCRIPTION

[0013] Combining the technical scheme and attached drawing, the specific implementations of this invention are shown as follows:

[0014] As shown in the sole FIGURE, the new experimental setup for large-amplitude three-degree-of-freedom free vibration wind tunnel test is composed of the rigid test model 1, the rigid circular rods 2, the rigid lifting arms 3, the arc blocks with grooves 4, the first lightweight high-strength thin strings 5, the first linear tensile springs 6, the first fixed pulley 7, the second thin strings 8, the second linear tensile springs 9, the second fixed pulley 10, and the bearings 11. The rigid test model 1 is connected with rigid rods 2 at each end. The rigid rods 2 are perpendicularly passed through the center of the rigid lifting arms 3 to ensure that the torsional center of the rigid test model 1 is on the same line with those of the rigid rods 2 and the rigid lifting arms 3; The arc blocks with grooves 4 are fixed at the both ends of rigid lifting arms 3, and the center of arc blocks 4 is coincide with that of the rigid lifting arms 3; The first lightweight high-strength thin string 5 wraps around the arc block 4, the upper end of the first lightweight high-strength thin string 5 is connected with the lower end of the vertical spring 6, and the lower end of the first lightweight high-strength thin string 5 is fixed at the bottom of the arc blocks 4; During the large-amplitude three-degree-of-freedom free vibration process, the arc blocks 4 rotate along the first lightweight high-strength thin strings 5, and the security of the setup can be ensured. The first lightweight high-strength thin strings 5 are vertically passed through the first fixed pulleys 7 to prevent any lateral tilt of the springs 6 during the lateral vibration of the rigid test model 1; The top ends of the second thin strings 8 is connected with bottom of the second linear springs 9; The second thin strings 8 curved around the second fixed pulleys 10, and their lower ends are connected with the bearing 11 that supported on the rigid rods 2; The bearing 11 can freely rotate around the rigid rods 2, and the friction should be as small as possible. During the lateral vibration of the rigid test model 1, the second linear tensile springs 9 only vertically deform, and hence the linear lateral stiffness requirement can be satisfied.