A 3D BEM-FEM methodology for simulation of high speed train induced vibrations

This work presents an efficient methodology for the analysis of vibrations in a railroad track system, induced by the passage of conventional and high-speed trains. To this end the Boundary Element Method is used to model the soil-tie system within the framework of impulse response techniques. Conventional Finite Element Methods along with Newmark's integration is used for the modeling of the rail system. The two methods are coupled at the tie-rail interface and the solution is obtained following a staggered, time marching scheme in an efficient manner. The methodology accounts for Soil-Structure Interaction and traveling wave effects. In addition, this work identifies the parameters that affect the efficient modeling of railroad track systems as they pertain to the proposed solution methodology.     

Effects of spatially structured vegetation patterns on hillslope erosion in a semiarid Mediterranean environment: a simulation study

A general trend of decreasing soil loss rates with increasing vegetation cover fraction is widely accepted. Field observations and experimental work, however, show that the form of the cover‐erosion function can vary considerably, in particular for low cover conditions that prevail on arid and semiarid hillslopes. In this paper the structured spatial distribution of the vegetation cover and associated soil attributes is proposed as one of the possible causes of variation in cover–erosion relationships, in particular in dryland environments where patchy vegetation covers are common. A simulation approach was used to test the hypothesis that hillslope discharge and soil loss could be affected by variation in the spatial correlation structure of coupled vegetation cover and soil patterns alone. The Limburg Soil Erosion Model (LISEM) was parameterized and verified for a small catchment with discontinuous vegetation cover at Rambla Honda, SE Spain. Using the same parameter sets LISEM was subsequently used to simulate water and sediment fluxes on 1 ha hypothetical hillslopes with simulated spatial distributions of vegetation and soil parameters. Storms of constant rainfall intensity in the range of 30–70 mm h^?1 and 10–30 min duration were applied. To quantify the effect of the spatial correlation structure of the vegetation and soil patterns, predicted discharge and soil loss rates from hillslopes with spatially structured distributions of vegetation and soil parameters were compared with those from hillslopes with spatially uniform distributions. The results showed that the spatial organization of bare and vegetated surfaces alone can have a substantial impact on predicted storm discharge and erosion. In general, water and sediment yields from hillslopes with spatially structured distributions of vegetation and soil parameters were greater than from identical hillslopes with spatially uniform distributions. Within a storm the effect of spatially structured vegetation and soil patterns was observed to be highly dynamic, and to depend on rainfall intensity and slope gradient. Copyright © 2005 John Wiley & Sons, Ltd.     

Studies on wind environment around high buildings in urban areas

High buildings or architectural complex in urban areas remarkably distort the urban surface wind fields. As the air flow approaches,local strong wind may appear around the buildings. The strong wind makes the pedestrians on sidewalks, entrances and terrace very uncomfortable and causes the pedestrian level wind environment problem. In this studies, hot-wire wind measurement, wind scouring in wind tunnel and numerical computation were carried out to evaluate the wind environment of tall buildings in the prevailing flow conditions in Beijing areas. The results obtained by three techniques were compared and mutually verified. The conclusions drawn from three approaches agree with each other. Also the advantages and limitations of each method were analyzed. It is suggested that the combination of different techniques may produce better assessment of wind environment around high buildings.     

Analysis of pressuremeter geometry effects in clay using critical state models

The conventional interpretation methods of pressuremeter testing effectively approximate pressuremeter membranes as infinitely long. As a result, the effects of the two‐dimensional geometry of pressuremeters are ignored, leading to an overestimation of soil shear strength by pressuremeter testing, as demonstrated in several previous studies. This paper presents results of a numerical study of two‐dimensional geometry effects on self‐boring pressuremeter tests in undrained clay. The results are obtained using critical state soil models with an effective stress formulation. This is in contrast to most (if not all) existing studies on pressuremeter geometry effects, which were based on perfectly plastic soil models (e.g. Yu (Cavity expansion theory and its application to the analysis of pressuremeters. DPhil Thesis, The University of Oxford, 1990), Yeung and Carter (Proc. 3rd Int. Symp. on Pressuremeters, 1990), and Houlsby and Carter (Géotechnique, 1993; 43 (4):567–576)). The present study suggests that the overestimation of soil strength due to the neglect of finite pressuremeter length is significantly affected by the soil model used in the calculations. It is found that for clays with a high overconsolidation ratio (OCR) the strength overestimation predicted using critical state soil models could be considerably smaller than that predicted using perfectly plastic soil models. The main conclusion of this numerical study is that care must be exercised before directly applying any numerically determined pressuremeter geometry correction factors in practice. Copyright © 2005 John Wiley & Sons, Ltd.     

