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  • 1.
    Burström, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Marjavaara, Daniel
    LKAB.
    Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres2017Ingår i: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, nr 1, s. 151-160Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Convective heat transport in a relatively thin porous layer of monosized particles is here modeled. The size of the particles is only one order of magnitude smaller than the thickness of the layer. Both a discrete three-dimensional system of particles and a continuous one-dimensional model are considered. The methodology applied for the discrete system is Voronoi discretization with minimization of dissipation rate of energy. The discrete and continuous model compares well for low velocities for the studied uniform inlet boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The new result is thus that a special correlation must be used when using a continuous model for flow perpendicular to a thin porous media in order to predict the dispersion in proper manner, especially in combination with higher velocities.

  • 2.
    Burström, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Liepaja University.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Marjavaara, Daniel
    LKAB Research and Development.
    Grate aerodynamic: Model strategies for gas flow through a 2D iron ore pellet bed2014Konferensbidrag (Refereegranskat)
  • 3. Frishfelds, Vilnis
    et al.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Flow-induced deformation of non-crimp fabrics during composites manufacturing2009Ingår i: Proceedings of ITP2009: Interdisciplinary Transport Phenomena VI: Fluid, Thermal, Biological, Materials and Space Sciences, October 4-9, 2009, Volterra, Italy, 2009, artikel-id ITP-09-52Konferensbidrag (Refereegranskat)
    Abstract [en]

    Flow induced alteration in permeability of deformable systems of fibres is studied. Low Reynolds number transversal flow through random arrays of aligned cylinders is considered by using a combined methodology of directly solving the twodimensional Navier-Stokes equations for the flow in the vicinity of a single fibre and minimisation of the dissipation rate in a system of fibres. The permeability of large random arrays increases always which is most apparent for compact systems with equal sized fibres. The permeability can also decrease but then for structured or small systems. The elastic deformations of fibre bundles are calculated basing microscopic fibre structure.

  • 4. Frishfelds, Vilnis
    et al.
    Hellström, J. Gunnar I.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mattsson, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Fluid flow induced deformation of porous medium: modeling of the no erosion filter test experiment2010Ingår i: Proceedings of the 3rd International Conference on Porous Media and its Applications in Science and Engineering: ICPM3, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    To study internal erosion in depth it is necessary to know either the detailed flow or how it varies in a statistical manner. It is also important to know how the internal erosion process initiates and progresses due to the fluid flow-induced forces. The underlying reason for this is that internal erosion will initiate exactly where the forces from the fluid are higher than the retaining forces that keep the particles together. Hence, a new model is here developed where fluid flow induced deformations of a large number of particles is studied. The model is applied to the No Erosion Filter test and simulated results resemble experimental results from the literature. The NEF test is used to investigate parameters such as the hydraulic conductivity and also in detail the process of internal erosion. The simulations are performed on different set-ups to exemplify successful and unsuccessful sealing. In the model, minimization of the dissipation rate of energy is accompanied with discretization of the system with modified Voronoi diagrams. Then Computational Fluid Dynamics is applied to solve the flow within each part of the Voronoi diagrams. Different parameters, such as the vorticity, calculated with the CFD-software are then used as input to the Monte Carlo-simulations. An overall good conformity between simulated results and experimental results from the literature is obtained.

  • 5.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Alteration of permeability caused by transversal flow-induced deformation of fibres during composites manufacturing2010Ingår i: Proceedings of The 10th International Conference on Flow Processes in Composite Materials (FPCM10): Monte Verità, Ascona, CH – July 11-15, 2010, 2010Konferensbidrag (Refereegranskat)
  • 6.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Flow-induced deformations within random packed beds of spheres2014Ingår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 104, nr 1, s. 43-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low Reynolds number flow-induced alterations of permeability of random packing of mono-sized spheres is studied. The number of spheres is several thousands and the porosities ranges between 0.4 and 0.6. The change of permeability is obtained for elastic deformations of the positions of the spheres using either of two methods. Each sphere is elastically attached to single points or the spheres that are connected via an elastic porous network. The system of spheres is divided into smaller volumes with Voronoi diagrams and the flow is derived by usage of a dual stream function. The local saturated flow fields are approximated as for close packed spheres and the overall flow pattern is obtained by minimising the dissipation rate of energy. The results show that the permeability for large random systems increases as a function of velocity and thus the deformation. The alteration is, however, much less than for two-dimensional cases like parallel cylinders. The relative increase in permeability becomes larger as the porosity increases from 0.4 to 0.6.

