Wyniki wyszukiwania - Biblioteka Nauki

1

Propagation and attenuation of seismic body waves in initially stressed dissipative medium

100%

Dey S. , Dutta D.

Acta Geophysica Polonica

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1998

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tom Vol. 46, nr 3

351-366

EN

The paper discussed the effect of initial stresses on the propagation and attenuation of seismic body waves in a dissipative medium. The study reveals that the presence of initial stresses has strong effect in the propagation and attenuation of seismic waves. The velocity of waves depends on the direction of propagation and pure longitudinal and transverse waves are available only in the direction of initial stress and perpendicular to it. In other directions, a longitudinal wave is accompanied by some rotation and a transverse wave by some dilatation. The study also shows that the presence of compressive initial stress increases the velocity of longitudinal wave but diminishes that of trahsverse wave. It is also observed taht the loss of longitudinal wave due to dissipation is maximum in the initially stress-free case and decreases as the initial stress increases. In the case of SV wave, the presence of initil stresses decreases the loss factor upto the point when the direction of propagation makes an angle of 55° with the direction of initial stress, and then increases.

2

Power-law velocity profile in turbulent boundary layers: An integral reynolds-number dependent solution

100%

Castro-Orgaz O. , Dey S.

Acta Geophysica

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2011

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tom Vol. 59, no. 5

993-1012

EN

Geophysical flows of practical interest encompass turbulent boundary layer flows. The velocity profile in turbulent flows is generally described by a log- or a power-law applicable to certain zones of the boundary layer, or by wall-wake law for the entire zone of the boundary layer. In this study, a novel theory is proposed from which the power-law velocity profile is obtained for the turbulent boundary layer flow. The new power-law profile is based on the conservation of mass and the skin friction within the boundary layer. From the proposed theory, analytical expressions for the power-law velocity profile are presented, and their Reynolds-number dependency is highlighted. The velocity profile, skin friction coefficient and boundary layer thickness obtained from the proposed theory are validated by the reliable experimental data for zero-pressure gradient turbulent boundary layers. The expressions for Reynolds shear stress and eddy viscosity distributions across the boundary layer are also obtained and validated by the experimental data.

3

Turbulent unsteady flow profiles over an adverse slope

100%

Bose S. K. , Dey S.

Acta Geophysica

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2013

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tom Vol. 61, no. 1

84--97

EN

When an unsteady free surface flow encounters an adverse slope, it results in a decelerating flow up th e adverse slope. The time dependent turbulent flow is treated here by appropriately reducing the two- dimensional Reynolds averaged Navier–Stokes equation along with the equation of continuity considering turbulence closure. With suitable choice of parameters, the resulting differential equations are numerically solved to compute free surface and st reamwise velocity profiles with time. It is found that initially the advancing free surface is convex upwards for a short time, followed by a jump of the free surface with a negative streamwise velocity that is a backwater rolling breaker due to deceleration of flow. At later time, however, the velocity becomes posi- tive, that is, the breakers roll forward. This dual feature of motion, that is a surge followed by rolling breakers, is repeated for sometime before the jumps stop. The theoretical analysis presented here is motivated by tidal bores propagating upstream in an estuarine river.

4

Splitter plate as a flow-altering pier scour countermeasure

80%

Khaple S. , Hanmaiahgari P. R. , Gaudio R. , Dey S.

Acta Geophysica

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2017

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tom Vol. 65, no. 5

957--975

EN

Results of an experimental study on the countermeasure of scour depth at circular piers are presented. Experiments were conducted for pier scour with and without a splitter plate under a steady, uniform clear-water flow condition. The results of pier scour without splitter plate were used as a reference. Different combinations of lengths and thicknesses of splitter plates were tested attaching each of them to a pier at the upstream vertical plane of symmetry. Two different median sediment sizes (d50 = 0.96 and 1.8 mm) were considered as bed sediment. The experimental results show that the scour depth consistently decreases with an increase in splitter plate length, while the scour depth remains independent of splitter plate thickness. In addition, temporal evolution of scour depth at piers with and without a splitter plate is observed. The best combination is found to be with a splitter plate thickness of b/5 and a length of 2b. Here, b denotes the pier diameter. An empirical formula for the estimation of equilibrium scour depth at piers with splitter plates is obtained from a multiple linear regression analysis of the experimental data. The flow fields for various combinations of circular piers with and without splitter plate including plain bed and equilibrium scour conditions were measured by using an acoustic Doppler velocimeter. The turbulent flow fields for various configurations are investigated by plotting the velocity vec-tors and the turbulent kinetic energy contours on vertical and horizontal planes. The splitter plate attached to the pier deflects the approach flow and thus weakens the strength of the downflow and the horseshoe vortex, being instrumental in reducing the equilibrium scour depth at piers. The proposed method of pier scour countermeasure is easy to install and cost effective as well.

5

A very simple approach for 3-D to 2-D mapping

80%

Dey S. , Abraham A. , Sanyal S.

