Defence Research and Development Laboratory

About: Defence Research and Development Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Turbulence & Mach number. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Influence of electron beam welding parameters on microstructure and Charpy impact properties of boron-added modified 9Cr-1Mo steel weld

Abstract: The effect of electron beam welding parameters on microstructure and ductile-to-brittle transition temperature (DBTT) of a boron-added modified 9Cr-1Mo steel weld is presented in this paper. Compared to the base metal, for the weld, the upper shelf energy is lower and the DBTT is significantly lower. While the influence of welding parameters on the upper shelf energy of the weld is insignificant, its influence on the transition region and the lower shelf region is quite significant due to the presence of delta-ferrite in the weld. High welding speed reduces the time available for transformation of delta-ferrite to austenite and results in retention of delta-ferrite in weld. Lower welding speed promotes completion of delta-ferrite to austenite transformation as cooling rate reduces which improves lower shelf energy.

Numerical simulation of nozzle flow field with jet vane thrust vector control

Abstract: Numerical simulations are performed to characterize the jet vane thrust vector control mounted in the rear of a rocket motor. The three-dimensional Navier—Stokes equations along with the K—e turbulence model are solved in a hybrid mesh consisting of an unstructured grid and a structured grid. All essential flow features including the complex compression/expansion wave interactions emanating from the vane surfaces and shrouds are captured by simulation. The computed side force coefficients are seen to vary linearly with chamber pressure and vane deflection angles. A theoretical correlation has been developed by a non-linear regression analysis from the computational fluid dynamics (CFD) database to predict the force and moment coefficients for different chamber pressures, vane deflection angle, and roll offset angle. The theoretical correlation compare very well with full CFD simulation as well as the experimental data.

An intelligent gain-based ant colony optimisation method for path planning of unmanned ground vehicles

Abstract: In many of the military applications, path planning is one of the crucial decision-making strategies in an unmanned autonomous system. Many intelligent approaches to pathfinding and generation have been derived in the past decade. Energy reduction (cost and time) during pathfinding is a herculean task. Optimal path planning not only means the shortest path but also finding one in the minimised cost and time. In this paper, an intelligent gain based ant colony optimisation and gain based green-ant (GG-Ant) have been proposed with an efficient path and least computation time than the recent state-of-the-art intelligent techniques. Simulation has been done under different conditions and results outperform the existing ant colony optimisation (ACO) and green-ant techniques with respect to the computation time and path length.

Constitutive Description of Tensile Flow Behavior of Cold Flow-Formed AFNOR 15CDV6 Steel at Different Deformation Levels

Abstract: The influences of cold deformation on the room temperature tensile stress-strain behavior of a flow-formed AFNOR 15CDV6 steel have been evaluated in the deformation range of 74-86% at a nominal strain rate of 6.67 × 10−4 s−1. Constitutive description of the tensile plastic flow has been illustrated through a comparative description of widely used empirical relationships proposed by Hollomon, Ludwigson, Pickering and Voce. Both the Voce and Pickering relations adequately describe the tensile flow behavior of all the specimens. Although the standard Ludwigson relation does not fit the experimental data satisfactorily, the fitting ability improves dramatically when a modified relation with the negative deviation compensating parameter has been employed. Physical interpretation of the fitting parameters based on observed microstructural features of the materials is further attempted. The variations in Ludwigson (n 2) and Voce (K v) parameters match well with the trend in the development of delamination cracks due to internal stress fields. Such behavior is directly linked to the uniform elongation of the materials. The tensile work hardening behavior has been elucidated by the differential and modified Crussard-Jaoul methods. Such analyses in corroboration with microstructural characterization indicate the development of internal stress field during highly constrained material flow in a banded structure. The consequence of this phenomenon is manifested in the formation of severe delamination cracks that significantly affect the uniform elongation of the specimens. Furthermore, the Estrin-Mecking analysis of microstructural attributes to the work hardening behavior points out the dynamic recovery controlled deformation mechanism in 86% deformed specimen.

Modelling and Simulation of Pseudolite-based Navigation: A GPS-independent Radio Navigation System

Abstract: The use of global positioning system (GPS) for precision guidance of weapons is being questioned due to its vulnerability of jamming and spoofing for non-military code users. In this paper a novel approach is proposed for guidance of weapons where use of GPS or other civilian Satellite-based navigation system is threatened. The proposed approach is modelled and simulated using SIMULINK for realistic trajectories and scenario. The results of simulation are validated with the actual GPS data.