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  • Engineering General  (8)
  • transient  (2)
  • L-curve method  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 39 (2000), S. 97-117 
    ISSN: 1573-1634
    Schlagwort(e): free convection ; boundary-layer ; horizontal surface ; transient ; heat flux
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract This paper presents an analytical and numerical study of transient free convection from a horizontal surface that is embedded in a fluid-saturated porous medium. It is assumed that for time $$\bar \tau 〈 0$$ steady state velocity and temperature fields are obtained in the boundary-layer which occurs due to a uniform flux dissipation rate q 1′′ on the surface. Then, at $$\bar \tau = 0$$ the heat flux on the surface is suddenly changed to q 2′′ and maintained at this value for $$\bar \tau 〉 0$$ . Firstly, solutions which are valid for small and large $$\bar \tau $$ are obtained. The full boundary-layer equations are then integrated step-by-step for the transient regime from the initial unsteady state ( $$\bar \tau = 0$$ ) until such times at which this forward marching approach is no longer well posed. Beyond this time no valid solutions could be obtained which matched the final solution from the forward integration to the steady state profiles at large times $$\bar \tau \to \infty $$ .
    Materialart: Digitale Medien
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  • 2
    ISSN: 1573-1634
    Schlagwort(e): porous medium ; convection ; boundary layer ; transient ; heat flux.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract An analysis is made of the transient free convection from a vertical flat plate which is embedded in a fluid-saturated porous medium. It is assumed that for time $$\overline \tau 〈 0$$ a steady state temperature or velocity has been obtained in the boundary-layer which occurs due to a uniform flux dissipation rate $$q_1^{\prime \prime } $$ . Then at time $$\overline \tau = 0$$ the heat flux on the plate is suddenly changed to $$q_2^{\prime \prime } $$ and maintained at this value for $$\overline \tau 〉 0$$ . An analytical solution has been obtained for the temperature/velocity field for small times in which the transport effects are confined within an inner layer adjacent to the plate. These effects cause a new steady boundary layer. A numerical solution of the full boundary-layer equations is then obtained for the whole transient from $$\overline \tau = 0$$ to the steady state, firstly by means of a step-by-step method and then by a matching technique. The transition between the two distinct solution methods is always observed to occur very near to the turning point of the plate surface temperature, a time at which the fluid temperature is close to its steady state profile. The solution obtained using the step-by-step method shows excellent agreement with the small time analytical solution. Results are presented to illustrate the occurrence of transients from both small and large increases and decreases in the levels of existing energy inputs.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 26 (1988), S. 1645-1664 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Numerical solutions are presented for the problem of steady laminar combined convection flows in vertical parallel plate ducts. Axial diffusion is neglected in the analysis and the resulting governing equations, which are of a parabolic nature, are expressed in an implicit finite difference scheme using a vorticity-stream function formulation and are solved using a marching technique. A constant wall temperature boundary condition is used and investigations are restricted to the case Pr = 0.72. A large range of values of the ratio Gr/Re is considered, -300 ≤ Gr/Re ≤ 70, and comparisons are made with the case of pure forced convection. For large values of the ratio |Gr/Re| reverse flow occurs in the duct. A modification to the standard marching technique is introduced and complete solutions are achieved for these situations for the first time. Results are presented in terms of velocity profiles, Nusselt numbers, friction factors and temperature distributions.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 6 (1973), S. 521-527 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Numerical methods are used to investigate the two-dimensional motion of a viscous incompressible fluid impulsively started past a flat plate of finite breadth at zero incidence to the uniform motion of the fluid at large distances from the plate. A step by step integration in time of Helmholtz's vorticity equation is used for Reynolds numbers 10-500.The magnetohydrodynamic case is also considered with the applied magnetic field at infinity parallel to the uniform stream and the non-conducting plate. Results for the Magnetic Reynolds number 50 and infinite, Viscous Reynolds number 50 and 0≤β≤2, where β is the ratio of the square of the Alfvén speed to the square of the main stream velocity, are presented.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 8 (1974), S. 771-781 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The steady two-dimensional, viscous, electrically conducting flow around a circular cylinder is investigated. The flow and magnetic field are uniform and parallel at large distances from the cylinder. The equations and boundary conditions are derived for arbitrary values of R, Rmand β, where R is the Reynolds number, Rm the magnetic Reynolds number and β, the ratio of the square of the Alfvén speed to the square of the main stream speed. Because of the large number of parameters involved, the numerical solution is restricted to R = 40, Rm = 1 and infinity and 0 ≤ β ≤ 4. Also the cylinder is taken to be a perfect conductor, this avoids having to compute the magnetic field within the cylinder.The numerical computations for the non-magnetic case, i.e. β = 0, are presented and are found to be in good agreement with existing results. The effect of increasing the strength of the magnetic field (i.e. increasing β) on the drag coefficient, the size and position of the standing vortex and the increasing effect of the upstream propagation of disturbances are examined.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 811-817 