  • 7.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mattsson, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Fluid flow induced internal erosion within porous media: modelling of the no erosion filter test experiment2011Ingår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 89, nr 3, s. 441-457Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An investigation of the potential to numerically model the no erosion filter test is performed here, where the flow through a large ensemble of particles is considered by applying minimisation of dissipation rate of energy on the ensemble that is discretised with modified Voronoi diagrams and Delaunay triangulation. Low-Reynolds number simulations are applied to each part of the Voronoi diagram using computational fluid dynamics. The mechanical friction between particles is modelled by increasing the effective viscosity for closely spaced particles. Microscopic mechanisms for successful and unsuccessful sealing of filters are obtained. The numerical results agree with previously presented experimental observations by Sherard and Dunnigan. A conformity is that the sealing starts from the end of the channel and continues outwards in the radial direction. The sealing implies that the permeability can be reduced several orders of magnitude during a test.

  • 8.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Jakovics, Andris
    Faculty of Physics and Mathematics, University of Latvia.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Automatic recognition and analysis of scanned non-crimp fabrics for calculation of their fluid flow permeability2007Ingår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 26, nr 3, s. 285-296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Automatic recognition of scanned images of distorted bi-axial fiber bundle arrangements is considered in order to obtain the overall permeability of the formed fiber network. Scanned images are pre-processed with color normalization followed by usage of a threshold to find the pixels belonging to the bundles, the threads keeping the bundles together, and the distinct gaps formed between the bundles. Since the scanned images virtually have a perfect grayscale, the intensity can be treated as a corresponding signal of the image. Next the regular character of the fiber network is investigated using Fourier analysis on the fiber bundles as well as on the threads. The direction, position, and spatial separation of the fiber bundle and the threads are obtained in this way. In order to recognize the bottom fiber bundle layer a fine structure technique is used. Small clusters falsely identified as belonging to the bottom bundle layer are removed by application of a threshold to the perimeter of the cluster. The gaps in the top bundle layer are identified more clearly in this way. Next, a local Fourier analysis is applied to obtain the local distortion of the bundle and the thread structure yielding the characteristic distribution of the gaps between the bundles. Finally the distribution of the width of the threads is obtained by simply identifying the minimal distance between the sides of the threads.

  • 9. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Formering av bubblor vid vätning av textil bestående av lager av raka fiberbuntar2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 90-Konferensbidrag (Övrigt vetenskapligt)
  • 10. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Influence of flow-induced deformations of fabrics on the formation and transport of bubbles during liquid moulding processes2011Ingår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 47, nr 2, s. 221-232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The viscous flow-induced deformation of non-crimp fabrics during liquid moulding processes, such as resin transfer moulding, and its influence on the creation of bubbles behind the liquid front are studied. A transverse flow with a low Reynolds number through random arrays of aligned cylinders is considered with account of changes in the transverse permeability of fibre bundles. A combined methodology of directly solving the two-dimensional Navier-Stokes equations for the flow in the vicinity of a single fibre and minimization of the dissipation rate in a system of fibres is employed. Sethian's level set method is used for transient calculations of the motion of the liquid-gas front, at which the capillary pressure is accounted for. The continuity is maintained, and local correlations between the dimensions of neighbouring gaps formed between bundles are used. The elastic deformations of the fibre bundles are calculated based on micromechanical analyses. The void fractions of inter-and intrabundle bubbles obtained differ for deformable and non-deformable fabrics, but both the cases compare well with those from real mouldings

