In order to study the safety and the comfort of high-speed trains running on a single-tower cable-stayed bridge under spatial gust,a dynamic model of wind-train-bridge analysis model is built based on the autoregressi...In order to study the safety and the comfort of high-speed trains running on a single-tower cable-stayed bridge under spatial gust,a dynamic model of wind-train-bridge analysis model is built based on the autoregressive method,the multi-body dynamics method and the finite element method.On this basis,the influence of spatial gust model loading,the suspension parameters change,wind attack angle and speed on the train-bridge system are analyzed by combining the time/frequency domain analysis and statistical methods.The results show that the spatial gust environment is one of the most important factors affecting safety and comfort and can make the calculation result tend to be conservative and more conducive.The response changes caused by K_(py),K_(px) and K_(sx) changes are nearly linear,while Ksy shows nonlinear characteristics and the most sensitivity.Wind attack angle at 75°and 90°has the greatest influence on the vehicle-bridge system.For ride comfort index,when pre-set wind speed(α=75°)reaches 20 m/s,the vertical acceleration firstly exceeds the limit value;when wind speed(α=90°)reaches 21.5 m/s,the lateral acceleration firstly exceeds the limit value,and the ride comfort of the vehicle cannot be guaranteed.For running safety index,when pre-set wind speed(α=75°)reaches 24.6 m/s,the wheel unloading coefficient firstly exceeds the limit;when pre-set wind speed(α=90°)reaches 24.5 m/s,the derailment coefficient firstly exceeds the limit,and the running safety cannot be guaranteed.The results can provide a suitable reference for the safe and stable operation of trains on the bridge.展开更多
Purpose:This study examined variation in foot strike types,lower extremity kinematics,and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara.Mexico.Methods:High speed video was used to study...Purpose:This study examined variation in foot strike types,lower extremity kinematics,and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara.Mexico.Methods:High speed video was used to study the kinematics of 23 individuals.13 who habitually wear traditional minimal running sandals(huaraches).and 10 who habitually wear modern,conventional running shoes with elevated,cushioned heels and arch support.Measurements of foot shape and arch stiffness were taken on these individuals plus an additional sample of 12 individuals.Results:Minimally shod Tarahumara exhibit much variation with 40%primarily using midfoot strikes,30%primarily using forefoot strikes,and30%primarily using rearfoot strikes.In contrast,75%of the conventionally shod Tarahumara primarily used rearfoot strikes,and 25%primarily used midfoot strikes.Individuals who used forefoot or midfoot strikes landed with significantly more plantarflexed ankles,flexed knees,and flexed hips than runners who used rearfoot strikes.Foot measurements indicate that conventionally shod Tarahumara also have significantly less stiff arches than those wearing minimal shoes.Conclusion:These data reinforce earlier studies that there is variation among foot strike patterns among minimally shod runners,but also support the hypothesis that foot stiffness and important aspects of running form,including foot strike,differ between runners who grow up using minimal versus modem,conventional footwear.展开更多
基金Project(20ZR1460700) supported by the Natural Science Foundation of Shanghai,ChinaProject supported by Shanghai Collaborative Innovation Research Center for Multi-network&Multi-modal Rail Transit,China。
文摘In order to study the safety and the comfort of high-speed trains running on a single-tower cable-stayed bridge under spatial gust,a dynamic model of wind-train-bridge analysis model is built based on the autoregressive method,the multi-body dynamics method and the finite element method.On this basis,the influence of spatial gust model loading,the suspension parameters change,wind attack angle and speed on the train-bridge system are analyzed by combining the time/frequency domain analysis and statistical methods.The results show that the spatial gust environment is one of the most important factors affecting safety and comfort and can make the calculation result tend to be conservative and more conducive.The response changes caused by K_(py),K_(px) and K_(sx) changes are nearly linear,while Ksy shows nonlinear characteristics and the most sensitivity.Wind attack angle at 75°and 90°has the greatest influence on the vehicle-bridge system.For ride comfort index,when pre-set wind speed(α=75°)reaches 20 m/s,the vertical acceleration firstly exceeds the limit value;when wind speed(α=90°)reaches 21.5 m/s,the lateral acceleration firstly exceeds the limit value,and the ride comfort of the vehicle cannot be guaranteed.For running safety index,when pre-set wind speed(α=75°)reaches 24.6 m/s,the wheel unloading coefficient firstly exceeds the limit;when pre-set wind speed(α=90°)reaches 24.5 m/s,the derailment coefficient firstly exceeds the limit,and the running safety cannot be guaranteed.The results can provide a suitable reference for the safe and stable operation of trains on the bridge.
基金a grant from the American School of Prehistoric Research (Harvard University)
文摘Purpose:This study examined variation in foot strike types,lower extremity kinematics,and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara.Mexico.Methods:High speed video was used to study the kinematics of 23 individuals.13 who habitually wear traditional minimal running sandals(huaraches).and 10 who habitually wear modern,conventional running shoes with elevated,cushioned heels and arch support.Measurements of foot shape and arch stiffness were taken on these individuals plus an additional sample of 12 individuals.Results:Minimally shod Tarahumara exhibit much variation with 40%primarily using midfoot strikes,30%primarily using forefoot strikes,and30%primarily using rearfoot strikes.In contrast,75%of the conventionally shod Tarahumara primarily used rearfoot strikes,and 25%primarily used midfoot strikes.Individuals who used forefoot or midfoot strikes landed with significantly more plantarflexed ankles,flexed knees,and flexed hips than runners who used rearfoot strikes.Foot measurements indicate that conventionally shod Tarahumara also have significantly less stiff arches than those wearing minimal shoes.Conclusion:These data reinforce earlier studies that there is variation among foot strike patterns among minimally shod runners,but also support the hypothesis that foot stiffness and important aspects of running form,including foot strike,differ between runners who grow up using minimal versus modem,conventional footwear.
