Study On Piezoelectric Ocean Energy Harvesting Technology Based On Vortex-induced Vibration

There are many fixed or floating structures in the ocean including anchor chains,mooring platforms,buoys,etc.Some microelectronic devices have weak power in some working modes.In order to utilize existing marine structures for marine en-ergy harvesting,these microelectronic devices can be powered without the need for complex structures.In this paper,a piezoelectric energy harvesting scheme based on vortex-induced vibration is proposed for floating and fixed ocean structures.The power generation performance of the vortex-induced vibration is studied.The main achievements are as follows:(1)For the floating ocean structures in the underwater environment,based on the vortex-induced vibration of the structures under ocean current,an energy harvest-ing scheme consisting of a bluff body and a multi-layer flexible piezoelectric compos-ite beam is proposed,which takes advantage of the bending deformation of flexible piezoelectric materials.The deformation converts the vortex-induced vibration of the bluff body into a continuous energy source used by the MEMS devices.Then,using the lift decomposition model and the Euler-Bernoulli beam assumption,the transverse vortex-induced vibration model of the bluff body and the bending deformation model of the multilayer piezoelectric composite beam are established respectively,and the mathematical model of the power generation performance of the structure is then ob-tained.The boundary condition processing method for the high-order partial differ-ential equations of composite beam vibrations is introduced.Then,the detailed pa-rameters of the scheme structure and the material property parameters are given.The two-dimensional simplified model based on the scheme structure is used to simulate the output voltage and power performance of the structure under different structural dimensions and working conditions.The effects of beam length and load resistance on the flow wake field and power generation performance of the device are investigated.The simulation results show that the vibration of composite beams with different beam lengths is dominated by different modes of vibration modes.Under the condition that the beam length is 3 times the bluff body's diameter and the load resistance is 200 k?,the maximum average output power of the device can be reach 7.3?W.(2)For the fixed ocean structures in the underwater environment,a piezoelectric vortex wake energy harvesting scheme-VIPEC(Vortex Induced Piezoelectric Energy Converter),consisting of a bluff body,a splitter plate and several piezoelectric patches is proposed.A smaller-sized piezoelectric ceramic is used in the scheme to reduce the structure's size.Firstly,a two-dimensional simplified model of the structure is estab-lished.Its mathematical model of the output voltage of the structure is established by combining the model's fluid and the piezoelectric governing equations.The detailed dimensional parameters and working parameters of the structure are given.Then,the effects of inlet flow velocity,splitter plate length,load resistance and other factors on structural hydrodynamic performance such as Strouhal number,lift phase differ-ence,root mean square values of lift coefficient,force arm,and wake field are studied though numerical simulation.Meanwhile,the effects of different flow velocities and resistance conditions on the average open circuit output voltage of the structure are also studied.The two-dimensional simulation results show that the maximum aver-age open circuit output voltage of the device can reach 2.3 m V under the condition that the length of the separation plate is 2.5 times the bluff body's diameter and the Reynolds number is 9×10~4.(3)The three-dimensional fluid-solid-piezoelectric coupling analysis of the pro-posed VIPEC device is carried out.Firstly,the simulation parameters of the fluid do-main,structural domain and piezoelectric module are elaborated.The displacement deflection response and output voltage response of the device under different working conditions are simulated and analyzed.Then,a miniature VIPEC experimental proto-type is fabricated according to the simulated structure size.A prototype experiment platform based on small circulating water tunnel is set up.Its power generation per-formance under different plate lengths,inflow velocities and load resistances is tested.Results of two-dimensional simplified simulation,three-dimensional coupled simula-tion and prototype experiment are compared.Then,the effects of load resistance on the power generation performance of the prototype under different working condi-tions are studied experimentally.It is found that the results obtained by the three-dimensional coupling simulation are in good agreement with those of the prototype experiments under the same working conditions.The two-dimensional simulation re-sults are generally a little bigger than the other two cases.However,it has a good guidance for the prototype design because of its low computational cost.The exper-imental results show that the maximum average open circuit output voltage of the device can reach 1.9 m V under the condition that the length of the splitter plate is 2.5times the bluff body's diameter and the Reynolds number is 9×10~4.(4)For the layout problem for multiple VIPEC structures,two design parameters,i.e.the latitudinal spacing and the longitudinal spacing,are selected as the layout optimization variables of two VIPECs,and the selected variable design space is di-vided into four regions.Then,several sampling points are chosen in the design space,and their hydrodynamic force and output voltage of the leading-following VIPECs at different sampling points are obtained by numerical simulation.Then,the Kriging surrogate model is used to establish the output voltage response surface model of the two VIPECs.The effects of design parameters on the lift coefficient and output voltage of two VIPECs and its overall flow field around the structure are analyzed.Then,the Kriging surrogate model of the overall average open circuit output voltage is estab-lished,and the particle swarm optimization algorithm is used to optimize the layout design parameters on the established response surface model to find the optimal de-sign parameters.Numerical verification of obtained optimal parameters is carried out.Finally,the overall output voltage performance of the two devices is improved by63.7%compared with the two independent ones.