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Roland Keunings - One of the best experts on this subject based on the ideXlab platform.

  • Flows in Polymers, Reinforced Polymers and Composites - Flows in Polymers, Reinforced Polymers and Composites
    SpringerBriefs in Applied Sciences and Technology, 2015
    Co-Authors: Christophe Binetruy, Francisco Chinesta, Roland Keunings
    Abstract:

    This book gives a detailed and practical introduction to complex flows of polymers and reinforced polymers as well as the flow of simple fluids in complex microstructures. Over the last decades, an increasing number of functional and structural parts, made so far with metals, has been progressively reengineered by replacing metallic materials by polymers, reinforced polymers and composites. The motivation for this substitution may be the weight reduction, the simpler, cheaper or faster forming process, or the ability to exploit additional functionalities. The present Brief surveys modern developments related to the multi-scale modeling and simulation of polymers, reinforced polymers, that involve a flowing microstructure and continuous fiber-reinforced composites, wherein the fluid flows inside a nearly stationary multi-scale microstructure. These developments concern both multi-scale modeling, defining bridges between the micro and macro scales - with special emphasis on the mesoscopic scale at which kinetic theory descriptions apply and advanced simulation techniques able to address efficiently the ever more complex and detailed models defined at different scales. This book is addressed to students (Master and doctoral levels), researchers and professionals interested in Computational Rheology and material forming processes involving polymers, reinforced polymers and composites. It provides a unique coverage of the state of the art in these multi-disciplinary fields

  • an overview of the proper generalized decomposition with applications in Computational Rheology
    Journal of Non-newtonian Fluid Mechanics, 2011
    Co-Authors: Francisco Chinesta, Amine Ammar, Adrien Leygue, Roland Keunings
    Abstract:

    We review the foundations and applications of the proper generalized decomposition (PGD), a powerful model reduction technique that computes a priori by means of successive enrichment a separated representation of the unknown field. The Computational complexity of the PGD scales linearly with the dimension of the space wherein the model is defined, which is in marked contrast with the exponential scaling of standard grid-based methods. First introduced in the context of Computational Rheology by Ammar et al. [3] and [4], the PGD has since been further developed and applied in a variety of applications ranging from the solution of the Schrodinger equation of quantum mechanics to the analysis of laminate composites. In this paper, we illustrate the use of the PGD in four problem categories related to Computational Rheology: (i) the direct solution of the Fokker-Planck equation for complex fluids in configuration spaces of high dimension, (ii) the development of very efficient non-incremental algorithms for transient problems, (iii) the fully three-dimensional solution of problems defined in degenerate plate or shell-like domains often encountered in polymer processing or composites manufacturing, and finally (iv) the solution of multidimensional parametric models obtained by introducing various sources of problem variability as additional coordinates.

  • ADVANCES IN THE COMPUTER MODELING OF THE FLOW OF POLYMERIC LIQUIDS 1
    2001
    Co-Authors: Roland Keunings, Batiment Euler
    Abstract:

    We review recent developments in the field of Computational Rheology applied to the prediction of the flow of polymeric liquids in complex geometries. After a brief discussion of the challenging rheological behaviour of polymers, we outline the hierarchy of available modeling approaches and point to important recent progress there. The two current avenues towards complex flow simulation are then visited, namely the macroscopic and micro-macro approaches. Throughout the paper, we refer to review and research publications that are representative of current trends in the field.

  • A SURVEY OF Computational Rheology
    2000
    Co-Authors: Roland Keunings
    Abstract:

    A survey is presented of the field of Computational Rheology applied to the analysis of viscoelastic effects in complex flows of polymeric fluids. First, I outline the modelling approaches adopted currently in numerical simulations and discuss the role of Computational Rheology within the general study of structured liquids. Developments in the macroscopic and micro-macro simulation strategies are then reviewed. Finally, I stress important unsolved problems and offer suggestions for future work.

  • Parallel finite element algorithms applied to Computational Rheology
    Computers & Chemical Engineering, 1995
    Co-Authors: Roland Keunings
    Abstract:

    We review the work of our research group over the last 4 years towards the development of efficient parallel finite element algorithms. Target applications are physical problems described by means of non-linear sets of partial differential or integro-differential equations of mixed type, and solved in complex geometries using unstructured finite element meshes. A typical example considered in this paper is the flow of viscoelastic fluids. The complexity of the governing equations is such that it prevents the use of established parallel numerical algorithms developed for elliptic problems. After a brief discussion of viscoelastic governing equations and related sequential numerical techniques, we describe a generic parallel approach to the assembly and solution of finite element equation sets. Automatic load balancing schemes and mesh partitioning methods are discussed. Finally, the proposed algorithms are evaluated in the simulation of viscoelastic Rows described by integral and differential constitutive equations. Results are reported for various distributed memory MIMD parallel computers, including the INTEL IPSC/860 hypercube, the CONVEX Meta Series, and a heterogeneous network of engineering workstations

João M. Nóbrega - One of the best experts on this subject based on the ideXlab platform.

