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  • 1.
    Holmvall, Martin
    et al.
    SCA R&D Ctr, SE-85121 Sundsvall, Sweden.
    Lindström, Stefan
    Royal Inst Technol, Dept Fibre & Polymer Technol, S-10044 Stockholm, Sweden.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Simulation of two-phase flow with moving immersed boundaries2011In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 67, no 12, p. 2062-2080Article in journal (Refereed)
    Abstract [en]

    A two-dimensional model for immiscible binary fluid flow including moving immersed objects is presented. The fluid motion is described by the incompressible Navier-Stokes equation coupled with a phase-field model based on van der Waals’ free energy density and the Cahn-Hilliard equation. The immersed boundary method has been utilised to handle moving immersed objects and the phase-field boundary conditions have been adapted accordingly. Numerical stability and execution time was significantly improved by the use of a new boundary condition which implements minimisation of the free energy in a direct way. Convergence toward the analytical solution was demonstrated for equilibrium contact angle, the Lucas-Washburn theory and Stefan’s problem. The proposed model may be used for two-phase flow problems with moving boundaries of complex geometry, such as the penetration of fluid into a deformable, porous medium.

  • 2.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Drolet, Francois
    FPInnovations-Paprican, 570 boul. St-Jean, Pointe-Claire, Québec, Canada.
    Lindström, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Transfer of a microfluid to a stochastic fibre network2011In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 27, no 7, p. 937-946Article in journal (Refereed)
    Abstract [en]

    The transfer of a microscopic fluid droplet from a flat surface to a deformable stochastic fibre network is investigated. Fibre networks are generated with different levels of surface roughness, and a two-dimensional, two-phase fluid-structure model is used to simulate the fluid transfer. In simulations, the Navier-Stokes equations and the Cahn-Hilliard phase-field equations are coupled to explicitly include contact line dynamics and free surface dynamics. The compressing fibre network is modelled as moving immersed boundaries. The simulations show that the amount of transferred fluid is approximately proportional to the contact area between the fluid and the fibre network. However, areas where the fluid bridges and never actually makes contact with the substrate must be subtracted.

  • 3.
    Kulachenko, Artem
    et al.
    KCL Science and Consulting.
    Lindström, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    FPInnovations.
    Strength of wet fiber networks-Strength scaling2009In: Papermaking Research Symposium 2009, Kuopio: University of Kuopio , 2009, p. 35-Conference paper (Other academic)
  • 4.
    Kulachenko, Artem
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Lindström, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Reinventing mechanics of fibre network2008In: Progress in Paper Physics Seminar, Helsinki: Helsinki University Press, 2008, p. 185-193Conference paper (Other academic)
  • 5.
    Lindström, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Modelling and simulation of paper structure development2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

     

     

     

     

     

    A numerical tool has been developed for particle-level simulations of fibre suspension flows, particularly forming of the fibre network structure of paper sheets in the paper machine. The model considers inert fibres of various equilibrium shapes, and finite stiffness, interacting with each other through normal, frictional, and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre–fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phases is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier–Stokes equations are employed tomodel themotion of the fluid medium.

    The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts well the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of

     

    multiple, straight, rigid fibres in a sheared suspension. Furthermore, model predictions of the shear viscosity and first normal stress difference were in fair agreement with experimental data found in the literature. Since the model is based solely on first principles physics, quantitative predictions could be made without any parameter fitting.

     

    Based on these validations, a series of simulations have been performed to investigate the basic mechanisms responsible for the development of the stress tensor components for monodispersed, non-Brownian fibres suspended in a Newtonian fluid in shear flow. The effects of fibre aspect ratio, concentration, and inter-particle friction, as well as the tendency of fibre agglomeration, were examined in the nonconcentrated regimes. For the case of well dispersed suspensions, semi-empirical relationships were found between the aforementioned fibre suspension properties, and the steady state apparent shear viscosity, and the first/second normal stress differences.

     

    Finally, simulations have been conducted for the development of paper structures in the forming section of the paper machine. The conditions used for the simulations were retrieved from pilot-scale forming trial data in the literature, and from real pulp fibre analyses. Dewatering was simulated by moving two forming fabrics toward each other through a fibre suspension. Effects of the jet-to-wire speed difference on the fibre orientation anisotropy, the mass density distribution, and three-dimensionality of the fibre network, were investigated. Simulation results showed that the model captures well the essential features of the forming effects on these paper structure parameters, and also posed newquestions on the conventional wisdom of the forming mechanics.

     

     

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  • 6.
    Lindström, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Paper structure modelling with particle-level process simulation2006In: Progress in Paper Physics Seminar, Miami, Ohio, 2006, p. 86-87Conference paper (Other scientific)
  • 7.
    Lindström, Stefan B.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Simulations of the Dynamics of Fibre Suspension Flows2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A new model for simulating non-Brownian flexible fibres suspended in a Newtonian fluid has been developed. Special attention has been given to include realistic flow conditions found in the industrial papermaking process in the key features of the model; it is the intention of the author to employ the model in simulations of the forming section of the paper machine in future studies.