  • 11.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Influence of flow-induced forces on creation of bubbles during resin transfer moulding in non-crimp fabrics2010Konferensbidrag (Refereegranskat)
  • 12. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling of particle deposition during impregnation of dual-scale fabrics2011Ingår i: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 40, nr 2, s. 65-69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The motion of particles through a system of permeable fibre bundles is considered. The system is discretisised with Voronoi diagrams and the dissipation rate of energy is minimised with respect to the stream function in a system with periodic boundary conditions. The flow of the particles is in the transversal direction to the fibre bundles and the particles are hindered to move out of the plane allowing for two-dimensional calculations. The motion of particles is assumed to be slow with respect to the flowrate so that particles are driven by the Stokesian force for stationary particles. In this case, the flow distribution is essentially dependent on the particle configuration and strictly follows the motion of particles. When testing different sizes of the particles, it is shown that there is a qualitative agreement between model and experiments previously performed. In particular, stationary flow leads to particle depositions in front of the fibre bundles and small particles move into the fibre bundles while large ones are stuck at the border

  • 13. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jacovics, Andris
    University of Latvia.
    Lattice gas analysis of liquid front in non-crimp fabrics2010Ingår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 84, nr 1, s. 75-93Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The liquid flow front during impregnation of non-crimp fabrics is considered. Irregularities in fibre bundle architecture lead to generation of bubbles at this front. The velocity of this interface is highly influenced by capillary forces mainly caused by the small fibres inside the bundles. In order to better understand which shapes the liquid front takes up at different conditions, a lattice gas model has been applied. First, the macroscopic properties of the solved gas in the liquid are discussed. Next, bubble inclusions are analyzed as to liquid-gas interface position and concentrations of minor component in each phase. The capillary effects at the fluid front are studied for systems both with and without gaps between the bundles. The flow in the interior of the fibre bundles is scrutinized, as well, by also considering the viscous stresses. The flow through unidirectional fabrics is considered by a one-dimensional model, which suggests that the liquid front inside bundles and gaps moves with the same speed when the liquid front inside the bundle has to catch up with the liquid front in the gap

  • 14. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jakovics, A.
    University of Latvia.
    Bubble motion through non-crimp fabrics during composites manufacturing2008Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 39, nr 2, s. 243-251Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bubbles motion through inter bundle channels in bi-axial non crimp fabrics is modelled. The scenario is that formed bubbles move with the resin through these channels and are trapped if the channels become too narrow. By usage of a permeability network model, existing criteria on bubble deformation and a variety of analytical and probabilistic methods it is found that the paths of the bubbles depend significantly on the position of the threads keeping the fabric together and the number of fibres crossing the interbundle channels. Another result is that the pressure difference over a trapped bubble increases with 50 % in a 3D geometry possible helping the bubble to escape. A third result is that, on average, the bubbles move biased to the direction of the tows. Finally it is found that the predicted void distribution of bubbles after a major part of bubbles have moved through the system are in qualitative agreement with experimental data.

  • 15. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jakovics, A.
    Recognition technique for analysis of permeability of clustered fibre network2006Ingår i: Book of abstracts: Fourteenth International Conference Mechanics of Composite Materials, May 29 - June 2, 2006, Riga, Latvia / [ed] V. Tamuzs, Institute of Polymer Mechanics, University of Latvia , 2006Konferensbidrag (Övrigt vetenskapligt)
  • 16. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jakovics, Andris
    Lattice-gas analysis of fluid front in non-crimp fabrics2008Ingår i: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19): Reykjavik, Iceland, August 17-21, 2008 / [ed] Sigurdur Brynjolfsson; Olafur Petur Palsson; Jong H. Kim, University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science , 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    The fluid flow front during impregnation of non-crimp fabrics is considered. Irregularities in fiber bundle architecture lead to generation of bubbles at the fluid front. The velocity of this interface is highly influenced by capillary forces mainly caused by the small fibers inside the bundles. In order to derive the shapes of the fluid front, a lattice-gas model has been applied. First, the macroscopic properties of the solved gas in the fluid are discussed. Next, the bubble inclusions are analyzed as to fluid-liquid interface position and concentrations of minor component in each phase. Finally, the flow in the interior of the fiber bundles is scrutinized, where the viscous stresses are considered, as well.

