The flow-induced vibration of a cylinder with two degrees of freedom near a rigid wall under the action of steady flow is investigated experimentally. The vibration amplitude and frequency of the cylinder and the vortex shedding frequency at the wake flow region of the cylinder are measured. The influence of gap-to-diameter ratio upon the amplitude response is analyzed. The experimental results indicate that when the reduced velocity (Vr) is in the range of 1.2 < Vr < 2.6, only streamwise vibration with small amplitude occurs, whose frequency is quite close to its natural frequency in the still water. When the reduced velocity Vr > 3.4, both the streamwise and transverse vibrations of the cylinder occur. In this range, the amplitudes of transverse vibration are much larger than those of streamwise vibrations, and the amplitudes of the streamwise vibration also get larger than those at the range of 1.2 < Vr < 2.6. At the range of Vr > 3.4, the frequency of streamwise vibration undergoes a jump at certain values of Vr, at which the streamwise vibrating frequency is twice as much as the transverse one. However, when the streamwise vibration does not experience a jump, its frequency is the same as that of the transverse vibration. The maximum values of second streamwise and transverse vibration amplitudes increase with increasing gap-to-diameter ratios.
The flow-induced vibrations of a cylinder are a fluid-structure interaction problem, which have a wide practical background. For example, the bridges and chimneys under wind actions in civil engineering, the risers and pipelines in offshore engineering, the heat exchangers tubes in chemical engineering, are prone to flow-induced vibrations, which have attracted wide interests from numerous researchers, e.g., Sarpkaya (1979), Griffin & Ramberg (1982), Bearman (1984), Parkinson (1989), Sumer & Fredsoe (1997), Williamson & Govardhan (2004). Most of previous researches have mainly focused.