Application of an optimum design technique for determining the coefficient of consolidation by using piezocone test data   总被引：4，自引：0，他引：4  

Y.S. Kim  S.R. Lee  Y.T. Kim 《Computers and Geotechnics》1997,21(4):885-293

For normally consolidated clay, several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation from piezocone test results. However, depending on assumptions and analytical techniques, it could vary considerably, even for a specific degree of consolidation. In this paper a method is proposed to determine a consistent coefficient of consolidation by applying the concept of an optimum design technique over all ranges of the degree of consolidation. Initial excess pore pressure distribution is assumed to be capable of being obtained by the successive spherical cavity expansion theory. The dissipation of pore pressure is simulated by means of a two-dimensional linear-uncoupled axi-symmetric consolidation analysis. The minimization of differences between measured and predicted excess pore pressure was carried out by the BFGS unconstrained optimum design algorithm with a one-dimensional golden section search technique. By analyzing numerical examples and in-situ test results, it was found that the adopted optimum design technique gives consistent and convergent results.  相似文献   

导水裂隙带高度预测途径探讨   总被引：3，自引：0，他引：3  

邹海  桂和荣 《江苏地质》1997,21(2):98-102

导水裂隙带高度是设计防水煤（岩）柱尺寸的主要技术参数，是煤矿防治水工作的重要内容。详细论述了其研究现状及发展趋势，并提出了履岩体地质环境，履岩体力学环境和数值模拟技术三位一体的综合预测评价方法。  相似文献   

Optimal weighting in the finite difference solution of the convection-dispersion equation     

H. Q. Wang  M. Lacroix 《Journal of Hydrology》1997,200(1-4):228-242

Oscillation and numerical dispersion limit the reliability of numerical solutions of the convection-dispersion equation when finite difference methods are used. To eliminate oscillation and reduce the numerical dispersion, an optimal upstream weighting with finite differences is proposed. The optimal values of upstream weighting coefficients numerically obtained are a function of the mesh Peclet number used. The accuracy of the proposed numerical method is tested against two classical problems for which analytical solutions exist. The comparison of the numerical results obtained with different numerical schemes and those obtained by the analytical solutions demonstrates the possibility of a real gain in precision using the proposed optimal weighting method. This gain in precision is verified by interpreting a tracer experiment performed in a laboratory column.  相似文献   

Extreme value theory based on the r largest annual events: a robust approach     

D. J. Dupuis 《Journal of Hydrology》1997,200(1-4):295-306

In Smith (1986, J. Hydrol. 86, 27–43), a family of statistical distributions and estimators for extreme values based on a fixed number r > = 1 of the largest annual events are presented. The method of estimation was numerical maximum likelihood. In this paper, we consider the robust estimation of parameters in such families of distributions. The estimation technique, which is based on optimal B-robust estimates, will assign weights to each observation and give estimates of the parameters based on the data which are well modeled by the distribution. Thus, observations which are not consistent with the proposed distribution can be identified and the validity of the model can be assessed. The method is illustrated on Venice sea level data.  相似文献   

大地电磁二维对称各向异性介质的有限元数值模拟   总被引：5，自引：0，他引：5       下载免费PDF全文

杨长福 《地震工程学报》1997,19(2):27-33

假定垂直轴为二维对称各向异性介质主轴之一，构造走向与另一主轴方向成任一夹角，用伽勒金（Ｇａｌｅｒｋｉｎ）有限元法和矩形网格，优化地合成总体刚度矩阵，使二维各向异性介质的基本方程形成有限元代数方程组，求出各节点场值，并利用ＭＯＭ法求出辅助场，进而求出张量阻抗等响应函数．同时还对有关文献的计算模型进行了数值模拟检验  相似文献   

Numerical Studies with a Regional Atmospheric Climate Model Based on Changes in the Roughness Length for Momentum and Heat Over Antarctica     

C. H. Reijmer  E. Van Meijgaard  M. R. Van Den Broeke 《Boundary-Layer Meteorology》2004,111(2):313-337

A regional atmospheric climate model is used toexamine the effect of changes in the roughnesslengths of momentum (_z0m) and heat (_z0h)on the structure of the lower atmosphere and on thesurface energy fluxes over Antarctica. Fourexperiments were carried out in which _z0mand/or _z0h were altered with respect to acontrol experiment. The changes consisted of (1) alowering of _z0m from a field aggregated froma vegetation map with an orographic correction basedon the European Centre for Medium-Range WeatherForecasts _z0m field, to a constant value of10^-3 m; and (2) a lowering of _z0h from a valueequal to _z0m to a constant value of 10^-3 mor a value dependent on the wind speed via a surfacerenewal model. A reduction of _z0m results in theexpected increase in near-surface wind speed. It alsoresults in an increase in the depth of the layer in whichsouth-easterly near-surface winds prevail, and in adecrease in the strength of the large-scale flow overthe continent, in particular in summer. In theescarpment region a decrease of _z0m is foundto result in too high wind speeds. Surface temperatureson average decrease while atmospheric temperaturesincrease, resulting in an increase of near-surfacestatic stability. Changes in roughness lengths donot significantly change the temperature profiles.The surface fluxes, on average found reduced, aremodelled best by using the _z0h based on thesurface renewal method.  相似文献   