K. Walters - One of the best experts on this subject based on the ideXlab platform.

  • The distinctive CFD challenges of Computational Rheology
    International Journal for Numerical Methods in Fluids, 2003
    Co-Authors: K. Walters, M.f. Webster
    Abstract:

    In this general lecture, we shall first outline the way Computational non-Newtonian fluid mechanics differs from conventional Computational fluid dynamics (CFD). We do this by briefly outlining the major historical developments in this relatively new field of science, which is conveniently called Computational Rheology. To illustrate essential features, we limit the discussion to the Oldroyd B, UCM and Phan-Thien/Tanner constitutive models. In order to provide a serious challenge to existing numerical codes, we describe some recent unpublished experimental results on flow through a contraction of constant viscosity (Boger) and also shear-thinning elastic liquids. Both planar and axisymmetric contractions are of interest, and pressure drops and observed flow structures provide the relevant points of contact between experiment and numerical prediction. Numerical codes developed at UWS involving a hybrid finite-element/finite-volume scheme for Oldroyd B and Phan-Thien/Tanner constitutive models are applied to the contraction-flow problems

  • Experimental dilemmas in non-Newtonian fluid mechanics and their theoretical resolution
    Korea-australia Rheology Journal, 2000
    Co-Authors: David V. Boger, K. Walters
    Abstract:

    There is no doubt that non-Newtonian Fluid Mechanics has made significant strides in recent years and there is a growing belief that the many provocative experimental phenomena and dilemmas now have a realistic possibility of being explained theoretically. We intend to illustrate this optimism by appealing to three important benchmark problems in non-Newtonian Fluid Mechanics, namely contraction flows, settling and die swell. Fig. 1 illustrates the process for the solution of viscoelastic fluid mechanics problems. In contrast to Newtonian fluid mechanics, non-Newtonian fluid mechanics has had to be concerned with the development of general constitutive equations for viscoelastic fluids. These constitutive equations should in principle lead to the definition of flow properties that need to be measured to define the viscoelastic fluid (rheometry) and to the development of the equivalent Navier Stokes equations for the solution of all possible boundary value problems. The process is completed by solution of the appropriate equations, where the methods of Computational fluid mechanics have been required; analytical methods for complex flows of viscoelastic fluids are generally not useful. The full story, illustrated in Fig. 1, then involves these various strands of activity and it will be necessary to consider at least four of them in some detail. For example, we shall need to be quite specific about the experimental conditions pertaining to the relevant phenomena. The flows are invariably complex and the ‘experimental dilemmas clearly refer to complex flows, where the flow domain often involves abrupt changes in geometry, and where the flow strength is high enough to permit a terminology which majors on ‘high Weissenburg numbers’ and ‘high Deborah numbers’. This is of course reasonable obvious, but it nevertheless needs to be stated. So we want to address the question: “How do elastic liquids behave in complex flows?” and it is immediately apparent that the answer must involve a consideration of how the same liquids behave in simple flows, so that obtaining rheometrical data on the test liquids is an essential part of the exercise. Such data, when available, serve more than one useful purpose; they certainly provide a foundation set of data, which must be accommodated in the associated mathematical model for the test liquids. That is to say, the constitutive equation, which is an essential ingredient in any theoretical resolution of the experimental dilemmas, has to be consistent with the rheometrical data. Indeed, if the model cannot simulate behaviour in simple flows, what chance does it have in complex flows?! Clearly, the choice of constitutive equation is central to the whole operation and this choice is far from trivial or obvious. Indeed, a constitutive model which satisfies the dual constraints of tractability and quantitative (or even semi quantitative) prediction may not exist! But that shouldn’t and doesn’t prevent a search for this missing link’; but it is wise to be aware of the possibility of disappointment. As is illustrated in Fig. 1, the constitutive model has to be solved in conjunction with the stress equations of motion and the equation of continuity, to predict and explain the experimental phenomena and dilemmas. Analytic solutions are out of the question so far as complex flows are concerned and Computational Rheology is now an established, if fairly recent science, which seeks theoretical answers to provocative experiments and phenomena. Computational Fluid Dynamics (CFD) has been an essential *Corresponding author: d. boger@chemeng.unimeb.edu.au 2000 by The Korean Society of Rheology Fig. 1. The procedure for the solution of a Non-Newtonian Fluid Mechanics problem.

