Calibration of Pipe Roughness Coefficient Based on Manning Formula and Genetic Algorithm

This paper presents a method to calibrate pipe roughness coefficient (i.e., Manning n-factor) with genetic algorithm (GA) under multiple loading conditions. Due to the old pipe age as well as deleting valves and blends in the skeleton of distribution network, most of the pipes in hydraulic model of practical water distribution system (WDS) are rough. The commonly used Hazen-Williams C-factor is therefore replaced by Manning n-factor in calibrating WDS hydraulic model. Adjustment to GA is designed, and the program efficiency is improved. A case study shows that the adjustment can save 60% of the total runtime. About 90% of the relative differences between simulated and observed pressures at monitoring locations are lower than 3%, which suggests that the proposed adjustment to the calibration is efficient and effective.

Hydraulic model with roughness coefficient updating method based on Kalman filter for channel flood forecast

A real-time channel flood forecast model was developed to simulate channel flow in plain rivers based on the dynamic wave theory. Taking into consideration channel shape differences along the channel, a roughness updating technique was developed using the Kalman filter method to update Manning＇s roughness coefficient at each time step of the calculation processes. Channel shapes were simplified as rectangles, triangles, and parabolas, and the relationships between hydraulic radius and water depth were developed for plain rivers. Based on the relationship between the Froude number and the inertia terms of the momentum equation in the Saint-Venant equations, the relationship between Manning＇s roughness coefficient and water depth was obtained. Using the channel of the Huaihe River from Wangjiaba to Lutaizi stations as a case, to test the performance and rationality of the present flood routing model, the original hydraulic model was compared with the developed model. Results show that the stage hydrographs calculated by the developed flood routing model with the updated Manning＇s roughness coefficient have a good agreement with the observed stage hydrographs. This model performs better than the original hydraulic model.

Study on roughness coefficient for unsubmerged reed in the Changjiang Estuary

The influence of density,foliage and stem flexibility on the roughness coefficients under unsubmerged conditions,such as Manning＇s n,is investigated experimentally.An instrumentation system has been developed for measuring the flow rate ranging from 0.1 to 0.3 L/s under the condition of different artificial foliated reeds.Based on the experimental results,the influence on the relationship between n with different density,foliage,flexibility and flow depth is discussed.It is found that the foliage and the density are the important factors affecting Manning＇s n.At a range of relatively low velocity and relatively large bending stiffness of stem,Manning＇s n is not influenced significanthy by the flexibility of stem.

Relative Depth Effects on Corrugated Culvert Roughness

Fish passage is important to the overall health of an ecosystem. Therefore, it is important to be able to accurately predict flow conditions within a stream crossing for high and low flow periods. This paper evaluates the effect of relative water depth on the hydraulic roughness of culverts at low discharge. A 21 m long, 0.8 m diameter corrugated steel pipe with 0.068 × 0.013 m annular corrugations was used. For relative depths below 0.5, Manning’s n was found to increase with decreasing relative depth. An equation was developed to predict relative depths below 0.5 within a corrugated steel pipe based on the corrugation height, slope and culvert diameter. While Manning’s equation does perform reasonably well, the percent difference from the measured to predicted water levels warrants the use of an additional prediction method at low flows.

冰盖流阻力与综合Manning糙率

给出了冰盖流分析的数学表述 ,考察了阻力项中的Manning糙率 .给出了完全封冻和不完全封冻冰盖流综合糙率的一般计算公式 .当冰盖比 f =1(完全封冻 )时化为Sabaneev公式 ,当 f =0 (完全明流 )时退化为床面糙率 .在长 32m、宽 0 .5m玻璃水槽中进行了实验验证 .利用ADV测流技术实测流速剖面 ,分析壁面切应力流速和分区平均流速以率定不同的壁面糙率 .

