Extended Finite Element Method for the Analysis of Discontinuities in Rock Masses   总被引：1，自引：0，他引：1  

Debasis Deb  Kamal C. Das 《Geotechnical and Geological Engineering》2010,28(5):643-659

The strength and deformability of rock mass primarily depend on the condition of joints and their spacing and partially on the engineering properties of rock matrix. Till today, numerical analysis of discontinuities e.g. joint, fault, shear plane and others is conducted placing an interface element in between two adjacent rock matrix elements. However, the applicability of interface elements is limited in rock mechanics problems having multiple discontinuities due to its inherent numerical difficulties often leading to non-convergent solution. Recent developments in extended finite element method (XFEM) having strong discontinuity imbedded within a regular element provide an opportunity to analyze discrete discontinuities in rock masses without any numerical difficulties. This concept is based on partition of unity principle and can be used for cohesive rock joints. This paper summarizes the mathematical frameworks for the implementation of strong discontinuities in 3 and 6 nodded triangular elements and also provides numerical examples of the application of XFEM in one and two dimensional problems with single and multiple discontinuities.  相似文献   

Intercomparison of Oceansat-2 and ASCAT Winds with In Situ Buoy Observations and Short-Term Numerical Forecasts     

S. Indira Rani  M. Das Gupta  Priti Sharma  V. S. Prasad 《大气与海洋》2014,52(1):92-102

Sea surface winds from the Oceansat-2 scatterometer (OSCAT) are important inputs to Numerical Weather Prediction (NWP) models. The Indian Space Research Organization (ISRO) recently updated the OSCAT retrieval algorithm in order to generate better products. An attempt has been made in this study to evaluate the updated OSCAT winds using buoy observations and the 6-hour short-term forecasts from the T574L64 model from the National Centre for Medium Range Weather Forecasting (NCMRWF) during the 2011 monsoon. The results of the OSCAT evaluation are also compared with those from the Advanced Scatterometer (ASCAT) on-board the Meteorological Operational Satellite-A (MetOp-A) which were evaluated in the same way. The root mean square differences (RMSDs) for wind speed and direction, are within 2?m?s^?1 and 20° for both scatterometers. The RMSDs for OSCAT are slightly higher than those for ASCAT, and this difference may be attributed in part to the difference in frequency and resolution of the scatterometer payloads. The bias and standard deviation for ASCAT winds are also lower than those for OSCAT winds with respect to the model short-range forecast, and this can be attributed to the regular assimilation of ASCAT winds in the model.  相似文献   

Lithium in Groundwater of Rajasthan     

Subhajyoti Das 《Journal of the Geological Society of India》2014,83(1):116-116

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Model dependence of transonic properties of accretion flows around black holes     

Sandip K. Chakrabarti †  Santabrata Das 《Monthly notices of the Royal Astronomical Society》2001,327(3):808-812

We analytically study how the behaviour of accretion flows changes when the flow model is varied. We study the transonic properties of the conical flow, a flow of constant height and a flow in vertical equilibrium, and show that all these models are basically identical, provided that the polytropic constant is suitably changed from one model to another. We show that this behaviour is extendible even when standing shocks are produced in the flow. The parameter space where shocks are produced remains roughly identical in all these models when the same transformation among the polytropic indices is used. We present applications of these findings.  相似文献   

Plasma instability at the inner edge of the accretion disk—I     

S. C. Tripathy  C. B. Dwivedi  A. C. Das  A. R. Prasanna 《Journal of Astrophysics and Astronomy》1993,14(2):103-114

In this paper, the analytical and numerical results of the stability analysis of the accretion disk at the inner boundary is presented. Including the effect of finite conductivity in the disk dynamics, a simple calculation considering only the radial perturbation has been carried out. Within local approximation, it is concluded that the disk is stable to Kelvin-Helmholtz and resistive electromagnetic modes whereas the magnetosonic mode can destabilise the disk structure.  相似文献   

Plasma instability at the inner edge of the accretion disk— II     

S. C. Tripathy  C. B. Dwivedi  A. C. Das  A. R. Prasanna 《Journal of Astrophysics and Astronomy》1993,14(3-4):167-179

A two-dimensional instability analysis for a magneto-keplerian disk flow around a compact object is presented here. Using the eigenvalue technique, linearly coupled perturbed equations have been numerically solved within the local approximation. It is concluded that Kelvin-Helmholtz, magnetosonic (fast and slow) and resistive electromagnetic modes exist. However, only the magnetosonic mode can destabilise the disk structure. Further, we discuss the properties of different modes as a function of disk parameters and plot the eigenmode structures for different physical quantities.  相似文献   

Characterization of Surface Geological Material in Northwest India and Adjoining Areas of Pakistan Using Normalized Difference Water Index,Land Surface Temperature and Silica Index     

Sanjay Das 《Journal of the Indian Society of Remote Sensing》2018,46(10):1645-1656

