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  • 1
    Electronic Resource
    Electronic Resource
    Three-dimensional studies on bicomponent extrusion (1990)
    Springer
    Rheologica acta 29 (1990), S. 71-87 
    Details
    ISSN: 1435-1528
    Keywords: Bicomponentextrusion ; free surfaceflows ; finite element method ; three-dimensional (3-D)-flows ; dieextrusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The present work is concerned with the mathematical modelling and numerical simulation of three-dimensional (3-D) bicomponent extrusion. The objective is to provide an understanding of the flow phenomena involved and to investigate their impact on the free surface shape and interface configuration of the extruded article. A finite element algorithm for the 3-D numerical simulation of bicomponent stratified free surface flows is described. The presence of multiple free surfaces (layer interface and external free surfaces) requires special free surface update schemes. The pressure and viscous stress discontinuity due to viscosity mismatch at the interface between the two stratified components is handled with both a double node (u−v−w−P 1 −P 2 −h 1 −h 2) formulation and a penalty function (u−v−w−P−h 1 −h 2) formulation. The experimentally observed tendency of the less viscous layer to encapsulate the more viscous layer in stratified bicomponent flows of side-by-side configuration is established with the aid of a fully 3-D analysis in agreement with experimental evidence. The direction and degree of encapsulation depend directly on the viscosity ratio of the two melts. For shear thinning melts exhibiting a viscosity crossover point, it is demonstrated that interface curvature reversal may occur if the shearing level is such that the crossover point is exceeded. Extrudate bending and distortion of the bicomponent system because of the viscosity mismatch is shown. For flows in a sheath-core configuration it is shown that the viscosity ratio may have a severe effect on the swelling ratio of the bicomponent system. Modelling of the die section showed that the boundary condition imposed at the fluid/fluid/wall contact point is critical to the accuracy of the overall solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01331802
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  • 2
    Electronic Resource
    Electronic Resource
    Three-dimensional non-isothermal extrusion flows (1989)
    Springer
    Rheologica acta 28 (1989), S. 121-133 
    Details
    ISSN: 1435-1528
    Keywords: Three dimensional flows ; die extrusion ; finite element method ; free surface flows ; non-isothermal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A three-dimensional (3-D) non-isothermal study of viscous free-surface flows with exponential dependence of viscosity on temperature is presented. The effects of non-isothermal conditions and/or geometry on the extrudate shape are investigated with a fully three-dimensional finite element/Galerkin formulation. Apart from the well known thermally induced extrudate swelling phenomenon, bending and distortion of the extrudate may occur because of temperature differences and/or geometric asymmetries. A temperature difference across the die can be imposed by heating or cooling the die walls, but can also arise because of asymmetric viscous heat generation due to the die geometry. Temperature differences affect velocity profiles because of the temperature dependence of viscosity and lead to extrudate bending, an effect known as “kneeing” in the fiber spinning industry. It is also shown numerically and confirmed experimentally that the die geometry induces extrudate bending even in the case of isothermal Newtonian flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01356973
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Spinal canal restoration by posterior distraction or anterior decompression in thoracolumbar spinal fractures and its influence on neurological outcome (1994)
    Springer
    European spine journal 3 (1994), S. 318-324 
    Details
    ISSN: 1432-0932
    Keywords: Thoracolumbar fractures ; Harrington rods ; Zielke device
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Thirty consecutive patients who had suffered unstable fractures and dislocations of the thoracolumbar spine mostly associated with neurologic impairment and bony encroachment on the spinal canal were treated either with Harrington distraction rods combined with sublaminar wires or with the Zielke-VDS device. These patients were subsequently assessed for neurologic outcome, spinal canal clearance, sagittal and coronal spinal deformity correction preoperatively and postoperatively with a minimum follow-up of 26 months. In the follow-up evaluation, the patients who underwent surgery with Harrington rods showed an overall improvement of their neurologic function of 90.9%, whereas all patients who underwent the Zielke operation improved. Preoperatively, positive correlations were found between the level of injury and Frankel grades; the cord lesion tended to demonstrate more severe neurologic deficit when compared with cauda equina ones (P 〈 0.001). Furthermore, dislocation accompanying the injury resulted in a more severe neurological deficit (P 〈 0.05). Harrington rods and Zielke device offer sufficient initial correction of the frontal spinal deformity but did not significantly either restore or maintain sagittal plane alignment. The Harrington series showed an overallimprovement of the segmental kyphosis of 26% (NS), with a subsequent loss of correction of 7.38% (NS) on the follow-up observation. The Zielke device produced an immediate, much better correction of the segmental posttraumatic kyphosis of 45% (NS), but a loss of correction of 22.9% (NS) was measured in the follow-up evaluation. Correction of the anterior and posterior vertebral height was shown to be better for the Zielke patient group. The coronal deformity was completely corrected equally well by the Harrington and Zielke devices. There was no statistically significant correlation between the degree of bony encroachment of the spinal canal and the initial Frankel grade. Additionally, no statistically significant correlation was found between correction of the sagittal deformity, restoration of anterior and posterior vertebral height, coronal deformity correction, and clearance of the vertebral canal. Concerning neurological status, no patient in either group was worse in the follow-up evaluation. A significant correlation was found between the age of the patient and the neurological improvement favoring young patients (P 〈 0.001).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02200144
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  • 4
    Electronic Resource
    Electronic Resource
    Three-dimensional extrudate swell of creeping Newtonian jets (1988)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 2088-2094 
    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: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690341222
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  • 5
    Electronic Resource
    Electronic Resource
    A finite element convergence study for shear-thinning flow problems (1988)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 8 (1988), S. 123-138 
    Details
    ISSN: 0271-2091
    Keywords: Finite elements ; Shear-thinning flow ; Convergence study ; Newton-Raphson ; Picard Dominant eigenvalue ; Broyden ; 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 solution of the non-linear set of equations arising from the application of the finite element method to non-Newtonian fluid flow problems often requires large amounts of computer time. Four iteration schemes (Picard, Newton-Raphson, Broyden and Dominant Eigenvalue method) are compared in three different flow geometries using a shear-thinning fluid model. Points of comparison involve the computer time necessary to converge the equations, ease of implementation, radius of convergence and rate of convergence.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650080202
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  • 6
    Electronic Resource
    Electronic Resource
    Interface determination in bicomponent extrusion (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 982-988 
    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: The unidirectional flow of two immiscible fluids with different viscosities in a long die of arbitrary shape is considered. Mathematically, the problem has a continuum of solutions corresponding to arbitrarily prescribed interface shapes, but experimental evidence indicates the existence of a unique interface shape with the less viscous fluid encapsulating the more viscous fluid. With the introduction of the minimum viscous dissipation principle, which postulates that the amount of viscous dissipation is minimized for a given flow rate, the problem becomes a nonlinearly constrained optimization problem. A generalized reduced gradient/finite element method combination is used to predict the interface shape when two inelastic fluids are considered. The effect of the viscosity ratio and flow-rate ratio on the interface shape is examined for different die geometries. Inner layer breakup phenomena are predicted and explained for complex die geometries.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760281507
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    Paper (German National Licenses)
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