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  • 1
    Electronic Resource
    Electronic Resource
    Finite rise time step strain modeling of nearly monodisperse polymer melts and solutions (1991)
    Springer
    Rheologica acta 30 (1991), S. 430-446 
    Details
    ISSN: 1435-1528
    Keywords: Step shear ; monodisperse polymers ; Stress relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The step shear strain experiment is one of the fundamental transient tests used to characterize the rheology of viscoelastic polymer melts and solutions. Many melts and solutions exhibit homogeneous deformation and stress relaxation; in these cases the transient dynamics can be modeled by completely ignoring momentum effects and imposing singular kinematics. Recently, however, it has been observed that there are certain classes of nearly monodisperse melts and solutions that exhibit anomalous nonhomogeneous deformation and stress relaxation (Morrison and Larson (1990), Larson, Khan, and Raju (1988), Vrentas and Graessley (1982), and Osaki and Kurata (1980)). We demonstrate that, for these classes, a finite rise time must be incorporated, some source of inhomogeneity must be present, and a small amount of added Newtonian viscosity is necessary. We examine five nonlinear and quasilinear models; the Johnson-Segalman, Phan Thien Tanner, Giesekus, White-Metzner, and Larson models. We determine which mathematical features of the models are necessary and/or sufficient to describe the observed experimental behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396529
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Cancellation of errors in the Higashitani-Pritchard treatment of hole pressures generated by viscoelastic liquids in creeping flow past a transverse slot (1990)
    Springer
    Rheologica acta 29 (1990), S. 310-322 
    Details
    ISSN: 1435-1528
    Keywords: Hole pressure ; error cancellation ; non-Newtonian fluid, HPBL equations ; modified hole pressure relation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Analytical studies of the hole pressure for non-Newtonian creeping flow past a transverse slot are pursued with particular interest in the formulation of Higashitani and Pritchard (HP). To correct the flaws in the treatment of HP's original work, a modified hole-pressure relation (MHPR) is employed. Some important mathematical properties of the MHPR are presented. By studying the MHPR in streamline coordinate formulation, we find a fortuitouserror cancellation phenomenon in the derivation of the HP formula: namely, the error caused by one key flaw is fortuitously cancelled out by the error introduced through another key flaw. For second-order fluids and Tanner's “viscometric model” (under certain assumptions) the cancellation of errors is proved to be exact. It is this cancellation of errors that provides a theoretical explanation for the paradox between an apparently flawed derivation and the fortunate success of the HP prediction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01339886
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The hole-pressure effect and viscometry (1992)
    Springer
    Rheologica acta 31 (1992), S. 521-534 
    Details
    ISSN: 1435-1528
    Keywords: Viscometry ; hole pressures ; theology ; Newtonian fluid ; non-Newtonian fluid ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract This paper provides an assessment of our current understanding of the hole-pressure effect and the role it plays in the field of viscometry. The discovery in 1968 by Broadbent, Kaye, Lodge and Vale that the use of pressure taps to measure the normal stress exerted on a boundary by a non-Newtonian material can lead to significant errors has opened up interesting new avenues for making viscometric measurements. The kinematical theory developed by Higashitani and Pritchard (1972) to estimate the hole pressure, to which a deeper understanding has recently been supplied by Yao and Malkus (1990), has formed the basis of many new developments in viscometry. It is interesting that such a simplistic theory for the hole pressure apparently has a rather wide range of applicability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00367007
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Boundary node correction and superconvergence in the FEM (1990)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 713-721 
    Details
    ISSN: 0271-2091
    Keywords: Boundary node correction ; Pressure smoothing ; Finite element method ; Superconvergence ; Posterior error analysis ; Multiple mesh extrapolation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Convergence improvement and superconvergence behaviour, obtained by the simple boundary node correction (BNC) procedure for certain stress-like variables of smoothed FEM solutions, are reported in this paper. The effectiveness of BNC is shown through three examples of steady flow problems, and a posterior error analysis based on the multiple-mesh extrapolation technique has been used for estimating the convergence rates.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650100608
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  • 5
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    Calculation of sensitivity derivatives in thermal problems by finite differences (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The optimum design of a structure subject to temperature constraints is considered. When mathematical optimization techniques are used, derivatives of the temperature constraints with respect to the design variables are usually required. In the case of large aerospace structures, such as the Space Shuttle, the computation of these derivatives can become prohibitively expensive. Analytical methods and a finite difference approach have been considered in studies conducted to improve the efficiency of the calculation of the derivatives. The present investigation explores two possibilities for enhancing the effectiveness of the finite difference approach. One procedure involves the simultaneous solution of temperatures and derivatives. The second procedure makes use of the optimum selection of the magnitude of the perturbations of the design variables to achieve maximum accuracy.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering; 17; Dec. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Application of the Hughes-LIU algorithm to the 2-dimensional heat equation (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An implicit explicit algorithm for the solution of transient problems in structural dynamics is described. The method involved dividing the finite elements into implicit and explicit groups while automatically satisfying the conditions. This algorithm is applied to the solution of the linear, transient, two dimensional heat equation subject to an initial condition derived from the soluton of a steady state problem over an L-shaped region made up of a good conductor and an insulating material. Using the IIT/PRIME computer with virtual memory, a FORTRAN computer program code was developed to make accuracy, stability, and cost comparisons among the fully explicit Euler, the Hughes-Liu, and the fully implicit Crank-Nicholson algorithms. The Hughes-Liu claim that the explicit group governs the stability of the entire region while maintaining the unconditional stability of the implicit group is illustrated.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-3599 , NAS 1.26:3599
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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