Defence Science Journal |
An analytical model explaining the functional characteristics of detonation type ram accelerator is presented. Major flow processes, namely, (i) supersonic flow over the cone of the projectile (ii) initiation of conical shock wave and its reflection from the tube wall, (iii) supersonic combustion, and (iv) expansion wave and its reflection are modelled. Taylor-Maccoll approach is adopted for modelling the flow over the cone of the projectile. Shock reflection is treated in accordance with wave angle theory for flows over the wedge. Prandtl-Mayer analysis is used to model the expansion wave and its reflection. Steady one-dimensional flow with heat transfer along with Rayleigh line equation for perfect gases is used to model supersonic combustion. A computer code is developed to compute the thrust produced by combustion of gases. Ballistic parameters like thrust-pressure ratio and ballistic efficiency of the accelerator are evaluated and their maximum values are 0.032 and 0.068, respectively. The code indicates possibility of achieving high velocity of 7 km/s on utilising gaseous mixture of 2H2 + ø2 in the operation. Velocity range suitable for operation of the accelerator lies between 3.8 - 7.0 km/s. Maximum thrust value is 33721 N which corresponds to the projectile velocity of 5 km/s.
Generalised Model for Aircraft vulnerability by Different Weapon Systems V.P. Singh & Yuvraj Singh The authors' earlier model for the vulnerability of aircraft where aircraft was considered as a combination of cylinder, cones and wedges has been extended to the case when structural data of aircraft as well as its vital parts are given in the form of three-dimensional curvilinear triangles. In the case of VT-fused ammunition, spherical normal distribution has been used to estimate the landing probability of the shell in a cylindrical vicinity region around the aircraft. Kill criteria of vital parts have been redefined.
Guided Missile with an Intelligent Agent
V.
Krishnabrahmam, N. Bharadwaj, K.N. Swamy
& V.V.S. Sarma
Guided missiles involve the use of a conventional deviated pursuit course like proportional navigation algorithm and its variants, which is optimal when the speed advantage of the guided missile is very high and the target maneouvering is minimal. Against the present-day aircraft, which employs fly-by-wire technology for high maneouverability and high speed, missiles need to have a much higher speed advantage or to use a combination of artificial intelligence and modern control algorithms. Results of Simulation of pursuit and evasion with an autonomous intelligent agent incorporated in the control loop are presented.
BackStability Criterion for a Finned Spinning Projectile The state-of-the-art in gull projectile technology has been used for the aerodynamic stabilisation. This approach is acceptable for guided and controlled rockets but the free-flight rockets suffer from unacceptable dispersion. Sabot projectiles with both spin and fins developed during the last decade need careful analysis. In this study, the second method of Liapunov has been used to develop stability criterion for a projectile to be designed with small fins and is made to spin in the flight. This criterion is useful for the designer.
Free Convection Flow of a Non-Newtonian Fluid in a Vertical Channel
Rita Choudhury & Alok Das
The steady two-dimensional free convection flow of a Walters fluid (model B') in a vertical channel one of whose walls is wavy, has been investigated analytically. The governing equations of the fluid and the heat transfer have been solved subject to the relevant boundary conditions by assuming that the solution consists of two parts: a mean part and disturbance or perturbed part. To obtain the perturbed part of the solution, the long wave approximation has been used and to solve the mean part, a well-known approximation used by Ostrach has been utilised. The relevant flow and the heat transfer characteristics, namely the skin-friction and the rate of heat transfer at both the walls have been discussed in detail.
Tagging of Explosives for Detection J.S. Gharia, R.K. Sinha, U.R. Nair, S.R. Nayak & R.M. Roy
The results of a study on estimation of shelf life of 2,3-dimethyl 2,3-dinitrobutane (DMNB)-tagged RDX and PETN explosives by monitoring DMNB depletion by high performance liquid chromatography and simultaneously recording the detectability of the tagged explosive composition using explosive vapour detector Model-97 HS. DMNB was incorporated in the explosive using methanol as solvent for DMNB and the explosive compositions were stored at 35, 55 and 75OC over a long period. Methods developed for preparing the homogeneously tagged composition with DMNB at 0.5 per cent level and for the analysis of DMNB for ensuring homogeneity of DMNB in the composition are described. The results show no change in compatibility and sensitivity on the incorporation of DMNB in the explosive. Estimation of shelf life of DMNB in the explosive was done for a period of storage of 202-304 days at different temperatures.
Evaluation of Chemical Protective Clothing: A Comparative Study of Breakthrough Times with Sulphur Mustard and a Simulant,1 ,3-Dichloropropane Beer Singh, M.V.S. Suryanarayana, S.M. Baronia, N.B.S.N. Rao, V.S. Tripathi, Darshan Lal & A.K. Sen
Carbon-coated non-woven fabrics were evaluated against vesicant sulphur mustard and 1,3-dichloropropane (DCP). Breakthrough times of these chemicals were compared and fitted in a linear equation. A correlation, better than 95 per cent was obtained. It is recommended that DCP be used in the evaluation and quality control of fabric in the chemical protective clothing manufacturing industries to reduce the exposure and risks of handling lethal chemicals. However, the clothing may be challenged with actual CW agents to determine their protective potentials, in the laboratory. Diffusion coefficients for DCP were also computed from the breakthrough data for carbon-coated fabric of different grades.
