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Two-dimensional structural vibration induced by fluid flow past a circular cylindrical body Chow, Yu-Min

Abstract

The investigation is concerned with the vibrational response of a circular cylindrical body when subjected to oscillating lift and drag forces of varying frequency. The cylindrical body was mounted on a long flexible cantilever and the stiffness of the cantilever could be varied to study the effects of resonance, amplitude and induced damping. An explanation of the two-dimensional excitation due to vortex shedding is presented. Both longitudinal and transverse vibrations were induced and the frequency of the excitation in the longitudinal direction was about twice that in the lateral. Therefore, for equal structural natural frequencies in the lateral and longitudinal directions, resonance in the lateral direction will occur at twice the velocity of the longitudinal resonance, assuming the Strouhal Number to be constant in this range. Coefficients of the elastic response forces, in both longitudinal and lateral directions near the lonitudinal resonance, were plotted for comparison. The development of irregularity in the lateral vibrating oscillogram caused by the longitudinal vibration was demonstrated. In the critical Reynolds Number range the effect of a fixed eddy-starter wire was investigated and the excitations in both lateral and longitudinal directions were altered. The resonance of longitudinal vibration occurs at V/V[subscript res] = 0.3 to 0.5. Lateral amplitude in this region is also increased. The peak of the curve: S[subscript y] vs R[subscript e], in the region of longitudinal resonance, approaches tengentially the curve: S[subscript x] vs R[subscript e]. The structural response coefficient of vibrating lift and drag rises at longitudinal resonance to a value of 3.0 to 8.0, but drops quickly after resonance. The damping coefficients of the structure are in the range of 0.25 to 0.60. Since the motion of the vibration may influence the oscillating lift and drag due to the eddy shedding, this study presents an investigation of the longitudinal and lateral resonances in a range of R[subscript e]: 5 × 10³ × 10⁵, and the interaction of the excitation between the oscillating lift and drag with the two-dimensional elastic response forces.

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