| There are many forms of fluid energy in nature.Fluid energy in the form of wind energy and ocean current energy has attracted more and more attention due to its wide existence,huge reserves,and pollution-free characteristics.Flow-induced vibration is a common phenomenon of fluid-solid interaction,and it is a way of transforming fluid energy into structural vibration energy.The flow-induced vibration type triboelectric nanogenerator（TENG）can efficiently convert the vibration energy generated in the flow-induced vibration process into electrical energy,which is a new fluid energy harvesting method.Harvesting fluid energy in ambient environment by TENG is helpful for realizing the self-powered of sensor node and sensor network.Effectively harvesting wind energy and ocean current energy has been realized by flow-induced vibration TENG in this paper.The research results are of great significance for innovating the energy supply mode of the sensing system and enriching the theory of fluid energy conversion.The research work of this article mainly includes the following aspects:（1）A vortex-induced vibration triboelectric nanogenerator（VIV-TENG）is designed and constructed.The vibration and power generation characteristics are studied.Reduced velocity and mass ratio are the key parameters that affect its vibration.Hence,this thesis studies the influence of reduced velocity and mass ratio on the amplitude,acceleration and lock-in region.The results show that the vortex-induced vibration of the square cylinder is divided into two branches.In the initial branch,the reduced velocity increases,the amplitude and acceleration of the square cylinder increase accordingly;while in the lower branch,the reduced velocity continues to increase,the amplitude and acceleration of the square cylinder are reduced accordingly.For system with high mass ratio,a larger lock-in region can be obtained by reducing the mass ratio appropriately.For a system with a mass ratio of 308.57,more PTFE balls results in the better the power generation performance within the lock-in region.In the maximum vibration range,even if the reduced velocity is changed,it will not affect its output,and the power generation performance remains stable in this range.When the reduced velocity is within the range of 29.49-44.48,the maximum output voltage is 115V and the maximum power density is 62.2 W/m3.（2）A flutter triboelectric nanogenerator（F-TENG）is designed and constructed.The vibration characteristics of the flexible membrane and the power generation characteristics of the F-TENG are studied respectively.Material stiffness and membrane sag ratio are the key parameters that affect its vibration.Hence,this part first studied the effects of different materials and sag ratios on the critical speed of the membrane.The results show that the higher the material stiffness and sag ratio,the higher the corresponding critical wind speed.Secondly,it analyzes its influence on power generation performance from two aspects of structural parameters and incoming flow conditions.The results show that there is a corresponding relationship between the membrane sag and the gap of the flow channel.When the ratio is 1:2,a better output performance can be obtained.When the structure dimension is 100×20×3mm,at a wind speed of 30m/s,the maximum output voltage can reach about114.1V,the output current can reach 17.9μA,the maximum power is 5.2m W,and the corresponding power density is 870 W/m3.The power generation performance of the F-TENG is tested under different incoming flow conditions.Its power generation performance can increase with the increase of the flow speed;its effective energy harvesting angle is 25°-155°;within the range of 10%turbulence,the power generation performance will increase with the increase of turbulence.（3）A novel moisture-proof flag-type triboelectric nanogenerator（flag-type TENG）is proposed to overcome the disadvantage of weak performance of TENG in humidity condition.The vibration and power generation characteristics of the flexible structure are studied.Bending stiffness and mass ratio are the key parameters that affect its vibration.Hence,this part studies the influence of bending stiffness and mass ratio on the amplitude,frequency and critical speed of the flag-type TENG.The results show that within the test range,as the bending stiffness decreases,the amplitude and vibration frequency of the flag-type TENG increase,while the critical speed decreases.When the mass ratio changes,the vibration frequency does not change significantly.The Strouhal number is in the range of 0.5-0.6,but when the mass ratio increases,the critical speed corresponding to the system will also increase.Secondly,the influence of bending stiffness,mass ratio and relative humidity on its power generation performance is studied.It is beneficial to reduce the bending stiffness and mass ratio within a certain range to obtain a larger output.Due to the waterproof ability,the power generation performance of the flag-type TENG will not decrease with the increase of relative humidity.After optimizing the layout,the output of the flag-type TENG with a dimension of 150×75mm can reach 36.72μW,corresponding to a power density of48 W/m3.Compared with the independently arranged flag-type TENG,the power is increased by nearly 40 times.（4）Combining the water-proof characteristics of the flag-type TENG,an underwater flag-shaped triboelectric nanogenerator（UF-TENG）for harvesting ocean current energy is further constructed.The combined structure of flexible electrodes printed with conductive ink,dielectric materials and waterproof tape realizes the harvesting of ocean current energy at extremely low flow speed.This part studies the influence of front bluff body,bending stiffness and mass ratio on the amplitude and critical speed of the UF-TENG.The use of a front bluff body can effectively increase its amplitude and reduce its critical speed.In turn,its power generation performance is enhanced.Meanwhile,as the bending stiffness decreases,the amplitude of the UF-TENG increases and the critical speed decreases.When the mass ratio increases,the critical speed corresponding to the system will decrease,which is obviously different from the vibration characteristics of the flag-type TENG in the air.Secondly,the influence of front bluff body,bending stiffness and mass ratio on power generation performance is studied.The results show that the front bluff body can effectively improve the power generation performance by reducing the bending stiffness and increasing the mass ratio.The UF-TENG with=0.55×10-4,/(2=4,*=1270 is compared with the UF-TENG installed with a bluff body ahead.At a flow speed of 0.461m/s,the open circuit voltage of the UF-TENG with a front bluff body can be increased by 170%,and the short-circuit current and the amount of transferred charge have also increased 100%and 167%,respectively.When the bending stiffness is reduced from 1.33×10-4 to 0.05×10-4,the output voltage can be increased from 6.2V to 14.4V.At a flow speed of 0.461m/s,when the mass ratio of the UF-TENG increases from 955 to 1590,the short-circuit current also rises from0.8μA to 1.43μA.The UF-TENG with a dimension of 175×87.5mm has a maximum output voltage of 14.4 V,a maximum output power of 9.1μW,and a corresponding power density of 22.4 W/m3. |
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