The vertical transport of air pollutants by convective clouds. Part III: Transport features of different cloud systems

The vertical transport features of gaseous pollutants, with a negative exponent profile of concentration, by dif-ferent types of convective cloud systems are numerically investigated by using a two-dimensional, reactionless convective cloud transport model. The results show that an isolated, weak storm is able to pump pollutant gas out PBL and transport it to the mid-troposphere, whereas a deep, intense thunderstorm can very efficiently transport air pollutants up to the mid and upper troposphere and laterally spread with anvil, forming an extensive concentration surge layer at altitude of ten-odd kilometers altitude. Each type of convective transport results in concentration re-duction in PBL. In a wind shear environment the transport efficiency of deep thunderstorm significantly increases and the pollutants enter into clouds on the downshear side at low-level and spread downwind in anvil layer. On the other hand, for a cumulus cloud with plenty of liquid water, the gas dissolution effect is increased, and the irreversible aqueous reactions, in extreme, may significantly weaken the vertical transports of pollutant gases even with solubility coefficients no more than 103 M atm-1.     

The practice of fast conditional simulations through the LU decomposition of the covariance matrix

The LU-matrix approach to conditional simulations allows fast generation of large numbers of realizations for a given stochastic process. Simplicity, flexibility, and quality are its main advantages. Its implementation for cases where dense grids and/or large numbers of conditioning data cause computational problems is discussed. A case study is presented.     

Weathering rates of sandstone in a semi-arid environment (Hunter Valley,Australia)

The rate of sandstone weathering in the semi-arid climate of the Hunter Valley, New South Wales, Australia has been estimated from observations of gravestone weathering in the area. The gravestone data points to two distinct stages in the weathering process. The first stage covering the first century of exposure is characterised by a relatively low recession rate of 0.5 mm/100 years. This is followed by a second stage in which the rate of weathering increases sharply to ca 2.5 mm/100 years. The non-linear nature of the weathering trends over time suggests that during the first century of exposure, structural changes took place within the sandstone material, which lay the foundation for accelerated weathering after further exposure. Laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region. Of the four processes examined, only the freeze–thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region.     

基于CFD技术的陡峭山体风场模拟方法研究

为更好将计算流体力学(CFD)技术应用于陡峭山体的风场模拟研究,文中对其中两个关键技术问题进行了研究,一是适宜的CFD解域顶高问题,二是入流边界条件设置方法问题。研究采用了香港国际机场的多普勒雷达径向速度观测资料,通过CFD模拟结果与观测结果对比验证展开研究。对于解域顶高,一般环境流体力学或建筑风工程领域要求顶高越高越好,例如5倍于地面障碍物的垂直高度,究其原因,主要是为了获得地面障碍物周边的整个流场结构,避免顶边界过低影响障碍物顶部流场的准确性。通过数值试验发现,若模拟关心的区域为较低海拔高度时,不必完全拘泥于该要求,对一座高度为1000m量级的山体进行模拟,顶高为3000和6000m的两组试验在边界层中低部给出的模拟结果没有显著差别。进行了3组边界条件设置方法的对比试验,结果表明单纯采用廓线法不足以充分描述来流信息,二维插值法尽管提供了更高分辨率的边界数据,但其结果总体上逊于0维插值法。研究表明,CFD可以很好地描述山地激发的涡旋/波动脱体运动,比单纯采用中尺度模式效果要好得多。在利用CFD工具研究复杂山地风场时,应本着"实用主义"的精神设置物理模型、参数和选取适当的方法、边界条件,以达到模拟精度和计算量的优化平衡,并足以用于研究所关心的具体问题。     

NUMERICAL SIMULATIONS OF β-GYRES IN TROPICAL CYCLONES

1INTRODUCTIONEversincethe1940抯,thetropicalcyclone(TC)hasbeenviewedasapointvortexorrigidvortex.Thepredictionissummedupasoneforairflowintheambientfield.Themethodusuallysucceeds.Thesteeringtheoryfortheairflowbecomesitstheoreticalfoundation.Thoughwithsomesuccess,theactualtrackofTCmovementcanbemuchdeviatedfromthesteeringcurrent,asseeninroutineforecastpractice.Withoutmuchchangesintheambientsteeringcurrent,theTCcanhaveunexpectedchangesinthedirection,speedofmotionorintensity.Atypicalexamplewo…     

