单沟槽沙坝海岸的裂流实验研究

该文实验研究了单沟槽沙坝海岸上产生的波生裂流流场,重点关注了不同波浪条件下流场水平形态以及最大裂流流速的变化.实验在波浪水槽中进行,采用规则波作为入射波浪,应用高精度浪高仪阵列和流速仪阵列,在全场范围内较密集地采集波面升高和流速数据,通过分析实验数据,获得全场波高、平均水面以及流速分布,对裂流及两个存在的补偿流进行了描述,分别比较和分析了不同波高对于裂流强度及整个流场形态的影响,并对最大离岸流速与波高间的关系进行了分析.     

沙坝海岸上裂流的数值模拟

建立了基于二阶完全非线性Boussinesq水波方程的二维波浪破碎数值模型,对沙坝海岸上产生的裂流进行了数值模拟研究。首先将文献[1]中给出的一组二阶完全非线性Boussinesq方程进行扩展,在动量方程中引入紊动粘性项模拟波浪破碎引起的能量耗散,采用窄逢法处理海岸动边界问题,并考虑了混合子网格效应以及水底摩擦。然后,在矩形网格上离散控制方程,采用有限差分方法和混合四阶Adams-Bashforth-Moulton预报矫正格式建立了数值模型。应用所建立模型对一带沟槽沙坝海岸上产生裂流的实验进行数值模拟,将计算的波高、增减水、时均流速、时均流场等与实验数据进行了比较。数值结果与实验结果吻合较好,这说明建立的数值模型是准确有效的,为下一步应用该模型模拟实际海岸上的裂流提供了研究基础。     

实时流场测量系统在河工模型试验中的应用

流场实时测量系统VDMS(以下简称VDMS),是运用数字摄像与粒子跟踪测速技术(PTV)研制开发的表面流场大范围同步测速与监控系统。该系统可快速方便地得到模型试验范围研究区域内的流场、断面流速分布及单个或多个测点的流速矢量变化过程,提高了试验的精度和效率。     

排沙漏斗流场特性与排沙机理研究

排沙漏斗是一种截沙率高、耗水率小的二级泥沙处理设施。为了进一步探明排沙漏斗的流场特性和排沙机理,该文采用声学多普勒流速仪(ADV)对排沙漏斗立轴螺旋流进行了三维流场测试,采用雷诺应力模型(RSM)和VOF方法数值模拟了排沙漏斗内清水流场,计算的水流时均流速分布与实测结果吻合良好。通过数值模拟方法得到了全面详细的排沙漏斗流场结构信息,并据此分析了排沙漏斗的排沙机理,提出二次流是排沙漏斗能够顺畅高效排沙的关键。     

水电厂超声波测流试验及CFD验算

对国网江西省电力公司柘林水电厂改造后的机组的效率进行了试验,试验过程中,选用了超声波法和流速仪法来测量其流量。试验结果表明,两种流量测量方式的实测结果存在着大约+2.37%的相对误差。针对存在的误差,对其成因开展了分析研究。分析结果表明,由于超声波法和流速仪法在测流时是同步进行的,这样就使得流速仪的支架影响到了超声波测流声道的流场分布,从而导致超声波法的测流结果出现了偏大的误差;为此,进一步对测流管道、流速仪支架及超声波的测流声道进行了CFD模拟和计算,得到流速仪支架对超声波测流结果的影响大约为+2.2%。经过对试验结果与CFD模拟结果进行对比分析,验证了流速仪支架是导致上述试验误差的主要原因。     

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。     

电波流速仪实验比测与使用方法研究

本文采用实验比测的方式,通过对不同厂家电波流速仪的检测,研究分析电波流速仪测流准确度的影响因素和使用方法,在水文测验中对提高电波流速仪测量精度有指导意义。     

水力光滑明渠流流速分布的新公式

采用一个新的湍流黏性模型研究水力光滑明渠流的流速分布,得到的结果与以往在明渠中所测的实验数据吻合较好。基于这个湍流黏性模型,推导出一个新的光滑明渠流外部区域的流速亏损规律,该表达式可以推广到内部区域,并提出一种新的确定内部区域流速分布的近似方法。运用本文给出的公式计算结果与由多普勒激光流速计所测的实验数据吻合良好。在只给出平均流速和水深的情况下,根据本文给出的公式可求得内外区域流速分布。     

