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The migration of a downsized crescent-shaped dune was investigated in a wind tunnel experiment.Quantified upwind influx and vertical oscillation of the sand bed were introduced to modulate the saturation level of the sand flux above the dune surface to affect dune evolution.The evolution was recorded by top-view photography and then abstracted as the evolution of self-defined characteristic quantities using a digital image processing algorithm.The results showed that,in contrast to the case for spanwise quantities,the evolution of streamwise quantities corresponds to a linear increase in the modulation magnitude more positively and in a monotonic and convergent manner.In contrast with quantities on the windward face,the changes in quantities with respect to the horns were nonmonotonic with time and almost uncorrelated with the variation in modulation strength,which reveals the distinctiveness of leeside evolution. 相似文献
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Rolf Russow Maik Veste Thomas Littmann 《Isotopes in environmental and health studies》2013,49(1):57-67
The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system:
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Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam);
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Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition.
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W. C. Kuru D. T. Leighton M. J. McCready 《International Journal of Multiphase Flow》1995,21(6):1123-1140
The mechanisms responsible for the initial growth of sand waves on the surface of a settled layer of particles are studied experimentally and theoretically. Experiments employ water-glycerin solutions of 1–14 cP and glass spheres (s = 2.4 g/cm3) that are either 100 or 300 μm in diameter. The particle Reynolds number and Shields parameter are of order one and the flow Reynolds number is of order 1000 to 10,000. Experimentally obtained regime maps of sand wave behavior and data on the wavelengths of the sand waves that first appear on the surface of the settled bed are presented. Turbulence in the clear liquid is not necessary for formation of waves and there is no dramatic change in behavior as the flowrate is increased across the turbulent transition. The initial wavelength varies as the Fronde number to the first power. Because a flowing suspension phase is observed before waves form, linear stability analysis of the clear-layer—suspension-layer cocurrent two-phase flow is presented. The suspension phase is modeled as a continuum that has an either constant or exponentially increasing viscosity. Neither of the models correctly predicts the wavelength for the first observed waves, their growth rate or their speed. However, the initial wavelength is found to agree well with the trajectory length for a saltating particle obtained from a model for forces on individual particles. 相似文献
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研究了新月形沙丘粗糙面的二次极化电磁散射. 结合射线追踪理论, 由一次散射面元的反射场照射到二次散射面元, 采用基尔霍夫近似推导了二次散射面元的二次极化散射场. 计算结果表明二次极化散射结果在特定的角度和类型范围内有显著影响. 在电磁波射向背风坡时可以发现其同极化散射截面在入射角较大时大于其他入射方向的结果, 入射角在休止角附近时的交叉极化散射截面出现峰值, 以及前后狭长沙丘之间的二次极化散射特别突出. 本文结果可用于反演分析沙漠地区的风场信息.
关键词:
新月形沙丘
二次极化散射
射线追踪
休止角 相似文献
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