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  • 201.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Aktivitet: Strömning i porösa material och dess relevans i vattenkraftsdammar2005Conference paper (Other (popular science, discussion, etc.))
  • 202. Lundström, Staffan
    Bubble transport through constricted capillary tubes with application to resin transfer molding1996In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 17, no 6, p. 770-779Article in journal (Refereed)
    Abstract [en]

    This paper describes and expounds a theoretical and experimental study of bubble motion through constricted capillary tubes. In the experiment, two liquidfilled capillaries are used. They have unequal radii and are glued together. Gas bubbles are injected into the larger capillary. Then the pressure required to force the bubbles through the constriction is measured for various liquids, bubble lengths, capillary radii and constriction geometry. It appears that the pressure directly follows Young's-Laplace law for capillary pressure. The results of the study are used to understand the bubble transport through fiber reinforcements, which generally takes place during the manufacturing of composites. The bubbles are carried if: (i) the pressure gradient is high enough, (ii) the surface tension of the liquid is low enough, (iii) the cross-sectional area of the channels in the reinforcement is sufficiently uniform. The theory reveals that the bubbles are more likely to be trapped on a small scale, i.e. within fiber bundles rather than on a large scale, i.e. between the bundles. It is also concluded that, if the bubbles are trapped at the resin flow front, a converging flow is better for the transport of the voids than a diverging flow.

  • 203.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effektiv tillverkning av högpresterande kompositer2000Conference paper (Other academic)
  • 204.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    From permeability modelling to particle deposition in human lung: an overview of activities at the Division of Fluid Mechanics, Luleå University of Technology2007In: SIAMUF: Seminarium Flerfasströmning, Stockholm: Swedish Industrial Association for Multiphase Flows , 2007Conference paper (Other academic)
    Abstract [en]

    Modelling of flow through porous media has been a main research track at the Division of Fluid Mechanics at Luleå University of Technology all since the derivation of Gebart's permeability model in 1992. This model for parallel cylinders has gained great attention and has been extended to flow through perturbed arrays as well as arrays with an arbitrary orientation. Even more, an apparent permeability of an idealized unidirectional reinforcement has been derived for power-law fluid flow perpendicular to the cylinders and the modelling is currently developed for high Reynolds number flow in connection to inner erosion in embankment dams. By usage of Computational Fluid Dynamics (CFD) also more complex structures have been modelled. An example of this is non-crimp fabrics that consists of fibres stitched together in bundles.The two-scale porosity that results is interesting as such but becomes even more fascinating if the impregnating fluid contains particles. It may then happen that the particles are filtrated at the boundaries of the fibre bundles, as visualised by m-PIV, and hence an in-homogenous distribution is obtained. CFD modelling is also introduced for drying of iron ore pellets. In this case heated air is allowed to flow through a bed of green pellets with high water content and the trick is to carry out this procedure without breaking the rather fragile pellets. The flow between the pellets is assumed to be turbulent and it is interesting to know to what extent variations in local flow velocity result in inhomogeneous drying and finally a variation in the properties of the dried and sintered pellets. Work has furthermore been done when dense fibre suspensions are forced to move in pressing of Sheet Moulding Compound. Experimental visualisations yield a complex flow and instead of taking a micromechanical approach inverse modelling is applied with increasing complexity of the rheological model. Recently, a study on the effects upon inhalation of micro- and nano-particles has been launched. A multiply bifurcated asymmetric 3D model, extending from trachea to the segmental bronchi has been developed and initial CFD calculations have been performed. The most critical factor in predicting deposition efficiency is particle size, but flow rate also matters. Information on distribution of deposited particles in every bifurcation unit is provided.

