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  • 1
    Electronic Resource
    Electronic Resource
    A theory to describe heat transfer during laminar incompressible flow of a fluid in periodic porous media (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 1738-1748 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, a theory is formulated that describes the heat transfer during the laminar flow of an incompressible fluid within a rigid periodic porous medium. To describe the macroscopic temperature distribution in porous media, the volume average concept is employed to derive the volume averaged energy equation. Previous researchers have used either the one-equation model with the local thermal equilibrium assumption between the various phases or the complex two-equation model to deal with the average temperatures of the solid phase and the fluid phase. Both types of models are derived and applied in a stationary observation frame. In this paper, we propose a generalized one-equation model by relaxing the local thermal equilibrium assumption between the phases and invoking the frame invariant principle. The three new terms arise due to the microscopic transient, convective, and conductive effects. By taking advantage of the objectivity of the generalized model, it is shown that the microscopic temperature distribution in a periodic unit cell results in a periodic heat flux boundary condition. The direct temperature solution is obtained in the periodic unit cell by solving the generalized volume averaged energy equation. A modified effective thermal conductivity tensor is calculated which encompasses the micro-convective effects encountered in porous media. An analytic study of a non-isothermal flow through two parallel thick plates is performed to explore the role of each new term in the generalized model. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870039
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  • 2
    Electronic Resource
    Electronic Resource
    Non-Linear response of a long, discontinuous fiber/melt system in elongational flows (1996)
    Springer
    Rheologica acta 35 (1996), S. 347-355 
    Details
    ISSN: 1435-1528
    Keywords: Elongation ; long discontinuous fiber filler ; forming, non-linear response ; PEKK
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The authors investigated the transient elongational behavior of a highly-aligned 600% volume fraction long, discontinuous fiber filled poly-ether-ketone-ketone melt with a computer-controlled extensional rheometer at 370°C. Prior experiments at controlled strain rate and stress produced τE + (t, $$\dot \varepsilon$$ ) and $$\dot \varepsilon$$ − (t, τE) similar to a shear dominated flow of a non-linear viscoelastic fluid. Stress relaxation following steady extension showed nonlinear effects in the change in stress decay rate with increasing strain rate. Continuous relaxation spectra showed a shift in the spectral peak to smaller values of λ with increasing strain rate. The Giesekus nonlinear constitutive relation modeled the elongation and stress relaxation with shearing rate at the fiber surface set by a strain rate magnification factor. Suitable for elongation, the model produced insufficient shift in the stress relaxation spectrum to account for the large change in stress decay rate exhibited in the experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403535
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical and analytical study to estimate the effect of two length scales upon the permeability of a fibrous porous medium (1995)
    Springer
    Transport in porous media 21 (1995), S. 1-17 
    Details
    ISSN: 1573-1634
    Keywords: Resin transfer molding ; permeability ; fibrous porous medium ; porous cylinders ; creeping flow ; length scales
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A fibrous porous medium with two length scales is modeled as a bed of porous cylinders aligned perpendicular to the flow of viscous fluid. The flow behavior is described using Stokes and Darcy flow equations in the regions around (higher length scale) and within the cylinders (lower length scale) respectively. The typical ratio of higher and lower length-scale regions enable us to invoke lubrication approximation and simplify the equations to develop a closed form solution for the overall permeability of this dual-scale porous medium. A parametric analysis is performed to explore the dependence of permeability on factors such as the volumetric ratio of higher and lower length-scale regions, permeability and size of inclusions in the smaller length-scale region. The analytical model is compared with the numerical results and the trend is compared with the experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00615332
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of orientation clustering in short-fiber composites (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 2651-2672 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: During flow of concentrated fiber suspensions, the proximity of the fibers induces interactions in their orientation space. These fiber-fiber interactions may lead to clustering in orientation of fibers and a nonhomogeneous fiber orientation field. An orientation cluster is a group of fibers in a specific neighborhood sharing the same orientation state. It is important to characterize clustering to understand and quantify fiber-fiber interactions. Such characterization will also be useful in the prediction of the mechanical and physical properties of the resulting composite material. An image of the fiber distribution at a location in a composite is divided into a number of partitions, and the variance of the fiber orientation states within the partitions, between the partitions and of the entire sample are compared to establish the existence and the extent of clustering in the orientation space. Statistical methods such as analysis of variances and techniques analogous to the scale of segregation used in mixing theory are modified and adopted to identify and quantify orientation clusters. Simulated examples that describe clustering quantitatively in magnitude and direction of planar orientations are presented. This method is then extended to identify clustering in model injection molding experiments performed in a center-gated square mold with suspensions of 1% and 10% volume fractions.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090281312
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  • 5
    Electronic Resource
    Electronic Resource
    Second-order boundary element method calculations of hydrodynamic interactions between particles in close proximity (1992)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 1063-1086 
    Details
    ISSN: 0271-2091
    Keywords: Boundary element method ; Local mesh refinement ; Convergence ; Small interparticle gap ; Adaptive subdomain integration ; Superparametric ; 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 second-order boundary element technique was developed to simulate the 3D hydrodynamic interactions between multiple particles of arbitrary shape. This paper reports the results of an extensive validation procedure aimed at demonstrating the convergence characteristics of the technique, especially in cases where the particles are in close proximity. The quadratic elements are superior to the lower-order elements in terms of accuracy, computer storage and CPU time required, thus resulting in a significant improvement in the overall computational efficiency. Superparametric discretization improves the accuracy over isoparametric discretization but lowers the convergence rate of the method. When the interparticle gap becomes very small (less than 1% of the particle radius), the numerical solution diverges owing to inaccurate determination of the element contributions in the gap region. An adaptive subdomain integration scheme was developed that dramatically improved the integration accuracy and provided convergent solutions for problems of very small gaps down to 0-01% of the particle diameter.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650140905
