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971.
In this article, an open channel flow resistance equation, deduced applying dimensional analysis and incomplete self-similarity condition for the flow velocity distribution, was tested using measurements carried out in a full-scale channel equipped with three types of riparian plants (Salix alba L., Salix caprea L. and Alnus glutinosa L.). In the experimental channel, having banks lined with boulders, the vegetation branches were anchored in a concrete bottom. For each species, the measurements were carried out with plants having different amounts of leaves, different plant density and plant area index. The relationship between the scale factor Γ of the velocity profile and the Froude number was separately calibrated by measurements carried out without and with vegetation. The component of Darcy-Weisbach friction factor corresponding to the riparian vegetation fv was calculated as the difference between the measured friction factor value (channel grain roughness + vegetation) and that calculated for the channel without vegetation in the same hydraulic conditions. Using these fv values, the relationship between the scale factor Γ and the Froude number was calibrated. In this last relationship, a scaling coefficient a varying with the investigated vegetation type was introduced. This coefficient, as expected, gives the highest friction factor values for vegetation having branches with leaves. The theoretical flow resistance law, coupled with the relationship for estimating the Γ function having a scaling coefficient different for each investigated vegetation type, allowed an accurate estimate of the Darcy-Weisbach friction factor (errors less than or equal to 20% for 82.6% of the investigated cases). Finally, for the investigated vegetation species that are characterized by a condition with few leaves or leafless, the scaling coefficient a resulted strongly related to the bending stiffness. This analysis demonstrated that the highest Darcy-Weisbach friction factors correspond to vegetation species characterized by the highest values of bending stiffness. The friction factor values calculated for this last condition are characterized by errors that were less than or equal to ±20% for 90.6% of cases.  相似文献   
972.
径流量变化对长江口水动力特性的影响   总被引:1,自引:0,他引:1  
为了研究径流量变化对长江口水动力特性的影响,利用MIKE21建立长江口水动力数学模型,分别模拟计算长江口不同径流量影响的潮流场,统计分析不同径流量时各汊道涨落潮量和净泄量以及分配比例;统计分析不同径流量对各汊道潮位变化的影响;统计分析不同径流量对北槽中下段水动力特性的影响。得到如下结论:1)径流量的变化对于涨潮分流的影响显著,随着径流量的增加,更多的潮流从北支、北港、南槽进入长江口内。当上游的径流动力增强,外海潮流受上游径流的阻挡,难以继续上溯。2)越是靠近上游,径流量的变化对平均潮位的影响程度越高,入海口处受径流的影响微弱;上游径流量越大,潮波向内陆传播越受阻,能量消耗越大,致使其动力减弱。3)径流量的变化对平均流速的影响与上述潮位变化类似,上游径流量越大,各汊道流速越大;越靠近海洋,径流影响越小。4)长江口北槽中下段转流时刻会出现平面对流现象。横向方向上普遍存在越堤水流,且南北导堤均为北向越堤流占优势。  相似文献   
973.
东罗火电厂灰渣堆置场的选址,以场地堆置灰渣后是否对客兰水库造成污染为前提。广西地质测井中心利用综合物探方法对场地的水文地质、工程地质和环境地质进行勘察评价。经工作,圈定了第四系土层和七条岩溶发育带,确定了一正断层位置,在四个钻孔中充电确定了地下水的流速和流向(主要为北西向和正北方向)。最后认为,场地堆置弃渣后,对位于南南东方向的客兰水库没有造成污染,为选址决策和施工设计提供了依据  相似文献   
974.
Summary. Phase velocity variations obtained in the previous paper are inverted by the Backus–Gilbert method for the velocity structure of the upper mantle. Spheroidal modes and toroidal modes in the period range of 125–260 s are used in the inversion. The data cannot constrain all six parameters in a transversely isotropic medium and we chose to perturb only two parameters, SH and SV velocities. SV velocities are resolved between the depths of about 200 and 400 km and SH velocities between 0 and 200 km. Resolution kernels have half-peak widths of about 200–300 km in depth, becoming broader for deeper target depths. SV velocity kernels show secondary peaks near the surface of the Earth, with widths varying from 50 to 100 km. The deeper the target depths, the wider the secondary peaks near the surface. SH velocity kernels do not possess such secondary peaks. The trade-off between SV and SH velocities is small. SV velocity is essentially determined by spheroidal modes and SH velocity by toroidal modes. Because of the broad width of the resolution kernels, the structure in the resolved region is difficult to detect from our data set; for example the differences in SV velocity structure between 250 and 350 km or the differences in SH velocity between 100 and 200 km are difficult to distinguish. Considering the horizontal resolution of about 2000 km, obtained in the previous paper, averaging kernels for 3-D structure are quite elongated in the horizontal dimension.  相似文献   
975.
