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An Aeroelastic Investigation of Wind Induced Vibrations of High-Mast Poles

par Peavy, Matthew
Président du jury Deconinck, Herman
Promoteur Degrez, Gérard
Co-Promoteur Puckett, Jay A
Publication Non publié, 2018-07-17

Thèse de doctorat

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Résumé :

High-mast light poles are used frequently to illuminate large areas such as motorways and parking lots. These poles are extremely tall with respect to their cross-section, reaching heights of more than 40 meters. These structures undergo a strong aeroelastic response due to wind, oftentimes resulting in fatigue cracking at the base. The purpose of the research is to better understand the effects of wind-induced vibrations of tall flexible structures using a combination of computational fluid dynamics and structural finite element codes. Field results of existing high-mast poles will be used to calibrate and verify the theoretical modeling.Periodic vortex shedding is observed to occur on these structures at certain wind velocities. The shedding of vortices causes pressure differences across the pole, resulting in a net driving force perpendicular to the direction of the wind. When the frequency of shedding, and thus the driving force, matches the natural frequency of the pole, excitation of the structure can be significant. This phenomenon is called lock-in. Poles that are repeatedly subjected to wind at lock-in velocity may suffer excessive deformation and fatigue damage. The aeroelastic response is especially significant, since the damping of the structural system is so small.In order to model the fluid-structure interaction, OpenFOAM libraries were compiled into a single application that combined a structural dynamic finite element code along with a mesh movement algorithm. The loosely coupled system applies the driving forces (integrated pressures) to the structure in a conventional serial staggered procedure. The coupling of the two domains and the mesh deformation calculationswere software written by the author. The 3-field solution formulation is implemented using a mesh movement algorithm based on a pseudo-elastic approach. Incompressible flow is assumed, as the lock-in velocities for the first three natural frequency modes ofthe pole are relatively low. Large Eddy Simulation is used for turbulence modeling.In conjunction with the University of Wyoming, two existing steel hexadecagonal high-mast poles in Wyoming, USA, were instrumented with accelerometers and anemometers. These data were used to calibrate and verify the structural, stiffness, damping, and response characteristics.A series of 14 simulations were run that increased in the difficulty of the domain being simulated. Different aspects of the pole aparatus were investigated individually, such as the taper and angle of incidence of flow. An atmospheric boundary layer model was incorporated. The final case resulted in the simulation of a 16-sided tapered pole subject to flow from an atmospheric boundary layer inlet, incorporating large eddy simulation turbulence modeling.