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  • Author: S Dutta, x
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Predictive Capability of Bedload Equations Using Flume Data

The study on bedload transport behaviour is widely explored from the last few decades and many semiempirical or empirical equilibrium transport equations are developed. The phenomenon is a very complex due to its varied physical properties like velocity, depth, slope, particle size in the alluvial system. In practical applications, these formulae have appreciable deviation from each other in derivation and also their ranges of applications are different. Here, bedload transports have been categorized into moderate bedload transport and intense bedload transport depending upon the Einstein bedload transport parameter. Based on large database of different bedload measurements, a comparative analysis has been performed to ascertain prediction ability of different bedload equations based on various statistical criteria such as the coefficient of determination, Nash-Sutcliffe coefficient and index of agreement. It has been found that equations based on shear stress have worked better than other approaches (discharge, probabilistic and regression) for flume observations.

Abstract

Systematic determination of the surface tension and surface excess values of aquo-organic mixtures (methanol + water, ethanol + water, isoprapanol + water, tertiary butanol + water and ethylene glycol + water) were made. Attempts were made to interpret the surface tension values of aquo-alcoholic mixtures in terms of structure of water and its interactions with alcohols, surface excess and excess surface tension values. Correlation of the structural properties of the solvent mixtures with surface excess and other related macroscopic properties were attempted.

Abstract

No-carrier-added (nca) rhenium isotopes (182,182m,183Re) were produced by irradiation with 30 MeV α particles on natural tantalum target. The short-lived 182,182mRe were allowed to decay and long-lived nca 183Re was separated from bulk tantalum matrix by aqueous biphasic system (ABS) using 2 M solutions of nine different salts, namely, Na2SO4, Na2SO3, NaHSO3, Na2S2O3, Na2HPO4, Na2CO3, Na-citrate, Na-tartrate, and (NH4)2SO4 as salt rich phases against 50% (w/w) PEG-4000 as polymer rich phase at room temperature. The influence of temperature and thermodynamic parameters Δ Hº and Δ Sº were obtained for the partition of 183Re and tantalum in these systems. Nca 183Re was extracted in high amount in polymer rich phases irrespective of the salt rich phases. Bulk tantalum showed tendency to remain in salt rich phases. ABSs with PEG-4000 polymer rich phase in combination with Na2SO4, Na2SO3, NaHSO3, Na2HPO4, Na2CO3, Na-citrate and Na-tartrate as salt rich phases at basic pH and at ambient temperature (27 ºC) offered single-step separation between nca 183Re and bulk Ta. When Na2S2O3 and (NH4)2SO4 were used as salt rich phase, slight extraction of bulk tantalum was observed in PEG-4000 rich phase. The dynamic dissociation constant of 183Re-PEG-4000 complex was measured by dialysis of the PEG-rich phase against de-ionised water. The k dissociation value was found as low as 0.0185 min−1. Therefore, it is possible to have pure 183Re in de-ionized water immediately after the dialysis.

Abstract

The present study makes an effort to understand the damage of earthen dams under static and seismic loading condition. To make the investigation more realistic, behaviour of earthen dams considering the occurrence of a phreatic line indicating the submerged zone due to seepage within the dam body is considered. In case of earthen dams, homogeneous or nonhomogeneous, the consideration of the occurrence of a phreatic line or seepage line through the dam body is an important part of the earthen dam design methodology. The impervious material properties in the submerged zone below the phreatic line due to seepage may differ a lot in magnitudes as compared to the value of the same materials lying above this line. Hence, to have the exact stress distribution scenarios within the earthen dam, the different material properties above and below the phreatic line are considered in this present study. The study is first carried out by two-dimensional as well as three-dimensional finite element analysis under static loading condition. The work is further extended to observe the effect of seepage due to the consideration of the phreatic line on dynamic characteristics of earthen dams. Free vibration analysis and seismic analysis based on the Complete Quadratic Combination (CQC) method by considering twodimensional and three-dimensional modeling are carried out to present the frequencies, mode shapes and the stress distribution pattern of the earthen dam.