Dynamic Design And Application Of Low-frequency And Broadband Nonlinear Energy Harvester For Freight Train

To improve operational safety and system reliability,real-time wireless health monitoring systems are necessary for freight trains.The reliance on batteries as power sources for monitoring sensors require extensive upkeep and replacement,which causes high maintenance costs and environmental issue.Therefore,developing self-powered maintenance-free wireless monitoring sensors integrated with energy harvesting is in urgent demand.Due to the low-frequency and broadband excitation,to collect the mechanical energy from the bogie frame is still a considerable challenge for conventional harvesters.To address this issue,we propose a compact ultralow-frequency and broadband energy harvester,and then introduce self-tuning,up-frequency and friction pendulum nonlinear mechnisems to effectively convert bogie mechanical energy to power wireless Bluethooth sensors.The research is summarized as followed:（1）To improve reliability of the theoretical analysis for nonlinear energy harvesters and investigate the relationship between the key parameters and the output performance,we propose a new Complex Dynamic Frequency（CDF）method.Numerical and experimental studies verify that the proposed CDF gives consistent and accurate predictions of the systems with both weak and strong nonlinearities due to the dynamic frequency factor.Furthermore,it obtains an implicit relationship between structural parameter and output performance,thus providing optimization basis for the low-frequency and broadband energy harvesters.（2）A compact ultralow-frequency and broadband piezoelectric energy harvester（UBPEH）is designed to effectively collect bogie lateral vibrations with a wide spectrum at ultralow frequencies（<15 Hz）with 0.5 g acceleration level.An improved model of UBPEH is established to optimize the parameters and arrangement of the magnetic spring and impact-stoppers.Theoretical and experimental results show that the prototyped UBPEH might operate in the range of 1-11 Hz,covering the representative frequencies of bogie vibrations on freight trains.An output power of605μW is achieved,and the generation capacity is sufficient to meet the energy demands of low-power wireless Bluetooth sensors.（3）To improve low-frequency bandwidth,the self-tuning mechnisem for the rotational excitation is introduced in the impact-driven frequency up-conversion.The design,theoretical analysis and experimental verification of frequency up-conversion rotary harvester（FURH）with the hybrid self-tuning and impact mechnisem are performed.The self-tuning technology reduces size of the UBPEH and enhances the power density.Results demonstrate that and the prototyped FURH generates 1.23 m W output power and the corresponding power density is up to 0.722 m W cm^-3.Besides,the pulse signal produced by triboelectic materials indirectly represents the operational condition of the train wheel hub.（4）Since the performance of the axle degradation when the classical low-frequency beam device is embedded the axle of wheelset,to address this issue,this work employs the friction pendulum and assembles a compact all-in-one on-rotor electromagnetic energy harvester（OREMEH）.Owing to the small volume,harvesters can be installed on the axle box and embedded the axle of wheelset to improve output power without impacting the performance of bogie frames.The power and corresponding power density are up to 32 m W and 1.982 m W cm^-3,respectively.The converted electricity successfully powers the daily electric appliance and the commercial wireless Bluetooth sensors.Additionally,the harvester realizes the dynamic feedback function of train hub speed.（5）Combined with the friction pendulum and contra-rotating technology,we present a new speed amplified electromagnetic energy harvester（SAEMEH）.The friction pendulum dynamic model and magnets arrangement are perfected to improve performance.The output power is 128 m W with power density being 636 m W cm^-3.It can meet the power supply requirements of multiple on-board sensors at the same time.Additionally,it serves as highly sensitive speed and early sensors to detect the motion state of the vehicle.