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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3990-3998 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this paper a two-dimensional model of fluid and heat flow in weld pools is considered and a solution methodology is presented that is based on a perturbation expansion with the Prandtl number as a small parameter. This allowed us to determine the temperature field efficiently and by using it to determine the location of the phase front to map the molten region into a semicircular region in which the Boussinesq form of the Navier–Stokes equations were solved. Doing so allows the domain to be represented with a much smoother phase boundary than is usual in phase change problems. The flow in the weld pool made with a moving laser shows vigorous convection on the solidification side of the weld pool and crowding of the isotherms on the melting side.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 2690-2701 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Previous experimental studies indicate that the steady two-dimensional flow in a lid-driven cavity becomes unstable and goes through a sequence of transitions before becoming turbulent. In this study, an analysis of this instability is undertaken. The two-dimensional base flow is computed numerically over a range of Reynolds numbers and is perturbed with three-dimensional disturbances. The partial differential equations governing the evolution of these perturbations are then obtained using linear stability analysis and normal mode analysis. Using a finite difference discretization, a generalized eigenvalue problem is formulated from these equations whose solution gives the dispersion relation between complex growth rate and wave number. An eigenvalue solver using simultaneous iteration is employed to identify the dominant eigenvalue which is indicative of the growth rate of these perturbations and the associated eigenfunction which characterizes the secondary state. This paper presents stability curves to identify the critical Reynolds number and the critical wavelength of the neutral mode and discusses the mechanism of instability through energy calculations. This paper finds that the loss of stability of the base flow is due to a long wavelength mode at a critical Reynolds number (Re) of 594. The mechanism is analyzed through a novel application of the Reynolds–Orr equations and shown to be due to a Goertler type instability. The stability curves are relatively flat indicating that this state will be challenged by many shorter wavelength modes at a slightly higher Reynolds number. In fact, a second competing mode with a wavelength close to the cavity width was found to be unstable at Re=730. The present results of the reconstructed flow based on these eigenfunctions at the neutral state, show striking similarities to the experimental observations.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 103-120 
    ISSN: 0271-2091
    Schlagwort(e): free surface ; free boundary problem ; segregated method ; finite elements ; extrusion ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An algorithm to simulate steady, viscous free surface flows is presented in this paper. A Picard-type approach wherein the flow and free surface updates are performed alternately is utilized to iterate for a solution. The procedure is intended for large-scale two- or three-dimensional problems. A surface-intrinsic co-ordinate system which facilities representation of general free surface shapes is used. Using a Galerkin finite element method (GFEM), two free surface updates, namely kinematic and normal stress updates are formulated. It is shown that the effects of surface tension, surface tension gradients and imposition of contact angles can be simulated elegantly within the framework of the GFEM. A novel feature of the updates is that the deformations are sought in a direction normal to the current iterate free surface shape, with the result that the method is ideally suited when used in conjunction with an automatic mesh generator. With the normal stress update a volume constraint can also be imposed. A segregated method is utilized to solve iteratively one degree of freedom at a time for the solution of the flow variables. As a result, the memory and disc space requirements are minimal. Sample problems in extrusion, coating and crystal growth are presented to clearly illustrate the convergence behaviour and accuracy of the algorithm.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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