  • 17. Frishfelds, Vilnis
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jakovics, Andris
    University of Latvia.
    Permeability of clustered fibre networks: modelling of unit cell2003Ingår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 39, nr 3, s. 265-272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper is focused on estimating the permeability of a clustered fiber network by variational methods. First, a laminar flow in ducts is considered by using polynomial trial functions. Then, a longitudinal flow through a square array is described by expanding the flow-rate field in trigonometric and Laurent series. Finally, a formal scheme for estimating the longitudinal permeability in a cluster with an irregular distribution of fibers is given. The irregular distribution is modeled by setting an individual effective radius for each fiber and then letting this fiber reach its minimum gravitational energy. The results obtained here form a basis for future predictions of the permeability of fibrous reinforcements.

  • 18.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling particulate flow during impregnation of dual-scale fabrics2011Ingår i: 18th International Conference on Composites Materials, ICCM 2011: Jeju; South Korea; 21 August 2011 through 26 August 2011, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Filtration of particles during impregnation of dual-scale fabrics is studied numerically for a number of configurations with a previously derived model. The initial position and size of the particles are varied. The main result is that structural composites can be tailor-made as to additional properties by such an approach.

  • 19.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, Staffan
    Mechanisms of flow-induced deformation of porous media2010Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 664, s. 220-237Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The study investigates creeping flow-induced alteration in the permeability of deformable particle systems. Low-Reynolds-number transversal flow through random arrays of aligned cylinders is considered by means of a combined methodology of directly solving the two-dimensional (2D) Stokes equations for the flow in the vicinity of two particles and minimising the dissipation rate in a system comprising thousands of particles. The results demonstrate that the more compact the system, the greater the possible relative change of permeability when a high flow rate is applied. The permeability of large random arrays always increases when increasing the flow rate, which is most apparent in compact systems with equal-sized particles. The permeability can sometimes decrease but only in structured or small systems.

  • 20.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Lundström, Staffan
    Mechanisms of fluid flow induced deformation of porous medium2009Ingår i: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Konferensbidrag (Refereegranskat)
  • 21.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Lundström, Staffan
    Mekanismer för flödesinducerad deformation av ett poröst material2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 103-Konferensbidrag (Övrigt vetenskapligt)
  • 22.
    Jourak, Amir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Derivation of dispersion coefficients in large random arrays of spheres and cylinders2012Konferensbidrag (Refereegranskat)
  • 23. Jourak, Amir
    et al.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Numerical derivation of dispersion coefficients for flow through three-dimensional randomly packed beds of monodisperse spheres2014Ingår i: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 60, nr 2, s. 749-761Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The longitudinal (DL) and transverse (DT) dispersion coefficients for flow through randomly packed beds of discrete monosized spherical particles are studied. The three-dimensional (3-D) porous-medium model consists of thousands of spherical particles that are divided into cells using Voronoi diagrams. The relationship between the variation of the dual stream function and the vorticity between neighboring particles is derived using Laurent series. The whole flow pattern at low particle Reynolds number is then obtained by minimization of the dissipation rate of energy with respect to the dual stream function. The DL is obtained by fitting the resulting effluent curve to a 1-D solution of a continuous model. The DT is obtained by fitting the numerical concentration profile to an approximate 2-D solution. The derived DL and DT values are in agreement with 3-D experimental data from the literature enabling a study of the effects of pore structure and porosity on DL and DT.