非接触式微波测流技术探讨

河道流速测量,目前常用旋桨式或旋杯式机械流速仪,有条件的测站可采用声学多普勒流速剖面仪（ADCP）（包括走航式和旁测式）进行测量。两种测量方式均为接触式测量,适用于一般河道的流速、流量测量,但是,对于大洪水、特大洪水特别是洪峰的测量,受自然环境和河道波浪的影响,两种测量方式均受到一定的限制。洪水、洪峰的测量,目前仍采用原始的浮标测量法。该测量方式需要人员多,测量周期长、测量精度低,尤其是山洪测量中测量人员人身安全受到威胁,于水文测量现代化的发展十分不协调。     

基于回归分析的表面流场粒子匹配算法

针对表面流速图像测试中高浓度粒子条件下测量误差大的问题,改进了最邻近匹配算法,提出基于回归分析的表面流场粒子匹配算法,即多帧回归粒子匹配算法。该算法综合粒子距离、运动轨迹、运动趋势等因素,应用一元线性回归分析法拟合粒子中心坐标,通过相关系数完成粒子匹配,实现最佳同源粒子追踪。运用多帧回归粒子匹配算法开发了改进型大尺度模型表面流场图像测试系统(ILSPIV),并将ILSPIV应用到八卦洲河工模型,ILSPIV和旋桨流速仪测量的断面垂线平均流速分布形态及数值基本一致,表明多帧回归粒子匹配算法能提升高浓度粒子条件下流速测量精度,更好地满足工程实践研究需求。     

Rip currents near coastal structures in Lake Michigan: Characterization and assessment for warnings

Rip currents near coastal structures commonly occur in Lake Michigan in the Great Lakes region of the United States. Lack of timely warning due to undocumented characteristics of rip currents and no assessment tool can contribute to tragic drownings incidents. In this paper, we characterized rip current occurrences near breakwater structures and developed an assessment tool for providing timely rip current warnings to beachgoers at the study site, City of Port Washington, WI. Characteristics of rip currents near the structure were observed from field measurements or visual images. Deflection rip currents had speeds of ～ 0.2 m/s and lasted for several hours. The rip current occurrences were associated with environmental proxies. It was found that rip currents can occur even when the water appears calm near the structure. A Structure Rip Checklist and Assessment Matrix (SRiCAM) with a four-tiered risk was developed and validated using observations. Furthermore, the SRiCAM was integrated into cyberinfrastructure with a data contingency plan to provide real-time warnings to the public. The applicability of the SRiCAM to other locations across Lake Michigan was further tested and results are promising. Overall, the SRiCAM has the potential to be widely extended to foster recreational water safety and resilience to rip current hazards in the Great Lakes.     

THREE-DIMENSIONAL NUMERICAL MODELLING OF THE WAVE-IN- DUCED RIP CURRENTS UNDER IRREGULAR BATHYMETRY

A process-based 3-D hydrodynamic model is established to simulate the rip current structures under irregular bathymetry.The depth-varying wave-induced residual momentum,the surface rollers,the turbulent mixing and the wave-current interactions are considered.Experimental datasets are used to validate the model,and it is shown that the model can effectively describe the 3-D structures of the rip currents in both normal and oblique wave incident cases.The flow patterns of the rip currents see various characteristics for different incident wave directions.In the normal incident case,pairs of counter-rotating primary circulation cells are formed,and an offshore rip flow occurs in the embayment troughs.The peak seaward velocities occur at the top of the bed boundary layer,and the undertow is incorporated in addition to the rip currents.In the oblique incident case,the longshore currents are dominant,which result in a meandering flow along the depth contour,and the undertow is weaker compared to that in the normal incident condition.     

