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  • 1
    Electronic Resource
    Electronic Resource
    The simultaneous use of 4×4 and 2×2 bilinear stress elements for viscoelastic flows (1993)
    Springer
    Computational mechanics 11 (1993), S. 341-354 
    Details
    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 Mixed finite elements for viscoelastic flows based on a 4×4 sub-linear interpolation for the extra stress components satisfy the Babuska-Brezzi condition and are highly stable. They have been proved to be quite satisfactory in solving problems with strong stress boundary layers. In this work, we examine the simultaneous use of 4×4 and 2×2 bilinear stress elements in an attempt to reduce the computational cost without sacrificing the accuracy. The 4×4 bilinear elements are employed in regions where the stress field is anticipated to be steep while the 2×2 elements carry the burden elsewhere with a much smaller number of stress nodes. Additional constraints along the sides shared by different elements are necessary in order to preserve conformity. The method is applied to the creeping flow of a Maxwell fluid around a sphere falling along the axis of a cylindrical tube. Results are given for three mixed finite element formulations: the Galerkin method, the consistent streamline-upwind/Petrov-Galerkin method (SUPG) and the non-consistent streamline-upwind method (SU). Particular emphasis is given on the calculated drag correction factors. The effect of the sphere/cylinder diameter ratio is also examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350092
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  • 2
    Electronic Resource
    Electronic Resource
    Predictions of Structure Breakdown, Buildup and Shear Banding in Semisolid Suspensions (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 141-143 (July 2008), p. 313-318 
    Details
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: When SSM material is subjected to a sudden transient the rate of buildup (aging) isnegligible compared to the rate of breakdown (shear rejuvenation). While this is generally true, dueto prolonged processing or the geometry the local shear rate in some regions may become equal orlower than the critical value, where aging becomes as important as shear rejuvenation. In this workwe simulate in detail shear rejuvenation and aging in semisolid slurries. Using a standardthixotropic model used widely for modeling SSM suspensions but a novel computational methodwe reveal and confirm numerically for the first time shear banding. The phenomenon is found to betime dependent where the material first yields fully and then, after a certain time the yielded frontretreats to form two distinct bands -one yielded and one unyielded. This phenomenon must beaccounted for in the evaluation of the material constants since the time scale of the process issimilar to the time scale of the phenomenon
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/24/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.141-143.313.pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Parameter Estimation for Semi-Solid Aluminum Alloys Using Transient Experiments (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 116-117 (Oct. 2006), p. 429-432 
    Details
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: A rotating vane-cup rheometer is used to determine the rheological properties of semi-solid slurries,and a procedure is established for characterizing the rheology with emphasis given to the proper andself-consistent evaluation of the material constants
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/22/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.116-117.429.pdf
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  • 4
    Electronic Resource
    Electronic Resource
    Ontogeny of the shi drum Umbrina cirrosa (Linnaeus 1758), a candidate new species for aquaculture (2005)
    Oxford, UK : Blackwell Science Ltd
    Aquaculture research 36 (2005), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The ontogeny of shi drum Umbrina cirrosa (Linnaeus 1758), a candidate new species for aquaculture, was studied throughout the entire larval phase. Geometric morphometric analysis revealed two clear inflection points (7.0 and 12.7 mm total length, TL) in the shape ontogeny of this species, separating the studied period into three phases of different allometric priorities. Spline graphs demonstrated that the major non-uniform shape ontogeny correlated with the development of the fins, the anterior dorsal area of the body, the caudal peduncle, the eye and the mouth. Concerning the morphological features, shi drum larvae are characterized by an upward anterior bending of the notochord. The ontogeny of the fins began with the formation of the pectoral buds (2.9 mm TL), continued with the notochord flexion (4.3 mm TL, associated with the caudal fin development), the appearance of the pelvic buds, the first anal rays (4.5 mm TL) and the first dorsal rays (4.8 mm TL). Shi drum juveniles presented 25 vertebrae and the following dominant fin types: D XI,23, AII,6, VI,5, P17 and C17.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.2005.01314.x
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  • 5
    Electronic Resource
    Electronic Resource
    On the stability of the shear flow of a viscoelastic fluid with slip along the fixed wall (1996)
    Springer
    Rheologica acta 35 (1996), S. 39-47 
    Details
    ISSN: 1435-1528
    Keywords: Shear flow ; Oldroyd-B model ; slip ; linear stability analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this paper we solve the time-dependent shear flow of an Oldroyd-B fluid with slip along the fixed wall. We use a non-linear slip model relating the shear stress to the velocity at the wall and exhibiting a maximum and a minimum. We assume that the material parameters in the slip equation are such that multiple steady-state solutions do not exist. The stability of the steady-state solutions is investigated by means of a one-dimensional linear stability analysis and by numerical calculations. The instability regimes are always within or coincide with the negative-slope regime of the slip equation. As expected, the numerical results show that the instability regimes are much broader than those predicted by the linear stability analysis. Under our assumptions for the slip equation, the Newtonian solutions are stable everywhere. The interval of instability grows as one moves from the Newtonian to the upper-convected Maxwell model. Perturbing an unstable steady-state solution leads to periodic solutions. The amplitude and the period of the oscillations increase with elasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366551