  • 24.
    Jourak, Amir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Herrmann, Inga
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Hedström, Annelie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Longitudinal dispersion coefficient: effects of particle-size distribution2013Ingår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 99, nr 1, s. 1-16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of particle-size distribution on the longitudinal dispersion coefficient (DL) in packed beds of spherical particles are studied by simulating a tracer column experiment. The packed-bed models consist of uniform and different-sized spherical particles with a ratio of maximum to minimum particle diameter in the range of 1–4. The modified version of Euclidian Voronoi diagrams is used to discretize the system of particles into cells that each contains one sphere. The local flow distribution is derived with the use of Laurent series. The flow pattern at low particle Reynolds number is then obtained by minimization of dissipation rate of energy for the dual stream function. The value of DL is obtained by comparing the effluent curve from large discrete systems of spherical particles to the solution of the one-dimensional advection-dispersion equation. Main results are that at Peclet numbers above 1, increasing the width of the particle-size distribution increases the values of DL in the packed bed. At Peclet numbers below 1, increasing the width of the particle-size distribution slightly lowers DL.

  • 25.
    Jourak, Amir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Herrmann, Inga
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Hedström, Annelie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Modeling of phosphate removal by fitra P in fixed-bed columns2011Ingår i: 2nd International Conference on Environmental Science and Technology , ICEST 2011 / [ed] Saji Baby; Bogdan Zygmunt, China, 2011, Vol. 2, s. 241-248Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.

  • 26.
    Jourak, Amir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Herrmann, Inga
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Hedström, Annelie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    The calculations of dispersion coefficients inside two-dimensional randomly packed beds of circular particles2011Konferensbidrag (Refereegranskat)
  • 27.
    Jourak, Amir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Herrmann, Inga
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Hedström, Annelie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    The calculations of dispersion coefficients inside two-dimensional randomly packed beds of circular particles2013Ingår i: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 59, nr 3, s. 1002-1011Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The longitudinal (DL) and transverse (DT) dispersion coefficients in two-dimensional (2D) randomly packed beds of circular particles in a laminar flow regime are derived. A 2D discrete system of particles is divided into cells using modified Voronoi diagrams. The relationship between the variation of the stream function and the averaged vortictiy is obtained from Computational Fluid Dynamics simulations. The whole flow pattern is then obtained by using the principle of energy dissipation rate minimization. The obtained values of DL agree well with 3D experimental data for all velocities investigated. At very high velocities, DT in 2D appears to be higher than 3D experimental data. In addition, the effects of particle size distribution, packing structure, and porosity on the DL and DT were studied. One result was that an increase in the width of the particle size distribution resulted in higher values of DL and DT at high velocities.

  • 28.
    Jourak, Amir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Herrmann, Inga
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Frishfelds, Vilnis
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Hedström, Annelie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Modelling of phosphate removal by Filtrap in a fixed-bed column2010Konferensbidrag (Övrigt vetenskapligt)
  • 29.
    Ljung, Anna-Lena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Endimensionell bäddmodell för simulering av torkning av järnmalmspellets2011Konferensbidrag (Refereegranskat)
    Abstract [sv]

    Järnmalmspellets är en högt förädlad produkt utvecklad av gruvindustrin för användning iexempelvis masugnar. För ett bandugnsverk sker pelletsprocessen huvudsakligen i fyra steg då en kontinuerlig bädd av pellets transporteras på rosterband genom torkzon, förvärmningzon,brännzon och kylzon. Genomströmmande luft används för att torka, sintra och kyla materialet ide olika zonerna. Då produktionen av järnmalmspellets är tids- och energikrävande finns deten naturlig drivkraft att förbättra processen så att produktionen kan optimeras medbibehållen produktkvalitet.För att i detalj studera torkzonen har en modell för konvektiv torkning av en enskildpellet tidigare tagits fram. Resultat från simuleringarna visar tydligt fyra torkningsfaser; i)förångning av vätska från pelletens yta, ii) förångning av vätska vid ytan samtidigt som vissinre förångning sker då ytan lokalt är torr, iii) torkning enbart på grund av inre förångningoch iv) kokning av vatten inuti pelleten [1]. Den framtagna torkningsmodellen har ävenapplicerats på en sfärisk geometri med syfte att undersöka hur fukthalten i inloppsluftenpåverkar torkningen [2]. Simuleringar visar att effekten av luftfuktighet främst uppkommeri början av den första torkningsfasen medan skillnaderna minskar i slutet av perioden då ettförlängt stadie av konstant torkhastighet fås vid höga luftfuktigheter.Ovanstående resultat visar att det är av stort intresse att även undersöka hur pellets i enpelletbädd påverkas av omgivande lufttemperatur och luftfuktighet. En endimensionellbäddmodell har därför utvecklats som ett komplement till enkulemodellen för attundersöka hur våttemperatur, pellettemperatur, torkhastighet etc. varierar som funktion avbäddhöjd i den första torkningsfasen. I modellen beräknas förångning från pelletsens ytamed motsvarande fukttransport genom den porösa bädden och det är därmed möjligt attutreda vilka områden i bädden som påverkas av eventuell återkondensation.

