SSOR-PCG方法在高拱坝整体大规模弹塑性有限元分析中的应用

我国目前设计和在建高拱坝地质情况复杂，因此需要对高拱坝进行专门研究，高拱坝整体行大规模弹塑性有限元分析是其方法之一。本文在岩土材料常用的D-P准则本构积分特性的基础上，利用其不用形成弹塑性刚度矩阵的特点，将对称超松弛预处理共轭梯度法(SSOR-PCG)应用于高拱坝整体大规模弹塑性分析。两个数值实例验证了SSOR-PCG方法用于弹塑性有限元计算的正确性和可行性。工程实例表明SSOR-PCG方法适宜应用于在个人计算机上对高拱坝整体大规模弹塑性有限元分析，满足计算速度和计算规模的要求。     

大体积混凝土结构仿真应力分析快速算法及应用

用有限元法进行模拟大体积混凝土结构施工过程温度应力仿真分析时，计算规模大，计算步数多，计算工作量十分庞大。为提高计算速度，从减少自由度数和加快有限元方程组的求解速度两方面分别提出了超级元算法和改进的对称逐步超松驰预处理共轭梯度法(SSOR—PCG法)，并简单介绍了这两种快速算法及所开发的三维有限元仿真计算程序在三峡工程中的两个应用实例。     

有限元超载法在拱坝整体安全分析中的应用

拱坝等水工混凝土结构体积庞大结构复杂,确保其安全稳定意义重大。针对拱坝整体安全分析问题,采用D-P屈服准则并利用超载法进行弹塑性有限元计算,根据特征点位移突变判据研究拱坝的整体健康状态。以某高拱坝为例进行有限元计算分析,计算结果表明其安全系数K应在5～5.5之间,并证明了有限元超载法在拱坝整体安全分析中的可行性。     

四寨水库高重力墩-拱坝整体非线性分析 和安全评价

为评价高重力墩对四寨拱坝的应力变形和抗滑安全的影响,建立了拱坝重力墩地基系统的有限元数值模型,其中考虑重力墩基础、右岸夹层和拱坝重力墩等交界面的非线性相互作用,以及基岩材料的弹塑性变形行为。分别采用水压超载法和折减强度参数法对重力墩拱坝系统进行数值模拟,并基于建议的重力墩安全评价指标对系统整体稳定性进行判定。分析表明,采用水压超载法计算的整体安全超载系数为2.5～3.0,折减强度参数法计算的整体稳定强度储备系数为2.0～3.0。参考已有的拱坝整体稳定分析统计数据,该工程的整体稳定安全系数相对较低。     

混凝土拱坝的极限分析

采用工程结构极限分析方法，利用已有的有限元计算程序并结合数学规划方法来推求拱坝的整体安全系数。作为弹塑性求解问题的简化方法，极限分析比传统的弹塑性增量计算效率更高、更实用。提出了适用于三维混凝土高拱坝结构极限下限分析的有限元数学规划算法。针对数学规划格式中未知变量过多的难点，采用有限元弹塑性增量计算中同一增量步上不同迭代步之间的应力差来构造缩减的自平衡应力场。采用序列二次规划算法直接求解下限分析的非线性规划问题，避免了线性化屈服条件造成的计算规模的大幅度增加。算例表明，提出的方法切实可行而且效率更高。     

高拱坝混凝土裂缝开合度仿真分析

基于三维接缝单元,模拟施工期拱坝裂缝开合行为,采用Newton-Raphson迭代法和预处理共轭梯度法开发了拱坝裂缝开度仿真计算程序模块,采用三维有限元仿真软件FZFX3D进行了考虑化学灌浆下裂缝开合度仿真分析[1];选取四种裂缝面单元刚度系数,通过对比得到本工程混凝土裂缝的缝面刚度系数取值;根据现场裂缝的实际处理情况,仿真模拟裂缝开合过程,并与实测裂缝计资料进行对比分析,绘制了裂缝开合度过程线和缝面开合度云图等,更加丰富、全面地展现了裂缝的开合状态。计算结果表明FZFX3D软件仿真分析裂缝开合状况良好。     

基于Linux机群的大型结构并行有限元系统研究

有限单元法在很多领域得到了应用,但对于大型和复杂结构,串行有限元程序很难有效地解决。研究了在PC机群上进行大规模并行有限元计算,以更好地发挥有限元在实际工程中的应用。组建了基于Linux系统的高性能并行计算机群。采用基于区域分解和预处理共轭梯度法来实现方程组的并行求解。基于以上方法,用C++、FORTRAN和MPI编程方法开发了并行有限元程序ADVPFEM。对龙马面板堆石坝的简化模型进行了线性三维有限元并行计算,得到了较好的效果。     

基于直接内力法的拱坝建基面稳定分析

提出适合分析拱坝建基面等效正应力的直接内力法，结合小湾高拱坝三维弹塑性有限元整体分析成果，研究分析了超载过程中拱端推力、推力角和抗滑安全系数的分布规律。研究结果表明，建基面抗滑安全系数衰减速度低于超载速度，高拱坝超载过程中各高程段的推力角均有所增加，这反映了拱坝具有较高超载能力的内在机制，也说明基于刚体极限平衡法对拱坝坝肩稳定分析成果偏于安全。     

高拱坝稳定安全度研究综述

针对我国西部兴起的高拱坝建设热潮,对目前高拱坝稳定安全度的分析方法进行了总结,主要方法有柔度系数法、安全系数法、可靠度方法和模型试验法。总结了拱坝的失效模式和失稳判据;对工程中最常用的安全系数法,系统阐述了计算安全度的数值方法和最新进展;得出拱坝安全度控制标准由局部安全度向整体安全度转变、安全度分析方法由确定性方法向不确定性方法发展的结论,另外常规的拱坝稳定数值分析方法如刚体极限平衡法和有限元法得到不断完善,新型数值方法在拱坝稳定分析中也有很好的应用前景。     

小湾高拱坝坝基浅层松弛区超载屈服研究

通过对小湾高拱坝坝基浅层松弛区的弹塑性分析,采用数值计算方法,揭示超载过程中坝基屈服发展规律,并采用坝基整体超载安全系数等方法评价大坝局部安全性、整体安全性以及两者之间的关系。通过分析认为小湾坝基浅层松弛区发生屈服尚属于局部问题,坝基整体超载安全度仍可达3~3.5。     

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.     

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.     

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.     

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.     

浅谈优化Vray渲染在制作三维场景的应用研究

用Vray三维渲染引擎来渲染三维场景,其质量和速度是由一些影响因素和参数设置决定的,不同的参数和因素,可以得出不同的三维渲染效果.因此,分析、优化三维渲染质量和速度的影响因素,正确、合理的选择参数对提高Vray最后渲染阶段的质量和速度非常重要.     

固结、渗流和沉积控制方程研究

本文从两相流体动力学的守恒方程出发，考虑固相、液相的相对运动，推导了可以考虑场的不均匀性和流体压缩性的统一形式的控制方程，并对方程所基于的物理概念和相互联系进行了必要的分析。通过对方程适当形式的表达，可导出用于大、小变形固结、渗流和沉积的简化方程，显示了在不同领域的三个理论存在一定的统一性。方程推导过程并未对本构关系加以限制，适用范围较广。依据实际问题的要求，作了不同形式的简化。     

四川省及重庆市中型水电站效益分析

该文分析了四川省及重庆市几座中型水电站的调查材料表明：四川省及重庆市中型水电站不仅在川渝主网和地方电网中起着很大的作用，并具有巨大的社会效益，同时还有综合利用效益，说明修建中型水电站的优越性．