A new approach for calculating strain for particulate media

Discrete element modelling is a viable alternative to conventional continuum‐based analysis for analysing problems involving localized deformations of particulate media. However, to aid in the interpretation of the results, it is useful to express the results of discrete element analyses in terms of the continuum parameters of stress and strain. A number of homogenization methods have been proposed to calculate strain in discrete systems; however, two significant limitations of these methods remain. First, none of these methods incorporate particle rotation effects satisfactorily, although significant particle rotation occurs in shear bands in both physical tests and numerical simulations of granular materials. Additionally, observations of the particle displacement fields in shear bands in granular materials indicate that the displacements within the localizations are erratic. Consequently, existing linear, local interpolation approaches produce substantial variations in the strain values calculated in adjacent elements in the region of localization, hindering clear visualization of the strain localization as it evolves. A new method of domain discretization for calculating strain is proposed. This method is capable of capturing particle rotation and employs a non‐local meshfree interpolation procedure capable of smoothing the erratic displacements in strain localizations, which better defines their evolution. The proposed method is validated for problems involving both two and three dimensions. A number of methods are compared with the proposed method and pertinent insights are made. Copyright © 2003 John Wiley & Sons, Ltd.     

热带印度洋持续暖海温对东亚初夏大气环流影响的数值研究

用改进的CCM1(R15L12)气候模式，模拟研究了1991年热带印度洋持续暖海温对东亚初夏季节大气环流的影响。结果表明，热带印度洋海温持续偏暖有利于初夏高原上空大气增温，从而有利于热带东风急流的发展北移和东亚南支西风急流的北跳，并引起5月份西太平洋副热带高压明显加强北抬。印度洋暖海温还引起初夏东亚大陆温度场回升。对南半球越赤道气流发展和南海夏季风的加强起到积极作用。上述特征加速了东亚初夏季节转换过程，有利于江淮梅雨较早发生。     

Seismic hazard zonation of Catalonia, Spain, integrating random uncertainties

In order to analyse the seismic hazard inCatalonia a new parametric earthquakedataset, in terms of macroseismicintensities, has been used. A newseismotectonic zonation of the area understudy and surrounding regions, which takesinto account the geologic and seismic data,is proposed. From these input data, anestimation of the seismicity of the variousseismotectonic zones has been carried outusing both stationary andnon-stationary models. As seismicity doesnot show important non-stationarities, ahazard analysis, has been carried out withthe parameters from the stationary model. Asensitivity study, using the Montecarlotechnique shows relatively smalluncertainties. For each point of thestudied area the maximum likely feltintensity was also considered. A seismichazard map combining the probabilistic anddeterministic models integratinguncertainties resulting from sensitivityanalysis is proposed.     

中国大陆科学钻探孔区反射地震剖面的数值模拟与分析

本初步分析了苏鲁超高压变质带大陆科学钻探孔区的地震波速度结构，在此基础上对在东海孔区三维反射地震勘探过井孔的NNW-SSE主剖面和该周围地区的DH99二维反射地震剖面进行了数值模拟分析。结果表明，数值理论模拟结果与三维反射主剖面地震波到时吻合良好，模拟法能实现有效的时深转换，也表明数值模拟中采用的速度结构是合理的。东海钻井孔区实施反射地震勘测，所得地震记录剖面图是单一P波记录，在超高压变质岩区反射地震记录图中S波的影响甚微。DH99二维反射地震剖面的模拟结果表明东海孔区2000米深度以上的密度，波速结构不随深度加大而变化；而且苏鲁超高压变质岩区地表浅层的地震波速和密度较高，是高速高密地区。岩心结果反映的反射地震阻抗差大的地段，数值模拟的理论剖面上强反射面与孔区反射地震剖面图中的强反射体基本吻合．它意味着在非沉积层的结晶岩区，反射地震勘测手段是研究地下复杂结构的有效方法。数值模拟方法可以进一步提取地震反射记录信息，是利用地震反射方法研究地球构造的一种有效的方法。     

Lateral and consolidation behaviors of seabed-type breakwater for very soft ground

A seabed-type of breakwater applicable to very soft ground without the need for soil improvement is newly developed. This type of soft-ground breakwater is expected to ensure sufficient lateral resistance and prevent excessive consolidation settlement due to self-weight of the breakwater. In this paper, lateral and consolidation behaviors of soft-ground breakwater were investigated by performing model tests and finite element simulations. The results revealed that the bottom wall and buoyant box, which are the main features of soft-ground breakwater, contribute to the increase in lateral resistance and to the control of the consolidation settlements, respectively, and that Terzaghi's consolidation theory could be conservatively adopted in deriving the consolidation settlements of soft-ground breakwater proposed herein.