Showing papers by "Vikram Sarabhai Space Centre published in 1984"
TL;DR: In this article, the thermal postbuckling behavior of isotropic circular plates has been studied through a simple finite element formulation and the accuracy of the solution by finite element method is established through a solution by Rayleigh-Ritz method for simply-supported circular plates.
32 citations
TL;DR: In this article, a master dynamic stability curve covering all the end conditions and slenderness ratios of the bar is presented in the non-dimensionalized form in a finite element formulation.
29 citations
TL;DR: In this article, the first two stages of the thermal decomposition of calcium oxalate monohydrate CaC 2 O 4 · H 2 O CaC2 O 4 CaCO 3 have been established from isothermal mass-change studies.
29 citations
TL;DR: In this paper, the authors report an unusual phenomenon of the development of two barium ion clouds from a single release around 200 km altitude, moving with different speeds indifferent directions, with a scale size of 15km.
24 citations
TL;DR: In this article, the postbuckling behavior of cylindrically orthotropic circular plates is investigated through a finite element formulation, with the plates resting on an elastic foundation and their edges are elastically restrained against rotation.
18 citations
TL;DR: In this paper, the effect of fibre orientation on the fundamental frequency of thin rectangular/square orthotropic plates was studied using a high precision triangular orthotropic finite element, which is useful in studying plates of arbitrary plan form and arbitrary fibre orientation.
17 citations
TL;DR: In this article, a finite difference solution for the transient nonlinear heat conduction equation in a finite slab with a radiation boundary condition is proposed, which enables accurate estimation of the surface temperature as well as prevention of oscillation of computed values at the surfaces.
Abstract: A finite difference solution for the transient nonlinear heat conduction equation in a finite slab with a radiation boundary condition is proposed. An implicit finite difference approximation is used which enables accurate estimation of the surface temperature as well as prevention of oscillation of computed values at the surfaces. A two-time level implicit method is used, while Taylor's forward projection method is employed for taking account of the nonlinearities. An iterative method is described which predicts unknown surface conditions. An example is illustrated which is typical of those that arise in practical applications. The results demonstrate that the method is remarkable in its stability to predict surface conditions without debilitation.
15 citations
14 citations
12 citations
TL;DR: In this article, Kumar et al. described a process for the oligomerization of methyl ester of dehydrated castor oil fatty acid over molybdenum oxide on silica-alumina catalyst.
Abstract: A process is described for the oligomerization of methyl ester of dehydrated castor oil fatty acid over molybdenum oxide on silica–alumina catalyst. The process is compared with thermal oligomerization. The nature of the reaction in both the processes are shown to be the same from the structural elucidation of the product despite the variation in product composition. The percentage of dimer in the product in both the processes is observed to attain an equilibrium value at around 270°C. The catalytic process is shown to follow a second-order kinetics with respect to the monomer, whereas the thermal reaction follows a first-order kinetics. The kinetic scheme derived for the catalytic process is shown to be consistent with the steps of the general mechanism proposed for oligomerization reactions over transition metal catalysts [V. G. Kumar, S. Venkatachalam, and K.V.C. Rao, J. Poly. Sci. Polym. Chem. Ed., 22, 3850 (1984)].
10 citations
TL;DR: In this article, a process for the conversion of methylricinoleate, the major castor oil, fatty acid ester, directly into esters of dimer and oligomer acids by using molybdenum oxide on a silica-alumina catalyst is described.
Abstract: A process is described for the conversion of methylricinoleate, the major castor oil, fatty acid ester, directly into esters of dimer and oligomer acids by using molybdenum oxide on a silica–alumina catalyst. The dehydration of the methylricinoleate into a corresponding mixture of conjugated and nonconjugated olefins and the oligomerization reaction took place side by side in a continuous column, fixed-bed reactor. The products are characterized by IR, 1H NMR, and MS. The fragmentation pattern in the mass spectrum of the dimeric species distilled from the mixture reveals that the product contains cyclic and acyclic isomeric structures. The mechanism of dimerization and oligomerization reactions to transition metal complexes and transition metal oxide catalyst systems is reviewed briefly and the possibility of a common mechanism for all similar systems is suggested. A general mechanism for oligomerization reactions to similar catalysts is proposed and the products of the present reaction are explained on the basis of the proposed mechanism.
