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1
Content available Optimization of process parameters of friction stir welded AA5082-AA7075 butt joints using resonance fatigue properties
Kumar G., Kumar R., Kumar R.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2020
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Vol. 68, nr 1
99--108
EN
In this work, experiments were carried out to quantify the behaviour of friction stir welded (FSW) AA5082-AA7075 butt joints under tensile loading and completely reversed fatigue loading. Different samples were prepared to identify optimum tool rotational and travel speeds to produce FSW AA5082-AA7075 butt joints with the maximum fatigue life. ANOVA was performed, which confirmed that both tool speed nad tool rotation speed affect the tensile strength of the weld. The samples exhibit a considerable difference in their fatigue life and tensile strenght. This difference can be accounted to the presence of welding defects such as surface defects and porosity. S-N curve plotted for the sample shows a significantly high fatigue life at the lower stress ranges. Fracture surfaces were also analysed under scanning electron microscope (SEM). Study of the fracture surface of the sample that failed under fatigue loading showed that the surface was mainly divided in two zones. The first zone was the area of fatigue crack growth where each stress cycle, slowly and gradually, helped in the growth of crack. The second zone was the region of fast fracture where the crack growth resulted in the failure of the joint instantaneously. The fracture surface study of the sample that failed under tensile loading showed that the mode of failure was ductile in nature.
2
Content available Swarm Intelligence-based Partitioned Recovery in Wireless Sensor Networks
Kumar G., Ranga V.
Journal of Telecommunications and Information Technology
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2018
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nr 3
70--81
EN
The failure rate of sensor nodes in Heterogeneous Wireless Sensor Networks is high due to the use of low battery-powered sensor nodes in a hostile environment. Networks of this kind become non-operational and turn into disjoint segmented networks due to large-scale failures of sensor nodes. This may require the placement of additional highpower relay nodes. In this paper, we propose a network partition recovery solution called Grey Wolf, which is an optimizer algorithm for repairing segmented heterogeneous wireless sensor networks. The proposed solution provides not only strong bi-connectivity in the damaged area, but also distributes traffic load among the multiple deployed nodes to enhance the repaired network’s lifetime. The experiment results show that the Grey Wolf algorithm offers a considerable performance advantage over other state-of-the-art approaches.
3
Content available remote Effects of Radiation and Porosity of the Medium on MHD Flow Past an Inclined Plate in the Presence of Hall Current
Rajput U. S., Kumar G.
Computational Methods in Science and Technology
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2017
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Vol. 23, No. 2
93--103
EN
The present study deals with an analysis of the effects of radiation and porosity of the medium on unsteady natural convection flow of a viscous, incompressible and electrically conducting fluid past an impulsively started inclined plate under the influence of transversely applied uniform magnetic field and Hall current. The medium of the flow is taken as porous. The governing equations involved in the present analysis are solved by the Laplace-transform technique. The results obtained are discussed with the help of graphs drawn for different parameters like thermal Grashof number, mass Grashof Number, Prandtl number, Hall current, radiation, permeability, magnetic field parameter and Schmidt number. The numerical values obtained for skin-friction and Nusselt number have been tabulated. The objective of this study is to analyze radiation and the porosity of the medium in the MHD flow model. In the study we found that the velocity in the boundary layer increases with the values of radiation and porosity of the medium. It is also observed that radiation and porosity of the medium increases the skin-friction at the wall surface. The results of the study are found to be in agreement with the actual flow. The importance of the problem can be seen in cooling of electronic components of a nuclear reactor, bed thermal storage and heat sink in the turbine blades.
4
Content available Energia wiatrowa, a globalne spowolnienie gospodarcze
Kumar G.
Nowa Energia
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2009
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nr 1
58--60
PL
Wydawać by się mogło, że żaden przemysł nie jest już odporny na rozprzestrzeniający się kryzys światowy. Jednak pewne branże są z pewnością w lepszej pozycji, aby zmierzyć się z obecnymi wyzwaniami, pokonać bariery i wykorzystać nowe możliwości. Sektor energii wiatrowej zdaje się być w takiej uprzywilejowanej sytuacji.
5
Content available remote On (phi)-instability of non-liner matrix Lyapunov systems
Murty M., Kumar G., Lakshmi P., Anjaneyulu
Demonstratio Mathematica
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2009
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Vol. 42, nr 4
731-743
EN
We prove necessary and sufficient conditions for phi-instability of trivial solutions of linear matrix Lyapunov systems and also sufficient conditions for phi-instability of trivial solutions of non-linear matrix Lyapunov systems.
6
Content available remote Initial and boundary value problems for fuzzy differential equations
Murty M., Kumar G.
Demonstratio Mathematica
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2007
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Vol. 40, nr 4
827-838
EN
This paper deals with the study of existence and uniqueness criteria for initial and boundary value problems associated with fuzzy differential equations of first and second order with the help of a modified Lipschitz condition.
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