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Träfflista för sökning "hsv:(NATURVETENSKAP) hsv:(Matematik) hsv:(Beräkningsmatematik) ;pers:(Nyman Ulf)"

Sökning: hsv:(NATURVETENSKAP) hsv:(Matematik) hsv:(Beräkningsmatematik) > Nyman Ulf

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1.
  • Kettil, Gustav, 1990, et al. (författare)
  • Novel Contact Forces for Immersed Boundary Paper Forming Simulations
  • 2015
  • Ingår i: Online proceedings: http://tappi.sclivelearningcenter.com/; PF2 - The Past, Present and Future of CFD Papermaking; PaperCon 2015 Atlanta April 19-22.
  • Konferensbidrag (refereegranskat)abstract
    • To be able to simulate the different processes involved in paper machines, models, numerical methods and algorithms have to be developed which capture as much as possible of the real physical phenomena. In this paper a model for calculation of the chemical and physical interaction between objects included in a fiber suspension is presented. The contact force model is based on DLVO theory [1, 2] and uses so-called contact points distributed along the fiber suspension objects. The contact model has been used in an existing framework to simulate the build-up of low density paper webs. In the framework fibers are modeled as elliptical cylinders whose movements are described by finite-strain beam theory which includes shearing. The fluid flow is computed using a Navier-Stokes solver and immersed boundary methods are utilized to resolve the flow around each fiber. For validation, the air permeability and thickness of the paper webs have been measured and compared with simulated data. The result demonstrates that the software can be used to simulate paper forming.
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2.
  • Andrä, Heiko, et al. (författare)
  • Micromechanical network model for the evaluation of quality controls of paper
  • 2011
  • Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 49-55
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we discuss the challenges in modelling and simulating infinitesimal and large deformations of cellulose fiber networks, mainly in the context of the prediction of quality controls for paper.Understanding the influence and sensitivity of macroscopic production parameters like grammage and thickness of paperboard and understanding the influence of the fiber suspension on the quality of paper is important for the development of better papers and for preserving raw materials and energy.The new simulation framework consists of the virtual stochastic paper structure generator PaperGeo, that was integrated in the GeoDict 1 software suite, and the finite element solver FeelMath (Finite Elements for Elastic Materials and Homogenization) for solving the equations of elasticity. The fibers and the contacts are modelled by using geometrically exact beams of Simo-type [1].The microstructural model and the fiber network model are validated against standard measurements of existing papers in the following way: At first we perform tensile and bending tests to measure the macroscopic stress-strain relations. In the next step we apply a representative macroscopic stress or strain onto the boundaries of realizations of the stochastic fiber network model and compute by homogenization the effective (stiffness) coefficients. Finally we compare the numerical results with the measurements.This procedure can also be used for an identification of elastic parameters on the microscale and to study the sensitivity of the effective (macroscopic) stiffness with regard to the parameters of the microstructure
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3.
  • Johnson, Tomas, 1979, et al. (författare)
  • A Multi-Scale Simulation Method for the Prediction of Edge Wicking in Multi-Ply Paperboard
  • 2015
  • Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:4, s. 640-650
  • Tidskriftsartikel (refereegranskat)abstract
    • When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to a mixture of water and hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to the paper industry as well as to packaging manufacturers. In this paper an extended multi-scale model of edge wicking in multi-ply paperboard is presented. The geometric and physical properties of the paperboard are modeled on the micro-scale, and include fillers and fines. The absolute air permeabilities and pore size distributions are validated with experimental and tomographic values. On the macro-scale random porosity and sizing distributions, time and sizing dependent contact angles, and inter-ply dependence are modeled. Arbitrary shapes of the paperboard are handled through an unstructured 3D surface mesh. Stationary and transient edge wicking simulations are validated against experiments with excellent agreement. The simulations show that the diffusive menisci between the liquid and air phases together with the two-ply model is necessary to achieve good agreement with the transient edge wicking experiments.
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4.
  • Mark, Andreas, 1980, et al. (författare)
  • Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
  • 2011
  • Ingår i: Paper360. - 1933-3684. ; 10:11, s. 23-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Paper forming is the first step in the paper machine where a fibersuspension leaves the headbox and flows through a forming fabric.Complex physical phenomena occur during paper forming due to theinteraction between fibers, fillers and fines as well as chemicalsadded to the suspension. Understanding this process is important forthe development of improved paper products because the configurationof the fibers during this step has a large influence on the finalpaper quality. Since the effective paper properties depend on themicro-structure of the fiber web, a continuum model is inadequate andthe properties of each fiber need to be accounted for in thesimulations.In the present work, a framework for microstructure simulation ofearly paper forming has been developed. The simulation frameworkincludes a Navier-Stokes solver and immersed boundary methods are usedto resolve the flow around the fibers. The fibers are modeled with afinite element discretization of the Euler-Bernoulli beam equation ina co-rotational formulation. The contact model is based on a penaltymethod and includes friction as well as elastic and inelasticcollisions.The fiber model and the contact model are validated against demandingtest cases from the literature with excellent results. Thefluid-structure interaction in the model is examined by simulating anelastic beam oscillating in a cross flow. Finally, a simulation ofearly paper forming is performed to demonstrate the potential of theproposed framework. The unique modeling approach can be used toincrease the fundamental understanding of paper forming and supportprocess optimization.
