Numerical research on a vortex shedding induced piezoelectric-electromagnetic energy harvester

To widen the operation wind speed bandwidth of a classic vortex shedding induced vibration piezoelectric energy harvester, a piezoelectric-electromagnetic hybrid energy harvester based on vortex shedding induced vibration is designed. The hybrid vortex shedding induced vibration energy harvester (HVSIVEH) includes a vortex shedding induced vibration piezoelectric energy harvester (VSIVPEH) and an electromagnetic vibration energy harvester (EVEH). The electromechanical coupled vibration model of the hybrid structure was established. By comparing the variations of the output power as a function of the wind speed of the HVSIVEH and the classic VSIVPEH, it is found that the power response curve of the HVSIVEH has two peaks. The hybrid structure can broaden the working wind speed range. The lower the requirement on the output power level, the more obvious the effect of widening the wind speed range. By the solution and analysis of the electromechanical coupled model, better values of related parameters of the HVSIVEH are obtained. The first and second peaks of the output power of the HVSIVEH show better values of 1.9 and 2.2 mW, respectively, under these parameters.

Dynamic characteristics of the over-actuated cutterhead driving system in tunnel machine

The cutterhead driving system of tunnel machine is over-actuated by redundant driving chains with inevitable load and parameter deviations. These deviations were rarely considered, and the researches on multi-motors synchronization and gear dynamics were usually isolated. In this paper, a novel electromechanical coupled model of the whole cutterhead driving system is established by connecting the vector-controlled motors via gear meshing system. Force transmissions between all coupled elements are investigated by analyzing rotational and translational dynamics, and the time-varying meshing stiffness and nonlinear backlash of both parallel pinions driving and multi-stage planetary reducer are considered. The phase and frequency features of meshing dynamics are also investigated. Comparative simulations are carried out with load and parameter deviations between multi-chains under two control structures, speed parallel control and torque master-slave control; some practical control principles are also concluded. The simulation results are verified and applied on a Φ2.5-m test rig. The consistent results indicate that, the meshing dynamics have the frequency components of carrier revolution and the meshing frequencies of both current planet and endmost pinion. Torque master-slave control could realize torque synchronization against all the adverse deviations while speed parallel control fails, and the vibration could be significantly reduced with lower rigidity in speed control.

An element-free Galerkin method for electromechanical coupled analysis in piezoelectric materials with cracks

We present an element-free Galerkin method for electromechanical coupled fracture analysis in piezoelectric materials. Singularity terms were introduced into the approximation function of the new method to describe the displacement and electric fields near the crack. The new method requires a smaller domain to describe the crack-tip singular field compared with the finite element method. Then, we computed the J-integrals of piezoelectric materials and investigated the effects of crack length on the computational precision. Numerical examples were used to highlight the accuracy of the new method compared with the analytical solutions and finite element method.