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  • 6
    Electronic Resource
    Electronic Resource
    Permeability characterization. Part 1: A proposed standard reference fabric for permeability (1995)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 16 (1995), S. 429-445 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A three-dimensionally woven fabric is proposed as a standard reference material for permeability characterization. The 3-D woven fabric requires care in cutting and handling, although it is more robust than 2-D woven or braided fabrics. If prepared carefully, the permeability of the 3-D woven fabric can be measured reproducibly within 15% in either radial flow or saturated 1-D flow geometries. The material was characterized for permeability in radial, unsaturated and saturated 1-D, and through-thickness flow geometries. The transient results demonstrated the importance of structural heterogeneity on the unsaturated flow behavior, and agree qualitatively with a simplistic model of flow in heterogeneous unsaturated porous media. The effects of heterogeneity were manifested in the proposed SRM by an increasing trend in the “unsaturated permeability.” Experiments were also conducted with a random mat that displayed transient flows dominated by wicking. The effects of wicking on the macroscopic flow behavior were manifested by transients in the “unsaturated permeability” in which a decreasing trend was observed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750160602
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  • 7
    Electronic Resource
    Electronic Resource
    Process modelling for manufacture of orthopedic implants from short fiber composites (1994)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 15 (1994), S. 7-17 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In the case of total hip joint replacement, it has been shown that matching of femur and implant stiffness would positively decrease the chances of resorption of bone and clinical failure of the procedure. Short fiber composites (SFC) which are biocompatible can offer high strength with stiffness comparable to that of natural bone and hence are an excellent candidate to replace metal alloys used in orthopedic implants. In this work a computational process simulation is presented to investigate the possibility of making an artifical hip implant which is most biocompatible. This simulation computes three dimensional flow induced fiber orientation in manufacturing of an SFC hip implant, estimates its mechanical properties, and predicts its “in vivo” response. This is done using a model 3-D geometry representing implanted femur. The potential use of such an approach is demostrated by comparing principal stresses at the interface of the bone and the implant for metallic and SFC implant which is manufactured using a variety of by proper selection of material and process variables one can potentially create implants which are most biocompatible.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750150103
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  • 8
    Electronic Resource
    Electronic Resource
    Permeability characterization. Part 2: Flow behavior in multiple-layer preforms (1995)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 16 (1995), S. 446-458 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Within the resin transfer molding (RTM) process, flow is generally characterized by the progression of a distinct, nonuniform flow front into the preform as a function of time. The flow front progression introduces unsaturated characteristics into RTM flow fields. As a result, the definition of an effective in-plane permeability (Keff) is used to determine the permeability of actual preforms as they fill with fluid. This Keff expression expands upon the original definition of Darcy's law by generalizing its applicability to unsaturated creeping flows. Results of experimentally obtained Keff for flow in single-layer preforms have been detailed for two common RTM materials, a random mat and a 3-D weave, in Part 1. In this paper (Part 2), we characterize the unsaturated and saturated permeabilities of multiple-layer preforms constructed from the random mat and 3-D weave materials characterized in Part 1. This work identifies the apparent permeability characteristics of a specific unsaturated multiple-layer flow that demonstrates behavior inherent to this important class of heterogeneous flows. Also, parallels are drawn between the unsaturated permeability behavior of complex 3-D weave materials and multiple-layer preforms.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750160603
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of periodic 3D viscous flows using a quadratic discrete Galerkin boundary element method (1994)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 18 (1994), S. 953-981 
    Details
    ISSN: 0271-2091
    Keywords: Galerkin boundary element method ; Unit-cell approach ; Traction discontinuities ; Suspension rheology ; High fibre aspect ratio ; flow through a porous medium ; 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 discrete Galerkin boundary element technique with a quadratic approximatión of the variables was developed to simulate the three-dimensional (3D) viscous flow established in periodic assemblages of particles in suspensions and within a periodic porous medium. The Batchelor's unit-cell approach is used. The Galerkin formulation effectively handles the discontinuity in the traction arising in flow boundaries with edges or corners, such as the unit cell in this case. For an ellipsoidal dilute suspension over the range of aspect ratio studied (1 to 54), the numerical solutions of the rotational velocity of the particles and the viscosity correction were found to agree with the analytic values within 0.2% and 2% respectively, even with coarse meshes. In a suspension of cylindrical particles the calculated period of rotation agreed with the experimental data. However, Burgers' predictions for the correction to the suspension viscosity were found to be 30% too low and therefore the concept of the equivalent ellipsoidal ratio is judged to be inadequate. For pressure-driven flow through a fixed bed of fibres, the prediction on the permeability was shown to deviate by as much as 10% from the value calculated based on approximate permeability additivity rules using the corresponding values for planar flow past a periodic array of parallel cylinders. These applications show the versatility of the technique for studying viscous flows in complicated 3D geometries.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650181005
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  • 10
    Electronic Resource
    Electronic Resource
    A numerical simulation of short fiber orientation in compression molding (1990)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 164-173 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A computer simulation has been developed to predict the orientation of fibers in a thin, flat part that is compression molded from sheet molding compound. The simulation combines a finite element/control volume simulation of the mold filling flow, a second order tensor representation of the fiber orientation state and a finite element calculation for the transient orientation problem. Sample results and comparison with experiments are presented. Predictions compare favorably with experiments on SMC (sheet molding compound) plaques and a model suspension of nylon fibers and silicon oil.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750110305
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