Das S.N.,Central Water and Power Research Station |
Shiraishi S.,Hokkaido University of Science |
Das S.K.,International Institute of Information Technology Bangalore
Acta Mechanica | Year: 2010
This paper investigates sway, roll and yaw motions of a floating body with the aim to determine coupled motion characteristics based on the order-wise analysis of hydrodynamic coefficients. To compute the hydrodynamic coefficients and wave force exerted on the floating body, we employ speed-dependent strip theory. The governing equations are solved analytically for linear restoring moment. For nonlinear restoring moment which is expressed as an odd-order polynomial of fifth degree in roll angle, we apply the Runge- Kutta-Gill method to solve the coupled equations. To investigate the effect of initial disturbances on sway, roll, yaw and speed of the body, numerical experiments have been carried out for a Panamax Container ship under the action of a sinusoidal wave of periodicity 11.2 s with varying wave height and speed. For the linear restoringmoment, we first derive associated motion equations for various cases based on the relative magnitude of the hydrodynamic coefficients. The order-wise analysis leads to the classification of coupled characteristics exhibiting the nature of coupling. For the nonlinear restoring moment, we notice that the initial disturbance plays an important role in the ship's stability. The effects of forward speed and variation in wave heights are illustrated through typical numerical experiments. © Springer-Verlag 2010.
Baghfalaki M.,University of Pune |
Das S.K.,Indian Defence Institute of Advanced Technology |
Das S.N.,Central Water and Power Research Station
International Journal of Applied Mechanics | Year: 2012
The paper deals with the mathematical modeling of response amplitude operator (RAO) and frequency-based analysis for coupled roll and yaw motions in regular waves. Prior to obtaining the RAO expressions for linearly coupled conditions, hydrodynamic coefficients are computed by using the strip theory formulation. We consider sinusoidal wave with frequency (ω) varying between 0.3 rad/s and 1.2 rad/s acts on beam to the floating body for zero forward speed. Two limiting cases corresponding to ω → 0 and ω → ∞ are considered and general expressions of RAO for intermediate frequencies are derived. Analytical result shows that the norm of RAO is maximum when ω ≈ ωn ≈ 0.74 for coupled roll and yaw motions. The asymptotic convergence of real part, imaginary part and norm of uncoupled yaw transfer functions are noticed with the increase of wave frequency. Using the normalization procedure and frequency based analysis; group based equations are formulated for each case. To understand the relative importance of the hydrodynamic coefficients, analytical solutions are obtained. The sensitivity analysis with respect to the initial conditions is investigated for roll and yaw motions. This study could be useful to model the floating body dynamics and corresponding wave loads in the design stage. © 2012 Imperial College Press.
Vivekanandan N.,Central Water and Power Research Station
Mausam | Year: 2011
Prediction of runoff is often important for optimal design of water storage and drainage works and management of extreme events like floods and droughts. Rainfall-runoff (RR) models are considered to be most effective and expedient tool for runoff prediction. Number of models like stochastic, conceptual, deterministic, black-box, etc. is commonly available for RR modelling. This paper details a study involving the use of Artificial Neural Network (ANN) and Regression (REG) approaches for prediction of runoff for Betwa and Chambal regions. Model performance indicators such as model efficiency, correlation coefficient, root mean square error and root mean absolute error are used to evaluate the performance of ANN and REG for runoff prediction. Statistical parameters are employed to find the accuracy in prediction by ANN and REG for the data under study. The paper presents that ANN approach is found to be suitable for prediction of runoff for Betwa and Chambal regions.
