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1.
对HG-670-13.7-YM9型锅炉再热出口主安全门导汽管弯头频繁发生漏泄原因进行了分析,指出了因温差过大而产生热应力是导致再热出口主安全门导汽管弯头频繁发生漏泄的主要原因,改进后,再热出口主安全门导汽管弯头频繁发生漏泄的现象基本消除。 相似文献
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针对新疆某高地温环境下的圆形隧洞,采用有限元分析程序,分别对不同围岩半径下的温度场分布进行模拟,并以不同围岩半径下围岩与支护接触面处的温度作为围岩合理计算范围取值的参考,结合有关理论分析的结果,确定出围岩最佳计算半径。在此基础上进一步研究隧洞施工期围岩温度、应力和位移场在热—应力耦合作用下的分布问题。研究结果表明,当围岩外部温度为80℃、隧洞内部温度为5℃时,隧洞开挖后考虑温度和应力共同影响下的围岩最佳计算半径为24 m。隧洞围岩温度沿围岩厚度方向呈非线性递增变化。与常温(20℃)情况相比,高地温的存在会使隧洞围岩最大主应力减小,同时也会在隧洞拱顶和底拱处产生拉应力。 相似文献
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彭博 《水资源与水工程学报》2019,30(1):226-231
以往研究针对三维内裂纹在单轴拉伸下的裂纹扩展与三维内裂纹尖端的应力强度因子变化较少,为定量化研究三维内裂纹单轴拉伸下的裂纹扩展与应力强度因子的变化,对不同预制内裂纹角度在拉伸荷载作用下的裂纹扩展规律进行了数值模拟研究,将裂纹扩展过程及最终破坏形态与已有研究进行了对比。计算结果表明:当预制裂纹角度为0°时,预制裂纹呈现自相似扩展,当预制裂纹为其他角度时,预制裂纹尖端出现翼裂纹扩展,预制裂纹角度为15°、30°、45°、60°时,翼裂纹与原预制裂纹分别呈18°、49°、64°与80°;随着预制裂纹与水平方向的角度增大,Ⅰ型应力强度因子逐渐减小,对于同一预制裂纹角度来说,预制裂纹短轴顶点上的Ⅰ型应力强度因子较其他方向要大;随着预制裂纹角度的增大,Ⅱ型应力强度因子整体上先增大后减小;对于同一种预制裂纹角度来说,预制裂纹的左端与右端(对应于距离为0,0. 5,1处)Ⅱ型应力强度因子达到最大,而预制裂纹短轴处顶点(对应于距离为0. 25和0. 75处)Ⅱ型应力强度因子达到最小为0;数值模拟结果与室内试验结果体现出较好的一致性。研究成果为正确认识轴拉情况下的三维裂纹扩展规律提供了一定的参考。 相似文献
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孟贺宗 《南水北调与水利科技(中英文)》1995,(1)
常峪口拱坝坝体下游面存在一长达101.5m的水平裂缝,经电算分析认为其成因有以下2个方面:①坝顶溢流堰加强了其所在拱的刚度,在拱梁协调变位中,拱承担了较大的负向荷载,使拱冠梁在高程1080m处产生了1.11MPa的拉应力,导致裂缝的发生。②坝区气温骤冷骤热,大陆性气候明显,由于坝体传热较慢,坝体温度变化滞后于气温变化,因此在气温骤降时,下游面不能自由收缩,产生温度应力,使裂缝进一步向广深方向发展。 相似文献
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为了解钢管弯头在内水作用下对钢管与PCCP管接头处的影响,确保在内水压力下临近弯头处的承插口处的水平位移值不超过允许限值,通过建立两种理论计算模型与有限元分析模型,对比分析钢管弯头处在内水压力作用下的摩擦力分布范围,探讨摩擦力作用下钢管位移计算方法,并提出此种情况下的设计处理方法。 相似文献
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李丽梅 《水科学与工程技术》2014,(4)
通过对廊涿干渠水平弯头、竖向弯头和检修阀井的抗滑稳定进行分析,得出廊涿干渠管道的抗滑稳定措施.对不满足稳定要求的水平弯头,采用在弯头两端焊接直钢管,并在管顶上0.5m以下范围的管道外与开挖基槽间浇筑C15混凝土镇墩的抗滑稳定措施.管道竖向弯头一般应控制在3°以内,通过接头借转实现.对于穿越公路、河流等埋深较大处的竖向转角宜小于15°,可将斜坡段、弯头与水平钢管焊接为整体,以解决竖向弯头的稳定问题.钢筋混凝土阀井一般可用于截断阀的抗滑镇墩. 相似文献
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一、工程概况东华大桥主桥为118m单孔带蝴蝶型副拱的提篮式钢箱系杆钢管拱桥,桥长119.3m,上跨江门河水道,采用两侧3.9%对称坡,坡顶设在主桥跨中,设半径为4000m,桥面全宽34.5m。主桥两片拱肋均由主拱和副拱组合而成,两主拱脚宽27.66m,拱顶处拱肋间距16.76m,主拱肋向内倾斜13°,主拱构成提篮式拱。主拱攻矢跨比为1/5,为直径1.5m钢管混凝土拱。两副拱向外倾斜10°。 相似文献
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为了研究PVC弯头的局部阻力和水流流态特征,对DN50和DN75两种PVC承插式90°弯头的水流特性利用CFD中的fluent软件进行了数值模拟,结果表明:不同管径弯头的局部阻力系数与雷诺数的关系曲线的变化趋势基本一致,压力在弯头拐角外侧压力最大,在下游管段内侧靠近弯头的位置压力最小。 相似文献
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以西安地铁5号线暗挖隧道为工程背景,采用降水加固与注浆加固2种地层加固措施,建立渗流-应力耦合数值计算模型,对富水黄土隧道地表沉降、洞周土体变形及力学效应进行了研究,并结合现场监测资料进行了验证。结果表明:降水加固隧道施工最大地表沉降是注浆加固的13.7倍,2种加固方案洞周土体变形规律一致,开挖10 d内变形值均达到稳定值的70%~80%左右;注浆加固下洞周土体均为压应力,降水加固开挖过程中在中隔壁及中隔板处土层出现拉应力;注浆加固下衬砌各部位受力均大于降水加固;降水加固塑性区极值是注浆加固的11.3倍,主要分布在两侧拱肩、拱腰及拱脚处;2种加固方案下地表沉降以及洞周土体变形的模拟值与监测值相近且变化规律基本一致。 相似文献
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根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。 相似文献
12.
The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects. 相似文献
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Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river. 相似文献
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In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment. 相似文献
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V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed
in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash
and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers
of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional
components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect
dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system,
configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants
of dry ash utilization and the advantages of producing of size-separated particles are considered.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed. 相似文献