基于SGA和SRFR的畦灌入渗参数与糙率系数优化反演模型(Ⅰ)——模型建立

利用基于地表非稳定流运动方程的地面灌溉模型对畦灌性能进行分析评价是改进传统地面灌溉方式、提高畦灌性能的重要举措,而准确地确定畦灌土壤入渗参数和田面糙率系数是改善畦灌性能模拟精度的重要前提。本文基于基本遗传算法SGA和地面灌溉一维模型SRFR建立的畦灌土壤入渗参数与田面糙率系数优化反演模型,可在给定的参数值域范围内开展多参数全局性寻优,利用计算机动态解析技术对SRFR模型执行程序进行解析处理,建立SGA与SRFR模型间的内部运行衔接方式,实现畦灌土壤入渗参数与田间面糙率系数优化反演过程的自动化运作,进而有效提高了参数寻优估值的工作效率。

基于SGA和SRFR的畦灌入渗参数与糙率系数优化反演模型Ⅱ——模型应用

利用作者开发的基于SGA和SRFR模型构建的畦灌土壤入渗参数和田面糙率系数优化反演模型,在不同田间灌溉实例条件下进行参数优化估值,分析评价依据地表水流推进(消退)数据估算得到的土壤入渗参数和田面糙率系数进行畦灌地表水流运动过程模拟的效果。结果表明,利用基于地表水流推进数据估算的参数可很好地模拟非稳定状态下的水流推进过程,但其模拟地表水流消退过程的效果却普遍较差,而采用基于地表水流消退数据估算的参数虽可较好地模拟稳定状态下的水流消退过程,但用其模拟水流推进过程的精度却有所下降,只有采用基于地表水流推进与消退组合数据估算的参数,才能获得较佳的综合模拟效果。与人工试算法和离散变量法估算的参数相比,基于SGA优化估值参数模拟的畦灌地表水流运动过程效果更好,SGA是改善参数估值精度的有效手段。

基于模糊粗糙集和D-S证据理论的多源灌溉信息融合方法

针对多源灌溉信息决策过程中不确定性信息难以融合的问题,提出了一种基于模糊粗糙集和D-S证据理论相结合的决策融合方法。运用模糊粗糙集理论,建立基本概率分配函数,计算各灌溉因子与灌溉决策之间的依赖程度,构建多个融合灌溉因子对灌溉决策的识别框架;然后运用改进的D-S证据理论,进行多源灌溉信息决策层级的融合,最终解决不确定信息的表达和合成问题。应用上述方法对华北地区冬小麦土壤水分、光合速率和气孔导度等信息进行灌溉决策融合,结果显示:灌溉决策的不确定性由融合前的最高38%降至9.84%,该方法可有效地提高灌溉决策精度,降低灌溉决策的不确定性。

S-粗集与它的知识遗传挖掘

利用S-粗集中的遗传知识及其遗传系数的概念,给出了知识的变异系数的概念;提出了变异系数属性依赖定理、遗传-变异关系定理;并给出了知识的遗传挖掘及其算法.

Numerical modeling of flow in continuous bends from Daliushu to Shapotou in Yellow River

The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.

Study of Bed Friction Factor for the Wu River Estuary

In this research the bed friction effect is estimated of a river estuary by use of hydrodynamic analysis. The on-site sampled data of the Wu River estuary is applied to the analysis. There are many dynamic factors that affect the flow characteristics in the estuary. The effect of tide on the generation of tidal current, bottom friction and geometry effect is the focus of this paper. The Wu River estuary is about 15 hn in length, with a small bottom slope and no physical obstruction; thus the incident wave at the estuary is considered a progressive wave with damping effect. The amplitude reduction and phase shift of the incident wave are analyzed. By the analysis of celerity reduction factor of the estuary, the estimated value of mean resistance coefficient M（μ ,κ）, damping modulus μ, and wave number κ for the sections at observation stations can be determined. Furthermore, data gathered from on-site observations are applied for validation. Finally, Manning＇ s coefficient for each section of the observation stations can be determined. It is found that the value of Manning＇ s coefficient is small downstream and increases towards upstream, and that the bed friction effect of an estuary varies largely. The estimated results of the paper are compared with the empirical formulas and the modified solution for practical application is discussed.

含植物河道曼宁阻力系数的研究

含植物河道的水流阻力不仅仅来源于边壁,传统的曼宁公式不能够直接用来计算这种河道的糙率。本文基于水流阻力等效原则,首次提出了一系列等效水力参数的概念,建立了等效综合曼宁糙率系数和等效植物附加曼宁系数的计算公式,并给出了能否使用水深代替水力半径的判别参数。使用刚性圆柱棒进行水槽试验,对植物在非淹没和淹没条件下的曼宁系数进行了计算和比较。试验结果验证了理论分析提出的关于判别参数的结论,并且表明使用水深计算的糙率在植物非淹没条件下可以用来表示植物引起的附加阻力。本文提出的等效综合曼宁糙率系数计算公式包含了植物的物理特性,因此具有普遍的应用价值,可以用来进行实际工程中糙率的计算。

