ADCP流量测验随机误差分析Ⅰ：随机不确定度预测模型

本文对ADCP流速测验随机误差引起的流量测验随机误差进行了分析，考虑了表层及底层盲区流速插补引起的误差以及由于走航测验对单砰标准差的放大，给出了ADCP流量测验随机不确定度预测模型。该模型表明，影响ADCP流量测验随机不确定度的参数可以分为三类：即ADCP系统性能参数、河流水力参数、测验作业参数。本文详细地分析了ADCP系统性能参数对流量测验随机误差的影响。本文提出的随机不确定度预测模型可以用于指导ADCP流量测验作业以保证测验精度满足要求。     

Estimating discharge in gravel‐bed river using non‐contact ground‐penetrating and surface‐velocity radars

Discharge measurement is a critical task for gravel‐bed channels. Under high‐flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage–discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact‐type velocity measuring is also subject to measurement errors and/or instrument failures by the high‐flow velocities, driftwood, stumps, and debris. This study developed a new real‐time method to estimate river discharge in gravel‐bed channels. A systematic measuring technology combining ground‐penetrating radar and surface‐velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross‐sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel‐bed reach of the Cho‐Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage–discharge relation and the index‐velocity method. The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage–discharge and index‐velocity methods.     

基于垂线流速模型的雷达法断面流量测流精度分析

利用雷达多普勒流速仪进行测流是目前成本较低的实时自动测流方法。传统的雷达多普勒流速仪获得断面单条垂线上的表面流速,一般采用代表流速法建模计算断面流量,导致水位变幅剧烈的断面测流误差较大。本文基于表面流速数据的垂线法测流模型,采用雷达式二合一传感器获得断面的垂线表面流速和水深实测数据计算断面流量,并以新田水文站断面测流为例,与缆道流速仪法的测流数据结果进行对比验证。结果表明垂线平均流速相对误差在 5%以内的合格率达到 75%,断面平均流速相对误差和断面流量相对误差在 5%以内的合格率均达到 67%,故仅需布设两个雷达测速仪即可达到相对误差小于 5%的高精度测流,在自动测流站中有较好的应用。     

Advantages of a mobile LSPIV method for measuring flood discharges and improving stage–discharge curves

This paper investigates the potential of fast flood discharge measurements conducted with a mobile LSPIV device. LSPIV discharge measurements were performed during two hydrological events on the Arc River, a gravel-bed river in the French Alps: a flood greater than the 10-year return period flood in May, 2008, and a reservoir flushing release in June, 2009. The mobile LSPIV device consists of a telescopic mast with a remotely controlled platform equipped with a video camera. The digital video camera acquired sequences of images of the surface flow velocities. Ground Reference Points (GRPs) were positioned using a total station, for further geometrical correction of the images. During the flood peak, surface flow velocities up to 7 m/s and large floating objects prevented any kind of intrusive flow measurements. For the computation of discharge, the velocity coefficient was derived from available vertical velocity profiles measured by current meter. The obtained value range (0.72–0.79) is consistent with previous observations at this site and smaller than the usual default value (0.85) or values observed for deeper river sections (0.90 typically). Practical recommendations are drawn. Estimating stream discharge in high flow conditions from LSPIV measurements entails a complex measurement process since many parameters (water level, surface velocities, bathymetry, velocity coefficient, etc.) are affected by uncertainties and can change during the experiment. Sensitivity tests, comparisons and theoretical considerations are reported to assess the dominant sources of error in such measurements. The multiplicative error induced by the velocity coefficient was confirmed to be a major source of error compared with estimated errors due to water level uncertainty, free-surface deformations, number of image pairs, absence or presence of artificial tracers, and cross-section bathymetry profiles. All these errors are estimated to range from 1% to 5% whereas the velocity coefficient variability may be 10%–15% according to the site and the flow characteristics. The analysis of 36 LSPIV sequences during both events allowed the assessment of the flood discharges with an overall uncertainty less than 10%. A simple hydraulic law based on the geometry of the three sills of the Pontamafrey gauging station was proposed instead of the existing curve that is fitted on available gauging data. The high flow LSPIV discharge measurements indicated that this new curve is more accurate for high discharges since they are evenly distributed in a ±10% interval around it. These results demonstrate the interest of the remote stream gauging techniques together with hydraulic analysis for improving stage–discharge relationships and reducing uncertainties associated with fast flood discharges.     

