Wyniki wyszukiwania - BazTech

1

Effect of seepage on change in stress distribution scenario in static and seismic behaviour of earthen dams

Nandi N., Roychowdhury A., Dutta S. C.

International Journal of Applied Mechanics and Engineering

|

2018

|

Vol. 23, no. 1

121--136

EN

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.

2

Change in flow separation and velocity distribution due to effect of guide vane installed in a 90° pipe bend

Kumar Saha S., Nandi N.

Mechanics and Mechanical Engineering

|

2017

|

Vol. 21, nr 2

353--361

EN

Present paper makes an effort to study the flow separation and velocity distribution for incompressible turbulent flow through 90° pipe bend due to the effect of guide vane installed in the bend portion. It has been observed here how the normalized velocity distribution profile changes if the guide vane is provided. k-ɛ turbulence model has been adopted for simulation purpose. After validating with existing experimental results, a detailed study has been performed for a particular Reynolds number and four different positions of guide vane. The value of Curvature ratio (Rc/D) has been considered as 1 for present study. The results obtained from the present study have been presented in terms of graphical form. A flow separation region was found at bend outlet for flow through 90° pipe bend without guide vane. This secondary flow separation region was absent for the cases which deals with the flow through 90° pipe bend with guide vane. Velocity distribution at seven different downstream positions have been presented in graphical form. Position to get a fully developed velocity distribution profile for each cases has been estimated on the basis of presented results.

3

Effect of Reynolds Number and Curvature Ratio on Single Phase Turbulent Flow in Pipe Bends

Dutta P., Nandi N.

Mechanics and Mechanical Engineering

|

2015

|

Vol. 19, nr 1

5--16

EN

Curved pipes are very often used in hydraulic systems facilitating compact, lightweight designs. But they can also be the cause of complex secondary flows as the curvature brings change of velocity profile, generation of vortices and production of hydraulic losses. In the present study, turbulent single phase flows through circular 90˚ curved bend for different curvature ratio (Rc/D = 1 to 5), defined as the bend mean curvature radius (Rc) to pipe diameter (D) is investigated numerically for different Reynolds number (Re) ranging from 1×105 to 10×105. The purpose of this study is to simulate numerically the flow pattern and characterize the swirling secondary flow in 90˚ bends. Flow simulation using CFD techniques are performed to understand these phenomena. The k − " model with SIMPLE method is used for present study. After validation of present model with published experimental data, a detail study has been performed to characterize the flow separation and the dependency of swirl intensity on Reynolds number and curvature ratio in 90˚ pipe bend for single phase turbulent flow.

4

A critical review of dam analysis methodologies

Sarkar P., Dutta S. CH., Nandi N.

International Journal of Applied Mechanics and Engineering

|

2003

|

Vol. 8, no 3

461-482

EN

Dams in many countries including India were primarily designed on the basis of approximate hand calculation based method. A frequent occurrence of floods due to a failure of such dams and embankments clearly points to the need of a review of the procedure of dam analysis methodologies and to suggest a reasonably accurate one. The paper is a limited effort for the same, based on three Indian dams. As a very preliminary step of the whole plan of checking the safety of Indian dams, an analysis of three dams having similar features as that of Chirpatia Dam (Rajasthan), an earthen embankment dam, Koyna Dam (Maharastra), a concrete gravity dam and the earthen embankment surrounding Ash Pond of Bakreswar Thermal Power Project (West Bengal), have been carried out with the help of two-dimensional and three-dimensional finite element discretisation under static loading conditions. The result is then compared with the corresponding results obtained from a conventional hand calculation based on approximate gravity method of analysis. The comparison of the results exhibited a considerable increase in compressive stresses in two-dimensional finite element analysis with respect to what is obtained in the conventional hand calculation based approximate gravity method. Both of these methods considered an in-plane stress distribution along a cross-section of the dam and hence, could not recognize any possibility of stress generation perpendicular to the cross-section. In this context, a three-dimensional study reveals that considerable stresses may generate even in the longitudinal direction of a dam that is generally ignored in hand calculation based gravity method of analysis and two-dimensional analysis due to the assumption of the two-dimensional nature of the problem. A rigorous finite element analysis also shows that even tensile stress may generate under static loading conditions which can hardly be predicted from the conventional method. It is also observed that hand calculation based on slip-circle method and two-dimensional analysis cannot adequately recognize the possibility of shear failure at many points in the body of the dam though their vulnerability due to itself and so it is necessary to point out by a rigorous three-dimensional modeling and analysis. Thus, the study suggests the unavoidable necessity of three-dimensional analysis for a safe design of dams.