5,150 research outputs found

    Hierarchical tapered bar elements undergoing axial deformation

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    A method is described to model the dynamics of tapered axial bars of various cross sections based on the well-known Craig/Bampton component mode synthesis technique. This element is formed in terms of the static constraint modes and interface restrained normal modes. This is in contrast with the finite elements as implemented in NASTRAN where the interface restrained normal modes are neglected. These normal modes are in terms of Bessel functions. Restoration of a few of these modes leads to higher accuracy with fewer generalized coordinates. The proposed models are hierarchical so that all lower order element matrices are embedded in higher order element matrices. The advantages of this formulation compared to standard NASTRAN truss element formulation are demonstrated through simple numerical examples

    Transient loads analysis for space flight applications

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    A significant part of the flight readiness verification process involves transient analysis of the coupled Shuttle-payload system to determine the low frequency transient loads. This paper describes a methodology for transient loads analysis and its implementation for the Spacelab Life Sciences Mission. The analysis is carried out using two major software tools - NASTRAN and an external FORTRAN code called EZTRAN. This approach is adopted to overcome some of the limitations of NASTRAN's standard transient analysis capabilities. The method uses Data Recovery Matrices (DRM) to improve computational efficiency. The mode acceleration method is fully implemented in the DRM formulation to recover accurate displacements, stresses, and forces. The advantages of the method are demonstrated through a numerical example

    Fe-spin reorientation in PrFeAsO : Evidences from resistivity and specific heat studies

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    We report the magnetic field dependence of resistivity (ρ\rho) and specific heat (CC) for the non-superconducting PrFeAsO compound. Our study shows a hitherto unobserved anomaly at TSRT_{SR} in the resistivity and specific heat data which arises as a result of the interplay of antiferromagnetic (AFM) Pr and Fe sublattices. Below the AFM transition temperature (TNPrT_N^{\rm{Pr}}), Pr moment orders along the crystallographic c axis and its effect on the iron subsystem causes a reorientation of the ordered inplane Fe moments in a direction out of the abab plane. Application of magnetic field introduces disorder in the AFM Pr sublattice, which, in turn, reduces the out-of-plane Pr-Fe exchange interaction responsible for Fe spin reorientation. Both in ρ\rho(TT) and d(C/T)/dTd(C/T)/dT curves, the peak at TSRT_{SR} broadens with the increase of HH due to the introduction of the disorder in the AFM Pr sublattice by magnetic field. In ρ\rho(TT) curve, the peak shifts towards lower temperature with HH and disappears above 6 T while in d(C/T)/dTd(C/T)/dT curve the peak remains visible up to 14 T. The broadening of the anomaly at TNPrT_N^{\rm{Pr}} in C(T)C(T) with increasing HH further confirms that magnetic field induces disorder in the AFM Pr sublattice.Comment: 8 pages, 10 Figure