By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow...By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow velocities and Reynolds stress. The results show that hydraulic characteristics in non-vegetation and vegetation layers are totally different. In a region above the vegetation, Reynolds stress distribution is linear, and the measured velocity profile is a classical logarithmic one. Based on the concept of new-riverbed, the river compression parameter representing the impact of vegetation on river is given, and a new assumption of mixing length expression is made. The formula for time-averaged velocity derived from the expression requires less parameters and simple calculation, and is useful in applications.展开更多
How can teachers teach English writing effectively? And how can students learn to write essays correctly? These seem to be two puzzling problems for Chinese teachers and learners.This paper aims to introduce a new tea...How can teachers teach English writing effectively? And how can students learn to write essays correctly? These seem to be two puzzling problems for Chinese teachers and learners.This paper aims to introduce a new teaching approach:the Length Approach,and discusses its merits.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50679061, 50709025,50749031)
文摘By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow velocities and Reynolds stress. The results show that hydraulic characteristics in non-vegetation and vegetation layers are totally different. In a region above the vegetation, Reynolds stress distribution is linear, and the measured velocity profile is a classical logarithmic one. Based on the concept of new-riverbed, the river compression parameter representing the impact of vegetation on river is given, and a new assumption of mixing length expression is made. The formula for time-averaged velocity derived from the expression requires less parameters and simple calculation, and is useful in applications.
文摘How can teachers teach English writing effectively? And how can students learn to write essays correctly? These seem to be two puzzling problems for Chinese teachers and learners.This paper aims to introduce a new teaching approach:the Length Approach,and discusses its merits.
文摘文中引入可靠度理论,根据几何约束分别确定避险车道驶入角和引道长度计算模型,基于不同模型构建驶入角和引道长度的可靠度功能函数,对驶入速度、车辆主线行车轨迹半径、驾驶员反应时间等相关参数进行统计并分析其分布规律,分别采用验算点法和蒙特卡罗法计算设计速度为120,100,80 km/h的避险车道驶入角和引道长度的可靠概率.以可靠概率大于95%为要求,对避险车道驶入角和引道长度进行可靠性设计,并给出不同主线设计速度对应的驶入角和引道长度的推荐值.结果表明:当设计的避险车道驶入角和引道长度值的可靠概率大于95%时,避险车道具有良好的安全性.对于设计速度分别为120,100,80 km/h的高速公路避险车道,在最不利情况下,计算得到满足可靠概率大于95%的驶入角推荐值分别为4°、4.2°、4.4°,引道长度推荐值分别为65,64,63 m.
