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21.
提出颗粒型砂介质在压实过程中的两种特征:孔隙填充状态和颗粒滑动状态;针对孔隙填充状态的力学行为特征,提出相对体积改变量(压实量)作为表征此状态的特征参量,研究了瞬时压缩模量与压实量的函数关系;针对型砂的颗粒滑动状态,提出具有强化效应的Mohr-Coulomb屈服条件,推导描述颗粒屈服滑动状态的增量本构方程、以及三轴压实过程条件下的状态本构方程,最后,就不同侧向压力下的三轴压缩试验、带模样的型砂压实试验的大量试验数据进行处理和验证。 相似文献
22.
地表温度对颗粒跃移轨迹的影响 总被引:2,自引:0,他引:2
为了研究由地表温度变化引起的向上的垂向气流对沙粒跃移运动的影响,本文给出了考虑近地表温度变化和水平来流风场作用下的沙粒的跃移运动。在定量给出不同时刻的近地表温度和垂向风速的基础上,计算了由于太阳辐射所引起的近地表层垂向气流对沙粒跃移运动的影响,发现:垂向风速在午后可达到1.5m/s并使得沙粒跃移轨迹的最大高度和长度分别增加55.56%和73.68%;同时,与不考虑温度效应的情况不同的是,沙粒跃移轨道最大高度将随粒径变化。 相似文献
23.
The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important
roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles
located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in
a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also
the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal
components can be obtained by the equal distance histogram method. It is found, according to the results of the χ2-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off
and incident velocities as well as their vertical components are described by the Gamma density function with different peak
values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal
and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed.
The project supported by the National Natural Science Foundation of China (10532040) and the Hundred Talents Project, the
Knowledge Innovation Project of Chinese Academy of Sciences (KZCX2-304). The English text was polished by Keren Wang. 相似文献
24.
将沥青混合料看作由粗骨料和沥青砂组成的两相复合材料,根据给定的级配生成凸多面体骨料,然后利用随机投放算法建立沥青混合料试样的三维随机模型.采用广义Maxwell模型刻画沥青砂的本构行为,其参数通过单轴蠕变实验获得.在对三维随机模型的有效性进行验证之后,采用参数化建模方法建立包含不同骨料分布、含量和级配的沥青混合料有限元模型,通过数值模拟研究骨料分布、含量和级配对沥青混合料蠕变行为的影响.结果表明:骨料分布对沥青混合料力学性质的影响较小;沥青混合料瞬时弹性模量随骨料含量的增加呈近似线性增大,而且弹性模量与骨料含量之间的关系曲线处于Paul上下边界内;在计算考虑的粒径范围内,骨料平均粒径越小,沥青混合料抵抗变形的能力越强. 相似文献
25.
26.
通过高速摄影系统对电火花气泡与不同沙粒底面间的相互作用进行了实验研究,并改变气泡与沙粒底面之间的距离.实验结果表明:气泡在与沙粒底面的相互作用中会产生两种明显不同的现象,即形成与近刚性壁面类似的气泡射流以及“蘑菇状”气泡,“蘑菇状”气泡撕裂形成两个气泡,随后产生两个反方向的沿轴线方向的射流.沙粒底面边界具有刚性与弹性两种特征.另外,随着气泡与沙粒底面之间的距离d的增大,气泡脉动周期先增大然后减小,存在气泡脉动周期峰值.对于不同的沙粒底面边界,出现气泡脉动周期峰值的距离d随着沙底粒径的增大而越小. 相似文献
27.
The flow patterns and wall stresses in a two‐dimensional louvered moving granular filter bed of quartz sand were investigated. The flow pattern histories of granular solids in the filter bed were recorded using a digital camcorder and a pressure gauge for simultaneously measuring the normal stresses as well as shear stresses of the granular solids. The static wall stress distributions produced by the granular solids were measured, and agreed with a theoretical prediction formed using the differential slice and Runge‐Kutta (order four) methods. The variations in the dynamic wall stresses with time in a moving granular filter bed were obtained and the effect of the louver angle upon the flow patterns and wall stresses was also investigated. Employing the results obtained by stress measurements and image processing, the wall pressure pulsation phenomena in a moving granular filter bed may be further understood. The results reported here provide fundamental information for the design of moving granular filter beds to act as high‐temperature flue gas cleanup filters. 相似文献
28.
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.
29.
30.
A numerical study of the turbulent air flow in a trench trap and the turbulent flow around a permeable sand fence is reported in this paper. The two-dimensional modified k–ε turbulence model proposed by Kato and Launder is used to predict the turbulent characteristics of the air flow. The discretization method for the governing equations is the three-step Taylor/Galerkin finite element method proposed by the authors. For the flow in a trench trap the numerical results are compared with experimental data obtained under realistic conditions using a large wind tunnel. For the air flow around a permeable sand fence a pressure loss model is used to represent the effect of the porosity of the fence on the flow field. © 1997 John Wiley & Sons, Ltd. 相似文献