Image Processing & Communications

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2006

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tom Vol. 11, no 2

75-82

EN

Many times we need to plot 3-D functions e.g., in many scientific experiments. To plot this 3-D functions on 2-D screen it requires some kind of mapping. Though OpenGL, DirectX etc 3-D rendering libraries have made this job very simple, still these libraries come with many complex pre-operations that are simply not intended, also to integrate these libraries with any kind of system is often a tough trial. This article presents a very simple method of mapping from 3-D to 2-D, that is free from any complex pre-operation, also it will work with any graphics system where we have some primitive 2-D graphics function. Also we discuss the inverse transform and how to do basic computer graphics transformations using our coordinate mapping system.

6

Interference of an upstream pier on local scour at downstream piers

80%

Khaple S. , Hanmaiahgari P. R. , Gaudio R. , Dey S.

Acta Geophysica

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2017

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tom Vol. 65, no. 1

29--46

EN

In this study, three kinds of pier arrangements were tested. They are (i) two piers in tandem, (ii) two piers in staggered arrangement, and (iii) three piers in symmetrically staggered arrangements. In the arrangement of two piers in tandem, the equilibrium scour depth at downstream pier decreases with an increase in downstream distance up to approximately eight times pier diameter and then increases with further increase in downstream distance. However, the scour depth at downstream pier is always smaller than that at upstream pier. In the arrangement of two staggered piers, the scour depth at the downstream pier for L/b = 4, where L is the offset distance and b is the pier diameter, is the same as that of the upstream pier at S = 8b, where S is the streamwise spacing or distance between piers. Further, for three piers in staggered arrangement, as the lateral spacing between downstream piers increases, the equilibrium scour depth at downstream pier decreases.

7

Turbulence in mobile-bed streams

80%

Dey S. , Das R. , Gaudio R. , Bose S.

Acta Geophysica

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2012

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tom Vol. 60, no. 6

1547-1588

EN

This study is devoted to quantify the near-bed turbulence parameters in mobile-bed flows with bed-load transport. A reduction in near-bed velocity fluctuations due to the decrease of flow velocity relative to particle velocity of the transporting particles results in an excessive near-bed damping in Reynolds shear stress (RSS) distributions. The bed particles are associated with the momentum provided from the flow to maintain their motion overcoming the bed resistance. It leads to a reduction in RSS magnitude over the entire flow depth. In the logarithmic law, the von Karman coefficient decreases in presence of bed-load transport. The turbulent kinetic energy budget reveals that for the bed-load transport, the pressure energy diffusion rate near the bed changes sharply to a negative magnitude, implying a gain in turbulence production. According to the quadrant analysis, sweep events in mobile-bed flows are the principal mechanism of bed-load transport. The universal probability density functions for turbulence parameters given by Bose and Dey have been successfully applied in mobile-bed flows.

8

Hiding inside html and other source codes

80%

Al-Quaheri H. , Dey S. , Sanyal S.

Image Processing & Communications

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2009

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tom Vol. 14, no 2-3

59-68

EN

Many steganographic techniques [1,2, 3, 4] were proposed for hiding secret message inside images, the simplest of them being the LSB data hiding [6, 7, 8, 9, 10, 11]. In this paper, we suggest a novel data hiding technique in an Html Web page [12] and also propose some simple techniques to extend the embedding technique to source codes written in any programming language (both case insensitive like Html, pascal and case sensitive languages like C, C++, Java) - an extension to [12]. We basically try to exploit the case-redundancy in case-insensitive language, while we try hiding data with minimal changes int the source code (almost not raising suspicion). Html Tags are case insensitive and hence an alphabet in lowercase and one in uppercase present inside an Html Tag are interpreted in the same manner by the browser, i.e., change in case in an web page is imperceptible to the browser. We first exploit this redundancy and use it to embed secret data inside an web page, with no changes visible to the user of the web page, so that he can not even suspect about the data hiding. The embedded data can be recovered by viewing the source of the Html page. This technique can easily be extended to embed secret message inside any piece of source-code where the standard interpreter of that language is case-insensitive. For case-sensitive programming languages we do minimal changes in the source code (e.g., add an extra character in the token identified by the lexical analyser) without violating the lexical and syntactic notation for that language) and try to make the change almost imperceptible.

9

Scour Downstream of Grade Control Structures under the Influence of Upward Seepage

80%

Shafai-Bejestan M. , Nabavi S. M. R. , Dey S.

Acta Geophysica

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2016

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tom Vol. 64, no. 3

694--710

EN

The installation of free falling jet grade control structures has become a popular choice for river bed stabilization. However, the formation and development of scour downstream of the structure may lead to failure of the structure itself. The current approaches to scour depth prediction are generally based on studies conducted with the absence of upward seepage. In the present study, the effects of upward seepage on the scour depth were investigated. A total of 78 tests without and with the application of upward seepage were carried out using three different sediment sizes, three different tailwater depths, four different flow discharges, and four different upward seepage flow discharge rates. In some tests, the three-dimensional components of the flow velocity within the scour hole were measured for both the cases with and without upward seepage. The scour depth measured for the no-seepage results compared well with the most accurate relationship found in the literature. It was found that generally the upward seepage reduced the downward velocity components near the bed, which led to a decrease in the maximum scour depth. A maximum scour depth reduction of 49% was found for a minimum tailwater depth, small sediment size, and high flow discharge. A decay of the downward velocity vector within the jet impingement was found due to the upward seepage flow velocity. The well known equation of D’Agostino and Ferro was modified to account for the effect of upward seepage, which satisfactorily predicted the experimental scour depth, with a reasonable average error of 10.7%.

