Publications Search Results

Now showing 1 - 10 of 60
  • Publication
    Simulation of viscoelastic squeeze flows for adhesive joining applications
    ( 2022)
    Ingelsten, S.
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    Mark, A.
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    Kádár, R.
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    Edelvik, F.
    A backwards-tracking Lagrangian-Eulerian method is used to simulate planar viscoelastic squeeze flow. The momentum and continuity equations are discretized with the finite volume method and implicit immersed boundary conditions are used to describe objects in the domain. The viscoelastic squeeze flow, which involves moving solid geometry as well as free surface flow, is chosen for its relevance in industrial applications, such as adhesive parts assembly and hemming. The main objectives are to validate the numerical method for such flows and to outline the grid resolution dependence of important flow quantities. The main part of the study is performed with the Oldroyd-B model, for which the grid dependence is assessed over a wide range of Weissenberg numbers. An important conclusion is that the load exerted on the solids can be predicted with reasonable accuracy using a relatively coarse grid. Furthermore, the results are found to be in excellent agreement with theoretical predictions as well as in qualitative resemblance with numerical results from the literature. The effects of different viscoelastic properties are further investigated using the PTT model, revealing a strong influence of shear-thinning for moderate Weissenberg numbers. Finally, a reverse squeeze flow is simulated, highlighting important aspects in the context of adhesive joining applications.
  • Publication
    A numerical multiscale method for fiber networks
    ( 2021)
    Görtz, M.
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    Kettil, G.
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    Målqvist, A.
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    Mark, A.
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    Edelvik, F.
    Fiber network modeling can be used for studying mechanical properties of paper [1]. The individual fibers and the bonds in-between constitute a detailed representation of the material. However, detailed microscale fiber network models must be resolved with efficient numerical methods. In this work, a numerical multiscale method for discrete network models is proposed that is based on the localized orthogonal decomposition method [4]. The method is ideal for these network problems, because it reduces the maximum size of the problem, it is suitable for parallelization, and it can effectively solve fracture propagation. The problem analyzed in this work is the nodal displacement of a fiber network given an applied load. This problem is formulated as a linear system that is solved by using the aforementioned multiscale method. To solve the linear system, the multiscale method constructs a low-dimensional solution space with good approximation properties [5, 2]. The method i s observed to work well for unstructured fiber networks, with optimal rates of convergence obtainable for highly localized configurations of the method.
  • Publication
    A Backwards-Tracking Lagrangian-Eulerian Method for Viscoelastic Two-Fluid Flows
    ( 2021)
    Ingelsten, S.
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    Mark, A.
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    Kádár, R.
    ;
    Edelvik, F.
    A new Lagrangian-Eulerian method for the simulation of viscoelastic free surface flow is proposed. The approach is developed from a method in which the constitutive equation for viscoelastic stress is solved at Lagrangian nodes, which are convected by the flow, and interpolated to the Eulerian grid with radial basis functions. In the new method, a backwards-tracking methodology is employed, allowing for fixed locations for the Lagrangian nodes to be chosen a priori. The proposed method is also extended to the simulation of viscoelastic free surface flow with the volume of fluid method. No unstructured interpolation or node redistribution is required with the new approach. Furthermore, the total amount of Lagrangian nodes is significantly reduced when compared to the original Lagrangian-Eulerian method. Consequently, the method is more computationally efficient and robust. No additional stabilization technique, such as both-sides diffusion or reformulation of the constitutive equation, is necessary. A validation is performed with the analytic solution for transient and steady planar Poiseuille flow, with excellent results. Furthermore, the proposed method agrees well with numerical data from the literature for the viscoelastic die swell flow of an Oldroyd-B model. The capabilities to simulate viscoelastic free surface flow are also demonstrated through the simulation of a jet buckling case.
  • Publication
    Numerical upscaling of discrete network models
    ( 2020)
    Kettil, G.
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    Målqvist, A.
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    Mark, A.
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    Fredlund, M.
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    Wester, K.
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    Edelvik, F.
