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Lindström, Stefan
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Publications (10 of 18) Show all publications
Holmvall, M., Lindström, S. & Uesaka, T. (2011). Simulation of two-phase flow with moving immersed boundaries. International Journal for Numerical Methods in Fluids, 67(12), 2062-2080
Open this publication in new window or tab >>Simulation of two-phase flow with moving immersed boundaries
2011 (English)In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 67, no 12, p. 2062-2080Article in journal (Refereed) Published
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.

Keywords
fluid-structure interaction, immersed boundary, moving boundary, two-phase flow
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-10571 (URN)10.1002/fld.2484 (DOI)000297736100018 ()2-s2.0-83255186838 (Scopus ID)
Projects
Nip Mechanics and Hydrodynamics in Flexo Post-Printing and Print Quality
Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
Holmvall, M., Uesaka, T., Drolet, F. & Lindström, S. (2011). Transfer of a microfluid to a stochastic fibre network. Journal of Fluids and Structures, 27(7), 937-946
Open this publication in new window or tab >>Transfer of a microfluid to a stochastic fibre network
2011 (English)In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 27, no 7, p. 937-946Article in journal (Refereed) Published
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.

Keywords
fibre network, flexo, fluid-structure interaction, fluid transfer, moving boundaries, two-phase flow
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-11295 (URN)10.1016/j.jfluidstructs.2011.06.003 (DOI)000295300900004 ()2-s2.0-80052260413 (Scopus ID)
Projects
Nip mechanics and hydrodynamics of flexo post printing and print quality
Available from: 2010-02-19 Created: 2010-02-19 Last updated: 2017-12-12Bibliographically approved
Lindström, S. & Uesaka, T. (2009). A numerical investigation of the rheology of sheared fiber suspensions. Physics of fluids, 21(8), 083301
Open this publication in new window or tab >>A numerical investigation of the rheology of sheared fiber suspensions
2009 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 21, no 8, p. 083301-Article in journal (Refereed) Published
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.

Keywords
Fibre suspension, Rheology, Simulation
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-8583 (URN)10.1063/1.3195456 (DOI)000270456500016 ()2-s2.0-70049091391 (Scopus ID)
Projects
The forest as a resource
Available from: 2009-02-17 Created: 2009-02-17 Last updated: 2017-12-13Bibliographically approved
Lindström, S., Uesaka, T. & Hirn, U. (2009). Evolution of the paper structure along the length of a twin-wire former. In: IAnson, SJ (Ed.), ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3. Paper presented at 14th Fundamental Research Symposium on Advances in Pulp and Paper Research (pp. 207-245). Bury, UK: Pulp Paper Fund. Res. Soc.
Open this publication in new window or tab >>Evolution of the paper structure along the length of a twin-wire former
2009 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Bury, UK: Pulp Paper Fund. Res. Soc., 2009
Keywords
Papermking, Forming, Fibre suspension, Simulation
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-9658 (URN)000281142700007 ()978-0-9545272-6-6 (ISBN)
Conference
14th Fundamental Research Symposium on Advances in Pulp and Paper Research
Projects
The forest as a resource
Available from: 2009-09-16 Created: 2009-09-16 Last updated: 2010-10-05Bibliographically approved
Lindström, S., Kulachenko, A. & Uesaka, T. (2009). New insights in paper forming from particle-level process simulations. In: Papermaking Research Symposium 2009 (pp. 38). Kuopio, Finland: University of Kuopio
Open this publication in new window or tab >>New insights in paper forming from particle-level process simulations
2009 (English)In: Papermaking Research Symposium 2009, Kuopio, Finland: University of Kuopio , 2009, p. 38-Conference paper, Published 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.

