Showing papers by "Defence Research Agency published in 2007"

Data fusion of secondary and primary surveillance radars for increased robustness in air-traffic monitoring

Abstract: The paper presents methods for increasing robustness of civil air-traffic monitoring systems, with secondary surveillance radars (SSR) and primary radars, against intentional jamming. Jamming could cause large problems to civil air traffic from an economically point of view as well as increase the risk for serious accidents. The methods are based on a sensor network and data fusion. In a sensor network false objects do not appear simultaneously in different sensors. Consequently, data fusion methods can be used to reveal false objects. The data fusion methods discussed are; statistical distance, covariance intersection and hidden Markov models (HMM). The statistical distance is used to associate data from different sensors. The covariance intersection is used to fuse data from different sensors. HMM is used to describe the behaviour of an aircraft. The paper discusses the use of these methods on this application and presents some simulation results.

Boundary element analysis of crack intersection, initiation and growth at pin loaded holes

Abstract: The dual boundary element method for the analysis of cracks in linear elastic materials has been previously generalised by the authors to allow for automatic remeshing when crack tips intersect other cracks or boundaries, and initiation and growth of small cracks at positions of high stress concentration. The new cracks are assumed to result from sudden events such as an overload or the subsequent stress redistribution when cracks intersect other cracks or holes. In this paper a crack at the edge of one hole in a row of pin-loaded holes is investigated; various values are considered for the stress at which new cracks may initiate. Two rows of aligned or staggered holes are examined also. The spacing between the holes was typical for lines of holes in overlap joints in plates. For the same load transfer between the plates, new cracks are initiated less readily and grow more slowly for a double row of aligned holes than for a single row or for staggered rows.