Transverse and longitudinal fluid flow modelling in fractured porous media with non‐matching meshes

A new discrete fracture model is introduced to simulate the steady‐state fluid flow in discontinuous porous media. The formulation uses a multi‐layered approach to capture the effect of both longitudinal and transverse permeability of the discontinuities in the pressure distribution. The formulation allows the independent discretisation of mesh and discontinuities, which do not need to conform. Given that the formulation is developed at the element level, no additional degrees of freedom or special integration procedures are required for coupling the non‐conforming meshes. The proposed model is shown to be reliable regardless of the permeability of the discontinuity being higher or lower than the surrounding domain. Four numerical examples of increasing complexity are solved to demonstrate the efficiency and accuracy of the new technique when compared with results available in the literature. Results show that the proposed method can simulate the fluid pressure distribution in fractured porous media. Furthermore, a sensitivity analysis demonstrated the stability regarding the condition number for wide range values of the coupling parameter.     

Proportional stress and strain paths in barodesy

Asymptotic behaviour of soil deserves particular attention: If soil is deformed with a proportional strain path, the resulting stress path approaches asymptotically a proportional stress path. In this arcticle, we review existing experimental evidence on this phenomenon and discuss it in the frame of barodesy. Here, the presented relation is a modification of a barodetic expression and includes Jáky's relation, inhibits tensile stress and is able to predict asymptotic stress ratios based on experimental findings. The proposed relation is compared with experimental data as well as with the so‐called stress‐dilatancy relations and other constitutive relations proposed so far. Copyright © 2015 John Wiley & Sons, Ltd.     

基于冰川钻孔温度的古气候重建研究进展北大核心CSCD

冰川内部温度与过去冰面温度变化密切相关,因此可以利用冰川钻孔温度对过去冰面温度变化过程进行重建。耦合的热传导-冰流物理模型与相关反演算法,是基于冰川钻孔温度进行古气候重建研究的理论基础和关键。论文收集了过去三十多年基于冰川钻孔温度进行古气候重建的研究文献,从冰川钻孔温度对气候变化的响应和古气候重建等方面进行了概述,并简要讨论了不同反演算法的优劣性和适用条件。尽管很多因素(如太阳辐射、融水等)都会对冰川钻孔温度造成影响,但两极或高纬地区的冷冰川钻孔温度能较好地反映气候变化历史。目前已通过这些不同地区的冰川钻孔温度,重建了末次冰期冰盛期以来不同时间尺度的气候变化历史,同时可与对应的冰芯记录相互印证。此外,通过冰川钻孔温度可以研究冰川与气温的耦合作用,并进一步预测冰川对未来气候变化的响应。利用中纬度冷冰川钻孔温度开展古气候重建的研究较少,未来加深这一方面的研究将有助于揭示中纬度高海拔地区的气候变化状况。     

基于最小作用原理的Richards方程变分解

经典的Richards入渗控制方程属于偏微分方程,具有强烈的非线性,难以求得解析解。以入渗时间为最小作用量,基于Richards方程建立关于入渗路径的时间泛函,将考虑重力项的非饱和土垂直入渗问题转化为泛函极值问题,并构造等价的Euler-Lagrange方程进行求解。计算结果表明,扩散系数D（?）与概化湿润锋距离具有函数关系,当扩散系数D（?）形式已知时,可求得最优路径下湿润锋处含水率、较远处湿润锋最小含水率、土壤含水率最大熵分布3个问题,并基于最优路径检验了本研究条件下,Boltzmann变换和线性变换求解Richards方程的精度。求解过程未引进新变量化简Richards方程,不改变原方程结构,因此其解具有普遍性,可作为非饱和土力学计算的一个补充。     

A geomorphological model of susceptibility to the effect of human interventions for environmental licensing determination (SHIELD)

Almost every country requires some form of environmental licensing prior to the inception of development projects that may affect the integrity of the environment and its social context. We developed a new conceptual and methodological model to instruct the assessment of the potential impacts posed by proposed projects. Susceptibility to Human Interventions for Environmental Licensing Determination (SHIELD) includes a novel geomorphological interpretation of the Environmental Impact Assessment (EIA). It considers the impact of human interventions on geomorphological processes and landscape functioning in the context of the entire ecosystem, going further than the classical concept of vulnerability. Estimated susceptibility of the site informs the screening stage, allowing local conditions to help define the criteria used in the process. Similarly, the level of detail of the environmental baseline is scoped by considering the degree of disturbance of natural processes posed by human intervention. Testing this geomorphological susceptibility model on different kinds of environments would allow shifting the environmental licensing practices from the prevailing anthropocentric and static conception of the environment towards an Ecosystem Approach. SHIELD addresses the need to improve the screening and scoping stages that form the basis of the rest of any EIA. SHIELD introduces several innovations to EIA including the incorporation of fuzzy logic, a preassembled database of contributions form experts, and a shifting of emphasis from the type of proposed intervention to the type of environment and its relative susceptibility.     

