Defence Science Journal
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Effect of Collector Voltage on the Large and Small Signal Modulation Characteristics of 980 nm Transistor Laser
Get PDFTheoretical analysis of Transistor Laser is carried out and the static and frequency responses for different collector voltages, under common emitter configuration are determined. The threshold current (Ith) is observed as 33mA and it increases linearly with reverse collector to base voltage (VCB). Meanwhile, the output optical power is found to decrease proportionately when VCB is increased. A maximum of 18.7GHz modulation bandwidth is observed when an input base current of 95 mA is applied at a fixed value of VCB (1V). The modulation bandwidth is found to decrease with increase in reverse VCB. The turn on delay increases with collector voltage. However, it decreases with increase in base current
Defence Science Journal
Get PDFIts objective is to stimulate study and research in science, fundamental and applied, in relation to the problems of Defence. It serves to bring to the notice of the scientists in universities and other research institutions the basic problems in Defence science, the work that is being done in this field and its importance and also the role of Defence Science in the progress of science generally. A properly conducted Defence Science Journal will go a long way in creating and sustaining interest amongst the research workers in universities and civil institutions, in Defence Science and Technolog
Selection of Optimal Air Independent Propulsion System using Forced Decision Matrix
Get PDFA project management decision tool viz., forced decision matrix (FDM) is implemented in this paper towards identification of a suitable optimal air independent propulsion (AIP) system for submerged vehicles. FDM is utilised in order to handle the trade-off from amongst multiple propulsion technologies. FDM is based on multi-attribute utility theory used extensively in decision analysis situations involving persuasive multiple alternatives. The efficiency and effectiveness of this methodology to tackle complex solutions is elaborated in this paper with appropriate calculations. A rational decision-making procedure is evolved using the FDM in order to select the best suited AIP technology for a submerged vehicle. It is inferred that FDM is an effective and potential tool towards identification of best suitable solution in a multi-option environment
Ballistic Limit Estimation Approaches for Ballistic Resistance Assessment
Get PDFThe armour technologist conducts ballistic impact testing either for evaluating armour materials and systems or for studying material’s defeating mechanism. Most standards make use of the ballistic limit velocity for ballistic assessment. This is the bullet impact velocity that leads to the protection perforation in 50 per cent of the cases. Various models have been emerged to estimate this key metric. The present article summarises the popular models developed for ballistic limit estimation. An attempt is made to point out models’ strength and weakness. First, the experimental set-up used for that goal is displayed. Next, a concise overview of ballistic limit estimation methods is presented. Lastly, a discussion is dedicated to model’s comparison and analysis. This literature survey reveals that the main drawback of already existing methods is that they are purely statistical. Moreover, existing methods are based on the normality assumption of perforation velocities which tends from -infinity to infinity. The main conclusion of this survey is that the presented methods offer a comparable accuracy in estimating the ballistic limit velocity. However, a given variability is remarked when extreme values estimation is of interest, impact velocities leading to low and high perforation probability. Finally, existing models’ performances decay with the reduction of the experimental sample size which represent a constraining requirement in ballistic resistance assessment
Anthropometric Measurement and Comparative Analysis of Ethiopian Army Personnel Across Age, Ethnicity, and Nationality
Get PDFThe anthropometric characteristics of the users depend upon the topography, nutrition, age, ethnicity, gender, and living conditions, and play a crucial role in the design of the equipment and the workspace to be used by them. This study aims to establish an anthropometry database for male Ethiopian army personnel and investigate the anthropometric variability across ethnicity, age, and with other countries, with the intention to facilitate ergonomic design and development of various facilities (e.g., equipment/ devices, and workspaces) for the Ethiopian army. Following the reliability assessment of the physical measurement technique, the anthropometric data from 250 Ethiopian male army personnel (four different ethnic groups at different age levels) were collected, and normality of the data set was tested. The anthropometric database of Ethiopian army personnel in terms of range, mean, standard deviation, percentile values (5th, 50th, and 95th) was documented. PCA was applied to select a smaller representative by reducing a larger set of variables for further statistical analysis and applications. ANOVA and follow-up posthoc test (Tukey’s HSD test) were carried out to compare anthropometric differences among different age groups and ethnic variations. The mean anthropometric differences were also compared with databases from other countries (India, Korea, and USA) using t-test. Significant variations were found when the anthropometry was compared between age, ethnicity, and cross-nationals. The findings indicate that variations in age, ethnicity, and geographical factors could have a significant impact on the ergonomic design of equipment and workspaces of Ethiopian army personnel
Enhancement of Fatigue Strength on SAE 1541 Steel Link Plate with Slip Ball Burnishing Technique
