This paper deals with a new set of two-degrees of freedom Vortex Induced Vibrations (VIV) experiments, with a relatively low mass-damping, elastically mounted rigid cylinder, in water. An experimental apparatus has been designed. Such device is a displacement-force-acceleration transducer and enables one to gather a great deal of relevant information. Experiments have been carried out in the S. Paul0 Research Technological Institute (IPT) Towing Tank, in a series of rims, which comprise crosswise, stream wise and coupled oscillations. Further interpretations of sub-harmonic resonance, coupling in-line and cross-flow vibrations are addressed.
In the present work, we are concerned with the vortex-induced vibrations of elastically mounted rigid and cantilevered cylinders in water flow, focusing on the hydro-elastic modal coupling in two different planes of vibration. As expected, the flexible cantilever showed a vortexinduced dynamic behavior neatly similar to the standard case of an elastically mounted rigid cylinder. In a second row of experiments, see Fujarra et al. (2001) a twin pair of structurally non-symmetric cantilevers was constructed. Those models were hydro-dynamically but not structurally axisymmetric, as bending stiffness values were quite different in both principal flexural planes. The principal plane of larger (around 16 times) bending stiffness was aligned with the flow, such that the smaller one was placed crosswise, according to the expected plane of vortex-induced vibrations. Experiments were performed in water channels with very small turbulence level and in both arrangements the vertical cantilevers were clamped just above the water surface. Despite the distinct measurements techniques and different laboratory facilities, results compared quite well, not only in terms of amplitude response as a function of reduced velocity but, particularly, in terms of frequency response ratio which as should be expected, exhibited an interesting double frequency, coupling in-flow with cross-flow vibrations.