2018年5月江苏极端降水事件发生前副热带高压异常及原因分析

本文利用NCEP/NCAR提供的2.5°×2.5°全球再分析数据,以2018年5月江苏两次极端降水事件发生前副高异常变化为研究对象,根据全型涡度方程定量计算了凝结潜热分布不均引起的涡源对副高迅速演变的诱发作用。研究发现,120°E处500 hPa 5月第1候副高脊线多年平均位置位于16°N附近,而2018年同期120°E的脊线则位于19°N附近,呈明显偏北的状态。2018年5月第1候东亚500 hPa位势高度距平场表现出南高北低的形态,有利于我国华东地区成为暖湿空气和干冷空气的交汇区,构成了江苏5月两次极端降水过程的有利环流背景。与对流层中层环流异常对应的是,同期115°~125°E之间850 hPa上8 g·kg^-1等比湿线位于28°N附近,较多年气候态偏北15°,强降水区内同期850 hPa比湿较往年偏多2~4 g·kg^-1,相应距平百分率可达50%~75%。且110°~120°E之间θ_se的340 K等值线5月第1候多年气候态位于13°N以南,但2018年同期却偏北至25°N附近,暖湿气团北进有利于强降水的发生。副高西伸北抬前,副高主体西侧和北侧均有凝结潜热加热区存在,说明潜热加热与副高演变关系密切。垂直剖面表明600 hPa为凝结潜热加热中心,向上加热率随高度减小,因此500 hPa处潜热加热率垂直梯度为负,使得500 hPa成为负涡源所在。因凝结潜热分布不均产生的负涡源,1~2 d便可形成与副高自身十分接近的负涡度值,足以诱发副高突变,该时间尺度与副高真实演变时间相符。负涡源中与凝结潜热垂直分布不均相关的部分起主要作用,而与凝结潜热水平分布不均相关的部分同时期产生的负涡度最多仅为前者的1/3左右,对副高突然西伸的作用较小。与凝结潜热相关的负涡源作为引发西太平洋副高异变的可能原因,其与副高的关系仍需进一步研究。     

基于紧密堆积理论的低密度固井水泥浆设计

合理的颗粒级配是提高固井水泥环内部密实度、早期力学强度和界面胶结能力的关键。基于此,本文从几种典型的连续颗粒级配的紧密堆积理论中优选出DFE进行固井水泥浆体系设计,并通过大量实验首次确定了适宜G级油井水泥基深水固井水泥浆体系设计的n值最优范围：0.33~0.40。结合激光粒度分析仪实测结果,在粒径≤3.38 μm、3.38~70.70 μm、≥70.70 μm三个范围内依次采用纳米CaCO₃（nano CaCO₃,以下简称“NC”）、G级油井水泥和漂珠,并按DFE（n=0.33~0.40）体积分布曲线进行混配。在此基础上,提出一种密度为1.50 g/cm³的低成本低温早强三元固相级配水泥浆体系,并与漂珠二元固相水泥浆体系和NC二元固相水泥浆体系的性能进行对比。研究结果表明：该三元体系水泥石的抗压强度、抗折强度和二界面胶结强度相比于漂珠二元体系和NC二元体系分别提高了7%~21.1%、13.4%~51.9%和41.4%~122.2%。三元体系的固井水泥石在垂向上的最大密度差为0.022 g/cm³。基于DFE设计的三元体系具有良好的流变性、稳定性和力学性能。DFE对于多元固井水泥浆体系的设计和应用具有一定的指导意义,在保证低密度的前提下能够有效地提高固井水泥石的早期强度和综合性能。     

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Acceptance of the international compensation regime for tanker oil pollution – And its implications for China

The international compensation regime for tanker oil pollution has been successful in providing adequate and prompt compensation to pollution victims in its member states. Nevertheless, the attitudes of different countries toward acceptance of this regime have varied considerably. This paper aims to explain three main factors in the acceptance of the regime, including: (1) The level of economic development; (2) the risk of exposure to tanker oil spills; and (3) the financial burden associated with adherence to the International Oil Pollution Compensation Fund (IOPC). Using both fuzzy-set Qualitative Comparative Analysis and an Ordered Probit model, this study found two patterns causing upper-middle and high income countries to have a high acceptance level: (a) Those facing a medium risk of oil spills and having a low financial burden; and (b) those facing a high risk of oil spills. The study reveals that, for a country with a high risk of exposure to tanker oil spills, such as China, with its improvement in economic status it is far better for it to join the IOPC Fund, so as to provide better protection both for potential pollution victims and for the marine environment. The results of this study can also be applied to other countries that are considering whether or not to accept the international compensation regime for tanker oil pollution.     

Human dignity: A fundamental guiding value for a human rights approach to fisheries?

Recently, a human rights approach has been center-staged within fisheries governance as a response to the limits of private property rights in reducing insecurity and vulnerability among fishers and fishing communities. Despite its growing adoption in international legal frameworks and among civil society organizations, the conceptual pitfalls of the human rights approach to fisheries (i.e., its neoliberal tendencies and the neglect of collective rights and social duties) raised by critical scholarship remain largely unsettled, leading to practical concerns about whether such a framework will ultimately benefit fishers on the ground. To further contribute to the debate, this article presents a nuanced discussion of the human rights perspective by introducing the concept of human dignity. Specifically, it argues that human dignity, with its greater conceptual scope and depth, could act as a foundational value with which to mitigate some of the shortcomings of the human rights approach. The purpose here is suggestive rather than definitive and is aimed at highlighting the link that has not been clearly made between human rights and human dignity. I argue that heightened attention to human dignity has the potential to create wider support for the human rights approach and ultimately help facilitate its efficacy in fisheries.