液化土层对地表加速度反应谱的影响   总被引：4，自引：0，他引：4  

孙锐  袁晓铭 《世界地震工程》2004,20(3):33-38

采用一种改进的有效应力方法研究土层液化对地表加速度反应谱的影响，分析中考虑了砂层的厚度、埋深和输入地震波的幅值和波型等因素。分析结果表明，土层液化使地表加速度反应谱的特征周期至少延长0．1秒以上，使原Ⅱ类场地变为Ⅲ类场地，高烈度时易变成Ⅳ类场地，反应谱中周期0．8秒-1．0秒是液化砂层加震或减震的一个分界点，液化对反应谱短周期分量具有一定的减震作用，而对长周期分量有非常显著的放大作用。  相似文献   

Resolution Sensitivity and Scaling of Large-Eddy Simulations of the Stable Boundary Layer   总被引：1，自引：5，他引：1  

Robert J. Beare  Malcolm K. Macvean 《Boundary-Layer Meteorology》2004,112(2):257-281

Large-eddy simulations (LES) of the continuously turbulent quasi-equilibrium stable boundary layer (SBL) are conducted with grid lengths in the range of 12.5 m to 2 m, in order to explore resolution sensitivity, and determine at what point grid convergence occurs. The structure of the mean potential temperature, winds, and turbulent fluxes varies significantly over this resolution range. The highest resolution simulations show a significant degree of convergence. The dimensionless momentum diffusivity asymptotes to a value of 0.06, corresponding to a limiting flux Richardson number of 0.15.Using the converged simulations, some scaling hypotheses underpinning first-order and second-order closure models are revisited. The effective Richardson number stability functions of the LES are compared with the forms often used in numerical weather prediction (NWP). The mixing implied by the LES is less than that used in NWP. The commonly used similarity profiles for heat and momentum fluxes, and the scalings for dissipation and pressure covariances are compared with the LES. This information could provide guidance for the next generation of SBL parametrization schemes.  相似文献   

Laboratory and Numerical Studies of the Convective Boundary Layer Capped by a Strong Inversion     

Yuji Ohya  Takanori Uchida 《Boundary-Layer Meteorology》2004,112(2):223-240

The convective boundary layer (CBL) with a wide range of stability is simulated experimentally using a thermally stratified wind tunnel, and numerically by direct numerical simulation (DNS). The turbulence structures and flow characteristics of various CBL flows, capped by a strong temperature inversion and affected by surface shear, are investigated. The various vertical profiles of turbulence statistics similar to those from the observed CBL in the field are successfully simulated in both the wind-tunnel experiment and in DNS. The comparison of the wind-tunnel data and DNS results with those of atmospheric observations and water-tank studies shows the crucial dependence of the turbulence statistics in the upper part of the layer on the strength of the inversion layer, as well as the modification of the CBL turbulence regime by the surface shear.  相似文献   

Large-Eddy Simulations of the Baroclinic Mixed Layer     

Zbigniew Sorbjan 《Boundary-Layer Meteorology》2004,112(1):57-80

The effects of baroclinicity, imposed on the dry mixed layer by the presenceof large-scale, horizontal temperature gradients, have been investigated basedon a large-eddy simulation model. The purpose of this investigation is to examinesimultaneous impacts of thermal stratification and shear in the atmospheric boundarylayer. For this purpose, five cases are considered – one barotropic, and four baroclinic.Based on the performed simulations, a new parametrization of the interfacial layer isproposed. The parameterization employs new interfacial scaling, which is valid at thetop of the mixed layer. In terms of new scales, dimensionless moments characterizingturbulence at the top of the shearless mixed layer are universal constants. In the shearedcase, dimensionless statistics of turbulence are shown to be functions of the interfacialRichardson number.  相似文献   

Countergradient Fluxes of Conserved Variables in the Clear convective and Stratocumulus-topped Boundary Layer: The role of the Entrainment Flux     

Stephan R. de Roode  Harm J. J. Jonker  Peter G. Duynkerke  Bjorn Stevens 《Boundary-Layer Meteorology》2004,112(1):179-196

Large-eddy simulations of a clear convective boundary layer (CBL)and a stratocumulus-topped boundary layer are studied. Bottom-upand a top-down scalars were included in the simulations, and theprinciple of linear superposition of variables was applied toreconstruct the fields of any arbitrary conserved variable.This approach allows a systematic analysis of countergradient fluxesas a function of the flux ratio, which is defined as the ratio betweenthe entrainment flux and the surface flux of the conserved quantity.In general, the turbulent flux of an arbitrary conserved quantityis counter to the mean vertical gradient if the heights where thevertical flux and the mean vertical gradient change sign do notcoincide. The regime where the flux is countergradient is thereforebounded by the so-called zero-flux and zero-gradient heights. Becausethe vertical flux changes sign only if the entrainment flux has anopposite sign to the surface flux, countergradient fluxes arepredominantly found for negative flux ratios. In the CBL the fluxratio for the virtual potential temperature is, to a good approximation,constant, and equal to -0.2. Only if the moisture contribution to thevirtual potential temperature is negligibly small will the flux ratio forthe potential temperature be equal to this value. Otherwise, theflux ratio for the potential temperature can have any arbitrary(negative) value, and, as a consequence, the fluxes for thepotential temperature and the virtual potential temperature willbe countergradient at different heights. As a practical application ofthe results, vertical profiles of the countergradient correction termfor different entrainment-to-surface-flux ratios are discussed.  相似文献   