  • 205. Lundström, Staffan
    In-plane permeability measurements1999Conference paper (Other academic)
  • 206. Lundström, Staffan
    Luftinneslutningar vid vätskeströmning genom en armering av fibrer1993In: Svenska mekanikdagar 1993: sammanfattningar av föredrag, Stockholm: Svenska nationalkommittén för mekanik , 1993Conference paper (Other academic)
  • 207. Lundström, Staffan
    Measurement of void collapse during resin transfer moulding1997In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 28, no 3, p. 201-214Article in journal (Refereed)
    Abstract [en]

    This paper considers the dissolution of cylindrical voids trapped between fibres during the resin transfer moulding process. To study the behaviour of the tiny voids, a system is used which consists of a transparent mould loaded with a glass fibre reinforcement. The mould is placed under a microscope and a small area of the preform is monitored during the injection of a vinylester resin. The length of the voids decreases at a relatively fast rate and they disappear in the order of minutes due to diffusion. The experimental results are rationalized through a theory showing how certain parameters influence the rate of dissolution. The investigation shows the significance of degassing the resin before injection. This is especially important when low pressures are utilized during injection.

  • 208. Lundström, Staffan
    Permeabilitet i planet för fibernätver1998Conference paper (Other academic)
  • 209.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability and void formation in RTM1993Licentiate thesis, comprehensive summary (Other academic)
  • 210. Lundström, Staffan
    Permeability of non-crimp stitched fabrics2000In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 31, no 12, p. 1345-1353Article in journal (Refereed)
    Abstract [en]

    Non-crimp stitched fabrics are becoming increasingly popular as reinforcing materials in high-performance composites due to their high mechanical properties. Hence, it is of interest to investigate the processability of this type of fabrics. Focus is here set on the permeability of the fabrics. The methods of this investigation are: (i) a theoretical analysis; (ii) microscopic studies of the geometry of the fabrics and (iii) measurements of the permeability. From the experiments, it is found that only small variations of the geometry change the permeability up to three times. Furthermore, the simple model proposed works surprisingly well in certain cases, while in others it fails to predict the permeability. From the experimental results and a comparison between the model and the experiments, some guidelines are presented how to design a high-permeable fabric.

  • 211. Lundström, Staffan
    Void elimination in the RTM-process1993Conference paper (Other academic)
  • 212.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Void formation and transport in manufacturing of polymer composites1996Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis void formation and removal during the Resin Transfer Moulding process are considered. The problem is examined by doing real moulding as well as mouldings under microscope, model experiment and analytical computations. The materials utilised are in most cases glass fibre reinforcements and vinylester resins. Many of the results are, however, of general character and should be applicable to other material combinations. From micrographs of cured laminates, two types of voids are identified: cylindrically shaped voids within the fibre bundles, and spherically shaped voids between the bundles. It is established that the voids are formed at the resin flow front and that the preform geometry strongly influences both the formation and the transport of the voids. The formed voids move with the resin towards the resin flow front if the pressure gradient is sufficiently high to force the voids through constrictions in the reinforcement. It is shown that the cylindrical voids are more likely trapped in constrictions than the spherical voids. Voids that stay trapped in the reinforcement can, however, escape if their volume is reduced. This is the case if the pressure around the void increases or if the conditions are such that entrapped gas dissolves into the resin. In all injections presented, the voids are concentrated towards the outlet side of the mould. The model experiments, however, indicate that in more coInplicated mould geometries voids may also be located in other areas. These are, for instance, areas where the pressure gradient is low, where the resin flow is poor and where a dry spot has formed. The most efficient way to decrease the void contents is to apply a vacuum on the outlet side of the mould. This decreases the size of the formed voids and make them more mobile. The mould must be air tight and the pressure on the outlet side of the mould must be higher than the boiling pressure of the resin at the processing temperature. In the thesis other methods to eliminate voids are considered such as to degas the resin before the injection, to apply a pressure during cure, to use resins and reinforcements that are compatible, to use reinforcements in which voids are mobile and to continue to fill the mould after complete filling with a high driving pressure. In the thesis, also the influence on the permeability of the detailed fibre geometry is treated. The result is that minor alterations in the geometry greatly change the permeability. Finally, a method which measures the impregnation of fibre bundles is tested.

