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771.
IntroductionSeismologistsbeganaftershocksequenceinvestigationasearlyasendofthe19thcentury.Theaftershockoccurrencefrequencyhasdifferentmodels,whichincludepowerfunctiondecaymodel(Omori,1894),hyperboladecaymodel(Utsu,1961).Mogi(1962)presentedthattheafter-shockoccurrencefrequencydecayedwithdifferentprinciplesduringdifferenttimephasesaftermainshocks.Henceforthseismologistshavestudiedalargenumberofaftershocksequencesbasedonthesemodels.Chineseseismologistsstudiedthetemporal-spatialcharacteristicsof… 相似文献
772.
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
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
773.
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775.
STUDY ON THE VARIATION IN THE CONFIGURATION OF SUBTROPICAL ANTICYCLONE AND ITS MECHANISM DURING SEASONAL TRANSITION-PART Ⅱ:SEASONAL TRANSITION INDICES OVER THE ASIAN MONSOON REGION 下载免费PDF全文
Based on the studies in Part Ⅰ (see Mao et al.2003),this paper further examines the relationship between the Asian summer monsoon onset and variation in meridional position of the warm temperature ridge with a zonal orientation in mid-upper troposphere.During the Asian monsoon bursting consequentially over the Bay of Bengal,South China Sea,and South Asia,in addition to the reversal of winds in the lower and upper troposphere and deep convection before and after the onset,the atmospheric meridional temperature gradient (MTG) in the vicinity of the ridge-surface of subtropical high (WEB defined in Part Ⅰ) exhibits a significant reversal.Since the establishment of temperature structure with higher over north than over south of the WEB in the mid-upper troposphere (200-500 hPa) characterizes the collective essential that the Asian summer monsoon bursts over different areas,the MTG in mid-upper troposphere,based on the thermodynamics associated with the seasonal transition,should be a reasonable index to measure the Asian monsoon onset.The definition for onset date is proposed,and the time series of onset date for different sections are determined.As compared with the onset dates determined by other indices such as 850-hPa zonal wind and OLR.correlation analyses indicate that the 850-hPa zonal wind is only regional index,but the MTG index is applicable universally to the Asian monsoon regime. 相似文献
776.
In this paper,a comprehensive analysis and review of the advances in the research of human body comfort degree is made.Based on the studies of human thermal equilibrium theories contributed by previous researchers,different apparent temperature models corresponding to different environments are set up in accordance with the current situation and the characteristics of metabolism in different groups of people in China.After case studies and comparison with present dominant human body comfort degree statistical models,it is proved that the apparent temperature models have high rationality and wide adaptability.Furthermore,the comfort scaling standard according to apparent temperature is suggested,which is suitable for the middle latitude regions in China. 相似文献
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778.
对于大多数速度场,地震波沿射线传播的初至波走时,可以用有限差分外推的方法在二维或三维数值网格上计算出来. 在保证精度的条件下,为提高计算效率和适应性,本文推导了基于任意矩形网格和局部平面波前近似的有限差分初至波走时计算方法. 另外,该方法对首波和散射波做了合适的处理,而且不会碰到传统射线法存在的阴影区和焦散区等问题. 简单模型和复杂的Marmousi模型试算的结果表明,该方法精度较高并适用于强纵、横向变速的复杂介质. 基于该方法的Kirchhoff叠前深度偏移, 在主要构造和目的层位置的成像效果上基本达到了波动方程法叠前深度偏移的位置成像效果. 由于未考虑续至波等有效能量,在成像的保幅性上不如波动方程法叠前深度偏移的效果,但其计算效率则明显高于全格林函数法和波动方程法. 相似文献
779.
Resolution Sensitivity and Scaling of Large-Eddy Simulations of the Stable Boundary Layer 总被引:1,自引:5,他引:1
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
780.
Zhengtong Xie Peter R. Voke Paul Hayden Alan G. Robins 《Boundary-Layer Meteorology》2004,111(3):417-440
A family of wall models is proposed that exhibits moresatisfactory performance than previousmodels for the large-eddy simulation (LES) of the turbulentboundary layer over a rough surface.The time and horizontally averaged statistics such asmean vertical profiles of windvelocity, Reynolds stress, turbulent intensities, turbulentkinetic energy and alsospectra are compared with wind-tunnel experimental data.The purpose of the present study is to obtain simulatedturbulent flows that are comparable with wind-tunnelmeasurements for use as the wind environment for thenumerical prediction by LES of source dispersion in theneutral atmospheric boundary layer. 相似文献