Direct measurement of the effect of non-submerged rigid vegetation-induced flow cross-section area variations on flow force in compound channel

In this experimental work, flow force in compound channel in presence of non-submerged vegetation was obtained via direct measurement method. The direct measurement method was used to address the inefficiency of the conventional energy-based methods for measuring the force within the body of highly rough flows. On this basis, the study was performed using a specially designed flume called knife-edge flume with a length of 14 m, a width of 1.07 m, and a height of 1.05 m at a stream bed grade of 10^-3. The flow force measurements were performed directly using a load cell in absence of the common errors that were otherwise associated with velocity measurement by inserting an external body into the flow. In this study, we examined non-submerged rigid vegetation layers with five different diameters (i.e., 20, 25, 30, 40, and 50 mm), three values of crossline spacing (i.e., 6, 8, and 10 cm), five values of crossline spacing (i.e., 8, 10, 12, 15, and 20 cm), and two different arrangements (i.e., ordered and non-ordered or cruciform) at three different positions (i.e., in the floodplain, in the main channel, and simultaneously in the floodplain and the main channel) by performing a total of 451 tests. The flow force exhibited the highest sensitivity to the increase in vegetation volume under the non-ordered arrangement. In this respect, the improvement in the flow force with increasing the percent volume of vegetation was much larger when the vegetation was arranged in a non-ordered rather than ordered fashion, with the effect of the vegetation been even more pronounced in the floodplain rather than the main channel. In addition, at a certain percent change of the flow force, the trough-vegetation flow velocity was higher under the ordered arrangement rather than the non-ordered arrangement, reflecting the more difficulty encountered by the flow as it passed through the non-ordered vegetation. Based on the analysis results, it was found that the flow force would change by 060% when the vegetation had grown in the floodplain with λ* values in the range of 0–1. In cases where the vegetation had grown in the main channel and simultaneously in the main channel and the floodplain, the flow force variations increased to 10–70% and 20–80% as the λ* changed from 0 to 10, respectively. Analyzing the results of the experiments and the vegetation-modified Reynolds number, a relationship was further presented for calculating the flow force in presence of non-submerged rigid vegetation in a compound channel.     

冲积扇发育过程中砾石颗粒对砂坝和沟流的控制作用——基于冲积扇水槽模拟实验

通过观察和记录冲积扇自旋回沉积模拟实验,研究在冲积扇的发育过程中,砾石颗粒对冲积扇在沉积过程中的控制机理。研究表明:在同一期洪水期的中期—后期,在冲积扇扇根片流带中,沟流发育的优势方向与砾石颗粒初期分布有着重要关系,同时砾石颗粒的分布还控制着沟流改道;在冲积扇的扇中发育过程中,由于砾石颗粒是在牵引流的搬运作用下运动,因此对沟道的控制作用便更多体现在对沟道形态的改造与砂坝的形成上。通过对比冲积扇剖面中出现的多期辫流水道叠置、砂坝和沟道的分布状态,就能够验证实验过程中冲积扇表面发生的现象。在实验过程中,冲积扇形成的规模是与碎屑流的动力、携带沉积物和沉积时间呈正比关系。在碎屑流的动力与携带的沉积物相对没有变化的稳定期内,扇根的砂坝与沟流、扇中的沟道都与砾石颗粒的作用密切相关。     

土石坝漫顶应急除险技术的试验研究

为避免土石坝漫顶后迅速溃决,采用水槽试验的手段对临时加高坝顶和在坝体下游面铺设防 水布两种工程除险措施进行了研究。试验发现,临时加高坝顶后,可以有效地减缓漫顶时间,推迟洪 峰的到来,但是临时加高坝顶会使坝前水位升高,使得溃坝形成的洪峰流量值增大,因此在实践中采 用该工程措施时要慎重。而在下游坡面铺设防水布后,可以有效地减缓下游面的冲刷速度,不仅可以 将整个溃坝历时延长,推迟洪峰的出现,同时形成的溃坝洪峰值也会有所降低,相比较而言,该措施 是一种比较适宜的工程应急除险措施。     

双向环形水槽流速分布规律试验研究

环形水槽以其能满足细颗粒泥沙沉降所需的距离要求、无流入口和流出口的影响已被广泛使用在细颗粒泥沙运动规律的研究中。为最大程度地削弱横向流,采用环形槽、剪力环同时反向旋转,拟合出剪力环和环形槽的最佳转速比曲线,并在清水率定的过程中采用旋浆式流速仪测量不同水深、多级转速下环形水槽的分层流速。试验数据表明环形水槽中线处垂线流速分布呈S型,流速在边界处有较大的梯度,在流场中心区域分布较均匀,可用三次函数进行拟合。流速沿槽宽呈线性分布,由外壁向内壁递减,使得各断面流速分布相同,可以模拟无限长直水槽。     

三屯河渠首渡槽工程槽身预制及安装

本文介绍了“U”型钢筋混凝土薄壳结构渡槽的预制及在三屯河安装施工方法。     

浅谈用空气输送斜槽输送粉状物料

空气输送斜槽在输送粉状物料方面得到广泛的应用,根据设计及现场使用情况,浅谈几点要素。     

U形渠道直壁式量水槽体型优化及在泾惠渠三支渠上的应用

本文对U形渠道直壁式量水槽的体型进行了优化,规范了量水槽的设计标准,根据优先数,对量水槽的喉道宽度进行了优选,结合泾惠渠三支渠U形渠道的实际情况,优选后的喉道宽度有5种,常用的只有3种。规定了量水槽的命名方法。为量水槽的标准化、工厂化生产奠定了基础。     

一种简支渡槽结构自振特性研究的方法

渡槽结构的模态分析是渡槽结构地震响应计算及抗震设计的基础。它包括自振频率的计算及主振型的分析,利用梁段有限元建立分析模型,用结构模态分析的QR法计算其自振圆频率及各阶振型,结果与Timoshenko弯扭耦合梁理论解符合得很好,这证明该建模及其计算方法是正确的、合理的。     

堰塞坝溃决特征和机理的试验研究

汶川震区泥石流沟道内存在大量地震诱发堰塞坝,溃决后极易形成泥石流,为研究其溃决特征和机理,通过松散堆积堰塞体的临界溃决试验,研究了在不同颗粒级配条件下,堰塞体溃决的临界溃决流量以及堰塞体溃决后的流量,得出:1堰塞体的临界溃决流量随颗粒中值粒径的增大而增大,在相同颗粒中值粒径条件下,临界溃决流量随颗粒的不均匀系数Cu的增大而减小,Cu50则临界溃决流量趋于固定值;2在上游来水流量较小时,增大来水流量后,下泄洪峰流量略有增加,堰塞体溃决产生的流量占洪峰流量比重较大,而来水流量较小,对溃决后洪峰流量的贡献也较小。     

推移质输沙率公式的统一形式

对以往的各种推移质输沙率公式中的水流强度指标进行了综合、归纳 ,提出了统一的水流强度指标形式 ,并由此推导出推移质输沙率公式的统一形式 .利用 75 7组实测水槽资料对该统一形式中的系数进行了率定 ,并与其它几个推移质输沙率公式比较表明 ,该统一形式具有相当高的精度