冰温度膨胀力室内模拟及影响因素试验研究

东北地区冬季气候寒冷,河渠、水库等水工建筑物在冬季由于结冰形成的冰盖会产生作用于水工建筑物上的静冰荷载。随着温度升高,冰盖板产生冰温度膨胀力,会对野外水工建筑物造成破坏。由于野外观测周期长,且多种条件限制野外实地观测,因此,为了研究冰盖的冰温度膨胀力及其相关影响因素,在低温环境模拟实验池内进行了冰温度膨胀力室内模拟试验,并对冰温、冰厚等相关影响因素进行了分析。结果表明:冰温度膨胀力产生于气温升高阶段,且随着温度的升高,冰温度膨胀力呈增大趋势。冰温度膨胀力发展到峰值时,对应冰温为?1.9 ℃,环境温度接近0 ℃,与野外实际观测结果相符。室内试验的最大冰温度膨胀力为118.7 kPa,试验的最大冰厚为10.65 cm,冰温度膨胀力的最大峰值出现在冰盖板的3.5 cm处,表明冰温度膨胀力的作用点在最大冰厚的1/3处,且冰温度膨胀力沿冰厚呈先增大后减小的分布。     

冰温度膨胀力室内模拟及影响因素试验研究

东北地区冬季气候寒冷,河渠、水库等水工建筑物在冬季由于结冰形成的冰盖会产生作用于水工建筑物上的静冰荷载。随着温度升高,冰盖板产生冰温度膨胀力,会对野外水工建筑物造成破坏。由于野外观测周期长,且多种条件限制野外实地观测,因此,为了研究冰盖的冰温度膨胀力及其相关影响因素,在低温环境模拟实验池内进行了冰温度膨胀力室内模拟试验,并对冰温、冰厚等相关影响因素进行了分析。结果表明:冰温度膨胀力产生于气温升高阶段,且随着温度的升高,冰温度膨胀力呈增大趋势。冰温度膨胀力发展到峰值时,对应冰温为-1.9℃,环境温度接近0℃,与野外实际观测结果相符。室内试验的最大冰温度膨胀力为118.7 kPa,试验的最大冰厚为10.65 cm,冰温度膨胀力的最大峰值出现在冰盖板的3.5 cm处,表明冰温度膨胀力的作用点在最大冰厚的1/3处,且冰温度膨胀力沿冰厚呈先增大后减小的分布。     

堤坝冻胀防护方法研究

在我国高纬度寒冷地区,各类水工建筑物常常受到冰荷载的不同程度的冻害,其中冰层温度膨胀力是造成建筑物破坏的主要荷载之一。冰层温度升高体积膨胀,而膨胀受到建筑物的约束,则冰层内部会产生温度膨胀力,很可能影响水工建筑物的正常运行,导致人力和物力的损失。本文提出了一种梯形槽式堤坝防护型式,通过梯形凹槽将原有的静冰压力分散,从而减少静冰压力对建筑物的冻害损伤程度,延长使用寿命,提高经济效益。最后通过防护效果检验发现:增大防护板梯形角,适当增加防护板厚度以及调整下梯形面长度和各梯形面之间比例都可以减少静冰压力,达到良好的防护效果。     

寒区水塘冰盖生长和消融分析

冰盖厚度是冰工程研究中最重要的特征参数之一。为明晰寒区静冰生长和消融的过程,准确计算冰盖厚度,通过分析影响静冰生消的各热力过程,建立了生长期和消融期冰厚计算的热力学模型,采用黑龙江省青花湖8号水塘的冰情观测数据对冰厚计算模型进行了验证,并分析了塘冰温度链观测数据。结果表明:提出的冰厚计算模型可用于精确预测冰盖厚度的生消过程;通过回归分析得到了表面冰温随气温和风速变化的表达式;冰层内的冰温变化与气温波动存在一定的响应关系,且随着冰深增加,冰温波动幅度减小;在冰盖生长期,冰下水体持续降温,随着水深的增加,水温变化速率逐渐减小;在冰盖消融期,水温先缓慢回升随后快速升高,最大升温速率可达0.13℃/d。研究成果可为寒区静冰生消分析及冰厚计算提供科学依据。     

