Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

DSC-TG studies on kinetics of curing and thermal decomposition of epoxy–ether amine systems

Abstract: The cure behavior of diglycidyl ether of bisphenol A with a simple ether amine (4,7,10, trioxa -1,13, tridecane diamine), system I and a polyether amine (polypropylene glycol block polyethylene glycol block polypropylene glycol bis 2 amino propyl ether), system II was compared by Differential Scanning Calorimetry. The exothermicity of the curing reaction of system I is higher than that of system II (316 ± 15 J g−1 for System I and 230 ± 15 J g−1 for system II). Kinetic parameters viz., activation energy, pre-exponential factor, and rate constant for curing were evaluated by Kissinger method and Kissinger–Akahira–Sunose isoconversion method. Both systems showed low glass transition temperatures and System II shows a much lower T g (−38 °C) than system I (26 °C). The thermogravimetric analysis of the two cured epoxy amine systems showed comparable thermal stability.

Optimal control of a pretwisted shearable smart composite rotating beam

Abstract: The optimal vibration control of a rotating, composite, pretwisted, single-celled box beam, exhibiting transverse shear flexibility and restrained warping, is analyzed. A higher-order shear deformation theory (HSDT) enabling satisfaction of traction-free boundary conditions is employed. An orthotropic host with Circumferentially Uniform Stiffness ply angle configuration and transversely isotropic sensors-actuator pairs that are surface embedded along the span are considered. The total output from sensors is fed to a controller and then uniformly applied to actuators. The extended Galerkin method, along with either instantaneous or classical LQR methods, is used. Instantaneous LQR provides greater response attenuation in case of sustained external forcing. Results are obtained for a linear spanwise variation of pretwist. Compared to the unshearable and first-order shearable (FSDT) models, the HSDT appears most sensitive to pretwist and – when a saturation constraint is considered – it predicts the lowest settling time. The HSDT predicts significant attenuation in response and power required as compared to the FSDT, the differences being especially pronounced for constrained input control. Parametric studies involving the ply angle, pretwist, and patch length are performed. An optimum pretwist that yields lowest response, power, and settling time is obtained. Its value differs when the saturation constraint is used. Tailoring provides greater attenuation at the expense of an increase in settling time. Using constrained input control, an order-of-magnitude reduction in power requirement is possible via tailoring. The results underscore the importance of shear strain variation across the beam wall, and also of synthesizing active control with tailoring, for achieving efficient control.

CloudSat observations of multi layered clouds across the globe

Abstract: Vertically resolved multi-layer cloud distributions over the globe using 4 years of CloudSat/CALIPSO observations during 2007–2010 are discussed. The quantitative information on the frequency of occurrence of one- to five-layered clouds across the globe is established, which are of immense importance from the global climate standpoint. After segregating the CloudSat observations into different seasons, the 4 years of mean global maps of frequency of occurrence of one to five-layered clouds are discussed in details. These global maps provide much needed quantification of vertically resolved multi-layer clouds by revealing when and where the frequency of occurrence of multi-layer clouds are maximum including the number of layers. On an average, it is observed that over the globe one-, two-, three-, four- and five-layer clouds occur 53, 20, 3.5, 0.4 and 0.04 % of the time respectively. High fraction of single layer clouds is observed over the descending limbs of Hadley cell where relatively large lower tropospheric stability is found. The regions where multi-layer clouds are more frequent are identified and discussed along with large scale circulation. Apart from quantifying the frequency of occurrence of multi-layer clouds, the latitudinal distribution of zonal mean occurrence of cloud base and top altitudes of each cloud layer is constructed for boreal winter and summer. These analyses provide the cloud base and top altitudes of one to five-layered clouds, which are important to understand the vertical structure of the multi-layered clouds. The significance of the present study lies in establishing the global distribution of vertically resolved multi-layer clouds and the role of large-scale dynamics in controlling their distribution for the first time.