变攻角双圆柱涡激振动响应研究

为了研究双圆柱在变攻角下的涡激振动机理,基于CFD (Computational Fluid Dynamics)耦合动力学及嵌套网格方法,建立了双自由度圆柱体涡激振动的高保真数值模型。通过与国内外实验数据对比,验证了数值模型及程序的准确性。然后,对雷诺数Re=0～8 000、约化速度U_r=2～13、来流攻角θ=0°～90°下圆柱体的振动响应、流体力特性、尾流模式开展了研究。仿真结果表明:当约化速度U_r=2～3时,随着来流攻角增加,上下游柱体横向位移差不断增大,柱体尾流模式经历了单钝体、2S(双单涡模式)、2S(同相同步或反相同步模式)的演变过程,此时柱体振幅较小;当U_r=4～8时,上下游柱体进入锁定区间,振幅均达到最大。与大攻角(θ=60°～90°)不同,由于小攻角下(θ=0°～30°)柱间存在较强的涡融合效应,相应的振幅较大些。特别的,受柱间屏蔽作用控制,小攻角下柱体最大振幅开始于更大的约化速度;当U_r=9～13时,大攻角下上下游柱体均脱离锁定区间,振幅与单圆柱趋于一致。相反,小攻角下柱体振动频率接近漩涡脱落频率,加之上游柱体尾流的单边促进作用,导致上下游柱体振幅一直处于较大值。研究结果可为相关海洋工程设计提供参考。     

双圆柱绕流的大涡模拟

基于FLUENT软件平台上的三维大涡模拟方法,对定常来流流场中的单圆柱及不同排列形式的双圆柱进行了水动力计算,并对圆柱周围的瞬时流场、时均流场以及圆柱受力进行了分析.分析结果表明,当Re=6×104时,串列双圆柱中上游圆柱受力明显大于下游圆柱,下游圆柱Gd、Cl的变化频率满足fd=2fl,两圆柱的脱涡频率近似相等,涡街的相位相同;并列双圆柱的Cd基本相等,且变化趋势有一定相似性,脱涡频率均接近单个圆柱,涡街的相位相反;交错45.排列的两个圆柱Cd基本相等,脱涡频率接近,下游圆柱的涡街相位明显滞后于上游圆柱.     

均匀来流中振动圆柱尾迹涡结构的数值研究

本文从涡量流函数形式的N-S方程出发,对于不同的振动频率、振幅,首次数值研究了均匀来流中沿任意方向(参见图1,0°相似文献   

三维圆柱绕流数值模拟湍流方法的选择

研究湍流模拟方法对三维圆柱绕流数值模拟精度的影响,分别采用雷诺平均法（RANS）中的κ-ω模型、SST模型以及大涡模拟法（LES）对亚临界区内雷诺数Re=3 900时的三维圆柱绕流进行数值计算,分析了圆柱体表面的受力、圆柱后流场时均速度特性与瞬时涡量分布情况。结果表明,当流体流过圆柱表面时,圆柱表面出现的与流速方向相反的负压力差区域使流体从圆柱表面分离,引起了不稳定的周期性交替脱落的湍流涡泄,从而在圆柱表面产生周期性波动的升力,同时在圆柱后近流场区域形成回流区。研究还发现,LES法对圆柱体的受力以及流场时均速度特性的模拟效果要优于κ-ω模型与SST模型;相较于前人利用浸入边界法得到的模拟结果,LES法的模拟精度也有了较大提升;同样,通过对瞬时流场涡量等值线图的分析,并与已有的模拟结果进行对比,发现LES法不但可以从整体上表现出漩涡的周期性脱落,而且对流场中不同位置的、复杂的小尺度湍流涡泄也描述得非常细致,得到的自由分离剪切层长度与湍流涡泄的卷曲度更符合湍流涡泄的特征。所以,在亚临界区,LES法对湍流的模拟效果相对较好。     

均匀流与振荡流作用下圆柱横向振荡水动力特性研究

真实海洋环境中由于波浪场的存在,单纯均匀流较少,研究均匀流与振荡流共同作用对圆柱横向振荡的影响显得十分必要。为此,在验证数值方法可靠的基础上,通过改变振荡流强度和运动圆柱的振幅和频率,分析圆柱所受作用力的变化特性。研究表明:升力系数的变化规律既受振荡流强度的影响也受圆柱振幅比的影响;振荡流弱且圆柱振幅比较小时,圆柱体受力、锁定和拍频与均匀流单独作用时相似;增大振荡流强度后,圆柱体的升力系数幅值一直较大,且尾流中漩涡脱落没有明显的规律。     

摆动柔性鳍尾涡流场的实验测试与分析

利用数字式粒子图像测速系统(DPIV)开展了摆动柔性鳍的尾流场测?分析了尾涡结构的演变过程.柔性尾鳍在一个摆动周期内产生两个反向卡门涡对.本文给出了沿涡对连线及其垂直方向上的速度分布,计算了涡对的速度环量,并初步构建出柔性尾鳍流场中的三维涡环模型.     

