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    7206 research outputs found

    FEM analysis of LTA-7 horizontal tail

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    A finite element structural analysis of the stabilizer portion of the horizontal tail has been performed using the MSC/NASTRAN package. The critical loading case is identified by subjecting the structure to loading corresponding to several different load cases. From NASTRAN stress output for these cases, the Va maneuvering 5700 kg ., n = 1.0, 0.2412c, elevator up deflection is seen to be critical. Stresses from this case are used to compute the margins in buckling for skin panels and shear webs. It is seen that stresses are within allowable limits but from the buckling point of view, while the skin panels are over-designed, the midspar web is under-designed and must be stiffened. Comparisons with the stress analysis results from the simple bending theory/shear flow analysis carried out by the ASDE/CAU design group show that there is scope for improvement in the design

    Thermoelectric power of cerium up to 6GPa

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    The thermoelectric power (TEP) of cerium has been measured up to 6 GPa. The results have been interpreted using the theories developed by Blandin and Hirst

    Effect of Environmental Exposures on the Aramid Fibre Kevlar

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    The effects of exposure of Kevlar 49 fibres to thermal, ultrasonic and chemical environments have been analysed. Both the tensile strength and the tensile modulus deteriorate with thermal exposures . However, the former is more sensitive than the latter. The prominent crystal structural changes induced by thermal exposures are reduction in crystallinity, molecular misalignment about the fibre axis, increase in the inter layer distance, changes in crystallite size and/or microstrain. Thermally induced macro changes include introduction of surface holes, partial hollowness near the core, localised thinning, material loss in the vicinity of surface impurities etc . The structural changes could be satisfactorily correlated with the corresponding changes in tensile properties . All the thermally induced effects are controlled by two parameters, viz ., the temperature (T) and the duration of the cumulative exposure to T, te,,,,,(T). The T-tcam(T) effect leads to the observation of isothermal decomposition of Kevlar over a range of temperatures which include T's, far below the reported decomposition temperature of 500/550 °C. A hitherto unknown direct correlation between X-ray diffraction peak positions and the tensile strength has also been identified . Exposure to ultrasonic waves introduces axial compression, evinced by the formation of kink bands, fibrillation and macro buckling . The unit cell of axially compressed fibres manifests an anisotropic deformation. The process of moisture uptake by Kevlar 49 fibres is controlled by the relative humidity (RH) of ambient atmosphere . The saturation moisture content is, however, determined by structural characteristics such as the degree of crystallinity, molecular alignment etc . The uptake of common organic solvents by Kevlar is dependent on the molar volume of the former

    Seismic qualification of directional valve

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    Seismic qualification tests on pneumatically operated directional valve were carried out in the shake table facility in Structural Integrity Division. Determination of the fundamental frequency for directional valve was carried out through exploratory vibration test as per ANSI B 16.41 Annexure E (Para E-3) to ascertain extent of flexibility as defined in the standard. Seismic (static) load test on same directional valve was also carried out to ascertain its capabilities to withstand the expected dynamic, seismic stresses and to ensure that the valves will not be subjected to performance degradation or malfunction under seismic conditions. This report describes the final seismic qualification documentation for directional valve manufactured by M/s Vijay Fire Protection Systems Ltd, Mumbai

    A numerical study of the role of vertical structure of vorticity during tropical cyclone genesis

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    An eight-level axisymmetric model with simple parameterizations for clouds and the atmospheric boundary layer was developed to examine the evolution of vortices that are precursors to tropical cyclones. The effect of vertical distributions of the vorticity, especially that arising from a merger of mid-level vortices, has been studied to provide support for a new vortex-merger theory of tropical cyclone genesis. The basic model was validated with the analytical results available for the spin-down of axisymmetric vortices. With the inclusion of the cloud and boundary layer parameterizations, the evolution of deep vortices into hurricanes and the subsequent decay is simulated quite well. Effects of several parameters such as initial vortex strength, radius of maximum winds, sea surface temperature and latitude (Coriolis parameter) on the evolution were examined. A new finding is the manner in which mid-level vortices of the same strength decay and how, on simulated merger of these mid-level vortices, the resulting vortex amplifies to hurricane strength in a realistic time-frame. The importance of the sea-surface temperature on evolution of full vortices has been studied and explained. Also it is found that the strength of the surface vortex determines the time taken by the deep vortex to amplify to hurricane strength

