| 1. |
- Andersson, Anders G., et al.
(author)
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Simulation of free surface flow in a spillway with the rigid lid and volume of fluid methods and validation in a scale model
- 2010
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In: Proceedings, Fifth European Conference on Computational Fluid Dynamics. - 9789899677814
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Conference paper (peer-reviewed)abstract
- Simulations on the spilling from a dam were performed and compared to experimental results from a physical scale model. Both mechanical and acoustic methods to measure the velocity were used. The model has three gates leading into the spillway that can be maneuvered separately. At first two of the gates were closed and the inlet flow was high enough to get a fully wetted outlet at the third gate. This case was simulated with a rigid lid approximation since the water surface was considered to be plane. The water surface level was taken from the scale model. In the second case, all three gates were open resulting in a free water surface through all the gates to the spillway. This case was simulated with the Volume of Fluids method were both water and air phase were considered. Water levels, velocities and the shape of the water surface were compared between simulations and experiments. The simulations capture both qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments.
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| 2. |
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| 3. |
- Håkanson, J. M., et al.
(author)
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Liquid permeability of an anisotropic fiber web
- 2005
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In: Textile research journal. - : SAGE Publications. - 0040-5175 .- 1746-7748. ; 75:4, s. 304-311
-
Journal article (peer-reviewed)abstract
- The Darcian permeability of a dense network of fibers with general orientation is examined experimentally and analytically. The permeability of a carded PA6 fiber web is measured in the three principal directions using a saturated parallel flow technique. A model is introduced that generalizes existing theories for unidirectional fiber arrays to fiber networks of general orientation distribution. The average drag on a given fiber is assumed to be independent of the overall fiber orientation distribution. A second-order orientation tensor describes the orientation dependence. Our generalization applied to the models of Gebart predicts reasonably well the in-plane permeability, but overestimates the out-of-plane permeability by a factor of four.
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| 4. |
- Håkansson, Johan, 1974, et al.
(author)
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Permeability of felts
- 2000
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In: Proc. Nordic Meeting on Materials and Mechanics, Aalborg 2000.
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Conference paper (peer-reviewed)
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| 5. |
- Håkansson, Johan, 1974, et al.
(author)
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Permeability of felts: Modelling
- 2000
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In: Annual Meeting of the AIChE Los Angeles, CA, November 12-17, 2000.
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Conference paper (peer-reviewed)
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| 6. |
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| 7. |
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| 8. |
- Lundström, Staffan, et al.
(author)
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Measurement of the permeability tensor of compressed fibre beds
- 2002
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In: Transport in Porous Media. - 0169-3913 .- 1573-1634. ; 47:3, s. 363-380
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
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| 10. |
- Lundström, Staffan, et al.
(author)
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Modelling of residual stresses and warpage in sandwich injection moulding
- 2003
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In: International polymer processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 18:1, s. 95-106
-
Journal article (peer-reviewed)abstract
- 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.
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| 11. |
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| 12. |
- Thålin, Charlotte, et al.
(author)
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Citrullinated histone H3 as a novel prognostic blood marker in patients with advanced cancer
- 2018
-
In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 13:1
-
Journal article (peer-reviewed)abstract
- Citrullinated histone H3 (H3Cit) is a central player in the neutrophil release of nuclear chromatin, known as neutrophil extracellular traps (NETs). NETs have been shown to elicit harmful effects on the host, and were recently proposed to promote tumor progression and spread. Here we report significant elevations of plasma H3Cit in patients with advanced cancer compared with age-matched healthy individuals. These elevations were specific to cancer patients as no increase was observed in severely ill and hospitalized patients with a higher non-malignant comorbidity. The analysis of neutrophils from cancer patients showed a higher proportion of neutrophils positive for intracellular H3Cit compared to severely ill patients. Moreover, the presence of plasma H3Cit in cancer patients strongly correlated with neutrophil activation markers neutrophil elastase (NE) and myeloperoxidase (MPO), and the inflammatory cytokines interleukin-6 and -8, known to induce NETosis. In addition, we show that high levels of circulating H3Cit strongly predicted poor clinical outcome in our cohort of cancer patients with a 2-fold increased risk for short-term mortality. Our results also corroborate the association of NE, interleukin-6 and -8 with poor clinical outcome. Taken together, our results are the first to unveil H3Cit as a potential diagnostic and prognostic blood marker associated with an exacerbated inflammatory response in patients with advanced cancer.