    The model considers inert fibres of various shapes and finite stiffness, interacting with each other through normal, frictional and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre-fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phase is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier-Stokes equations are employed to model the motion of the fluid medium.

    The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple straight, rigid fibres in a sheared suspension. Model predictions of the viscosity and first normal stress difference were in good agreement with experimental data found in the literature. Since the model is based solely on first-principles physics, quantitative predictions could be made without any parameter fitting.

    Download full text (pdf)
    FULLTEXT01
  • 8.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Kulachenko, Artem
    KCL Science and Consulting.
    Uesaka, Tetsu
    FPInnovations.
    New insights in paper forming from particle-level process simulations2009In: Papermaking Research Symposium 2009, Kuopio, Finland: University of Kuopio , 2009, p. 38-Conference paper (Other academic)
    Abstract [en]

    By virtue of the recent developments in simulation techniques for fibre suspensions flows, it is now possible to directly simulate forming of the paper sheet at a particle level under realistic flow conditions. This opens up a window of opportunity to better understand the microscale development of the paper structure, and to attribute particular features of the structure to different drainage elements.The simulations are based on a particle-level fibre suspension model, in which fibres are represented by chains of cylindrical fibre segments. The fibre model includes curled shapes and the torsion and bending of the fibres. It also captures the two-way interactions between the fibres and the fluid phase. The fluid motion is integrated from the Navier--Stokes equations.To illustrate the usage of the simulation tool, a sample parametric study of the effects of different fibre furnishes on the paper structure and wet strength is presented. Such an investigation could almost as easily have been performed with experiments. Simulations, however, have some advantages: First, the cost is almost nothing as compared to pilot trials. Secondly, the parameters of the simulations can be controlled one at a time, whereas in pilot trials, changing one process parameter will affect the others. Thirdly, every detail of the evolving paper structure is accessible at every instant in the simulations. That is, the forming process needs no longer be considered a "black box". Simulations also have some drawbacks. For instance, it is not possible to include the smallest particles, due to their vast number, while maintaining sufficiently large flow geometry. Therefore, simulations must target paper grades of low fines contents.In this communication, the pros and cons of particle-level simulations are discussed, and put into the context of previous forming and dewatering models in the literature. The development of the paper microstructure predicted in the simulations shows that thickening is the dominant forming mechanism, while filtration only occurs in the most dilute end of the typical range of consistencies used in the industry. This predicted behaviour is compared with the conventional view of dewatering, which holds filtration as the dominant forming mechanism.

     

  • 9.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A model for flexible fibres in viscous and inert fluid2007In: 61st Appita annual conference and exhibition, Gold Coast, Australia, 6-9 May 2007, 2007 International paper physics conference, 6pp [Carlton, Australia: Appita, 2007, 2007, p. 23-28Conference paper (Other scientific)
    Abstract [en]

    A model is proposed for simulating the motion of flexible fibres in fluid flow. Care has been taken to include typical papermaking conditions into the validity range of the model. Fibres are modelled as chains of fibre segments, whose motion is governed by Newton's second law. The fluid motion is calculated from the three-dimensional incompressible Navier-Stokes equations. By enforcing momentum conservation, the two-way coupling between the solids and fluid phase is taken into account. Fibre-fibre interactions as well as self-interactions include normal, frictional and lubrication forces. Furthermore, the model considers nonlaminar fibre-fluid interactions and particle inertia. Simulation results were compared with experimental data found in the literature. The model predicts very well the orbit period of rigid fibre motion in shear flow. Quantitative predictions were made for the amount of bending of flexible fibres in shear flow. It was also possible to reproduce the different regimes of motion of flexible fibres in shear flow, ranging from rigid motion to coiled motion and self-entanglement.

  • 10.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    A numerical investigation of the rheology of sheared fiber suspensions2009In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 21, no 8, p. 083301-Article in journal (Refereed)
    Abstract [en]

    Particle-level simulations are performed to study the rheology of monodispersed non-Brownian fibers suspended in a Newtonian fluid in shear flow. The effects of fiber aspect ratio, concentration, and interparticle friction on the stress tensor of the suspension in the steady state and on the tendency of fiber agglomeration are investigated. Semiempirical expressions for the steady state apparent shear viscosity and the steady state first and second normal stress difference were obtained for the case of well dispersed suspensions in the nonconcentrated regimes. The simulation predictions of the specific viscosity were in fair agreement with previous experimental investigations.

  • 11.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Effects of interparticle friction on the rheology of fibre suspensions2008In: 5th European Congress on Computational Methods in Applied Sciences and Engineering: TS318, Computational Materials Mechanics V, 2008Conference paper (Refereed)
  • 12.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Particle-level simulation of forming of the fiber network in papermaking2008In: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 46, no 9, p. 858-876Article in journal (Refereed)
    Abstract [en]

    A model for particle-level simulation of fiber suspensions has been used to simulate paper sheet forming on a roll-blade former. The fibers were modeled as chains of fiber segment, flowing and interacting with the medium and with each other. The incompressible three-dimensional Navier-Stokes equations were used to describe the fluid motion. Real pulps were analyzed to provide raw material data for the simulations. Dewatering was simulated by moving two model forming fabrics toward each other through a fiber suspension. Close examination of the dewatering process revealed that no large concentration gradients develop through the thickness of the pulp suspension. In this sense, twin-wire dewatering does not resemble a filtration process. The effects of the jet-to-wire speed difference on the network structure of the paper were investigated. The structural features of interest were fiber orientation anisotropy, mass density distribution and three-dimensionality of the fiber network. It was demonstrated that these simulated structural features were in qualitative agreement with experimental data found in the literature.

