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41.
Effects of Temperature and Humidity upon the Entrainment of Sedimentary Particles by Wind 总被引:2,自引:0,他引:2
Cheryl Mckenna Neuman 《Boundary-Layer Meteorology》2003,108(1):61-89
Aeolian transport of sedimentary particles is a well-recognized phenomenon in cold regions, but the effect of low temperature (T) and specific humidity (q) upon particle entrainment has not previously been investigated. This study reports on wind-tunnel experiments (-12 °C T 32 °C, and 1 g kg-1 q 10 g kg-1) that suggest the aerodynamic drag required to entrain sand sized particles can be 30% lower in cold or high latitude settings, as compared to hot deserts. For any given regional wind velocity, this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature.The influence of air temperature and humidity upon the threshold for particle motion is determined by three physical processes: (1) The effect of air viscosity and density on the fluid drag force acting to dislodge sedimentary particles; (2) the effect of viscosity on the turbulent wake shed from these particles, and the frequency and magnitude of burst-sweep events; and (3) the development of inter-particle cohesion via adsorbed water. This study considers the relative importance of each of these processes. The threshold friction velocity model of Shao and Lu is revised to incorporate the inter-particle force associated with hygroscopic water. It is found to perform well when tested against the experimental data obtained for this study. 相似文献
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介绍了EOS卫星上携带的MODIS传感器的主要特点以及用MODIS资料进行林火监测的原理。根据近年来使用MODIS资料进行林火监测的应用情况,对自动判识火点所需设置的门槛值进行了分析和探索,找到了一种能快速、简便地设置ch21和ch21-ch31门槛值的方法,并通过实例证明该方法在林火监测中是可行的和有效的。 相似文献
44.
Ulrich C. E. ZANKE Prof Institute of Hydraulic Engineering University of Technology Darmstadt Germany 《国际泥沙研究》2001,16(1)
l PROBLEMS AND AlMSSediments may be transported close to the bed, rolling and sliding, as we1l as susPended in the flow. Forvarious reasons the theoretical treatment of the bed-load problem has been exceptionally difficult. Noanalytical solution had been fOund uP to now, beginning with Du Buat (l786), Huebbe (l86l) and DuBoys (I 879). Since the aPProach of Du Boys numerous new attemPts have been catried out, mostly of anempirical nature. Consequently they are not generally valid an… 相似文献
45.
本文简要介绍了应用门限自回归方法处理浑沌时间序列,建立了浑沌时间序列自回归预报模型,并用其进行外推预报的基本方法及步骤。作者运用该方法建立了云南及滇西、滇东和滇西南等三个片区的半年最大震级序列的震级预报模型。由此预测了1991年上半年模型相应地区可能发生的最大地震震级。 相似文献
46.
Physical model tests have been performed in two different wave flumes to analyse the threshold of stone movement and quantify the frequency and length of displacements due to head-on wave attacks at a reshaping breakwater. Data on stone movements were obtained from the observation of cumulative displacements at the end of each wave attack and from video records during the attack. Threshold conditions, frequency of movement and displacement length are expressed as function of a suitably modified stability number.A simple model is defined relating longshore transport due to oblique wave attack to stone mobility. The transport model is based on the assumption that movement statistics is affected by obliquity only through the appropriate mobility index and that stones move during up- and down-rush in the direction of incident and reflected waves. Without any calibration, results compare favourably with experimental data available in literature in the range of low mobility conditions where movement statistics was observed. A calibration is provided in order to obtain an accurate transport formula valid in a wide mobility range i.e. for reshaping breakwaters and up to gravel beaches. 相似文献
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General approximate analytical solutions are developed for one-dimensional consolidation with consideration of the threshold gradient under a time-dependent loading. A comparison is made between the present solution and some available numerical solutions for a particular case, and the results show that the approach employed in this article is reasonable. The influence of the threshold gradient and the loading period on consolidation behaviour is investigated, and the results show that the moving boundary of seepage moves downward gradually. The greater the threshold gradient is, the slower the boundary moves. The excess pore pressure will not be completely dissipated at the end of consolidation, and the larger the threshold gradient is, the greater the residual excess pore pressure is. The average degree of consolidation considering the threshold gradient defined by settlement is different from that defined by pore pressure. Moreover, the greater the threshold gradient is, the larger the average degree of consolidation in terms of strain, whereas the smaller the average degree of consolidation in terms of stress. It is also shown that the longer the loading period is, the longer the time moving boundary takes to reach the bottom of the layer, and the greater the average degree of consolidation is. 相似文献
49.
地震综合预报的权重集成法 总被引:2,自引:0,他引:2
本文提出一种地震综合预报方法,即权重集成法。该方法首先根据各单项前兆或方法历史预报的错报率,计算其权重值,据此建立权重集成预报方程。其后据此方程采用历史回代法求其权重集成值P,最后根据历史上对应有震的权重集成的最小值和对应无震的最大值,求出权重集成值的临界阀值P_0。当P≥P_0时则作有震预报,否则作无震预报。该方法简便、综合性强。 相似文献
50.