Experimental and theoretical study of coupled influence of flow velocity increment and particle size on particle retention and release in porous media

Experimental and theoretical studies were carried out to investigate the coupled influence of flow velocity increment and particle size on the retention and release of particles in porous media. Particle release was examined through measurement of changes in effluent particle concentrations, and particle retention was assessed through measurement of the final spatial distribution of particles remaining in the soil columns after the experiments. Particle release curves were simulated using a convection-dispersion model that includes the instantaneous release of the line source. Fitted model parameters were used to gain insights into the mechanisms that control particle retention and release. When the flow velocity increment was 0.0435 cm/s, the peak concentration of particles decreased with increasing flow velocity until the latter approached a critical level, beyond which the particle concentration increased. Particle wedging and fouling were considered the primary mechanisms that controlled particle retention and release beyond the critical particle velocity. In experiments with large flow velocity increments, small particles exhibited lower particle mass fraction than large particles as particle wedging and fouling increased with particle size. The range of longitudinal dispersivity decreased with an increasing particle size and flow velocity increment. Moreover, the mean particle velocity increased with the mean interstitial fluid velocity. The mean particle velocity profile was highly sensitive to the particle size at low velocity increments. In general,particle release rates increased with both flow velocity and velocity increment. The mass of the released particles provides further evidence that particle wedging and fouling are the major factors that control particle release in sand columns.     

河流流量与悬沙测验误差评估体系

本文根据河流流量与悬移质泥沙测验的基本过程，应用误差经典理论，约定了误差的统计模型和类型，建立了直接测量量源误差的试验分类和评估准则，导出了断面流量、断面输沙率和断面平均含沙量的误差传递合成公式，从而改进和完善了河流流量与悬移质泥沙测验传统与现行的误差评估方法，形成了较完备的误差评估体系。     

Effect of the Three Gorges Reservoir on vertical distribution of suspended sediment concentration and estimation accuracy of depth-average concentration in downstream reaches

The sediment regime in the middle Yangtze River has been significantly changed from quasi-equilibrium to nonequilibrium since the impoundment of the Three Georges Reservoir (TGR). To understand the effects of the TGR on vertical distribution of suspended sediment concentration (SSC) and estimation accuracy of mean concentration, vertical sediment concentration and flow velocity data at the Shashi and Jianli hydrological stations in the reach before and after the impoundment were collected. Comparisons and analysis of vertical profiles of SSC before and after the TGR impoundment show that after the impoundment of the TGR, due to the coarsening of sediment particle size, the reduction in sediment load, and the significant decrease in sediment saturation, the vertical distribution of SSC in the downstream reaches became more uneven under medium and low water flows, which was reflected in the vertical gradient and the fluctuation degree of SSC significantly increased. In addition, the depth-average sediment concentrations were calculated by the selected-point method and the mean values calculated by the “multi-point method” were regarded as the “true mean” to evaluate the accuracy of the mean value calculated by the “few-point method.” It was found that the relative errors for the selected-point method were mainly positive before impoundment but mainly negative after impoundment. Additionally, the correction factors of one-point, two-point, and three-point methods and the position of the near-bed substituted point for the five-point method were given to reduce the error when the point measurements were used to calculate the depth-average sediment concentration in the downstream reaches.     

