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961.
J. M. Edwards 《Boundary-Layer Meteorology》2009,132(2):349-350
The structure of the radiatively dominated stable boundary layer is analysed using idealized calculations at high vertical
and spectral resolution. The temperature profile of a nocturnal radiative boundary layer, developing after the evening transition,
is found to be well described in terms of radiative cooling to the surface, although radiative exchanges within the atmosphere
become increasingly important with time. The treatment of non-black surfaces is discussed in some detail and it is shown that
the effect of reducing the surface emissivity is to decrease rather than to increase the radiative cooling rate in the surface
layer. It is also argued that an accurate assessment of the impact of non-black surfaces requires careful attention to the
spectral and directional characteristics of the surface emissivity. A polar nocturnal boundary layer, developing above snow-covered
ground, is simulated and found to reach a slowly evolving state characterized by a strong radiative divergence near the surface
that is comparable to observed values. Radiative boundary layers are characterized by large temperature gradients near the
surface.
An erratum to this article can be found at 相似文献
962.
20世纪60年代初期,Tóth基于定水头上边界条件推导出解析解,得出多级次地下水流系统,是水文地质学里程碑式的突破,成功地解决了一系列理论和实际问题。但Tóth解析解存在的缺陷也长期沿袭:单纯重视数学模拟而忽视物理机制;将地形控制地下水位看成是普适性规律;忽视给定水头上边界数学模拟的失真。这些缺陷,尤其是忽视物理机制探究,不仅妨碍Tóth理论自身发展,而且导致地下水流系统理论尚未被国际水文地质界普遍接受。参照河流动力学中应用的最小能耗率原理,类比提出地下水流最小能耗率的表达式。基于已有的通量上边界地下水流模式数值模拟结果,进一步探究物理机制,归纳得出地下水流系统遵循最小能耗率原理的结论。 相似文献
963.
Overcoming two inherent limitations presented by the standard bonded-particle model (BPM), the flat-jointed model still lacks extensive application. This study hereby conducts a comprehensive investigation on the application of the flat-jointed model in rock mechanics study. First, after a careful examination on the mechanical behavior of the flat-joint contact, a systematic calibration has been conducted to build numerical models matching the mechanical properties of Carrara marble. Second, the validated model is used to simulate the fracturing behavior of marble specimens containing a single or en-echelon flaws. Finally, the appearance of particle flow code (PFC) models has been compared with the results obtained from optical observation in order to establish a possible correlation between PFC models and real marble regarding microcracking behavior. Discussions suggest that to remove the particle size effect, the model resolution (ratio of sample dimension to the average particle diameter) should be larger than 30 in the flat-jointed model and 150 in the BPM, respectively. Results from the above investigations suggest that the flat-jointed model is capable of matching both the mechanical properties and fracturing behavior of Carrara marble. The numerical model is more reliable to predict the fracturing path at the instant of initiation than at failure. Development of initial fractures is not only controlled by the magnitude of tension force but also influenced by the extent of distribution of tension force. The appearance and components of a fracture in flat-jointed models probably reveal not only its property (tensile or shear) but also the corresponding microcracking behavior of real rocks. 相似文献
964.
Traditional consolidation theories cannot provide good predictions of consolidation settlement in land reclamation because of their assumptions that the influence of soil's self-weight is often neglected, and the drainage boundary is considered as fully pervious/impervious. In view of these limitations, an analytical solution is derived for one-dimensional self-weight consolidation problems with a continuous drainage boundary using the finite Fourier sine transform method. Following the classical Terzaghi's small strain theory, the soil's self-weight is considered to produce consolidation settlement in dredged materials with a constant coefficient of consolidation. The continuous drainage boundary can essentially describe the time-dependent variation of drainage capacity at the interface between two adjacent soil layers. By reducing the interface parameters, the effectiveness of the calculation is demonstrated against the Terzaghi's solution. The influence of interface parameters and soil's self-weight stress coefficient on self-weight consolidation is discussed. As expected, the rate of consolidation considering the self-weight stress is faster, although the dependency of consolidation rate on the material property of void ratio is neglected. Moreover, the plane of maximum excess pore-water pressure is estimated as a function of time factor, based on which a design chart is developed to optimize the layout of horizontal drains in land reclamation. 相似文献
965.
