Numerical and experimental study on the performance of an electromagnetic energy harvester distributed along drill-string

•The centrifugal softening effect is combined with an oscillator with clearance to achieve a bi-stable energy harvester.•The harvester can harvest low frequency rotation and vibration energy of drill-string in the downhole harsh environment.•Harvester & drill-string coupled dynamic model is built to analyze performance of the harvester.•The maximum average power of a single harvester near the vertical-well bottom can reach 2 w. Real-time measurement of the downhole information from sensors distributed along a slender drill-string plays an important role in oil and gas drilling. However, an urgent problem is how to provide power to the downhole sensor network. In this study, combining with the centrifugal softening effect and an oscillator with clearance, a bi-stable electromagnetic energy harvester (EMEH) is proposed to enhance the energy harvesting performance in the low-frequency rotation of the drill-string. The discrete dynamic equations of the coupled EMEHs & drill-string system are established by using the finite difference method and Lagrange's equations. The accuracy of the numerical simulation is validated through model test, and the effects of damping, excitation amplitude, speed and gravity on the performance of a single EMEH are analyzed through numerical simulation. Then, the coupled dynamic model is used to simulate and analyze the performance of the EMEHs in the drilling process of vertical wells and deviated wells. The numerical results show that the resonant frequency of EMEH is related to the excitation amplitude and rotating speed. It first decreases and then increases with the increase of the excitation amplitude, which can cover most frequencies below the resonant frequency of the linear system with δi0 = 0 mm. The variation range of the resonant frequency decreases with the increase of rotating speed. In vertical wells, the output power of EMEH increases with the increase of drill-string depth, and the maximum output power at the well bottom can reach 2.0 W. In deviated well, the output power is mainly generated by the continuous rotation of the drill-string and gravity, which increases with the increase of the well inclination. The results show that the output power of a single EMEH can meet the power demand of most downhole sensors. [Display omitted]