Optimizing sampling strategies for estimating mean water quality in lakes using geostatistical techniques with remote sensing

In planning a sampling regime, it is desirable that the sampling procedure should involve minimum estimation error for a given sample size or minimum sampling effort for a given accuracy. Two approaches for matching sampling effort to accuracy may be used: a classical approach, which ignores spatial dependence between observations, and uses a random scheme; and a geostatistical approach, which exploits spatial dependence, and uses a systematic scheme. Four Airborne Thematic Mapper images of two British lakes were processed to provide a chlorophyll index, reflecting variations in chlorophyll‐a concentration. Spatial structure was characterized using the variogram, and the modelled variogram was used in Kriging to plan sampling regimes for estimating the mean chlorophyll. For a given sample size, the systematic scheme incurred less error than the random scheme; and for a given error, the systematic scheme required smaller sample sizes than the random scheme. The relative advantage of the systematic approach over the random sampling approach increased with an increase in sample size and an increase in the proportion of variance in the data that was spatially dependent. This paper demonstrates that the sampling regime must be calibrated to the spatial dynamics of the lake under investigation, and suggests that remote sensing is the ideal means by which to determine such dynamics.     

基于ADCP实时指标流速的感潮段断面流量计算

长江下游感潮河段水位-流量关系曲线无法确定。针对传统测流方式存在的监测频次偏少、无法实现流量过程推求等问题,建立了ADCP在线测流系统。根据一段时期内在线测流系统中ADCP实时指标流速监测值与断面平均流速实测值,建立了两者间的多元线性回归模型,并进行求解,获得了模型的回归系数。以南京水文实验站2010年11月至2011年12月之间的监测资料为例,通过以上方法计算实时指标流速的回归系数,并结合水位和河底高程求得过水断面流量。与实测流量对比表明,该模型具有较好的拟合效果,计算精度较高,可广泛地应用于流量的实时报汛及整编。     

Velocity and concentration measurements in initial region of submerged round jets in stagnant environment and in coflow

Velocity and concentration fields are measured in submerged round jets in a stagnant environment and in coflow using laser Doppler anemometry and laser-induced fluorescence. Measurements are made in the initial region within distances of 40 jet exit diameter at jet Reynolds number between 1000 and 5000 and coflow-to-jet velocity ratio from 0 to 0.43. Different behaviors of jet spreading and dilution are found in jets at three different ranges of Reynolds number in which the jets are classified as initially laminar, transitional or turbulent. In the zone of established flow, the jet centerline velocity and concentration decay with downstream distance at different rates in the three groups of jets. For jets in coflow, axial development of normalized forms of centerline mean excess velocity and mean concentration at different velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale. Turbulence properties inside a jet are increased by the presence of a strong coflow. Inside the zone of flow establishment, some strange features are observed on jet turbulence properties. The length of zone of flow establishment increases from the turbulent jets, to the transition jets and to the laminar jets. The zone lengths for concentration are shorter than those for velocity by one to two jet exit diameters. Both lengths are shortened further in the presence of a coflow. For jets a stagnant environment and in the strong jet flow region of jets in coflow, jet widths increase linearly with downstream distance in transitional and turbulent jets. Self-similarity of radial profiles of mean velocity or excess velocity, mean concentration, turbulence intensities and concentration fluctuation level is explored in the zone of established flow.     

坡面水流水动力模型研究

随着城市规模的快速增长,立交桥等陡坡道路建设过程中面临的积水问题越来越受到重视。为研究变坡水槽降雨径流的水力学特征,借鉴一维坡面流的基本方程,以 Roe 格式近似黎曼解方法为基础,建立了模拟自然降雨条件下不同坡度坡面流运动情况的数学模型,通过人工降雨实验验证了16 种工况下流速的拟合情况。实验结果显示,实测值和计算值之间的相对误差在0. 6% ～17. 4%之间波动,总体上维持在15%以内。计算值和实测值表明,坡面流速、水深跟降雨强度和坡度均成正比关系,符合实际情况。同时,两者之间表现出较好的拟合度,说明了该模型具备模拟坡面薄层水流的能力。     

