An efficient discontinuous Galerkin method for advective transport in porous media     

Jostein R. Natvig  Knut&#x;Andreas Lie  Birgitte Eikemo  Inga Berre 《Advances in water resources》2007,30(12):2424-2438

We consider a discontinuous Galerkin scheme for computing transport in heterogeneous media. An efficient solution of the resulting linear system of equations is possible by taking advantage of a priori knowledge of the direction of flow. By arranging the elements in a suitable sequence, one does not need to assemble the full system and may compute the solution in an element-by-element fashion. We demonstrate this procedure on boundary-value problems for tracer transport and time-of-flight.  相似文献   

Micro- to mesoscale evolution of beaches in response to climatic shift: observation and conceptual modelling (Brittany,France)     

Regnauld  Hervé  Binois  Sandrine  Fouqué  Christophe  Lemasson  Loic 《Geologie en Mijnbouw》1998,77(3-4):323-332

In the framework of the European project 'Climate change and coastal evolution in Europe', the microscale (< 1 year) morphological evolution of beaches in Brittany (W France) has been monitored for some years and linked to immediate forcings, the first one being tides (with a 13-m tidal range), and the second storm intensity. For the same sites, a mesoscale (decades) evolution was reconstructed from air photographs and historical data. The evolution is forced first of all by human activities, and secondly by climatic shift: wind direction changes and average wind velocity evolution. These results were used to build and calibrate a model of coastal behaviour. The model is based on a simple sediment cell (input – transit – output) and simulates the movements of volumes of sands under successive morphodynamic processes. Each of these processes is modelled (in terms of volume exchanges) and parameterized by the relevant atmospheric element. Thus, the model is not deterministic but simulates different probabilities for atmospheric events and morphological response. The model runs for one year and produces realistic sediment accumulation values and coastal retreat rates. When run for half a century, results are also quite comparable to the field data. Storm frequency changes appear to be an important element for the evolution, but the main and first forcing is the availability of sediment.  相似文献   

Large deformation three-dimensional static analysis of deep water marine risers     

Michael M. Bernitsas  John E. Kokarakis  Asjhar Imron 《Applied Ocean Research》1985,7(4):178-187

The problem of static three-dimensional, nonlinear, large deformation response of a marine riser is formulated within small strain theory and solved numerically. This type of analysis is necessary, for the new generation of drilling and production risers. The mathematical model takes properly into account the effects of internal and external pressure and the complete nonlinear boundary conditions, without linearizing the follower forces. The extensibility or inextensibility condition is used as the constitutive relation in the tangential direction. Torsion and bending are coupled. The external load and the boundary conditions are deformation dependent. A solution method is developed based on an incremental finite element algorithm, which involves a prediction-correction scheme. In the correction phase deformation dependent quantities are updated. The extensibility or inextensibility condition is used to reduce the degrees of freedom of the system. The numerical results of the developed computer code compare very well with available semi-analytical and numerical solutions. Three numerical applications are used to demonstrate the importance of large deformation, nonlinear and three-dimensional analyses.  相似文献   

Improving alternative livelihood interventions in marine protected areas: A case study in Tanzania     

《Marine Policy》2016

Alternative livelihood programmes are often used in multipleuse marine protected areas as incentives, compensation for lost opportunities, or as intervention strategies for poverty alleviation. Yet little is known about their impacts on biodiversity conservation and the well-being of the targeted communities. This study focuses primarily on alternative livelihood projects undertaken among selected groups of individuals, in six villages, located in the Mnazi Bay-Ruvuma Estuary Marine Park (MBREMP), Mtwara district, southern Tanzania. The aim was to investigate how the processes involved in the implementation of these new livelihood activities contributed to the expected outcomes of providing good returns to reduce community's dependency on the sea and improve conservation. Data were collected through focus group discussions with selected members of local community, who actively took part in the projects; key informant interviews with conservation personnel and district fisheries officials; questionnaire surveys of a random sample of project beneficiary households; and a review of pertinent documents. The overwhelming majority of survey respondents (90%) reported that the projects were allocated inappropriately. Interviews and focus groups further revealed that the purpose of alternative projects was not sufficiently clear and that many beneficiaries perceived that these projects were initiated simply to comply with the MBREMP regulations. Overall, 70% of survey respondents stated that the project activities could not compete with the income gained from fisheries. An analysis of documents further revealed that almost all projects began to flounder when funding from the MBREMP came to an end. This was because they were not supported beyond the pilot phase and, thereafter, insufficient revenue was generated to maintain running costs. Improved targeting and design of livelihood interventions will ensure that the projects achieve the goals of providing alternatives for fishers, increasing well-being and improving biodiversity conservation.  相似文献   

What is local about local environmental governance? Observations from the local biodiversity action planning process     

James Evans 《Area》2004,36(3):270-279

In line with the tenets of sustainable development, environmental policy has privileged action at the local level. This paper explores how the local has been manifested in practice, drawing upon an extensive qualitative study of biodiversity action planning in Birmingham, UK, undertaken between 1999 and 2002. Analysis highlights the embedded and geographically uneven character of the process, and a number of local path dependencies are identified that act to both constrain and enable the process. It is concluded that environmental policy tends to accept the positive rhetoric of local action rather uncritically. In practice, the local is manifested in a number of different ways, with highly heterogeneous effects.  相似文献   

