排序方式： 共有30条查询结果，搜索用时 31 毫秒
21.
Digital terrain modelling using Corona and ALOS PRISM data to investigate the distal part of Imja Glacier, Khumbu Himal, Nepal 总被引：2，自引：2，他引：0
This study used Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM images to generate digital terrain models (DTMs) of the distal part of Imja Glacier,where a few supraglacial ponds (～0.07 km 2) expanded into the large Imja Glacier Lake (Imja Tsho,～0.91 km 2) between 1964 and 2006.DTMs and subsequently derived topographical maps with contour intervals of 1 m were created from the high-resolution images (Corona in 1964 and ALOS in 2006) in the Leica Photogrammetric Suite (LPS) platform.The DTMs and topographic maps provided excellent representation of the elevation and micro-topography of the glacier surface,such as its supra-glacial ponds/lake,surface depressions,and moraine ridges,with an error of about +/-4 m (maximum).The DTMs produced from the Corona and ALOS PRISM images are suitable for use in studies of the surface change of glaciers.The topographical maps produced from the Corona data (1964) showed that part of the dead ice in the down-glacier area was even higher than the top of the lateral moraine ridges,while the glacier surface in the up-glacier area was noticeably lower than the moraine crests.This suggests more extensive melting of glacier ice in the up-glacier area before 1964.The average lowering of the glacier surface from 1964 to 2006 was 16.9 m for the dead-ice area west of the lake and 47.4 m for the glacier surface east of the lake;between 1964 and 2002,the lake surface lowered by 82.3 m.These figures represent average lowering rates of 0.4,1.1,and 2.2 m/year for the respective areas. 相似文献
22.
23.
The design of seismic resistant concrete gravity dam necessitates accurate determination of hydrodynamic pressure developed in the adjacent reservoir. The hydrodynamic pressure developed on structure is dependent on the physical characteristics of the boundaries surrounding the reservoir including reservoir bottom. The sedimentary material in the reservoir bottom absorbs energy at the bottom, which will affect the hydrodynamic pressure at the upstream face of the dam. The fundamental parameter characterizing the effect of absorption of hydrodynamic pressure waves at the reservoir bottom due to sediment is the reflection coefficient. The wave reflection coefficient is determined from parameters based on sediment layer thickness, its material properties and excitation frequencies. An analytical or a closed-form solution cannot account for the arbitrary geometry of the dam or reservoir bed profile. This problem can be efficiently tackled with finite element technique. The need for an accurate truncation boundary is felt to reduce the computational domain of the unbounded reservoir system. An efficient truncation boundary condition (TBC) which accounts for the reservoir bottom effect is proposed for the finite element analysis of infinite reservoir. The results show the efficiency of the proposed truncation boundary condition. 相似文献
24.
The rapid expansion of agriculture, industries and urbanization has triggered unplanned groundwater development leading to severe stress on groundwater resources in crystalline rocks of India. With depleting resources from shallow aquifers, end users have developed resources from deeper aquifers, which have proved to be counterproductive economically and ecologically. An integrated hydrogeological study has been undertaken in the semi-arid Madharam watershed (95 km2) in Telangana State, which is underlain by granites. The results reveal two aquifer systems: a weathered zone (maximum 30 m depth) and a fractured zone (30–85 m depth). The weathered zone is unsaturated to its maximum extent, forcing users to tap groundwater from deeper aquifers. Higher orders of transmissivity, specific yield and infiltration rates are observed in the recharge zone, while moderate orders are observed in an intermediate zone, and lower orders in the discharge zone. This is due to the large weathering-zone thickness and a higher sand content in the recharge zone than in the discharge zone, where the weathered residuum contains more clay. The NO3 ? concentration is high in shallow irrigation wells, and F? is high in deeper wells. Positive correlation is observed between F? and depth in the recharge zone and its proximity. Nearly 50 % of groundwater samples are unfit for human consumption and the majority of irrigation-well samples are classed as medium to high risk for plant growth. Both supply-side and demand-side measures are recommended for sustainable development and management of this groundwater resource. The findings can be up-scaled to other similar environments. 相似文献
25.
Chia-Chuan Liu Jyoti Prakash Maity Jiin-Shuh Jean A. H. M. Selim Reza Zhaohui Li Bibhash Nath Ming-Kuo Lee Kao-Hung Lin Prosun Bhattacharya 《Environmental Earth Sciences》2012,66(5):1513-1523
Fluid and mud samples were collected from Wushanting (WST), Hsiaokunshui (HKS), Yenshuikeng (YSK), Kuantzeling (KZL), and
Kunshuiping (KSP) mud volcanoes of southwestern Taiwan. Concentrations of major ions and trace elements in mud volcanic fluids
were analyzed to find the possible linkage to elevated arsenic (As) concentrations in the Chianan plain groundwater. The elevated
Na+, K+, and Cl− concentrations indicated possible marine origin of the fluids. The trace element concentrations in the mud volcanic fluids
were generally low, but the As concentrations were up to 0.12 mg/L. High contents of As, Fe, and Mn were observed in the mud
samples. Saturation index calculations indicated that both carbonate and oxide minerals acted as potential sinks for As in
the mud volcanic fluids. Arsenic in the dewatering fluids and muds may be transported by the subsurface flow and surface streams
as suspended solids and eventually deposited in the Chianan plain aquifers. Under reducing conditions, As may be released
from the host minerals (such as Fe- and Mn-oxides/hydroxides), thereby causing widespread groundwater As pollution. 相似文献
26.
