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  • 1
    Electronic Resource
    Electronic Resource
    Elongational viscosity by fiber spinning (1990)
    Springer
    Rheologica acta 29 (1990), S. 385-389 
    Details
    ISSN: 1435-1528
    Keywords: Fiber-spinning ; elongationalviscosity ; integral model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Isothermal melt, fiber-spinning was recently analyzed by means of a nonlinear, integral, constitutive equation that incorporates shear history effects, spectrum of relaxation times, shear-thinning, and extension thinning or thickening when either the drawing force or the draw ratio is specified. The predictions agreed with experimental data on spinning of polystyrene, low-density polyethylene, and polypropylene melts. The predicted apparent elongational viscosity along the threadline (which, as shown in this work, must be identical to that measured experimentally by fiber spinning type of elongational rheometers) is compared with the true elongational viscosity predicted by the same constitutive equation under well-defined experimental conditions of constant extension rate, independent of any strain history. It is concluded that the apparent elongational viscosity, as measured by fiber-spinning, approaches the true elongational viscosity at low Weissenberg numbers (defined as the product of the liquid's relaxation time multiplied by the extension rate). At moderate Weissenberg numbers, the two viscosities may differ by an order of magnitude and their difference grows even larger at high Weissenberg numbers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01376788
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  • 2
    Electronic Resource
    Electronic Resource
    Fiber spinning of viscoelastic liquid (1987)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 33 (1987), S. 834-842 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fiber spinning process of viscoelastic liquid is successfully analyzed by means of a nonlinear integral constitutive equation, finite-element discretization, and Newton iteration. The process is cast and studied both as an initial value problem, which requires the specification of the drawing force, and as a two-point boundary value problem, which requires the specification of the draw ratio. Solutions are obtained up to high elasticity, high draw ratio, and large drawing force. The results agree with the analytic asymptotic solution for Newtonian liquid, with existing numerical solutions in the limiting case of the upper-convected Maxwell liquid, and with available experimental data on spinning of polystyrene melt at 170°C and low-density polyethylene at 150°C.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690330516
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  • 3
    Electronic Resource
    Electronic Resource
    Stability of multilayer extrusion of viscoelastic liquids (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 710-724 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A linear stability analysis of multilayer plane Poiseuille flow of Oldroyd-B liquids with shear rate dependent viscosities is performed for an arbitary number of layers. Asymptotic solutions at long wavelengths and numerical solutions at wavelengths of O(1) are obtained for two-dimensional infinitesimal disturbances. The asymptotic solutions are identical for viscoelastic and Newtonian liquids in two- and three-layer flows, except for nearly geometrically symmetric configurations in three-layer flows. Multilayer flows of viscoelastic liquids can be stable at all wavelengths; thus, operating diagrams of stable flows can be constructed. Symmetric and nearly symmetric configurations in three-layer flows are unstable when the core layer is more viscous than the cuter layers. For highly elastic liquids, stability is not influenced by elasticity, whereas shear thinning always destabilizes the flow. The analysis provides guidelines to avoid interfacial instabilities, which originate inside dies of multilayer extrusion.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690360508
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  • 4
    Electronic Resource
    Electronic Resource
    Laminar Newtonian jets at high Reynolds number and high surface tension (1988)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 1559-1562 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690340918
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  • 5
    Electronic Resource
    Electronic Resource
    Three-dimensional streamlined finite elements: Design of extrusion dies (1992)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 13-24 
    Details
    ISSN: 0271-2091
    Keywords: Streamlined finite elements ; Extrusion ; Free surface flows ; Die design ; Three-dimensional flows ; Three-dimensional finite elements ; 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: A method to determine three-dimensional die shapes from extrudate swell and vice versa is presented using a three-dimensional Galerkin finite element method based on a streamlined formulation with the fluid velocities and pressures represented by triquadratic and trilinear basis functions respectively. The three-dimensional streamlined method, an extension of the two-dimensional formulation, uses successive streamsurfaces to form a boundary-conforming co-ordinate system. This produces a fixd, computational domain leaving the spatial location of the elements as unknowns to be determined with the standard primary variables (u, v, w, p). The extrudate produced by a die of a given shape is considered for moderate Reynolds numbers. Finally, the method is extended to address the problem of die design, where a die profile is sought to produce a target extrudate shape.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650140103
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  • 6
    Electronic Resource
    Electronic Resource
    A new outflow boundary condition (1992)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 587-608 
    Details
    ISSN: 0271-2091
