Defence Science Journal
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Blind Recognition of Parameters of Reed Solomon Code from Intercepted Erroneous Codewords
Get PDFError correcting codes are designed for reliable transmission of digital information over a noisy channel. Several papers have been published on blind identification of binary FEC codes but papers reported on the identification of non-binary error correcting codes are less. Due to its strong error correction capability, RS (Reed-Solomon) code is being used widely. So technique for blind recognition of RS code is required to analyse intercepted signal as well as for intelligent communication. This paper presents a technique for extraction of parameters of Reed-Solomon code from intercepted demodulated bitstream. The proposed algorithm is very simple and hence it is very practical for hardware implementation. Our approach has been verified using MATLAB simulation
Radiological Consequences Modelling for a Land Based Operations Environment
Get PDFRadiological Dispersive Devices (RDD) are often portrayed as weapons used by radical (asymmetric) forces, however they can also be used in a regular war. In this study, a hypothetical scenario where an asymmetric force contaminates the battlefield, by detonating an RDD prior to the soldier’s arrival without being detected, is simulated. The software HotSpot was used due to its speed and conservative results which can help inform the decisions made by the commanding officers. HotSpot performs a Gaussian simulation of the radioactive dispersion in the environment. The plumes that arise from the explosion are considered to be affected by the atmospheric conditions. In this study, those conditions are represented by the Pasquill-Gifford stability classes. The results of the simulation show that remaining stationary, if the contaminated area size is not affected by the PG class variation, may increase the radiological risk. It is better to move the soldiers around in order to avoid additional exposure, however that may also be a challenge for various reasons including changes in the shape of the contaminated area. Nevertheless, the variations in local PG classes gain importance as the distance from the release point increases
Qualification Testing, Evaluation and Test Methods of Gas Generator for IEDs Applications
Get PDFIn this work, the design qualification testing, evaluation and test methods of gas generator using double base (DB) propellant having square flake shape is explained for an improvised explosive devices (IEDs) applications. Various kinds of the gas generators are used to save life of an aeronaut in the fastest way from the disable fighter aircraft. Due to their ruggedised design, compactness, safe transportation, repeatability in performance and quick operation, the gas generator are used. The gas generator is designed and developed keeping functional, mechanical and structural requirements in mind. The gas generators are subjected to the various qualification tests, electrical characterisation followed by closed vessel (CV) firings at hot and cold temperatures. The gas generators after the successful qualification tests are validated through the ground trials i.e. dynamic firing of disruptor during the development phase. The damage caused due to impact of the projectile is assessed in terms of crater as acceptance criteria at stand-off distance of 0.5 m and 1m. The gas generator discussed in this research article is used to disrupt the suspected IEDs by creating a high-speed jet using water-jet disruptor. In conclusion, after successful qualification testing, the gas generator for IEDs application meets all the specifications as per user’s requirements
Data driven TRL Transition Predictions for Early Technology Development in Defence
Get PDFThis paper proposes the framework of TRL (Technology Readiness Level) transition predictions for early technology development in defense. Though predicting future TRLs is an important planning tool, it has been studied less actively than the other critical issues on TRL, and previous studies mostly have resorted to domain experts. The proposed framework is data-driven and utilises both explanatory and predictive modelling techniques. As a case study, the proposed framework is applied to real technology development data from DTiMS (Defense Technology InforMation Service) which is identified as a key resource. The result of explanatory modelling shows that the two predictor variables, TRL before R&D and project cost, are statistically significant for future TRLs. Also, popular predictive models are fitted and compared with various performance indices using 10-fold cross validation. The two selected predictive models are linear regression and support vector machine models with the lowest prediction errors
Effect of a Jet Control Device on the Process of Missile and Internal Weapons Bay Separation
Get PDFTo ensure that the missile is safely separated from the internal weapons bay, the jet is used to control the process of missile separation, which is mounted on the front edge of the bay. The length-to-depth ratio of the bay was L/D=8, the diameter of the missile was d1 =0.178 m, the diameter of the jet was d2 =0.05 m . The FLUENT software was combined with our group-developed code under the platform of a user-defined function (UDF) to solve the flow field and the six-degrees-of-freedom (6DOF) of missile. The detached eddy simulation method and dynamic mesh technology were used in the numerical calculations. The boundary condition of missile, bay, and aircraft was no-slip wall condition. The boundary condition of the jet was the pressure-inlet. The pressure far-field boundary was selected as other boundaries. The constraint of the ejection device on the missile was considered. It was found that the jet control device thickens the shear layer, so the shear layer with more gradual velocity gradients, which is beneficial to the separation of missile. The distance between the internal weapons bay and the missile in the positive z-direction with the jet is 1.74 times that without the jet at t=0.5 s. In the case of the jet control device, the pitching angle of the missile ranged from 0.93° to -3.94° , the angular motion range of the missile with the jet is smaller than that without. The jet can make the characteristics of the flow field friendly, and enable the missile to separate from the bay quickly, stably, and safely
