Defence Research and Development Organisation
Defence Research and Development Organisation
Bhateja A.K.,Defence Research and Development Organisation |
Kannan V.,Delhi Technological University
Communications in Computer and Information Science | Year: 2017
Many mathematical, engineering and cryptographic applications require the solution of sparse linear equations over large order finite fields. The Gaussian elimination is a standard algorithm used for the above. However, its use remains limited because of its implementation difficulty for large matrices. For large and sparse linear systems the iterative Lanczos and Wiedemann are the most efficient techniques. However, the computation intensive matrix vector multiplications in these algorithms make them unsuitable for large systems, increasing the computation time due to constant accesses to the RAM and hard disk for fetching and storing data. In this paper we present a cache optimized implementation of the Lanczos and Wiedemann algorithm that can be used for very large matrices even when there is not sufficient cache to store all the non zero matrix elements. Our algorithm makes optimal use of the cache, decreases the number of memory accesses and therefore reduces the time taken for the algorithms to provide a solution. The results show an improvement of 16% in Lanczos and 13% in Wiedemann in the execution time, with number of equations as 105 and same numbers of variables over the field of order 529 bits. © Springer Nature Singapore Pte Ltd. 2017.
Deb D.,Indian Institute of Technology Guwahati |
Bhattacharjee R.,Indian Institute of Technology Guwahati |
Vengadarajan A.,Defence Research and Development Organisation
2016 IEEE Uttar Pradesh Section International Conference on Electrical, Computer and Electronics Engineering, UPCON 2016 | Year: 2017
MIMO radar covers a broad class of systems having multiple antennas at transmit and/or receive. The performance of the MIMO radar varies widely based on the system configuration. The waveform for MIMO radar can be orthogonal or correlated. In case of correlated waveform the covariance matrix has to be decided based on various system parameters before proceeding to waveform design. In many scenarios the waveform transmitted from different transmit elements are fully orthogonal. The use of orthogonal waveform ensures that the contribution of each transmit element can be extracted at the receiver and combined transmit-receive beamforming can be done. Irrespective of the processing involved the requirement to design orthogonal waveform mandates that they have impulse like autocorrelation and very low cross-correlation. This paper proposes to use phase randomised FH sequence for obtaining this objective. This also provides a large number of orthogonal waveforms. The study is also carried out to quantify the improvement in sidelobe level and doppler tolerance of the proposed waveform. © 2016 IEEE.
Krishna Murthy S.V.S.S.N.V.G.,Indian Defence Institute of Advanced Technology |
Kumar B.V.R.,Indian Institute of Technology Kanpur |
Nigam M.,Defence Research and Development Organisation
Applied Mathematics and Computation | Year: 2015
This study examines natural convection from a hot cubical structure buried inside a fluid saturated porous media under suction/injection induced forced flow conditions. The numerical computations are carried out by a segregated finite element approach under the paradigm of domain decomposition technique. Suitable sparse data structures and algorithms are designed for efficient implementation on a cluster of PCs called ANUCLUSTER under ANULIB parallel processing environment. The parallel numerical simulations are carried out for various values of Ra and for different sizes of isothermal hot cubical objects. Results have been presented in the form of Nusselt number, temperature and velocity vector plots. © 2015 Elsevier Inc. All rights reserved.
Grandhi R.K.,Defence Research and Development Organisation |
Grandhi R.K.,Aerospace Systems Design and Analysis Group |
Roy A.,Indian Institute of Technology Kharagpur
Journal of Spacecraft and Rockets | Year: 2017
A transverse side jet in a supersonic crossflow causes a significant region of separated flow in its vicinity. This separation alters the effectiveness of the jet in producing control forces and moments. In this study, numerical simulations are carried out in order to estimate this change in effectiveness. The effect of a number of parameters such as the angle of attack, angle of yaw, jet pressure ratio, injection Mach number, and presence or absence of a flare aft of the injection are studied. For the geometry considered, it is seen that the effectiveness is enhanced significantly as the angle of attack, angle of yaw, or the jet pressure ratio are increased. The jet injection Mach number does not have a significant effect as long as the jet pressure ratio and jet mass flow rate are unchanged. Copyright © 2017 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
Mansukhani J.,Defence Research and Development Organisation |
Chakrabarti S.,Indian Institute of Technology Kharagpur
2013 International Conference on Computer Communication and Informatics, ICCCI 2013 | Year: 2013
Orthogonal frequency division multiplexing (OFDM) modulation using orthogonal subcarriers reduces the delay spread by increasing robustness to multipath fading and can use overlapped bandwidth due to orthogonality on frequency domain. The main drawback of Orthogonal Frequency Division Multiplexing (OFDM) systems is the high peak-to average power ratio (PAPR), which significantly reduces the efficiency of the transmit high power amplifier (HPA). Several methods have been proposed in the literature to reduce the peak power of OFDM signals and substantial gains were reported. In SLM technique of PAPR reduction, side information needs to be transmitted for demodulation while degrading transmission efficiency. Though many studies have been carried out to analyze the performance of various PAPR reduction methods for land, the studies for sea environment is hardly addressed in literature. In this paper, we have analyzed the effectiveness of SLM technique utilizing cyclic shifting of pilots for Marine Channel. © 2013 IEEE.
