| 1. |
- Andrä, Heiko, et al.
(författare)
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Micromechanical network model for the evaluation of quality controls of paper
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 49-55
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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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| 2. |
- Hansson, Julia, 1978, et al.
(författare)
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Greenhouse gas performance of heat and electricity from wood pellet value chains – based on pellets for the Swedish market
- 2015
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Ingår i: Biofuels, Bioproducts and Biorefining. - 1932-1031 .- 1932-104X. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Increased bioenergy demand has triggered a discussion on the sustainability of solidbiomass-based fuels and a system for sustainability criteria has been discussed within the EU.This paper assesses the greenhouse gas (GHG) emissions for heat and electricity from selectedwood pellet value chains for the Swedish market and the associated potential emissions reduction inrelation to fossil fuels using a life cycle assessment (LCA) perspective, and in relation to the approachdescribed in recent EU policy developments. Nine different wood pellet value chains for heat and/or power production in Sweden are assessed (including pellets from Sweden, Latvia, Russia, andCanada). Selected assumptions are varied in a sensitivity analysis. The total factory-gate GHG emissionsat the conversion facility for the wood pellet value chains studied, range between 2 and 25 gCO2-eq/MJ pellets with Swedish pellets at the lower end, and Russian pellets using natural gas fordrying the raw material at the higher end. Imported pellets from Latvia, Russia, and Canada that usebiomass for drying may also reach relatively low levels of GHG emissions. The potential GHG reductionas compared to a certain fossil fuel default energy comparator is 64–98% for the electricity producedin the pellet value chains studied and 77–99% for the heat produced. Thus, many wood pelletvalue chains on the Swedish market will most likely be able to meet strict demands for sustainabilityfrom a GHG perspective.
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| 3. |
- Johnson, Tomas, 1979, et al.
(författare)
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A Multi-Scale Simulation Method for the Prediction of Edge Wicking in Multi-Ply Paperboard
- 2015
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:4, s. 640-650
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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. |
- Kettil, Gustav, 1990, et al.
(författare)
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Novel Contact Forces for Immersed Boundary Paper Forming Simulations
- 2015
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Ingår i: Online proceedings: http://tappi.sclivelearningcenter.com/; PF2 - The Past, Present and Future of CFD Papermaking; PaperCon 2015 Atlanta April 19-22.
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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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| 5. |
- Mark, Andreas, 1980, et al.
(författare)
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Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
- 2011
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Ingår i: Paper360. - 1933-3684. ; 10:11, s. 23-30
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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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| 6. |
- Mark, Andreas, 1980, et al.
(författare)
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Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 283-290
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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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| 7. |
- Mark, Andreas, 1980, et al.
(författare)
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Modeling and Simulation of Paperboard Edge Wicking
- 2012
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:2, s. 397-402
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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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| 8. |
- Mark, Andreas, 1980, et al.
(författare)
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Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 41-47
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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. |
- Sultanian, Pedram, et al.
(författare)
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Prediction of survival in out-of-hospital cardiac arrest: the updated Swedish cardiac arrest risk score (SCARS) model
- 2024
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Ingår i: EUROPEAN HEART JOURNAL - DIGITAL HEALTH. - 2634-3916.
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Tidskriftsartikel (refereegranskat)abstract
- Aims Out-of-hospital cardiac arrest (OHCA) is a major health concern worldwide. Although one-third of all patients achieve a return of spontaneous circulation and may undergo a difficult period in the intensive care unit, only 1 in 10 survive. This study aims to improve our previously developed machine learning model for early prognostication of survival in OHCA.Methods and results We studied all cases registered in the Swedish Cardiopulmonary Resuscitation Registry during 2010 and 2020 (n = 55 615). We compared the predictive performance of extreme gradient boosting (XGB), light gradient boosting machine (LightGBM), logistic regression, CatBoost, random forest, and TabNet. For each framework, we developed models that optimized (i) a weighted F1 score to penalize models that yielded more false negatives and (ii) a precision-recall area under the curve (PR AUC). LightGBM assigned higher importance values to a larger set of variables, while XGB made predictions using fewer predictors. The area under the curve receiver operating characteristic (AUC ROC) scores for LightGBM were 0.958 (optimized for weighted F1) and 0.961 (optimized for a PR AUC), while for XGB, the scores were 0.958 and 0.960, respectively. The calibration plots showed a subtle underestimation of survival for LightGBM, contrasting with a mild overestimation for XGB models. In the crucial range of 0-10% likelihood of survival, the XGB model, optimized with the PR AUC, emerged as a clinically safe model.Conclusion We improved our previous prediction model by creating a parsimonious model with an AUC ROC at 0.96, with excellent calibration and no apparent risk of underestimating survival in the critical probability range (0-10%). The model is available at www.gocares.se.
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| 10. |
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