Transverse Galloping Oscillations
Transverse galloping oscillations of a linear dynamic structure are nonlinear due to the effect of the fluid force. As comparisons between theoretical and experimental results show, it is adequate to measure the forces on a model in a steady flow and apply the results for the dynamic system. The differential equations for the system can be solved either by using a polynomial expression for the aerodynamic force or by a numerical solution in the phase-plane. It is shown that the usually applied criterion by Den Hartog is not sufficient for stability. The very important influence of turbulence on the stability is shown for rectangular cross-sections. Theoretical and experimental investigations concerning the influence of yaw on the stability show, that the onset wind velocity increases with increasing yaw angle. If the critical galloping wind speed is close to the resonance wind speed, mutual effects of the two phenomena may occur. A structure with closely spaced modal frequencies may vibrate in a multi-mode way or in one mode only, as shown by changing the mass distribution of a bridge tower.
KeywordsWind Speed Turbulence Intensity Vortex Resonance Initial Amplitude Separate Shear Layer
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- Simiu, E., Scanlan, R.H.: Wind effects on structures 2nd ed, John Wiley andSons, 1986Google Scholar
- Parkinson, G.V.: Mathematical models of flow-induced vibrations of bluff bodies, in: Naudascher E.: Flow-induced structural vibrations, Springer 1974, 81–128.Google Scholar
- Novak, M.: Galloping oscillations of prismatic structures, J. of the ASCE, vol. 98, No. EM1, 27–46, (1972).Google Scholar
- Den Hartog, J.P.: Mechanische Schwingungen, Springer Verlag, 1936.Google Scholar
- Novak, M.: Galloping and vortex induced oscillations of structures, Proc. of the 3rd Int. Conf. on Wind Effects on Buildings and Structures, Tokyo 1971, 799–809.Google Scholar
- Mijata, T., Miyazaki M.: Turbulence effects on aerodynamic response of rectangular bluff cylinders, Proc. 5th Int. Conf. on Wind Eng. Fort Collins 1974 (Ed. Cermak, J.E.) Vol. 1, 631–642.Google Scholar
- Skarecky, R.: Yaw effects on galloping instability, J. of the Eng. Mech. Div., Proc. ASCE 101 EM6 (1975) 739–754.Google Scholar
- Wawzonek, M.A., Parkinson, G.V.: Combined effects of galloping instability and vortex resonance, Wind Engineering, Proc. of the 5th Int. Conf. Fort Collins 1979 (Ed. Cermak J.E.) 673–684.Google Scholar