基于质点-网格模式的海冰厚度变化过程数值模拟

根据渤海冰情,在海冰动力学和热力学研究基础上,应用一种质点-网格海冰模式于渤海海域.该模式采用了质点-网格法,有效地避免了传统模式的数值扩散问题.该模式采用了冰厚分布函数,用多种类型冰代替用于渤海业务预报的平整冰、堆积冰和开阔水3-level模式.进行理想场的数值试验,模拟冰厚变化动力过程.还使用该模式和业务预报模式对于实际渤海冰情进行了不同个例的预报试验,发现该模式在提高冰外缘线预报精度方面有一定的优势.     

云南石林喀斯特露石径流输出及其影响因素探究

喀斯特露石具有重要的生态功能,但关于露石承接降水后的石面径流及其影响因子研究仍然很少.本实验选择云南石林的石漠化、人工林、原生林生态系统,布设露石径流收集装置,收集并测量不同降雨事件后的露石石面径流,测定露石承接降水面积和粗糙度.结果表明:(1)在3.92 mm到72.31 mm的降雨范围内,露石承接降雨量与露石径流量...     

地下连续墙施工影响应力重分布的数值模拟

对武汉市某超大型超深基坑10幅邻近地连墙跳跃式施工过程进行了三维有限差分数值模拟。数值模拟步骤依次为泥浆护壁成槽开挖、混凝土浇筑及混凝土硬化3个过程。泥浆护壁成槽开挖及混凝土浇筑分别采用常静液压力和变静液压力的方式加载,混凝土的硬化过程采用变弹性模量和泊松比的线弹性实体单元完成。数值计算结果与实测数据吻合较好。对单个跳跃式开挖过程墙上土压力的监测揭示了地下连续墙施工影响应力重分布的变化规律。模拟施工完成后10幅地下连续墙上的土压力值沿墙长度方向随静止土压力值上下波动,波谷出现在槽段连接处附近,波峰接近槽段中心轴,波动幅度大小与土体深度有关。分析表明,泥浆压力、混凝土灌注压力及土压力差值是影响墙后应力重分布波动幅度的主要原因,适当的泥浆重度及合理的注浆方式能避免土体扰动。     

Scattering of radiation by free electrons. The angle-averaged redistribution function

Elementary events of photon scattering by a chaotically moving monoenergetic electron gas are examined to obtain the redistribution function (RF). It is pointed out that in many problems and, in particular, the interaction of background radiation with the intergalactic plasmas of rich galactic clusters, it is sufficient to have the angle-averaged RF. Expressions are obtained for the averaged RF and its asymptotes which describe the redistribution function for low frequency radiation. The question of determining the frequencydependent absorption coefficient is discussed. __________ Translated from Astrofizika, Vol. 49, No. 3, pp. 475–485 (August 2006).     

Transformation of South African industrial fisheries

South African industrial fisheries have been dominated by a few large companies. The Marine Living Resources Act (MLRA) of 1998 emphasised that equity was to be achieved by redistribution through co-operative strategies among stakeholders. Instead, the reallocation of fishing rights has been treated as a resource management issue rather than a socio-economic challenge. Further, the institutional structures for transformation have been inappropriate. This paper investigates the institutional dynamics and discrepancies associated with transformation and concludes that the process became locked in a path dependency, which will eventually undermine the intentions of transformation.     

2000~2010年南京都市区人口空间变动特征研究

利用南京市第五次、第六次人口普查数据研究南京都市区2000~2010年人口空间变动及其规律。研究发现,① 10 a间南京都市区各地域人口均呈现增长态势,近郊区成为人口增长最为剧烈的区域;人口重心逐渐向南移动,同时人口分布的核心区域有向内收敛的趋势。② 根据测定系数、F检验与图像分析的综合判断,对数正态模型能够较好拟合人口分布的单核心结构,两年份曲线的变化表明郊区化的主体仍然是近郊区,尚未发展到远郊化的程度。多核心模型的拟合表明南京都市区已初步形成多核心结构,且主中心对人口仍具有强大吸引力;而多核心与单核心模型同时具有良好的拟合效果说明多核心结构尚未发育成熟。③ 南京都市区人口分布的空间异质性越来越高,人口分布趋于复杂,表明都市区正在向更加高级的阶段发展。     

