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This paper investigates the possibility of interpreting progressive shear failure in hard soils and soft rocks as the result of shear propagation of a pre‐existing natural defect. This is done through the application of the principles of fracture mechanics, a slip‐weakening model (SWM) being used to simulate the non‐linear zone at the tips of the discontinuity. A numerical implementation of the SWM in a computation method based on the boundary element technique of the displacement discontinuity method (DDM) is presented. The crack and the non‐linear zone at the advancing tip are represented through a set of elements, where the displacement discontinuity (DD) in the tangential direction is determined on the basis of a friction law. A residual friction angle is assumed on the crack elements. Shear resistance decreases on elements in the non‐linear zone from a peak value at the tip, which is characteristic of intact material, to the residual value. The simulation of a uniaxial compressive test in plane strain conditions is carried out to exemplify the numerical methodology. The results emphasize the role played by the critical DD on the mechanical behaviour of the specimen. A validation of the model is shown through the back analysis of some experimental observations. The results of this back analysis show that a non‐linear fracture mechanics approach seems very promising to simulate experimental results, in particular with regards to the shear band evolution pattern. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Guiomar Rotllant Carles G. Simeó Guillermo Guerao Marta Sastre Daniel F. R. Cleary Ricardo Calado Alicia Estévez 《Marine Ecology》2014,35(3):298-307
The spider crab Maja brachydactyla is an important commercial species in Europe and supports intensive fisheries in the NE Atlantic. A field survey was performed to assess long‐term and consecutive interannual (2005–2010) variation of the biochemical composition of newly hatched larvae of M. brachydactyla. Larval biochemical profiles differed significantly among years, with pronounced differences being recorded in 2010. Differences among batches of newly hatched larvae were mainly explained by the contribution of triacylglycerols and, to a lesser degree, by protein and lipid content. The use of different nutrition indices is discussed. The biochemical composition of newly hatched larvae from M. brachydactyla was highly variable, even though surveyed broodstock was obtained from the same local population and was always sampled during the same season. The unpredictable biochemical profiles of newly hatched larvae may condition their survival and recruitment. This largely overlooked aspect of larval variability should be considered in future fisheries management strategies and captive production of marine organisms that still rely on wild seeds. 相似文献
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Filippo Giorgi Erika Coppola Francesca Raffaele Gulilat Tefera Diro Ramon Fuentes-Franco Graziano Giuliani Ashu Mamgain Marta Pereira Llopart Laura Mariotti Csaba Torma 《Climatic change》2014,125(1):39-51
We analyze changes of four extreme hydroclimatic indices in the RCP8.5 projections of the Phase I CREMA experiment, which includes 21st century projections over 5 CORDEX domains (Africa, Central America, South America, South Asia, Mediterranean) with the ICTP regional model RegCM4 driven by three CMIP5 global models. The indices are: Heat Wave Day Index (HWD), Maximum Consecutive Dry Day index (CDD), fraction of precipitation above the 95th intensity percentile (R95) and Hydroclimatic Intensity index (HY-INT). Comparison with coarse (GPCP) and high (TRMM) resolution daily precipitation data for the present day conditions shows that the precipitation intensity distributions from the GCMs are close to the GPCP data, while the RegCM4 ones are closer to TRMM, illustrating the added value of the increased resolution of the regional model. All global and regional model simulations project predominant increases in HWD, CDD, R95 and HY-INT, implying a regime shift towards more intense, less frequent rain events and increasing risk of heat wave, drought and flood with global warming. However, the magnitudes of the changes are generally larger in the global than the regional models, likely because of the relatively low “climate sensitivity” of the RegCM4, especially when using the CLM land surface scheme. In addition, pronounced regional differences in the change signals are found. The data from these simulations are available for use in impact assessment studies. 相似文献
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Samson Hagos L. Ruby Leung Yongkang Xue Aaron Boone Fernando de Sales Naresh Neupane Maoyi Huang Jin-Ho Yoon 《Climate Dynamics》2014,43(9-10):2765-2775
Land use and land cover (LULC) over Africa have changed substantially over the last 60 years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties of model simulated response in the African monsoon system and Sahel precipitation due to LULC change using a set of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Although the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature. The relationship between the model responses to LULC change and the climatologists of the control simulations is also examined. Simulations that are climatologically too dry or too wet compared to observations and reanalyses have weak response to land use change because they are in moisture or energy limited regimes respectively. The ones that lie in between have stronger response to the LULC changes, showing a more significant role in land–atmosphere interactions. Much of the change in precipitation is related to changes in circulation, particularly to the response of the intensity and latitudinal position of the African Easterly Jet, which varies with the changes in meridional surface temperature gradients. The study highlights the need for measurements of the surface fluxes across the meridional cross-section of the Sahel to evaluate models and thereby allowing human impacts such as land use change on the monsoon to be projected more realistically. 相似文献
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Emily Tyler Anya Boyd Kim Coetzee Marta Torres Gunfaus Harald Winkler 《Climate Policy》2013,13(6):770-776
The MAPS programme, which seeks to deepen mitigation ambition in developing countries, is engaged in exploring the concepts of Nationally Appropriate Mitigation Actions (NAMAs) and Low Carbon Development Strategies (LCDS) from a developing country perspective. Here, climate mitigation practitioners in six developing countries were surveyed for their understanding of these concepts (anonymous, personal communications with climate mitigation practitioners in Argentina, Brazil, Chile, Colombia, India, and South Africa). It is found that there is much scope for clarity and conceptual elaboration in this policy space. NAMAs are largely interpreted as mitigation activities packaged for submission to the United Nations Framework Convention on Climate Change (UNFCCC) registry, but are not held to constitute the full set of mitigation activity in a developing country. New terminology may be needed to describe this broader set. A tighter interpretation of LCDS to distinguish between a strategic or coordinating policy action may be useful. Other themes arising include the way ‘national appropriateness’ is reflected in the concepts, and the role of international policy in deepening mitigation action in developing countries. 相似文献
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