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| 13. |
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| 14. |
- Aitomäki, Yvonne, et al.
(author)
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Vacuum infusion of cellulose nanofibre network composites : Influence of porosity on permeability and impregnation
- 2016
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In: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 95, s. 204-211
-
Journal article (peer-reviewed)abstract
- Addressing issues around the processing of cellulose nanofibres (CNF) composites is important in establishing their use as sustainable, renewable polymer reinforcements. Here, CNF networks of different porosity were made with the aim of increasing their permeability and suitability for processing by vacuum infusion (VI). The CNF networks were infused with epoxy using two different strategies. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated. Calculated fill-times for CNF networks with 50% porosity were the shortest, but are only less than the gel-time of the epoxy if capillary effects are included. In experiments the CNF networks were clearly wetted. However low transparency indicated that impregnation was incomplete. The modulus and strength of the dry CNF networks increased rapidly with decreasing porosity, but their nanocomposites did not follow this trend, showing instead similar mechanical properties to each other. The results demonstrated that increasing the porosity of the CNF networks to ≈ 50% gives better impregnation resulting in a lower ultimate strength, a higher yield strength and no loss in modulus. Better use of the flow channels in the inherently layered CNF networks could potentially reduce void content in these nanocomposites and thus increase their mechanical properties.
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| 15. |
- Aitomäki, Yvonne, et al.
(author)
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Vacuum Infusion of Nanocellulose Networks of Different Porosity
- 2015
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In: 20th International Conference on Composite Materials. - : ICCM.
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Conference paper (peer-reviewed)abstract
- Cellulose nanofibres (CNF) have shown good potential as sustainable, biobased reinforcing materials in polymer composites. Addressing issues around the processing of these composites is an important part of establishing their use in different applications. Here, CNF networks of different porosity are made from nanofibrillated hardwood kraft pulp with the aim of increasing the impregnation of the CNF networks and to allow vacuum infusion to be used. Two different vacuum infusion strategies: in-plane and out of plane were used to infuse the CNF networks with a low viscosity epoxy. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated and compared to a micro-fibre based network. Using the out-of-plane permeability measurements and Darcy’s law, the fill-time was calculated and showed that the CNF network with 40% porosity had the lowest fill-time when an out-of-plane impregnation strategy is used. However this exceeded the gel-time of the epoxy system. In experiments, the resin reached the other side of the network but low transparency indicated that wetting was poor. The dry CNF preforms showed a very strong dependence on the porosity with both modulus and strength increasing rapidly at low porosity. Interestingly, the composite based on the 60% porosity network showed good wetting particularly with the in-plane infusion strategy, exhibiting a much more brittle fracture and a high yield strength. This shows that in CNF composites produced by VI, lowering the fibre volume content of the CNF composites gives better impregnation resulting in a lower ultimate strength but higher yield strength and no loss in modulus.
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| 16. |
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| 17. |
- Alfredsson, Magnus, et al.
(author)
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Funktionskriterier för vägkonstruktioner : Förstudie
- 2010
-
Reports (other academic/artistic)abstract
- Det projekt som här rapporteras har som syfte att identifiera och beskriva de svårigheter och möjligheter som totalentreprenader medför, respektive erbjuder, för alla parter. Målet är att utveckla totalentreprenader på ett sådant sätt att branschens effektivitet ökas. Denna rapport är en förstudie där det studerats vilka krav som byggherren ska ställa på utföraren av en vägkonstruktion i en totalentreprenad med funktionsansvar och hur utföraren ska verifiera kraven. Arbetet har genomförts med medlemmar från olika aktörer i branschen och omfattat främst litteraturstudier och intervjuer. Kunskaper och erfarenheter har sammanställts och analyserats för att slutligen kondenseras ned till ett antal förslag till fortsatt arbete.Förstudien har pekat ut ett antal områden som viktiga för att påskynda framtida utveckling av totalentreprenader:Terminologi – idag råder viss begreppsförvirringAnalys av funktionella krav i tidigare projektTrafikantkravMiljökravUtveckling av funktionella krav i samverkanVäghållarekonomiRegelbetingade begränsningar av funktionella kravUppföljning och underlättande av erfarenhetsackumuleringImplementering av nya mått och mätmetoder
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| 18. |
- Almqvist, Andreas, et al.