冰温度膨胀力的有限元分析

本文在对冰温度膨胀力的作用机理作简要分析的基础上，将有限元方法引入到冰温度膨胀力的计算中，对工程中常见的两类边界条件(即固定约束和摩擦约束)下的冰温度膨胀力进行了计算。通过对计算结果的分析，得到以下结论：从与现场实测数据的比较来看，有限元计算的结果比较合理。可以在设计中应用；冰盖一侧固定约束、另一侧摩擦约束时。冰作用于固定约束边上的膨胀力会产生高度的应力集中；两侧都是摩擦约束的膨胀力远小于其它约束时的冰膨胀力；温升率对直立墙上冰膨胀力沿冰厚分布的影响远大于对斜坡的影响。     

骤然降温作用下混凝土箱形渡槽横向温度应力分析

阐述了箱形渡槽横向温度应力产生的原因,根据箱形渡槽的温度边界特点,给出了箱形渡槽骤然降温的温差分布形式,并将箱身横向温度应力分成板厚范围内非线性温差自约束应力和箱身横向框架约束应力两部分,按照温度自约束应力的平衡特点和等效线性化的原则,导出了横向自约束应力和非线性温差分布修正系数的计算公式。对深圳水库渡槽的计算表明:骤然降温作用下混凝土箱形渡槽槽身外表面将产生可观的横向温度应力,会导致槽身混凝土出现纵向裂缝,应通过施加横向预应力,提高其抗裂能力。     

利用现场观测和力学试验确定设计冰力学参数

以斜坡结构物二维冰力计算公式为理论依据,给出平原水库设计所需要的冰力学参数的合理取值。通过开展水库冬季冰面现场观测,得到冰层第二次爬坡发生时的等效应变速率、典型冰温;结合大量的冰力学性质的试验研究,给出在护坡工程中最不利条件下,即冰层第二次爬坡时水库冰弯曲强度、弹性模量及冰与护坡材料间动摩擦系数的设计取值。     

混凝土温度裂缝产生原因与防止措施

1 混凝土裂缝产生的原因混凝土在凝结硬化过程中,水泥水化反应产生的水化热会使混凝土温度升高。对于厚大体积混凝土,由于散热条件差,产生大量的水化热积蓄在混凝土块体内部,从而使其明显升温,混凝土温度的变化,会使混凝土产生温度变形。若此变形受到约束,必将产生温度应力。如果此应力为拉应力,且超过混凝土的抗拉强度时,混凝土就会产生温度裂缝。     

大体积混凝土温度裂缝观测及分析

试验结合闸墩混凝土温度裂缝控导研究,进行现场混凝土温度和应变观测.依据观测结果,分析了大体积混凝土早期温度和应变的分布及变化规律,混凝土中心层和表面层应变与温差的变化关系.计算结果表明,由于温度应力大于混凝土实际抗拉强度,导致混凝土产生裂缝.表层混凝土应变实测值与理论计算值结果相近,变化趋势相同.     

大体积混凝土裂缝的成因及防治措施

水利工程施工期间或在其运行期间,大体积混凝土会产生收缩裂缝,产生裂缝的原因很多,如:受内外温度差和外部约束的影响,大体积混凝土结构产生温度应力和应变,此种应力与应变如果超过混凝土结构的承受极限,就会产生温度裂缝。笔者结合多年工作经验,分析了大体积混凝土产生裂缝的原因,并结合工程案例探讨了温控防裂的措施。     

Full-scale investigations of high concrete dams under rigorous climatic conditions

Conclusions An evaluation of the operation and condition of large hydraulic structures under rigorous climatic conditions can be accomplished by means of full-scale investigations and observations. This includes investigations of the temperature regime, stresses, cracking, opening of joints, displacements, of the structure and rock foundation, and percolation and ice regimes. Full-scale investigations and observations on the Mamakan, Bukhtarma, Ust'-Kamenogorsk, Bratsk, and Krasnoyarsk dams revealed a quite considerable role of thermal effects on the static operation of structures located in a rigorous climatic zone: on their stress state, displacements, and percolation. Simultaneously difficulties were revealed in the performance of full-scale investigations related with the specific operating conditions. The experience obtained showed that a number of problems of the method and equipment of full-scale investigations and observations under rigorous climatic conditions require further elaboration. Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 10, pp. 23–28, October, 1974.     