  • Computational Rheology: a new science
    Endeavour, 1993
    Co-Authors: Marcel Crochet, K. Walters
    Abstract:

    In recent years research on the mechanics of nonNewtonian fluids, hitherto very intractable, has made remarkable progress. This is due not only to experimental and theoretical advances but to the availability of greatly improved computing resources. The results have far-reaching industrial applications, especially in extrusion processes.

Alexandre M. Afonso - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study on micro-scale extensional viscoelastic flows
    Journal of Non-Newtonian Fluid Mechanics, 2020
    Co-Authors: Rafael A. Figueiredo, Alexandre M. Afonso, Cassio M. Oishi, Manuel A. Alves
    Abstract:

    Abstract The capillary thinning dynamics can be considered one of the fingerprints of extensionally-dominated viscoelastic flows. Notably, the rheological behavior of complex fluids in extensional flow has been investigated in different rheometric devices, as for instance in the Capillary Breakup Extensional Rheometer (CaBER), the Dripping-onto-Substrate (DoS) rheometry, or the Rayleigh Ohnesorge Jetting Extensional Rheometer (ROJER). In recent years, the Computational Rheology community has made a considerable effort to better understand the interplay of viscoelasticity and capillarity effects in such transient rheometric experiments. In this work, we present a numerical study on the dynamics of extensional flows of dilute polymeric solutions at small scales. Our numerical investigation focus primarily on the potential of using small scale two-phase extensional viscoelastic flows as suitable platforms for performing rheometry of weakly viscoelastic polymer solutions. In particular, we have adopted the setup used in the experiments of Sousa et al. [Rheol. Acta 56 (2017) 11–20]. In such set up, the filament stretching is conducted using oil as an outer phase, avoiding sample evaporation, or allowing visualization of the filament interior. In order to handle with the moving interface problem, we have employed a two-phase viscoelastic fluid flow solver, based on a finite differences scheme. In this methodology, the interface between the fluids is approximated by the volume-of-fluid interface reconstruction algorithm, and a second-order operator-split method is used to solve the advection equation. We observed a negligible influence of the use of different types of low viscosity oils as outer fluid on the measurement of the sample relaxation time. We also found that the use of an external low viscosity immiscible oil did not prevent the formation of beads-on-a-string structures.

  • A numerical study of the Kernel-conformation transformation for transient viscoelastic fluid flows
    Journal of Computational Physics, 2015
    Co-Authors: Fernando P. Martins, Alexandre M. Afonso, Cassio M. Oishi, Manuel A. Alves
    Abstract:

    This work presents a numerical application of a generic conformation tensor transformation for simulating highly elastic flows of non-Newtonian fluids typically observed in Computational Rheology. In the Kernel-conformation framework 14, the conformation tensor constitutive law for a viscoelastic fluid is transformed introducing a generic tensor transformation function. The numerical stability of the application of the Kernel-conformation for highly elastic flows is ultimately related with the specific kernel function used in the matrix transformation, but also to the existence of singularities introduced either by flow geometry or by the characteristics of the constitutive equation. In this work, we implement this methodology in a free-surface Marker-And-Cell discretization methodology implemented in a finite differences method. The main contributions of this work are two fold: on one hand, we demonstrate the accuracy of this Kernel-conformation formulation using a finite differences method and free surfaces; on the other hand, we assess the numerical efficiency of specific kernel functions at high-Weissenberg number flows. The numerical study considers different viscoelastic fluid flow problems, including the Poiseuille flow in a channel, the lid-driven cavity flow and the die-swell free surface flow. The numerical results demonstrate the adequacy of this methodology for high Weissenberg number flows using the Oldroyd-B model. We analyze a generic conformation tensor transformation for simulating the HWNP.The numerical scheme is constructed in the context of finite differences.The numerical study considers transient benchmarks in Computational Rheology.Complex flows are solved, including the die-swell free surface problem.

