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Aiming to improve the energy harvesting efficiency under low wind speed, we propose a dual auxiliary beam galloping triboelectric nanogenerator (GTENG) in this work. The structural design of a single main beam and a pair of auxiliary beams enables the device to work under a higher vibration frequency when triggered by wind. A stable and improved working frequency of about 4.6 Hz was observed at various wind speeds. The device started to vibrate at a wind speed of 1.7 m/s and generated an output voltage of about 100 V. The outputs of this GTENG approach to saturation at a wind speed of around 5 m/s. The output voltage and short-circuit current reached 260 V and 20 μA, respectively. A maximum power of about 1 mW was obtained under a wind speed of 5.7 m/s with a load of 33 MΩ. Moreover, the effectivity and long-term stability of the device were demonstrated under low wind speeds. A digital watch is powered for 45 s after charging a 47 μF capacitor for 120 s at a wind speed of 3.1 m/s.

This letter presents an idea of employing sphere as a bluff body subjected to cross flows for improving piezoelectric energy harvesting from flow-induced vibrations (FIVs). Unlike cylindrical bluff bodies used in most of previous studies, the proposed harvester with sphere configuration can be freely settled in horizontal and vertical directions without reconfiguration. Experimental results show that the aspect ratio (length of beam to diameter of sphere) and mass ratio between sphere and beam have great effects on output performance of the energy harvester. It is found that the optimal aspect ratio and mass ratio are 1.7 and 0.15 where the harvester has a broadband lock-in between 2 m s −1 and 6 m s −1 and a maximum output average power of 190 µW. This is attributed to variations of the natural frequency and aerodynamic force varying with the sphere diameter, resulting in multiple modes responses to significantly enhance the output power. Furthermore, the output comparison between sphere-and cylinder-based energy harvesters indicates that sphere is superior in the case of horizontal placement, while for the vertical placement as the wind speed is below 4 m s −1 it is better to use sphere, but beyond 4 m s −1 , cylinder is superior within the considered wind speed region. The present study gives a new design for effectively harvesting energy from FIVs according to available wind speed.

A cantilevered pipe conveying fluid can lose stability via flutter when the flow velocity becomes sufficiently high. In this paper, a dry friction restraint is introduced for the first time, to evaluate the possibility of improving the stability of cantilevered pipes conveying fluid. First, a dynamical model of the cantilevered pipe system with dry friction is established based on the generalized Hamilton’s principle. Then the Galerkin method is utilized to discretize the model of the pipe and to obtain the nonlinear dynamic responses of the pipe. Finally, by changing the values of the friction force and the installation position of the dry friction restraint, the effect of dry friction parameters on the flutter instability of the pipe is evaluated. The results show that the critical flow velocity of the pipe increases with the increment of the friction force. Installing a dry friction restraint near the middle of the pipe can significantly improve the stability of the pipe system. The vibration of the pipe can also be suppressed to some extent by setting reasonable dry friction parameters.