The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity character...The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity characteristics,rigid bamboo circular cylinders are chosen as the model emergent vegetation.In the experiments,the density of the vegetation takes various values while all other flow parameters are kept constant.A 3-D acoustic Doppler velocimeter(ADV)is used to measure the local flow velocities for different vegetation densities.The results show that the existence of the vegetation patch leads to an increase of the depth-averaged velocity on the right and left sides behind the vegetation patch,and it increases monotonically with the vegetation density.For different vegetation densities,the lateral distribution of the stream-wise velocity behind the vegetation patch follows approximately an S-shaped profile when a≤60 m-1,and a logarithmic profile if a>60 m-1.The vertical distribution of the stream-wise velocity along the channel varies with the vegetation density and also follows an S-shaped distribution in a certain range,with the locations and the ranges being affected by the vegetation density.展开更多
针对地铁隧道内列车车厢所组构的双狭长受限空间,开展隧道内纵向通风对列车车厢火灾烟气温度特性影响的研究。考虑隧道内通风风速平行于列车车厢侧向开口的独特特征,研究不同纵向通风风速和热释放速率下隧道内列车车厢火灾的烟气最高温...针对地铁隧道内列车车厢所组构的双狭长受限空间,开展隧道内纵向通风对列车车厢火灾烟气温度特性影响的研究。考虑隧道内通风风速平行于列车车厢侧向开口的独特特征,研究不同纵向通风风速和热释放速率下隧道内列车车厢火灾的烟气最高温升和近火源区纵向温度分布。结果表明:由于双重受限边界的限制,先前经典的单狭长受限空间所得最高烟气温升预测模型(LI Y Z等)过低地预测了车厢顶棚下方烟气温度,特别是v’>0.19的工况;此外,由于隧道内强制风流通过车厢侧向开口对车厢火灾的独特作用机制,本文所研究工况中隧道内纵向气流对车厢烟气温度特性的影响并不显著。通过对比他人试验验证和分析,提出了列车车厢顶棚下方最高烟气温升及近火源区的经验预测模型。展开更多
Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on a...Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51539007,51479128 and 51609160)the National Key Research and Development Program of China(Grant No.2016YFC0402302).
文摘The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity characteristics,rigid bamboo circular cylinders are chosen as the model emergent vegetation.In the experiments,the density of the vegetation takes various values while all other flow parameters are kept constant.A 3-D acoustic Doppler velocimeter(ADV)is used to measure the local flow velocities for different vegetation densities.The results show that the existence of the vegetation patch leads to an increase of the depth-averaged velocity on the right and left sides behind the vegetation patch,and it increases monotonically with the vegetation density.For different vegetation densities,the lateral distribution of the stream-wise velocity behind the vegetation patch follows approximately an S-shaped profile when a≤60 m-1,and a logarithmic profile if a>60 m-1.The vertical distribution of the stream-wise velocity along the channel varies with the vegetation density and also follows an S-shaped distribution in a certain range,with the locations and the ranges being affected by the vegetation density.
文摘针对地铁隧道内列车车厢所组构的双狭长受限空间,开展隧道内纵向通风对列车车厢火灾烟气温度特性影响的研究。考虑隧道内通风风速平行于列车车厢侧向开口的独特特征,研究不同纵向通风风速和热释放速率下隧道内列车车厢火灾的烟气最高温升和近火源区纵向温度分布。结果表明:由于双重受限边界的限制,先前经典的单狭长受限空间所得最高烟气温升预测模型(LI Y Z等)过低地预测了车厢顶棚下方烟气温度,特别是v’>0.19的工况;此外,由于隧道内强制风流通过车厢侧向开口对车厢火灾的独特作用机制,本文所研究工况中隧道内纵向气流对车厢烟气温度特性的影响并不显著。通过对比他人试验验证和分析,提出了列车车厢顶棚下方最高烟气温升及近火源区的经验预测模型。
文摘Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.
