Dynamic Analysis And Design Of Micro-power Generator Based On Cross-flow Induced Vibrations

Micro wireless sensors are widely employed in national defense and military,environmental monitoring,remote monitoring,and other engineering fields.The traditional dry battery power supply method restricts the wide use of micro wireless sensors in terms of service life,environmental pollution,and installation.The way of energy supply based on fluid energy harvesting has advantages of environmental protection and low maintenance cost,which has been widely concerned due to broad potential applications in green and continuous energy supply for micro wireless sensors.However,the conversion efficiency of rotating energy harvesting devices based on turbines is not prominent at low flow velocities due to the influence of internal friction and electromagnetic damping.Therefore,in this thesis,several energy harvesting methods based on flow-induced vibration are proposed.According to the electromechanical coupling effect and fluid-structure coupling dynamics,novel small energy harvesting devices are designed to improve the energy harvesting performance at low flow velocities.The main research work and achievements include:(1)A strategy of introducing nonlinear magnetic forces to harvest energy from vortexinduced vibrations is proposed.The deigned structure shows monostable and bistable vibration characteristics with magnetic forces.The natural frequency of the structure can be changed by adjusting the relative position of the magnets,then the lockin region of wind speed can be shifted to the left or right.Therefore,the resonance wind speed of the structure can be controlled according to the wind speed conditions.When the magnet spacing is small,the vibration of the structure shows softening behavior,which can greatly widen the resonance wind speed range of energy harvesting and hence improve the harvesting performance.(2)A VIV energy harvesting system based on interference cylinder configuration is designed.The results show that the introduction of an interference cylinder can make the vibration response of energy harvester shift from vortex-induced vibration to galloping oscillation,which can significantly widen the lock-in region.Besides,the cross-section of the interference cylinder also has a significant influence on the energy harvester’s performance.It is observed that the rectangular cross-section interference cylinder has a better effect on improving the energy harvesting performance compared to others.(3)A galloping energy harvesting structure based on Halbach magnet array is proposed.The theoretical dynamic model of the energy harvester is established.It is found that the critical wind speed of galloping can be adjusted by changing the external resistance,so as to realize the harvesting of wind energy at low wind speed.The experimental results also show that the output power of the designed galloping energy harvester is higher than that of the previous wind energy harvesting devices.(4)A galloping energy harvesting model based on the piezoelectric-electromagnetic hybrid conversion mechanism is proposed and analyzed.The theoretical model based on distributed parameters is established,which is verified by experiments.The influence of piezoelectric resistance and electromagnetic resistance on critical wind speed is explored by linear analysis.The output power of the energy harvester under different load resistancesc is analyzed by nonlinear analysis.The results show that the change of external resistance affects structural damping,thus the vibration response intensity and total output power also changes with varying the external resistance.(5)A galloping nanogenerator based on triboelectric effect is designed,which can effectively harvest triboelectric energy through impact behaviors induced by galloping at low wind speed.The dynamic behavior and output voltage of the device are studied by establishing a theoretical model,which is verified by the experimental data.The results show that the open voltage of up to 200 V can be generated at the wind speed of 1.4m/s.Besides,the output voltage has a great relationship with the designed configuration of the flexible main/auxiliary beam.The 12-9 configuration is suitable for low wind speed energy harvesting,while the 12-12 configuration is better for high wind speed.