Impact of Water Vapor on Elevation-dependent Climate Change     

ZHANG Xianzhou  WANG Ling  HE Yongtao  DU Mingyuan  ZHANG Jing  SHI Peili  YU Chengqun  ZHANG Yangjian 《资源与生态学报(英文版)》2017,8(1):5-9

Elevation dependency amongst climate change signals has been found in major mountain ranges around the world, but the main factors causing this dependency have not been clarified. In this study, four different datasets of observation and reanalysis for China were used to examine the elevation dependency of climate change. A lack of consistency was found in dependency between warming magnitude and elevation across the Tibetan Plateau and China. However, a dependency of climate change on water vapor was detected whereby the temperature trend initially increased at low specific humidity, and then decreased as specific humidity increased. At ground level the maximum trend in temperature appeared in the specific humidity range 2.0-3.0 g kg^-1. This suggests that water vapor is a mediator of climate change and may be responsible for elevation-dependent climate change.  相似文献   

基桩可靠度分析的统计相关性评价方法     

李典庆 《岩土力学》2008,29(3):633-638

为了评估不同失效准则对基桩可靠度的影响,传统的方法是引入失效准则偏差系数。然而目前所定义的失效准则偏差系数使得偏差系数和基本随机变量之间具有一定的相关性,直接将偏差系数的统计参数用于基桩可靠度分析是不尽合理的。为此,基于线性回归理论提出了新的失效准则偏差系数的定义,并采用Spearman秩相关系数方法检验了偏差系数和基本随机变量之间的相关性。采用算例分析了偏差系数和基本随机变量之间的相关性对基桩可靠度的影响。结果表明,传统的失效准则偏差系数的定义使得偏差系数和基本随机变量之间具有一定的相关性,提出的通用的失效准则偏差系数能够有效地消除这种相关性。偏差系数与基本随机变量之间的相关性对偏差系数的均值具有明显的影响,但对变异系数基本没有影响。此外,偏差系数与基本随机变量间的相关性对基桩可靠指标具有明显的影响,基桩可靠度分析中应该消除这种相关性。  相似文献   

主成分分析技术在遥感蚀变信息提取中的应用研究综述   总被引：1，自引：0，他引：1  

吴志春  叶发旺  郭福生  刘文恒  李华亮  杨羿 《地球信息科学学报》2018,20(11):1644-1656

主成分分析是目前遥感蚀变异常信息提取常用方法之一,该方法具有对影像大气校正质量要求不高、实现简单、提取效果好、效果稳健等优点,广受地质工作者的青睐。根据输入影像的数量及类型、主成分分析的次数等,本文将主成分分析分为标准主成分分析、特征向量主成分分析、定向主成分分析、二次主成分分析、不同影像间的主成分分析等5种类型。其中,特征向量主成分分析又可细分为4个波段特征向量主成分分析和3个波段特征向量主成分分析。在上述分类的基础上,系统介绍了各种主成分分析及蚀变信息主分量的选择,尤其是对特征向量主成分分析的Crosta技术和定向主成分分析的软落叶技术进行了详细阐述。并以TM/ETM+、ASTER影像为例,对部分应用主成分分析提取蚀变异常信息的实例进行了分析,认为：在基岩裸露区,不同主成分分析都可以很好地提取铁化、泥化蚀变信息;在中、低植被覆盖区,采用标准主成分分析、Crosta技术、改进的Crosta技术、软落叶技术、“掩膜/抑制干扰信息+主成分分析”等方法可以有效地提取蚀变异常信息;高植被覆盖区多采用主成分分析生成的蚀变信息主分量进行彩色合成,再通过对彩色影像进行目视解译的方式判断蚀变的类型和范围。其中,“掩膜+Crosta技术”、“掩膜+软落叶技术”、二次主成分分析等方法在高植被覆盖区也可以取得较好的应用效果;对于干扰信息种类众多、岩性复杂的地区,可根据干扰信息、岩性种类划分成若干个小区,再根据每个小区实际情况采用不同的蚀变提取方法,最后将每个小区内提取的蚀变信息进行合并。  相似文献   

Financial caps for oil pollution damage: A historical mistake?     

Michael Faure  Hui Wang   《Marine Policy》2008,32(4):592-606

The limitation of liability (known as financial caps) of the ship owner has a long tradition in maritime law in general and in the marine oil pollution compensation regime in particular. This paper uses the economic instrument to critically analyze such a mechanism, in order to answer the question if the financial caps are indeed a historical mistake.  相似文献   

基于贝叶斯网的象山港网箱养殖水环境指标建模     

滕丽华  杨季芳 《海洋湖沼通报》2009,(1)

贝叶斯网络具有强大的推理能力,能与先验知识和数据结合,进行定性和定量分析,提供了1条有效的处理预测问题的途径,本文首先介绍了贝叶斯网络基本理论及其特点,并讨论如何学习贝叶斯网络结构,然后由专家知识和给定数据,采用基于依赖分析的贝叶斯网络学习算法构造了海底网箱养殖水环境指标间的贝叶斯网结构模型.该模型能有效的表达网箱养殖环境各个指标之间的因果关系和影响程度,实验结果表明,试验数据显示准确性是92.3%,kappa指数是0.882.以上证明该方法是有效可行的,表明贝叶斯网络是一种很有前途的预测评价方法.  相似文献