横观各向同性岩体地基中赋存裂纹断裂力学分析

采用无双材料对偶边界元方法分析了半无限横观各向同性岩体地基中赋存的正方形裂纹,裂 纹面上作用着法向均布力,横观各向同性岩体地基的各向同性面平行于半无限域自由面。数值计算得 到了该类裂纹的应力强度因子值。根据数值结果讨论了横观各向同性岩体地基弹性参数、裂纹面对各 向同性面的倾角赋存裂纹应力强度因子的影响。结果表明,岩体地基弹性系数、裂纹面对各向同性面的 倾角对裂尖应力强度因子有明显影响。在弹性系数中,弹性模量对应力强度因子的影响最为敏感。     

Quantifying the influence of cold water intrusions in a shallow,coastal system across contrasting years: Green Bay,Lake Michigan

We present water column thermal structure for two climatically different years: 2012, which experienced abnormally warm spring and summer air temperatures preceded by a relatively low ice winter and 2013, which experienced cooler than average spring and average summer air temperatures and preceded by average ice conditions. Mean bottom water temperatures for the season and during cold water intrusions were significantly warmer in 2012 than 2013 leading to a significantly reduced stratified season in 2012. Cold water intrusions were driven into southern Green Bay by southerly winds while intrusions were terminated when winds switched to persistent northerly winds. 2012 observed a significant increase in northerly winds relative to 2013, decreasing cold water intrusion presence and duration but winds did not fully explain the difference in thermal conditions for southern Green Bay. These cold bottom waters drive stratification in polymictic southern Green Bay while dimictic waters were found to have significantly warmer bottom temperatures during 2012 and a deeper mixed layer. Our observations suggest that relatively shallow (<20?m), seasonally stratified systems may not increase in stratification strength and duration under a warming climate; rather, changing wind climatology and surface heat flux can inform the degree to which the mixing regime can be expected to change and impact stratification and thermal structure of coastal systems. We discuss the biogeochemical implications of different thermal regimes, particularly within the context of multiple drivers of physical water column structure in eutrophic, stratified coastal systems.     

The influence of dynamic ice formation on hydraulic heterogeneity in steep streams

During winter, different types of ice formation are commonly observed in northern boreal stream systems. Although largely overlooked today, river ice has profound effects on in‐stream hydraulics and therefore ice processes should be considered in freshwater stream management and assessment. In particular, limited knowledge exists about the impacts of dynamic ice formation on stream environments. Results presented from the changes of in‐stream heterogeneity in three steep stream environments caused by dynamic ice formation demonstrate that the formation of anchor ice and anchor ice dams may induce significant backwater effects by increasing wetted areas (maximum 43%) and water depths (maximum 241%) and reducing water velocities (maximum 70%); independent of minimal changes in discharge. Consequently, stream environments are transformed from fast‐flow to slow‐flow areas, even on a short temporal scale (<12 h). Furthermore, the anchor ice build‐up initiated static (surface) ice formation due to reduced local water velocities upstream ice dams. Thus, dynamic ice formation plays a key role in the balanced ice regime in steep stream environments and contributes largely to stable static ice cover in these environments. Observations from the present study suggest that the current paradigm emphasizing the role of discharge as the main controller of in‐stream heterogeneity may call for a modification in steep streams that experience seasonal ice formation. This is particularly important if future hydraulic‐/habitat models and assessment tools are to be implemented in freshwater management to realistically characterize steep stream environments in cold climate regions on a seasonal scale. Copyright © 2009 John Wiley & Sons, Ltd.     

A modeling study of ice–water processes for Lake Erie applying coupled ice-circulation models

A hydrodynamic model that includes ice processes and is optimized for parallel processing was configured for Lake Erie in order to study the ice–water coupling processes in the lake. A hindcast from April 2003 to December 2004 with hourly atmospheric forcing was conducted. The model reproduced the seasonal variation of ice cover, but the development of ice extent in January and its decay in March somewhat preceded the observations. Modeled lake circulation in ice-free seasons is consistent with previous studies for Lake Erie. Thermal structure of the lake was reasonably comparable to both satellite-derived observations and in-situ measurements, with mean differences ranging from − 2 °C to 4 °C, depending on the season. The impacts of ice–water stress coupling and basal melting of ice were examined based on numerical experiments. The results show that: 1) ice–water stress coupling significantly dampens the subjacent lake circulation in winter due to packed ice cover that slows down the surface water, and 2) basal melting of ice contributes to widespread ice cover in the lake. The demonstrated model validity could lead to further studies of ice–water processes in the lake, including interannual variation and impacts on ecosystems.     