TL;DR: An Indo-Soviet collaborative experiment on Ozonesonde Intercomparison was conducted at TERLS in March 1983 as discussed by the authors, which yielded data on ozone vertical profiles from eleven rocketsondes, seven balloon-sondes and four sets of Umkehr observations.
TL;DR: In this article, the authors investigated the thermal postbuckling behavior of tapered columns through finite element analysis and provided empirical results in the form of linear thermal load and empirical formulae for the ratios of nonlinear thermal load to linear thermal buckling load.
TL;DR: In this paper, a method was proposed for the determination of kinetic parameters from isothermal experiments which eliminates the use of the integrated form of fractional decomposition function, g(α), and, hence, the kinetic assumption concerning the mechanism of reaction.
TL;DR: In this paper, the authors used a high precision, plane stress, triangular element to determine the stress concentration factor in a tensile strip with a large circular hole, and obtained the values of a/w where a is the diameter of the hole and w is the width of the strip.
TL;DR: In this article, a high-precision triangular orthotropic finite element is developed to study the stability aspects of orthotropic plates as a function of fibre orientation under arbitrary loading. But this element is not suitable for high-dimensional meshes.
01 Jan 1984
Abstract: The results obtained in a study to evaluate the effect of a phenol formaldehyde resin on the adhesion of a polysulphide sealant is presented. The adhesion of the sealant is improved significantly by the incorporation of phenol formaldehyde resin. This is explained on the basis of increased boundary layer strength and the results obtained are compared with the ‘theory of attachment site’. Addition of phenol formaldehyde resin to the sealant caused an increase in cross-link density, ultimate tensile strength, stress at 100% elongation, hardness and a decrease in ultimate elongation and water absorption. The observed property changes are explained on the basis of polymer-filler interactions. Higher concentrations of phenol formaldehyde resin in the sealant caused a decrease in bond strength, cross-link density and mechanical properties. This is attributed to the lesser extent of cure of polysulphide resin.
TL;DR: In this article, the authors studied cylindrically orthotropic circular plates with a constraint on the fundamental frequency when the effect of geometric nonlinearity is included, and derived the optimality criterion and recurrence relations.
TL;DR: Several polyamides of p-phenylenedioxydiacetic acid (PDDA) were synthesized by the low-temperature solution polycondensation techniques as discussed by the authors, and the polymers were characterized by infrared (IR) and H1-NMR spectra.
Abstract: Several polyamides of p-phenylenedioxydiacetic acid (PDDA) were synthesized by the low-temperature solution polycondensation techniques. Six different diamines were condensed independently with p-phenylenedioxydiacetyl chloride (PDC) in a mixture of N-methyl pyrolidone (NMP) and hexamethyl phosphoramide (HMPA). The polymers were obtained in 80–95% yield and possessed inherent viscosities in the range 0.32–0.81 dL/g. The polymers were characterized by infrared (IR) and H1-NMR spectra. The solubility, density, crystallinity, and thermal stability of the polyamides were also determined. A model diamide (MDA-1) was also synthesized from aniline and PDC to confirm the formation of polyamides from diamines.
TL;DR: In this article, the authors highlight the applications of Bayesian techniques for estimating the reliability parameters for aerospace-electronic systems and propose a method of quantifying the prior density parameters from the pre-test knowledge, such as reliability prediction etc.
TL;DR: In this paper, a correlation has been drawn between strength and failure modes observed through scanning electron microscopy (SEM) in large numbers of Kevlar/epoxy composite specimens tested by the NOL ring method.
