The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo-...The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo- lation preprocessing, the sensitive zones of feedrate variations are processed with acceleration-deceleration control. By using the proposed algorithm, the machining accuracy is guaranteed and the feedrate is adaptively adjusted to he smoothed. The mechanical shock imposed in the servo system is avoided by the first and the second time derivatives of feedrates. A simulation of NURBS interpolation is given to demonstrate the validity and the effectiveness of the algorithm. The proposed interpolator can also be applied to the trajectory planning of the other parametric curves.展开更多
Based on 3D, steady N-S equations and k-e turbulence model, Fluent was employed to do numerical simulation for lateral aerodynamic performance of 6-axis X2K double-deck container trains with two different loading form...Based on 3D, steady N-S equations and k-e turbulence model, Fluent was employed to do numerical simulation for lateral aerodynamic performance of 6-axis X2K double-deck container trains with two different loading forms, and speed limits of the freight trains were studied. The result indicates that under wind environment： 1） As for vehicles without and with cross-loaded structure, aero-pressure on the former is bigger, but air velocity around the latter is larger; 2） When sideslip angle θ=0°, the airflow is symmetry about train vertical axis; when θ〉0°, the airflow is detached at the top of vehicles, and the air velocity increases above the separated line but decreases below it; 3） With θ increasing, the lateral force on the mid vehicle firstly increases but decreases as θ=75°; 4） When the 6-axis X2K fiat car loads empty boxes of a 40 ft and a 48 ft at 120 km/h, the overturning wind speed is 25.19 m/s, and the train should be stopped under the 12th grade wind speed.展开更多
Supercavitating flow around a slender symmetric wedge moving at variable velocity in static fluid has been studied. Singular integral equation for the flow has been founded through distributing the sources and sinks o...Supercavitating flow around a slender symmetric wedge moving at variable velocity in static fluid has been studied. Singular integral equation for the flow has been founded through distributing the sources and sinks on the symmetrical axis. The supereavity length at each moment is determined by solving the singular integral equation with finite difference method. The supercavity shape at each moment is obtained by solving the partial differential equation with variable coefficient. For the case that the wedge takes the impulse and uniformly variable motion, numerical results of time history of the supercavity length and shape are presented. The calculated results indicate that the shape and the length of the supercavity vary in a similar way to the case that the wedge takes variable motion, and there is a time lag in unsteady supercavitating flow induced by the variation of wedge velocity.展开更多
Setting reliable speed limits on roads has always been a challenging process of designers and road agencies. In this paper the results of a methodology for setting speed limits on rural roads of all categories in Gree...Setting reliable speed limits on roads has always been a challenging process of designers and road agencies. In this paper the results of a methodology for setting speed limits on rural roads of all categories in Greece is presented based on international research and an extensive drivers attitudes＇ survey. The 85th percentile speed has proven in this case to be the decisive criterion for establishing reliable speed limits or advisory speeds in most cases. The resulted 10 km/la increase in legal speed limits on freeways and express rural highways did not validate any fears that accident rates or frequencies would increase. On the contrary an 8% decrease of crashes was observed in a period of about three years after the implementation of the increased speed limits level on the rural highway network of the country.展开更多
基金Supported by the Natural Science Foundation of Jiangsu Province(BK2003005)~~
文摘The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo- lation preprocessing, the sensitive zones of feedrate variations are processed with acceleration-deceleration control. By using the proposed algorithm, the machining accuracy is guaranteed and the feedrate is adaptively adjusted to he smoothed. The mechanical shock imposed in the servo system is avoided by the first and the second time derivatives of feedrates. A simulation of NURBS interpolation is given to demonstrate the validity and the effectiveness of the algorithm. The proposed interpolator can also be applied to the trajectory planning of the other parametric curves.
基金Project supported by Scholarship Award for Excellent Doctoral Student granted by Ministry of Education,ChinaProject(2012QNZT029) supported by the Fundamental Research Funds for the Central Universities of China+1 种基金Project(CX2010B122) supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProject(2010ybfz088) supported by the Foundation of Excellent Doctoral Dissertation of Central South University,China
文摘Based on 3D, steady N-S equations and k-e turbulence model, Fluent was employed to do numerical simulation for lateral aerodynamic performance of 6-axis X2K double-deck container trains with two different loading forms, and speed limits of the freight trains were studied. The result indicates that under wind environment： 1） As for vehicles without and with cross-loaded structure, aero-pressure on the former is bigger, but air velocity around the latter is larger; 2） When sideslip angle θ=0°, the airflow is symmetry about train vertical axis; when θ〉0°, the airflow is detached at the top of vehicles, and the air velocity increases above the separated line but decreases below it; 3） With θ increasing, the lateral force on the mid vehicle firstly increases but decreases as θ=75°; 4） When the 6-axis X2K fiat car loads empty boxes of a 40 ft and a 48 ft at 120 km/h, the overturning wind speed is 25.19 m/s, and the train should be stopped under the 12th grade wind speed.
基金Sponsored by the National Natural Science Foundation of China(Grant No.10832007)
文摘Supercavitating flow around a slender symmetric wedge moving at variable velocity in static fluid has been studied. Singular integral equation for the flow has been founded through distributing the sources and sinks on the symmetrical axis. The supereavity length at each moment is determined by solving the singular integral equation with finite difference method. The supercavity shape at each moment is obtained by solving the partial differential equation with variable coefficient. For the case that the wedge takes the impulse and uniformly variable motion, numerical results of time history of the supercavity length and shape are presented. The calculated results indicate that the shape and the length of the supercavity vary in a similar way to the case that the wedge takes variable motion, and there is a time lag in unsteady supercavitating flow induced by the variation of wedge velocity.
文摘Setting reliable speed limits on roads has always been a challenging process of designers and road agencies. In this paper the results of a methodology for setting speed limits on rural roads of all categories in Greece is presented based on international research and an extensive drivers attitudes＇ survey. The 85th percentile speed has proven in this case to be the decisive criterion for establishing reliable speed limits or advisory speeds in most cases. The resulted 10 km/la increase in legal speed limits on freeways and express rural highways did not validate any fears that accident rates or frequencies would increase. On the contrary an 8% decrease of crashes was observed in a period of about three years after the implementation of the increased speed limits level on the rural highway network of the country.
