Defence Science Journal
Not a member yet
3794 research outputs found
Sort by
Mitigation of Blast Induced Acceleration using open cell natural rubber and Synthetic Foam
Get PDFIn addition to high pressure generated by explosion, the induced high acceleration can also cause severe injuries to occupants and structural damage, especially in anti-vehicular land mine blast scenario. This problem has not been studied well and only few techniques to reduce the deadly effect of high acceleration are reported in literature. In the present work, the mitigation of blast induced acceleration using add-on layers of open cell natural rubber and synthetic foam on rigidly fixed composite plate has been studied experimentally under increasing blast wave strengths. The blast wave strength was varied by increasing quantity of plastic explosive from 0.150 kg to 0.550 kg. The induced vibration in the composite plate due to impingement of blast wave was measured in terms of acceleration using piezoelectric accelerometer. It was observed that the sharp rising acceleration signals were transformed into a slowly rising and low amplitude signals with the addition of foam. The mitigation of high frequencies and amplitude of acceleration signals was also verified with the fast Fourier transform study. The rubber foam shows better acceleration mitigation than synthetic foam. This study has suggested that the material like rubber and synthetic foam can be used for mitigating the acceleration resulting from the impact of blast wave
Particle Swarm Optimisation of Hole Quality Characteristics in Laser Trepan Drilling of Inconel 718
Get PDFInconel-718 is a nickel based super alloy and is extensively in use for working at very high temperature (upto 2000 °C) such as aero engine gas path equipment, nuclear equipment etc. Drilling micro size hole in such material with laser beam has been a proven choice and laser drilling process produces geometrically and dimensionally improved hole. Hole geometrical features can be improved further if laser drilling system operated at optimal input parameter setting. This paper experimentally investigates the behavior of hole geometrical features hole circularity and hole taper in laser trepan drilling of Inconel -718 sheet. Optimal value of laser input parameters for improved hole circularity and reduced hole taper have been suggested with the help of computational intelligence technique particle swarm optimisation. The effect of each laser input parameter on hole quality characteristics are also discussed and demonstrated graphically. Finally the experimental validation of the predicted results has been carried out
Accurate Tracking of Manoeuvring Target using Scale Estimation and Detection
Get PDFCamera zoom operation and fast approaching/receding target causes scaling of acquired target in video frames. Fast moving target manifests in large inter-frame motion. In general, non-uniform background degrades performance of tracking algorithms. Fast Fourier transform (FFT)-based Correlation algorithms improve tracking in this scenario, but their applications is limited to small inter-frame motion. Increasing search region has implication on execution speed of the algorithms. Rapid target scaling, non-uniform background and large inter-frame motion of target hinder accurate and long term visual tracking. These challenges have been addressed for extended target tracking by augmenting fast discriminative scale space tracking (fDSST) algorithm with probable target location prediction and target detection. Localisation of fast motion has been achieved by applying fused outputs of Kalman filter and quadratic regression based prediction before applying fDSST. It has helped in accurate localisation of fast motion without increasing search region. In each frame, target location and size have been estimated using fDSST and further refined by target detection near this location. Smoothing and limiting of trajectory and size of detected target has enhanced tracking performance. Experimental results show considerable improvement of precision, success rate and centre location error tracking performance against state-of-the-art trackers in stringent conditions
Venous Thrombosis could be Gender Specific, Women Beware!
Get PDFVenous thrombosis (VT) is the third major cause of mortality in the world after heart attack and stroke. Its two major clinical manifestations are deep vein thrombosis (DVT) and pulmonary embolism (PE) which are serious medical conditions but often remain under-diagnosed. Although rate of occurrence of venous thrombosis in men is slightly higher, a number of studies have pointed out that woman poses higher risk of venous thromboembolism (VTE) compared to men at various stages of life. Risk of VTE increases in women’s life particularly with use of oral contraceptives, during pregnancy and with exogenous administration of hormones like in post-menopausal hormone therapy. Various reports show that these factors increase risk of DVT and PE by several folds. DVT is considered as an important cause of maternal death in western countries. It is often asymptomatic and its signs and symptoms are similar to those of normal pregnancy. The hormonal changes at various stages of life and less physical activity increase the risk of VTE by blood flow stasis. It is extremely important for women to know the stages of life when they are prone to develop VTE, about its prevention and treatment. Detailed studies on differences in clinical manifestations of VTE between men and women are lacking. This review focusses on assessing the increased risk of VTE and its prognosis in women based on available literature
Influence of Initial State Errors on Perturbation Guidance Accuracy
