Speed-flow relationship is the fundamental for the traffic simulation and traffic volume forecast. Traditional quadratic polynomial model can’t reflect the saturate flow at signal intersections. In order to determine...Speed-flow relationship is the fundamental for the traffic simulation and traffic volume forecast. Traditional quadratic polynomial model can’t reflect the saturate flow at signal intersections. In order to determine the speed-flow relationship at signal intersections, the speed and time-headway of vehicles at two signal intersections were investigated and the accuracy of software used to get the speed was tested. After vehicle starting-up from queuing, the time-headway reduces gradually with the increase of speed. The relationship of power exponential function between speed and time-headway is formulated. Traffic volume can be calculated by the vehicle time-headway. Then the speed-flow relationship was developed and an S-shaped curve model was built in this paper. In the S-shaped curve model, traffic flow approaches to the saturate when the speed doesn’t increase. Thus, S-shaped curve model is better to describe the speed-flow relationship at signal intersection. The results can provide a reference to determine the parameters in traffic simulation and for the study of level of service of intersections.展开更多
为探究火箭橇水刹车装置不同速度下的高速撞水问题,基于VOF(volume of fluid)多相流模型,综合考虑流体可压缩性,空化效应以及流动湍流特征,建立高速水刹车装置撞水数值计算模型,并通过与高速入水试验结果数据进行对比,验证了数值方法的...为探究火箭橇水刹车装置不同速度下的高速撞水问题,基于VOF(volume of fluid)多相流模型,综合考虑流体可压缩性,空化效应以及流动湍流特征,建立高速水刹车装置撞水数值计算模型,并通过与高速入水试验结果数据进行对比,验证了数值方法的有效性与稳定性。针对不同速度条件下水刹车装置的撞水过程进行数值计算,获取撞水飞溅流场演化与冲击载荷数据。结果表明:高速水刹车装置撞水过程形成特有的飞溅流动现象,流场演化分为初始、发展、稳定3个阶段,稳定阶段产生上扬飞溅、侧翼飞溅、底部飞溅3个典型特征,局部空化效应导致飞溅流动具有明显的多相掺混特性;撞水冲击先后经历首次尖劈尖端入水冲击以及二次尖劈型面过渡区域撞水冲击,稳定阶段压力载荷中心位于尖劈过渡区域,可达到局部125 MPa以上;不同冲击速度对撞水飞溅流场状态影响不大,v=850 m/s工况首次加速度峰值是v=340 m/s工况的7.5倍,二次加速度峰值达到了6.5倍,因此撞水冲击速度的增加对刹车装置的结构安全性威胁极大。展开更多
文摘Speed-flow relationship is the fundamental for the traffic simulation and traffic volume forecast. Traditional quadratic polynomial model can’t reflect the saturate flow at signal intersections. In order to determine the speed-flow relationship at signal intersections, the speed and time-headway of vehicles at two signal intersections were investigated and the accuracy of software used to get the speed was tested. After vehicle starting-up from queuing, the time-headway reduces gradually with the increase of speed. The relationship of power exponential function between speed and time-headway is formulated. Traffic volume can be calculated by the vehicle time-headway. Then the speed-flow relationship was developed and an S-shaped curve model was built in this paper. In the S-shaped curve model, traffic flow approaches to the saturate when the speed doesn’t increase. Thus, S-shaped curve model is better to describe the speed-flow relationship at signal intersection. The results can provide a reference to determine the parameters in traffic simulation and for the study of level of service of intersections.
