Forward-modeling of co-evolution of turbidity currents,sediment transport,and cyclic steps in the Rio Muni Basin     

Peng Hu  Yue Li  Chenglin Gong  Wei Li 《国际泥沙研究》2023,38(2):175-190

Previous quantitative studies of field-scale cyclic steps are mostly based on analysis of field data. Such studies have shed light on the erosion/deposition patterns over these morphological features as well as the magnitudes of the turbidity current parameters back estimated using the measured geometry data. However, it remains unclear to what extent such back estimated hydraulic features and erosion/deposition patterns can be numerically reproduced by process-based numerical models. Here, a tw...  相似文献   

钢筋混凝土L形柱分析时平截面假定的适用范围   总被引：5，自引：2，他引：3  

陈娟  陈滔  黄宗明 《地震工程与工程振动》2006,26(1):111-115

本文选取剪跨比和弯扭比这两个影响平截面假定成立的主要参量,在截面层次上以截面应变误差分析作为平截面假定成立的定量判定依据,构件层次上以两种模型得出的柱顶侧向位移误差作为依据,对处于弹性阶段的L形柱平截面假定的适用性进行了探讨,得出了不同受力情况下平截面假定适用的最小剪跨比。  相似文献   

关于滑坡稳定性在滑坡安全系数取值中的作用讨论     

方玉树 《中国地质灾害与防治学报》2007,18(3):149-153

在工程界存在着滑坡安全系数取值应考虑滑坡稳定性高低、对稳定系数较低的滑坡应采用较大的安全系数的思想。考虑滑坡稳定性的具体方式有两种:①考虑滑坡的实际稳定状态或变形情况;②考虑设计工况下的稳定系数。考虑滑坡稳定性的理由也有两种:①变形急剧势必危害较大;②滑坡在治理后的安全储备可用"安全储备系数"(即下滑力按安全系数放大后的剩余下滑力与下滑力不作改变时的剩余下滑力之比)来衡量,而"安全储备系数"存在着随稳定系数的减小而减小的规律。文章的研究表明,滑坡变形越急剧滑坡危害越大的规律是不存在的,滑坡"安全储备系数"既不能衡量滑坡在治理后的安全储备,也不随滑坡稳定系数的减小而减小,滑坡安全系数与稳定系数无关,将安全系数取值与稳定系数大小挂钩会导致诸多不合理现象产生。因此,滑坡安全系数取值不应考虑稳定系数大小。  相似文献   

Sensitivity of the dynamics of volcanic eruption columns to their shape     

Yasuhiro Ishimine 《Bulletin of Volcanology》2006,68(6):516-537

This paper presents a one-dimensional steady-state model to investigate the sensitivity of the dynamics of sustained eruption columns to radius variations with height due to thermal expansion of the entrained air, and decreases in atmospheric pressure with height. In contrast to a number of previous models using an equation known as the entrainment assumption, the new model is based on similarity arguments to derive an equation set equivalent to the model proposed by Woods [Bull Volcanol 50:169–193, 1988]. This approach allows investigation of the effect of gas compressibility on the entrainment rate of ambient air, which has been little examined for a system in which a decrease in pressure significantly affects the density stratification of a compressible fluid. The new model provides results that include two end members: one in which the volume change within the eruption columns affects only the radial expansion without changing the vertical motion, and the other is the converse. The Woods [Bull Volcanol 50:169–193, 1988] model can be regarded as being between those two end members. The range of uncertainty arises because the extremely high temperature of discharged materials from a volcanic vent, and the exceptional terminal height of the eruption columns, allow significant expansion of the gas component in the eruption columns, making them behave differently from common turbulent plumes. This study indicates that the maximum height of the eruption columns is affected considerably by this uncertainty, particularly when the eruption columns extend above a height of 10 km, at which the pressure is about one-fourth the pressure at the ground surface. Column collapse may also be suppressed in wider parameter ranges than previously estimated. However, the uncertainty can be reduced by measuring column radii through a vertical profile during actual volcanic eruptions. Accordingly, this paper suggests that appropriate observation of eruption column shapes is essential for improving our understanding of the dynamics of eruption columns.  相似文献   

边坡框架梁文克尔简化计算方法及工程应用     

陈国周  王建春  林智勇 《地质力学学报》2018,24(6):822-827

为了改进边坡框架梁的计算方法,基于文克尔地基梁假定,考虑框架梁与土体的互相作用,通过关键点拟合的方法,把指数函数和三角函数简化为一元二次函数,推导出边坡框架梁的简化计算公式。该方法被应用于福建一处边坡支护工程,采用锚索框架梁支护,施工过程中对边坡进行位移监测。研究结果表明,传统的文克尔地基梁计算需要求解微分方程,计算过程比较复杂,不适合设计中使用,而简化后的计算方法容易掌握,可以方便计算出框架梁的端部弯矩和跨中弯矩。边坡位移监测结果表明该简化计算方法安全可行。研究结果对边坡框架梁的工程设计有一定的参考作用。   相似文献   

水资源与环境投入产出研究进展及关键问题          下载免费PDF全文

许新宜  杨中文  王红瑞  俞淞  刘虹利 《干旱区地理》2013,36(5):818-830

随着投入产出分析理论不断完善和发展,其应用研究领域不断得到拓展和深化。以投入产出理论发展入手,重点对水资源与环境投入产出研究作评述,提出研究中存在的关键问题。介绍了投入占用产出与灰色投入产出分析理论的提出与发展,两者均是对传统投入产出理论的有效补充和完善。阐述了水资源在区域各部门间的投入产出规律,总结了环境投入产出研究中结合其他分析方法的投入产出模型。大量文献资料显示,在国内外水资源与环境投入产出模型的发展与近期研究中,水资源消耗分析与虚拟水研究是水资源投入产出分析研究热点,环境排污分析与环境影响分析研究是环境投入产出分析的重点。提出并分析了内部技术假设和部门总合对投入产出分析结果的影响,指出该两大关键问题急需探索解决。最后,就投入产出分析研究现状提出几点展望。  相似文献