水文测验中两种测速垂线精简算法比较研究

随着中小河流治理项目的推进,改革水文测验方式,探索测流方式方法技术创新势在必行。本研究依托南京信息工程大学学生水文测验教学实习过程中组织开展的2次测速垂线优化精简实验,收集了渔梁水文站2次多测速垂线流量测验数据,针对原精简算法在流量误差最小的寻优过程中可能删去最有代表性的垂线这一问题,设计了直接寻求流量误差最小的测速垂线组合的新算法,并深入分析了两种精简算法对流量误差的影响。结果表明:测站目前采用的常测法选取的13根固定垂线代表性较好,流量测验精度较高;对比原算法,新的垂线精简算法在相同垂线数目下,流量误差更小,测验精度更高;由新算法,特殊水情下单垂线测流可考虑将垂线位置布设在起点距84 m处;流量相对误差大小随着优选垂线数量的增加呈指数递减规律。本研究所提的垂线精简算法有助于提高实验的精度,可为基层水文站开展垂线精简分析工作,进行测流方式改革提供参考。     

Prediction of longitudinal dispersion coefficient in natural streams by prediction map

Longitudinal dispersion coefficient can be determined by experimental procedures in natural streams. Many theoretical and empirical equations that are based on hydraulic and geometric characteristics have been developed from the field experiments of longitudinal dispersion coefficient. Regression analysis, which carries some restrictive assumptions such as linearity, normality and homoscedasticity, was used to derive some of these equations. Generally speaking, results obtained from regression analyses are not that accurate as these assumptions are often not satisfied completely. In this study, a method called Prediction Map (PM) is developed based on geostatistics to predict longitudinal dispersion coefficient from measured discharge values, shear velocities, and other conventional parameters of the hydraulic variables and normalized velocity with the objective of overcoming the drawbacks indicated above. As part of this method, a new procedure called Iterative Error Training Procedure (IETP) was developed to minimize prediction error. The prediction error level was reduced after implementing the IETP. PM was compared with various regression models by taking analyzed errors (average relative error percentage and root mean square error), coefficient of efficiency, coefficient of determination and Scatter Index as performance evaluation criteria. The results of the study indicate that the PM approach can perform very well in predicting longitudinal dispersion coefficient by applying IETP. The presented approach yielded lower average relative error percentage, root mean square error and Scatter Indices, and higher coefficient of efficiency and coefficient of determination values compared to the regression models. One of the important advantages of the PM method is that valuable interpretations and a prediction map can be extracted from the resulting contour maps, and as a result, more accurate predictions can be obtained compared to regression analysis.     

太湖水库弯曲溢洪道水流特征及优化措施研究

为了研究太湖水库弯曲溢洪道内的水流特征,并提出针对性的优化措施,采用数值模拟和物理模型试验相结合的方法,模拟试验了溢洪道的典型下泄方案,从保证水流平稳、横断面流速分布均匀、消减冲击波的角度出发,研究分析了泄槽水流特征优化的措施。结果表明:特征水流边界条件下,原设计方案泄槽内由于弯道的环流特性,水流在弯道内会产生横向冲击波;弯道右侧最大水深为6.23 m,最大水面差为5.91 m,水面差均值为3.05 m;弯道及下游直线段受冲击波的影响流速横向梯度较大。采用优化方案后,相同水流边界条件下泄槽内横向水面差减小,流速分布更加均匀,动水压强的集中情况有所改善。最大水面差下降至2.27 m,泄槽内水面差均值下降至1.31 m;各测量断面流速变异系数最大值由设计方案的58.98%降至3.94%;弯道测量断面最大压强下降48.79%。研究成果可从水力学角度为相关或相似工程的设计和实施提供参考建议。     

HW—1000型非接触式超声波水位计测量误差分析与检验

HW－1000型非接触式超声波水位计的工作原理是超声波传播反射原理，测量精度如何主要取决于对空气介质温度这个影响因素的处理方法，另外，对声波往返传播时间间隔的测量也会产生误差．通过对各项误差对总误差的贡献进行分析和计算，得出HW-1000型超声波水位计可采用双目标实时校准法，测量误差仅与校准杆A、B之间的王巨离和声波在传感器往返至校准杆A、B至水面之间的传播时间误差有关．满量程测量误差理论值小于水文测验规范规定的±2cm的要求．并且还可以看出双目标实时校准法不仅与声速无关，而且计时误差引起的各项误差中，有一部分可抵消，从而得到了对总误差的补偿．     