10

Propagation of torsional surface waves in a heterogeneous half-space under a rigid layer

80%

Dey S. , Gupta S. , Gupta A. , Prasad A.

Acta Geophysica Polonica

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2001

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tom Vol. 49, nr 1

113-118

EN

The paper discusses the possibility of propagation of torsional surface waves in a heterogeneous half-space under a rigid layer. The study reveals that, under the assumed conditions, torsional surface waves propagate in the medium. The velocities of torsional surface waves have been calculated numerically and are presented in a graph. It is observed that as the density of the medium increases the velocity of torsional wave front increases too. As a particular case it has been shown that in a homogeneous half-space under a rigid layer, a torsional wave does not propagate.

11

A Simple Architecture for Computing Moments and Orientation of an Image

80%

Dey S. , Bhattacharya B. B. , Kundu M. K. , Acharya T.

Fundamenta Informaticae

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2002

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tom Vol. 52, nr 4

285-295

EN

In this paper, a new methodology for computing orientation of a gray-tone image by the method of moments is described. Orientation is an essential feature needed in many image processing and pattern recognition tasks. Computation of moments is accomplished by a new projection method that leads to a fast algorithm of determining orientation. Using a simple architecture, the proposed algorithm can be implemented as a special purpose VLSI chip. The hardware cost of the proposed design is significantly lower compared to that of the existing architecture.

12

A Co-processor for Computing the Euler Number of a Binary Image using Divide-and-Conquer Strategy

70%

Dey S. , Bhattacharya B. B. , Kundu M. K. , Bishnu A. , Acharya T.

Fundamenta Informaticae

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2007

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tom Vol. 76, nr 1-2

75-89

EN

Euler number is a fundamental topological feature of an image. The efficiency of computation of topological features of an image is critical for many digital imaging applications such as image matching, database retrieval, and computer vision that require real time response. In this paper, a novel algorithm for computing the Euler number of a binary image based on divide-and-conquer paradigm, is proposed, which outperforms significantly the conventional techniques used in image processing tools. The algorithm can be easily parallelized for computing the Euler number of an N ×N image in O(N) time, with O(N) processors. Using a simple architecture, the proposed method can be implemented as a special purpose VLSI chip to be used as a co-processor.

13

Influence of ecological factors on the patterns of fish species richness in tropical Indian rivers

61%

Das M. K. , Naskar M. , Mondal M. L. , Srivastava P. K. , Dey S. , Rej A.

Acta Ichthyologica et Piscatoria

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2012

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tom 42

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nr 1

EN

Background. Rivers in India harbouring a rich diversity of fish are at present subjected to intense anthropogenic stress leading to degradation of the habitat. An understanding of the complex ecological variables determining species richness in these rivers is lacking. The relation between the ecological parameters (climate, hydrology, and morphometry) and the fish species richness were assessed in fourteen major rivers of India. Materials and Methods. The data of seven ecological variables of fourteen major rivers of India for the years 1994–2009 were quantitatively analysed for determining their influence on fish species richness. Principal factor analysis (PFA) was carried out for dimension reduction and eliminating collinearity. Subsequently, fish richness was regressed on the retained factors under generalised linear model (GLM) for determining contribution of factors towards species richness in rivers. Results. The most influential determinants of species richness were the factors such as: surface area of the river basin (0.439) followed by fish habitat availability potential (0.326) a synthesis of the variables rainfall, discharge and sediment load. The predicted loss of fish species is evident at a 10% alteration in the ecological variables of the rivers. Conclusion. The predicted loss of fish species richness is indicated at a10% alteration of the habitat factors in most of the rivers and can be useful for river planners and conservationists.

14

Dynamical downscaling approach for wintertime seasonal-scale simulation over the Western Himalayas

61%

Tiwari P. , Kar S. , Mohanty U. , Dey S. , Sinha P. , Raju P. , Shekhar M.

Acta Geophysica

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2014

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tom Vol. 62, no. 4

930--952

EN

The performance of RegCM4 for seasonal-scale simulation of winter circulation and associated precipitation over the Western Himalayas (WH) is examined. The model simulates the circulation features and precipitation in three distinct precipitation years reasonably well. It is found that the RMSE decreases and correlation coefficient increases in the precipitation simulations with the increase of model horizontal resolutions. The ETS and POD for the simulated precipitation also indicate that the performance of model is better at 30 km resolution than at 60 and 90 km resolutions. This improvement comes due to better representation of orography in the high-resolution model in which sharp orography gradient in the domain plays an important role in wintertime precipitation processes. A comparison of model-simulated precipitation with observed precipitation at 17 station locations has been carried out. Overall, the results suggest that 30 km model produced better skill in simulating the precipitation over the WH and this model is a useful tool for further regional downscaling studies.