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41.
Aerodynamic Parameters of Regular Arrays of Rectangular Blocks with Various Geometries 总被引：8，自引：8，他引：0
The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic
parameters characterising arrays—the drag coefficient (C
d
), roughness length (z
o) and displacement height (d)—are used for analysis. C
d
is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are
estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63
arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of
the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated
C
d
and z
o of the staggered arrays peak against the plan area index (λ
p
) and frontal area index (λ
f
), in contrast with values for the square arrays, which are less sensitive to λ
p
and λ
f
. In addition, the square arrays with a wind direction of 45° have a considerably larger C
d
, and the wind direction increases z
o/H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z
o is more remarkable when λ
f
exceeds 20%, and the discrepancy in z
o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C
d
is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity
of the heights of buildings on urban aerodynamic parameters vary greatly with λ
p
and λ
f
; hence, these effects should be taken into account by considering the roughness packing density. 相似文献
42.
Constraining slip rates and spacings for active normal faults 总被引：1，自引：0，他引：1
Numerous observations of extensional provinces indicate that neighbouring faults commonly slip at different rates and, moreover, may be active over different time intervals. These published observations include variations in slip rate measured along-strike of a fault array or fault zone, as well as significant across-strike differences in the timing and rates of movement on faults that have a similar orientation with respect to the regional stress field. Here we review published examples from the western USA, the North Sea, and central Greece, and present new data from the Italian Apennines that support the idea that such variations are systematic and thus to some extent predictable. The basis for the prediction is that: (1) the way in which a fault grows is fundamentally controlled by the ratio of maximum displacement to length, and (2) the regional strain rate must remain approximately constant through time. We show how data on fault lengths and displacements can be used to model the observed patterns of long-term slip rate where measured values are sparse. Specifically, we estimate the magnitude of spatial variation in slip rate along-strike and relate it to the across-strike spacing between active faults. 相似文献
43.
基于Ｂｉｏｔ的饱和孔隙弹性介质的运动方程和利用复变函数方法，本文研究了无限饱水孔隙弹性空间中由常速运动源所产生的位移场。考虑了两种类型源：ａ．沿无限空间水平轴运动的斜向集中力源；ｂ．运动双力偶源。关于力源的运动速度，考虑了４种情形：ａ．力源的运动速度Ｕ小于饱水孔隙弹性介质的三种体波速度一亚音速情形；ｂ．速度Ｕ小于介质的第一纵波过度和横波速度，但大于第二纵波速度─—弱跨音速情形；ｃ．速度Ｕ小于第一纵波速度，但大于横波速度和第二级波速度─—强跨音速情形；ｄ．速度Ｕ大于介质的所有三种体波速度─—超音速情形。结果表明，在跨音达和超音速情形里，解呈现出与力源相联系的平面冲击波特征，位移出现了相应的跳跃。 相似文献
44.
45.
Grumusols (Vertisols), though having a uniformly high clay content with depth, commonly exhibit a coarsening upward in the sand fraction, either of skeletal grains or of nodules. The non-uniform way in which the wetting front advances in swelling clay soils, with preferred advance and swelling around the coarse grains, produces upward directional forces and uplifting of the grains, thus producing the observed textural differentiation in the coarse fraction. From observations of slickenside distribution in the profile, and using published data on the ratio of lateral to vertical stresses and swelling pressure distribution with depth, a concept of optimum depth for slickensides is developed. Generally at 150–200cm, below the depth of cracking, this depth depends in part on climatic conditions. Below the optimal depth increased overburden pressure and smaller moisture variations restrain the extent of swelling and deformation, above it drying produces cracks and obliterates large slickensides, though a strong bimasepic microfabric remains. The extent of intrapedonic turbation was estimated from measurements of the volume of cracks and of surface material falling into the cracks. It indicates a turnover time of several hundred to a few thousand of years. This agrees with the known increase of radiocarbon ages of organic matter (MRT) with depth which in Vertisols (Grumusols) is only slightly slower than in non-turbating Udolls (Chernozems) and Udalfs (Lessivés). The moderate rate of homogenization due to intrapedonic turbation does not prevent the development of a normal organic carbon profile and it is slower than the upswelling of coarse grains by upward directional forces. The development of shear planes and slickenside structures is a rapid process and not dependent on turbation. 相似文献
46.
Existing empirical models for estimating liquefaction-induced lateral spread displacement (DLL) have been derived from a dataset poorly distributed with respect to earthquake magnitude and source distance, and also produced from different tectonic source types and faulting mechanisms. Both the poor distribution and mixed tectonic source types and faulting mechanisms of the data have an adverse impact on the reliability of the empirical models. To overcome these problems in the development of empirical models, we replace the direct use of magnitude and source distance with pseudo-displacement derived from spectral acceleration attenuation models that are well supported by earthquake data, and use a modification factor to account for effects of the non-linear soil response. Attenuation models derived from very large and reasonably well-balanced datasets have been selected, one being a Japanese attenuation model and other being a combination of the Sadigh et al. model and the Youngs et al. model. These models are capable of accounting for the effects of earthquake tectonic source type and faulting mechanism. We determined the model coefficients by selecting the pseudo-displacements calculated for a number of spectral periods to achieve an unbiased distribution of residuals with respect to earthquake magnitude and source distance. Sensitivity analyses have been carried out based on the new and existing models, and show that the new model is more robust than the existing models. Comparison with a limited number of data from the 1997 Kocaeli, Turkey earthquake suggests our model provides comparable liquefaction-induced lateral displacement DLL estimates. 相似文献
47.
除了深、大断裂等复杂断层以外，研究一般断层都需利用岩层、岩脉等各自的迹线。迹线的产状实质上是空间二斜面相交线的产状，属于立体几何学等数学范畴。地质上早就用赤平投影等方法估测。本文中数学计算方法是对前人方法的补充，精度可高达分、秒。介绍的产状网虽属估测，但制作简便。求解断层两盘相对运动力和总断距等的方法，美国有毕令斯的画法几何，前苏联有莫尔恰诺夫和瓦依涅尔曼的图解分析法。本文的迹线计算法避免了繁杂的作图过程，而所得结果和美、苏方法相同。
文章还对断层擦痕、牵引褶皱及断层旁侧派生的节理能否指示相对运动，提出新见。 相似文献
48.
49.
50.
弹性位错理论是研究地震震源正演和反演的重要工具之一. 单相介质位错理论求得的地面变形场是稳定的、不变的，而实际地震后的地面变形场是变化的. 本文利用集中力作用下无限空间中两相饱和介质Green函数的柱函数表达式，通过弹性运动方程积分解的Helmholtz方程的Hansen矢量变换，再叠加自由表面影响场的方法求得两相饱和介质半无限空间位错位移场. 本文结果结合Nur的DD模式，在进水排水的假说下能解释地震后地面变形场的变化. 相似文献