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991.
基于中尺度数值模式WRF,选取新疆两次强降水过程,设计3个试验方案,其中试验1为控制试验,试验2提高分辨率,试验3提高分辨率并调整物理参数化方案,初步评估不同分辨率和参数化方案对新疆区域2m温度、10m风速、降水预报的影响。结果表明:(1)提高分辨率对2m温度、10m风速模拟精度均有提高,2m温度预报精度提高约0.5℃,降低了日间温度模拟冷偏差;10m风速预报精度提高约0.5m/s,降低了风速模拟正偏差;但提高分辨率后,模式出现虚假降水预报的情况。(2)提高分辨率并调整物理参数化方案后,2m温度模拟误差略有减小,模拟偏差减小约0.2℃;10m风速模拟误差增大约0.5m/s,模拟偏差增大超过0.5m/s;对降水落区、量级的模拟精度显著提高,减小了降水中心的模拟强度,对虚假降水预报有一定修正。 相似文献
993.
Macroscopic criteria for Green type porous materials with spheroidal voids: application to double porous materials 下载免费PDF全文
Combined effects of matrix plastic compressibility and void shape are investigated for ductile porous materials. To this end, a spheroidal volume containing a confocal spheroidal (prolate or oblate) void subjected to uniform strain rate boundary conditions has been first studied. A Green type matrix is chosen as a prototype for investigating effects of plastic compressibility. This is carried out by using a kinematics limit analysis theory from which a closed‐form expression of the macroscopic criterion is established for the considered class of materials. These results are then extended to ductile porous materials made up of a green matrix containing randomly oriented spheroidal voids. In the framework of a two‐step homogenization procedure, the obtained results are implemented to describe the macroscopic behavior of double porous materials involving spherical voids at the microscale and randomly oriented and distributed spheroidal voids at the mesoscale. For validation purpose, the new derived criteria are assessed and validated by comparing their predictions to available upper bounds and numerical data from literature. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
994.
Selection of sand models and identification of parameters using an enhanced genetic algorithm 下载免费PDF全文
Numerous constitutive models of granular soils have been developed during the last few decades. As a consequence, how to select an appropriate model with the necessary features based on conventional tests and with an easy way of identifying parameters for geotechnical applications has become a major issue. This paper aims to discuss the selection of sand models and parameters identification by using genetic algorithm. A real‐coded genetic algorithm is enhanced for the optimization with high efficiency. Models with gradually varying features (elastic‐perfectly plastic modelling, nonlinear stress–strain hardening, critical state concept and two‐surface concept) are selected from numerous sand models as examples for optimization. Conventional triaxial tests on Hostun sand are selected as the objectives in the optimization. Four key points are then discussed in turn: (i) which features are necessary to be accounted for in constitutive modelling of sand; (ii) which type of tests (drained and/or undrained) should be selected for an optimal identification of parameters; (iii) what is the minimum number of tests that should be selected for parameter identification; and (iv) what is the suitable and least strain level of objective tests to obtain reliable and reasonable parameters. Finally, a useful guide, based on all comparisons, is provided at the end of the discussion. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
995.
This paper presents the closed‐form solutions for the elastic fields in two bonded rocks induced by rectangular loadings. Each of the two bonded rocks behaves as a transversely isotropic linear elastic solid of semi‐infinite extent. They are completely bonded together at a horizontal surface. The rectangular loadings are body forces along either vertical or horizontal directions and are uniformly applied on a rectangular area. The rectangular area is embedded in the two bonded rocks and is parallel to the horizontal interface. The classical integral transforms are used in the solution formulation, and the elastic solutions are expressed in the forms of elementary harmonic functions for the rectangular loadings. The stresses and displacements in the rocks induced by both the horizontal and vertical body forces are also presented. The numerical results illustrate the important effect of the anisotropic bimaterial properties on the stress and displacement fields. The solutions can be easily implemented for numerical calculations and applied to problems encountered in rock mechanics and engineering. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
996.
Influence of core property on multi-electron process in the collisions of q=6-9 and 11 isocharged sequence ions with Ne is investigated in the keV/u region. The cross-section ratios of double-, triple-, quadruple- and total multi-electron processes to the single electron capture process as well as the partial ratios of different reaction channels to the relevant multi-electron process are measured by using position-sensitive and time-of-flight techniques. The experimental data are compared with the theoretical predictions including the extended classical over-barrier model, the molecular Columbic barrier model and the semi-empirical scaling law. Results show a core effect on multi-electron process of isocharge ions colliding with Neon, which is consistent with the results of Helium we obtained previously. 相似文献
997.
