Wind Tunnel Vibration Device Using Thin Strings to Prevent Spring Tilt
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Solution Overview
Problem
Traditional wind tunnel testing devices for vertical-torsional coupled free vibration cannot maintain linear stiffness and frequency constants during large-amplitude vibrations, leading to significant testing errors, especially for structures like the Tacoma Narrows Bridge where torsional amplitudes exceed 35°.
Innovation Solution
A wind tunnel test device comprising a rigid deck model, lightweight rigid rods, lightweight rigid circular hubs, and high-strength thin strings, where the first thin strings allow vertical-torsional coupled free vibration without spring tilt, and the second thin strings restrict lateral vibration, maintaining linear tensile stiffness and constant frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional vertical springs are used to suspend the deck model for coupled free vibration testing, then the device structure is simple and convenient, but during large-amplitude torsional vibrations the springs tilt and the vertical stiffness cannot remain linear, causing significant testing errors
Solution Approach 1:
The suspension system is segmented into two independent functional components: vertical springs that maintain constant vertical stiffness, and horizontal strings that constrain lateral displacement. This segmentation allows each component to perform its specific function without interfering with the other, preventing the coupling of vertical and lateral motions that causes spring tilting in traditional single-spring systems.
Solution Approach 2:
The horizontal strings act as intermediary constraints between the model and the support structure. These strings provide lateral stabilization without affecting vertical motion, serving as a mediator that decouples the vertical vibration function from lateral displacement, thereby preventing spring tilting while maintaining testing simplicity.
2Adaptability or versatility
If the torsional amplitude is increased to test large-amplitude vibrations (e.g., 35° like Tacoma Narrows Bridge), then the testing capability is improved, but the spring tilt increases and testing errors become unacceptable
Solution Approach 1:
The system dynamically adapts to large-amplitude vibrations through the horizontal strings, which can freely rotate around their connection points on the model. This dynamic configuration allows the strings to accommodate large torsional amplitudes without restricting the vertical vibration motion, enabling accurate testing across a wide range of amplitudes from small to large (35° and beyond).
3Measurement precision
If the second thin strings are added to restrict lateral vibration, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The horizontal constraints are implemented using thin strings rather than rigid structural elements. These flexible thin strings provide the necessary lateral constraint function while adding minimal structural complexity, weight, and cost to the system, making the enhancement practically implementable.
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
Enables accurate large-amplitude vertical-torsional coupled free vibration testing by avoiding nonlinearities, ensuring constant stiffness and frequency, and allowing tests previously impossible with conventional devices, with low cost and easy installation, and minimal mechanical damping.
Implementation Method 1
The linear vertical translational and torsional stiffness of the system can be realized by the linear tensile rigidity of springs
Implementation Method 2
The linear tensile stiffness of the first thin strings 4 and the second thin strings 6 are much larger than those of the vertical springs 5
Data Source
AI summary
A large-amplitude vertical-torsional coupled free vibration testing device for wind tunnel test. The large-amplitude vertical-torsional coupled free vibration device for wind tunnel test includes rigid deck model, lightweight rigid rods, lightweight rigid circular aluminium hubs, the first thin strings, linear tensile vertical springs, and the second lightweight strings. Large-amplitude vertical-torsional coupled free vibrations of rigid deck models can be realized by using this device, in which the springs vertically deform without any tilt. In the traditional free vibration device, the spring may obviously tilt, and the linear torsional stiffness cannot be ensured. The device can be conveniently installed and the initial angle of attack can be easily adjusted. The extreme low and stable mechanical damping ratio required for large-amplitude vibrations can be readily guaranteed, owing to the invocation of the negligible rolling friction between the thin strings and the hub.