城市人工湖动态换水水位对流速分布影响

水位和流速是人工湖维持生态的关键因子,为探究人工湖水位对流速分布的影响,基于二维水动力模型对雁鸣湖流场进行数值模拟,研究单因素水位对流速影响和实测换水水位对流速时空分布的影响。结果显示:水位是水动力影响因素之一,低水位时的湖泊流速大于高水位时期,水位变化时的平均流速介于高低水位流速之间,水位对环流影响较小。在实测换水期间,高水位时水位分布无明显差异,水深自上游至下游逐级递增;低水位时水位分布出现差异,河滩裸露,水深分布差异较大;水位变化时,湖泊上游至下游水位呈梯度变化,水深随水位变化;流速时空分布验证了单因素水位对流速的影响,并表明不同水位对流速大小及分布影响有所差异。雁鸣湖水位和流速的模拟结果表明,人工湖水位变化能改善湖泊水动力,可为人工湖水情管理提供科学参考。     

探针杆挠曲水流场测量误差修正方法及其收敛性

提出挠流阻力引起探针杆挠曲造成水流场测量误差的迭代计算修正方法。分析该方法的收敛性及收敛方式。结果表明：通常情况下该方法是收敛的。计算流速矢量具有从两侧交替和右侧逼近实际流速矢量两种收敛方式，该方法可用于探针杆挠曲引起的流速场测量误差的修正计算。     

远距离输沙干渠的临界纵坡研究

挟沙水流一般要求比同等条件清水水流更大的能坡．才能保持泥抄不淤。本文在非均质输抄水流不淤流速研究基础上，提出输沙平衡条件下渠道临界最小纵坡的确定方法，论证了输沙渠道能坡的两部分组成，可澄清对挟沙水流阻力的分歧认识。经实际资料验证．文中提出的临界纵坡及输-抄渠道断面的确定方法可用于引黄远距离输沙干渠的设计．也为黄河中下游节水减淤的高含抄放淤渠道提供计算依据。文中对影响干渠纵坡的有关因素进行了分析，并附有计算例子。     

Uncertainties in the Methods of Flood Discharge Measurement

This study demonstrates an application of uncertainty analysis in evaluating methods of discharge measurement including: the velocity-area, rating curve and efficient methods based on the probabilistic velocity distribution equation. The measurement of river discharge plays a large part in the distribution of water resources. The conventional methods of discharge measurement are costly, time-consuming, and dangerous. Therefore the efficient method of discharge measurement which bases on the relationship between maximum and mean velocities being constant was employed to justify its alternative for the conventional methods: velocity-area and rating curve methods. Distribution test was applied to investigate the statistical properties of the uncertainties involved in the three methods of discharge measurement. Latin hypercube sampling (LHS) method was employed accordingly to assess the discharge features of the three methods of discharge measurement. The main purpose of this study is to quantify the uncertainty involved in several discharge measurement methods and justify the availability and reliability of using the efficient method as an alternative of the conventional methods. Results show that the correlation analysis also validates that the efficient method is a more reliable method than the rating curve method to yield accurate discharge measurements. Moreover, it also yielded comparably accurate measurements as those by the velocity-area method.     

基于简易PIV的圆柱绕流压力场重构

采用简易粒子成像测速仪(PIV)装置测量入口流速为14.3 cm/s时圆柱绕流的速度场,运用有限容积法和直接积分法重构压力场。对比Fluent模拟速度场结果,分析简易PIV的速度场测量误差;对比Fluent模拟压力场结果,分析基于Fluent模拟速度场以及PIV实测速度场的不同算法重构压力场误差。结果表明:在简易PIV系统中,摄像机采用适合的空间分辨率与时间分辨率能有效减小速度场测量误差。基于Fluent模拟速度场数据,当给定第一边界条件时,有限容积法的压力场重构误差小于直接积分法,均方根误差分别为1.73%,8.99%;基于PIV实测速度场,有限容积法的压力场重构误差大于直接积分法,均方根误差分别为26.58%,12.72%;降低速度场误差与获取准确的边界条件均能有效提高压力场重构精度。通过采用低成本的PIV装置,探究获取流体的瞬态压力场重构方法,降低了PIV中重构压力场的成本。