This article contains the tomographic problem's solution of the radiants distribution study by the meteor radar data. It was received the distribution of meteors velocities for the parts of celestial sphere with angular dimensions 10° × 10° and 1° × 1°. Was shown that the angular dimensions of most of radiants are equal 1° – 3° and larger part of the sporadic background looks like a totality of microstreams.  相似文献   
976.
本文介绍了1991年3月5日一个与3N级光学耀斑伴生的喷泉状爆发日珥。用Hα线观测从开始到结束整个过程共持续约50分钟时间,日珥的最大投影高度15.9万公里,视向速度分布表明,日珥主要以较大的速度向着观测者的运动,最大速度每秒120公里。  相似文献   
977.
978.
本文论述群速和能量传播速度的基本概念,并对相速、群速及能量传播速度的联系及区别作了讨论。  相似文献   
979.
The effect of randomly distributed cracks on the attenuation and dispersion ofSH waves is theoretically studied. If earthquake ruptures are caused by sudden coalescence of preexisting cracks, it will be crucial for earthquake prediction to monitor the temporal variation of the crack distribution. Our aim is to investigate how the property of crack distribution is reflected in the attenuation and dispersion of elastic waves.We introduce the stochastic property, in the mathematical analysis, for the distributions of crack location, crack size and crack orientation. The crack size distribution is assumed to be described by a power law probability density (p(a) a fora minaa max according to recent seismological and experimental knowledge, wherea is a half crack length and the range 13 is assumed. The distribution of crack location is assumed to be homogeneous for the sake of mathematical simplicity, and a low crack density is assumed. The stochastic property of each crack is assumed to be independent of that of the other cracks. We assume two models, that is, the aligned crack model and the randomly oriented crack model, for the distribution of crack orientation. All cracks are assumed to be aligned in the former model. The orientation of each crack is assumed to be random in the latter model, and the homogeneous distribution is assumed for the crack orientation. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.We observe the following features common to both the aligned crack model and the randomly oriented crack model. The attenuation coefficientQ –1 decays in proportion tok –1 in the high frequency range and its growth is proportional tok 2 in the low frequency range, wherek is the intrinsic wave number. This asymptotic behavior is parameter-independent, too. The attenuation coefficientQ –1 has a broader peak as increases and/ora min/a max decreases. The nondimensional peak wave numberk p a max at whichQ –1 takes the peak value is almost independent ofa min/a max for =1 and 2 while it considerably depends ona min/a max for =3. The phase velocity is almost independent ofk in the rangeka max<1 and increases monotonically ask increases in the rangeka max>1. While the magnitude ofQ –1 and the phase velocity considerably depend on the orientation of the crack in the aligned crack model, the above feature does not depend on the crack orientation.The accumulation of seismological measurements suggests thatQ –1 ofS waves has a peak at around 0.5 Hz. If this observation is combined with our theoretical results onk p a max, the probable range ofa max of the crack distribution in the earth can be estimated for =1 or 2. If we assume 4 km/sec as theS wave velocity of the matrix medium,a max is estimated to range from 2 to 5 km. We cannot estimatea max in a narrow range for =3.  相似文献   
980.
GVAD技术及其在新一代天气雷达中的应用   总被引:1,自引:1,他引:0  
李瑞义  杨洪平  赵坤  李锐锋 《气象》2018,44(4):511-517
天气雷达中VAD技术可求取雷达站上空水平风垂直廓线,梯度VAD技术(简称GVAD技术)为克服传统VAD技术受速度模糊影响较大而被提出。文中首先从理论上对GVAD技术进行模拟分析,再将其应用于新一代天气雷达实际探测的台风与大范围强降水速度模糊个例,分析其应用效果。理论模拟表明,GVAD技术较传统VAD技术可有效克服速度模糊对反演水平风垂直廓线的影响,加入的模拟噪声,也通过低通滤波方法有效抑制;在两次实际应用个例中,GVAD技术可较好克服速度模糊影响,但方位径向速度中的小波动或者噪声会在径向速度方位梯度中放大,尽管利用低通滤波进行了平滑,但其对反演水平风精度有较大影响,尤其影响水平风速反演精度,在个例中GVAD技术反演风速较传统VAD技术平均偏弱2~3m·s~(-1),模拟部分方位缺失并不影响GVAD技术的反演精度。需进一步研究减少新一代天气雷达径向速度资料中小波动或者噪声对GVAD技术应用影响的方法。  相似文献   
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