Get PDFThe inertial navigation system is aligned and leveled before the launch of a long-range vehicle. However, the initial state errors caused by the non-uniformity of the Earth can influence the parameters in flight dynamics, which will bring about serious uncertainty for the impact point of a long-range vehicle. Firstly, this paper analyses the influence mechanism of initial state errors on nominal trajectory, navigation trajectory and guidance trajectory. Then, a propagation model of engine-cutoff state deviation caused by initial state errors is derived under the condition of without-guidance. On this basis, an accuracy analytical solution of initial state errors on perturbation guidance is finally proposed to obtain the real impact-point of the long-range vehicle. In the simulations, the influence properties of initial state errors on perturbation guidance is analysed, give influence regularities of single initial state error, and obtain the statistical properties of engine-cutoff state deviations and impact-point deviation by Monte Carlo technique. From the simulation results, it seems that the navigation state tracks the nominal state. However, the real impact- point deviation has not been truly eliminated, instead of the almost target-hit deviation calculated by navigation output. The proposed analytical guidance accuracy model can be rapidly computed to provide a compensation for guidance and control system to improve hit accuracy
Rapid Transfer Alignment of SINS with Measurement Packet Dropping based on a Novel Suboptimal Estimator
Get PDFTransfer alignment (TA) is an important step for strapdown inertial navigation system (SINS) starting from a moving base, which utilises the information proposed from the higher accurate and well performed master inertial navigation system. But the information is often delayed or even lost in real application, which will seriously affect the accuracy of TA. This paper models the stochastic measurement packet dropping as an independent identically distributed (IID) Bernoulli random process, and introduces it into the measurement equation of rapid TA, and the influence of measurement packet dropping is analysed. Then, it presents a suboptimal estimator for the estimation of the misalignment in TA considering the random arrival of the measurement packet. Simulation has been done for the performance comparison about the suboptimal estimator, standard Kalman filter and minimum mean squared estimator. The results show that the suboptimal estimator has better performance, which can achieve the best TA accuracy
Numerical Analysis and Measurement of Electric field Strength inside GTEM Cell at GSM Frequencies
Get PDFA miniaturised gigahertz transverse electromagnetic (GTEM) cell is designed and fabricated to generate uniform electric (E-) field, essential for studying the radio frequency exposure effect on tissue equivalent liquids at global system for mobile (GSM) communication frequencies (914 MHz and 2.10 GHz). The simulation procedure is discussed and its results are compared with measurement data. The E-field strength inside the GTEM cell is scanned using a microstrip based E-field probe and complete uncertainty evaluation procedure is discussed. Theoretically, simulated and measured E-field strength is reported with expanded uncertainty
Parametric Study of the Reltron Oscillators
Get PDFIn this paper, effect of the input DC electrical parameters, such as, pulse shape, cathode voltage and the postacceleration voltage on the performance of reltron oscillator have been investigated. For this purpose, a typical reltron oscillator has been designed and simulated. The mode of excitation, resonant frequency and electric field patterns in the RF modulation cavity of the reltron structure has been studied through electromagnetic simulation. The RF output performance and effect of DC electric pulse shape is studied through 3D PIC simulation. To get a practical insight of the excitation signal effect on the performance of device operation, various pulse shapes with different rise, hold and fall time have been studied the pulse of hold time 70 ns and rise and fall time of 5 ns gives maximum stable RF power. Device parametric analysis for the different cathode and post-acceleration voltages has also been investigated. With a beam current of 750 A, cathode voltage of 200 kV and post-acceleration voltage of 800 kV, the device provides ~350 MW with ~46% efficiency
Real Time Non uniformity Correction Algorithm and Implementation in Reconfigurable Architecture for Infra red Imaging Systems
Get PDF In modern electro-optical systems, infra-red (IR) imaging system is an essential sensor used for day and night surveillance. In recent years, advancements in IR sensor technology resulted the detectors having smaller pitch, better thermal sensitivity with large format like 640.512, 1024.768 and 1280.1024. Large format IR detectors enables realisation of high resolution compact thermal imager having wide field-of view coverage. However, the performance of these infrared imaging systems gets limited by non uniformity produced by sensing element, which is temporal in nature and present in spatial domain. This non uniformity results the fixed pattern noise, which arises due to variation in gain and offset components of the each pixel of the sensor even when exposed to a uniform scene. This fixed pattern noise limits the temperature resolution capability of the IR imaging system thereby causing the degradation in system performance. Therefore, it is necessary to correct the non-uniformities in real time. In this paper, non uniformity correction algorithm and its implementation in reconfigurable architectures have been presented and results on real time data have been described
Winter Thermohaline Features along 10 degree N in the Bay of Bengal
No full textTo commemorate the contributions made by Indian Naval Ship (INS) Kistna during the first International Indian ocean expedition programme a scientific cruise was planned in the Bay of Bengal during November 2017 onboard INS Sagardhwani. The objective was to study the thermohaline properties along 10 °N in the Bay of Bengal and understand the sound channel characteristics in the region. A fresh water cap of ~20 m thickness is noticed in the top layers of the Bay of Bengal occupying the region extending from 83 °E – 93 °E. A prominent anti-cyclonic eddy was noticed around 10 °N centered between 90 °E and 93 °E, a negative sea level (west of 90 °E) co-exists with a positive sea level anomaly to its east along the observational tracks along 10 °N. The climatological temperature and salinity sections also shows the same features as observed along the transect. The study also sheds light on the deep sound channel characteristics along the 10 °N channel