Land surface temperature (LST) shows negative correlation with the Normalized Difference Water Index (NDWI). Variability in the degree of correlation between LST and NDWI is ascribed to the physical character of specific geological material. Northwest India exhibits various landforms with different geological materials and has been broadly classified into four zones. Structural ridges of Aravalli Mountain of different rock compositions show strong variability both in NDWI (range 1.154, SD?=?0.0599) and in LST (range 24 °C and SD?=?2.54). Negative LST–NDWI correlation in this sector is partially linear. Western Thar Desert, having homogenous silica sand of lower emissivity shows least variability in its NDWI (range 0.88, SD?=?0.027) and moderate variability in its LST (20 °C, SD?=?2.389). Strong negative correlation of LST with NDWI is exhibited here. Band ratio Silica map in this sector shows strong positive correlation with LST. The eastern part of the Thar desert with mixed rocky knobs, and wind-blown sand shows low variability in NDWI (range 0.85) as well as LST (range 15 °C). Area in Indus–Bias–Sutlej River basin, dominated with fluvial sediments with lesser amount of windblown sediments, show low variability of NDWI (0.85) and moderate variability of LST (range 23 °C). In the areas, around Luni river higher NDWI trend is recorded, which is unrelated to present drainage trends indicating presence of palaeo-drainage. In addition, high NDWI and high LST bearing linear zones at places are interpreted as structural lineaments/faults based on pattern, moisture content and thermal high.  相似文献   

Accuracy Assessment of Digital Elevation Model Generated by SAR Stereoscopic Technique Using COSMO-Skymed Data     

Ritesh Agrawal  Anup Das  A. S. Rajawat 《Journal of the Indian Society of Remote Sensing》2018,46(10):1739-1747

Radargrammetry technique using the stereoscopic synthetic aperture radar (SAR) images is used for the generation of a digital elevation model (DEM) of a region requires only the amplitude images. SAR stereoscopic technique is analogous to the stereo-photogrammetric technique where the optical stereoscopic images are used for DEM generation. While the advantages of the SAR images are their indifference to atmospheric transparency and solar illumination conditions, the side-looking geometry of the SAR increases the complexity in the SAR stereo analysis. The availability of high spatial and temporal resolution SAR data in recent years has facilitated generation of high-resolution DEM with greater vertical accuracy using radargrammetric technique. In the present study, attempt has been made to generate the DEM of Dehra Dun region, India, from the COSMO-Skymed X-band SAR data-pair acquired at 8 days interval through the radargrammetry technique. Here, radargrammetric orientation approach has been adopted to generate the DEM and various issues and processing steps with the radargrammetry technique have been discussed. The DEM was validated with ground measured elevation values using a differential global positioning system and the root-mean-square error of the DEM was found as 7.3 m. The DEM was compared with the reference DEM of the study area generated from the Cartosat-1 stereo data with a model accuracy of 4 m.  相似文献   

Understanding the cause and effect relationship of debris slides in Papum Pare district,Arunachal Himalaya,India     

Das  Ratan  Phukon  Parag  Singh  T. N. 《Natural Hazards》2022,110(3):1735-1760

Natural Hazards - Slope failures are recurrent phenomena during the Indian Summer Monsoon (ISM) season in the mountainous regions of Arunachal Himalaya, NE India, with a consequent damaging impact...  相似文献   

Probabilistic estimates of future changes in California temperature and precipitation using statistical and dynamical downscaling   总被引：1，自引：0，他引：1  

David W. Pierce  Tapash Das  Daniel R. Cayan  Edwin P. Maurer  Norman L. Miller  Yan Bao  M. Kanamitsu  Kei Yoshimura  Mark A. Snyder  Lisa C. Sloan  Guido Franco  Mary Tyree 《Climate Dynamics》2013,40(3-4):839-856

Sixteen global general circulation models were used to develop probabilistic projections of temperature (T) and precipitation (P) changes over California by the 2060s. The global models were downscaled with two statistical techniques and three nested dynamical regional climate models, although not all global models were downscaled with all techniques. Both monthly and daily timescale changes in T and P are addressed, the latter being important for a range of applications in energy use, water management, and agriculture. The T changes tend to agree more across downscaling techniques than the P changes. Year-to-year natural internal climate variability is roughly of similar magnitude to the projected T changes. In the monthly average, July temperatures shift enough that that the hottest July found in any simulation over the historical period becomes a modestly cool July in the future period. Januarys as cold as any found in the historical period are still found in the 2060s, but the median and maximum monthly average temperatures increase notably. Annual and seasonal P changes are small compared to interannual or intermodel variability. However, the annual change is composed of seasonally varying changes that are themselves much larger, but tend to cancel in the annual mean. Winters show modestly wetter conditions in the North of the state, while spring and autumn show less precipitation. The dynamical downscaling techniques project increasing precipitation in the Southeastern part of the state, which is influenced by the North American monsoon, a feature that is not captured by the statistical downscaling.  相似文献