  • 213. Lundström, Staffan
    Void formation and transport in the RTM process1994In: Moving forward with 50 years of leadership in advanced materials: 39th International SAMPE Symposium and Exhibition / [ed] Ken Drake, Covina, Calif: Society for the Advancement of Material and Process Engineering , 1994Conference paper (Refereed)
  • 214. Lundström, Staffan
    Void formation in RTM: from model experiments to practical results1996Conference paper (Other academic)
  • 215. Lundström, Staffan
    Void movement and dissolution in resin transfer moulding1996In: 1996 First joint topical conference on processing, structure and properties of polymeric materials, New York: American Institute of Chemical Engineers, 1996Conference paper (Refereed)
  • 216. Lundström, Staffan
    Void transport in resin transfer moulding1996In: Conference proceedings: Fourth International Conference on Flow Processes in Composite Materials, FPCM, 9 - 11 September 1996, Prifysgol Cymru, Aberstwyth, the University of Wales. FPCM 4, University College of Wales, 1996Conference paper (Refereed)
  • 217.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Booth, Shirley
    Chalmers University of Technology.
    Journals based on applications: an attempt to improve students' learning about composite materials2000In: Kvalitetskonferens 2000, Högskoleverket , 2000Conference paper (Other academic)
  • 218.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Booth, Shirley A
    Chalmers University of Technology.
    Journals based on applications: an attempt to improve students' learning about composite materials2002In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, Vol. 27, no 2, p. 195-208Article in journal (Refereed)
    Abstract [en]

    In a course on composite materials for fourth-year students at Chalmers University of Technology, students are required to write journals as a complement to the more traditional teaching approach. The journals comprise a series of reports relating the theory currently being treated to an application object, and are sent to the teacher by e-mail for comments. These give the students the opportunity to make use of the theoretical knowledge they meet in each section of the course by reflecting on how it is applicable to a real application. The goal is for better, more integrated understanding, in that, on the one hand, the students should understand the importance of each part of the course and, on the other hand, they should be able to relate the parts to one another, and to practical application. In this paper, we describe the goals and strategies of the change to teaching, we analyse the ways that students approach the journal writing task and we discuss ways in which the journals can improve the quality of student learning.

  • 219. Lundström, Staffan
    et al.
    Christoffe, N.
    Toll, S.
    Compression behaviour of a fibre network with a distribution of fibre size and material1997In: Proceedings of The Polymer Processing Society, Europe/Africa Region Meeting: August 19-21, Gothenburg Sweden, Polymer Processing Society , 1997Conference paper (Refereed)
  • 220.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Jacovics, Andris
    University of Latvia.
    Bubble formation and motion during impregnation of fabrics2009In: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Conference paper (Refereed)
  • 221.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Latvian University.
    Jacovics, Andris
    Latvian University.
    Bubble formation and motion in non-crimp fabrics with perturbed bundle geometry2008In: FPCM-9. The 9th International Conference on Flow Processes in Composite Materials: Montréal (Québec), Canada 8 - 10 July 2008, 2008Conference paper (Refereed)
    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.

  • 222.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Jakovics, Andris
    University of Latvia.
    A statistical approach to permeability of clustered fibre reinforcements2004In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 38, no 13, p. 1137-1149Article in journal (Refereed)
    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.

  • 223.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Jakovics, Andris
    Faculty of Physics and Mathematics, University of Latvia.
    Bubble formation and motion in non-crimp fabrics with perturbed bundle geometry2010In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, no 1, p. 83-92Article in journal (Refereed)
    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.

