Dynamical Design Of Rotational Compressive-mode Piezoelectric Energy Harvester And Its Property Investigation

Sensors that provide critical information about jet engine performance are widely installed on static components but are rarely found on rotors.Inaccessibility of rotors,extremely high centrifugal force and lack of reliable power supplies,etc.,largely inhibit the development of sensing technology in rotational machinery.To overcome the issues,this dissertation presents a new monitoring method,integrating energy harvesting technology with wireless sensors to achieve long-term online direct monitoring of rotors.Energy harvesters,used to generate power from ambient vibration,are sustainable alternatives to batteries for achieving self-sustained longterm operation of electronic devices.Thus,the proposed approach not only breaks limitations from wired connections that are weighty and vulnerable to failures,but also solves battery issues.This work paves a new way for developing future online monitoring systems for advanced jet engines and other rotating machinery applications.This study takes the lead to assess the energy harvesting potential in high-RPM turbine engines.Considering the harsh condition of jet engines,this study proposes a method to harvest the energy from the rotational parts of the jet engine and convert it into electricity,meanwhile largely avoiding the adverse effect from the centrifugal force.By utilizing structural nonlinearity,force amplification mechanism,and the piezoelectric effect,a high-efficiency compressive-mode piezoelectric energy harvester(HC-PEH)that is characterized by high power output and wide working bandwidth is developed.To investigate the energy harvesting system analytically,a lumped-parameter model is developed,where the nonlinear stiffness,nonlinear damping,nonlinear piezoelectricity,and the static beam deformation caused by the centrifugal force and gravity are taken into account.The analytical solutions closely render experimental results and estimate a 172% growth in frequency bandwidth when exploiting the centrifugal force for bandwidth up-conversion.A HC-PEH prototype,weighing 21 grams,is fabricated and tested under two types of excitations:1)translational harmonic vibration,and 2)rotation.Better performance is observed in the rotational excitation case for the HC-PEH.Comparing with the traditional cantilever bending-mode energy harvesters,the proposed HC-PEH shows completely better performance in power generation,working bandwidth,and structural strength under translational and rotational excitations.For demonstration,a 22.52-gram improved HC-PEH prototype was tested under the rotational excitation from 0 to 2100 rpm.It shows a maximum output power of 78.87 m W,1 m W-and 10 m W-bandwidths of 22.5 Hz and 11.17 Hz,and can simultaneously light up 112 LEDs and a selfpowered wireless sensor system when the rotation speed is over 1100 rpm.The result well validates a sufficient suite of innovations for achieving the self-powered technology in the rotational parts of jet engines.Since the performance of the HC-PEH deteriorates when used in rotational environments with an offset distance,to overcome this problem,a method of using a magnetic force is proposed in this dissertation.The performance of the magnetically coupled and the normal rotational HC-PEH systems with offset distances are experimentally studied.The results show the proposed method is feasible and significantly improves the performance(peak-peak voltage)by 258.2%.To attain comprehensive insight into the electromechanical behaviors of the system,a theoretical model with consideration of nonlinear stiffness,nonlinear damping,and nonlinear piezoelectricity is developed.The governing equations of the system are obtained by using Hamilton’s principle and their approximate analytical solution is derived via the harmonic balance method.The simulation results closely render the experimental data and the developed model is verified to be reliabe.Based on the developed theoretical model,a parametric study is performed and the results indicate that the best performance improvement can be obtained via tuning the parameters related to the magnetic force,the centrifugal force,and the initial deformation of the elastic beams.This work helps overcome a major obstacle for the application of rotational energy harvesting.A modeling and dynamic analysis of a rotational HC-PEH with partially thickened bow-shaped beams are presented in this dissertation.Based on the EulerBernoulli beam theory,the extended Hamilton’s principle and the Galerkin discretization,the governing equations of the rotational HC-PEH system are formulated.The developed distributed-parameter model is validated against experimental data and a good agreement is achieved.The stability and the nonlinear dynamic behavior of the rotational HC-PEH system in conditions of different offset distances and preloaded axial forces are investigated by numerical simulation results.A parametric study of the parameters directly related to the system design is also performed to provide fundamental guidance for understanding the electrical output performance and modulating the voltage-rotation speed responses of the harvester.The result shows that the design parameters of the bow-shaped beam and the PZT plate have apparent effects on the electrical output of the harvester system.This work well solves the problem that the lumped-parameter model falis to provide a physical insight for the structure of the HC-PEH.Effects of the bending-torsional coupled vibration due to the misalignment of the centroid and the torsional axis,on the performance of the HC-PEH are studied experimentally and theoretically,respectively under translational displacement and rotational force excitations.Distributed-parameter models of the system respectively under translational and rotational excitations are developed.To validate the models,the finite element(FE)analysis and the experiment are performed.The simulation results by the method of this study closely render the modal result obtained by the FE method and the experimental result of the voltage response,respectively.The effects of parameters related to the torsional vibration on the hardening response,steadystate response,and the jump-down phenomenon activated by the torsional vibration are revealed.The results show that the torsion-induced chaotic motion can activate the jump-down phenomenon,largely reducing the performance of the HC-PEH.Additionally,when under translational excitations,the occurrence of the torsioninduced jump-down phenomenon is sensitive to the system’s initial state and can be mitigated or even avoided by increasing the preloaded axial force and the misalignment of the centroid and the torsional axis,or extremely varying the torsional moment of inertia of the proof mass.By comparison,when under rotational excitations,the only effective approach to alleviating the adverse effect is tuning the mass moment of inertia.This work provides further guidance for the design of the HC-PEH and similar fixed-fixed beam structures and lays a solid foundation for their engineering applications.