Stochastic bifurcation characteristics of cantilevered piezoelectric energy harvester

Stochastic bifurcation characteristics of cantilevered piezoelectric energy harvester were studied in this paper. Von de Pol differencial item was introduced to interpret the hysteretic phenomena of piezoelectric ceramics, and then the nonlinear dynamic model of piezoelectric cantilever beam subjected to axial stochastic excitation was developed. The stochastic stability of the system was analyzed, and the steady-state probability density function and the joint probability density function of the dynamic response of the system were obtained, and then the conditions of stochastic Hopf bifurcation were analyzed. Numerical simulation shows that stochastic Hopf bifurcation appears when bifurcation parameter varies, which can increase vibration amplitude of cantilever beam system and improve the efficiency of piezoelectric energy harvester. Finally, the theoretical and numerical results were proved by experiments. The results of this paper are helpful to application of cantilevered piezoelectric energy harvester in engineering fields

THE DEVELOPMENT OF A REAL-TIME FEEDBACK SYSTEM IN WEIGHTLIFTING

The purpose of this study was to develop a real-time feedback system (RTFS), which can provide weightlifters some useful information, such as the heights of the bar, video clip and so on, immediately after finishing their attempts under training conditions. A Kinect was used to capture the depth data and RGB video, the methods of the pattern recognition and algorithm were established, and the software was developed to identify the barbell and calculate the 3-D data of barbell COM (Centre of Mass). An experiment was carried out to compare the data from RTFS and that from 3D analysis based on video to check the reliability of RTFS. The results showed that the data of barbell COM obtained by RTFS can describe the movement of barbell sufficiently. This new system can help weightlifters to diagnose their skills and improve their training effectively