不同水力压裂顺序下煤层气井组应力干扰效应研究—以沁水盆地柿庄南区块为例

煤层气井常采用井网布置方式进行开发，不同的水力压裂顺序引起不同的应力干扰效应。为了查明不同水力压裂顺序下煤层气井间应力干扰效应，本文以沁水盆地柿庄南区块3组煤层气井网15口井为研究对象，应用ABAQUS 有限元模拟软件，模拟了煤层气井网中3种水力压裂顺序（先周围后中心、对角、先中心后周围）的应力分布特征及干扰效应，提出了相应的水力压裂顺序建议。结果表明：当施工排量为6.00 8.00 m3/min，液量为430.00 580.00 m3时，（1）先周围后中心、对角、先中心后周围压裂时，距中心井、对角线井、周围井不同距离，依次分为应力释放区、集中区和原始应力区。先周围后中心压裂时，中心井三区范围依次为≤15.00 m、15.00 140.00 m、＞140.00 m。对角压裂时，对角线井三区范围依次为≤60.00 m、60.00 150.00 m、＞150.00 m。先中间压裂时，周围井三区范围依次为≤60.00 m、60.00 144.00 m、＞144.00 m。（2）煤层气井网采用四点法布置，井间距超过300.00 m，可有效避免煤层气井之间的应力干扰。降低煤层气井压裂时的施工难度。     

土壤颗粒组成影响137Cs含量的初步实验结果

放射性核素¹³⁷Cs作为人类核试验的产物,以其独特的理化性质而成为研究土壤侵蚀和泥沙沉积一种良好的示踪源。在¹³⁷Cs的再分配过程中,土壤颗粒组成是影响土壤¹³⁷Cs的重要因子。一般认为,土壤中的¹³⁷Cs活度主要与粘粘含量有关,但这要取决于原生沉积物的颗粒组成。通过选取共和盆地主要的三种土壤类型,采集0~30cm的混合样品,进行入工筛分,测定不同粒径成分的¹³⁷Cs含量。初步实验表明,砂质土的¹³⁷Cs活度与平均粒径之间呈负指数关系,0.01~0.1mm组分对¹³⁷Cs含量的影响最为显著;壤质土的¹³⁷Cs活度主要与粗粉砂(0.01~0.05mm)含量有关,与137Cs活度主要与原生沉积物的颗粒特性和粒度有关.¹³⁷Cs一旦被原生沉积物颗粒吸附,在以后的土壤颗粒再分配过程中,是很难被置换掉的。     

Effect of physical parameters on static undrained resistance of sandy soil with low silt content

Previous researches concerning the behavior of sand mixed with non-plastic fine show that the void ratio related to sand grains (e_c) plays a more important role in comparison with the total void ratio, where soil undrained resistance will be improved due to increase in FC at the constant e_c. In spite of this fact, the recent works indicate that e_c is unable to show perfectly the role of the non-plastic fines that are in voids between sand grains. For this reason, an equivalent void ratio (e_c)_eq has been defined that takes into account the non-plastic fine participation ratio in the soil bearing skeleton. In the present work, the generality of the expression of (e_c)_eq is verified. For this, a set of static undrained triaxial tests were performed. The results of tests indicate that the undrained behavior of a given sand mixed with different percentages of non-plastic fine can be described by (e_c)_eq. But if the grading curves of sand change, we cannot find a logic retention between (e_c)_eq and undrained resistance of soil, unless the physical and mechanical characteristics of soil are well introduced in expression of (e_c)_eq.     

Void distributions in samples of Ottawa sand

The void distribution of saturated specimens of Ottawa sand is presented. The presence of water inside the sand specimen is detected using the magnetic resonance imaging (MRI) technique. The void distribution of the sample was determined from the image. The specimen was prepared in a non-metallic triaxial cell and was put insie a MRI apparatus to obtain the image. Two sample preparation methods (wet tamping and dry pluviation) were used to illustrate the uniformity of the samples in the initial state. The void distribution along the height of the sample and the three-dimensional orientational void distribution at different locations inside the sample were analysed. The results indicate that the sample generated by the dry-pluviation method is more uniform than the sample generated by the wet-tamping method. When the wet-tamping sample preparation technique is used, the dense sample is more uniform than the loose sample. The development of voids was investigated by a sample loaded inside the MRI device under drained compression condition. The void distribution along the height of the sample at different stages was observed. This work has demonstrated the feasibility of using the MRI technique to examine void distribution in granular material.