Showing papers by "Vikram Sarabhai Space Centre published in 1979"
TL;DR: The results of the detailed analyses of two disturbance events are presented in this article, showing that the global scale current system associated with a bay-type disturbance undergoes large changes even within the duration of the disturbance.
60 citations
TL;DR: In this paper, the nocturnal and seasonal variations of equatorial ionospheric scintillations are presented and classified into two classes, namely, class I and class II depending on their fading rates and association with bottomside spread-F.
54 citations
TL;DR: In this article, the first two stages of the thermal decomposition of calcium oxalate monohydrate have been established from non-isothermal thermogravimetric studies, and the rate-controlling processes are phase boundary reactions; the dehydration step assumes spherical symmetry whereas the decomposition step follows cylindrical symmetry.
38 citations
TL;DR: In this article, the existence of retrograde elliptic periodic orbits is established through suitable velocity components, and the eccentricity of these periodic orbits increases with the oblateness of the primary.
Abstract: At critical mass the triangular equilibria in the planar restricted three-body problem, when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion, are in general unstable due to the presence of secular terms in the solutions of linearized equations of motion in the vicinity of these points. Existence of retrograde elliptic periodic orbits is established through suitable velocity components. The eccentricity of these orbits increases with the oblateness.
29 citations
TL;DR: In this paper, a finite element formulation for analyzing large amplitude free flexural vibrations of elastic plates of arbitrary shape is developed for analyzing stress distributions in the plates, deflection shape and nonlinear frequencies.
26 citations
TL;DR: In this article, the thermal decomposition of three commercial samples of carboxy-terminated polybutadiene (PBCT) resins was studied by thermogravimetric analysis (TGA) at heating rates varying from 2° to 100°C/min.
Abstract: The thermal decomposition of three commercial samples of carboxy-terminated polybutadiene (PBCT) resins was studied by thermogravimetric analysis (TGA) at heating rates varying from 2° to 100°C/min. Kinetic parameters of the decomposition process at different heating rates were evaluated by means of the Fuoss method.1 The decomposition process and the activation energy values are found to be dependent on heating rate. Mass-spectrometric analysis of the decomposition products shows that the pyrolysis products of PBCT resins are mainly low molecular weight hydrocarbons: ethylene, acetylene, butadiene, propadiene, vinylcyclohexene, etc. The rates of evolution of these hydrocarbon products vary with the carboxy content of the PBCT resin. Based on this, a carbonium ion mechanism has been suggested for the thermal decomposition. The data generated from this work are of importance for a consideration of the mechanism of combustion of composite solid propellants based on PBCT binders.
21 citations
TL;DR: In this article, the postbuckling behavior of elastic circular plates is studied using a simple finite element formulation and the final linearized eigenvalue problem is solved by using three numerical methods and all these methods are found to yield accurate results for moderately large deflections.
10 citations
TL;DR: In this paper, the authors derived expressions for the burning rate pressure exponent and the temperature sensitivity of AP-based and HMX-based CMDB propellants in terms of the respective physical constants.
Abstract: The object of this paper is to obtain expressions for the burning rate pressure exponent and the temperature sensitivity of AP-based and HMX-based CMDB propellants in terms of the respective physical constants on the basis of a recently developed model of combustion for CMDB propellants and to examine the effects, if any, on these two parameters, of the changes in propellant composition, AP particle size and pressure. Computer programs were developed for this purpose and the results obtained for typical sets of input data presented in the paper. While the results of the calculation indicate a markedly strong dependence of the pressure exponent and the temperature sensitivity on pressure and composition for both AP-based and HMX-based CMDB propellants, the parameters are characterized by far lesser dependence on AP particle size for the AP-based propellant.
8 citations
TL;DR: In this paper, a simple algorithm to compute the stiffness matrix for a triangular plate bending element, without numerical integration, is presented, which brings about a substantial saving in computer time, and can be used to calculate the bending element's stiffness matrix.
Abstract: This communication presents a simple algorithm to compute the stiffness matrix for a triangular plate bending element, without numerical integration. This brings about a substantial saving in computer time.
8 citations
7 citations
TL;DR: The method suggested in this paper utilizes a pneumatic capacitor, one boundary of which is formed by the liquid level, to modulate a fluid amplifier feedback oscillator to make this method attractive for process-control applications.