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  • 6
    Electronic Resource
    Electronic Resource
    Extrusion of a compressible Newtonian fluid with periodic inflow and slip at the wall (1996)
    Springer
    Rheologica acta 35 (1996), S. 531-544 
    Details
    ISSN: 1435-1528
    Keywords: Extrudate swell ; compressible Newtonian flow ; slip ; time-dependent flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract We explore a mechanism of extrusion instability, based on the combination of nonlinear slip and compressibility. We consider the time-dependent compressible Newtonian extrudate swell problem with slip at the wall. Steady-state solutions are unstable in regimes where the shear stress is a decreasing function of the velocity at the wall. Compressibility provides the means for the alternate storage and release of elastic energy, and, consequently, gives rise to periodic solutions. The added novelty in the present work is the assumption of periodic volumetric flow rate at the inlet of the die. This leads to more involved periodic responses and to free surface oscillations similar to those observed experimentally with the stick-slip instability. To numerically simulate the flow, we use finite elements in space and a fully-implicit scheme in time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396505
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  • 7
    Electronic Resource
    Electronic Resource
    A singular finite element for Stokes flow: The stick-slip problem (1989)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 9 (1989), S. 1353-1367 
    Details
    ISSN: 0271-2091
    Keywords: Singular finite elements ; Stokes flow ; Stress singularity ; 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: Abrupt changes in boundary conditions in viscous flow problems give rise to stress singularities. Ordinary finite element methods account effectively for the global solution but perform poorly near the singularity. In this paper we develop singular finite elements, similar in principle to the crack tip elements used in fracture mechanics, to improve the solution accuracy in the vicinity of the singular point and to speed up the rate of convergence. These special elements surround the singular point, and the corresponding field shape functions embody the form of the singularity. Because the pressure is singular, there is no pressure node at the singular point. The method performs well when applied to the stick-slip problem and gives more accurate results than those from refined ordinary finite element meshes.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650091105
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  • 8
    Electronic Resource
    Electronic Resource
    Singular finite elements for the sudden-expansion and the die-swell problems (1990)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 357-372 
    Details
    ISSN: 0271-2091
    Keywords: Singular finite elements ; Die swell ; Sudden expansion ; 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 singular finite element method is used to solve the sudden-expansion and the die-swell problems in order to improve the accuracy of the solution in the vicinity of the singularity and to speed up the convergence. The method requires minor modifications to standard finite element schemes, and even coarse meshes give more accurate results than refined ordinary finite element meshes. Improved normal stress results for the sudden-expansion problem have been obtained for various Reynolds numbers up to 100 using the singular elements constructed for the creeping flow problem. In addition, the normal stresses at the walls appear to be insensitive to the singularity powers used in the construction of the singular basis functions. The die-swell problem is solved using the singular elements constructed for the stick-slip problem. The singular elements accelerate the convergence of the free surface dramatically.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650100402
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  • 9
    Electronic Resource
    Electronic Resource
    The integrated singular basis function method for the stick-slip and the die-swell problems (1991)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 1251-1265 
    Details
    ISSN: 0271-2091
    Keywords: Singular basis functions ; Finite elements ; Stick-slip problem ; Die-swell problem ; 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: We further develop a new singular finite element method, the integrated singular basis function method (ISBFM), for the solution of Newtonian flow problems with stress singularities. The ISBFM is based on the direct subtraction of the leading local solution terms from the governing equations and boundary conditions of the original problem, followed by a double integration by parts applied to those integrals with singular contributions. The method is applied to the stick-slip and the die-swell problems and improves the accuracy of the numerical results in both cases. In the case of the die-swell problem it considerably accelerates the convergence of the free surface profile with mesh refinement. The advantages and disadvantages of the ISBFM when compared to other singular methods are also discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650131005
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  • 10
    Electronic Resource
    Electronic Resource
    A singular function boundary integral method for the Laplace equation (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 127-134 
    Details
    ISSN: 1069-8299
    Keywords: Laplace equation ; singularities ; boundary integral method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The authors present a new singular function boundary integral method for the numerical solution of problems with singularities which is based on approximation of the solution by the leading terms of the local asymptotic expansion. The essential boundary conditions are weakly enforced by means of appropriate Lagrange multipliers. The method is applied to a benchmark Laplace-equation problem, the Motz problem, giving extremely accurate estimates for the leading singular coefficients. The method converges exponentially with the number of singular functions and requires a low computational cost. Comparisons are made to the analytical solution and other numerical methods.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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