(author)
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Flow in thin domains with a microstructure : Lubrication and thin porous media
- 2017
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In: AIP Conference Proceedings. - : AIP Publishing. - 0094-243X .- 1551-7616. ; 1798
-
Journal article (peer-reviewed)abstract
- This paper is devoted to homogenization of different models of flow in thin domains with a microstructure. The focus is on applications connected to the effect of surface roughness in full film lubrication, but a parallel to flow in thin porous media is also discussed. Mathematical models of such flows naturally include two small parameters. One is connected to the fluid film thickness and the other to the microstructure. The corresponding asymptotic analysis is a delicate problem, since the result depends on how fast the two small parameters tend to zero relative to each other. We give a review of the current status in this area and point out some future challenges.
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| 19. |
- Alnersson, Gustaf, et al.
(author)
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3D-flow and and fibre orientation modelling for compression moulding of SMC
-
Other publication (other academic/artistic)abstract
- Two different numerical models for compression moulding of Sheet Moulding Compound are discussed and compared, with one being a more traditional flow model implemented in the 3DTimon commercial software, and the other being a more advanced flow model implemented in more general fluid dynamics software. The focus will be on comparing the resulting fibre orientations.
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| 20. |
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| 21. |
- Alnersson, Gustaf, et al.
(author)
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3D flow and fibre orientation modelling of compression moulding of A-SMC: simulations and experimental validation in squeeze flow
- 2023
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In: Functional Composite Materials. - : Springer Nature. - 2522-5774. ; 4
-
Journal article (peer-reviewed)abstract
- Sheet Moulding Compound (SMC) based composites have a large potential in industrial contexts due to the possibility of achieving comparatively short manufacturing times. It is however necessary to be able to numerically predict both mechanical properties as well as manufacturability of parts.In this paper a fully 3D, semi-empirical model based on fluid mechanics for the compression moulding of SMC is described and discussed, in which the fibres and the resin are modelled as a single, inseparable fluid with a viscosity that depends on volume fraction of fibres, shear strain rate and temperature. This model is applied to an advanced carbon-fibre SMC with a high fibre volume fraction (35%). Simulations are run on a model of a squeeze test rig, allowing comparison to experimental results from such a rig. The flow data generated by this model is then used as input for an Advani-Tucker type of model for the evolution of the fibre orientation during the pressing process. Numerical results are also obtained from the software 3DTimon. The resulting fibre orientation distributions are then compared to experimental results that are obtained from microscopy. The experimental measurement of the orientation tensors is performed using the Method of Ellipses. A new, automated, accurate and fast method for the ellipse fitting is developed using machine learning. For the studied case, comparison between the experimental results and numerical methods indicate that 3D Timon better captures the random orientation at the outer edges of the circular disc, while 3D CFD show larger agreement in terms of the out-of-plane component. One of the advantages of the new image technique is that less work is required to obtain microscope images with a quality good enough for the analysis.
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| 22. |
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| 23. |
- Alnersson, Gustaf, et al.
(author)
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Numerical Study of the 3D-Flow Characteristics During Compression Moulding of SMC
- 2019
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In: Proceedings of the 2019 International Conference on Composite Materials. - : RMIT University. ; , s. 1571-1581
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Conference paper (other academic/artistic)abstract
- A numerical model for compression moulding of Sheet Moulding Compound is presented. The model is based on fluid mechanics and the SMC charge is modelled as a fluid with a viscosity that is dependent on the charge temperature, the fibre volume fraction of the material and the shear strain rate. Trends observed in the simulations regarding the shape of the flow front agree with experimental observations in previous studies. The simulations also yield that the type and magnitude of initial heating effects the initial flow to a large extent.
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| 24. |
- Alnersson, Gustaf, et al.
