CHAMP重力场恢复时域法和空域法比较研究

利用CHAMP数据恢复重力场的解算方法分为时域法和空域法.本文首先介绍了这两种方法恢复CHAMP重力场的基本原理和算法,分析了它们的优缺点.针对空域法中的延拓误差和格网化误差进行了讨论.计算表明:延拓误差中的截断误差部分影响量级约0.001 m2·s-2(均方误差意义下),最大误差仅为0.11 m2·s-2,可完全忽略;延拓误差中的参考重力场模型误差影响随参考场选取的不同而有所差异,整体而言小于0.1 m2·s-2,但最大误差可达1.3 m2·s-2,采用高精度的参考重力场模型能大大减小延拓误差影响.目前最常用的格网化方法包括加权平均方法和最小二乘配置方法,计算表明,利用30天的CHAMP数据进行2°×2°格网化处理,加权平均法的格网化误差在0.13 m2·s-2量级,最大误差可达1.58 m2·s-2,而最小二乘配置法的格网化误差在0.006 m2·s-2量级,最大误差仅为0.15 m2·s-2,明显优于加权平均法.文章最后对时域法和以快速最小二乘配置(FSC)为代表的空域法恢复60阶次的CHAMP重力场的精度进行了比较,结果表明:两种方法的得到的重力场模型精度相差不大,整体而言,时域法略优于空域法.     

Stochastic dynamic response of dam–reservoir–foundation systems to spatially varying earthquake ground motions

In this paper, stochastic dynamic responses of dam–reservoir–foundation systems subjected to spatially varying earthquake ground motions are investigated using the displacement-based fluid finite elements. For this purpose, variable-number-node two-dimensional (2D) fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a computer program SVEM, which is used for stochastic dynamic analysis of solid systems subjected to spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes incoherence, wave-passage and site-response effects. The incoherence effect is examined by considering the Harichandran and Vanmarcke coherency model. The effect of the wave passage is investigated by using various wave velocities. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. The Sar?yar concrete gravity dam, constructed in Turkey is selected for numerical example. The ground motion is described by filtered white noise and applied to each support point of the 2D finite element model of the dam–reservoir–foundation system. The record of Kocaeli earthquake in 1999 is used in the analyses. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for four cases. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic dynamic response of dam–reservoir–foundation systems.     

Fast segmentation algorithms for long hydrometeorological time series

A time series with natural or artificially created inhomogeneities can be segmented into parts with different statistical characteristics. In this study, three algorithms are presented for time series segmentation; the first is based on dynamic programming and the second and the third—the latter being an improved version of the former—are based on the branch‐and‐bound approach. The algorithms divide the time series into segments using the first order statistical moment (average). Tested on real world time series of several hundred or even over a thousand terms the algorithms perform segmentation satisfactorily and fast. Copyright © 2008 John Wiley & Sons, Ltd.     

Inversion of a Lagrangian time domain random walk (TDRW) approach to one-dimensional transport by derivation of the analytical sensitivities to parameters

Lagrangian approaches are well suited to transport in contrasted media but have been considered irrelevant when inversion is envisioned. The randomness of results for the same transport scenario adds to the rough evaluation by perturbation of the sensitivities, yielding an inaccurate search of parameters. It is shown here how a Time Domain Random Walk (TDRW) method can be inverted by deriving the sensitivities analytically. The calculations are very rapid and provide a precise evaluation of the descent directions followed by a Gauss–Newton optimizer. The method handles advection–dispersion + retention by matrix diffusion or sorption with first-order kinetics and proves its worth in all cases. Since analytical sensitivities are available, calculations are rigorous and allow discussing the inversion feasibility, the accuracy of the sought parameters, according to the predominant mechanism involved in the transport scenario.     