Qiuan Zhu Hong Jiang Xiaohua Wei Changhui Peng Xiuqing Fang Shirong Liu Guomo Zhou Shuquan Yu Weiming Ju 《水文研究》2010,24(4):429-445
The Integrated Biosphere Simulator is used to evaluate the spatial and temporal patterns of the crucial hydrological variables [run‐off and actual evapotranspiration (AET)] of the water balance across China for the period 1951–2006 including a precipitation analysis. Results suggest three major findings. First, simulated run‐off captured 85% of the spatial variability and 80% of the temporal variability for 85 hydrological gauges across China. The mean relative errors were within 20% for 66% of the studied stations and within 30% for 86% of the stations. The Nash–Sutcliffe coefficients indicated that the quantity pattern of run‐off was also captured acceptably except for some watersheds in southwestern and northwestern China. The possible reasons for underestimation of run‐off in the Tibetan plateau include underestimation of precipitation and uncertainties in other meteorological data due to complex topography, and simplified representations of the soil depth attribute and snow processes in the model. Second, simulated AET matched reasonably with estimated values calculated as the residual of precipitation and run‐off for watersheds controlled by the hydrological gauges. Finally, trend analysis based on the Mann–Kendall method indicated that significant increasing and decreasing patterns in precipitation appeared in the northwest part of China and the Yellow River region, respectively. Significant increasing and decreasing trends in AET were detected in the Southwest region and the Yangtze River region, respectively. In addition, the Southwest region, northern China (including the Heilongjiang, Liaohe, and Haihe Basins), and the Yellow River Basin showed significant decreasing trends in run‐off, and the Zhemin hydrological region showed a significant increasing trend. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
998.
Biodegradation and oil mixing in Silurian sandstone reservoirs of the Tarim Basin, one of the largest composite basins in China, were investigated by analyzing the molecular characteristics and stable carbon isotopic signatures of low-molecular-weight (LMW) saturated hydrocarbons and high-molecular-weight (HMW) asphaltenes. Detection of 25-norhopanes and 17-nortricyclic terpanes in most Silurian tar sands from the Tabei Uplift in the Tarim Basin suggests a much greater degree of biodegradation here than in the Tazhong Uplift. This explains the relatively more abundant tricyclic terpanes, gammacerane, pregnane and diasteranes in tar sands from the Tabei Uplift than in those from the Tazhong Uplift. Hence, care must be taken when assigning oil source correlations using biomarkers in tar sands because of the biodegradation and mixing of oils derived from multiple sources in such an old composite basin. Asphaltenes in the tar sands seem to be part of the oil charge before biodegradation, depending on the relative anti-biodegradation characteristics of asphaltenes, the similarity in carbon isotopic signatures for asphaltenes and their pyrolysates, and the consistent product distribution for flash pyrolysis and for regular steranes in asphaltene pyrolysates, regardless of whether the tar sands were charged with fresh oil. According to the relative distributions of regular steranes and the relatively abundant 1,2,3,4-tetramethylbenzene significantly enriched in 13C, the oil sources for asphaltenes in the tar sands might be related to lower Paleozoic marine source rocks formed in euxinic conditions. Nevertheless, the relatively low abundance of gammacerane and C28 regular steranes observed in asphaltene pyrolysates and residual hydrocarbons, within limited samples investigated in this work, made a direct correlation of oils originally charged into Silurian tar sands with those Cambrian source rocks, reported so far, seem not to be possible. Comparison of carbon isotopic signatures of n-alkanes in asphaltene pyrolysates with those of LMW saturated hydrocarbons is helpful in determining if the abundant n-alkanes in tar sands are derived from fresh oil charges after biodegradation. The limited carbon isotopic data for n-alkanes in LMW saturated hydrocarbons from the tar sands can be used to classify oils charged after biodegradation in the composite basin into four distinct groups. 相似文献
999.
A new method for platform design, named parametric platform design method (PPDM), is presented in this paper in order to improve the mobile platform design efficiency. In this method, an integrated parametric system that fully considers the characteristics of the platform is developed, which significantly optimizes the design process with the top–bottom design concept. In the parametric system, the main geometric dimensions are taken as parameters, while the topology between the structure members, the function requirements and the safety requirements are converted into geometric constraints. By geometric constraint solving (GCS), a set of parameters that satisfy all the given constraints are determined, and then the design scheme is obtained by several core algorithms, such as parametric tank subdivision, 3D stability calculation, parametric structure design, FEM preprocessing, etc. The parametric method greatly increases the changeability and the reusability of the platform model, and concurrent design is well supported. As the model is driven by parameters, PPDM is an excellent method for optimization design. As a result, PPDM has incomparable advantages on the design efficiency over traditional methods. 相似文献
1000.