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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 29 (1990), S. 281-297 
    ISSN: 1435-1528
    Keywords: Separability ; irreversibility ; KBKZ model ; reversing step strains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The hypotheses of separability and irreversibility, which have greatly improved the accuracy of constitutive models of the KBKZ type are tested in reversing step shear and elongational deformations. A reversing double-step deformation is a severe test for constitutive models and a new rheometer has been developed to perform this type of deformation, both in shear and elongation, in a single machine. Test results of a commercial low-density polyethylene melt are reported here with model predictions. In particular, the performance of the KBKZ-type integral model and a differential analogue is considered. Wagner's idea of irreversibility and the KBKZ-equivalent ideas of Larson are tested with these data. While these versions show a moderate agreement with experiment, the irreversible integral model gives an accurate fit and emerges clearly as the best description of polymer melts in these flows.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 30 (1991), S. 341-356 
    ISSN: 1435-1528
    Keywords: Three-dimensional finite elements ; free surface flows ; three-dimensional die extrusions ; extrudate swell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The present paper considers the problem of predicting extrudate shapes from asymmetrical dies for Newtonian fluids. The flow is fully three-dimensional and an exploration of finite elements is made with a view to finding accurate, stable and economical schemes. A number of elements are compared and we conclude that some of the Fortin elements are most useful on the grounds of computational overhead and solution accuracy. These are used to investigate some symmetrical (square dies) and asymmetrical (unequal lip) planar and general L-shaped die flows. Finally, we show that in an unconstrained extrudate the final shape must be such that particles describe a helix in space; special cases include circular flow and rectilinear flow.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 31 (1992), S. 44-54 
    ISSN: 1435-1528
    Keywords: Rigid polyvinyl chloride (PVC) ; constitutive equations ; recoil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Polyvinyl chloride (PVC) is widely used in industry, but it is difficult to find any extensive discussion of theological relations that describe it. The present paper discusses the behaviour of rigid PVC in extensional deformations at various temperatures. In the tests, a step elongation was applied at an initial time, then after a delay the specimen was cut, permitting recoil. Both linear and nonlinear strain regimes were studied; the linear relaxation properties (relaxation function, storage modulus) were cross-checked with eccentric-disk measurements. In the non-linear strain regime a single-integral constitutive equation of the KBKZ Wagner type was used. Separability of time and strain effects was demonstrated in our tests and so a “damping function” could be found which was only a function of strain. Video recordings of recoil were made, and detailed predictions of the strain-time behaviour were checked against experiments. Various constitutive equation proposals were used in the comparison, and the separated kernel integral irreversible model performed reasonably well; some other models of a differential type, and a Doi-Edwards model were not as accurate.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 13 (1994), S. 443-457 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We discuss a finite volume method for computing solutions of steady incompressible viscoelastic fluid flows. A fourth-order Runge-Kutta method is used in the explicit time-stepping scheme. The computations are carried out mainly on unstructured grids on Newtonian, inelastic and differential-type constitutive equations, which include the Oldroyd-B and the upper-convected Maxwell models. The performance of the scheme on unstructured grids is investigated, with particular reference to the stick-slip problem for the modified upper-convected Maxwell fluid. The results are compared with those obtained by using the finite element method whenever possible.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 8 (1991), S. 409-422 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper, we extend the explicitly elliptic momentum equation (EEME) formulation to a class of constitutive equations of the Maxwell type without the Newtonian solvent viscosity and apply it to a simplified Phan-Thien-Tanner (PTT) model. In the coupled finite element approach, the Galerkin method is applied to the modified momentum equations and the continuity equation, while the streamline upwind Petrov/Galerkin method is applied to the constitutive equations. The program is used to study the flow past a sphere placed at the centreline in a cylindrical tube using unstructured meshes. Our numerical results for the Maxwell model agree excellently with previous results from Lunsmann et al. (1989) up to a Weissenberg number of 2. New results for the PTT model are presented up to a Weissenberg number of about 4.5. It is found that the flow exhibits shear thinning behaviour in the drag force versus the Weissenberg number. The drag behaviour is remarkably similar to the viscosity flow curve.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We present an element residual method for obtaining an a posteriori error estimate of a finite element method and an adaptive h-refinement procedure for flows of the modified upper-convected Maxwell (MUCM) fluid with a solvent viscosity. The element residual method is applied to the Poiseuille flow to assess the accuracy of the error estimate. The adaptive h-refinement procedure based on the error estimate is applied to the flow past a cylindrical tube in a duct.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 30 (1991), S. 499-510 
    ISSN: 1435-1528
    Keywords: Sphere ; viscoelastic flow ; numerical analysis ; inertia ; shear-thinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Numerical solutions are presented for the flow past a sphere placed at the centreline of a cylindrical tube for Reynolds numbers ranging from 0 to 150, using a boundary element method. Fluids are modelled by a variety of constitutive equations including the Newtonian, the Carreau and the Phan-Thien-Tanner models. The influence of inertia, shear-thinning and fluid elasticity on the flow field, drag and the pressure drop force-drag ratio is examined. Some results are compared with available experimental data.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 32 (1993), S. 526-531 
    ISSN: 1435-1528
    Keywords: Extrudate swell ; compressibility ; viscoelasticity ; computation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract There are few computations of polymer forming processes which include compressibility. Here we estimate the effect of compressibility in Newtonian and PTT fluids on extrudate swell and stick-flip flow. Changes of the order of a few per cent occur in swelling, which is in accord with expectations.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 1805-1823 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An algorithm for generating unstructured tetrahedral meshes by the advancing front technique is presented. Emphasis is placed on the construction of tetrahedral elements. Several measures are employed to prevent difficult situations. A control line/surface scheme is used to specify element size. Numerical examples are provided to show the performance of the algorithm.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 1990-07-01
    Print ISSN: 0148-6055
    Electronic ISSN: 1520-8516
    Topics: Physics
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