A novel elastic suspension system for wind tunnel section model studies

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Abstract

A novel three-degree-of-freedom (DOF) suspension system has been developed for the wind-tunnel section model study of wind-excited vibrations of flexible structures. This system enables simultaneous vertical, horizontal, and torsional motion of the suspended model and captures the effect of coupling between different degrees of freedom of a flexible structure immersed in a dynamic flow field. It utilizes pneumatic bushings that glide along polished steel shafts in the vertical and horizontal directions of motion. Torsional assemblies are used to generate torsional motion of the model. Force measurement is accomplished with compact strain-gage type force transducers that allow precise placement for accurate measurements. Static measurements are also possible by restraining the desired DOF. Vibration frequencies of the system are tuned with combinations of springs. System damping is low due to the low-friction pneumatic bushings, restriction of coil spring wire to small diameters, and highly polished stainless steel guide shafts. Relatively large displacements can be generated by the suspension system, if required. Results from two experiments on aeroelastic studies are presented to demonstrate the functioning of the suspension system. The effect of including the lateral motion on the coupled-mode response is illustrated.

Section snippets

Introduction and background

Wind loads are induced on a structure as a result of a complex interaction between wind and structure. These loads are quite capable of producing large-amplitude motions of the flexible structure that may be catastrophic. The interaction of wind flow with structures can be classified under aerodynamic and aeroelastic effects [1], [2]. The aerodynamic effect refers to the fluctuating nature of the wind and its interaction with the structure, such as buffeting which is defined as the unsteady

Component description and assembly of the elastic suspension system

The components that were used to assemble the three-DOF elastic suspension system are described here. This system enables simultaneous vertical, horizontal, and torsional motion of the suspended model and is capable of capturing the effect of coupling between different degrees of freedom of a section model subjected to wind loading.

Stay-cable vibration study

Stay cables are typically arranged on a cable-stayed bridge in combinations of inclination and yaw. In the section model study of stay cables, it was necessary to have the capability to arrange the section model in similar combinations of inclination and yaw. In addition, full-scale observations had demonstrated [11] that stay cable vibration is actually two-dimensional, i.e., the vibration tends to be elliptic rather than constrained along a particular axis. To allow elliptic motions of the

Summary

A three-DOF elastic suspension system has been developed that can be used for section-model testing in wind tunnels. The three-DOF system would be highly capable of studying aerodynamic and aeroelastic phenomena like across-wind galloping, rain-wind induced cable vibration, torsional divergence, flutter instability, buffeting, etc. Displacement time histories generated by unsteady aerodynamic forces acting on a section model can be recorded with the help of appropriate data acquisition system.

Acknowledgements

The authors acknowledge the financial support provided by Texas Department of Transportation, and Department of Aerospace Engineering, Iowa State University.

References (12)

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