  • 13.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Simulation of paper structure development in a roll-blade former2008In: Progress in Paper Physics Seminar, Espoo: Helsinki University Press, 2008, p. 139-141Conference paper (Other academic)
  • 14.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Simulation of semidilute suspensions of non-Brownian fibres in shear flow2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 2, p. 024901-Article in journal (Refereed)
    Abstract [en]

    Particle-level simulations are performed to study semidilute suspensions of monodispersed non-Brownian fibers in shear flow, with a Newtonian fluid medium. The incompressible three-dimensional Navier-Stokes equations are used to describe the motion of the medium, while fibers are modeled as chains of fiber segments, interacting with the fluid through viscous drag forces. The two-way coupling between the solids and the fluid phase is taken into account by enforcing momentum conservation. The model includes long-range and short-range hydrodynamic fiber-fiber interactions, as well as mechanical interactions. The simulations rendered the time-dependent fiber orientation distribution, whose time average was found to agree with experimental data in the literature. The viscosity and first normal stress difference was calculated from the orientation distribution using the slender body theory of Batchelor [J. Fluid Mech. 46, 813--829 (1971)], with corrections for the finite fiber aspect ratios. The viscosity was also obtained from direct computation of the shear stresses of the suspension for comparison. These two types of predictions compared well in the semidilute regime. At higher concentrations, however, a discrepancy was seen, most likely due to mechanical interactions, which are only accounted for in the direct computation method. The simulated viscosity determined directly from shear stresses was in good agreement with experimental data found in the literature. The first normal stress difference was found to be proportional to the square of the volume concentration of fibers in the semidilute regime. As concentrations approached the concentrated regime, the first normal stress difference became proportional to volume concentration.

  • 15.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Simulation of the motion of flexible fibres in viscous fluid flow2007In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 11, article id 113307Article in journal (Refereed)
    Abstract [en]

    A model for flexible fibers in viscous fluid flow is proposed, and its predictions compared with experiments found in the literature. The incompressible three-dimensional Navier-Stokes equations are employed to describe the fluid motion, while fibers are modeled as chains of fiber segments, interacting with the fluid through viscous and dynamic drag forces. Fiber segments, from the same or from different fibers, interact with each other through normal, frictional and lubrication forces. Momentum conservation is enforced on the system to capture the two-way coupling between phases. Quantitative predictions could be made, and showed good agreement with experimental data, for the period time of Jeffery orbits in shear flow, as well as for the amount of bending of flexible fibers in shear flow. Simulations, using the proposed model, also successfully reproduced the different regimes of motion for threadlike particles, ranging from rigid fiber motion to complicated orbiting behavior, including coiling and self-entanglement.

  • 16.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Stochastic Modelling of Paper Structure. Effects of Forming Section2005In: Proceedings, 5th Biennal Johan Gullichsen Colloquium, Helsinki, 17. Nov. 2005, Helsinki: The Finnish Paper Engineers' Association , 2005, p. 25-35Conference paper (Other scientific)
    Abstract [en]

    A new model for particle-level simulation of forming was developed. A set of process parameters and a statistical description of the stock were provided as inputs to the model and a three-dimensional model paper was produced. This allowed the analyses of the relations between process parameters and structural properties of the formed sheet. Numerical experiments were set up to study the effects of the yarns of the forming fabric on the surface distributions of fillers and fines and to investigate the fibre orientation anisotropy and specific formation as functions of the jet-to-wire speed ratio.

  • 17.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Suspensions of flexible fibres in flows of decaying turbulence2006In: Euromech, Sundsvall: Department of Natural Sciences, Mid Sweden University , 2006Conference paper (Refereed)
  • 18.
    Lindström, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Hirn, Ulrich
    Graz University of Technology.
    Evolution of the paper structure along the length of a twin-wire former2009In: ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3 / [ed] IAnson, SJ, Bury, UK: Pulp Paper Fund. Res. Soc. , 2009, p. 207-245Conference paper (Refereed)
    Abstract [en]

    A particle-level numerical model is used to simulate forming with a twin-wire former configuration. The development of the paper structure along the length of the former is observed to explain the effects ofthe dewatering elements on the paper structure at different jet-to-wire speed ratios, consistencies, and target basis weights. The simulations indicate that most of the structure development takes place in the initial part of forming (forming roll) and, in some instances, at the drop to atmospheric pressure after the forming roll. Dramatic effects onthe through-thickness fibre orientation anisotropy are observed when the consistency is varied by changing the jet thickness, while changes in basis weight had less impact. The through-thickness concentration gradient was almost uniform throughout the forming process, except in the lower range of typical papermaking consistencies. This indicates that the dewatering mechanism is normally thickening, rather than filtration.

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