  • 224.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Jakovics, Andris
    University of Latvia.
    Transport of bubbles in non-crimp fabrics during resin transfer moulding2008In: Proceedings of the XV International Conference on Mechanics of Composites Material, MCM-2008, 2008Conference paper (Other academic)
  • 225. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    An evaluation of the mould filling simulation code TIMS1992Report (Other academic)
  • 226. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Effect of perturbation of fibre architecture on permeability inside fibre flows1995In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 29, no 4, p. 424-443Article in journal (Refereed)
    Abstract [en]

    The influence on the permeability inside fibre tows from fibre packing arrangement and non-uniform fibre diameter is investigated. The analysis mainly consider flow transverse to the fibres and is based on the fibre geometry. Perturbations from perfect quadratic and hexagonal arrangements of fibres at constant fibre volume fraction are considered. The importance of microgeometry on permeability is pointed out and it is indicated how to deal with this problem. The analysis shows that the fibre transverse permeability is strongly dependent on the fibre size distribution. When an arrangement of equally sized fibres is continuously changed from quadratic to hexagonal it is furthermore found that the transverse permeability is highest just before the packing gets hexagonal. The analysis is also applied to a simple FORTRAN code to simulate removal of fibers from a quadratic arrangement. The simulations shows that the transverse permeability decreases with increased number of removed fibres under constant fibre volume fraction.

  • 227. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Influence from process parameters on void formation in resin transfer molding1994In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 15, no 1, p. 25-33Article in journal (Refereed)
    Abstract [en]

    The influence of different process variables on the void content in resin transfer modling (RTM) has been investigated experimentally. The moldings were made in a flat mold filled by a parallel flow from one edge of the laminate to the other. The viods were found concentrated in a narrow region close to the ventilation side of the laminate. The void volume fraction in this region was almost constant and dropped over a short distance to basically no voids in the rest of the laminate. Micrographs from cross sections in different directions revealed that the voids were of two different types, long cylinderical bubbles inside the fiber bundles. An efficient way of reducing the void content was to use vacuum assistance during mold filling. This technique was benefical both for the magnitude of the void content and for the extent of the void region. The void content with the highest level of vacuum assistance (≈ 1 kPa absolute pressure), was practically negligible. Strong indications for void generation by mechanical entrapment at the flow front was found. The lowering of the void content with vacuum assistance can be interpreted as aresult of compression of voids when the vacuum is released and a higher mobility of voids created at a lower pressure.

  • 228.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Void formation in RTM with and without vacuum assistance2002In: Proceedings of the PPS European Regional Meeting, 2002Conference paper (Refereed)
  • 229. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Lundemo, C.Y.
    Void formation in RTM1993In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 12, no 12, p. 1339-1349Article in journal (Refereed)
    Abstract [en]

    The problem of void formation in composites processing is very important since the physical and mechanical properties as well as the finish of the product are strongly influenced by the presence of voids. Examples of properties that are adversely affected by voids are the strength and the weather resistance of the composite. The knowl edge about void formation in the RTM process is still very limited compared to what is known about autoclave production of composites, and it is not clear whether the voids are created by diffusion growth, mechanical entrapment or some other mechanism.

  • 230. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Sandlund, Erik
    In-plane permeability measurements on fibre reinforcements by the parallel flow technique1998In: Proceedings of the 7th International Conference on Fibre Reinforced Composites / FRC '98, Composites: April 15-17, Newcastle upon Tyne, UK / [ed] A. G. Gibson, Luleå: Luleå tekniska universitet, 1998, p. 146-154Conference paper (Refereed)
  • 231. Lundström, Staffan
    et al.
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jekabsons, Normunds
    Laboratory for Mathematical Modeling of Environmental and Technological Processes, Department of Physics and Mathematics, Latvia University, Riga.
    Jakovics, Andris
    Laboratory for Mathematical Modeling of Environmental and Technological Processes, Department of Physics and Mathematics, Latvia University, Riga.
    Wetting dynamics in multiscale porous media: porous pore-doublet model, experiment and theory2008In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 54, no 2, p. 372-380Article in journal (Refereed)
    Abstract [en]

    Fiber reinforced composite materials often consist of fibers gathered in bundles. Thus, during manufacturing, a liquid resin impregnates a multiscale porous medium. For wetting systems the capillary pressure jump becomes much higher in the smaller pores, i.e., within the bundles, and in addition to any applied pressure gradient there will be a local driving pressure gradient between the small- and large-scale areas. Such gradients will influence mechanisms, such as void formation and particle filtration. Hence, it is of interest to clarify the mechanisms for the wetting in general and the influence from the detailed geometry of the fiber network in particular. In this article, a porous pore-doublet model is studied in order to determine if an overflow of liquid can explain a leading flow in the smaller capillaries, and at which conditions it takes place. Experiments, as well as theoretical calculations on this generic geometry show that the leading front can be in the smaller capillary, as well as in the larger one. The outcome is dependent on the actual permeability of the porous material being a parameter that determines to what extent the larger capillary feeds the smaller one.

