Impact dampers are usually used to suppress single mode resonance. The goal of this paper is to clarify the difference when the impact damper suppresses the resonances of different modes. A cantilever beam equipped wi...Impact dampers are usually used to suppress single mode resonance. The goal of this paper is to clarify the difference when the impact damper suppresses the resonances of different modes. A cantilever beam equipped with the impact damper is modeled. The elastic contact of the ball and the cantilever beam is described by using the Hertz contact model. The viscous damper between the ball and the cantilever beam is modeled to consume the vibrational energy of the cantilever beam. A piecewise ordinary differential-partial differential equation of the cantilever beam is established, including equations with and without the impact damper. The vibration responses of the cantilever beam with and without the impact damper are numerically calculated. The effects of the impact absorber parameters on the vibration reduction are examined. The results show that multiple resonance peaks of the cantilever beam can be effectively suppressed by the impact damper. Specifically, all resonance amplitudes can be reduced by a larger weight ball. Moreover, the impacting gap is very effective in suppressing the vibration of the cantilever beam. More importantly, there is an optimal impacting gap for each resonance mode of the cantilever beam, but the optimal gap for each mode is different.展开更多
The low power and narrow speed range remain bottlenecks that constrain the application of small-scale wind energy harvesting.This paper proposes a simple,lowcost,and reliable method to address these critical issues.A ...The low power and narrow speed range remain bottlenecks that constrain the application of small-scale wind energy harvesting.This paper proposes a simple,lowcost,and reliable method to address these critical issues.A galloping energy harvester with the cooperative mode of vibration and collision(GEH-VC)is presented.A pair of curved boundaries attached with functional materials are introduced,which not only improve the performance of the vibration energy harvesting system,but also convert more mechanical energy into electrical energy during collision.The beam deforms and the piezoelectric energy harvester(PEH)generates electricity during the flow-induced vibration.In addition,the beam contacts and separates from the boundaries,and the triboelectric nanogenerator(TENG)generates electricity during the collision.In order to reduce the influence of the boundaries on the aerodynamic performance and the feasibility of increasing the working area of the TENG,a vertical structure is designed.When the wind speed is high,the curved boundaries maintain a stable amplitude of the vibration system and increase the frequency of the vibration system,thereby avoiding damage to the piezoelectric sheet and improving the electromechanical conversion efficiency,and the TENG works with the PEH to generate electricity.Since the boundaries can protect the PEH at high wind speeds,its stiffness can be designed to be low to start working at low wind speeds.The electromechanical coupling dynamic model is established according to the GEH-VC operating principle and is verified experimentally.The results show that the GEH-VC has a wide range of operating wind speeds,and the average power can be increased by 180%compared with the traditional galloping PEH.The GEH-VC prototype is demonstrated to power a commercial temperature sensor.This study provides a novel perspective on the design of hybrid electromechanical conversion mechanisms,that is,to combine and collaborate based on their respective characteristics.展开更多
The magnitude and stability of power output are two key indices of wind turbines. This study investigates the effects of wind shear and tower shadow on power output in terms of power fluctuation and power loss to esti...The magnitude and stability of power output are two key indices of wind turbines. This study investigates the effects of wind shear and tower shadow on power output in terms of power fluctuation and power loss to estimate the capacity and quality of the power generated by a wind turbine. First, wind speed models, particularly the wind shear model and the tower shadow model, are described in detail. The widely accepted tower shadow model is modified in view of the cone-shaped towers of modem large-scale wind turbines. Power fluctuation and power loss due to wind shear and tower shadow are analyzed by performing theoretical calculations and case analysis within the framework of a modified version of blade element momentum theory. Results indicate that power fluctuation is mainly caused by tower shadow, whereas power loss is primarily induced by wind shear. Under steady wind conditions, power loss can be divided into wind farm loss and rotor loss. Wind farm loss is constant at 3a(3a- 1)R^2/(8H^2). By contrast, rotor loss is strongly influenced by the wind turbine control strategies and wind speed. That is, when the wind speed is measured in a region where a variable-speed controller works, the rotor loss stabilizes around zero, but when the wind speed is measured in a region where the blade pitch controller works, the rotor loss increases as the wind speed intensifies. The results of this study can serve as a reference for accurate power estimation and strategy development to mitigate the fluctuations in aerodynamic loads and power output due to wind shear and tower shadow.展开更多
基金the National Natural Science Foundation of China(No.11772181)the Program of Shanghai Municipal Education Commission(No.2019-01-07-00-09-E0018)the Key Research Projects of Shanghai Science and Technology Commission(No.18010500100)。
文摘Impact dampers are usually used to suppress single mode resonance. The goal of this paper is to clarify the difference when the impact damper suppresses the resonances of different modes. A cantilever beam equipped with the impact damper is modeled. The elastic contact of the ball and the cantilever beam is described by using the Hertz contact model. The viscous damper between the ball and the cantilever beam is modeled to consume the vibrational energy of the cantilever beam. A piecewise ordinary differential-partial differential equation of the cantilever beam is established, including equations with and without the impact damper. The vibration responses of the cantilever beam with and without the impact damper are numerically calculated. The effects of the impact absorber parameters on the vibration reduction are examined. The results show that multiple resonance peaks of the cantilever beam can be effectively suppressed by the impact damper. Specifically, all resonance amplitudes can be reduced by a larger weight ball. Moreover, the impacting gap is very effective in suppressing the vibration of the cantilever beam. More importantly, there is an optimal impacting gap for each resonance mode of the cantilever beam, but the optimal gap for each mode is different.