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5.
  • Mark, Andreas, 1980, et al. (författare)
  • Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
  • 2011
  • Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 283-290
  • Konferensbidrag (refereegranskat)abstract
    • Paper forming is the first step in the paper machinewhere a fiber suspension leaves the headbox and flowsthrough a forming fabric. Understanding this processis important for the development of improved paperproducts because the configuration of the fibers duringthis step has a large influence on the final paperquality.The simulation framework includes IBOFlow, a stateof-the-art Navier-Stokes solver, and PaperGeo, the virtualpaper structure generator in GeoDict. ImmersedBoundary Methods are used to resolve the flow aroundthe fibers. The fibers are modeled with a finite elementdiscretization of the Euler-Bernoulli beam equationin a co-rotational formulation. The contact modelis based on a penalty method and includes friction aswell as elastic and inelastic collisions.The fiber model and the contact model are validatedagainst demanding test problems from the literaturewith excellent result. The fluid-structure interaction inthe model is examined by simulating an elastic beamoscillating in a cross flow. Finally, a simulation of initialpaper forming is performed, which demonstratesthe capabilities of the simulation framework.
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6.
  • Mark, Andreas, 1980, et al. (författare)
  • Modeling and Simulation of Paperboard Edge Wicking
  • 2012
  • Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:2, s. 397-402
  • Tidskriftsartikel (refereegranskat)abstract
    • When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to paper industry as well as to packaging manufacturers. The aim of this paper is to present a new analytical theory for prediction of the edge wicking properties of paperboard. The theory is based on Darcy’s law and the ideal gas law to describe the physical behavior of water flow in paperboard. The theory is compared to a recently published multi-scale framework and with pressurized edge wick experiments. The agreement is very good for paperboard samples of different sizes. The conclusion from the work is that both analytical theory and detailed simulations are useful to predict edge wicking properties of paperboard material.
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7.
  • Mark, Andreas, 1980, et al. (författare)
  • Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model
  • 2012
  • Ingår i: Tappi Journal. - 0734-1415. ; 11:6, s. 9-16
  • Tidskriftsartikel (refereegranskat)abstract
    • When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to paper industry as well as to packaging manufacturers. In this paper a multi-scale framework is proposed that allows for detailed simulation of the edge wicking process.On the fiber micro-scale virtual paper models are generated based on input from tomographic and SEM images. A pore morphology method is used to calculate capillary pressure curves, and on the active pores one-phase flow simulations are performed for relative permeabilities. The results as functions of saturation and porosity are stored in a database. The database is used as input for two-phase flow simulations on the paper macro-scale. The resulting fluid penetration is validated against pressurized edge wick measurements on paper lab sheets with very good agreement. The proposed multi-scale approach can be used to increase the understanding of how edge wicking in paperboard packages depends on the micro-structure.
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8.
  • Mark, Andreas, 1980, et al. (författare)
  • Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model
  • 2011
  • Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 41-47
  • Konferensbidrag (refereegranskat)abstract
    • When liquid paperboard based package material ismade aseptic, unsealed edges of the board are exposedto a liquid front which in some circumstances may soakthe material to some extent. This is not desired since itmay lead to aesthetic as well as functional defects. Inorder to make a priori predictions of the edge wickingproperties of a given paper material, something whichis of great interest to paperboard industry as well aspackaging manufacturers, micro simulations are required.To calculate the penetration of fluid in the open edgeof a paper sheet a multi-scale framework is developed.On the fiber micro-scale, virtual paper models are generatedin PaperGeo [6]. In IBOFlow [7] a pore morphologymethod is used to calculate capillary pressurecurves, and the active pores one-phase flow simulationsare performed for relative permeabilities. Theresult is a database of capillary pressure curves andrelative permeabilities as functions of saturation andporosity. The database is used as an input for a twophaseflow simulation on a 2D virtual macro sheet tocalculate the penetration of fluid in the paper. Themulti-scale framework is validated against pressurizededge wick measurements with good agreement.
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9.
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10.
  • Svenning, Erik, 1986, et al. (författare)
  • Multiphase Simulation of Fiber Suspension Flows Using Immersed Boundary Methods
  • 2012
  • Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:2, s. 184-191
  • Tidskriftsartikel (refereegranskat)abstract
    • Fiber suspension simulations are challenging since they involve transient fluid flow with immersed solid objects subject to large displacements and rotations. In the present work, a beam model in co-rotational formulation is coupled with a fluid solver using immersed boundary methods. The model is used to simulate a fiber in a shear flow and excellent agreement is found with Jeffery's equations. The shapes of fibers deforming in a shear flow are found to be in qualitative agreement with shapes observed in experiments.The flow of a fiber suspension is studied by simulating early paper forming with one-way and semi-two-way coupling. It is found that the flow through the fiber web needs to be resolved in order to predict the retention of fibers in the fiber web.
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