  • 232.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Lindmark, Elianne
    Flow design of guiding device for downstream fish migration2010In: Rivers Research and Applications: an international journal devoted to river research and management, ISSN 1535-1459, E-ISSN 1535-1467, Vol. 26, no 2, p. 166-182Article in journal (Refereed)
    Abstract [en]

    Downstream migrating smolt must be guided around hydropower plants to avoid fish mortality due to the turbines. In Piteå River, which is already regulated, open spillways serve this purpose but few fish find this route. Hence, action must be taken to enhance downstream fish migration. One way to attract the fish to the spillways is to direct the surface flow towards them by means of a guiding device. The hydrodynamic design of one such device is outlined using numerical calculations of the flow upstream the spillways and by the assumption that the fish moves near the surface of the water. A number of geometries are evaluated by starting from a straight impermeable barrier that extends 2 m down from the water surface and stretches over a part of the river. A major result is that it is possible to redirect the surface water towards the spillways at very low spilling rates which means high energy efficiency. Another finding was that the device should stretch over a large part of the river. For optimal functionality, the spilling should match the guiding device geometry. High spilling implies that the guiding has a low impact while for low spilling the geometry is crucial for successful downstream migration.

  • 233.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Holmgren, Allan
    Dissolution of gas into liquid resins during compression moulding2008In: 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 , 2008Conference paper (Refereed)
    Abstract [en]

    During compression moulding of sheet moulding compounds air bubbles are formed that can deteriorate several properties of the final composite. The story of such bubbles is directly set by the local pressure distribution during pressing. This pressure can be found from experiments or numerical simulations but it is however also necessarily to derive criteria for the motion of the bubbles as well as relationships for the dissolution rate of the gas enclosed in the bubbles. In order to full-fill the latter a number of experiments have been performed. The results follow neatly Henry's law up to a pressure of 6 bar and the rate of dissolution is very much dependent of the type of gas studied. When applying the results to the process in focus it is found that even very large bubbles can be dissolved into the liquid resin during manufacturing.

  • 234.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Holmgren, Allan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Dissolution of voids during compression moulding of SMC2010In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 29, no 12, p. 1826-1837Article in journal (Refereed)
    Abstract [en]

    During compression molding of sheet molding compounds air bubbles are formed that can deteriorate several properties of the final composite. The story of such bubbles is directly set by the local pressure distribution during pressing. A number of experiments have therefore been performed in order to derive the relation between the pressure and dissolution rate of some gases into relevant resins. The experimental results follow Henry's law up to a pressure of 0.7 MPa and the rate of dissolution is highest for CO2 in pure polyester. When applying the results to the process in focus it is found that even large bubbles can be dissolved into the liquid resin during manufacturing. Hence, there is a potential to produce parts with very low void content.

  • 235.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Högberg, Sofie
    Simulation of nanoparticle flow and deposition inthe human respiratory airways using CFD2006In: 2nd International Symposium Nanostructured and Functional Polymer-based Materials and Composites: Lyon, May 29 - 31,2006, Impact press, 2006Conference paper (Refereed)
  • 236.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nordlund, Markus
    Investigation of transient flow behaviour in dual-scale porous media with micro particle image velocimetry2006In: Proceedings, 4th International Scientific Colloquium Modelling for Material Processing, 2006, p. 117-122Conference paper (Refereed)
    Abstract [en]

    Injection processing of composite materials most often includes infiltration of a thermoset resin into a multi-scale porous fabric. Controlling the fluid flow within the multiscale fabric is essential for the quality of the final composite material, since the transport of fluid between regions with different scales plays an important role in phenomena such as void formation and filtration of particle doped resins. In this work, the transient flow behaviour in dual scale porous media is investigated with Micro Particle Image Velocimetry in order to enhance the knowledge and control of the processing of multi-scale composites so that their quality can be improved. Experiments show that the fluid transport between the two scales can be controlled by the injection velocity. Validation of the measured velocity fields furthermore shows excellent agreement with theory.

