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971.
岩体材料的各向异性导致其中的光滑裂纹在扩展后会变为折线裂纹。对于折线裂纹,其折线处裂纹面外法线方向不惟一,不能用连续单元离散。为此,在光滑裂纹问题方法的基础上,引入4种新的不连续单元来离散折线处裂纹面,建立了适用于折线裂纹问题的对偶边界元方法,该方法基于横观各向同性基本解。算例验证表明,该方法具有较好的精度。最后用该方法分析了横观各向同性岩体中的折线裂纹,得到了该类裂纹的应力强度因子。当裂纹面上作用法向均布力,横观各向同性岩体介质中的矩形光滑裂纹发生弯折时,折线两侧的裂纹面在张开时存在抑制效应,从而导致折线裂纹裂尖应力强度因子小于原光滑裂纹。同时还发现,随裂纹面的逐渐弯折,其裂纹面对各向同性面的倾角发生变化,因此,其裂尖断裂特性还受到岩体各向异性的影响。 相似文献
972.
利用傅里叶级数计算任意函数形式的弹性纵波垂直通过非线性结构面的透射波和反射波的速度波形。采用双曲模型描述结构面的变形特性,基于位移不连续模型,结合波振面处动量守恒定律,推导了弹性纵波垂直通过非线性结构面的基本方程。假设应力波在含结构面岩体中传播时,结构面的存在不改变应力波波形函数的最小正周期,运用傅里叶级数理论和周期延拓方法,得到了任意函数形式的弹性纵波垂直入射时透射波和反射波速度波形的傅里叶级数解,并验证了傅里叶级数解是合理的。利用傅里叶级数解,分析了单一频率的正弦谐波入射至结构面时,透射波中各阶谐波的振幅和相位与谐波阶数的关系。研究结果表明,各阶谐波的振幅与阶数呈负指数关系衰减,前7阶谐波振幅的衰减指数为谐波阶数的二次函数,当谐波阶数大于7时,衰减指数为谐波阶数的一次函数;各阶谐波的相位与谐波阶数呈线性关系。 相似文献
973.
昆明大板桥岩溶地下水系统污染边界及其防污性能研究 总被引:2,自引:2,他引:0
大板桥岩溶地下水系统是滇东断陷盆地区较典型的裸露—覆盖型岩溶地下水系统,文章中定义了岩溶地下水系统污染边界,进行了大板桥岩溶地下水系统分级,即大板桥裸露—覆盖型岩溶水一级系统及横山—龙泉寺裸露型子系统和大板桥—阿地村覆盖型子系统两个二级子系统,确定了大板桥岩溶地下水系统侧向边界、裸露区顶界、裸露型子系统与覆盖型子系统的边界及覆盖区顶界四种裸露—覆盖型岩溶地下水系统污染边界,并对边界防污性能进行了研究,认为裸露区顶界防污性能弱、裸露型子系统与覆盖型子系统的侧向边界防污性能较弱,覆盖区顶界防污性能强。 相似文献
974.
The objective of the study presented herein is to develop an understanding of the predictive trends of four different liquefaction severity index frameworks, with emphasis on the utility of the frameworks for assessing liquefaction vulnerability in Christchurch, New Zealand. Liquefaction induced land damage was widespread following the four major earthquakes in Christchurch (Mw 5.9–7.1) between 4 September 2010 and 23 December 2011. As part of the rebuilding effort, a major focus, to date, has been on assessing/developing approaches for evaluating vulnerability to liquefaction induced damage in future events. The four liquefaction severity index frameworks that are evaluated herein are: the one-dimensional volumetric reconsolidation settlement (SV1D), the Liquefaction Potential Index (LPI), and two new liquefaction severity indices developed following the major earthquakes in Christchurch, namely the Ishihara inspired LPI (LPIISH) and the Liquefaction Severity Number (LSN). To assess the predictive trends of the four severity index frameworks, the H1–H2 boundary curves developed by Ishihara (1985) are used as a reference of comparison. In large part, the severity index frameworks serve the same purpose as the Ishihara boundary curves, but they alleviate some of the difficulties in implementing the Ishihara boundary curves for assessing the highly stratified soil profiles that underlie much of Christchurch. A parametric study was performed wherein relatively simple soil profiles are evaluated using all the procedures and contour plots of calculated SV1D, LPI, LPIISH, and LSN values were superimposed onto the Ishihara boundary curves. The results indicate that the LPIISH and LSN indices yield similar trends as the Ishihara boundary curves, whereas the SV1D and LPI indices do not. Furthermore, little field data is available to assess the severity indices for the scenarios where the trends in the LPIISH and LSN indices differ. 相似文献
975.