Bhosekar V.V.,Central Water and Power Research Station |
Bhosekar V.V.,Indian Institute of Technology Bombay |
Jothiprakash V.,Indian Institute of Technology Bombay |
Deolalikar P.B.,Central Water and Power Research Station
Journal of Hydraulic Engineering | Year: 2012
Orifice spillways are in vogue for the dams in the hilly regions where the spillway has to serve the dual function of flood disposal and flushing of sediment through the reservoir. Deep-seated orifice spillways are subjected to cavitation damage as the cavitation index drops below the critical cavitation index of 0.2 because of negative pressures on the profile and high flow velocities. Aerators are provided for mitigating cavitation damage. Design guidelines for aerator of orifice spillways are scanty and not reported much in the literature so far; thus, there still remains gray area in the field of spillway aerator design. The present study investigates the performance of an offset aerator with and without a ramp for deep-seated orifice spillway on a physical and numerical model. Performance of the aerator for varying discharges, heads, and gate openings is studied for varying cavity subpressures. Results with respect to jet length, cavity subpressure and air entrainment coefficients are presented in the form of nondimensional plots. From this study, the nondimensional jet length is in the range of 2 to 35 and increases as the cavity subpressure, approaches atmospheric pressure. It is also found that the air entrainment increases with increase in Froude number, ramp height and cavity pressure. From the present study results, equations for jet length and air entrainment coefficient are developed and are presented for the orifice spillway aerator. © 2012 American Society of Civil Engineers.
Bhowmick S.,Central Water and Power Research Station
Geotechnical and Geological Engineering | Year: 2016
Vp/Vs and Poisson’s ratio (σ) of subsurface strata are important parameters in the foundation study for the assessment of lithology, quality and strength of the rock, structural disturbances and saturation condition prior to the construction of huge civil structure like Nuclear Power Plant. The present work in this paper, showing the evaluation of overburden thickness, assessing quality and compactness of rock and identifying structural disturbance using Vp/Vs and Poisson’s ratio, is based on the fact that Vp/Vs is a better indicator of lithology (Mokhtar et al. in Porosity and heterogeneity effect on Vp/Vs ratio in carbonate rocks from a reservoir in the Middle East, Milan, 2012) than individual velocity values i.e. Vp and Vs. Moreover Vp/Vs and Poisson’s ratio both indicate the quality of rock (Bahremandi et al. in J Sci Res Rev 12:015–019, 2012) and structural disturbances within rock in terms of cracks, fractures or joints (Barton in Rock quality, seismic velocity, attenuation, and anisotropy, Taylor & Francis, London, 2006) etc., which is helpful in deciding the load bearing capacity of the foundation. The value of Vp and Vs, used in this paper, are taken from four research papers where Vp and Vs as a function of depth are studied with examples of Kalpakkam Nuclear Power Project, Tamilnadu (Boominathan in Curr Sci 87(10):1388–1397, 2004), Kakrapar Atomic Power Plant, Gujarat (Wadhwa et al. in J Ind Geophys Union 13(1):9–16, 2009), Kaiga Atomic Power Plant, Karnataka (Wadhwa et al. in J Ind Geophys Union 14(1):21–30, 2010) and Tarapur Atomic Power Plant, Maharashtra (Wadhwa et al. in J Ind Geophys Union 9(2):137–146, 2005) in Indian subcontinent. © 2016 Springer International Publishing Switzerland
Gupta I.D.,Central Water and Power Research Station
Natural Hazards | Year: 2013
The use of recent ground motion prediction equations in probabilistic seismic hazard analysis (PSHA) with area type of seismic sources requires defining the probability distributions of various source-to-site distance metrics with finite fault rupture taken into account. This task is rendered very difficult due to large epistemic uncertainties involved in specifying the details of the causative faults for area sources of diffused seismicity. However, it may generally be possible to constrain the strike and dip angles for fault ruptures in area sources from regional seismotectonic and geological information. This paper proposes to estimate the various finite fault distance measures from a site to a location in an area source by averaging the distances for several fault rupture scenarios with randomly distributed strike and dip over specified ranges. To consider the spatial distribution of the seismicity, the paper then provides the guidelines for defining the distance distributions by assigning suitable weight factors to the distance estimates for a grid of locations in the source area. The PSHA computation based on the distance distributions thus defined is shown to provide quite realistic and objective estimate of the hazard. © 2012 Springer Science+Business Media Dordrecht.
