A MASCOTTE-based characterization of MCSs over Spain, 2000–2002

A 3-year Mesoscale Convective Systems (MCSs) database, which extends from 2000 to 2002, has been built for the Iberian Peninsula and the Balearic Islands using the objective method MASCOTTE (MAximum Spatial COrrelation Technique). It was originally developed to track the evolution of convective systems over the Amazon region; after modifications, it is able to track MCS evolution even with an hour and a half of missed images and provides essential information of both dynamical and morphological characteristics of MCSs. MASCOTTE is tested against a visual and subjective method, and is found to offer advantages such as automation and a simple and efficient operation that make it very useful for building large MCS databases.Thirty-five MCSs were found between June and October, most of them originated along the Mediterranean coast and near the Pyrenees, showing an increasing occurrence from June to September, when the maximum is found. The regions most influenced by MCS occurrences are Balearic Islands, Valencia, Catalonia, Murcia and the Basque Country. The MCSs tend to be small, short-lived and linear, usually moving eastward or northeastward with low velocities.The MCSs-associated precipitation presents high variability, ranging from 80 to 0 mm h⁻¹ as maximum hourly records. Two different convective regions are identified based on MCS behavior in extreme precipitation events: Northern Spain (the Basque Country) with abundant and continuous precipitation regime but little MCS influence, and the Mediterranean coast, where precipitation is sporadic but much more intense.     

格子玻尔兹曼方法及其在大气湍流研究中的应用

文章的目的是对格子玻尔兹曼方法进行系统的介绍，格子玻尔兹曼方法(Lattice Boltzmann Method)的出现直接来源于20世纪60年代的元胞自动机(Cellular Automata)思想，而这一方法用于解决流动现象时，又可以追溯到19世纪的分子运动论，求解的是Boltzmann提出的玻尔兹曼输运方程，因此将这一方法称为格子玻尔兹曼方法，之前也被称为格子气自动机(Lattice Gas Automaton)。该方法多用于研究复杂现象，如材料晶体凝聚时的生长过程、城市土地利用的演化等方面。在20世纪70年代由Hardy、Pomeau和Pazzis建立了第一个用于研究流体运动的格子气自动机，此后，这一方法被广泛用来模拟各种流动问题，诸如二相流、孔隙介质中的渗流等，并根据这一方法开发了相应的商业软件PowerFlow。同时，格子玻尔兹曼方法由于其在微观水平描述运动的特点，成为研究湍流的一个很好的数值计算工具，特别是用其进行直接数值模拟(DNS)计算，成为继传统的差分法、有限体积法和谱方法之后的又一有力的手段。而作为大气运动的一个主要现象的大气湍流，比普通湍流更加复杂，在这里着重介绍了大气湍流的特点和应用格子玻尔兹曼方法模拟湍流的发展过程。     

大埋深条件下降雨入渗补给的初步分析

运用SWAP模型对太行山山前平原--河北省栾城县田间土壤水分运动进行了数值模拟.从土水势及土壤含水量等方面,初步分析了降雨灌溉入渗补给条件下土壤水分运动的规律.通过分析和讨论,探求了大埋深条件下降雨入渗过程,初步揭示了降雨入渗对地下水位变化的影响.     

Reliability analysis of drilled shaft behavior using finite difference method and <Emphasis Type="Italic">Monte Carlo</Emphasis> simulation

Load displacement analysis of drilled shafts can be accomplished by utilizing the “t-z” method, which models soil resistance along the length and tip of the drilled shaft as a series of springs. For non-linear soil springs, the governing differential equation that describes the soil-structure interaction may be discretized into a set of algebraic equations based upon finite difference methods. This system of algebraic equations may be solved to determine the load–displacement behavior of the drilled shaft when subjected to compression or pullout. By combining the finite difference method with Monte Carlo simulation techniques, a probabilistic load–displacement analysis can be conducted. The probabilistic analysis is advantageous compared to standard factor of safety design because uncertainties with the shaft–soil interface and tip properties can be independently quantified. This paper presents a reliability analysis of drilled shaft behavior by combining the finite difference technique for analyzing non-linear load–displacement behavior with Monte Carlo simulation method. As a result we develop probabilistic relationships for drilled shaft design for both total stress (undrained) and effective stress (drained) parameters. The results are presented in the form of factor of safety or resistance factors suitable for serviceability design of drilled shafts.     

