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Ramakrishna Rao B.,Naval Materials Research Laboratory | Ramakrishna Rao B.,Indian Institute of Technology Madras | Srinivas M.,Naval Science and Technological Laboratory | Shah A.K.,Panipat Institute of Engineering and Technology | And 2 more authors.
Intermetallics | Year: 2013

A new thermodynamic parameter PHSS (PHSS = ΔHC(ΔSσ/kB)(ΔS C/R)) is proposed, to describe and predict the glass forming ability (GFA) of Fe based alloys. Here ΔHC is the chemical enthalpy of mixing, ΔSσ is the mismatch entropy and ΔS C is the configurational entropy. The PHSS parameter incorporates enthalpy of mixing, size mismatch and the number of elements in the systems which influence GFA significantly. It was observed from rapid solidification processing (RSP) and mechanical alloying (MA) studies that, all alloys with PHSS in between -0.55 kJ/mol to -6.00 kJ/mol would form glass in the Fe-Zr-B system. MA and RSP experiments on multi-component Fe-Cr-Ni-Zr-B alloys indicated that PHSS is a better parameter to predict GFA of the system than PHS, a parameter used in earlier studies. It was also observed that bulk metallic glass (BMG) forming alloys can be observed in between a PHSS range of -3.00 kJ/mol to -6.00 kJ/mol, with the maximum thickness of the BMG increasing with decreasing PHSS within the above range. © 2012 Elsevier Ltd. All rights reserved.


Rao S.K.,Naval Science and Technological Laboratory
IETE Journal of Research | Year: 2010

Target motion analysis (TMA) using conventional passive bearing together with frequency measurements is explored. This approach offers one tactical advantage over the classical bearings-only TMA. It makes the ownship maneuver superfluous. In this paper, TMA is carried out using an unscented Kalman filter (UKF). The inclusion of range, course, and speed parameterization is proposed in the UKF target state vector to obtain the convergence of the solution fast. Finally the results of one scenario in Monte-Carlo simulation are presented. © 2010 by the IETE.


Koteswara Rao S.,Naval Science and Technological Laboratory | Linga Murthy K.S.,Andhra University | Raja Rajeswari K.,Andhra University
IET Radar, Sonar and Navigation | Year: 2010

Underwater manoeuvring target rarely tracked using bearings-only measurements available from Hull mounted array (HA) without a proper manoeuvre by the observer. This problem is solved by administering data fusion techniques on bearings available from towed array and HA. Song and Speyer's and Galkowski and Islam's modified gain bearings only extended Kalman filter is exploited for estimation of target motion parameters. Online pre-processing is carried out to reduce the amplitude of the noise, compute the estimated bearings if the bearing measurement is not available and to find out variance of the noisy measurement which is used in Kalman filter. The spurious measurements are made invalid. The performance evaluation of the algorithms is done in Monte-Carlo simulation and results obtained for two typical geometries are presented. © 2010 The Institution of Engineering and Technology.


Suryanarayana C.,Naval Science and Technological Laboratory | Satyanarayana B.,Andhra University
International Journal of Naval Architecture and Ocean Engineering | Year: 2010

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at 4.5° angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll. © SNAK, 2009.


Das H.N.,Naval Science and Technological Laboratory | Kapuria S.,Indian Institute of Technology Delhi
Journal of Fluids and Structures | Year: 2016

Marine propellers are designed to work for a particular operating condition. However, a propeller often requires to operate at different off-design conditions, when its hydrodynamic efficiency drops. In this paper, a comprehensive numerical study is presented on the use of bend-twist coupling of composite propeller blades for improving their hydrodynamic efficiency at off-design conditions. The analysis is carried out on a full-scale propeller of diameter 4.2 m, considering the complete viscous turbulent flow, as the loading and deformation of model propellers that have been typically studied in literature for this purpose cannot be extrapolated to a full-scale prototype propeller. The open water performance is estimated using the finite volume method employing the pressure based RANS equation for the steady, incompressible, turbulent flow. The deformation analysis is done using the finite element method based on the first order shear deformation theory for composite laminates. The fluid-structure interaction is incorporated in an iterative manner. The effect of laminate configurations on the maximum twist achieved in the blade is studied for four different composite materials. The numerical study reveals that, within the limits of material safety, the twist generated in the deformed propeller using commonly used composite materials is inadequate to create any noticeable change in the hydrodynamic efficiency. When the material failure is ignored, however, it is possible to generate sufficient deformation and twist that can cause appreciable improvement in the hydrodynamic performance. © 2015 Elsevier Ltd.

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