Tripathy G.R.,Central Water and Power Research Station |
Shirke R.R.,Central Water and Power Research Station |
Kudale M.D.,Central Water and Power Research Station
Journal of Rock Mechanics and Geotechnical Engineering | Year: 2016
Blasting used for rock excavation is associated with ground vibrations having potential damage to surrounding structures. The extent of damage produced in a structure depends largely on ground motion characteristics, dynamic characteristics of structure and the type of geological strata on which it is founded. The safety of surrounding structures against blast vibrations is a cause of concern. However, use of a systematic approach to rock blasting helps to complete the excavation safely in time without endangering the safety of surrounding structures. Various steps are commonly adopted at construction sites to ensure safety of engineered structures against blast vibrations, e.g. adopting a suitable safe vibration level, developing site-specific attenuation relation, estimating safe charges for different distances, designing blasting pattern, and monitoring vibrations during actual blasting. The paper describes the details of studies conducted for ensuring safety of an 85 years old masonry dam and green concrete of varying ages during excavation of about 30,000 m3 of hard rock in Maharashtra, India. The studies helped to complete the rock excavation safely in time and the safety of the dam was ensured by monitoring blast vibrations during actual rock excavation. © 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.
Andrade R.,Central Water and Power Research Station
International Journal of Geophysics | Year: 2014
In hard rock terrain, fractured aquifers comprise the major source of groundwater availability where the phreatic aquifer is desaturated. Identification of fracture zones in hard rock terrain and potential groundwater source delineation had been a perennial problem in hydrology. The purpose of this paper is to highlight the study over a small watershed area, in a granite terrain, wherein an attempt was made to delineate and map the fractured aquifer using numerical (factor) analysis of the conventional vertical electrical sounding data, which was obscure in curve matching technique. This numerical approach in concatenation with resistivity imaging or other techniques would prove to be an effective tool in groundwater exploration. © 2014 Rolland Andrade.
Gupta I.D.,Central Water and Power Research Station
Soil Dynamics and Earthquake Engineering | Year: 2010
From an analysis of a limited number of strong-motion data recorded in northeast Indian region, the in-slab earthquakes along the Indo-Burmese subduction zone are found to be characterized by much larger ground motion amplitudes than that for the earthquakes along other subduction zones around the world. Specific type of source, propagation path and site geologic condition may perhaps simultaneously be responsible for such anomalous behaviour. The empirical attenuation relations developed by Atkinson and Boore  using a global database for subduction zone earthquakes have been therefore suitably modified to be more appropriate for the northeast India. The modified relationships are developed by combining the data for both horizontal and vertical components of motion. The response spectra of the accelerograms recorded in northeast India from earthquakes with widely varying magnitude and distance are, in general, found to match very well with the predictions from the modified attenuation model. The proposed model can thus be used to obtain more realistic estimate of the contribution of in-slab subduction zone earthquakes to seismic hazard in the northeast Indian region. © 2010 Elsevier Ltd. All rights reserved.
Kudale M.D.,Central Water and Power Research Station
Indian Journal of Marine Sciences | Year: 2010
Coastal areas are varied in physical features. The coastline shows constantly varying nature due to tidal effects and seasonal changes in wave and wind climate. Occasional cyclones in the region also have influence on the overall morphology. It is necessary to understand the coastal processes and predict likely effects before undertaking any coastal project. Developments of major/minor ports and fishery harbours consist of the construction of coastal structures like breakwaters, jetties, groynes and reclamation bunds. Developments of the ports also involve the dredging and disposal activities to maintain the required depths for navigation. These coastal structures and the dredging activities interfere in the coastal processes of the region. Modifications in the coastal processes have large impact on the coastline. Major morphological impact is felt in the coastal region having high rate of longshore littoral drift. Accumulation of sediments on the updrift side and erosion of the downdrift side is inevitable in these regions. Sand bypassing is one of the best solutions to mitigate this problem. Sand bypassing should form an integral part of any port development project at the planning stage.