    Non-Destructive Evaluation—A Pivotal Technology for Qualification of Composite Aircraft Structures

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    Tremendous advances in composite materials and a deeper understanding of their behavior have been responsible for the increased use of composites in the development of advanced, new generation civil and military aircraft. Composites play an important role in any aircraft development programme and are strong contenders to their metal counterparts due to their significant contributions towards improving strength, stiffness, fatigue properties & weight reduction. As materials, structural design & processing have evolved, strong emphasis is placed on effective & reliable damage detection, durability and damage tolerance. As a consequence, Non-destructive Evaluation (NDE) has also undergone significant advances towards meeting the growing demands of quality assurance. Advanced Composites Division (ACD) of National Aerospace Laboratories (NAL), has been involved in the development of composite structures for both civil and military aircraft for over a decade and a half. Innovative composite processing methods like co-curing/co-bonding have been successfully employed to realize airworthy structures. The role of NDE in the development of these structures has been critical and not limited to damage detection alone. On several occasions, NDE has provided valuable inputs towards improving design and process parameters. In-spite of the complexity of the structures, stringent quality requirements and tight delivery schedules, NDE has been successful in certifying these composite structures for airworthiness. This paper discusses the implementation of key NDE techniques like ultrasonics, radiography, acoustic emission and thermography for reliable flaw detection, characterization and quality assurance of composite aircraft structures

    Crystal and molecular structure of the discogen bis[1,3-di(p-n- Decylphenyl)propane-1,3-dionato]paliadium(ll)

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    The transition metal containing discogen, bis[1,3-di(p-n-decylphenyl)propane-1 ,3-dionato ]paliadium(II)crystallizes in the triclinic space group pI with one molecule in a unit cell of dimensions a = 10.260(2), b = 12.961(2), c = 13.403(2)A., ex= 110.54(1), f3= 101.75(1) and 'I = 98.44(lt. The crystal structure was solved by direct methods and refined using full matrix least squares procedure. The palladium atom is lying on an inversion center. The decyl chains are fully extended in an all trans conformation. In the crystal structure, the molecules form a tilted columnar arrangement. The angle between the normal to the core and the column axis is 68xB0;. Each column is surrounded by six others. Along the13; column axis, adjacent palladium atoms are separated by 10.26A

    Thermally induced structural changes in Nomex fibres

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    Thermally aged Nomex fibres manifest several residual effects viz. reduction in X-ray crystallinity, weight loss and deterioration in tensile characteristics. Surface damages in the form of longitudinal openings, holes, material deposits etc have also been observed. Based on the data from thermally exposed fibres, the time needed for states of zero tensile strength and modulus have been predicted

    CFD simulation using FLUENT and RANS3D - A validation exercise

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    The present work involves two-dimensional numerical simulation of three benchmark problems like (i) Laminar flow in a lid driven cavity (ii) Turbulent flow past a backward facing step and (iii) turbulent flow past NACA0012 aerofoil, using in-house flow solution code RANS3D and the commercially available FLUENT code. The results obtained using these codes are compared with the available measurement data and/or other computations

    Design of 1 :7 .645 scale LCA high speed air intake model

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    This report details the mechanical design aspects of the 1:7.645 scale LCA high speed air intake model. The model is intended to generate intake data in the transonic range 0.7 & 1.3 by Aeronautical Development Agency. The model has been designed for testing in the S2MA ONERA wind tunnel facilities. The 1:7.645 scale model is basically a composite model with metallic bulkheads/inserts and mainly consists of front fuselage, the wing, the canopy, interchangeable front duct modules, the rear portion of the CFRP duct, the main bulkhead, the heat exchanger duct, the sting, kulite rake, rear portion of the metallic duct including venturi, butterfly valve and diffuser. The kulite rake, the sting and the rear portion of the duct available with ONERA is made use of in the present model design. The steel bulkhead provides anchor support for the model in the tunnel through a flange mounted sting. The model has been designed to meet all the requirements of ONERA regarding model design and construction. For the design of the present model, the critical loads are scaled down from the load data of the 1:4.405 scale model. Structural analysis based on strength of materials approach has been carried out on the components of the model viz. forward fuselage, main bulkhead, air intake duct, and the splitter plate. FEN analysis has been carried out on the wing which is supposed to be the critical element of the model. The stress analysis shows that adequate margins of safety are available for all the components of the model


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