Get PDFThis research paper describes a technique for the enhancement of the fatigue strength of the chain link plate in the drive system of a military armoured vehicle. SAE 1541 steel link plates of chains were subjected to cyclical tensile stress due to repeated loading and un-loading conditions. The crack was getting originated from the pitch hole and growth perpendicular to the chain pulling load, due to fatigue mechanism. In general plate holes are manufactured using the conventional process. An additional novel technique called the slip ball burnishing (SBB) method is applied for improving the hole properties. The improvement is made by producing local plastic deformation, improving surface finish and compressive residual stress throughout in the pierced hole. Both the conventional process (CP) and the SBB technique have been evaluated by optical, profile, surface roughness and micro harness tests. Experimental fatigue test validations were done in both chain samples using the Johnson-Goodman method. SBB chains passed 3x106 cycles at the load of 17.61 kN and CP chains passed 3x106 cycles at the load of 13.92 kN. The conclusion was that SBB made a significant improvement of 26.51 per cent of fatigue strength compared to CP
Experimental and Numerical Study of Magnetorheological Clutch with Sealing at Larger Radius Disc
Get PDFIn the existing magnetorheological clutch, there is a problem of improper transmission of torque or inefficiency in the transmission of torque. Research is carried out to improve the design of the magnetorheological clutch. Using simulation techniques and experimental study, a new seal at the outer radius is designed to improve the torque transmission of the magnetorheological clutch. The fluid flow between the input and output shafts are studied using COMSOL Multiphysics v5.3a software. The optimized design of the seal is subjected to experimental study and torque transmitted is measured. The results show an improvement in the torque transmission with the introduction of the new seal
Electrochemical Biosensors for Point of care Applications
Get PDFBiosensor refers to powerful and innovative analytical tool involving biological sensing element and transducer with broad range of applications, such as diagnosis, drug discovery, biomedicine, food safety and processing, environmental monitoring, security and defense. Recent advances in the field of biotechnology, microelectronics, and nanotechnology have improved the development of biosensors. Glucometers utilizing the electrochemical determination of oxygen or hydrogen peroxide employing immobilised glucose oxidase electrode seeded the discovery and development of biosensors. Molecular recognition based on geometry and forces of interaction play an important role in the biosensor development. The advent of nanotechnology led to highly efficient and sensitive biosensors. They also provide an effective immobilisation matrix for the various bioreceptors. Enzymatic and their mimetic (metalloporphyrin)-based biosensors for reactive oxygen, nitrogen species and cytochrome c will also be discussed. The role of antibodies and their applications in immunosensors development for cytochrome c and superoxide dismutase will be highlighted. The electrochemical biosensors are less expensive, miniaturised and used for point-of-care applications. Further, the fabrication of labVIEW based virtual biosensor instrumentation and microcontroller based portable biosensor for wide variety of applications also devices will be presented
Development of an Energy Efficient Stern Flap for Improved EEDI of a Typical High speed Displacement Vessel
Get PDFThe surge in maritime trade is leading to large scale deployment of high-speed displacement ships by all nations. Cargo vessels are designed for a voyage in pre-determined routes at consistent speeds. On the other hand, high-speed displacement vessel engines designed with a capability to cater for top speeds are under-utilised during their normal course of operation. This sub-optimal utilisation impacts efficiency and increases emissions. In this study, a most favourable stern flap is designed for reducing the energy efficiency design index of a typical high-speed displacement vessel with a slender hull. CFD simulations and experimental model testing were conducted for 12 different stern flap configurations for determining most favourable flap design in the Froude no of 0.17-0.48. Performance of the most favourable stern flap was established by calculating, energy efficiency design index (EEDI) and fuel consumption based on typical operating profile. NOx, VOC and PM emissions were estimated in with and without flap condition. Studies demonstrated that the stern flap reduced effective power demand, average fuel consumption and emissions by about 8 per cent, which when considered for the ship’s operating life cycle, are significant. The most favourable stern flap reduced EEDI by 3.74 units and 1.98 units as compared to the bare hull condition and the required EEDI respectively, thereby demonstrating that EEDI could be used as an index to indicate stern flap efficiency
Study on Friction Sensitivity of Passive and Active Binder based Composite Solid Propellants and Correlation with Burning Rate
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Friction sensitivity of composite propellants and their ingredients is of significant interest to mitigate the risk associated with the accidental initiation while processing, handling, and transportation. In this work, attempts were made to examine the friction sensitivity of passive binder: Hydroxy Terminated Polybutadiene/Aluminium/Ammonium Perchlorate and active binder: (Polymer + Nitrate Esters)/Ammonium Perchlorate/Aluminium/Nitramine based composite propellants by using BAM Friction Apparatus. As per the recommendation of NATO standard STANAG–4487, the friction sensitivity was assessed by two methods: Limiting Frictional load and Frictional load for 50% probability of initiation (F50). The test results showed that the active binder based formulations were more vulnerable to frictional load as compared to the formulations with passive binders. Examination of a comprehensive set of propellant compositions revealed that the particle size distribution of Ammonium Perchlorate and burn rate catalysts were the most influential factors in dictating the friction sensitivity for HTPB/Al/AP composite propellants. For active binder/AP/Al/Nitramine composite propellants, the formulation with RDX was found more friction sensitive with a sensitivity value of 44 N as compared to its HMX analog (61 N). The correlation studies of friction sensitivity, burning rate, and thermal decomposition characteristics of HTPB/Al/AP composite propellants is described