含淹没植被明渠水位及糙率变化试验研究

采用概化水槽试验研究了在不同植物间距、水流条件下,含淹没植被明渠水位、曼宁糙率系数的变化特征,给出了含淹没植被明渠的糙率经验公式.试验结果表明:相同的流量、水深条件下,明渠的水位壅高值和水面比降均随植物间距的减小而逐渐增大,当植物枝叶相互间贴近或交叉时,植物对明渠水位、比降的影响程度相对较大;水深基本相同、植物排列方式相同的情况下,随着流量的增加,水面比降基本呈线性增大趋势;水深相同的条件下,含淹没植被明渠糙率受水流流速的影响较小.

地表糙度与水力糙率系数的关系

通过室内人工模拟降雨实验,初步探讨了地表糙度与水力糙率系数间的关系,得出了两者表征阻力特征相 一致的阈值为0.979,并回归得到小于该值求算地表糙度的计算模型y=2.4234e0.30051n(x),R=0.769,其中Y为 地表糙度;X为曼宁糙率系数。

含植物河道水动力学研究进展

提出了基于河道管理、河流修复与水资源可持续发展的含植物明渠水动力学研究理念,强调了含植物明渠水动力学研究的重要意义。从含植物水流的时均阻力特性、紊流机理的物理模型试验研究及数值模拟计算研究等几方面,深入介绍了国内外关于含植物明渠水动力学研究进展。指出:必须进一步解决对柔性植物枝叶形状及柔韧度的相似模拟;建立柔性植物的刚度、水流特性及阻力特性之间的定量规律;进一步研究含植物水流各向异性的紊流特性;发展更为精细的大涡数值模型来研究水深较大的复杂的各向异性紊流等有待于深入探讨的问题。

根据水流推进过程预测Horton入渗公式参数和田面平均糙率系数

通过分析畦田水流特征,结合Horton入渗公式,在满宁公式的基础上,根据水量平衡原理建立了利用水流推进过程确定土壤入渗参数和田面糙率系数的方法。同时,利用实验资料对所提出的方法进行了检验,结果表明利用该方法所推求的入渗参数和糙率系数,零惯量模型预测的推进过程和消退过程与实测数据相一致。

畦灌糙率系数的变异规律及其对灌水质量的影响

糙率系数是地面灌溉设计和管理的基本参数之一。为了更好地进行地面灌溉系统的设计和管理,研究了畦灌糙率系数的变异规律,并分析了其对灌水效果的影响。在110m的畦田长度上,观测了水流推进过程及沿程各点的水深,采用曼宁公式的数值解法估算了26条畦田的田面糙率系数,分析了其变异规律,评价了糙率系数对灌水质量评价指标的影响。结果表明,裸地畦田的平均糙率系数在0.038左右,其变异程度为中等强度。对试验区域内各畦田灌水模拟结果显示,当采用平均糙率系数模拟灌水效果评价指标时,与采用各畦田实际糙率系数相比,灌水效率指标最大相对误差达6.48%,灌水均匀度最大相差66.67%。因此,在实际地面灌溉设计与管理中,糙率系数的这种差异性不可忽略。

田间曼宁糙率系数的推求

曼宁糙率系数是描述地表水流运动的重要参数之一，但目前对于特定地块表面糙率的确定尚没有一种理想的方法。本文提出了一种根据田间水流推进资料来计算曼宁糙率的新方法。该方法以水量平衡原理为基础，用迭代法求解。经在不同地区、不同土壤类型和地面状况的田间观测数据验证，结果令人满意。

植物对明渠水流的影响

基于理论推导及其简化处理，并结合部分水槽试验资料的回归分析，建立了明渠植树后床面相对切应力、糙率与树木因子ＦＶ之间的计算关系。

含淹没植物的水流阻力试验研究

河道中存在水生植物会改变水流阻力,在大多数情况下会导致水位抬高,降低河道的泄洪能力。然而,水生植物的存在对河道治理、边滩保护、水质净化等起积极作用。为了探索河道中水生植物对水流阻力的影响,在实验室水槽中进行了不同密度的流淹没刚性植物水流试验,观测了沿程的水位变化,计算了水面坡降,基于试验资料分析了雷诺数、植物密度对糙率系数的影响,并建立拖曳力同植物水流特征粗糙度对数关系表达式,丰富了植物条件下明渠流动的试验观测资料数据库。