Piezoelectric Wind Energy Harvesters Enhanced By Interaction Between Vortex-Induced Vibration And Galloping

The wind energy harvester based on the wind-induced vibration mechanism can convert ambient wind energy into electricity.As the ideal electric source of wireless sensor nodes,it possess the adatages of structural simplicity,long lifespan,maintenance free and non-pollution.Since the wind speed in most natural environments is relatively low,it is of great significance to develop wind energy harvesters with high output power in the moderate and low wind speed regions.Current energy harvesters based on wind-induced vibration utilizes only a single wind-induced vibration mechanism.The critical wind speed for vortex-induced vibration(VIV)energy harvesters is relatively low,but the output power is relatively low.The output power for galloping-based energy harvester is relatively high,but the critical wind speed is also relatively high as well.Previous results in the field of the wind resistance of civil engineering have revealed that the coupling effect between VIV and galloping increases structural responses in low wind speed region and therefore lead to higher risk of structural failure.Based on the studies mentioned above,this dissertation carries out further studies on the implementation,modeling and design of VIV-galloping interactive piezoelectric wind energy harvester(PWEH),and the fabricated PWEH prototype has low onset speed and high output power.This type of devices are promising in the field of wireless sensing.The main contents of this dissertation include:First,the structure,working principle and implementation method of the VIV-galloping interactive PWEH are analyzed based on the classical VIV and galloping theory.The PWEH prototypes enhanced by interaction between VIV and galloping are firstly developed,and the theoretical model is validated by comparing with experiments.The results show that the interaction between VIV and galloping can be realized by adjusting shape,dimensions,mass of bluff body and dimensions of beam.It is also shown that the interaction between VIV and galloping is beneficial to enhance the output performance of the PWEH in the moderate and low wind speed regions.Second,based on the Tamura-Shimada model,the theoretical model for VIV-galloping interactive PWEH is established by considering the effects of the inverse piezoelectric effect in the differential equation of motion,and introducing the coupled circuit equation relating the electrical output to the structural deformation.The effect of aerodynamic coefficients on VIV is analyzed.One PWEH prototypes with the full VIV-galloping interaction and the other with low interaction between VIV and galloping regions are fabricated.The experimental results show that the theoretical model is accurate enough for these devices.Then,based on the proposed theoretical model,the influence of the structural parameters of the PWEH on the output performance is studied.Aiming at maximum output power,the beam length,electrode length and side length of square cross-sectioned bluff body are optimized with the constant total volume of PWEH.The optimization results are verified by experiments and the experimental results shows that the critical wind speed of the prototype is about 1.8-2.0 m/s and the maximum output power and power density,that is,580.7?W and 83.0?W/cm~3 at the wind speed of 11.6m/s.Finally,according to the output characteristics and the energy demand of the electrical load,the power management circuit of the VIV-galloping interactive PWEH is designed.The experimental results show that,the time required to charge a 100?F storage capacitor from 0 to 4 V is approximately 3890,245,126,and 59 seconds,and the time needed to charge from 3 to 4 V is about 1740,117,39,and 16 seconds at the wind speed of 3.0,4.0,5.2 and 8m/s,respectively.The enhancement effect of interaction between VIV and galloping provides a new method for the development of wind energy harvester with low critical wind speed and high electrical output.The experiments prove that the interaction between VIV and galloping is an effective method to improve output performance for PWEH operating in the moderate and low wind speed regions.Additionally,the proposed theoretical model has been verified by experiments,which may be referred in the optimization of VIV-galloping interactive PWEH.