离散涡方法在串列圆柱和张力腿平台绕流中的应用

海洋立柱和立柱群绕流是经典的流体力学问题,研究立柱排列方式、雷诺数和来流方向等因素对尾流形态和受力特性的影响,具有重要的理论和现实意义。传统的CFD方法大多存在计算时间长、难以处理复杂边界和数值耗散等不足。离散涡方法是将N-S方程表达成拉格朗日形式并用涡量-速度表示出来,不存在数值耗散,同时能使计算效率大幅提升。该文采用离散涡方法对不同间距比下串列双圆柱绕流的尾流特征和受力特性进行了研究,结果表明当间距比为2和3时,漩涡脱落仅发生在下游圆柱上,而上游圆柱不发生漩涡脱落现象,上游圆柱阻力系数为正数,下游圆柱阻力系数为负数;而当间距比为4时,上下游圆柱上均发生了明显脱涡现象,且上游和下游阻力系数均为正数。用离散涡方法对简化的张力腿平台模型进行了数值计算,研究了不同雷诺数及不同来流方向的绕流特征和受力特性,并与实验结果进行对比,表明不同流向角下张力腿平台的尾流形态为典型的2S脱涡模型。且除0°外,在其他不同角度下阻力系数随着雷诺数的增加先减小后保持平稳。     

均匀流中横向振荡圆柱绕流场的数值分析

针对工程中关心的振荡圆柱绕流问题，采用同位网格系统中的SIMPLE算法求解N-S方程，以及动网格技术模拟圆柱的运动边界。对均匀来流中的横向振荡圆柱绕流场进行数值模拟，计算了振荡圆柱升力系数、阻力系数随时间的变化曲线，以及不同相位时的流线矢量图和涡量等值线分布图。为验证模型的可靠性，对静水中的振荡圆柱流场进行模拟。与实验及数值计算结果吻合较好。     

均匀来流中振动圆柱层迹涡结构的数值研究

本文从涡量流函数形式的Ｎ－Ｓ方程出发，对于不同的振动频率，振幅首次数值研究了均匀来流中沿任意方向振动的圆柱粘性绕流的涡脱泻现象。文中着重探讨了近迹复杂的涡结构及其非定常演经过程，不仅能够再现实验研究中所发现的一些重要的流动现象，同时还进一步预示了某些新的流场结构，使数值计算起到与实验研究相辅相成的作用。     

振荡流下细长柔性圆柱涡激振动数值分析

涡激振动是造成立管疲劳破坏的最主要原因之一。目前,多数柔性圆柱涡激振动的数值模拟与模型试验,都是基于均匀流、剪切流和阶梯流等稳定流作用下,而振荡流作用下的柔性圆柱涡激振动研究相对较少。实际远洋深海情况下,细长柔性立管所处的海洋环境更为复杂,因而有必要深入研究复杂流场作用下的柔性圆柱涡激振动现象。该文采用切片法并基于开源Open FOAM平台开发的细长柔性立管流固耦合求解器viv-FOAM-SJTU,进行振荡流作用下细长柔性圆柱的涡激振动数值模拟。该文主要研究不同振荡流周期对细长柔性圆柱涡激振动的影响。数值模拟结果表明振荡周期与柔性圆柱涡激振动半振荡周期内的"锁定"区域大小密切相关,同时也观察到了间歇性涡激振动,模态跃迁等现象以及涡激振动的产生、锁定和消亡过程。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

Serial discontinuities in a Rocky mountain river. II. Distribution and abundance of trichoptera

River regulation in the headwaters and middle reaches of the Gunnison River, Colorado, significantly altered distributions and abundances of Trichoptera fauna. Twenty-five species were collected from mainstream samples, with the greatest species richness occurring at an unregulated, rhithron segment above the central reach dams. At sites immediately below the three hypolimnial-release dams and a reregulation dam, species richness was reduced 35–90 per cent and abundance > 95 per cent. Net-spinning caddisflies were the dominant trichopterans at unregulated sites; Arctopsyche grandis in the upper reaches (218 organisms, 586 mg dry mass m^?2) and Hydropsyche cockerelli, H. occidentalis and Cheumatopsyche pettiti in the lower river (9041 total organisms, 6621 mg m^?2), downstream from the last dam. The observed distributional pattern of low trichopteran densities in dam tailwaters and high hydropsychid densities at sites 60–80 km below the central reach dams is a classic expression of continuum resets and adjustments in response to stream regulation as predicted by the Serial Discontinuity Concept.     