TL;DR: In this paper, the stressed vibration behavior of orthotropic square/rectangular plates under arbitrary in-plane loading and arbitrary fiber directions was studied using an orthotropic high-precision triangular plate bending element.
TL;DR: In this paper, the thermal decomposition kinetics of carboxy-terminated polybutadiene (CTPB)-NH4ClO4 propellant with NH4BF4 as an additive to suppress the first exotherm of NH4CLO4 were investigated.
Abstract: Premature reignition of controllable solid propellant motors, a factor affecting the extinguishment reliability, has been attributed to the first exotherm of NH4ClO4. Detailed studies were made(1) on suppressing the first exotherm of NH4ClO4 with the use of materials like NH4BF4, NH4PF6, (NH4)2TiF6 etc. The present paper deals with the thermal decomposition kinetics of carboxy-terminated polybutadiene (CTPB)-NH4ClO4 propellant with NH4BF4 as an additive to suppress the first exotherm of NH4ClO4.
The techniques employed in this study include: differential scanning calorimetry (DSC) for the thermal decomposition studies, and strand-burner for the measurement of propellant burning rates. DSC experiments were conducted on the propellants at pressures of ambient, 17 kg/cm2 and 40.82 kg/cm2; at a constant heating rate under an inert atmosphere of nitrogen. The burning rate of the propellant samples were determined in the pressure range of ambient to 70 kg/cm2 in an atmosphere of nitrogen.
The burning rates were found to increase with pressure at each of the concentrations of the additive. The decrease in burning rate with the increase in concentration of the additive, at pressures of 35 kg/cm2 and below is attributed to the excess of ammonia formed during the decomposition of both NH4ClO4 and NH4BF4. At pressures above 35 kg/cm2, the increase in burning rate with the increase in concentration of the additive is attributed to the increased concentration of the metal ion (boron) in NH4BF4. These observations are in agreement with those of Mayer(1) et al., and Glaskova(2).
TL;DR: In this paper, the results for the uniform beam given in Eqs. (16) and (17) can be seen to be in good agreement when trigonometric and algebraic functions are used for the displacements.
Abstract: Numerical Results The results for the uniform beam given in Eqs. (16) and (17) can be seen to be in good agreement when trigonometric and algebraic functions are used for the displacements. These results are also in good agreement with the finite element results presented earlier. Table 2 presents \L and 7 values for both breadthand depth-tapered columns for three values of ft (0.0, 0.2, and 0.4). Again, the results from trigonometric and polynomial distributions are in close agreement. Further, it can be seen that for breadth-tapered columns, the linear buckling load decreases with increasing taper. The effect of nonlinearity (from 7 values) can be seen to be relatively greater in the case of depth-tapered columns and it becomes pronounced when large depth tapers are considered. Also, the effect of nonlinearity decreases with increasing breadth taper, whereas the effect increases with increasing depth taper.
TL;DR: Wang et al. as discussed by the authors proposed a study of thermal constriction resistance at the Interface of Double Tubes and showed that double tubes have better thermal properties than other two-dimensional geometric configurations.
Abstract: Schneider, G.E. and Yovanovich, M.M., "Thermal Resistance of Two-Dimensional Geometries Having Isothermal and Adiabatic Boundaries," AIAA Paper 80-1471; also Heat Transfer and Thermal Control, Progress in Astronautics and Aeronautics, Vol. 78, 1981, edited by A. Crosbie, pp. 179-201. Wang, J.C.Y. and Nowak, E.S., "A Study of Thermal Constriction Resistance at the Interface of Double Tubes," Proceedings of the 7th International Heat Transfer Conference, Vol. 2, Munich, 1982, pp. 87-92. Wang, J.C.Y. and Nowack, E.S., "Solution of Constriction Resistance in Cylindrical Surfaces with an Isothermal Condition at the Contact Land," ASME Paper 81-WA/HT-5, Nov. 1981.