太原盆地地下水资源模拟研究

山西省太原盆地由于地下水长期超采,引发了地下水降落漏斗、地面沉降等环境地质问题。通过GMS建立地下水水流三维数值模型,基于模型预测了现状开采条件下地下水水位的变化趋势,并提出合理利用地下水资源的措施,为地下水资源的优化管理提供科学依据。     

多级次地下水流系统的最小能耗率原理初探

20世纪60年代初期,Tóth基于定水头上边界条件推导出解析解,得出多级次地下水流系统,是水文地质学里程碑式的突破,成功地解决了一系列理论和实际问题。但Tóth解析解存在的缺陷也长期沿袭：单纯重视数学模拟而忽视物理机制;将地形控制地下水位看成是普适性规律;忽视给定水头上边界数学模拟的失真。这些缺陷,尤其是忽视物理机制探究,不仅妨碍Tóth理论自身发展,而且导致地下水流系统理论尚未被国际水文地质界普遍接受。参照河流动力学中应用的最小能耗率原理,类比提出地下水流最小能耗率的表达式。基于已有的通量上边界地下水流模式数值模拟结果,进一步探究物理机制,归纳得出地下水流系统遵循最小能耗率原理的结论。     

河北省北部晶质石墨矿层岩(矿)石地球化学特征与成因分析

晶质石墨是一种新兴战略矿产。近年在河北省北部发现了多处大中型晶质石墨矿床,主要赋矿层位于新太古代崇礼上岩群、古元古代红旗营子岩群等,具有良好的成矿潜力。通过系统的野外地质调查与采样、分析测试工作,详细研究了赋矿层位的岩相学、地球化学特征,并对碳质来源进行了分析。结果表明:赋矿岩石主要为含石墨黑云斜长变粒岩、片麻岩与透辉岩,原岩恢复以砂泥质碎屑岩、钙质沉积岩为主。主量元素含量变化较大, SiO₂含量为38.90%～80.42%, CaO+MgO为2.05%～31.93%, Al₂O₃为1.50%～15.34%;稀土元素含量为79.1～321.4μg/g, PAAS标准化分布模式一般具有右倾或较平坦分布特征, δCe略具负异常,部分具有δEu异常。微量元素特征指示沉积环境为滨浅海环境,部分地区存在富氧条件,局部为还原环境或存在热液加入。石墨中碳同位素值为–26.0‰～–20.7‰,主要来源于生物成因有机碳;大理岩碳同位素值为–3.8‰～1.1‰,主要来源于碳酸盐岩成因无机碳。区内晶质石墨矿层分布受到地层、岩性、岩相控制,含矿...     

雄安至北京大兴国际机场快线起步区地下段结构抗浮设防水位取值研究

抗浮设防水位直接影响到地下结构的安全与建设费用,在地下结构建设中至关重要,因此,科学合理地确定地下结构的抗浮设防水位具有巨大的社会意义和经济价值。本文以“雄安新区至北京大大兴国际机场快线地下工程段”为研究对象,系统分析了研究区水文地质条件以及地下水位年内年际动态变化规律,利用数值模拟法和类比预测法确定了地下结构抗浮设防水位标高建议值。结果表明,该场地区域浅层地下水水位埋深一般为5.0～20.0m,地下水水位标高一般为–10.0～1.0m。近五年场地浅层地下水水位标高一般为–5～–10 m,埋深一般为3.0～15.0 m,地下水位逐年升高,回升速率约1.0 m/a。地下结构抗浮设防水位标高取值建议取使用期抗浮设防水位采用数值模拟法预测结果。该成果服务了“雄安新区至北京大兴国际机场快线(R1线)”项目场地抗浮设计,为雄安新区重大工程建设项目的抗浮安全设计提供了示范。     

国内外常用的空气质量模式介绍

人们对空气污染问题的关注促进了空气质量数值模式的发展。至今,空气质量模式已经发展了三代。目前,国内外常用的模式有ISC3,ADMS,AERMOD,Models-3,CAPPS等。应该根据实际问题的需求选择合适的模式。