Wind Tunnel Vibration Setup Using Arc Blocks and Pulleys
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Solution Overview
Problem
Traditional wind tunnel testing devices for three-degree-of-freedom coupled free vibrations of bridge deck models are inadequate for large-amplitude tests due to nonlinear factors such as lateral spring deflections, increased mechanical damping, and tilting vertical springs, which lead to inaccurate stiffness and damping measurements, especially at high torsional amplitudes.
Innovation Solution
A novel experimental setup featuring a rigid test model connected with rigid circular rods and lifting arms, lightweight high-strength strings, arc blocks with grooves, and linear tensile springs with fixed pulleys, ensuring minimal lateral tilt and constant vibration frequencies by maintaining the vertical and torsional stiffness through controlled deformations and reduced friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional vertical and lateral springs are used for small-amplitude vibrations, then the setup is simple and convenient, but the springs tilt and deflect during large-amplitude vibrations which deteriorates linear stiffness property and increases mechanical damping
Solution Approach 1:
The patent introduces rigid lifting arms with arc blocks as intermediary components between the model and the springs. The arc blocks guide the spring forces to always act vertically through their centers, preventing lateral deflection and tilt during large-amplitude vibrations. This intermediary mechanism ensures the springs maintain linear stiffness characteristics even when the model undergoes large torsional and lateral movements.
Solution Approach 2:
The patent employs arc-shaped lifting arms with precisely curved geometries. The arc blocks are designed with radii matching the rotation centers, ensuring that spring forces remain perpendicular to the lifting arms throughout the vibration cycle. This curved geometry enables the system to accommodate large-amplitude torsional vibrations (up to 35 degrees) while maintaining constant vertical spring orientation and linear stiffness properties.
2Adaptability or versatility
If large torsional amplitude vibrations are tested, then realistic wind-induced vibration conditions can be investigated, but traditional springs will obviously tilt and significantly deteriorate linear mechanical stiffness
Solution Approach 1:
The patent employs arc-shaped lifting arms with precisely curved geometries. The arc blocks are designed with radii matching the rotation centers, ensuring that spring forces remain perpendicular to the lifting arms throughout the vibration cycle. This curved geometry enables the system to accommodate large-amplitude torsional vibrations (up to 35 degrees) while maintaining constant vertical spring orientation and linear stiffness properties.
Solution Approach 2:
The patent transforms the mechanical configuration parameters by using rigid lifting arms with fixed arc radii rather than flexible spring mounts. The arc block radii are specifically chosen to match the model's torsional and lateral vibration centers, ensuring that the spring attachment points remain at constant vertical distances from the rotation centers throughout the vibration cycle, thereby maintaining constant stiffness parameters.
3Device complexity
If vertical springs are used for torsional vibration support, then the setup is compact, but the springs tilt during lateral-torsional vibration which increases mechanical damping and affects modal mass
Solution Approach 1:
The patent introduces rigid lifting arms with arc blocks as intermediary components between the model and the springs. The arc blocks guide the spring forces to always act vertically through their centers, preventing lateral deflection and tilt during large-amplitude vibrations. This intermediary mechanism ensures the springs maintain linear stiffness characteristics even when the model undergoes large torsional and lateral movements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The setup allows for accurate, linear free vibration testing at large amplitudes by maintaining constant vibration frequencies and avoiding nonlinearities, thereby providing reliable stiffness and damping measurements without the errors associated with traditional methods.
Implementation Method 1
linear tensile springs
Implementation Method 2
fixed pulleys
Implementation Method 3
rigid lifting arms
Data Source
AI summary
An experimental setup for three-degree-of-freedom large-amplitude free vibration in a 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 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.