Fish community structure in natural and engineered habitats in the Kansas River

We investigated fish assemblage structure in engineered (rip‐rap) and natural habitats (log jams and mud banks) in the Kansas River USA to determine if natural structures had higher abundance and diversity of fishes at a local spatial scale. A total of 439 randomly selected sites were boat electrofished from May to August 2005 and 2006. Mean species diversity and richness were significantly higher in rip‐rap than log jams and mud banks. Mean relative abundance (CPUE; number of fish collected per hour electrofishing) of six of the 15 most common fishes (>1% of total catch) were most abundant in rip‐rap, two were most abundant in log jams, and none in mud banks. Rip‐rap had the highest relative abundance of fluvial specialist and macrohabitat generalists, whereas mean CPUE of fluvial dependents was highest in log jams. Although a discriminant function analysis indicated that nine size classes (eight species) discriminated among three habitat types, the high misclassification rate (38%) suggested a high degree of fish assemblage overlap among the habitats. Although previous work has suggested that engineered structures (rip‐rap) and urbanization are linked to reduced biotic diversity or reduced growth of fish species, our results suggest that at a local scale rip‐rap may not have the same negative impacts on fish assemblages. Published in 2009 by John Wiley & Sons, Ltd.     

Effects of grade control structures on the macroinvertebrate assemblage of an agriculturally impacted stream

Nearly 400 rock rip‐rap grade control structures (hereafter GCS) were recently placed in streams of western Iowa, USA to reduce streambank erosion and protect bridge infrastructure and farmland. In this region, streams are characterized by channelized reaches, highly incised banks and silt and sand substrates that normally support low macroinvertebrate abundance and diversity. Therefore, GCS composed of rip‐rap provide the majority of coarse substrate habitat for benthic macroinvertebrates in these streams. We sampled 20 sites on Walnut Creek, Montgomery County, Iowa to quantify macroinvertebrate assemblage characteristics (1) on GCS rip‐rap and at sites located (2) 5–50 m upstream of GCS, (3) 5–50 m downstream of GCS and (4) at least 1 km from any GCS (five sites each). Macroinvertebrate biomass, numerical densities and diversity were greatest at sites with coarse substrates, including GCS sites and one natural riffle site and relatively low at remaining sites with soft substrates. Densities of macroinvertebrates in the orders Ephemeroptera, Trichoptera, Diptera, Coleoptera and Acariformes were abundant on GCS rip‐rap. Increases in macroinvertebrate biomass, density and diversity at GCS may improve local efficiency of breakdown of organic matter and nutrient and energy flow, and provide enhanced food resources for aquatic vertebrates. However, lack of positive macroinvertebrate responses immediately upstream and downstream of GCS suggest that positive effects might be restricted to the small areas of streambed covered by GCS. Improved understanding of GCS effects at both local and ecosystem scales is essential for stream management when these structures are present. Copyright © 2007 John Wiley & Sons, Ltd.     

Bryophytes as a special mesohabitat for meiofauna in a rip‐rapped channel

Rock rip‐rap is commonly used by river engineers for bank stabilization. However, there is a general lack of information on invertebrate communities inhabiting these structures. This study examines the permanent and temporary meiofauna dwelling in dense clumps of an aquatic moss Fontinalis antipyretica growing on rock rip‐rap along a side channel of the Morava river, Czech Republic. We estimated the amount of fine particulate matter (total trapped matter, TM) trapped in the moss as both a habitat and food source for meiofauna. Total mean numbers of the moss‐dwelling meiofauna per 10 g dry weight of moss and 1 m² of the bottom area were 253 917 ± 178 335 (mean ± SD) and 7 160 461 ± 5 029 047 individuals, respectively, during October 1999–November 2000. Out of 20 operational taxonomic units, Bdelloidea was the dominant group with about 76% of the total meiofauna numbers followed by Monogononta (11.23%), Nematoda (6.38%), Chironomidae (4.08%) and Oligochaeta (1.06%). Coarse trapped matter (500–1000 µm) contributed about 4% to the total, medium TM (100–500 µm) around 14% and the finest TM (30–100 µm) 82%. Organic matter (OM) forms 10% of the total TM. The seasonal variations in TM, OM and mineral matter and their size fractions have significantly correlated (Spearman rank correlation coefficient, P < 0.05 or 0.01) with densities of Oligochaeta, Hydrachnidia, Cladocera, Harpacticoida, nauplii of Copepoda, Chironomidae. In regulated channels, rock rip‐rap overgrown by aquatic bryophytes is desirable because it increases the spatial diversity of habitats and supports considerably higher numbers of meiofauna compared to the gravel bed and may substantially contribute to the stream metabolism. Copyright © 2002 John Wiley & Sons, Ltd.     