Development of the Great Lakes Ice-circulation Model (GLIM): Application to Lake Erie in 2003–2004

To simulate ice and water circulation in Lake Erie over a yearly cycle, a Great Lakes Ice-circulation Model (GLIM) was developed by applying a Coupled Ice-Ocean Model (CIOM) with a 2-km resolution grid. The hourly surface wind stress and thermodynamic forcings for input into the GLIM are derived from meteorological measurements interpolated onto the 2-km model grids. The seasonal cycles for ice concentration, thickness, velocity, and other variables are well reproduced in the 2003/04 ice season. Satellite measurements of ice cover were used to validate GLIM with a mean bias deviation (MBD) of 7.4%. The seasonal cycle for lake surface temperature is well reproduced in comparison to the satellite measurements with a MBD of 1.5%. Additional sensitivity experiments further confirm the important impacts of ice cover on lake water temperature and water level variations. Furthermore, a period including an extreme cooling (due to a cold air outbreak) and an extreme warming event in February 2004 was examined to test GLIM's response to rapidly-changing synoptic forcing.     

基于应力空间变换的原状软土本构模型

根据原状土的高刚度、明显的非线性和各向异性特点，给出了原状土的应力空间和应力增量变换公式。在变换应力空间，屈服面、边界面只能在允许的应力空间中运动(等向硬化或运动硬化)，从而合理地反映了土体各向异性与应力路径的影响.借助边界面与损伤的概念建立了可以反映原状软土从小应变到大应变的力学特性的本构模型.土体弹性变形用横观各向同性模型来描述，提出了一种新的边界面与加卸载准则，它同时考虑了塑性体应变与塑性剪应变对原状土体结构性的损伤.与有关试验结果对比表明，本模型是合理的。     

基于梁单元的薄壁筒桩与土相互作用分析

用三维梁单元模拟混凝土薄壁筒桩的受力变形特征,用薄层接触面单元模拟桩与土体之间的相互作用,薄壁圆筒表面上的结点线位移用梁单元出口结点的线位移和转角位移表示,根据静力平衡条件提出了由接触面约束内力和桩上作用荷载求解桩体内力的计算公式,从而建立了桩土相互作用的有限元分析方法。对某工程薄壁筒桩在水平荷载作用下的桩体变形和内力进行分析,并与现场试验结果进行了比较,结果表明上述分析方法是正确的。     

基于应变能的拱坝体型优化设计

考虑静力荷载作用下双曲拱坝的安全性，对最大主拉应力、拉应力区范围、整体安全度和抗屈折稳定等安全指标进行了综合分析。提出以坝体应变能指标作为拱坝体型优化的安全目标函数，建立拱坝体型优化设计模型并采用进化策略进行求解。以白鹤滩拱坝为例，优化体型与初始体型相比，体积方量减少1.58万m3，坝体应变能、最大主拉应力、最大主压应力以及位移等结构响应量都得到了降低，优化效果明显。     

A three-dimensional model of Lake Superior with ice and biogeochemistry

The formation of winter ice on Lake Superior has been shown to be important in determining the annual thermal cycle of the lake and long-term trends of surface water temperature increase. However, modeling studies of Lake Superior to date have not included dynamic and thermodynamic ice cover. These physical characteristics of the lake in turn can have significant impacts on biogeochemical cycling within the lake. We present a new three-dimensional model of Lake Superior that includes a dynamic and thermodynamic ice model and a biogeochemical model. Results from the model forced by observed meteorological conditions for the period 1985 to 2008 are discussed and compared with available observations. Modeled long-term interannual trends in increasing water temperature and decreasing ice cover are compared with observed rates. In the model, total annual gross primary productivity is found to correlate positively with mean annual temperature and negatively with mean winter ice-cover magnitude.