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In order to operate wireless electronic devices at locations that are not conveniently accessible for wiring or battery replacement, energy harvest techniques have been developed to convert harvested environmental mechanical energy to electrical energy, which can be used for convenient device operation or battery charging. Due to the strong electromechanical coupling effect, piezoelectric materials are employed for this purpose. Recently, piezoelectric energy harvesters that are composed of flexible piezoelectric films or strips are adopted for converting mechanical energy from ambient fluids induced vibrations into electric energy[Carroll (2002); Akaydin et al. (2010); Allen and Smits (2001); Peng and Zhu (2009); Zhu and Peng (2009)]. To extract energy as much as possible, the harvesters are usually designed as resonant devices operating near resonance. We study a new piezoelectric structure for energy harvesting from flow-induced vibration. It consists of a properly poled and electroded flexible piezoelectric ceramic cylinder (Fig. 1) in a perpendicular flow. The transverse force from the flow [Fung (1969)] drives the cylinder into flexural vibrations with an electrical output. An analytical solution is obtained from which the output power and efficiency of the harvester versus outer electrodes angle are calculated and examined. For a cylinder of 40 cm in length and 1 cm in diameter in flowing air with a speed of 5 m/s, the output power is of the order of 10^-3 watt (Fig. 2). It becomes significantly higher if the flow speed is increased. The nonlinear behaviors of this energy harvester near resonance are analyzed subsequently. The geometrically-nonlinear effect of the cylinder is studied with considering the in-plane extension incidental to the large deflection. The boundary electric charges generated from two deformation modes, flexure and in-plane extension, were distinguished with each other because the charge corresponding to the latter mode produces no contribution to the output current. Numerical results on output powers show that there are multivaluedness and jump behaviors (Fig. 6). Based on both the linear and nonlinear results, how to design the energy harvester to get the maximum output power is discussed.