Sankar H.R.,Gandhi Institute of Technology and Management |
Srikant R.R.,Gandhi Institute of Technology and Management |
Krishna P.V.,Gandhi Institute of Technology and Management |
Rao V.B.,Defence Research and Development Organisation |
Babu P.B.,National Institute of Technology Warangal
International Journal of Automotive and Mechanical Engineering | Year: 2013
Conventional materials are being replaced in the field of engineering by composite materials, due to their tailorable properties and high specific properties. These materials are extensively used in structural applications. Damping is one of the important properties of the materials used in structures, and needs to be enhanced in order to reduce structural vibrations. In the present work, the improvement of the material damping of glass fabric epoxy composites with particle rubber inclusions is studied. The effect of particle size on the damping and stiffness parameters at different frequencies and temperatures is studied experimentally. Considerable enhancement in damping without significant reduction in stiffness is observed at lower particle sizes. The damping property in both bending and shear modes is more with 0.254 mm rubber particle inclusions among the selected sizes. A lower reduction in stiffness is observed with the inclusion of lower particle sizes (0.254 mm and 0.09 mm) when compared with higher particle sizes. An ANN-based prediction model is developed to predict these properties for a given frequency/temperature and particle size. The predicted values are very close to the experimental values with an maximum error of 5%. © Universiti Malaysia Pahang.
Bhardwaj A.,TERI University |
Joshi P.K.,TERI University |
Snehmani,Snow and Avalanche Study Establishment Research and Development Center |
Singh M.K.,Snow and Avalanche Study Establishment Research and Development Center |
And 3 more authors.
Cold Regions Science and Technology | Year: 2014
Supraglacial debris significantly hampers the mapping of glaciers using remote sensing data. A semi-automated approach for the mapping of debris-covered glacier was applied, which combined the inputs from thermal and optical remote sensing data and the Digital Elevation Model (DEM) derived morphometric parameters. A thermal mask that delineates the supraglacial debris extent was generated by the thresholding of surface temperature layer obtained from Landsat TM/ETM. + thermal band satellite data. The extent of clean glacier ice was identified by band ratioing and thresholding of TM/ETM. + 4 and TM/ETM. + 5 bands. Morphometric parameters like slope, plan curvature and profile curvature were rearranged in similar surface groups using the technique of cluster analysis. All these masks were vectorized and final classification maps were generated using geographic information system (GIS) overlay operations. The areal extent of semi-automated outlines of Hamtah and Patsio Glaciers derived from cluster analysis varied from manually derived outline using pan-sharpened Landsat ETM. + September 2000 image by -. 1.3% and -. 1.6%, respectively. Year 2011 classification map for Patsio Glacier was compared with the field observations and a high correlation and overall accuracy (~. 91%) were observed. The same classification methodology was adopted for images of years 2000 and 1989 for Patsio Glacier to observe the effects of varying snow cover patterns on adopted methodology. Also the methodology was adopted and verified for Hamtah Glacier, with different geometry and terrain conditions as compared to Patsio Glacier. Although the spatial resolution limitation of ASTER GDEM and Landsat TM/ETM. + thermal band limits the automated mapping of small debris-covered glaciers, the outcomes are still favorable enough to apply such methodologies for mapping different types of debris-covered glaciers in the future. © 2014 Elsevier B.V.
Dash A.P.,Indian Institute of Technology Madras |
Velmurugan R.,Indian Institute of Technology Madras |
Prasad M.S.R.,Defence Research and Development Organisation |
Sikarwar R.S.,Defence Research and Development Organisation
Thin-Walled Structures | Year: 2016
Improvement of stability of thin isotropic shell in the presence of soft elastic filler has been investigated. Critical buckling loads for empty and filled cylinder have been studied both experimentally and theoretically using FE analysis. Various percentage of cross sectional filling are examined as a parametric variation. Nonlinear analysis with proper geometric imperfection modeling is carried out to represent correct behavior of soft elastic filler. The experimental results and FE analysis corroborate well to establish this improvement in buckling strength. It is observed that critical buckling load of the cylinder subjected to external pressure improves upto an extent of five times depending upon percentage of filling. It is concluded that improved strength can be utilized for more efficient design of thin tubular shells. © 2015 Elsevier Ltd.
Yadav T.,Defence Research and Development Organisation |
Rao A.M.,Defence Research and Development Organisation
Communications in Computer and Information Science | Year: 2015
Recent trends in targeted cyber-attacks has increased the interest of research in the field of cyber security. Such attacks have massive disruptive effects on organizations, enterprises and governments. Cyber kill chain is a model to describe cyber-attacks so as to develop incident response and analysis capabilities. Cyber kill chain in simple terms is an attack chain, the path that an intruder takes to penetrate information systems over time to execute an attack on the target. This paper broadly categories the methodologies, techniques and tools involved in cyber-attacks. This paper intends to help a cyber security researcher to realize the options available to an attacker at every stage of a cyberattack. © Springer International Publishing Switzerland 2015.
Ghosh S.,Defence Research and Development Organisation |
Mukhopadhyay S.,Indian Institute of Technology Kharagpur
IEEE Transactions on Aerospace and Electronic Systems | Year: 2011
In this paper an acceleration model and a jerk model are proposed for estimation of the kinematic state of reentry ballistic targets (RBTs) using extended Kalman filters (EKF). The models proposed here use the equations of target kinematics only and do not assume any model parameterization for variation of the ballistic coefficient and air density a priori, as found in the literature. The novelty lies in estimation of the ratio (γ) of air density and ballistic coefficient and its time derivatives using a separate Kalman filter (KF) (γ-filter) which utilizes pseudo measurements of γ computed from the velocity and acceleration estimated by the EKF at each time step. The parameter γ and its derivatives estimated by the γ-filter are, in turn, used for the estimation of position, velocity, acceleration, and jerk in the EKF. The use of the pseudo measurements of γ makes the algorithms inherently adaptive to variations of the ballistic coefficient and air density during reentry. A comparative assessment of several dynamic models for reentry of ballistic targets reported in the literature and those proposed here demonstrates that the estimation errors in velocity and acceleration are significantly less for the proposed models compared with the existing ones. © 2011 IEEE.