Defence Science Journal
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A Computing Model for Design of Flexible Buoyancy System for Autonomous Underwater Vehicles and Gliders
Get PDFModern design approaches are conceived and utilised in an integrated loop covering system statics, dynamics, optimisation, and others. In this regard this paper presents a computing based integrated design approach for a flexible buoyancy system (FBS) aimed towards the applications in autonomous underwater vehicles and gliders. The primary design alternatives for the FBS are: piston and pump driven and both are investigated. The primary design of autonomous underwater vehicles and gliders is computed from first principle of mechanics and defined in the computer aided design model and it is implemented in the Matlab*TM. Lastly, to show the application of the present approach, a design example is presented for a water depth of 6000 m
Characterization of High Porous PZT Piezoelectric Ceramics by different Techniques
Get PDFUltimate properties of a porous ceramic is highly process dependent. In this study, prevalent porous ceramics fabrication methods (Freeze casting, Foam reticulation and Burnable Plastic Sphere (BURPS) method) have been compared by fabricating the porous lead zirconate titanate (PZT) based piezoelectric ceramics. Field Emission Scanning electron microscopy (FESEM) studies were carried out to study the pore size and distribution of the ceramics. Hydrostatic co-efficients increased tremendously on incorporation of porosity which led to Hydrostatic Figure of Merit of 7480 in Foam reticulation samples (porosity 86%). The three dimensionally interconnected networks in the freeze casted samples led to lowest acoustic impedance (6 MRayls) despite not having the lowest density
Similarity Analysis of Projectile Penetration into Concrete
Get PDFThis paper presents a dimensionless model for the depth of penetration (DOP) of a projectile penetrating into a concrete target, based on the similarity theory involving intermediate asymptotics, complete similarity, and incomplete similarity. The calculated numerical results are in good agreement with previous experimental data, including two sets of full-scale and twenty-four sets of sub-scale penetration of non-deformable projectiles into concrete targets. Moreover, compared with several empirical and semi-empirical DOP models, the new model is applicable within a relatively broader range, including the penetration of both sub-scale and full-scale projectiles. For the limitations of the validity, dimensionless parameters Π3 = ϕt/ϕ larger than 12, Π4 = (ϕ3fc)/(Mv02) smaller than 0.1, and the initial impact velocity of the projectile less than about 900 to 1000m/s are necessary for the model
Assessment of Invisible Areas and Military Objects in Mountainous Terrain
Get PDFDuring war activities, the evaluation of invisible areas and military armors in mountainous terrain is very important for assessment of operational-tactical situation in battlefield. This information can be used for prevention of an enemy sudden attack. In given paper, the quantitative method of the assessment of invisible areas and military objects in mountainous terrain is developed and offered by using Unmanned Aerial Vehicle. The probabilities of detection of invisible area or enemy object by using 1 and n UAVs are calculated. Previously obtained data by ArcGIS software (GIS technology) have been used for calculations and evaluations the number of invisible areas and military objects. The analysis of the dependence of effectiveness of revealing and localization areas and military objects on UAV number has been carried out. It was established that for quantitative analysis of invisible areas it is more efficiently to use one UAV, but for detection of armored vehicles and military objects it is more efficiently to use several UAV. Our experiments in mountainous conditions had shown that at flight height 300 m and battle-front 2,5 km putting 3-5 UAVs is real. In this case, all of them perform operational mission and return to base
Capturing an Evader Using Multiple Pursuers with Sensing Limitations in Convex Environment
Get PDFA modified continuous-time pursuit-evasion game with multiple pursuers and a single evader is studied. The game has been played in an obstacle-free convex environment which consists an exit gate through which the evader may escape. The geometry of the convex is unknown to all players except pursuers know the location of the exit gate and they can communicate with each other. All players have equal maximum velocities and identical sensing range. An evader is navigating inside the environment and seeking the exit gate to win the game. A novel sweep-pursuit-capture strategy for the pursuers to search and capture the evader under some necessary and sufficient conditions is presented. We also show that three pursuers are sufficient to finish the operation successfully. Non-holonomic wheeled mobile robots of the same configurations have been used as the pursuers and the evader. Simulation studies demonstrate the performance of the proposed strategy in terms of interception time and the distance traveled by the players.
Performance Analysis of GaN/AlGaN HEMTs Passivation using Inductively Coupled Plasma Chemical Vapour Deposition and Plasma Enhanced Chemical Vapour Deposition Techniques
Get PDFIn the present paper SiN thin film has been studied as a passivation layer and its effect on AlGaN/GaN HEMTs is investigated using two different deposition techniques i.e PECVD and ICPCVD. AlGaN/GaN HEMTs devices passivated with optimised SiN film have delivered lower gate leakage current (from μA to nA). Device source drain saturation current (Ids) increased from 400mA/mm to ~550 A/mm and the peak extrinsic trans-conductance increased from 100 mS/mm to 170 mS/mm for a 0.8 μm HEMT device. The optimised SiN passivation process has resulted in reduced current collapse and increased breakdown voltage for HEMT devices.
