Combining the computational fluid dynamics-based numerical simulation with the forced vibration technique for extraction of aerodynamic derivatives, an approach for calculating the aerodynamic derivatives and the crit...Combining the computational fluid dynamics-based numerical simulation with the forced vibration technique for extraction of aerodynamic derivatives, an approach for calculating the aerodynamic derivatives and the critical flutter wind speed for long-span bridges is presented in this paper. The RNG k-ε turbulent model is introduced to establish the governing equations, including the continuity equation and the Navier-Stokes equations, for solving the wind flow field around a two-dimensional bridge section. To illustrate the effectiveness and accuracy of the proposed approach, a simple application to the Hume Bridge in China is provided, and the numerical results show that the aerodynamic derivatives and the critical flutter wind speed obtained agree well with the wind tunnel test results.展开更多
The accurate evaluation of the lodging resistance of maize plants can provide a basis for the breeding of lodging-resistant cultivars and the regulation of cultivation measures.However,the traditional methods for eval...The accurate evaluation of the lodging resistance of maize plants can provide a basis for the breeding of lodging-resistant cultivars and the regulation of cultivation measures.However,the traditional methods for evaluating maize lodging resistance in terms of plant morphology and stalk mechanical strength have certain limitations.The objective of this research was to develop a device for determining the critical wind speed of maize stalk breaking.The device was equipped with a centrifugal fan to supply airflow and was powered by a frequency conversion motor.The frequency converter adjusted the motor speed and thus adjusted the wind speed.The wind speed decreased first and then increased with increasing height above the outlet of the device,and maximum wind speed can reach 40 m/s.This device was convenient for transportation in the field,has a low cost,and can quickly,accurately,and objectively determine the lodging resistance.Field tests showed that the device ran stably for a long time.The coefficient of variation of three repeated measurements was between 1.5%and 4.8%for four maize cultivars.The new device can measure the critical wind speed of maize lodging and identify the lodging resistance for different maize cultivars,cultivation practices,and plant health conditions,and can thus overcome barriers to measuring the maize lodging resistance under natural wind conditions.展开更多
Critical wind speed can play an important guiding role in developing an initial train operation schedule and knowledge of it mayprevent safety risks for a train. Hence, the efficient and accurate calculation of the cr...Critical wind speed can play an important guiding role in developing an initial train operation schedule and knowledge of it mayprevent safety risks for a train. Hence, the efficient and accurate calculation of the critical wind speeds of trains is critical. Thisstudy addresses this topic and focuses on the influence of different methods on the calculation of the critical wind speed. The resultreveals that the five-mass and three-mass methods can both be used to determine the critical wind speed of a train more quicklywith acceptable accuracy, but these two methods overestimate the crosswind safety risk of the train.With the increase of the train’soperating speed, the nonlinearity of the vehicle system is further enhanced. In particular, the influence of the rollingmotion betweenthe car body and the bogie is more prominent, and the results of the five-mass method and the multi-body simulation method tendto be the closest. Last but not least, the damping parameters and inertial forces ignored by the quasi-static method will effectivelyreduce the wind forces transmitted to the track, resulting in a smaller overturning coefficient and higher critical wind speed.展开更多
The study of tree leaf aerodynamics is useful to tree protection, solar panel design and development of new power generation technology. 73 tulip leaves were tested in suspended condition and with front as well as bac...The study of tree leaf aerodynamics is useful to tree protection, solar panel design and development of new power generation technology. 73 tulip leaves were tested in suspended condition and with front as well as back surface of the lamina facing wind. Three types of vibrating statuses, two types of steady statuses, and five critical wind speeds were observed. The existence probabilities of the statuses and criticals, the probability density distribution of every critical over the range of wind speed 0-27 m/s, and the expected values of the criticals were obtained by statistics. The critical Reynolds number, defined by critical wind speed and lamina length, shows an increasing trend with increasing the lamina area or length to width ratio of the lamina, but it shows no trend of increase or decrease with increasing the length ratio of petiole to lamina.展开更多
基金National Natural Science Foundation of China Under Grant No. 50278029
文摘Combining the computational fluid dynamics-based numerical simulation with the forced vibration technique for extraction of aerodynamic derivatives, an approach for calculating the aerodynamic derivatives and the critical flutter wind speed for long-span bridges is presented in this paper. The RNG k-ε turbulent model is introduced to establish the governing equations, including the continuity equation and the Navier-Stokes equations, for solving the wind flow field around a two-dimensional bridge section. To illustrate the effectiveness and accuracy of the proposed approach, a simple application to the Hume Bridge in China is provided, and the numerical results show that the aerodynamic derivatives and the critical flutter wind speed obtained agree well with the wind tunnel test results.