  • 30.
    Ljung, Anna-Lena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Marjavaara, Daniel
    Discrete and continuous modelling of heat and mass transport in drying of a bed of iron ore pellets2012Ingår i: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 30, nr 7, s. 760-773Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Drying of a porous bed of iron ore pellets is here considered by modeling a discrete two-dimensional system of round pellets. As a complement to the two-dimensional model, a continuous one-dimensional model enabling fast calculations is developed. Results from the discrete model show that the temperature front advances faster in areas with large distances between the pellets. In areas with low flow speed, the temperature of the pellets increases with a relatively slow rate. The water inside these pellets will therefore remain for a long time. The continuous model fits the discrete model very well for a regular distribution of equal-sized particles. A discrete model with irregular packing will, compared to the continuous model, show a larger variation in the distribution of temperature and moisture content in the final phase of drying.

  • 31.
    Lundström, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Jacovics, Andris
    University of Latvia.
    Bubble formation and motion during impregnation of fabrics2009Ingår i: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Konferensbidrag (Refereegranskat)
  • 32.
    Lundström, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Latvian University.
    Jacovics, Andris
    Latvian University.
    Bubble formation and motion in non-crimp fabrics with perturbed bundle geometry2008Ingår i: FPCM-9. The 9th International Conference on Flow Processes in Composite Materials: Montréal (Québec), Canada 8 - 10 July 2008, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    The behaviour of the fluid front during impregnation of non-crimp fabrics has been considered. Particular attention is paid to creation of bubbles at the fluid front and a virtual 3D model mimicking biaxial fabrics has been build for this purpose. The saturated fluid flow is governed by Navier-Stokes Equations and Darcy law while capillary pressure has been accounted for at the fluid flow front. Continuity is furthermore preserved. The influence of perturbation in the bundle geometry has been investigated where it turns out that local correlations of dimensions of neighbouring gaps formed between the bundles are of highest importance. Focus is set on inter-bundle bubbles, where a previously built model for bubble dynamics is used based on a probabilistic approach for bubbles moving, slitting, merging, dying, and shaping. The obtained void fractions of inter-bundle bubbles at different levels of vacuum applied at the liquid flow front is compared to those from real mouldings with rather good conformity.

  • 33.
    Lundström, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Jakovics, Andris
    University of Latvia.
    A statistical approach to permeability of clustered fibre reinforcements2004Ingår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 38, nr 13, s. 1137-1149Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The focus is set on mesoscale modelling of permeability of real fabrics used in composite manufacturing. Of particular interest is the effect of expected perturbations from perfect geometries, such as fibre bundle crimp, on the permeability. To start with, variational methods are used to calculate the perme-ability of individual gaps between fibre bundles. Based on this study a network of unit cells is formed enabling studies of two- and three-dimensional flow through the structure. From such an analysis the overall permeability of an arbitrary distribution of unit cell permeabilities can be calculated. Here random and controlled distributions are simulated. The former is an approximate representation of a continuous strand mat and the latter may describe Non-Crimp Fabrics. The result is that for random distributions, the permeability decreases with the maximum variation in unit cell while for a controlled permeability distribution the overall permeability can as well increase as decrease depending on the type of perturbation. In both cases the type of flow: one-, two- or three-dimensional strongly influence on the quantitative result. Hence, for the type of fabrics studied, it is necessary to model the full 3D-flow through to get a correct permeability value.