    ISSN: 0271-2091
    Schlagwort(e): SIMPLE-like algorithms ; average correction technique ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This note develops an average correction technique for accelerating the rate of convergence of the SIMPLE-like algorithm by implementing the average pressure correction method as proposed by Wen and Ingham (Int. j. numer. methods fluids, 17, 385-400 (1993); 19, 889-903 (1994)) with an average velocity correction. The technique is illustrated by considering the classical problem of fluid flow over a backward-facing step using (i) no average correction, (ii) an average velocity correction, (iii) an average pressure correction and (iv) both average velocity and pressure corrections. When both average velocity and pressure corrections are employed, it is found that the number of iterations required for convergence is almost independent of the initial guessed values of fluid velocity and pressure and the fastest rate of convergence may be achieved.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 19 (1994), S. 889-903 
    ISSN: 0271-2091
    Schlagwort(e): SIMPLE-like algorithm ; Average pressure correction ; Paper filter ; Turbulent flow ; Sampler ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The control volume, finite difference method and the k-∊ tubulence model are employed in a numerical simulation of the turbulent fluid flow both outside and inside a blunt cylindrical sampler which houses a paper filter in its chamber. The presence of a paper filter, which has a very large resistance, results in a large pressure drop across the filter and this causes difficulties in making the SIMPLE or the SIMPLEC scheme converge. In order to improve the rate of convergence of the SIMPLE-like algorithm when the resistance of the filter is very large, an average pressure correction formula is proposed. Based on global mass conservation, a line average pressure correction for the paper filter is derived using a modified Darcy law for a porous medium. A combination of this formula and the SIMPLE-like algorithm can rapidly build up the pressure drop across the filter and hence dramatically improve the rate of convergence of the iterative scheme. Comparisons of the convergence histories and the numerical results for the fluid flow when using SIMPLE and SIMPLEC with the average pressure correction method show that the average pressure correction method for dealing with the paper filter significantly accelerates the rate of convergence of the iterative scheme.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 479-492 
    ISSN: 0029-5981
    Schlagwort(e): boundary element method (BEM) ; singular value decomposition (SVD) ; L-curve method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: This study investigates the numerical solution of the Laplace and biharmonic equations subjected to noisy boundary data. Since both equations are linear, they are numerically discretized using the Boundary Element Method (BEM), which does not use any solution domain discretization, to reduce the problem to solving a system of linear algebraic equations for the unspecified boundary values. It is shown that when noisy, lower-order derivatives are prescribed on the boundary, then a direct approach, e.g. Gaussian elimination, for solving the resulting discretized system of linear equations produces an unstable, i.e. unbounded and highly oscillatory, numerical solution for the unspecified higher-order boundary derivatives data. In order to overcome this difficulty, and produce a stable solution of the resulting system of linear equations, the singular value decomposition approach (SVD), truncated at an optimal level given by the L-curve method, is employed. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 385-400 
    ISSN: 0271-2091
    Schlagwort(e): SIMPLE-LIKE algorithm ; Average pressure correction ; Sampler flows ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A pressure correction formula is proposed for the SIMPLE-like algorithm in order to improve the rate of the convergence when solving laminar Navier-Stokes equations when there is rapidly varying pressure. Based on global mass conservation, a line average pressure correction is derived by integration of the momentum equation for approximate one-dimensional flow. The use of this formula with the SIMPLE-like algorithm can rapidly build up the pressure distribution in the region where the pressure undergoes a very large change, which normally causes the rate of convergence of the SIMPLE or the SIMPLEC schemes to be slow. In order to illustrate the technique, the performances of SIMPLE and of SIMPLEC with the average pressur correction are investigated for axisymmetric flow past and through a sampler. A comparison of these two techniques shows that the average pressure correction proposed in this paper significantly accelerates the rate of convergence.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 577-584 
    ISSN: 0271-2091
    Schlagwort(e): Cascade ; Cavitating flows ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The purpose of this research is to consider the flow through a cascade of bluff bodies, behind which there exist cavities, by using the free streamline theory. When the wake extends to infinity, both the free surface and the velocity on the free surface are unknown and the cavitation number cannot be specified arbitrarily. Given the geometry of the cascade, a numerical method is described in which we obtain the shape of the free surface and the cavitation number. We obtain the relationship between the contraction coefficient, cavitation number and drag coefficient.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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