Laboratory Evaluation of Dibenz (b,f)-1,4-Oxazepine for the Protection of Nylon Tapes against Rodents Attack M.J. Mendki, Shri Prakash, P.K. Gutch, R.C. Malhotra, K.M. Rao, Jagat Singh & I. Hussain
The efficacy of dibenz (b,f)-1 ,4-oxazepine (CR), a potent sensory irritant and deltamethrin a well known insecticide, in providing protection to the multi-element nylon tapes, used as aircraft arresters at airports have been evaluated. The results obtained indicate that 5 per cent CR-admixed UV resistant nylon tapes got adequate protection against attacks from wild type laboratory bred Rattus rattus for up to l 60 days. CR treatment was found to be water wash resistant against 7, 30 and 60 days protection offered by 3, 4 and 5 per cent deltamethrin, respectively.
Performance Decrement by Exposure to Sub-Lethal Doses of Ionising Radiations S.K. Mukherjee
Under many circumstances, exposure to ionising radiation can impede performance significantly. Aider large doses, lethal or supra-lethal, behavioural effects are rapid (within minutes), but up to l 0 Gy, performance deficits develop rather slowly and are long-lasting. All tasks are not equally radiosensitive; tasks with complex and demanding requirements may be disrupted even at low radiation doses (<I Gy). Combined injuries can act synergistically with radiation exposure to greatly increase behavioural deficits. Most of the radioprotectors developed to date are themselves behaviourally toxic at radio protective as well as non-protective doses and the adverse effects are further aggravated in the presence of radiation. A very limited number of radio protectors have been found to give behavioural radio protection at very low, almost non-toxic doses.
Nitramine-Based High Energy Propellant Compositions for Tank Guns R.S. Damse & Haridwar Singh
Six different RDX-based gun propellant compositions have been formulated and studied to select the most suitable composition for tank gun ammunition in terms of higher force constant at relatively lower flame temperature (To). Ballistic performance of the compositions was evaluated on the basis of closed vessel test. Heat energy was determined using a bomb calorimeter. Sensitivity, thermal characteristics, stability and mechanical properties of the compositions were studied for assessing their suitability for application. The composition containing 65 per cent RDX and 28 per cent nitrocellulose was found to provide higher level of force constant at relatively lower To, reasonably good burning rate characteristics and mechanical properties.
Automatic Dispersion Measurements of Helical Slow-Wave structure S.J. Rao, S. Subramanian, S.K. Datta & R. Seshadri An experimental setup for computer-controlled automatic measurement of dispersion characteristics of helical slow-wave structures (SWSs) has been described. A non-resonant perturbation technique was employed for this purpose. The dispersion characteristics of a practical X-Ku band helical SWS were studied using this experimental setup. The experimental results have shown good agreement with analytical results obtained using an equivalent circuit approach for an X-Ku band helix SWS.
Effect of Different Chemical Environment on Porous Silicon Amita Gupta, Alok Jain & V.K. Jain Properties of porous silicon (PS) are found to be sensitive towards different chemical environment. Because of its large surface area, it is highly reactive and can adsorb chemical vapours. The present study shows that photo conductivity and photo luminescence (PL) properties are changed significantly in the presence of acetone, ammonia and steam vapours and can be used to identify and sense these chemical environment. These results also suggest that the molecules adsorbed on the pores change the transport mechanism of carriers in PS, leading to increase or decrease in conductivity. On the other hand, surface states on the enormous PS surface are modified under different chemical environment, leading to change in visible PL.
Influence of Hardness on Perforation Velocity in Steel Armour Plates
In an earlier investigation, the influence of hardness on tempered steel arm our plates of 20 mm thickness, impacted by 20 mm diameter steel ogive-shaped projectile at normal, was studied. Additional data is investigated with relation to the perforation velocity of the plates. It is observed that the plate perforation velocity and the plate plugging velocity decrease with increasing plate hardness.
Weighted Generalised Directed-Divergence Measure to Assess Military Requirements G.P. Tripathi In the present paper, a weighted information theoretic measure has been used to compare and assess the military requirements of a country with other countries to meet the challenge of future battles. A measure of weighted directed-divergence based on m probability distributions has been proposed and a probability distribution 'closest' to these m probability distributions is obtained. The closest probability distribution provides a reasonably adequate measure and thus enables one to apply this technique in real life situation, viz., assessment of balanced military requirements for a country: consensus ranking, pattern recognition, etc.