Optimizing layout of pumping well in irrigation district for groundwater sustainable use in northwest China 总被引:1,自引:0,他引:1 下载免费PDF全文
Optimizing layout of pumping well plays a vital role in curbing the groundwater level decline. A novel optimization model is presented in this study. First, the optimal well number is obtained by taking into account factors of local economy and environment based on nonlinear programming model. Then, the well spatial layout assessment model is attained based on information entropy weight and technique for order preference by similarity to ideal solution (TOPSIS). After that, the relative closeness to positive ideal solution of alternative (ci) on the rationality of well spatial layout in cultivated land is calculated, and a set of alternatives are ranked according to the descending order of ci. Finally, the well optimization layout is obtained by combining the optimal well number with well spatial layout assessment result based on the GIS data of pumping wells. As a case study, this method was applied in Yongchang Irrigation District of Shiyang River Basin, the arid region of northwest China. Results show that under the conditions of sustainable use of water resources, the irrigation district needed 724 wells for irrigation, with a decrease of 31.0% when compared with the existing number of wells. The wells with low flow rate and operating efficiency distributed in high density where groundwater is over‐exploitation were recommended to be closed. This well optimization layout method is expected to play a significant role in helping make plans for exploiting groundwater at more sustainable level, curbing the groundwater level decline trend, and improving the local ecological environment. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
976.
采用规则网格有限差分方法对二维平面弹性波动方程进行差分离散,得到相应的弹性波动方程的有限差分方程,再将弹性波动方程的差分格式与吸收边界、自由边界的离散形式结合形成弹性波动方程有限差分方程解决问题的主体,将其应用于含方形凹陷半无限非均匀介质的模型中进行数值模拟,得到此离散化模型中不同时刻不同节点的位移值。针对具体算例,运用上述方法结合科学计算软件MATLAB和结果后处理软件DIFEM ISOLINE PLOTER得到不同时刻的水平方向位移等值线图与接收器测量点处的合成位移记录,讨论非均匀介质、吸收边界、方形凹陷等对波动特性的影响。 相似文献
977.
978.
The base of the Campanian Stage does not have a ratified Global Stratotype Section and Point (GSSP); however, several potential boundary markers have been proposed including the base of the Scaphites leei III ammonite Zone and the base of the paleomagnetic Chron C33r. Calcareous nannofossil assemblages from the Smoky Hill Member of the Niobrara Formation in the central Western Interior Seaway, USA were analyzed from two localities to determine relevant biohorizons and their relationships to these potential boundary markers. In a previous study, the Aristocrat Angus 12-8 core (Colorado) was astrochronologically dated and constrained using macrofossil zonations and radiometric ages. The Smoky Hill Member type area (Kansas) provides an expanded interval with good to excellent nannofossil preservation.Five biohorizons are useful for recognition of the Santonian/Campanian transition within the Smoky Hill Member type area, and three are useful in the Aristocrat Angus 12-8 core. The first occurrences (FOs) of Aspidolithus parcus parcus and Aspidolithus parcus constrictus, as well as the last occurrences (LOs) of Zeugrhabdotus moulladei, Helicolithus trabeculatus specimens larger than 7 μm, and Zeugrhabdotus biperforatus are in close stratigraphic proximity to the base of the Scaphites leei III Zone and the base of Chron C33r. 相似文献
979.
A two-and-a-half-dimensional (2.5-D) coupled finite element–boundary element (FE–BE) model is presented to simulate the three-dimensional dynamic interaction between saturated soils and structures with longitudinally invariant geometries. A regularized 2.5-D boundary integral equation for saturated porous media is derived that avoids the evaluation of singular traction integrals. The 2.5-D coupled FE–BE model is established by using the continuity conditions on the soil–structure interface. The developed model is verified through comparison with an existing semi-analytical method. Two case studies of a tunnel embedded in a poroelastic half-space and the efficiency of a vibration isolating screen are presented. 相似文献
980.
Conodont species Iapetognathus fluctivagus and Iapetonudus ibexensis are documented for the first time from Australia. The former is the primary marker internationally defining the base of the Ordovician, and the latter is also a distinctive species previously recorded only from the base of the Ordovician in North America. Both species were recovered from a single sample in the Kandie Tank Limestone of the Kayrunnera Group, located about 50 km west of White Cliffs in far western New South Wales. Other species recovered from this sample include Prooneotodus spp., Cordylodus lindstromi, Cordylodus proavus, Hirsutodontus simplex, Teridontus nakamurai and Variabiloconus sp. Recognition of the Iapetognathus fluctivagus Biozone in the Kandie Tank Limestone supports its correlation with the Green Point section (Global Stratigraphic Section and Point for the base of the Ordovician) in western Newfoundland and the Lawson Cove section of Utah (Auxiliary Stratigraphic Section and Point), as well as sections in Asia and South America. Review of other sections in Australia and elsewhere spanning the Cambrian–Ordovician boundary confirms that, in the absence of I. fluctivagus, the presence of C. lindstromi is a good proxy for this level. 相似文献