Abstract: Many process-control systems are air-operated. In such an environment, it would be desirable and economical to use pneumatic sensors. Bubble-back pressure sensors perform quite satisfactorily, but in case of viscous inflammable and slurry-like liquids with a tendency to froth, this level sensor is inadequate. The method suggested in this paper utilizes a pneumatic capacitor, one boundary of which is formed by the liquid level, to modulate a fluid amplifier feedback oscillator. The absence of moving parts and economy obtained makes this method attractive for process-control applications. The system has been mathematically modeled and simulated on an IBM 360/44 digital computer. Experimental values compare fairly well with the theoretical results. For the range tested, the sensor is found to have a linear frequency variation with the liquid level Extended running in the laboratory shows that the system is very reliable. This system has been found insensitive to temperature variations of up to 15°C.
TL;DR: In this paper, a general method of solution for the vibration of rectangular plates with any type of time-dependent boundary conditions is developed by an extension of the method of Mindlin and Goodman.
TL;DR: In this article, the VHF backscatter radar-measured electric field changes in the equatorial electrojet and the simultaneous surface magnetic field changes are analyzed to determine quantitatively the ionospheric contribution ΔFI to the storm-time geomagnetic field perturbation ΔFD.
Abstract: Experimental identification of the electric current systems in the ionosphere and magnetosphere during magnetic storms is a fundamental problem. We report here a new approach to resolving the relative contributions of ionospheric and magnetospheric currents to the storm-time geomagnetic field variations at equatorial latitudes. In this approach, the VHF backscatter radar-measured electric field changes in the equatorial electrojet and the simultaneous surface magnetic field changes are analysed to determine quantitatively the ionospheric contribution ΔFI to the storm-time geomagnetic field perturbation ΔFD. The magnetospheric contribution ΔFM is then determined from: ΔFD=ΔFI+ΔFM (1) This method has yielded extremely interesting results for the magnetic storm of 15 February 1978. It has a great potential for providing valuable new insights into the nature and time evolution of the complex storm-time current systems in the ionosphere and magnetosphere.
TL;DR: In this article, the effect of free-stream non-uniformities such as source flow and wake-like free stream velocities on a trailing blunt body was studied.
Abstract: The knowledge about the position of the detached shock and the aerodynamic forces acting upon a booster front during upper stage (sustainer) jet impingement on a separated booster is needed in connection with the problem of stage separation in the atmosphere for a multistage launch vehicle. The jet flow is squeezed in by the free-stream and characterised by a non-uniform transverse variation of flow properties. The flow field analysis of a trailing blunt body in such a non-uniform flow has been limited to experimental studies only. Most of the prior analytical treatments were restricted to the study of the effect of free-stream non-uniformities such as source flow and wake-like free-stream velocities on blunt bodies. A somewhat related problem of supersonic, underexpanded jet impingement upon an infinite flat plate in the absence of external stream has been studied by Belov et al and Gummer and Hunt.
TL;DR: In this article, the free transverse vibrations of a beam composed of variable thickness layers are studied on the basis of Timoshenko shear theory and the differential equations governing the transverse motion of the beam are solved to determine the frequencies by using the quintic spline collocation technique.
TL;DR: In this article, large amplitude free vibration characteristics of cylindrically orthotropic, tapered circular plates elastically restrained against rotation at the edges, were obtained using a simple finite element formulation.
TL;DR: In this article, large amplitude free vibration characteristics of tapered circular plates elastically restrained against rotation are studied using the finite element method using the linear frequency parameter and ratios of nonlinear to linear periods.
TL;DR: In this paper, the postbuckling behavior of spring-hinged cantilever columns has been investigated using Galerkin finite element method and the governing nonlinear differential equation with variable coefficients has been solved.
TL;DR: The manipulator described in this paper provides versatile remote control and may be constructed economically.
Abstract: For biological experiments requiring manipulations under a microscope, it is necessary to have remote control for the manipulator. Available systems offer the required accuracy at a high cost. Passive micromanipulators are economical but are deficient in performance, the most serious defects being the inability to attenuate operator-induced vibrations and lack of speed control The manipulator described in this paper provides versatile remote control and may be constructed economically.
TL;DR: The structure of pre-oxidised acrylic fiber made in the presence of steam is somewhat similar to the structure reported by various earlier works as discussed by the authors, but in this case, there is an increase in the diameter of the fibre and there is the possibility of presence of peroxide group.