  • The Finite Volume Method in Computational Rheology
    Finite Volume Method - Powerful Means of Engineering Design, 2012
    Co-Authors: Alexandre M. Afonso, Monica Oliveira, Paulo J. Oliveira, Manuel A. Alves, Fernando T. Pinho
    Abstract:

    The finite volume method (FVM) is widely used in traditional Computational fluid dynamics (CFD), and many commercial CFD codes are based on this technique which is typically less demanding in Computational resources than finite element methods (FEM). However, for historical reasons, a large number of Computational Rheology codes are based on FEM. There is no clear reason why the FVM should not be as successful as finite element based techniques in Computational Rheology and its applications, such as polymer processing or, more recently, microfluidic systems using complex fluids. This chapter describes the major advances on this topic since its inception in the early 1990’s, and is organized as follows. In the next section, a review of the major contributions to Computational Rheology using finite volume techniques is carried out, followed by a detailed explanation of the methodology developed by the authors. This section includes recent developments and methodologies related to the description of the viscoelastic constitutive equations used to alleviate the high-Weissenberg number problem, such as the log-conformation formulation and the recent kernel-conformation technique. At the end, results of numerical calculations are presented for the well-known benchmark flow in a 4:1 planar contraction to ascertain the quality of the predictions by this method.

  • Further developments on theoretical and Computational Rheology
    2010
    Co-Authors: Alexandre M. Afonso
    Abstract:

    Tese financiada pela FCT - Fundacao para a Ciencia e a Tecnologia, Ciencia.Inovacao2010, POPH, Uniao Europeia FEDER

Johannes M. Soulages - One of the best experts on this subject based on the ideXlab platform.

  • Coupled models for polymer synthesis and Rheology to determine branching architectures and predict flow properties
    Rheologica Acta, 2019
    Co-Authors: Chinmay Das, Daniel J. Read, Johannes M. Soulages
    Abstract:

    Advance in Computational Rheology allows for in silico predictions of the viscoelastic responses of arbitrarily branched polymer melts. While detailed branching structure is required for the Rheology predictions, Rheology itself is often the most sensitive tool to detect low levels of branching. With rheological experiments and Computational modeling of a set of nominally linear and model comb ethylene-butene copolymers, we show that coupled models for the synthesis and Rheology can integrate diverse measurements, incorporating inherent experimental uncertainties. This approach allows us to achieve tight bounds on the branching structures of the constituent molecules. Next, we numerically explore the effects of the numbers and molar masses of side arms in comb polymers on the viscoelastic responses in both the linear and nonlinear regimes. Such Computational exploration can aid in designing specific polymers suitable for a given processing scenario. Graphical abstract Coupled models for synthesis and Rheology allow tight bounds on branching architecture and parametric exploration of flow properties of statistically branched polymers.

  • Coupled models for polymer synthesis and Rheology to determine branching architectures and predict flow properties
    Rheologica Acta, 2019
    Co-Authors: Chinmay Das, Daniel Read, Johannes M. Soulages
    Abstract:

    Advance in Computational Rheology allows for in silico predictions of the viscoelastic responses of arbitrarily branched polymer melts. While detailed branching structure is required for the Rheology predictions, Rheology itself is often the most sensitive tool to detect low levels of branching. With rheological experiments and Computational modeling of a set of nominally linear and model comb ethylene-butene copolymers, we show that coupled models for the synthesis and Rheology can integrate diverse measurements, incorporating inherent experimental uncertainties. This approach allows us to achieve tight bounds on the branching structures of the constituent molecules. Next, we numerically explore the effects of the numbers and molar masses of side arms in comb polymers on the viscoelastic responses in both the linear and nonlinear regimes. Such Computational exploration can aid in designing specific polymers suitable for a given processing scenario.

  • Modeling of Synthesis and Flow Properties of Propylene–Diene Copolymers
    Macromolecules, 2014
    Co-Authors: Chinmay Das, Daniel Read, Johannes M. Soulages, Pradeep P. Shirodkar
    Abstract:

    Copolymerization with nonconjugated dienes offers an attractive route for introducing long-chain branching in polypropylene. From a simplified set of rate equations for such copolymerization with a metallocene catalyst, we derive the probabilities of branch formation at different stages of the reaction in a semibatch reactor. Using these probabilities, we generate an ensemble of molecules via a Monte Carlo sampling. The knowledge of the branching topology and segment lengths allows us to compute the flow properties of the resins from Computational Rheology. We compare our model predictions with existing experimental data, namely the molar mass distribution and small amplitude oscillatory shear response, for a set of resins with varying diene content. The Rheology data suggest that the entanglement time τe depends sensitively and in a well-defined fashion on the diene content.