Naval Science and Technological Laboratory

Vishākhapatnam, India

Naval Science and Technological Laboratory

Vishākhapatnam, India
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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.

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.

Tatavolu V.R.,Naval Science and Technological Laboratory | Panchumarthy S.R.,Andhra University
Journal of Computer Science | Year: 2013

Research on Active Vibration Control System (AVCS) is being carried out to reduce structural vibrations caused by unwanted vibrations in many application areas such as in space, aircraft structures, satellites, automobiles and civil structures (bridges), particularly at low frequencies. The unwanted vibration may cause damage to the structure or degradation to the structure's performance. The AVCS comprises physical plant, a sensor to detect the source vibration, a DSP based electronic controller using an actuator connected to the structure generates a counter force that is appropriately out of phase but equal in amplitude to the source vibration. As a result two equal and opposite forces cancel each other by the principle of super position and structure stops vibrating. The main objective of this research work is to develop an embedded computer based real time AVCS for reducing low frequency tonal vibration response of a vibrating flexible cantilever beam by automatic modification of the vibrating beam's structural response and to verify the performance of the developed system experimentally. The developed AVCS is a generic design platform that can be applied for designing adaptive feed forward AVC and feedback AVC. This study presents the vibration control methodology adapted for reducing tonal vibration generated by a sine generator connected to the primary source actuator attached to one end of the cantilever beam. The secondary actuator is attached to the beam on the other end through the AVCS to reduce primary vibration by destructive interference with the original response of the system, caused by the primary source of vibration. Adaptive feed forward Active Vibration Control (AVC) technique is used with Filtered-X Least Mean Square (FxLMS) algorithm using FIR digital filter. A cantilever beam was considered as plant and embedded computer based AVCS was tested and evaluated using an experimental setup. The experimental results are presented for the cantilever beam excited at one of its natural frequency using active vibration control system and an appreciable reduction was achieved up to 20 dB. © 2013 Science Publications.

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.

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.

Praveen P.C.,Naval Science and Technological Laboratory | Krishnankutty P.,Indian Institute of Technology Madras
Indian Journal of Marine Sciences | Year: 2013

Present study consists the effect of variation of the vehicle length on the hydrodynamic forces and moments of axisymmetric underwater vehicles due to angle of attack. Five different vehicle lengths are used for this study (L/D varying between 10 and 15) by experimental, numerical and empirical methods. Experimental investigation is done in a tow tank using a VPMM. Numerical analysis is carried out using commercial CFD code Fluent 6.2. The empirical estimation is based on method suggested by Allen & Perkins. Results show that the linear coefficients vary linearly with L/D, while the nonlinear coefficients vary nonlinearly with L/D for the range tested.

Srinivas M.,Naval Science and Technological Laboratory | Adapaka S.K.,Naval Science and Technological Laboratory | Neelakantan L.,Indian Institute of Technology Madras
Journal of Alloys and Compounds | Year: 2016

The microstructure and corrosion behavior of Al-0.5Mg-0.08Sn-0.08Ga (wt%) anode material solutionized at different temperatures ranging from 400 to 550 °C is studied. Thermal analysis reveals that Sn is soluble in the Al alloy in this temperature range. Microstructural observation shows maximum solubility of Sn above 450 °C. Electrochemical investigations in 3.5 wt% NaCl and 9 M NaOH solution reveals lower corrosion and hydrogen evolution rates for the specimen solutionized at 450 °C. Though Sn is soluble above 450 °C, the corrosion slightly increases at higher solutionizing temperatures due to the segregation Ga at the surface. The corrosion and hydrogen evolution rate are higher when Sn is present as precipitate and causes localized (pitting) type of corrosion. On the contrary, presence of Sn in solid solution improves the corrosion resistance and decreases the hydrogen evolution rate. Hence, it can be concluded that the presence of Sn in solid solution is essential for reducing the corrosion rate and the distribution of the Sn plays a major role in the corrosion behavior of Al-Mg-Sn-Ga alloys. © 2016 Elsevier B.V.

Naidu C.C.,Naval Science and Technological Laboratory | Stalin E.S.,Naval Physical Oceanographic Laboratory
International Conference on Microelectronics, Computing and Communication, MicroCom 2016 | Year: 2016

Establishing an underwater wireless acoustic communication link for practical applications is still a difficult task because of the severe channel conditions. Doppler and range spread are extremely high for under water channels (UWC) compared to ordinary radio channels. Moreover, the ever varying nature of the UWC increases the uncertainty in predicting the worst case values of doppler spread and range spread. In recent years, orthogonal frequency division multiplexing (OFDM) has emerged as the single solution to most of the problems in wireless communication systems. OFDM has dominated over single carrier modulation techniques mainly because of the simple, robust and low complexity receiver design with high data rate and high band width efficiency. But, it is only very recently that people have started exploring the usage of OFDM for UWC. In this paper, the design, modeling and testing of coded OFDM based underwater acoustic communication system for high data rate applications is explained. © 2016 IEEE.

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.

Kumar A.S.,Naval Science and Technological Laboratory | Rao V.B.,Naval Science and Technological Laboratory | Sinha R.K.,High Energy Materials Research Laboratory | Rao A.S.,High Energy Materials Research Laboratory
Propellants, Explosives, Pyrotechnics | Year: 2010

Aluminized high explosives are known to give better underwater performance. All explosive formulations for underwater targets are filled into warheads and shells by casting method. TNT, a high explosive is used as casting medium due to its lower melting point. Plastic bonded explosives are fast replacing TNT-based high explosive formulations for the reasons that they are more insensitive and low vulnerable explosives with better shelf life. Few aluminized plastic bonded explosive formulations based on RDX, aluminum, and HTPB have been processed, varying the aluminum content from 0 to 35% and evaluated underwater. The present paper discusses the experimental methodology adopted to evaluate the above formulations for their ballistic parameters, viz., peak over pressure and impulse. Explosion bulge tests have been conducted with each explosive formulation and extent of bulge in test plates is presented and compared with a standard underwater explosive, viz., HBX-3. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

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