  • 237.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nordlund, Markus
    Numerical calculations of the permeability of non-crimp fabrics2003In: ICCM-14: 14th International Conference on Composite Materials : July 14-18, 2003, San Diego, California, USA, Dearborn, Mich: Arctic Monitoring and Assessment Programme, 2003Conference paper (Refereed)
  • 238. Lundström, Staffan
    et al.
    Sandlund, E.
    Permeability and Compression of RTM Reinforcements1997In: Composites and sandwich structures: Proceedings of the Second North European Engineering and Science Conference NESCO II / [ed] Jan Bäcklund; Dan Zenkert; B.T. Åström, Cradley Heath: EMAS , 1997, p. 317-330Conference paper (Refereed)
  • 239. Lundström, Staffan
    et al.
    Stenberg, R.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Gasbubblors blockering av strömning i kapillärrör1995In: Svenska mekanikdagar 1995: Lund 31 maj-2 juni : [sammanfattning av föredrag], Stockholm: Svenska nationalkommittén för mekanik , 1995Conference paper (Other academic)
  • 240. Lundström, Staffan
    et al.
    Stenberg, R.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Bergström, R.
    Ahlström Glassfibre OY.
    Partanen, H.
    Ahlström Glassfibre OY.
    Birkeland, P. A.
    Devold AMT, Langevåg.
    In-plane permeability measurements: a Nordic round-robin study2000In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 31, no 1, p. 29-43Article in journal (Refereed)
    Abstract [en]

    Three methods to measure the in-plane permeability are compared. The methods are based on the wetting and saturated parallel flow techniques and the wetting radial flow technique. It is found that the stability of all three methods is very good. The best repeatability in the results is obtained with the wetting parallel flow technique. A main drawback of this method is, however, that the samples are not saturated hence, the saturated parallel flow method is suggested for continued evaluation. The standard deviation from repeatable measurements of this method is 14 and 20% for the two fabrics tested. By a round-robin comparison at three laboratories it is found that the reproducibility of the saturated parallel flow technique is in the same range as the repeatability of the method. Furthermore, it is shown that the liquid tested and the pressure applied have very small influence on the results. It is clear that most of the scatter is due to the sample preparation and variations in the material. Accordingly, a continued work should be concentrated on improvements of the sample preparation, and development of methods to reduce the influence, from small errors, in sample preparation on the results.

  • 241. Lundström, Staffan
    et al.
    Stenberg, R.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Bergström, R.
    Partanen, H.
    Birkeland, PA
    In-plane permeability measurements: stability, repeatability and reproducibility1999In: ICCM-12 Europe: 12th International Conference on Composite Materials ; Palais des Congrès, Paris [July 5th - 9th] 1999 / [ed] Thierry Massard, Tours: ICCM , 1999Conference paper (Refereed)
  • 242. Lundström, Staffan
    et al.
    Strömbeck, L.A.
    RTM för alla1997In: Plastforum (1992), ISSN 1104-1501, no 3, p. 70-71Article in journal (Other (popular science, discussion, etc.))
  • 243.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sundlöf, Henrik
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Holmberg, J. Anders
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Modeling of power-law fluid flow through fiber beds2006In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 40, no 3, p. 283-296Article in journal (Refereed)
    Abstract [en]

    An apparent permeability of an idealized unidirectional reinforcement is derived for power-law fluid flow perpendicular to the fibers. The reinforcement consists of regularly ordered, parallel fibers arranged in a quadratic or hexagonal pattern. The expression is obtained starting from first principles for low Reynolds number, incompressible and isothermal flow and is expressed in terms of the radius of the fibers, the fiber volume fraction, and the power-law index. The model is successfully verified with computational fluid dynamic simulations.