宁南深层岩溶地下水系统三维数值模拟   总被引：2，自引：0，他引：2  

李向全  侯新伟  张莉 《地球科学进展》2004,(Z1)

宁南“南北古脊梁”岩溶裂隙水系统的储水空间以岩溶裂隙为主,岩溶水的空间分布明显受南北向大型断裂构造控制。根据水动力场和水化学场特征,划分了3个相对独立的岩溶水子系统。通过三维数值模拟计算,确定了马渠—洪河岩溶水子系统天然资源量和可开采资源量,为本区的地下水合理开发利用提供了科学依据。  相似文献   

地基GPS气象学研究的主要问题及最新进展   总被引：11，自引：0，他引：11  

宋淑丽  朱文耀  廖新浩 《地球科学进展》2004,19(2):250-259

目前大多数映射函数在低高度角时精度都比较差，发展适应低高度角的映射函数，提高低高度角观测值的利用率，研究大气的水平梯度是目前地基GPS气象学的主要研究任务，发展随时空变化的动态映射函数也是国际上的一个主要研究问题。由于PWV不能提供水汽分布的三维信息，求定GPS信号斜路径方向上的水汽SWV，以及利用SWV层析大气的垂直结构是目前国际上 GPS气象学的研究前沿。文中总结了目前国际上SWV的求定及层析水汽三维结构的主要方法，及存在的问题。把GPS探测的水汽同化到数值天气预报中，以提高数值预报的能力是GPS气象学研究的目的，作者介绍了目前水汽在数值预报模型中的同化情况。另外还回顾了利用GPS观测结果进行全球气候变化和大气折射环境研究的进展。  相似文献   

美国长期生态研究计划：背景、进展和前景   总被引：1，自引：3，他引：1  

赵士洞 《地球科学进展》2004,19(5):840-844

由美国国家科学基金会支持的长期生态研究计划于1980年启动，至今在理论研究、开发技术和服务社会方面都取得了举世瞩目的成就。该计划的发展分为 3个阶段，每一阶段大约为10年。在其发展的第一个阶段，是以研究站所代表的生态系统为研究对象，主要开展了生态系统的过程与格局方面的研究并系统采集和存贮了有关数据；在1990 -2000年的第二个发展阶段中，其研究工作的重点是开展跨站的网络研究和人类活动对生态系统的影响，以揭示生态系统的过程与格局在较大空间尺度上的特征；按照规划，美国长期生态研究计划的发展进入到第三个阶段后，其工作的重点是开展综合研究、进行生态预测和更好地为社会发展服务，同时加强生物多样性的研究和信息学的发展。  相似文献   

The role of diapycnal mixing for the equilibrium response of thermohaline circulation     

Rezwan Mohammmad  Johan Nilsson 《Ocean Dynamics》2004,54(1):54-65

Using a zonally averaged, one-hemispheric numerical model of the thermohaline circulation, the dependence of the overturning strength on the surface equator-to-pole density difference is investigated. It is found that the qualitative behavior of the thermohaline circulation depends crucially on the nature of the small-scale vertical mixing in the interior of the ocean. Two different representations of this process are considered: constant vertical diffusivity and the case where the rate of mixing energy supply is taken to be a fixed quantity, implying that the vertical diffusivity decreases with increasing stability of the water column. When the stability-dependent diffusivity parameterization is applied, a weaker density difference is associated with a stronger circulation, contrary to the results for a fixed diffusivity. A counterintuitive consequence of the stability-dependent mixing is that the poleward atmospheric freshwater flux, which acts to reduce the thermally imposed density contrast, strengthens the thermally dominated circulation and its attendant poleward heat transport. However, for a critical value of the freshwater forcing, the thermally dominated branch of steady states becomes unstable, and is succeeded by strongly time-dependent states that oscillate between phases of forward and partly reversed circulation. When a constant vertical diffusivity is employed, on the other hand, the thermally dominated circulation is replaced by a steady salinity-dominated state with reversed flow. Thus in this model, the features of the vertical mixing are essential for the steady-state response to freshwater forcing as well as for the character of flow that is attained when the thermally dominated circulation becomes unstable.Responsible Editor: Jin-Song von Storch  相似文献