Surveying for Water Resources

Abstract

A professional Land Surveyor (Geomatician) describes the Hydrogeologists' survey requirements of a major water resources assessment for the government of The Sultanate of Oman (1992 to 1996). The need for objective specifications is stated. Specialist terms like geoid, spheroid, Mean Sea Level are explained and how to relate spheroidal levels to the geoid. Methods like traditional survey, satellite survey, and photogrammetry are introduced. The paper encourages coordinated working for the benefit of water resource assessment and recommends employment of the professional land surveyor for major studies.     

库水波动下库岸边坡地下水浸润线解析解及误差分析

解析法是库岸边坡地下水浸润线计算中便于实际应用的方法,但该方法须基于若干假定并对潜水运动基本方程线性化后才能求解。针对各假定和线性化过程建立不同的地下水渗流数学模型,用解析法和有限元法解答上述数学模型,分析各误差大小及其规律。结果表明：库岸垂直处理带来的误差要小于方程线性化处理和不考虑非饱和渗流带来的误差,而且它们都随渗透系数变大而减小;在三峡库区库水调度情况下,假定库水位等速变化带来的误差对大多岸坡而言可以忽略;计算库岸边坡地下水浸润线时,解析法只适用于水位变化幅度相比含水层厚度较小,且几何边界规则、岩土结构简单、岩土体渗透性较好时的情况。     

Changes in Summer Irrigated Crop Area and Water Use in Southeastern Turkey from 1993 to 2002: Implications for Current and Future Water Resources

Changes in summer irrigated cropland acreage and related water use are estimated from satellite remote sensing and ancillary data in semi-arid Southeastern Turkey where traditionally dry agricultural lands are being rapidly transformed into irrigated fields with the help of water from the Euphrates-Tigris Rivers. An image classification methodology based on thresholding of Landsat NDVI images from the peak summer period reveals that the total area of summer irrigated crops has increased three-fold (from 35,000 ha to over 100,000) in the Harran Plain between 1993 and 2002. Coupled analysis of annual irrigated crop area from remote sensing and potential evapotranspiration based estimates of irrigation water requirements for cotton indicate a corresponding increase in agricultural water use from about 370 million cubic meters to over one billion cubic meters, a volume in accordance with the state estimates. These estimates have important implications for understanding the rapid changes in current agricultural withdrawals in Southeastern Turkey and form a quantitative basis for exploring the changes in future water demands in the region. For example, expansion of irrigated lands have led to a steady decrease in potential evaporation due to increased roughness and decreased humidity deficit in the Harran Plain. Assuming that the changes in future evaporation conditions will be of similar nature, water use for irrigation is expected to decrease over 40 percent in future irrigation sites. Incorporating this decrease in overall planning of the irrigation projects currently under construction should lead to improved management, and by extension, sustainability of water resources in the region.     

The Impact of Economic Development on Water Pollution: Trends and Policy Actions in Malaysia

The paper examines the impact of development activities on water pollution in Malaysia. Hence, the main objective of this paper is not just to examine the trends of development-induced water pollution around the region of the country but to know where the problems are and the policy measures taken by the government. It evaluates the probable causative relationship between problems introduced due to technology employed in water pollution control and governmental policy measures. It examines the relationship between development indicators as sources of pollution and polluted rivers over a period of 12 years. The findings of the paper have shown that despite the policy enforcement actions against the identified sources of water pollution, all the three development indicators (chosen based on those identified sources) still accounted for high percentage of river pollution in Malaysia. The findings of the paper were used to identify the central fact of the location of the problem. Some crucial conclusions of where the problems likely to be, as reflected in the findings, are: (a) the issue of interactive-effects between pollutants that many policy-makers are not aware of. This is when policy measures concentrate only on one source of water pollution; (b) the enforcement strength and/or effectiveness of policy measures themselves; (c) financial constraints to invest in appropriate technology especially sewerage systems for controlling human source of water pollution in the country; as well as those confronting small polluting industries (d) finally, lack of cooperation between government and private business firms to comply with regulatory policies for water pollution control.     

浅淡溢洪道改扩建方案与选择

溢洪道改扩建和进行溢洪道方案布置，要择优选取溢洪道进口型式、防冲消能工，以使其工程量省、施工快、运行管理方便     

Intangible Flood Damage Quantification

Flooding is a natural disaster that may cause tremendous tangibleand intangible damage to the national economy. The tangible damage assessment, i.e. the monetary value of all direct and indirect physical damages, has already been studied, whileintangible damages have not yet been taken into account. Thisarticle, therefore, is the first systematic attempt to assess bothtangible and intangible damages. The new proposed Anxiety-Productivity and Income Interrelationgship Approach (API) has been developed to quantify the intangible damage in monetary terms. The Bangkok area has been selected as the research area because several severe flood events have occurredthere over the last two decades. The 1983 Bangkok flood caused 6600 million baht in damage, according to estimates by the National Statistical Office (NSO). This article examines the totalflood damage (including the intangible damage) at different flood magnitudes. Case studies with and without flood mitigation projects are studied and compared. Furthermore, thisarticle also discusses the improvements over the conventional approach offered by the new API methodology.