Testing and Evaluation of High Energy Portable Laser Source used as a Target Designator along with a Laser Seeker
Get PDFPrecision guided munitions are often driven with the help of a special kind of laser beam, pointing onto the target of interest which can be a ground based stationary target or a moving one. The laser source which is popularly known as target designator is a key element in this and plays a vital role in performing any laser guided bombings. In this paper a testing methodology and evaluation technique is described for such a portable high energy laser source. The parameters of the designator are tested in laboratory environment as well as verified in field conditions. The measured and tested parameters are laser source energy, pulse repetition frequency, laser wavelength accuracy and pulse width. A laser guided bomb seeker is also used to test with and verify different designator parameters specially the pulse repetition frequency (PRF) in field conditions. The PRF is generally set in the seeker manually and the designators are fired onto a target for different PRFs and energy levels. If the PRF of the seeker matches with that of the designator then it locks onto the target and if different it does not. In this experiment one more designator is also fired onto a different target within the field of view of the seeker with the same parameters except the energy level. The seeker changes its position to the target having higher energy density provided pulses are within its detection window
Detection and Identification of Camouflaged Targets using Hyperspectral and LiDAR data
Get PDFCamouflaging is the process of merging the target with the background with the aim to reduce/delay its detection. It can be done using different materials/methods such as camouflaging nets, paints. Defence applications often require quick detection of camouflaged targets in a dynamic battlefield scenario. Though HSI data may facilitate detection of camouflaged targets but detection gets complicated due to issues (spectral variability, dimensionality). This paper presents a framework for detection of camouflaged target that allows military analysts to coordinate and utilise the expert knowledge for resolving camouflaged targets using remotely sensed data. Desired camouflaged target (set of three chairs as a target under a camouflaging net) has been resolved in three steps: First, hyperspectral data processing helps to detect the locations of potential camouflaged targets. It narrows down the location of the potential camouflaged targets by detecting camouflaging net using Independent component analysis and spectral matching algorithms. Second, detection and identification have been performed using LiDAR point cloud classification and morphological analysis. HSI processing helps to discard the redundant majority of LiDAR point clouds and support detailed analysis of only the minute portion of the point cloud data the system deems relevant. This facilitates extraction of salient features of the potential camouflaged target. Lastly, the decisions obtained have been fused to infer the identity of the desired targets. The experimental results indicate that the proposed approach may be used to successfully resolve camouflaged target assuming some a priori knowledge about the morphology of targets likely to be present.
Evaluation of Local Feature Detectors for the Comparison of Thermal and Visual Low Altitude Aerial Images
Get PDFLocal features are key regions of an image suitable for applications such as image matching, and fusion. Detection of targets under varying atmospheric conditions, via aerial images is a typical defence application where multi spectral correlation is essential. Focuses on local features for the comparison of thermal and visual aerial images in this study. The state of the art differential and intensity comparison based features are evaluated over the dataset. An improved affine invariant feature is proposed with a new saliency measure. The performances of the existing and the proposed features are measured with a ground truth transformation estimated for each of the image pairs. Among the state of the art local features, Speeded Up Robust Feature exhibited the highest average repeatability of 57 per cent. The proposed detector produces features with average repeatability of 64 per cent. Future works include design of techniques for retrieval of corresponding regions
Microencapsulation of Paraffin Wax Microspheres with Silver
Get PDFMicroencapsulation of phase change materials (PCMs) with metallic shell materials is a very innovative and challenging task. This can mitigate the problems related to thermal barrier for conventional nonconductive shell materials as well as enhance mechanical properties of PCM microcapsules. Such microcapsules can be integrated into microelectronic devices for their intermittent thermal management in mission critical components. The present work is aimed at developing a new method to synthesise phase change material encapsulated with metallic shell material and characterising the same. Paraffin wax microspheres were first synthesised and then encapsulated with silver through in situ chemical reduction. Further more, a new set of experiments were identified to analyse the quality of encapsulation. The thermal properties were investigated under differential scanning calorimeter and thermogravimetric analyser. The average diameter of paraffin wax microspheres (PW) is found to be ±329 μm. It reveals from DSC analysis that the enthalpy of fusion is minimum for PW@Ag-PVA amongst all others. Accordingly, higher deposition of Ag is possible for PW@Ag-PVA. This is also supported by TGA results where PW@Ag-PVA has only 40 per cent mass loss and the remaining samples have 100 per cent. However, even for PW@Ag-PVA the encapsulation is found incomplete. The present work provides knowhow of the difficulties associated with encapsulation of PCMs with metallic shell material