A Combined Three-Dimensional Geological-Geostatistical-Numerical Model of Underground Excavations in Rock

Summary. This paper exploits geological and borehole geotechnical data obtained in the exploratory phase of a tunneling project to investigate in a first place if the kriging interpolation scheme may effectively reproduce the spatial variability of rock mass quality (Rock Mass Rating, RMR) in the vicinity of tunnels. For this purpose a quick solver in Fortran has been developed that performs variography analysis of 3D spatial data, fast kriging estimations of RMR between borehole sampling locations at the centroids of the elements of the numerical model, and model validation. For the purpose of an integrated underground excavation design, a step further is made by incorporating into the 3D mechanical numerical model of the rock mass, the three-dimensional (3D) solid geological model, thus coupling the geology with the ground (geotechnical) model (i.e. each element of the numerical model is assigned a geological material). The mechanical properties of each finite difference cell (or Representative Elementary Volume) of the ground model were then prescribed according to its geological type, the spatial heterogeneity of the rock mass expressed quantitatively with the kriging model, and the upscaling calculations of the mechanical properties of the intact rocks determined in the laboratory, based on the size-effect (strength dependence on size) and Damage Theory. Furthermore, a preliminary numerical simulation of the advance of unsupported tunnels in the model of the heterogeneous rock mass was performed for illustration purposes.     

Digital Image Based Approach for Three-Dimensional Mechanical Analysis of Heterogeneous Rocks

Summary This paper presents a digital image based approach for three-dimensional (3-D) numerical simulation and failure analysis of rocks by taking into account the actual 3-D heterogeneity. Digital image techniques are adopted to extract two-dimensional (2-D) material heterogeneity from material surface images. The 2-D image mesostructures are further extrapolated to 3-D cuboid mesostructures by assuming the material surface as a representation of the inner material heterogeneity within a very small depth. The iterative milling and scanning system is set up to generate the 3-D rock mesostructures. A Hong Kong granite specimen is used as an example to demonstrate the procedure of 3-D mesostructure establishment. The mechanical responses and failure process under the conventional Brazilian tensile test condition are examined through numerical analyses. The stress distribution, crack propagation process and failure model of heterogeneous material cases are simulated with a finite difference software. The numerical results indicate that material heterogeneity plays an important role in determining the failure behavior of rocks under external loading.     

西藏波密县古乡沟泥石流模型试验中的模型砂配制

对西藏古乡沟泥石流模型试验中的模型砂配制进行了研究,旨在保证模型试验的合理性和科学性,从而为泥石流灾害防治工程提供可靠的设计依据。通过对泥石流形成区和堆积区样品的粒径分析,根据模型试验的目的和条件,选定模型的几何比尺为1∶100,但模型砂的配制采用泥砂分段模拟法,原型中小于0.1 mm的颗粒不缩小,仍按重量百分比配制;原型中大于0.1 mm的颗粒按相似比尺缩小后用小于0.1 mm模型砂代替。并通过模型样品的选用和粒径组合对泥石流体以及堆积扇的模型砂配制过程进行了详细的分析研究,使模型试验获得了比较好的结果。     

利用天气数值预报产品建立贵州黔西南州分县温度预报方程的方法及应用

利用2002～2004年1～12月EC、T213天气数值产品的温度格点实时分析资料、预报资料以及贵州省黔西南州8个测站观测资料,从160个样本中筛选出相关较好的因子,利用多元回归统计模型,以及根据地理环境,天气形势分型造成的温度差值(ΔT)为逐步订正值,建立黔西南州分县温度预报方程。在2005年11月～2006年2月应用中取得较好效果,预报误差小于±3.0℃,平均误差1.3℃。     

Far-field simulation of the 1946 Aleutian tsunami

We present hydrodynamic far-field simulations of the Aleutian tsunami of 1946 April 1, using both a dislocation source representing a slow earthquake and a dipolar one modelling a large landslide. The earthquake source is derived from the recent seismological study by López and Okal, while the landslide source was previously used to explain the exceptional run-up at Scotch Cap in the near field. The simulations are compared to a field data set previously compiled from testimonies of elderly witnesses at 27 far-field locations principally in the Austral and Marquesas Islands, with additional sites at Pitcairn, Easter and Juan Fernández. We find that the data set is modelled satisfactorily by the dislocation source, while the landslide fails to match the measured amplitudes, and to give a proper rendition of the physical interaction of the wavefield with the shore, in particular at Nuku Hiva, Marquesas. The emerging picture is that the event involved both a very slow earthquake, responsible for the far-field tsunami, and a major landslide explaining the near-field run-up, but with a negligible contribution in the far field.