SUMMARYMethods based on exponential finite difference approximations of h 4 accuracy are developed to solve one and two-dimensional convection-diffusion type differential equations with constant and variable convection coefficients. In the one-dimensional case, the numerical scheme developed uses three points. For the two-dimensional case, even though nine points are used, the successive line overrelaxation approach with alternating direction implicit procedure enables us to deal with tri-diagonal systems. The methods are applied on a number of linear and non-linear problems, mostly with large first derivative terms, in particular, fluid flow problems with boundary layers. Better accuracy is obtained in all the problems, compared with the available results in the literature. Application of an exponential scheme with a non-uniform mesh is also illustrated. The h 4 accuracy of the schemes is also computationally demonstrated.

Design and development of a novel Ultra Wide Band (UWB) panel Radar Absorbing Material (RAM) with Radar Cross Section Reduction (RCSR) of 10 dB (minimum) from 1.7 GHz. to 25 GHz. using hexagonal resistive patch Frequency Selective Surface (FSS) is presented in this paper. The four layers RAM is analyzed using transmission line model (TLM) and full-wave analysis of the design is carried out using HFSS v15 simulation software. The resistive FSS layers are designed as electrically very thin PCBs using 0.2 mm thick FR4 substrate. The prototype RAM is developed as a panel of size (280 mm x 280 mm). The thickness of panel RAM is 16.8 mm. and the weight is 190 gm. Monostatic RCS measurements are carried out on RAM in microwave anechoic chamber. Experimental and simulation results agree very well.

Atomistic simulation of initial <100> oriented FCC Cu nanowires shows a novel coupled temperature-pressure dependent reorientation from <100> to <110> phase. A temperature-pressure-induced solid-solid <100> to <110> reorientation diagram is generated for Cu nanowire with varying cross-sectional sizes. A critical pressure is reported for Cu nanowires with varying cross-sectional sizes, above which an initial <100> oriented nanowire shows temperature independent reorientation into the <110> phase. The effect of surface stresses on the <100> to <110> reorientation is also studied. The results indicate that above a critical cross-sectional size for a given temperature-pressure, <100> to <110> reorientation is not possible. It is also reported here that for a given applied pressure, an increase in temperature is required for the <100> to <110> reorientation with increasing cross-sectional size of the nanowire. The temperature-pressure-induced solid-solid <100> to <110> reorientation diagram reported in the present paper could further be used as guidelines for controlling the reorientations/shape memory in nano-scale applications of FCC metallic nanowires.

This paper presents the design and flight validation of an embedded fiber Bragg gratings (FBG) based structural health monitoring (SHM) system for the Indian unmanned aerial vehicle (UAV), Nishant. The embedding of the sensors was integrated with the manufacturing process, taking into account the trimming of parts and assembly considerations. Reliable flight data were recorded on board the vehicle and analyzed so that deviations from normal structural behaviors could be identified, evaluated and tracked. Based on the data obtained, it was possible to track both the loads and vibration signatures by direct sensors' cross correlation using principal component analysis (PCA) and artificial neural networks (ANNs). Sensor placement combined with proper ground calibration, enabled the distinction between strain and temperature readings. The start of a minor local structural temporary instability was identified during landing, proving the value of such continuous structural airworthy assessment for UAV structures.

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