Composition and Assemblage Characteristics of Magnetic Minerals in Layer S_(5-1) of Xifeng and Duanjiapo Sections     

贾蓉芬  彭先芝  周正  刘德汉  王冠鑫  王德强 《中国地球化学学报》2004,23(3)

Magneticmineralsintheloess paleosolseriesaccountforabout 1 % -2 %ofthetotal (LiuTungshengandZhangZhonghu ,1 962 ) .Duetotheiraerolianorigin ,themagneticmineralsarecomplicatedincomposition ,largeingrainsizerange ,andsignificantlydifferentincrystallinity .Asaresult,researchonthesemagneticmineralswouldbesetwithalotofdifficulties.Previousre searchersemployedopticalmicroscopic ,X raydiffractionandM ssbauerspectrometrictechniquestostudythemagneticmineralsintheloess paleosolseries,andchieflyontheb…  相似文献   

山区三维地震勘探大时差静校正及时深转换     

何黄生  陈光明刘威周峰岩  陈国忠 《中国煤田地质》2004,16(2):34-36

山地煤矿采区地形条件复杂，正确进行大时差静校正是处理好二维地震勘探资料的重要一环。大时差静校正会改变煤层反射波时间(t0)及双曲线特征，为减小校正误差，需设立一个CMP面，将校正量分为高频分量和CMP校正量。在地形高差变化剧烈的山地，不能用高于地表面的统一基准面为零线进行时深转换，须进行充填层时差(△t)校正，将统一基准面校正到地表面，再以地表面为零线进行时深转换成图。以便准确无误的展示煤层赋存形态，提高构造图精度。  相似文献   

Simulation of oasis breeze circulation in the arid region of the Northwestern China   总被引：2，自引：0，他引：2  

U Shihua  AN Xingqin  CHEN Yüchun 《中国科学D辑(英文版)》2004,47(Z1)

In this paper, the process of oasis-desert circulation (ODC) is simulated by MM5V3.5 model through designing an ideal oasis-desert scheme and assuming that initial atmosphere is at rest (V = 0). The findings showed that the key of forming special oasis boundary structure is the difference of energy and water between oasis and desert. The evaporation of oasis surface consumes heat energy, and the low temperature of oasis causes an oasis breeze circulation (OBC), which drives an ODC with a downdraft over the oasis and an updraft over the desert. Later, the cold, dry and stable boundary over oasis is gradually formed, on the contrary,the atmospheric boundary over desert on the edge of oasis is hot, humid and unstable and its height is about 600 hPa. The updraft over the desert forms a wet ring that acts as a vertical wall weakening the low-level moisture exchange between the oasis and desert. The downdraft of OBC increases the atmospheric stability that reduces the oasis evaporation. The low-level outflow from the oasis (into the desert) prevents the dry, hot air flowing from the desert into the oasis.Thus an oasis self-preservation mechanism may be formed due to OBC. The horizontal area influenced by oasis is twice as oasis area and the vertical range is four times as oasis. The ODC is strong in the daytime and reaches the strongest at 17:00, and the influenced area is the largest at 20:00.  相似文献   

The effect of an interface boundary layer on the resonance properties of a buried structure     

Y. S. Karinski  V. V. Shershnev  D. Z. Yankelevsky 《地震工程与结构动力学》2004,33(2):227-247

This paper presents a model for the analysis of the diffraction of plane waves at a cavity in an infinite homogeneous linear elastic medium supported by a segmented lining. An elastic boundary layer is introduced between the cavity lining and the infinite medium. The boundary layer is simulated by ‘elastic boundary conditions’ in which the stress is proportional to the relative displacement of the lining and of the surrounding medium boundary. A closed‐form analytical solution of the problem was obtained using the Fourier–Bessel series, the convergence of which was proven. It was shown that the number of series terms required to obtain a desired level of accuracy can be determined in advance. Using amplitude–frequency response analysis it was shown that the boundary layer produces additional ‘pseudo‐resonance’ frequencies that depend on the layer properties. These frequencies are almost identical to the eigenvalues obtained from the simple analysis of a segmented elastically supported lining. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

土壤的冷生构造及其对阿拉斯加土地利用的意义     

C. L Ping  M.T. Jorgeson  Y.L. Shur 《冰川冻土》2004,26(Z1):1-7

Cryogenic structure (patterns made by ice inclusions) in seasonally frozen and permafrost-af-fected soils result from ice formation during freezing. Analysis of cryogenic structures in soils is essential to our understanding of the cryogenic processes in soils and to formulating land use management interpretations. When soils freeze, the freezing front moves downward and attracts water moving upward resulting in mainly horizontal lenticular ice formation. Platy and lenticular soil structures form between ice lenses in upper active layer. The reticular soil structure usually forms above the permafrost table caused by freeze-back of the permafrost. The upward freeze-back resulted in platy soil structure and the volume changes following the annual freeze-thaw cycle resulted in vertical cracks. The combined result is an ice-net formation with mineral soils embedded in the ice net. The upper permafrost layer that used to be a part of the active layer has an ice content exceeding 50% due to repeated freeze-thaw cycles over time. The mineral soils appear in blocks embedded in an ice matrix. The permafrost layer that never experienced the freeze-thaw cycle often consists of alternate layers of thin ice lens and frozen soils with extreme hard consistence and has relatively lower ice content than the ice-rich layer of the upper permafrost. Ice contents and thaw settling potentials associated with each cryogenic structure should be considered in engineering and land use interpretations.  相似文献