Dynamic analysis of strain localization in water‐saturated clay using a cyclic elasto‐viscoplastic model     

B. Shahbodagh Khan  M. Mirjalili  S. Kimoto  F. Oka 《国际地质力学数值与分析法杂志》2014,38(8):771-793

A computational framework is presented for dynamic strain localization and deformation analyses of water‐saturated clay by using a cyclic elasto‐viscoplastic constitutive model. In the model, the nonlinear kinematic hardening rule and softening due to the structural degradation of soil particles are considered. In order to appropriately simulate the large deformation phenomenon in strain localization analysis, the dynamic finite element formulation for a two‐phase mixture is derived in the updated Lagrangian framework. The shear band development is shown through the distributions of viscoplastic shear strain, the axial strain, the mean effective stress, and the pore water pressure in a normally consolidated clay specimen. From the local stress–strain relations, more brittleness is found inside the shear bands than outside of them. The effects of partially drained conditions and mesh‐size dependency on the shear banding are also investigated. The effect of a partially drained boundary is found to be insignificant on the dynamic shear band propagation because of the rapid rate of applied loading and low permeability of the clay. Using the finer mesh results in slightly narrower shear bands; nonetheless, the results manifest convergency through the mesh refinement in terms of the overall shape of shear banding and stress–strain relations. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Introducing a new conceptual instantaneous unit hydrograph model based on a hydraulic approach     

Setareh Khaleghi  Mohammad Parvin Nia 《水文科学杂志》2013,58(13-14):1967-1975

ABSTRACT

A novel approach is introduced for simulation of instantaneous unit hydrographs (IUHs). The model consists of a series of linear reservoirs that are connected to each other, and is referred to as the inter-connected linear reservoir model (ICLRM). By assuming the flow between two reservoirs is a linear function of the difference between the water levels in the reservoirs, a system of first-order linear differential equations is obtained as the ICLRM governing equation. By solving the equations, the discharge from the last reservoir is considered as an IUH. A small-scale laboratory device was constructed for the simulation of IUHs using the model. By studying four hydrographs extracted from the literature, and simulating them using both the ICLRM and the Nash model, it is concluded that the ICLRM can predict these hydrographs more accurately than the Nash model. Due to the simplicity of the construction and operation of the ICLRM and, more importantly, its visual aspect, the ICLRM may be considered as an effective educational tool for studying IUHs.  相似文献   

Particulate air pollution from wildfires in the Western US under climate change     

Jia Coco Liu  Loretta J. Mickley  Melissa P. Sulprizio  Francesca Dominici  Xu Yue  Keita Ebisu  Georgiana Brooke Anderson  Rafi F. A. Khan  Mercedes A. Bravo  Michelle L. Bell 《Climatic change》2016,135(3-4):655-668

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Precipitation variability assessment of northeast China: Songhua River basin   总被引：1，自引：0，他引：1  

Muhammad Imran Khan  Dong Liu  Qiang Fu  Muhammad Azmat  Mingjie Luo  Yuxiang Hu  Yongjia Zhang  Faiz M Abrar 《Journal of Earth System Science》2016,125(5):957-968

Variability in precipitation is critical for the management of water resources. In this study, the research entropy base concept was applied to investigate spatial and temporal variability of the precipitation during 1964–2013 in the Songhua River basin of Heilongjiang Province in China. Sample entropy was applied on precipitation data on a monthly, seasonally, annually, decade scale and the number of rainy days for each selected station. Intensity entropy and apportionment entropy were used to calculate the variability over individual year and decade, respectively. Subsequently, Spearman’s Rho and Mann–Kendall tests were applied to observe for trends in the precipitation time series. The statistics of sample disorder index showed that the precipitation during February (mean 1.09, max. 1.26 and min. 0.80), April (mean 1.12, max. 1.29 and min. 0.99) and July (mean 1.10, max. 1.20 and min. 0.98) contributed significantly higher than those of other months. Overall, the contribution of the winter season was considerably high with a standard deviation of 0.10. The precipitation variability on decade basis was observed to increase from decade 1964–1973 and 1994–2003 with a mean value of decadal apportionment disorder index 0.023 and 0.053, respectively. In addition, the Mann–Kendall test value (1.90) showed a significant positive trend only at the Shangzhi station.  相似文献   

From hazard to impact: flood damage assessment tools for mega cities     

Albert S. Chen  Michael J. Hammond  Slobodan Djordjević  David Butler  David M. Khan  William Veerbeek 《Natural Hazards》2016,82(2):857-890

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Assessment of spatial variations in water quality of Garra River at Shahjahanpur,Ganga Basin,India     

Khan  Mohd Yawar Ali  Khan  Babra  Chakrapani  Govind Joseph 《Arabian Journal of Geosciences》2016,9(8):1-11

Arabian Journal of Geosciences - A comprehensive study on the chemical considerations of thermal waters (springs and geothermal wells) on the performance of solute geothermometers in predicting the...  相似文献   

The geochemistry of uranium occurrences and speciation in groundwater of Chinnar sub basin,South India     

CS Suma  K Srinivasamoorthy  K Saravanan  S Gopinath  R Prakash  A Faizal Khan 《Arabian Journal of Geosciences》2016,9(18):703

An attempt has been made in Chinnar sub basin of Dharmapuri district, South India to isolate the geochemistry of uranium occurrences in groundwater. The geology of the area is mainly of charnockite and granite gneiss. Groundwater samples were collected for two different seasons post and pre monsoon in two different litho units (granite gneiss and charnockite) and analysed for major, minor and uranium concentrations. Higher uranium (18.45 μg L^?1) has been recorded during pre monsoon season in granite gneiss with increasing pH. The saturation index calculation for the groundwater isolated minerals like uaraninite, coffinite, haiweeite and soddyite to be precipitating and uranium oxides like UO_2.25, UO_2.25beta, UO_2.33beta as oversaturated. The Eh-pH diagram attempted represents solubility of uraninite within the pH range of 6.0 to 8.0. The study isolate uranium in groundwater of the study area is controlled by the presence of (U₄O₉) uranium oxide.  相似文献   