    Keywords: Open boundary conditions ; Backward-facing step ; Unbounded flow ; Free boundary condition ; 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: Boundary conditions come from Nature. Therefore these conditions exist at natural boundaries. Often, owing to limitations in computing power and means, large domains are truncated and confined between artificial synthetic boundaries. Then the required boundary conditions there cannot be provided naturally and there is a need to fabricate them by intuition, experience, asymptotic behaviour and numerical experimentation. In this work several kinds of outflow boundary conditions, including essential, natural and free boundar conditions, are evaluated for two flow and heat transfer model problems. A new outflow boundary condition, called hereafter the free boundary condition, is introduced and tested. This free boundary condition is equivalent to extending the validity of the weak form of the governing equations to the synthetic outflow instead of replacing them there with unknown essential or natural boundary conditions. In the limit of zero Reynolds number the free boundary condition minimizes the energy functional among all possible choices of outflow boundary conditions. A review of results from applications of the same boundary conditions to several other flow situations is also presented and discussed.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650140506
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  • 7
    Electronic Resource
    Electronic Resource
    An inverse finite element method with an application to extrusion with solidification (1989)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 9 (1989), S. 541-555 
    Details
    ISSN: 0271-2091
    Keywords: Inverse finite elements ; Solidification ; Extrusion ; Metal casting ; 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: The flow and solidification of planar jets are analysed by means of an efficient inverse isotherm finite element method. The method is based on a tessellation that is constructed by isotherms as characteristic co-ordinate lines transverse to the flow direction. Thus opposite sides of finite elements lie on isotherms. The method allows the simultaneous determination of the location of the isotherms with the primary unknowns, namely, the velocity, the pressure, the temperature and the location of the free surface. Thus the determination of the location of the solidification front (which is known to pose significant computational difficulties) is automatic. This facilitates the control of the location of the solidification front by controlling macroscopic variables such as the flow rate, the cooling rate and the capillary design. The location of the solidification may then be suitably chosen to influence the frozen-in orientation and structure in extrusion of high-performance materials such as composites and polymers, in continuous casting of metals and in growth of crystals.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650090505
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of high-speed continuous casting with inverse finite elements (1991)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 1207-1223 
    Details
    ISSN: 0271-2091
    Keywords: Inverse finite elements ; Metal casting ; Extrusion ; Solidification front ; 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: A recently proposed inverse isotherm finite element method is further extended in order to account for processes with distorted isotherms. With this method a variety of problems can be solved which require the explicit calculation of characteristic material lines along with the common field of unknowns in transport phenomena. The method is applied to high-speed metal casting, where the location and shape of the extensive solidification front is calculated simultaneously with the primary unknowns, the velocity and the pressure, whereas the temperature is fixed at the moving nodes of the finite element tessellation. This is achieved by solving the energy equation inversely along with the rest of the conservation equations, i.e. the temperature field is fixed and its location is calculated. Empirical correlations may be derived which give the shape of the solidification front as a function of the process parameters. This may be used to improve the control means of metal casting, which is currently based on one-dimensional approximate analyses.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650131002
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  • 9
    Electronic Resource
    Electronic Resource
    Film casting of viscoelastic liquid (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 67-75 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Melt film-casting is analyzed by means of a nonlinear integral constitutive equation that incorporates shear history effects, spectrum of relaxation times, shear thinning, and extension thinning or thickening. Film temperature and thickness profiles are predicted. The effects of shear-thinning, relaxation time, and die-design on the final film thickness are evaluated. Temperature variations are investigated by means of the pseudo-time concept. The process dependence on the rheological characteristics of the viscoelastic fluid, the die-design through the history effects, the conditions at the take-up end, and the film temperature is discussed. Predicted film and temperature profiles of casting of polypropylene are compared with experimental data taken from the literature.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760310203
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  • 10
    Electronic Resource
    Electronic Resource
    Compound matrix method for eigenvalue problems in multiple connected domains (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Communications in Applied Numerical Methods 8 (1992), S. 811-818 
    Details
    ISSN: 0748-8025
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An algorithm based on a compound matrix method is presented for solving difficult eigenvalue problems of n equation sets in connected domains that are coupled through (n - 1) sets of interfacial boundary conditions, when n is an arbitrary number. As an example, a linear stability problem of n-layer plane Poiseuille flow is formulated. The resulting Orr-Sommerfeld equations form a set of stiff differential equations at high wavenumbers, which are solved accurately for various combinations of parameters.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1630081104
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