 

Place, publisher, year, edition, pages
Kuopio, Finland: University of Kuopio, 2009
Keywords
Fiber suspension, Papermaking, Paper structure, Simulation
National Category
Forest Science
Identifiers
urn:nbn:se:miun:diva-9211 (URN)978-951-27-1016-4 (ISBN)
Projects
The forest as a resource
Available from: 2009-06-24 Created: 2009-06-24 Last updated: 2010-02-25Bibliographically approved
Kulachenko, A., Lindström, S. & Uesaka, T. (2009). Strength of wet fiber networks-Strength scaling. In: Papermaking Research Symposium 2009 (pp. 35). Kuopio: University of Kuopio
Open this publication in new window or tab >>Strength of wet fiber networks-Strength scaling
2009 (English)In: Papermaking Research Symposium 2009, Kuopio: University of Kuopio , 2009, p. 35-Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Kuopio: University of Kuopio, 2009
Keywords
fiber network model, weak-link scaling
National Category
Forest Science
Identifiers
urn:nbn:se:miun:diva-9210 (URN)978-951-27-1016-4 (ISBN)
Projects
The forest as a resource
Available from: 2009-06-24 Created: 2009-06-24 Last updated: 2010-02-25Bibliographically approved
Lindström, S. & Uesaka, T. (2008). Effects of interparticle friction on the rheology of fibre suspensions. In: 5th European Congress on Computational Methods in Applied Sciences and Engineering: TS318, Computational Materials Mechanics V.
Open this publication in new window or tab >>Effects of interparticle friction on the rheology of fibre suspensions
2008 (English)In: 5th European Congress on Computational Methods in Applied Sciences and Engineering: TS318, Computational Materials Mechanics V, 2008Conference paper, Published paper (Refereed)
Keywords
friction, rheology, fibre suspension, simulation
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-6827 (URN)6029 (Local ID)6029 (Archive number)6029 (OAI)
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-20 Created: 2008-11-02 Last updated: 2011-09-05Bibliographically approved
Lindström, S. (2008). Modelling and simulation of paper structure development. (Doctoral dissertation). Sundsvall: Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University
Open this publication in new window or tab >>Modelling and simulation of paper structure development
2008 (English)Doctoral 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.

 

 

Place, publisher, year, edition, pages
Sundsvall: Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, 2008. p. 64
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 60
Keywords
Forming, Fibre, Paper, Fibre suspension, Paper structure, Simulation, Rheology
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-7003 (URN)978-91-86073-10-7 (ISBN)
Public defence
2008-10-28, O102, Mid Sweden University, Holmgatan 10, Sundsvall, 09:30 (English)
Opponent
Supervisors
Available from: 2008-11-12 Created: 2008-11-12 Last updated: 2009-03-19Bibliographically approved
Lindström, S. & Uesaka, T. (2008). Particle-level simulation of forming of the fiber network in papermaking. International Journal of Engineering Science, 46(9), 858-876
Open this publication in new window or tab >>Particle-level simulation of forming of the fiber network in papermaking
2008 (English)In: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 46, no 9, p. 858-876Article in journal (Refereed) Published
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.

Keywords
fiber suspension, forming, dewatering, fiber, paper, fiber network, simulation
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-4582 (URN)10.1016/j.ijengsci.2008.03.008 (DOI)000258021900002 ()2-s2.0-44949106201 (Scopus ID)5733 (Local ID)5733 (Archive number)5733 (OAI)
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-20 Created: 2008-11-14 Last updated: 2017-12-12Bibliographically approved
Kulachenko, A., Uesaka, T. & Lindström, S. (2008). Reinventing mechanics of fibre network. In: Progress in Paper Physics Seminar (pp. 185-193). Helsinki: Helsinki University Press
Open this publication in new window or tab >>Reinventing mechanics of fibre network
2008 (English)In: Progress in Paper Physics Seminar, Helsinki: Helsinki University Press, 2008, p. 185-193Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Helsinki: Helsinki University Press, 2008
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-6828 (URN)6030 (Local ID)6030 (Archive number)6030 (OAI)
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-20 Created: 2008-11-02 Last updated: 2013-03-25Bibliographically approved
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