  • 34.
    Lundström, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Jakovics, Andris
    Faculty of Physics and Mathematics, University of Latvia.
    Bubble formation and motion in non-crimp fabrics with perturbed bundle geometry2010Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, nr 1, s. 83-92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The motion of the liquid front during impregnation of non-crimp fabrics has been considered by using Sethian's level set method. Particular attention is put on the creation of bubbles at the liquid front and a virtual 3D model mimicking biaxial fabrics has been built for this purpose. The saturated fluid flow is governed by the Navier-Stokes Equations and Darcy law, while capillary pressure has been accounted for at the liquid flow front and continuity maintained. The influence of perturbation in the bundle geometry has been investigated. Local correlations of the dimensions of neighbouring gaps formed between the bundles are of paramount importance. Focus is on inter-bundle bubbles. An existing model for bubble dynamics is used based on a probabilistic approach for bubbles moving, splitting, merging, and dissolving. The same approach was used for intra-bundle bubbles, the difference being that their motion appears to be much slower. The obtained void fractions of inter-bundle bubbles at different vacuum levels applied at the liquid flow front are compared to those from real mouldings with a high degree of conformity.

  • 35.
    Lundström, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Jakovics, Andris
    University of Latvia.
    Transport of bubbles in non-crimp fabrics during resin transfer moulding2008Ingår i: Proceedings of the XV International Conference on Mechanics of Composites Material, MCM-2008, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 36.
    Lundström, T. Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Modeling filtration of particulate flow during impregnation of dual-scale fabrics2013Ingår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 47, nr 15, s. 1907-1915Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Filtration of particles during impregnation of dual-scale fabrics is studied numerically for a number of geometries and initial positions of the particles by improving a previously derived model for a high density of the particles. The initial position and size of the particles are varied. The main result is that structural composites can be tailor-made as to additional properties by such an approach

  • 37.
    Lundström, T. Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Transversal flow-induced deformation of fibres during composites manufacturing and the effect on permeability2013Ingår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 32, nr 15, s. 1129-1135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low Reynolds number flow of a viscous fluid through bundles in non-crimp stitched fabrics is considered for different arrangements of the fibres within the bundles. Using a previous derived model, two-dimensional Navier–Stokes solutions are sampled for the flow between a few fibres with a subsequent minimisation of the dissipation rate in the total system of fibres. Based on the detailed geometry of the fabrics flow induced elastic deformations of the fibre bundles are then derived and the overall permeability is computed for different pressure gradients. The permeability of random arrays of a large number of as well mono-dispersed as poly-dispersed fibres increases as the flow-induced deformation increases and despite the relative shift of the fibres is small the overall change in permeability is essential. For a system with gaps between bundles the change in permeability depends on the orientation of the flow field with respect to the geometry studied while for a regular packing the alteration in permeability is negligible.

  • 38. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Jakovics, A.
    University of Latvia.
    Permeability network model for non-crimp fabrics2006Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 37, nr 6, s. 826-835Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work a global permeability model is developed and applied to a biaxial Non-crimp stitched fabric (NCF). This model focuses on a detailed meso-scale description of the fabric geometry, which takes into account the local permeability distribution in a fabric due to perturbations of the geometry as well as the geometrical features which arise from the stitching process. It is shown in this work that these features significantly affects the global permeability. The influence of the amount and type of perturbation of a fabric is also studied in this work. It is shown that perturbation of the fabric geometry affect the global permeability but not as much as the stitching process. The model developed is finally validated with experimental permeability data and it is suggested how to use the model for an arbitrary lay-up.

  • 39. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Jakovics, Andris
    Application of permeability network model to non-crimp fabrics2004Ingår i: The XIII International Conference on Mechanics of Composite Materials, 2004Konferensbidrag (Refereegranskat)
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