(author)
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Review of the Numerical Modeling of Compression Molding of Sheet Molding Compound
- 2020
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In: Processes. - : MDPI. - 2227-9717. ; 8:2
-
Research review (peer-reviewed)abstract
- A review of the numerical modeling of the compression molding of the sheet molding compound (SMC) is presented. The focus of this review is the practical difficulties of modeling cases with high fiber content, an area in which there is relatively little documented work. In these cases, the prediction of the flows become intricate due to several reasons, mainly the complex rheology of the compound and large temperature gradients, but also the orientation of fibers and the micromechanics of the interactions between the fluid and the fibers play major roles. The details of this during moldings are discussed. Special attention is given to the impact on viscosity from the high fiber volume fraction, and the various models for this. One additional area of interest is the modeling of the fiber orientation.
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| 25. |
- Alnersson, Gustaf
(author)
-
Towards 3D modelling of Compression Moulding of SMC
- 2021
-
Licentiate thesis (other academic/artistic)abstract
- The automotive industry is facing ever increasing demands for reduced emissions, and lightweight solutions are thusly required. One field that has significant potential in this regard is composite materials, which can offer a good combination of weight reduction and mechanical properties. However, the rapid development cycles in the automotive industry mean that tools for numerical modeling are necessary, both regarding manufacturing processes and prediction of mechanical properties. The material that has been of interest for this work is Sheet Moulding Compound (SMC). SMC consists of sheets of resin and chopped fibres. When used for manufacturing the sheets are cut into appropriate size and shape. The cut sheets are then placed in a pre-heated mould. When this mould is closed, the sheets melt and the fibre-filled resin flows out and fills the mould cavity; the resin then cures and solidifies. A significant advantage of SMC compared to other composite solutions is that the process has comparatively short cycle times, which is a necessity for automotive applications. However, it is a rather complicated process to model numerically for a number of reasons, including the complex rheological properties of the charge, the often rather significant temperature gradients throughout the thickness, often complicated three-dimensional effects in the flow, and the chopped fibres present in the charge. These fibres will move and change orientation as the charge is pressed, which is a significant challenge to model properly.The first part of this work is a review and discussion of the difficulties described above, and some solutions that have been suggested. The second part concerns a suggestion for a three-dimensional flow model for the compression moulding process, which takes into account factors that have been suggested to influence the flow behavior, such as temperature distribution and shear strain rate. Some simulation results are presented along with comparison to previous experimental results, and similar flow patterns are observed serving as a qualitative validation. The third part concerns the expansion of this model to include the effects of the flow on the fibre orientation.
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| 26. |
- Altorkmany, Lobna, et al.
(author)
-
Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems
- 2018
-
In: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 141, s. 435-443
-
Journal article (peer-reviewed)abstract
- The objective of the current study is to analyze the effect of different working parameters on the thermal performance of the Anti-Bact Heat Exchanger system (ABHE). The ABHE system is inspired by nature and implemented to achieve continuous disinfection of Legionella in different human-made water systems at any desired disinfection temperature. In the ABHE system, most of the energy is recovered using an efficient plate heat exchanger (PHE). A model by Engineering Equation Solver (EES) is set-up to figure out the effect of different working parameters on the thermal performance of the ABHE system. The study shows that higher supplied water temperature can enhance the regeneration ratio (RR), but it requires a large PHE area and pumping power (PP) which consequently increase the cost of the ABHE system. However, elevate temperature in use results in a reduced PHE area and PP, which accordingly reduce the cost of the ABHE system. On the other hand, the EES-based model is used to study the effect of the length and the width of the plates used in the PHE on the RR and the required area of the PHE. Finally, taking into account the geometrical parameters, flow arrangement and the initial operating conditions of the PHE, the EES-based model is used to optimize the PHE in which its area is minimized, and the RR of the ABHE system is maximized.
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| 27. |
- Altorkmany, Lobna, et al.
