Ability to accelerate, decelerate, recover and sprint again, is a crucial ability for team sports, athletes are forced in repeatingthis actions several times during matches. The objective parameters that influence res...Ability to accelerate, decelerate, recover and sprint again, is a crucial ability for team sports, athletes are forced in repeatingthis actions several times during matches. The objective parameters that influence resistance to sprints are their duration and recovery.The aim of this study was to analyze performance of young under 18 football players on high intensity running thresholds with the useof GPS 20 Hz （K-Sport Universal, Montelabbate, Italy）. We have analyzed three football matches of Marche Amateur under 18Championship （Italy） during 2017 season, using 10 GPS, one for each players except the goalkeeper. In order to better define a moreaccurate PPM （players performance model）, the players that have been substituted were removed from analysis, using only data fromfull match to build database. Total of detection is 26, with an average of 8.6 players for match divided by role. Our result according withliterature shows that in total distance, the role that obtained higher value was external midfielder and forward traveled more distance insprint.展开更多
Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and pu...Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approach–The computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology.The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind,the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.Findings–The aerodynamic force of trains’intersection has little effects on the derailment factor,lateral wheel-rail force and vertical acceleration of train,but it increases the offload factor of train and significantly increases the lateral acceleration of train.The crosswind has a significant effect on increasing the derailment factor,lateral wheel-rail force and offload factor of train.The offload factor of train is the key factor to control the threshold of train speed.The impact of the aerodynamic force of trains’intersection on running safety cannot be ignored.When the extreme values of crosswind wind speed are 15 m$s1,20 m$s1 and 25 m$s1,respectively,the corresponding speed thresholds for safe running of train are 350 km$h1,275 km$h1 and 200 km$h1,respectively.Originality/value–The research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.展开更多
A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flot...A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.展开更多
文摘Ability to accelerate, decelerate, recover and sprint again, is a crucial ability for team sports, athletes are forced in repeatingthis actions several times during matches. The objective parameters that influence resistance to sprints are their duration and recovery.The aim of this study was to analyze performance of young under 18 football players on high intensity running thresholds with the useof GPS 20 Hz （K-Sport Universal, Montelabbate, Italy）. We have analyzed three football matches of Marche Amateur under 18Championship （Italy） during 2017 season, using 10 GPS, one for each players except the goalkeeper. In order to better define a moreaccurate PPM （players performance model）, the players that have been substituted were removed from analysis, using only data fromfull match to build database. Total of detection is 26, with an average of 8.6 players for match divided by role. Our result according withliterature shows that in total distance, the role that obtained higher value was external midfielder and forward traveled more distance insprint.
基金supported by the National Natural Science Foundation of China(Project no.52078489)and the Fundamental Research Funds for the Central Universities of Central South University(Project no.2021zzts0772)to which the authors are most grateful.
文摘Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approach–The computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology.The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind,the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.Findings–The aerodynamic force of trains’intersection has little effects on the derailment factor,lateral wheel-rail force and vertical acceleration of train,but it increases the offload factor of train and significantly increases the lateral acceleration of train.The crosswind has a significant effect on increasing the derailment factor,lateral wheel-rail force and offload factor of train.The offload factor of train is the key factor to control the threshold of train speed.The impact of the aerodynamic force of trains’intersection on running safety cannot be ignored.When the extreme values of crosswind wind speed are 15 m$s1,20 m$s1 and 25 m$s1,respectively,the corresponding speed thresholds for safe running of train are 350 km$h1,275 km$h1 and 200 km$h1,respectively.Originality/value–The research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.
文摘A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.
