STYLE AND CONSEQUENCE OF STRAIN PARTITION IN THE NORTHEAST MARGIN OF QINGHAI—TIBET PLATEAU     

Shen Xuhui  Ding Guoyu  Tian Qinjian  Wei Kaibo  Chen ZhengweiWT  ”BX 《地学前缘》2000,(Z1)

STYLE AND CONSEQUENCE OF STRAIN PARTITION IN THE NORTHEAST MARGIN OF QINGHAI—TIBET PLATEAU  相似文献   

自适应网格加密求解洞室围岩塑性区   总被引：2，自引：0，他引：2  

王建华  钟俊彬  陈振建 《岩土力学》2000,21(3):201-204

在弹塑性交界面上存在应力跳跃。 将应力跳跃值作为加密网格的准则, 不仅可使应力计算精度大幅度提高, 而且可求出塑性区的形状。 针对塑性区求解这一具体问题, 提出了一种修正的网格加密准则。 通过改变影响围岩塑性区的几个主要影响因素, 进行了大量的数值计算, 结果表明所提出的修正加密准则能正确地求出围岩塑性区的形状和大小。  相似文献   

Coupled computations for an elastic‐perfectly plastic soil using adaptive mesh refinement     

M. A. Hicks 《国际地质力学数值与分析法杂志》2000,24(5):453-476

An adaptive mesh refinement algorithm has been developed for non‐linear computations in geomechanics, based on a smoothed stress–strain finite element formulation. This uses estimates of error in the incremental shear strain invariant to guide the regeneration of unstructured meshes at regular intervals during loading. Following each mesh‐update, no re‐analysis of previous increments with the new mesh is necessary. Algorithm performance has been investigated by analysing a passive earth pressure problem using a linear elastic‐perfectly plastic Mohr–Coulomb soil model. Perfectly drained behaviour has been considered, as have partially drained situations using hydromechanical coupling, while undrained behaviour has been approximated using time steps close to zero. In all cases, mesh adaptivity has been successful in capturing regions of high strain gradient. The results have been compared with analytical solutions. Accurate computations of limit load and shear band orientation have been obtained for a wide range of material dilation angles. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

吉林省矿产资源勘查区块的划分及编号办法     

杨清泉  刘恩锋 《吉林地质》1999,18(1):57-62

矿产资源勘查实行区块登记制度。本文详细说明了区块的划分及编号办法,并对吉林省１：５万图幅安区块办法进行了划分及编号,这对更好地管理吉林省矿产资源勘查项目有重要意义。  相似文献   

基于高阶累积量的自适应波束形成     

赵犁丰  傅坚  刘桂云 《中国海洋大学学报(自然科学版)》2000,30(4)

常规波束形成器仅限于利用信号的二阶统计特性。作者采用高阶累积量估计期望信号的导向矢量 (Steering Vector) ,实现了一种基于高阶累积量的自适应波束形成器 (HCAB)。该波束形成器利用信号的更高阶统计特性 ,减少了对阵列流型的依赖 ,具有较好的容差性 ,能自动跟踪信号。数值模拟实验表明该波束形成器工作良好。  相似文献   

The ALFA Laser Guide Star: Operation and Results     

R. Davies  A. Eckart  W. Hackenberg  T. Ott  D. Butler  M. Kasper  A. Quirrenbach 《Experimental Astronomy》2000,10(1):103-121

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Adaptive Optics on Large Telescopes   总被引：2，自引：0，他引：2  

A. Glindemann  S. Hippler  T. Berkefeld  W. Hackenberg 《Experimental Astronomy》2000,10(1):5-47

Observations withground based telescopes suffer from atmospheric turbulence.Independent of the telescope size the angular resolution inthe visible is equivalent to that of a telescope with adiameter of 10–20 cm. This effect is caused by the turbulentmixing of air with different temperatures in the atmosphere.Thus, the perfect plane wave from a star at infinity isaberrated before it enters the telescope. In the following,we will discuss the physical background of imaging throughturbulence, using Kolmogorov statistics, and the differenttechniques to sense and to correct the wave-front aberrationswith adaptive optics. The requirements for the control loop ofan adaptive optics system are discussed including formulas forthe limiting magnitude of the guide star as a function of thewave-front sensing method, of the quality of the wave-frontsensor camera, and of the degree of correction. Finally, ashort introduction to deformable mirror technology will begiven followed by the presentation of a new method to measureand to distinguish individual turbulent layers in order toincrease the isoplanatic angle.  相似文献   