    In this paper a numerical multiscale method for discrete networks is presented. The method gives an accurate coarse scale representation of the full network by solving sub-network problems. The method is used to solve problems with highly varying connectivity or random network structure, showing optimal order convergence rates with respect to the mesh size of the coarse representation. Moreover, a network model for paper-based materials is presented. The numerical multiscale method is applied to solve problems governed by the presented network model.
  • Publication
    Investigating the sensitivity of particle size distribution on part geometry in additive manufacturing
    ( 2020)
    Sagar, V.R.
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    Lorin, S.
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    Göhl, J.
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    Quist, J.
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    Cromvik, C.
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    Mark, A.
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    Jareteg, K.
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    Edelvik, F.
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    Wärmefjord, K.
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    Söderberg, R.
    Selective laser melting process is a powder bed fusion additive manufacturing process that finds applications in aerospace and medical industries for its ability to produce complex geometry parts. As the raw material used is in powder form, particle size distribution (PSD) is a significant characteristic that influences the build quality in turn affecting the functionality and aesthetics aspects of the end product. This paper investigates the effect of PSD on deformation for 316L stainless steel powder, where three coupled in-house simulation tools based on Discrete Element Method (DEM), Computational Fluid Dynamics (CFD), and Structural Mechanics are employed. DEM is used for simulating the powder distribution based on the different particle size distribution of the powder. The CFD is used as a virtual test bed to determine thermal parameters such as density, heat capacity and thermal conductivity of the powder bed viewed as a continuum. The values found as a stochastic function of the powder distribution is used to test the sensitivity of the melted zone and distortion using Structural Mechanics. Results showed significant influence of particle size distribution on the packing density, surface height, surface roughness, the stress state and displacement of the melted zone. The results will serve as a catalyst in developing geometry assurance strategies to minimize the effect of particle size distribution on the geometric quality of the printed part.
  • Publication
    Robot spray painting trajectory optimization
    ( 2020)
    Gleeson, D.
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    Jakobsson, S.
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    Salman, R.
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    Sandgren, N.
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    Edelvik, F.
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    Carlson, J.S.
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    Lennartson, B.
    In the manufacturing industry, spray painting is often an important part of the process. Especially in the automotive industry, the perceived quality of the final product is closely linked to the exactness and smoothness of the painting process. For complex products or low batch size production, manual spray painting is often used. But in large scale production with a high degree of automation, the painting is normally performed by industrial robots. There is a need to improve and simplify the generation of robot trajectories used in industrial paint booths. A method for spray paint optimization is presented, which can be used to smooth out an initial trajectory and minimize paint thickness deviations from a target thickness. By fitting a spline function to experimental data, an applicator footprint profile is determined, which is a two-dimensional reference function of the applied paint thickness. This footprint profile is then projected to the geometry and used as a d eposition model at each point along the trajectory. The positions and durations of all trajectory segments are used as optimization variables. They are modified with the primary goal to obtain a paint applicator trajectory, which will closely match a target paint thickness when executed. The algorithm is shown to produce satisfactory results on both a simple 2-dimensional test example, and a nontrivial industrial case of painting a tractor render. The final trajectory shows an overall thickness close to the target thickness, and the resulting trajectory is feasible to execute directly on an industrial robot.
  • Publication
    Computationally efficient viscoelastic flow simulation using a Lagrangian-Eulerian method and GPU-acceleration
    ( 2020)
    Ingelsten, S.
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    Mark, A.
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    Jareteg, K.
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    Kádár, R.
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    Edelvik, F.