基金This study was supported by the National Key Research and Development Program of China(Grant No.2018YFD0100206)the Central Public-interest Scientific Institution Basal Research Fund(Grant No.Y2019PT07)+1 种基金the China Agriculture Research System(CARS-02-25)the Agricultural Science and Technology Innovation Project of Chinese Academy of Agricultural Sciences.
文摘The accurate evaluation of the lodging resistance of maize plants can provide a basis for the breeding of lodging-resistant cultivars and the regulation of cultivation measures.However,the traditional methods for evaluating maize lodging resistance in terms of plant morphology and stalk mechanical strength have certain limitations.The objective of this research was to develop a device for determining the critical wind speed of maize stalk breaking.The device was equipped with a centrifugal fan to supply airflow and was powered by a frequency conversion motor.The frequency converter adjusted the motor speed and thus adjusted the wind speed.The wind speed decreased first and then increased with increasing height above the outlet of the device,and maximum wind speed can reach 40 m/s.This device was convenient for transportation in the field,has a low cost,and can quickly,accurately,and objectively determine the lodging resistance.Field tests showed that the device ran stably for a long time.The coefficient of variation of three repeated measurements was between 1.5%and 4.8%for four maize cultivars.The new device can measure the critical wind speed of maize lodging and identify the lodging resistance for different maize cultivars,cultivation practices,and plant health conditions,and can thus overcome barriers to measuring the maize lodging resistance under natural wind conditions.
基金the China Na-tional Postdoctoral Program for Innovative Talents(Grant No.BX2021379).
文摘Critical wind speed can play an important guiding role in developing an initial train operation schedule and knowledge of it mayprevent safety risks for a train. Hence, the efficient and accurate calculation of the critical wind speeds of trains is critical. Thisstudy addresses this topic and focuses on the influence of different methods on the calculation of the critical wind speed. The resultreveals that the five-mass and three-mass methods can both be used to determine the critical wind speed of a train more quicklywith acceptable accuracy, but these two methods overestimate the crosswind safety risk of the train.With the increase of the train’soperating speed, the nonlinearity of the vehicle system is further enhanced. In particular, the influence of the rollingmotion betweenthe car body and the bogie is more prominent, and the results of the five-mass method and the multi-body simulation method tendto be the closest. Last but not least, the damping parameters and inertial forces ignored by the quasi-static method will effectivelyreduce the wind forces transmitted to the track, resulting in a smaller overturning coefficient and higher critical wind speed.
基金financially supported by the National Natural Science Foundation of China(11172286)
文摘The study of tree leaf aerodynamics is useful to tree protection, solar panel design and development of new power generation technology. 73 tulip leaves were tested in suspended condition and with front as well as back surface of the lamina facing wind. Three types of vibrating statuses, two types of steady statuses, and five critical wind speeds were observed. The existence probabilities of the statuses and criticals, the probability density distribution of every critical over the range of wind speed 0-27 m/s, and the expected values of the criticals were obtained by statistics. The critical Reynolds number, defined by critical wind speed and lamina length, shows an increasing trend with increasing the lamina area or length to width ratio of the lamina, but it shows no trend of increase or decrease with increasing the length ratio of petiole to lamina.