In this work, we have considered different candidates of dark energy such as tachyonic field, DBI-essence, hessence, k-essence and dilaton dark energy in the framework of f-essence cosmology and investigated the consequences for their co-existence. Also we have reconstructed the potential functions and the scalar fields in this scenario. The potential function can be directly obtained in terms of fermionic kinetic term and fermionic Lagrangian density. 相似文献
27.
A. BurmanParsuram Nayak P. AgrawalDamodar Maity 《Soil Dynamics and Earthquake Engineering》2012,34(1):62-68
A time domain transient analysis of a concrete gravity dam and its foundation has been carried out in a coupled manner using finite element technique and the effect of Soil-Structure Interaction (SSI) has been incorporated using a simplified direct method. A two dimensional plane strain dam-foundation model has been used for the time history analysis to compute the stresses and displacements against earthquake loading considering the effect of soil-structure interaction. An effective boundary condition has been implemented by attaching dashpots to the vertical boundaries. The material damping effects have also been considered and the dam and foundation have both been modeled as linear, elastic materials. To achieve a greater degree of accuracy, the displacements and stresses calculated in the free-field analysis have also been added to those developed in the complete dam-foundation analysis. The proposed algorithm has been simulated for the case of two published problems and in both the cases the results have been found to be in close agreement. The proposed technique is quite simple and easy to implement in the computer code. The outcomes of the results show the efficacy of the developed method. 相似文献
28.
Meenu Ramadas Rajib Maity Richa Ojha Rao S. Govindaraju 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(6):1583-1599
Streamflows are influenced by various hydroclimatic variables in complex ways. Accurate prediction of monthly streamflows requires a clear understanding of the dependence patterns among these influencing variables and streamflows. A graphical modeling technique, employing conditional independence, is adopted in this study to quantify the interrelationships between streamflows and a suite of available hydroclimatic variables, and to identify a reduced set of relevant variables for parsimonious model development. The nodes in the undirected graph represent relevant variables, and the strengths of the connections among the variables are learnt from the data. The graphical modeling approach is compared to the state-of-the-art method for predictor selection based on partial mutual information. For a synthetic benchmark dataset and a watershed in southern Indiana, USA, the graphical modeling approach shows more discriminating results while being computationally efficient. Along with artificial neural networks and time series models, results of the graphical model are used for formulating a variational relevance vector machine to predict monthly streamflows and perform probabilistic classification of hydrologic droughts in the watershed being studied. The parsimonious models developed for prediction at different lead times performed as well as the non-parsimonious models during both the calibration and testing periods. Drought forecasting for the study watershed at 1-month lead time was performed using the two selected predictors—soil moisture and precipitation anomalies alone, and the model performance was evaluated. The graphical model shows promise as a tool for predictor selection, and for aiding parsimonious model development applications in statistical hydrology. 相似文献
29.
Experimental investigation of the impacts of coherent flow structures upon turbulence properties in regions of crescentic scour 总被引：1，自引：0，他引：1 
下载免费PDF全文
下载免费PDF全文 This study examines the spatial distributions of third‐order moments of velocity fluctuations, the turbulent kinetic energy (TKE) fluxes, and the conditional statistics of Reynolds shear stress across the equilibrium crescentic scour structures generated upstream of short horizontal static cylinders. Detailed velocity data were collected using three‐dimensional (3D) micro‐acoustic Doppler velocimeter (ADV) across and within the equilibrium scour marks. The analysis reveals that the positive and negative values of third‐order moments associated with the level bed surface and the scour holes are directly related to coherent structures. The components of TKE flux are discussed for the near‐bed region of the level bed surface and scour holes in relation to sweep–ejection events. A cumulant‐discard method is applied to the Gram‐Charlier probability distribution of two variables to describe the statistical properties of the term u′w′. The conditional statistics of the Reynolds shear stress show a good agreement with the experimental data. The distribution of the joint probability density function in the near‐bed region changes cyclically along the scour hole depending on the bottom fluid velocity, which implies a change from upward to downward flux of momentum and vice versa. Both the ejection and sweep events at near‐bed points on the level surface are more important than within the scour region; and in contrast, both events are stronger for the scour marks than the level bed surface at the outer layer. Sweeps dominate over ejections for the scour hole induced by smaller diameter and ejections dominate for larger diameter. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
30.
Potential of support vector regression for prediction of monthly streamflow using endogenous property 总被引：2，自引：0，他引：2
In the recent past, a variety of statistical and other modelling approaches have been developed to capture the properties of hydrological time series for their reliable prediction. However, the extent of complexity hinders the applicability of such traditional models in many cases. Kernel‐based machine learning approaches have been found to be more popular due to their inherent advantages over traditional modelling techniques including artificial neural networks(ANNs ). In this paper, a kernel‐based learning approach is investigated for its suitability to capture the monthly variation of streamflow time series. Its performance is compared with that of the traditional approaches. Support vector machines (SVMs) are one such kernel‐based algorithm that has given promising results in hydrology and associated areas. In this paper, the application of SVMs to regression problems, known as support vector regression (SVR), is presented to predict the monthly streamflow of the Mahanadi River in the state of Orissa, India. The results obtained are compared against the results derived from the traditional Box–Jenkins approach. While the correlation coefficient between the observed and predicted streamflows was found to be 0·77 in case of SVR, the same for different auto‐regressive integrated moving average (ARIMA) models ranges between 0·67 and 0·69. The superiority of SVR as compared to traditional Box‐Jenkins approach is also explained through the feature space representation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献