基于互相关函数的单孔法波速测试优化算法

土的剪切波速是岩土工程领域的一个重要参数。建筑场地类别划分、地基饱和砂土液化判别、地震反应分析等都依赖于剪切波速,由于其重要性,对它的测定技术和精确程度应重点研究。针对工程中广泛采用的单孔法剪切波速测试,提出了一种基于互相关函数计算土层剪切波速的优化算法。克服了传统数据处理方法中经常遇到的负波速、波速数值明显过大或过小和同一土层各测点波速差别较大等4种不合理因素,提高了数据分析的精度和效率。     

Third-Order Moment Closure Through A Mass-Flux Approach

The parameterization of the third moments, the flux of the heat flux and the flux of the potential temperature variance, is considered. It is shown that present parameterizations of these moments using the mass-flux approach with a `top-hat' profile assumption lead to a significant underestimation, resulting in an inaccurate representation of second moments in the convective boundary layer. It is also shown that the underestimation is a result of the `top-hat' profileassumption in which the sub-plume contributions to the total fluxes are ignored. By including these contributions a new parameterization is proposed, whichsatisfies the physical requirements of symmetry andrealizability, and gives results that are in fair agreement with thelarge-eddy simulation data.     

矿物材料热膨胀定量计算

热膨胀是矿物材料的重要属性之一 ,它的研究在理论和实际应用中都具有非常重要的意义。热膨胀系数的定量计算可分为经验晶体化学方法和理论计算方法。定量计算是一种有效地获得热膨胀系数的方法 ,也是预测不同温度范围热膨胀系数的有效方法 ,通过定量计算获得大部分矿物的热膨胀系数是可能的。经验晶体化学方法只能获得有关矿物的平均热膨胀数据 ,而单纯的理论模型无法适应所有晶体结构的热膨胀系数的计算。建立在理论模型基础上的热膨胀系数的计算必须应用经验晶体化学方法针对不同结构类型进行有效地调整。这样有必要对热膨胀数据进行分类整理 ,在此基础上根据矿物的热膨胀特性对矿物进行分类 ,然后再针对不同矿物类型采用不同的模型进行计算。     

应用切割单元法对海底管道局部冲刷数值模拟

采用SIMPLEC算法的有限体积法,求解非定常流动的N-S方程,采用k-ω紊流模型,通过模拟均匀无粘性推移质的冲刷和淤积,得到海底管道由搁置在海床上的状态变为悬跨状态这一过程的管道周围局部海床冲刷情况,建立了海底管道局部冲刷的二维数值模型。海底管道从搁置在底床上到冲刷悬空的过程中,管道周围的空间产生了拓扑变化,这给采用贴体网格并在计算过程中进行网格重构的传统方法带来了很大困难,而采用切割单元法,把物体轮廓从静止的背景直角坐标结构化网格中切割出去,计算过程中不需要传统意义的网格重构过程。数值模型预测的海底管道周围局部冲刷结果与Mao的物理模型实验实测结果及Liang和Cheng等的数值模拟结果符合较好,验证了模型的准确性。     

地理学区域研究与区域历史地理学的取向

地理学的区域研究传统由来已久,后形成了独立的分支学科——区域地理学,经历了古代地志的分区书写、区域差异的描述解释、空间关系的定量分析和社会过程的深度建构4 个阶段的发展过程。区域地理学演进中遭遇的计量革命与理论创新,实质上是对传统区域学派过分强调区域所导致的静止、孤立的研究僵局的打破与修正,是区域地理学不断总结和完善自身的发展之路。区域历史地理学的学科性质、研究范式与研究内容和方法深受区域地理学的影响和启发,并形成了连续的地理剖面复原研究、区域的景观文化生态研究、区位与结构—功能体系研究和分区分类分级的综合研究等多个分支。与西方相比,中国区域历史地理学的研究在研究内容和方法方面显得比较滞后,今后应加强对特定地方的社会、文化及经济空间的深度剖析,进一步深化人地关系理论及研究方法,不断拓展研究思维的深度和广度,争取有更多、更有影响力的区域历史地理研究成果问世。     

A probabilistic/deterministic approach for the prediction of the sediment transport rate

In this paper we present a probabilistic/deterministic model for the evaluation of the sediment transport rate in a stream. Starting from Einstein’s theory, the approach was obtained by trying to overcome some of the intrinsic limitations. The approach is based on two distinct probability functions, one relevant to the detachment of grains and the second relevant to the length of particle jumps. The sediment transport rate is obtained by integrating the distribution of the ranges of the particle jumps multiplied by the average particle velocity. The relationship for the average ranges of particle jumps is an opportune combination of the Einstein and Yalin expressions. The final formulation was calibrated by means of a large number of experimental data and also by comparison with some of the most widely-used empirical formulas. The results show a better agreement between theory and experiments than do the other theories analyzed.