Experimental and numerical modelling of second mode resonance of slender structures subjected to vortex-induced vibrations

Experimental and numerical modelling of second mode resonance of slender structures subjected to vortex-induced vibration

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Wind engineering has become a cornerstone of modern structural design. Underestimating or neglecting wind effects can lead to severe consequences, as demonstrated by historical failures such as the collapse of the Tacoma Narrows Bridge in 1940. Even in less extreme cases, wind-induced actions can result in serviceability issues or fatigue damage over time.

Over recent decades, research in this field has expanded significantly, supported by advances in wind tunnel testing, computational tools, and analytical methods. Despite this progress, aeroelastic phenomena remain comparatively understudied. They arise from interactions between aerodynamic forces and structural motion, making them difficult to predict.

This thesis focuses on improving the understanding of Vortex-Induced Vibrations (VIV) on slender structures, such as wind turbines. VIV occur when wind flows around a bluff body and vortices are shed alternately from each side. This generates oscillating forces that, when synchronised with the natural frequency of the structure, result in non- negligible vibrations of the structure.

Most existing models assume uniform shedding along a portion of the structure height. However, for slender structures, evidence suggests that this occurs in multiple distinct zones with different correlation characteristics. As a result, higher vibration modes, not only the fundamental mode, may play a significant role in the structural response.

To investigate the existence of these multiple synchronisation zones, this work combines wind tunnel experiments with numerical simulations. The objective is to better characterise the behaviour of slender structures subjected to VIV and to contribute to the development of more reliable design approaches for their protection.