Investigating The Effectiveness of Piezo Stripe Actuators on Flexible Cylinder’s Dynamic Response under Vortex-induced Vibrations

Abstract

In this paper, we investigate the effectiveness of piezo stripe actuators in manipulating the flexible cylinder’s dynamic response under vortex-induced vibrations. To do this, we test several low aspect ratio flexible cylinders in a recirculating flow channel where we apply a disruption to the cylinder’s response using piezoelectric actuators. In the experiments, we test two cylinders where cylinder 1 is comprised of two piezo stripe actuators bonded at the structural second mode antinode of a rectangular beam, whereas cylinder 2 is comprised of 3 piezo stripe actuators bonded at the structural third mode anti-node of a rectangular beam. The beam characteristics were identified such that the cylinder would oscillate up to fourth mode in the in-line direction while keeping the cross-flow mode shape constant with first mode. As a result of this study, it is observed that piezo stripes are capable of altering the flow-induced vibration response of the cylinders at different reduced velocities. For example, at low reduced velocities where in-line motions dominate, activation of the second mode in in-line results in a decrease in the total in-line and cross-flow response. In addition, the disruption from the piezo actuators could result in a reduction in the system’s higher harmonic frequencies. The fact that a small excitation in one direction can induce significantly different dynamic behaviors in the other direction in the form of vibration reduction or amplification is of special relevance to deep-water offshore marine structures since the flow conditions are generally multi-directional. Another interesting observation is that, a flexible cylinder under uniform flow conditions can excite with even modes in the in-line direction. It is hypothesized that this is because of the asymmetric mass distribution provided by the piezo attachment and cable connections within the cylinder which breaks the total symmetric fluid loading on the cylinder.