Research On Wave Energy Acquisition Technology Of Vortex-induced Piezoelectric-electromagnetic Hybrid Power Generation

The ocean wireless sensor can measure the hydrometeorological elements such as wave height,ocean current,sea temperature,tide level,wind speed,air pressure and so on,which provides an important reference for sea navigation.The long-term energy supply of wireless sensor is one of the most popular topics in recent study,so the research on wave energy acquisition technology of vortex-excited piezoelectric-electromagnetic composite power generation oscillating water column is carried out in this paper.The key problems to be solved include the hydrodynamics of the interaction between waves and the gas chamber of oscillating water column,and the theoretical calculation model of piezoelectric-electromagnetic hybrid power generation which based on the vortex-induced high-frequency vibration of Karmlan vortex street effect.The operating principle of wave-driven piezoelectric-electromagnetic hybrid power generation is as follows:waves enter the energy collection chamber to form an oscillating water column and compress the gas in it,then the compressed gas flows through the bluff body placed at the exit of the gas chamber to produce vortex-induced vibration.This process achieves the conversion from low-frequency wave motion to high-frequency vortex-induced vibration.The piezoelectric-electromagnetic hybrid power generation structure is subjected to vortex-induced vibration,and the power generation system outputs electric energy based on the positive piezoelectric effect and the law of electromagnetic induction.The calculation and analysis obtained the influencing factors of the gas chamber pressure,vibration to increase the gas vibration frequency,and the optimal parameters of the energy harvesting system.The main research details of this paper is as follows:(1)The hydrodynamic model of the oscillating water column gas chamber is established.Based on the potential flow theory,using the Green's function method to solve the mathematical model,the theoretical results of air chamber pressure are obtained.In order to verify the process of theoretical calculation,a hydrodynamic finite element analysis model of the interaction between oscillating water column and gas chamber is established by using(CFD)commercial software of computational fluid dynamics based on Naviere-Stokes equation.The theoretical calculation results are in good agreement with the simulation results,which verifies the validity of the theoretical calculation model.Based on the mathematical solution model of air chamber pressure,it is obtained that when the draft depth of the front wall of the air chamber is 0.3 m,the wave period is 1.5s,and the maximum pressure generated in the air chamber is 60Pa.The vortex-induced vibration is produced by the cylindrical bluff body placed at the exit of the gas chamber,which increases the vibration frequency of the gas.It is calculated that when the diameter of the bluff body is 0.025m and the gas velocity at the outlet of the gas chamber is 11.6m/s,the vibration frequency can reach 95Hz after the gas flows through the bluff body.(2)Based on the positive piezoelectric effect,the force and energy conversion process of circular piezoelectric vibrator are analyzed,and the mathematical calculation model of piezoelectric energy collector is established.The effects of structural parameters of air chamber,wave and piezoelectric vibrator on the performance of piezoelectric power generation are discussed.The calculation results show that when the radius ratio of the piezoelectric oscillator is 0.5 and the thickness ratio is 0.66,the output open-circuit voltage of the piezoelectric oscillator energy collector is 8.59V and the energy is 3.71×10-6J.In order to verify the validity of the theoretical calculation,an experimental test platform is set up to test the effect of the size of the piezoelectric vibrator on the power generation performance.The piezoelectric experimental results are in good agreement with the theoretical calculation results.(3)The theoretical analysis process of wave energy of vortex-induced piezoelectric-electromagnetic hybrid power generation is studied.By using electromagnetic induction and positive piezoelectric effect,the mathematical model of composite power generation is established.And the effects of structural characteristic parameters,external load and vibration frequency on the performance of composite energy collector are obtained.The research shows that when the external load of the piezoelectric system is 490k?,the external load of the electromagnetic system is 4k?,and the wave enters the gas chamber of the oscillating water column to form a vortex-induced vibration frequency of 85Hz,the maximum output power of the composite power generation system is 3.3mW.And at the same frequency,the output power of the independent piezoelectric power generation system is 2.5mW.The output power of the electromagnetic power generation system is 1.08mW.The output power of the composite power generation system is 1.32 times that of the piezoelectric power generation system and 3.05 times that of the electromagnetic power generation system.The piezoelectric-electromagnetic hybrid power generation effectively improves the output power of the system,which provides a new technical reference for the energy supply of the ocean buoy wireless sensor.