Is it Worth the Money? The Functionality of Engineered Shallow Stream Banks as Habitat for Juvenile Fishes in Heavily Modified Water Bodies

Heavily modified water bodies (HMWB) are characterized by monotonous and straightened channel morphologies with high degrees of bank enforcement. They often lack shallow bank habitats, which are considered important for critical life stages of fishes. In this study, three principle options to engineer shallow stream zones were assessed concerning the value of the created habitats for larval, juvenile and adult stages of fishes in 30 sites from three HMWB. The construction scheme of the juvenile habitats comprised different degrees of embankment ranging from rip‐rap structures with steep bank angles to almost nature‐like construction schemes with very flat river‐banks and sparing usage of structural enrichment such as boulders and dead wood. In general, the differences between the three habitat types were more pronounced in density of different life stages than in the presence or absence of species or certain life stages. A steep bank angle and a high degree of engineering such as placement of rip‐rap embankment, boulders or dead wood structure in the habitats were hardly accepted by early larval and juvenile stages of rheophilic fishes. In contrast, the construction scheme of a nature‐like habitat with a flat bank angle (<10%), low water depth (mean = 24 cm) and a sparing usage of coarse woody debris (CWD) and boulders had the highest success. Other investigated habitat types did not provide additional benefit, neither in terms of supporting additional species and life stages, nor in high individual numbers and should thus only be implemented when land for restoration is scarce and nature‐like habitats cannot be realized. Copyright © 2016 John Wiley & Sons, Ltd.     

龙颈上水库土坝加固防渗设计

文章通过对龙颈上水库土坝工程地质条件的分析和土坝防渗方案的比选后,采用坝体劈裂帷幕灌浆与坝基帷幕防渗的设计方案对水库土坝实施培厚加高及防渗处理。并对处理后的坝体渗流及坝坡稳定进行了分析计算,结果表明,坝体上、下游坝坡在各种工况下,坝坡稳定安全系数均满足规范要求。     

Evaluation of flow regime of turbidity currents entering Dez Reservoir using extended shallow water model

In this study, the performance of the extended shallow water model （ESWM） in evaluation of the flow regime of turbidity currents entering the Dez Reservoir was investigated. The continuity equations for fluid and particles and the Navier-Stokes equations govern the entire flow of turbidity currents. The shallow water equations governing the flow of the depositing phase of turbidity currents are derived from these equations. A case study was conducted on the flow regime of turbidity currents entering the Dez Reservoir in Iran from January 2002 to July 2003. Facing a serious sedimentation problem, the dead storage of the Dez Reservoir will be full in the coming 10 years, and the inflowing water in the hydropower conduit system is now becoming turbid. Based on the values of the dimensionless friction number （ Nf ≤1 ） and dimensionless entrainment number （ NE≤ 1 ） of turbidity currents, and the coefficient of determination between the observed and predicted deposit depths （R2 = 0.86） for the flow regime of negligible friction and negligible entrainment （NFNE）, the flow regime of turbidity currents coming into the Dez Reservoir is considered to be NFNE. The results suggest that the ESWM is an appropriate approach for evaluation of the flow regime of turbidity currents in dam reservoirs where the characteristics of turbidity currents, such as the deposit depth, must be evaluated.     

混凝土电化学脱盐模拟及其影响因素分析

电化学方法可以用来对含有氯离子的混凝土进行脱盐。电流密度的大小和环境温度的高低是影响电化学脱盐效率的主要因素,过大的电流密度会对钢筋混凝土的性能产生一定影响,而较低的温度会降低脱盐效率。基于氯离子输运方程和温度对氯离子扩散系数的影响,建立了氯离子输运数值模型,得到了不同工作电流密度和温度下混凝土的电化学脱盐效率。结果表明：温度对脱盐效果影响显著,较高温度（303.15 K）时的氯离子渗透系数是较低温度（273.15 K）时的8.8倍;随着温度的升高,取得同样脱盐效果所需要的电流越小,即在较高温度环境下可以使用较低电流达到较高的脱盐效率。