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.

A nonlocal continuum mechanics model to estimate the material property of single-walled carbon nanotubes

Abstract: A subject of current technological interest is that of nanotechnology. It would appear that nonlocal continuum mechanics could potentially play a useful role in analysis related to nanotechnology applications. The present work explores this potential in the context of a specific application. The length scales associated with nanotechnology are often sufficiently small to call the applicability of classical continuum models into question. Atomic and molecular models, while certainly conceptually valid for small length scales, are difficult to formulate accurately and are almost always computationally intensive. Nonlocal continuum models represent attempts to extend the continuum approach to smaller length scales while retaining most of its many advantages. Therefore, continuum models need to be extended to consider the scale effect in nanomaterial studies. This can be accomplished through proposing nonlocal continuum mechanics models, where the internal size scale could be simply considered in constitutive equations as a material parameter. Usually, the magnitude of the nonlocal parameter e0, determines the nonlocal effect in the analysis. The modeling and analyses of nanostructures based on flexural displacement, require an accurate estimate of nonlocal scaling parameter. Such an attempt is made in the present work. From the present analysis, the value of the scale coefficient (e0a, a is carbon-carbon bond length) is recommended to be about 0.11 nm for the application of the nonlocal theory in the analysis of carbon nanotubes.

A Predictive Explicit Guidance Scheme for Ballistic Missiles

Abstract: A new approach to the design of ballistic missile guidance is presented in this paper. The proposed method uses the missile model to predict the likely impact point at every guidance cycle and apply course corrections based on the predicted impact point (PIP) deviations. The algorithm also estimates the in-flight thrust variation from nominal and accordingly updates the model to reduce the uncertainty in the prediction of the impact point. The performance of the algorithm is tested through 6-DOF simulation. The simulation results show excellent performance of the proposed guidance scheme in nominal & off nominal cases. Defence Science Journal, 2013, 63(5), pp.456 -461 , DOI:http://dx.doi.org/10.14429/dsj.63.2575

Use of digitally filtered inflow conditions for LES of flows over backward facing steps

Abstract: Large eddy simulations (LES) of subsonic and supersonic boundary layers separating at backward facing steps are performed for validating a hybrid flow solver and testing the digital filtering approach for specifying the inflow turbulence. The broadband spectra of eddies in the approaching boundary layers resulting from filtering properly trigger the shear layer instabilities leading to significant improvements in predictions of first and second order turbulence statistics when compared to those resulting from use of uncorrelated noise for generating inflow turbulence. This seems to be true even though the distance between the inflow boundary and the step is about the same or less than in most of the LES of this kind of flows reported in literature and not sufficient to establish an equilibrium boundary layer with correct phase information before the flow reaches the step. The density/entropy disturbances resulting from non-solenoidal inflow do not seem to adversely affect the predictions in the subsonic case. The digital filtering approach does, however, generate acoustic disturbances that contaminate the expansion fan generated at the corner and lead to slight overpredictions in turbulence levels downstream in the supersonic case.

Roll autopilot design of a tactical missile using higher order sliding mode technique

Abstract: Tactical missiles are used against various aerial/ground targets which can be stationary or maneuvering. Tactical missiles should have highly efficient control scheme in order to intercept such targets with acceptable miss distance. It is known that aerodynamic characterization of the missile with high accuracy is very difficult. In addition to this, the inability to model the external disturbances make the autopilot design very difficult. Hence, the need for a robust control arises in the presence of parametric uncertainties and unmodelled external disturbances. Sliding Mode Control (SMC) which has got invariance property against external disturbances and the model inaccuracies has been applied to this plant. This paper concentrates on application of higher order sliding mode control for the roll autopilot design of a tactical missile. Conventionally, the roll autopilot is designed with roll angle and roll rate feedbacks. The addition of roll acceleration feedback helps to obtain a tighter control of roll dynamics especially during high angle of attack requirements. However, the roll acceleration is neither measurable nor estimable by numerical differentiation of roll rate feedback. A differentiator based on Super Twisting Algorithm (STA) is explored to estimate roll acceleration from roll rate measurement. The use of roll acceleration feedback in the autopilot ensures tight control of roll dynamics. The robust sliding mode control gains are designed using Linear Matrix Inequalities (LMI) based technique.