A coupled 3‐dimensional bonded discrete element and lattice Boltzmann method for fluid‐solid coupling in cohesive geomaterials 下载免费PDF全文
This paper presents a 3D bonded discrete element and lattice Boltzmann method for resolving the fluid‐solid interaction involving complicated fluid‐particle coupling in geomaterials. In the coupled technique, the solid material is treated as an assembly of bonded and/or granular particles. A bond model accounting for strain softening in normal contact is incorporated into the discrete element method to simulate the mechanical behaviour of geomaterials, whilst the fluid flow is solved by the lattice Boltzmann method based on kinetic theory and statistical mechanics. To provide a bridge between theory and application, a 3D algorithm of immersed moving boundary scheme was proposed for resolving fluid‐particle interaction. To demonstrate the applicability and accuracy of this coupled method, a benchmark called quicksand, in which particles become fluidised under the driving of upward fluid flow, is first carried out. The critical hydraulic gradient obtained from the numerical results matches the theoretical value. Then, numerical investigation of the performance of granular filters generated according to the well‐acknowledged design criteria is given. It is found that the proposed 3D technique is promising, and the instantaneous migration of the protected soils can be readily observed. Numerical results prove that the filters which comply with the design criteria can effectively alleviate or eliminate the appearance of particle erosion in dams. 相似文献
966.
A framework was developed to address the automatic optimization of the level of geometric detail required for stress analysis of underground excavations in mining, which was presented in the companion paper. The motivation for optimizing the mesh geometry stems from the over‐discretization of computational domain as the digital mine model is built while our knowledge of some of the input parameters is quite limited. Thus, the accuracy of the solution is not expected to be increased with a finely discretized mesh, only the computation time does. Therefore, it is acceptable if the results obtained from an optimized model have accuracy comparable to the uncertainty in input data (e.g. rock mass properties, geology, etc.). Although the mesh optimization framework automates the geometry optimization and reduces computation time, the accuracy of the solution from the resulting geometry must be evaluated to ensure the quality of the solution at the ‘region of interest’. Both a priori (mesh quality) and a posteriori (solution quality) measures are employed along with recording the mesh optimization time. Finally, the applicability of the mesh optimization framework is demonstrated by analysing a number of mining and civil engineering underground models. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
967.
辽宁岫岩金矿是岩浆热液成因的石英脉型金矿床,然而矿区内的一系列石英脉体尽管其空间分布上关系密切,但其矿化程度却有显著差异。本文就这种差异的原因从区域构造应力场-岩体形态-岩石力学性质-控矿(脉)断裂的性质及时、空定位的相关上进行了深入分析探讨,认为岩体形态、岩石物理力学性质是影响断裂时、空定位和性质的主要因素,而且是控制矿化程度差异的根本因素。井由此推断,在1 ̄#,2 ̄#断裂带南东侧延伸的深部有望找到矿体。 相似文献
968.
结合气象观测和大气边界层探测资料,分析了1990年1月2日重庆雾的声雷达回波特征,并与1989年12月30日雾的回波作了比较。结果表明,雾顶回波高度与逆温和相对湿度的转折高度一致;雾顶回波在雾的成熟期呈现波动,在消散期有一下降过程。上午大气污染物地面浓度的变化与逆温混合层状况有密切关系,混合层较薄且持续时间较长时,地面浓度较大 相似文献
969.
本文研究了UHF-RFID(超高频-射频识别)环境下的移动目标定位问题,提出了一种结合自适应卡尔曼滤波和BVIRE(边界虚拟参考标签)的移动机器人定位方法,即B-AKF(Boundary-Adaptive Kalman Filter)定位方法.首先,利用UHF-RFID系统对移动机器人进行初始定位,其次,考虑模型和噪声统计特性不确定性,采用自适应卡尔曼滤波方法对机器人的运动状态进行预测和更新,并引入自适应因子补偿噪声方差不确定性问题.最后,搭建了基于UHF-RFID的定位实验平台,并通过实验研究表明,相比于传统的线性BVIRE和线性卡尔曼滤波方法,所提出的自适应卡尔曼滤波方法具有更高的定位精度和更强的鲁棒性能. 相似文献
970.