Piezoelectric Effect Based Oscillating Water Column Wave Energy Generation Numerical Simulation Analysis

Wireless sensor network technology is widely used in marine monitoring.The traditional battery life is limited to power the sensor node. It is difficult to replace the batteries when they exhausted. Wind and solar energy are susceptible to weather. In order to provide continuous and reliable energy for low powered micro sensor distributing on the sea surface. An oscillating water column piezoelectric generation model is presented in this paper.The driving force is the air compressed by water column. In this structure the generator and seawater is separated in air chamber. So the power plant avoided being corroded by seawater. Piezoelectric generation system is simple, small in size, no pollution, low cost, high output power density, which suits for environment vibration energy harvesting. The theoretical calculation model for the gas pressure in the chamber is established based on the linear wave theory. The Green function is solved with the multidimensional Chebyshev polynomial and asymptotic expansive fast approximation method. Then the velocity of the flow field and the chamber pressure are derived. The mathematical model of circular piezoelectric vibrator under pressure is established based on the piezoelectric and the material mechanics theory. The output charge, voltage and electric power producing on the piezoelectric oscillator membrane are calculated with the micro-element method.The pressure in the air chamber will be affected by the factors that is the incident wavelength L, the wave period T, the amplitude a0 and the front wall draft depth d while the ocean wave period T is 1.8s, the incident wave will resonate with the surface wave in the air chamber when it reaches the front wall of the chamber. The pressure is 65Pa in the OWC chamber. When the draft depth d is 0.3m the pressure in the air chamber reaches the highest. Then the wave energy harvesting efficiency is optimal.The oscillation amplitude of the water column increases with the the incident amplitude in the chamber,and the pressure increases following by the oscillation amplitude.The energy produced by the circular piezoelectric oscillator membrane is aEfected by the thickness of the piezoelectric layer hp, the substrate hm, the adhesive layer hb,the substrate radius a and so on. The calculation results shows that the output charge Qg and the power Pg decrease gradually with the thickness of the piezoelectric layer hp increasing. The open circuit voltage Vg is 47V when the piezoelectric layer thickness is 0.175mm. The output power reach highest while the substrate thickness hm is 0.25mm, the charge is 5.58×10-6C, the open circuit voltage is 32V, and the out power is 176?W. The output power decreases gradually with the thickness of the adhesive layer hb increasing. On the contrary the power increases gradually with the increasing of the diameter a of the piezoelectric oscillator substrate. At the same time the power from the piezoelectric oscillator will be affected by the different elastic materials such as beryllium bronze, silicon, aluminum, steel, carbon fiber which is selected as the piezoelectric oscillator substrate. The analysis results show that the generation system produces the most electric power with the Beryllium bronze as a substrate. This paper discusses the affection about the output power by the incident wave period T, the front wall draft depth d and the incident amplitude a0. When the wave period T is 1.8s, the generation produces the maximum energy, the charge is 7.98×10-6 C, the open circuit voltage is 36V, the output power is 151?W. When the draft depth d is 0.3m, the energy generated by the power generation unit is the largest,the charge is 7.98×10-6C,the open circuit voltage is 36V,the output power is 151 pW.The results show that the output power increases with the incident amplitude a0 increasing.This paper research on the composite circular piezoelectric oscillator generation theoretical model driven by oscillating water column. The energy harvesting progresses include the wave energy harvesting and pressure conversion in the gas chamber. The system analysis in this paper provides a theoretical model to calculate ocean wave energy harvesting and to improve the new generator structure. The wave energy harvesting model realizes the self-powered wireless sensors.