三峡工程大江截流水文科技工作综述     

季学武 《水文》1999,(1):2-5

长江三峡工程大江截流的水文泥沙实时信息与预报成果是大江截流优化设计、科学研究,安全度汛,施工组织和调度决策的重要依据。长江水利委员会水文局根据与中国长江三峡开发总公司鉴定的合同,在总结葛洲坝等工程截流经验的基础上,创造性地应用当今世界上可靠、先进的技术,创建了三峡大江截流水文泥沙监测系统和龙口水文预报模型,及时提供了各项水文信息预报成果,技术资料齐全,成果可靠,圆满地完成了合同所确定的各项任务,为  相似文献   

Formation stability after hydraulic fracturing     

Panos Papanastasiou 《国际地质力学数值与分析法杂志》1999,23(15):1927-1944

This paper investigates stress changes resulting from fracturing in a weak formation and estimates the reduced risk of formation failure. The analysis is based on fracture propagation and closure of a plane strain elasto–plastic fracture. It is shown that during fracture propagation the area near the fracture tip undergoes plastic deformation, with the result that the in situ stresses there are significantly reduced from the original compressive state. The stress relief is driven by the reduction of the minimum in situ stress and the consistency condition which requires the stress state to remain on the yield or failure envelope. After fracture closure, due to permanent deformation the stress state does not return to its original state, as in the case of elastic material. The risk of formation failure, which is quantified with the introduction of a yield factor, is significantly reduced after fracturing and closure. The residual width from plastic deformation results in a non-uniform closure stress on proppant with higher values near the tip and lower value near the wellbore which is detrimental to the stability of proppant. The closure stress becomes more uniform with increasing fracture length. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Late Triassic initial closure of the Mongol-Okhotsk Ocean in the western segment: Constraints from sedimentological,detrital zircon ages and paleomagnetic evidence     

《Gondwana Research》2024

The Mesozoic evolution of the Mongol-Okhotsk Ocean (MOO) has significantly affected the configuration of the modern Asian continent. Although a scissor-like closure of the MOO has long been proposed, when and how the MOO closed are still hotly debated, especially the timing of initial closure of the MOO in its western segment, hindering our understanding of both the evolution of the MOO and tectonics of the northern Asian continent. In order to uncover the timing of initial closure of the MOO, we performed a multidisciplinary study in sedimentology, detrital zircon U-Pb dating and paleomagnetic on the Late Triassic clastic strata from the Tarvagatay Block and the Amuria Block (AMB) on the both sides of the Mongol-Okhotsk Suture. The upper Triassic strata on both sides of the suture were dominated by plant fossil-bearing alluvial-fluvial facies sediments, which unconformably overlain pre-Triassic geological units, indicating a terrestrial setting after the closure of the MOO. Detrital zircon U-Pb dating results revealed consistent age distribution patterns for samples from both sides of the suture with a predominant peak at ∼253–251 Ma and a secondary peak at ∼359–357 Ma, representing two main arc magmatic events during the bidirectional subduction of the MOO in the Late Devonian-Early Carboniferous and Late Permian-Early Triassic. Coeval Late Triassic paleomagnetic poles were obtained from the northern AMB and Tarvagatay Block, revealing a comparable paleolatitude of the AMB (∼31–33°) and Tarvagatay Block (∼32–34°) in the Late Triassic, arguing for that the western segment of the MOO should have closed at the Late Triassic. The compilation of sedimentology, detrital zircon U-Pb dating, magmatic and paleomagnetic evidence provides integrated constraints on the Late Triassic initial closure of the MOO in its western segment.  相似文献   

河口大型围垦工程中龙口水动力特点     

潘丽红  朱建荣  俞相成  赵楠 《海洋工程》2010,28(1)

河口大型围垦工程围区吞吐潮量大,河口滩势条件复杂,龙口位置选择和极值流速确定是工程设计中的关键环节。以两个典型河口大型围垦工程龙口为例,从水动力分析角度提出合理的龙口平面选址和龙口渡汛时因地制宜的结构布置。在青草沙水库工程中,龙口位置的确定充分利用围区原有深槽的过流能力,以保证库区内外及时水交换,并兼顾到围堤实施顺序与工程区整体河势环境相协调,避免口门进出水引起工程河段滩地的大冲大淤,也确保了堤基安全。龙口渡汛需要面临长时间大潮汛过流考验,龙口流速大小决定了龙口结构的保护方案和后期的合龙方案,常规使用的堰流计算方法能较为准确地计算龙口流量和断面平均流速过程,数值模型能对大型龙口流速空间分布情况进行很好的模拟,是常规计算方法的重要补充。计算结果表明口门横向上中心流速大于口门两侧流速,在纵向上底坡内外两侧顶角处水流受重力作用加强,垂向断面收缩,在涨、落急时刻分别形成大流速区,是龙口结构布置时重点抗冲保护区域,需要设置抗冲性较强、自重大且联接牢固的护面材料。此外,同一潮周期内涨急流速通常大于落急流速也是其重要水动力特点。  相似文献   

近海区域二阶紊流封闭模型的比较研究   总被引：1，自引：0，他引：1  

张卓  宋志尧  孔俊 《海洋通报》2010,29(1)

将雷诺应力方程不同封闭方式归结为稳定函数的差异,并以此作为区分标准,总结了6种国内外采用过的稳定函数并以统一的形式列出,分析不同紊流模型稳定函数的分布和影响因素,并且通过实验资料进行了比较分析,发现(1)2000年后提出的3种稳定函数得到的临界理查德森数大于2000年前的3种,更符合实际情况,这与其在压强应变相关项和浮力相关项中增加了旋转效应和重分布效应有关;(2)尽管这3种模型考虑的因素更加全面,但在某些特定场合下,如边界层,与实验的吻合程度反不如前3种较早的稳定函数,反映了封闭模型本身存在的缺陷。最后,提出了二阶紊流封闭模型还待解决的问题。  相似文献