Control of flow‐induced vibrations in Nitinol‐reinforced composite beams Free

Flow‐induced vibrations of flexible fiberglas composite beams are attenuated by activating optimal sets of NIckel and TItanium alloy wire, called NITInol, which are embedded inside these beams. The dynamic and thermal characteristic of the Nitinol‐reinforced composite beams are determined by monitoring the vibration's modes, as well as the temperature of the wires and beam during various activation and de‐activation strategies of the Nitinol wires. The resulting shift of the vibration modes, which accompanies the activation of the Nitinol wires, is utilized to influence the fluid‐structure interaction in such a way that results in attenuating the flow‐induced vibrations. Experiments are conducted on 30‐cm‐long and 0.156‐cm‐thick prototypes of these beams that are mounted in a clamped‐clamped fashion inside a wind tunnel. The effect of varying the flow speed on the induced vibrations is determined with and without the activation of the Nitinol wires. The results obtained indicate that there is an optimal number of Nitinol wires that should be activated to attain the maximum frequency shift. This number ensures a balance between the amount of strain energy added to the composite beam and the softening effect imparted to the resin used due to the heating of the Nitinol wires. With such optimal configuration, it was possible to shift the first mode of vibration from 42 to 61 Hz in about 3 min during the activation phase. About 6 min was required to bring the beam back to its original frequency during the de‐activation phase. At steady‐state conditions, vibration attenuations in excess of 60% were attained near and at the resonance. [Work supported under a grant from ARC.]