Complexity measurement of regional groundwater resources system using improved Lempel-Ziv complexity algorithm     

Dong Liu

  Dan Zhao
  Qiang Fu
  Qiuchen Wu
  Yongjia Zhang
  Tianxiao Li
  Khan M Imran
  Faiz M Abrar
《Arabian Journal of Geosciences》2016,9(20):746

In this paper, the self-adaptive artificial fish swarm algorithm (SAAFSA) is used to optimize the coarse graining of segment numbers, which are used in the Lempel-Ziv complexity algorithm. This approach improves the Lempel-Ziv complexity (LZC) algorithm of equal probability coarse graining. As a case study, the complexities of monthly series of groundwater depth were analyzed at seven farms in the Hongxinglong Administration. GIS technology was used to create spatial distributions of monthly groundwater depths. A projection pursuit model based on the SAAFSA was established and used for complexity attribution analysis at selected farms with different degrees of complexity. The three selected farms, Hongqiling, 852, and Youyi, each represent a certain degree of complexity. Further analysis shows that precipitation, evaporation, temperature, and human activities are the primary factors that cause complexity variations in local groundwater depth. The results reveal the evolution of the complexity characteristics of local groundwater depth and provide scientific evidence for the need to effectively allocate regional water resources. Additionally, the proposed method can be applied in complexity analyses of other hydrologic features, as well as in research regarding nonlinear time series in economic, engineering, medical, and signal analyses.  相似文献   

Diversity patterns of free‐living marine nematodes in the southwest continental shelf off Bay of Bengal and their link to abiotic variables          下载免费PDF全文

Kapuli Gani Mohamed Thameemul Ansari  Somasundharanair Lyla  Syed Ajmal Khan  Punyasloke Bhadury 《Marine Ecology》2016,37(3):631-644

Marine sediments in continental shelf ecosystems harbor a rich biodiversity of benthic communities. In this study, the spatial and temporal diversity and community assemblages of free‐living marine nematodes were studied by sampling at six depths and over 3 years from the southwest continental shelf off Bay of Bengal, one of the least explored tropical shelf ecosystems. The dominant marine nematode species were related with abiotic variables as part of this study. The effects of sediment granulometry generally decreased with increasing depth and the highest nematode density and species diversity were recorded on coarse sand (shallower depths). Multivariate analysis of the nematode community data showed that community structure differed significantly among depths as well as among years. Statistical analyses showed significant correlations between the nematode community and abiotic variables. Sediment texture, organic matter, water pressure and depth profile were crucial factors for determining diversity, vertical profile and feeding types of the nematode community. Other environmental factors, including anthropogenic pressure, did not have an effect on nematode diversity except for the presence of some tolerant species (Metachromadora spp., Sabatieria spp. and Siplophorella sp.). This study represents a baseline of knowledge of free‐living marine nematode communities that can be used in the future to compare nematode assemblages from temperate shelf ecosystems.  相似文献   

Sequence stratigraphic analysis of Eocene Rock Strata,Offshore Indus,southwest Pakistan     

Natasha Khan  Khaista Rehman  Sajjad Ahmad  Jamil Khokher  M. Iqbal Hajana  M. Hanif 《Marine Geophysical Researches》2016,37(3):207-228

In this study, seismic data from two wells (Pak G2-1 and Indus Marine-1C) and age diagnostic larger benthic foraminifera (LBF) within drill cuttings has been used for the first time to identify depositional sequences within the carbonates in the Offshore Indus Basin, Pakistan. The Offshore Indus is tectonically categorized as a passive continental margin where carbonates occur as shelf carbonates in the near offshore and on volcanic seamounts in deeper waters. Seismic data analysis has indicated the presence of minor faults and carbonate buildups above the igneous basement in the south. Patterns of the seismic reflections enabled definition of three seismic facies units identified as: Unit 1 basement, represented by chaotic, moderate amplitude reflection configuration; while parallel bedding and the drape of overlying strata is typical character of Unit 2, carbonate mound facies. The younger Miocene channels represent Unit 3. The diagnosis of Alveolina vredenburgi/cucumiformis biozone confirmed the Ilerdian (55–52 Ma) stage constituting a second order cycle of deposition for the Eocene carbonates (identified as Unit 2). The carbonate succession has been mainly attributed to an early highstand system tract (HST). The environmental conditions remained favorable leading to the development of keep-up carbonates similar to pinnacle buildups as a result of aggradation during late transgressive system tract and an early HST. The carbonate sequence in the south (Pak G2-1) is thicker and fossiliferous representing inner to middle shelf depths based on fauna compared to the Indus Marine-1C in the north, which is devoid of fossils. Three biozones (SBZ 5, SBZ 6 and SBZ 8) were identified based on the occurrence of LBF. The base of the SBZ 5 zone marks the larger foraminifera turnover and the Paleocene–Eocene (P–E) boundary. The LBF encountered in this study coincides with earlier findings for the P–E boundary. Our findings indicate that the entire Ilerdian stage ranges from 55.5 to 52 Ma that was the episode of warmer water conditions on the carbonate shelves leading to the diversification of K-strategist larger foraminifera. The larger foraminiferal assemblage encountered in this study confirms the findings. The possible indication of stratigraphic-combination traps, revealed as reflection terminations, make carbonate mounds in the south a potential exploration target.  相似文献