Research On Flow-induced Vibration And Energy Harvesting Performance Of Cylinderical Piezoelectric Energy Harvesters

With widely application of the low energy consumed electronic devices,such as wireless electronic devices,sensor and micro electro mechanical systems,the issue of energy supply for those devices has attracted the attention of researchers.The traditional energy sources(electronics,batteries)must be replaceed regularly because of limited power supply,which is especially unfavourable for the human inaccessible places,including deep sea,remote sea,virgin forest,aerospace,human body,etc.Therefore,researchers should explore continuous energy supply method.Energy harvesting using piezoelectric materials is one of popular methods for converting environmental vibration energy to electricity.The environmental vibration energy includes wind energy,water energy,tidal energy and mechanical energy,etc.Water energy is an important new energy for its advantages of high energy density,widespread,green,sustainable utilization,etc.For the high velocity water flow,hydro-electric stations can be used to convert kinetic energy to electricity for human.However,water flow mainly exists in nature with low velocity condition.For the low velocity water flow,this thesis proposes the new energy harvesting method based on piezoelectric energy harvesters(PEHs)under flow induced vibration.The method will be a promising application with both advantages of water energy and piezoelectric energy harvesting.The thesis investigates the vibration responses and energy harvesting performances of the single PEH,including PEH with compound pendulum vibration and PEH compound bend-torsion vibration based on the vortex-induced vibration(VIV).The first method is good for space utilization of water field and energy harvesting application in low velocity water flow because of its low resonance response frequency and low vortex-induced resonance water velocity.The second method couples bending vibration and torsion vibration,which effectively enhances the performance at the relatively high velocity water flow compared traditional PEH with bending vibration.The couplied fluid-structure-electric mathematic models are established based on piezoelectric energy harvesting with vortex-induced compound pendulum vibration and piezoelectric energy harvesting with vortex-induced compound bend-torsion vibration,respectively.The mathematic models have coupled the VIV theory,piezoelectric theory and energy method.The effect of added mass and added fluid damping of water flow are also considered.Effects of water velocity,parameters of the PEH structure and load resistance on vibration response and energy harvesting performance of the both piezoelectric energy harvesting method are investigated numerically based on the above couplied mathematic models.It is found that vibration modes of both harvesters are the VIV.Vibration response and energy harvesting performance of both harvesters first increase until reaching peak value,then decrease with the increase of water velocity.Maximum value can be obtained at vortex-induced resonance.Vibration frequencies increase with the water velocity generally.However,the vibration frequency will be locked in around with the nature frequency of the harvester because of the “Lock-in” characteristic of the VIV.Increasing cylinder diameter,cylinder mass and decreasing piezoelectric beam length can enhance the energy harvesting performance at vortex-induced resonance,and increase the water velocity for vortex-induced resonance at the same time,which is not suitable for energy harvesting in low velocity water flow.Both increasing immersed length of cylinder and cylinder length are conducive to enhance the vibration response and energy harvesting performance.The optimal resistance can be achieved for maximum output power.The optimal resistance increases with increase of cylinder diameter and decreases with increase of water velocity.Single PEH could not meet the energy needed in many conditions.Given this situation,this thesis proposes energy harvesting method using two PEHs with fluid induced vibration.Vibration response and energy harvesting performance of two compound pendulum vibration harvesters are investigated in side-by-side and tandem arrangements.Simulation mathematic model of fluid-structure-electric interaction for two harvesters is established to explore the coupled effects between harvester and flow field,harvester and harvester.Energy harvesting performances of two PEHs are investigated by simulation method.It is found that vibration mode of the upstream harvester is the VIV and vibration mode of downstream harvester is the VIV coupled wake-induced vibration(WIV)during tandem arrangement.The vibration responses of both upstream and downstream harvesters are different with different space ratio.When the space ratio is small,the coupling effects of two harvesters are large,which enhances the vibration response and energy harvesting performance of both harvesters.With increasing space ratio,the coupling effects decrease and output power of both harvesters decrease too.Due to the wake effect,the vibration response and energy harvesting performance of upstream harvester are larger than those of downstream harvester at low water velocity range(0.174 m/s-0.272 m/s).The vibration response and energy harvesting performance of downstream harvester are much larger than those of upstream harvester at relative high water velocity range((29)0.272 m/s).For the two side-by-side harvesters,the vibration responses and energy harvesting performances will be enhanced because of coupling effect when the space ratio is small.The vibration response and energy harvesting performance of both the left and right harvesters in side-by-side arrangement are the same and the vibration modes of both harvesters are the VIV.The hydrodynamic experimental system and test platform is designed and set up.Three sets of experimental prototypes are developed.Energy harvesting performances of single PEHs are measured use experimental platform.The experimental results are in good agreement with the numerical results,which verifies the validity of both the mathematic models.Energy harvesting system with two tandem PEHs and two side-by-side PEHs are developed,respectively.Energy harvesting performances of two PEHs are measured.The comparison between experimental and simulation results verifies the validity of the simulation analysis.