Showing papers by "Vikram Sarabhai Space Centre published in 1982"

On Linear Stability of Triangular Libration Points of the Photogravitational Restricted Three-Body Problem Wien the More Massive Primary is an Oblate Spheroid

Abstract: It is well known that the triangular points of the restricted three-body problem are linearly stable for the mass ratio \(0\langle\mu\langle{\mu_0}=\frac{1}{2}-\sqrt{69}/18=0.03852089\ldots\), the critical mass value. The range of the mass parameter giving rise to stable triangular solutions decreases when the more massive primary (Subba Rao — Sharma, 1975) or both the primaries (Bhatnagar — Hallan, 1979) are oblate spheroids with their equatorial planes coincident with the plane of motion. If the more massive primary is a source of radiation, the value of critical mass decreases with the increase in the radiation force (Chernikov,1970).

A modification of the rule of mixture in estimating strengths of a Composite

Abstract: Strengths of a composite when determined by actual tests shows a lower value than those obtained through theoretical estimation by applying the simple rule of mixtures. This discrepancy has been attributed largely to the presence of defects in the composite like debonding, porosities, cracks etc. To establish a design criteria to a more practically closer strength values an empirical formulae is presented. The formulae accounts for defect level upto 30%. The results were obtained through computational facilities using IBM (360/44) Computer. The drop in strength with increasing defect level is shown to occur and the effect is more predominant when defects are more in fibres than in matrix.

Poly(organophosphazenes). Some aspects of synthesis, catalysis and characterization

Abstract: The catalytic effects of three typical metal salts, HgCl2, Hgl2, and ZnCl2, on the ringopening polymerization of (PNCl2)3/(PNCl2)4 in terms of the hard/soft concept for acids and bases were studied. The influence of the nature and the concentration of the initiators on the onset of gelation, the extent of polymerization, and on the polymer molecular weight is described. A new technique to follow the substitution reaction of chlorine in poly(dichlorophosphazene) by the 4-methylphenoxy group is proposed.

On the Detonation Characteristics of CHNO‐Type Condensed Explosives. A parameter study

Abstract: The object of the present paper is to carry out a parametric study which takes into consideration the variations of the detonation characteristics such as CJ pressure, CJ temperature, velocity of detonation (VOD), and gas volume of CHNO-based condensed explosive systems in connection with the changes in input parameters like loading density and heat of formation of the explosive in question. Meaningful equations which describe adequately the interrelationships between the parameters were derived for a typical CHNO-type explosive. The study is likely to be of considerable help in determining the variations in the magnitudes of the detonation parameters corresponding to a given change in the relevant input characteristics. The results of such studies should also be important in estimating the uncertainty of a parameter, like VOD, arising from the uncertainty in the heat of formation of the explosive which is often determined experimentally and whose values is often of questionable validity. The principal features that emerge from the investigations in this paper are: (1) while CJ pressure and VOD tend to increase sizably with the loading density of the explosive, CJ temperature and CJ volume decrease with an increase in the loading density; and (2) all the four parameters, viz., CJ pressure, CJ temperature, VOD, and CJ volume increase, however, being of a marginal nature, barring the CJ temperature whose variations with the heat of formation are not insignificant.

A generalized computer simulation model for obtaining sol‐gel distributions in infinite polymeric networks

Abstract: Computer simulation is well-known to be a very efficient and powerful tool, applicable to a wide variety of situations. The present paper is concerned, in some detail, with a computer simulation model for obtaining the sol and gel fractions in polymeric networks. Apart from yielding the values of these parameters, even in situations that are characterized by a considerable amount of complexity, and where, as a consequence, the relevant mathematical procedures have not yet reached a stage of finality, the model developed in this paper can be of value in arriving at a satisfactory overall perspective of the chemical process as a whole. It yields results which enables one to answer such questions as where a crosslinking can occur or how the sol is distributed. Appropriate modifications that are called for in the model in investigating more complex situations are also indicated in the paper. Die Computersimulation hat sich als ein sehr leistungsfahiges Mittel erwiesen, das sich vielfach verwenden last. Die gegenwartige Arbeit befast sich mit einem Simulationsmodell, das der Ableitung der Sol- bzw. Gelfraktionen von Polymernetzwerken dient. Das in dieser Arbeit entwickelte Modell liefert die Werte fur diese Grosen auch in Fallen, die durch betrachtliche Komplexitat charakterisiert sind und in denen folglich die mathematischen Verfahren unvollkommen bleiben. Abgesehen davon kann dieses Modell von viel Wert sein, da es eine Gesamtperspektive des ganzen chemischen Verfahrens darbietet. Die sich ergebenden Resultate bieten die Moglichkeit, einige Fragen zu beantworten, wie z.B., wo die Vernetzung vorkmmen kann und wie das Sol verteilt ist. Auf geeignete Modifikationen dieses Modells, die zur Untersuchung komplizierterer Falle erforderlich werden, wird dabei hingewisen.

Estimation of interdendritic undercooling during freezing of ternary and quaternary aluminium alloys

Abstract: Expressions have been developed for the maximum interdendritic supercooling during the freezing of ternary and quaternary systems The actual undercoolings during freezing of several ternary and quaternary aluminium base alloys have been computed Using available data for the measured diffusion coefficients and assuming reasonable values for other diffusion coefficients, it is shown that the interdendritic supercooling does not exceed one degree centigrade in all the aluminium alloys investigated In fact, in most of the alloys it is less than a tenth of a degree centrigrade

Effect of Burning Rate Modifiers on Propellant Performance. A theoretical study

Abstract: The addition of burning rate enhancers or suppressers in solid propellant composition is seen to affect the energy level considerably. In the present paper, an attempt is made to quantify such effects. Even though the study is carried out over the theoretical values of the performance parameters, the trends in the variations and the corrections occurring therefrom for the inclusion of burning rate modifiers seem to be applicable to the delivered or the actual values also more or less equally.

A Penalty Function Approach to the Optimization of Chemical Propellant Systems using the fletcher‐powell algorithm

Abstract: This article presents an efficient numerical algorithm for determining, for a given metallized propellant system, the optimum combination of reactants which can fetch the maximum specific impulse, and also the salient features of the associated computer program. The optimization procedure is based on the Fletcher-Powell technique with the objective function being augmented by a penalty term to accommodate the constraints. Numerical results for the optimization, obtained by means of a computer program written in FORTRAN IV on the IBM-360 computer for a representative propellant system, are also presented in this note.