2 Loop Nonlinear Dynamic Inversion Fuel Flow Controller Design for Air to Air Ducted Ramjet Rocket
Get PDFFuel Flow controller based ramjet propulsion system have a flexibility to change rocket velocity depending on guidance requirement by controlling the fuel flow rate as a function of atmospheric conditions like altitude, Mach no. and angle of attack. In this paper, Design objectives & requirements of fuel flow controller have been brought out from guidance loop for air-to-air target engagement. 2-loop non-linear dynamic inversion (DI) based controller design has been proposed to track the commanded thrust and to meet the time constant requirement as a function of altitude, Mach no. and angle of attack. The outer thrust loop is to control commanded thrust and to generate the demand for gas generator pressure loop and inner pressure loop is to meet outer loop demand by controlling throttle valve area. The engine state space plant model has been adapted with improvement of existing model. Throttle valve actuator specifications requirement are also brought out
Frangibility Quantification of Frangible Bullet upon Impact on a Hard Target
Get PDFThe article presents a new method of quantitative evaluation of the degree of disintegration, called frangibility of frangible bullets, based on shooting experiments. On the basis of the dependence of the Frangibility Factor of the bullet on its impact velocity, the frangibility index is determined as a quantifier of the projectile’s ability to disintegrate into fragments applied for a certain range of interest. The method can be used to assess the ability to disintegrate into fragments of various types of bullets, preferably frangible bullets produced by powder metallurgy technologies. The proposed method was used to quantify the frangibility of five experimental frangible bullets
Adaptive True Proportional Navigation Guidance Based On Heuristic Optimization Algorithms
Get PDFThe PN-guidance (Proportional Guidance) still continues to be improved, because it is the simplest, cheapest and most reliable algorithm. One of the most important techniques to improve PN-guidance is to adapt the navigation constant depending on time. In this study, first, the entire adaptation methods for PN-guidance are classified, then the adaptation process is online achieved by using heuristic optimization during guiding the missile. The novelty of this study is that the heuristic optimization approach is used at the first time to update the navigation constant of PN-guidance. It is considered that having short program code, fast convergence speed and just simple algebraic computations without derivative are vital advantages of heuristic algorithms using into missile systems. In this scope, an Adaptive True-PN (ATPN) guidance algorithm is designed by optimizing navigation constants varying according to the target behavior. The results show that while the acceleration gap of the pitch axis decreases 21.8%, the acceleration gap of yaw axis reduces 39.68%. These reductions mean that while the missile guided by ATPN is maneuvering, it is exposed to less acceleration and less strain.
 
FPGA based Identification of Frequency and Phase Modulated Signals by Time Domain Digital Techniques for ELINT Systems
Get PDFIn this paper, a decision tree algorithm based on time-domain digital technique is developed for the identification and classification of diverse radar intra-pulse modulated signals for the electronic intelligence system in real-time. This includes linear frequency modulation, non-linear frequency modulation, stepped frequency modulation and bi-phase modulation. The received signal is digitised and the instantaneous phase and high accuracy instantaneous frequency are estimated. The instantaneous amplitude is also estimated to get the start and stop of the pulse. Instantaneous parameters are estimated using a moving autocorrelation technique. The proposed algorithm is employed on the instantaneous frequency and the modulation is identified. The modulation type and modulation parameter are important for unique radar identification when similar radars are operating in a dense environment. Simulations are carried out at various SNR conditions and results are presented. The model for algorithm is developed using a system generator and implemented in FPGA. These results are compared when the proposed algorithm is used with the existing digital in-phase and quadrature-phase (DIQ) technique of instantaneous frequency and amplitude estimation
Statistical Evaluation of Burning Rate Data of Composite Propellants Obtained from Acoustic Emission Technique
Get PDFThe acoustic emission technique has been considered to be one of the most reliable and robust methods for the measurement of the steady burning rate of composite propellants. In this work, attempts were made to quantify the measurement variability of the burning rate of composite solid propellants by acoustic emission method using statistical tools. A total of 1100 individual measurements were subjected to statistical treatment. The combination of confidence interval and repeatability limit delineated the extent of natural dispersion in the burning rate measurement data. The very high coefficient of variation values for the propellant compositions, having a burning rate of more than 25 mm s–1 raised concerns about the suitability of the acoustic emission method for high burning rate compositions. The Reliability interval approach was employed to determine the statistically significant sample size for different composite propellants having a burning rate range of 5–31 mm s–1. The entire set of data was screened for identification of outlying observation using the Dixon Q test, and the extent of contamination was quantified. Moreover, the application of statistical techniques could have far-reaching implications for quality control perspectives of burning rate measurement by acoustic emission and could be implemented as reference tolerance limits and preventive measures for ensuring the good health of the instrument as well as propellant processing