    A recently proposed Lagrangian-Eulerian method for viscoelastic flow simulation is extended to high performance calculations on the Graphics Processing Unit (GPU). The two most computationally intensive parts of the algorithm are implemented for GPU calculation, namely the integration of the viscoelastic constitutive equation at the Lagrangian nodes and the interpolation of the resulting stresses to the cell centers of the Eulerian grid. In the original CPU method, the constitutive equations are integrated with a second order backward differentiation formula, while with the proposed GPU method the implicit Euler method is used. To allow fair comparison, the latter is also implemented for the CPU. The methods are validated for two flows, a planar Poiseuille flow of an upper-convected Maxwell fluid and flow past a confined cylinder of a four-mode Phan Thien Tanner fluid, with identical results. The calculation times for the methods are compared for a range of grid resolut ions and numbers of CPU threads, revealing a significant reduction of the calculation time for the proposed GPU method. As an example, the total simulation time is roughly halved compared to the original CPU method. The integration of the constitutive equation itself is reduced by a factor 50 to 250 and the unstructured stress interpolation by a factor 15 to 60, depending on the number of CPU threads used.
  • Publication
    A Lagrangian-Eulerian framework for simulation of transient viscoelastic fluid flow
    ( 2019)
    Ingelsten, S.
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    Mark, A.
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    Edelvik, F.
    A novel framework for simulation of transient viscoelastic fluid flow is proposed. The viscoelastic stresses are calculated at Lagrangian nodes which are distributed in the computational domain and convected by the fluid. The coupling between the constitutive equation and the fluid momentum equations is established through robust interpolation with radial basis functions. The framework is implemented in a finite volume based flow solver that combines an octree background grid with immersed boundary techniques. Since the distribution of the Lagrangian node set is performed entirely based on spatial information from the fluid solver, the ability to simulate flows in complex geometries is therefore as general as for the fluid solver itself. In the Lagrangian formulation the discretization of the convective terms in the constitutive equations is avoided. No re-formulation of the constitutive equation is required for stable solutions. Numerical experiments are performed of UCM and Oldroyd-B fluids in a channel flow and of a four mode PTT fluid in a confined cylinder flow. The computed flow quantities consistently converge and agree excellently with analytical and numerical data for fully developed and transient flow.
  • Publication
    Numerical investigation of upstream cylinder flow and characterization of forming fabrics
    ( 2019)
    Kettil, G.
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    Mark, A.
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    Wester, K.
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    Fredlund, M.
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    Edelvik, F.
    In this work, the fundamentals of upstream flow over cylinders and forming fabrics are investigated, and measures for characterization of fabrics are proposed. Two-dimensional flow over one cylinder, two cylinders, and one and two rows of cylinders, are analysed numerically. By studying different configurations and various Reynolds numbers, the upstream flow features are characterized. It is concluded that cylinders have a short range of upstream flow impact, shortest for rows of cylinders with small spacings. For R e - [ 10, 80 ]Re\in [10,80], the Reynolds number dependency is weak. It is shown that a downstream row positioned in tandem has negligible impact on the upstream flow, while a displaced second row influences the upstream flow if the spacing in the first row is larger than one diameter. The pressure drop required to drive the flow over the cylinders depends non-linearly on the porosity of the configuration. Flow measures of the upstream flow are proposed, which in addition to the volume flow per area are used to characterize fabric flow properties. The conclusions from the cylinder study also hold for industrial fabrics, and it can be explained how properties of the fabric influence the final paper. The wave-length of flow periodicity is studied in relation to drainage marking. This study demonstrates that simulations can greatly improve pure experimental-based fabric characterization.
  • Publication
    A multiscale methodology for simulation of mechanical properties of paper
    ( 2018)
    Kettil, G.
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    Malqvist, A.
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    Mark, A.
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    Edelvik, F.
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    Fredlund, M.
    ;
    Wester, K.
    In this work a multiscale framework developed for simulation of mechanical properties of paper is presented. The framework consists of two major parts. In the first part the forming process of a paper machine is simulated using the fiber suspension model developed in [8]. Fluid dynamics together with an advanced contact calculation method enables detailed simulation of the lay down process. The resulting paper sheet is used as input to the second part of the framework. In the second part the fiber configuration attained from the unique forming simulations is transformed into a network representation, enabling simulation of mechanical properties. The paper mechanics is governed by a fiber network model. To study macroscale properties a novel numerical upscaling method for networks has been developed. In this paper the complete simulation methodology is outlined and discussed.