Decomposition algorithms for system reliability estimation with applications to interdependent lifeline networks          下载免费PDF全文

Roger Paredes  Leonardo Dueñas‐Osorio  Isaac Hernandez‐Fajardo 《地震工程与结构动力学》2018,47(13):2581-2600

Reliability and risk assessment of lifeline systems call for efficient methods that integrate hazard and interdependencies. Such methods are computationally challenged when the probabilistic response of systems is tied to multiple events, as performance quantification requires a large catalog of ground motions. Available methods to address this issue use catalog reductions and importance sampling. However, besides comparisons against baseline Monte Carlo trials in select cases, there is no guarantee that such methods will perform or scale well in practice. This paper proposes a new efficient method for reliability assessment of interdependent lifeline systems, termed RAILS, that considers systemic performance and is particularly effective when dealing with large catalogs of events. RAILS uses the state‐space partition method to estimate systemic reliability with theoretical bounds and, for the first time, supports cyclic interdependencies among lifeline systems. Recycling computations across an entire seismic catalog with RAILS considerably reduces the number of system performance evaluations in seismic performance studies. Also, when performance estimate bounds are not tight, we adopt an importance and stratified sampling method that in our computational experiments is various orders of magnitude more efficient than crude Monte Carlo. We assess the efficiency of RAILS using synthetic networks and illustrate its application to quantify the seismic risk of realistic yet streamlined systems hypothetically located in the San Francisco Bay Region.  相似文献   

Numerical modelling of downstream migrating antidunes          下载免费PDF全文

Nils Reidar B. Olsen 《地球表面变化过程与地形》2017,42(14):2393-2401

A numerical model is presented that compute the geometrical dimensions and movement of downstream migrating antidunes. The model solves the Navier–Stokes equations together with the k‐epsilon turbulence model to find the water flow field over the bedforms. A two‐dimensional width‐averaged grid is used. The bed elevation changes are computed by solving the convection–diffusion equation for suspended sediments and bedload, together with the Engelund–Hansen sediment transport formula. The free surface is computed with an algorithm based on water continuity in the surface cells. Non‐orthogonal adaptive grids were used, moving vertically with the computed location of the bed and the free water surface. The numerical model was tested on data from a physical model study where regular downstream migrating antidunes had been observed. The numerical model started out with a flat bed and the trains of antidunes formed over time. Many of the physical processes observed in earlier studies were replicated by the numerical model. Four dune parameters were computed in the current tests: The antidune wavelength, height and celerity, together with the average water depth. The antidune wavelengths were best predicted with an accuracy of 3 to 8% compared with the measurements. The antidune heights were computed with a deviation of 11 to 25% compared with an empirical formula. The water depths over the antidunes were predicted with an accuracy of 3 to 9% related to the measured values. The average antidune celerity was the parameter with largest deviation: For the coarsest grid it was overpredicted with 37%. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A modelling approach for estimating suspended sediment concentrations for multiple rivers influenced by agriculture     

Zacharie Sirabahenda  André St-Hilaire  Simon C. Courtenay  Ashley Alberto  Michael R. Van Den Heuvel 《水文科学杂志》2017,62(13):2209-2221

A data-driven model based on an adaptive neuro-fuzzy inference system (ANFIS) was tested for the estimation of suspended sediment concentrations within watersheds influenced by agriculture. ANFIS models were developed using different combinations of inputs such as precipitation, streamflow, surface runoff and the watershed vulnerability index. A multi-watershed ANFIS model was also developed combining the datasets from all studied watersheds. The best results were obtained from a combination of precipitation, streamflow and watershed vulnerability index as input variables. Nash-Sutcliffe coefficients were improved for the multi-watershed ANFIS compared to watershed-specific ANFIS models. The introduction of the erosion vulnerability index significantly improved the ability of the ANFIS model to estimate suspended sediment concentrations within the watersheds. Furthermore, the inclusion of this index opens the possibility of using the ANFIS model to investigate the impact of land-use changes on sediment delivery.  相似文献