  • 244.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Toll, S.
    Chalmers University of Technology.
    Modelling of residual stresses and warpage in sandwich injection moulding2003In: International polymer processing, ISSN 0930-777X, E-ISSN 2195-8602, Vol. 18, no 1, p. 95-106Article in journal (Refereed)
    Abstract [en]

    Sandwich injection moulding offers the possibility of combining materials with different properties and, for instance, hide a recycled constituent within a virgin ditto. This attractive potential puts great demands on the manufacturing and therefore also on the process modelling. In particular the effect on the final stress state and the deformation of the part due to the heterogeneity of the material must be clarified. This topic is addressed in this study. To start with it is confirmed that expressions for the temperature field can be much simplified without major loss of accuracy in the solution. This enables us to take an analytical approach to the modelling and the resulting equations can be solved on a spread-sheet or with a simple code. It is also shown that the derived models compare well to experiments made with a two-layered structure, indicating that the models presented can be used to estimate changes of processing conditions or material properties for sandwich structures.

  • 245.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Toll, S.
    Chalmers University of Technology.
    Håkansson, J.M.
    Chalmers University of Technology.
    Measurement of the permeability tensor of compressed fibre beds2002In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 47, no 3, p. 363-380Article in journal (Refereed)
    Abstract [en]

    A new method to measure the permeability tensor of highly compressed fibre beds is developed. The method is based on saturated parallel flow and is evaluated through experiments with various textile materials: press fabrics used in papermaking and fibre reinforcements designed for composites. Since the materials are in the form of sheets, two measuring cells are used, one for the principal in-plane permeabilities and the other for the out-of-plane permeability. A unique feature is that the edge and the bulk flow are measured separately, so that any influence from enhanced or suppressed edge flow may be eliminated. The technique is evaluated with good results in terms of scatter in the measured permeability and the influence of test geometry, pressure, and liquid properties.

  • 246. Lundström, Staffan
    et al.
    Zetterberg, M.
    In-plane permeability of non-crimp-stitched fabrics1998Conference paper (Other academic)
  • 247. Lundström, Staffan
    et al.
    Zetterberg, M.
    Modelling of the permeability of non-crimp-stitched fabrics1999In: Proceedings of the Fifth International Conference on Flow Processes in Composite Materials, FPCM-5: Robbins Centre, University of Plymouth, 12-14 July 1999 / Advanced Composites Manufacturing Centre, Department of Mechanical and Marine Engineering, Plymouth: University of Plymouth Press, 1999Conference paper (Refereed)
  • 248.
    Lundström, T. Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Modeling filtration of particulate flow during impregnation of dual-scale fabrics2013In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 47, no 15, p. 1907-1915Article in journal (Refereed)
    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

  • 249.
    Lundström, T. Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Transversal flow-induced deformation of fibres during composites manufacturing and the effect on permeability2013In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 32, no 15, p. 1129-1135Article in journal (Refereed)
    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.

  • 250.
    Lundström, T. Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Rahkola, Mattias Brynjell
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Green, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Evaluation of Guiding Device for Downstream Fish Migration with In-field Particle Tracking Velocimetry and CFD2015In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 8, no 3, p. 579-589Article in journal (Refereed)
    Abstract [en]

    The performance of a fish guiding device located just upstream a hydropower plant is scrutinized. The device is designed to redirect surface orientated down-stream migrating fish (smolts) away from the turbines towards a spillway that act as a relatively safe fishway. Particles are added up-stream the device and the fraction particles going to the spillway is measured. A two-frame Particle Tracking Velocimetry algorithm is used to derive the velocity field of the water. The experimental results are compared to simulations with CFD. If the smolts move passively as the particles used in the study the guiding device works very well and some modifications may optimize its performance. In-field Particle Tracking Velocimetry is a suitable technique for the current case and the results compare well with numerical simulations.

234567 201 - 250 of 327
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