This paper studies a novel enhanced energy-harvesting method to harvest water flow-induced vibration with a tandem arrangement of two piezoelectric energy harvesters (PEHs) in the direction of flowing water, through simulation modeling and experimental validation. A mathematical model is established by two individual-equivalent single-degree-of-freedom models, coupled with the hydrodynamic force obtained by computational fluid dynamics. Through the simulation analysis, the variation rules of vibration frequency, vibration amplitude, power generation and the distribution of flow field are obtained. And experimental tests are performed to verify the numerical calculation. The experimental and simulation results show that the upstream piezoelectric energy harvester (UPEH) is excited by the vortex-induced vibration, and the maximum value of performance is achieved when the UPEH and the vibration are resonant. As the vortex falls off from the UPEH, the downstream piezoelectric energy harvester (DPEH) generates a responsive beat frequency vibration. Energy-harvesting performance of the DPEH is better than that of the UPEH, especially at high speed flows. The maximum output power of the DPEH (371.7 μW) is 2.56 times of that of the UPEH (145.4 μW), at a specific spacing between the UPEN and the DPEH. Thereupon, the total output power of the two tandem piezoelectric energy harvester systems is significantly greater than that of the common single PEH, which provides a good foreground for further exploration of multiple piezoelectric energy harvesters system.

The dynamic of human body with three-dimensional (3D) anatomical structure is not considered in the vehicle system dynamics. Moreover, the dynamic of the lumbar spine is not studied in the finite element (FE) model of the seated human, and the influence of external conditions on it is not considered. The aim of the study is to propose a comprehensive dynamic model and an analysis method to study the dynamic of the lumbar spine in a complex system. It is investigated by extracting the first six modals of different lumbar spine FE models (eight models), and the dynamic responses of the lumbar spine under white noise excitation are analyzed by random response method. It is found that the mode deformation and the resonant frequencies of the lumbar spine in vivo and vitro model are significantly different, and the peak response value of the lumbar spine is at the resonant frequency. It is concluded that the influence of vibration on the lumbar spine could be more comprehensively and visually studied by analyzing the displacement response power spectrum of FE model of the seated human body. This study provides a new method and reference for the subsequent study of the vibration behavior of the lumbar spine in complex system (especially in vehicle system dynamics), and the finding is helpful for us to find more and better protection methods of human body.