Research On Oscillating Water Column Piezoelectric Power Generation Technology Based On Vortex Induced Frequency Escalation

With the continuous development of micro-electromechanical technology and sensing technology,wireless sensor networks are widely used in the field of marine environmental monitoring.At present,most of the buoy sensors in wireless sensor networks are powered by submarine cables or batteries,with limited used life and environmental pollution.The application of economic and environmental wave energy to drive piezoelectric ceramics to generate micro-power supply for monitoring network in the far sea has become a hot topic in China and abroad.However,the wave energy is mostly contained in the relatively narrow frequency band centered on the wave,while the natural frequency of the piezoelectric generator element is relatively high,so it is difficult to generate electric power efficiently under resonance conditions.This project put forward an oscillatory water column piezoelectric power generation device based on vortex-induced frequency escalation,which introduced a blunt body into the outlet of traditional oscillatory water column air chamber,for using the excitability of vortex vibration to drive the piezoelectric cantilever beam to collect energy,so as to realize the conversion of environmental low frequency excitation to high frequency excitation required by piezoelectric power generation.This project used ANSYS finite element software to conduct simulation analysis to the two components of the oscillatory water column wave energy acquisition device and the frequency-upped vortex-induced vibration piezoelectric power generation device respectively.The main research contents are as follows:In order to collect wave energy effectively,this project designed a hemispherical multi-directional wave energy collecting oscillating water column air chamber to improve wave capture efficiency.On the basis of fluid simulation analysis software(FLUENT),fluid dynamics continuity hypothesis and the incompressible viscous fluid Navier-Stokes equation(N-S equation),a model of hemispherical oscillating chamber and three-dimensional numerical wave flume was established under the condition of regular wave normal incidence.The wave capture ability of the air chamber without and with the back wall was analyzed comparatively.According to the analysis on the effects of the opening angle of the back wall channel,the thickness of the front wall and the water depth of the front wall on the energy output of air chamber of oscillating water column,this project concluded that adding the back wall of the chamber and reasonably changing the opening angle of the back wall channel can significantly improve the wave energy capture efficiency,increasing the thickness of the front wall of the chamber and reducing the water depth of the front wall can effectively improve the pressure at the top of the chamber and the velocity of the outlet,so as to provide high quality aerodynamic force for the subsequent secondary energy conversion.To study the frequency-upped vortex-induced vibration piezoelectric power generation device,a two-dimensional flow model around a bluff body was established without considering the deformation of a piezoelectric cantilever beam,and the frequency rise effect of vortex shedding caused by air flow through blunt body blocking under different inlet velocity and different blunt body shape was analyzed.It was concluded that the air flow with large pressure difference and high frequency can be obtained in the wake region of the circular bluff body,and the vortex shedding frequency could be increased by increasing the velocity and decreasing the diameter of circular blunt body.Then the piezoelectric cantilever beam model was established without considering the vortex shedding of the flow field.The influence of different piezoelectric materials and different structure sizes on the natural frequency of piezoelectric cantilever beam was studied.It was concluded that the natural frequency of PZT-5H cantilever beam was lower,and the natural frequency of cantilever beam could be reduced by increasing beam length and decreasing beam thickness.Finally,the three-dimensional flulid-solid-electric coupling model of piezoelectric power generation device with vortex-induced vibration was established on the basis of determining the frequency raising effect of the flow field and the natural frequency of the piezoelectric cantilever beam.It is used to compare and analyze the free end displacement and output voltage of the piezoelectric cantilever beam in the flow field without bluff body and with bluff body,and to study the influence of the horizontal distance between the bluff body and the cantilever beam and the offset distance of the cantilever beam on the output voltage of the piezoelectric cantilever beam.The maximum output voltage of 9.96 V was obtained by simulation.