基金the National Natural Science Foundation of China (Nos. 11802091and 12172127)the Hunan Province Science and Technology Innovation Program of China(Nos. 2020JJ3019 and 2019RS2044)the Scientific Researchof Hunan Provincial Department of Education of China (No. 21A0463)
文摘The low power and narrow speed range remain bottlenecks that constrain the application of small-scale wind energy harvesting.This paper proposes a simple,lowcost,and reliable method to address these critical issues.A galloping energy harvester with the cooperative mode of vibration and collision(GEH-VC)is presented.A pair of curved boundaries attached with functional materials are introduced,which not only improve the performance of the vibration energy harvesting system,but also convert more mechanical energy into electrical energy during collision.The beam deforms and the piezoelectric energy harvester(PEH)generates electricity during the flow-induced vibration.In addition,the beam contacts and separates from the boundaries,and the triboelectric nanogenerator(TENG)generates electricity during the collision.In order to reduce the influence of the boundaries on the aerodynamic performance and the feasibility of increasing the working area of the TENG,a vertical structure is designed.When the wind speed is high,the curved boundaries maintain a stable amplitude of the vibration system and increase the frequency of the vibration system,thereby avoiding damage to the piezoelectric sheet and improving the electromechanical conversion efficiency,and the TENG works with the PEH to generate electricity.Since the boundaries can protect the PEH at high wind speeds,its stiffness can be designed to be low to start working at low wind speeds.The electromechanical coupling dynamic model is established according to the GEH-VC operating principle and is verified experimentally.The results show that the GEH-VC has a wide range of operating wind speeds,and the average power can be increased by 180%compared with the traditional galloping PEH.The GEH-VC prototype is demonstrated to power a commercial temperature sensor.This study provides a novel perspective on the design of hybrid electromechanical conversion mechanisms,that is,to combine and collaborate based on their respective characteristics.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 11632011, 11572189, and 51421092), and the China Postdoctoral Science Foundation (Grant No. 2016M601585).
文摘The magnitude and stability of power output are two key indices of wind turbines. This study investigates the effects of wind shear and tower shadow on power output in terms of power fluctuation and power loss to estimate the capacity and quality of the power generated by a wind turbine. First, wind speed models, particularly the wind shear model and the tower shadow model, are described in detail. The widely accepted tower shadow model is modified in view of the cone-shaped towers of modem large-scale wind turbines. Power fluctuation and power loss due to wind shear and tower shadow are analyzed by performing theoretical calculations and case analysis within the framework of a modified version of blade element momentum theory. Results indicate that power fluctuation is mainly caused by tower shadow, whereas power loss is primarily induced by wind shear. Under steady wind conditions, power loss can be divided into wind farm loss and rotor loss. Wind farm loss is constant at 3a(3a- 1)R^2/(8H^2). By contrast, rotor loss is strongly influenced by the wind turbine control strategies and wind speed. That is, when the wind speed is measured in a region where a variable-speed controller works, the rotor loss stabilizes around zero, but when the wind speed is measured in a region where the blade pitch controller works, the rotor loss increases as the wind speed intensifies. The results of this study can serve as a reference for accurate power estimation and strategy development to mitigate the fluctuations in aerodynamic loads and power output due to wind shear and tower shadow.