(author)
-
Experimental and Simulation Validation of ABHE for Disinfection of Legionella in Hot Water Systems
- 2017
-
In: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 116, s. 253-265
-
Journal article (peer-reviewed)abstract
- The work refers to an innovative system inspired by nature that mimics the thermoregulation system that exists in animals. This method, which is called Anti Bacteria Heat Exchanger (ABHE), is proposed to achieve continuous thermal disinfection of bacteria in hot water systems with high energy efficiency. In particular, this study aims to demonstrate the opportunity to gain energy by means of recovering heat over a plate heat exchanger. Firstly, the thermodynamics of the ABHE is clarified to define the ABHE specification. Secondly, a first prototype of an ABHE is built with a specific configuration based on simplicity regarding design and construction. Thirdly, an experimental test is carried out. Finally, a computer model is built to simulate the ABHE system and the experimental data is used to validate the model. The experimental results indicate that the performance of the ABHE system is strongly dependent on the flow rate, while the supplied temperature has less effect. Experimental and simulation data show a large potential for saving energy of this thermal disinfection method by recovering heat. To exemplify, when supplying water at a flow rate of 5 kg/min and at a temperature of 50 °C, the heat recovery is about 1.5 kW while the required pumping power is 1 W. This means that the pressure drop is very small compared to the energy recovered and consequently high saving in total cost is promising.
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| 28. |
- Andersson, Anders, et al.
(author)
-
Describing fish passage in a river confluence with telemetry and CFD
- 2016
-
Conference paper (peer-reviewed)abstract
- The confluence between hydropower tailrace and the old river bed in Stornorrfors in the river Umeälven in the northern part of Sweden has shown to be the largest obstacle for upstream migrating salmon and sea trout during the migrating season. Fish are attracted to the high flow rate from the tailrace and will not migrate upstream in the old river bed being the passage to the fishway leading past the hydropower dam. By triangulating the movements of radio tagged fish using eight antennas in the confluence, it is here possible to describe the individual fish tracks left by radio tagged fish during the migrating season. These tracks are then compared with three-dimensional Computational Fluid Dynamics (CFD) simulations of the confluence. By simulating the most common combinations of turbine flow and spill flow in the old river bed it is then possible to find correlations between individual fish movements and flow parameters such as velocity, turbulence intensity or vorticity for different flow combinations. It was previously assumed that fish had trouble locating the old river bed, the results of the triangulation however shows that most fish finds the old river bed within a few days but does not chose to migrate until several days (or weeks) later. The main issue to be solved is therefore not how to attract the fish to the old river bed but rather how to create favorable conditions in the old river bed so that migrating fish are more inclined to take that path upstream.
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| 29. |
- Andersson, Anders G., et al.
(author)
-
A numerical study of the location and function of the entrance of a fishway in a regulated river
- 2010
-
In: 8th International Symposium on ECOHYDRAULICS. ; , s. 277-284
-
Conference paper (peer-reviewed)abstract
- Simulation driven design with Computational Fluid Dynamics has been used to evaluate the flow downstream a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed and the measurements were used to validate the simulations. The measurements indicate a more unstable flow than the simulations and the tailrace jet from the turbines is stronger in the simulations. The simulations are however considered to capture the important features of the flow in a way that makes them viable for attraction water simulations. A fishway entrance was included in the simulations and the subsequent attraction water was evaluated for two positions and two angles of the entrance at different turbine discharges. Results show that both positions are viable and that a position where the flow from the fishway does not have to compete with the flow from the power plant will generate superior attraction water. Simulations were also performed further downstream where the flow from the turbines meets the old river bed which is the current fish passage for upstream migrating fish. A modification of the old river bed was made in the model as one scenario to generate better attraction water. This considerably increases the attraction water although it cannot compete with the flow from the tailrace tunnel.
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| 30. |
- Andersson, Anders G., et al.
(author)
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A study of the location of the entrance of a fishway in a regulated river with CFD and ADCP
- 2012
-
In: Modelling and Simulation in Engineering. - : Hindawi Limited. - 1687-5591 .- 1687-5605. ; 2012
-
Journal article (peer-reviewed)abstract
- Simulation-driven design with computational fluid dynamics has been used to evaluate the flow downstream of a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed, and the measurements were used to validate the simulations. The measurements indicate a more unstable flow than the simulations, and the tailrace jet from the turbines is stronger in the simulations. A fishway entrance was included in the simulations, and the subsequent attraction water was evaluated for two positions and two angles of the entrance at different turbine discharges. Results show that both positions are viable and that a position where the flow from the fishway does not have to compete with the flow from the power plant will generate superior attraction water. Simulations were also performed for further downstream where the flow from the turbines meets the old river bed which is the current fish passage for upstream migrating fish. A modification of the old river bed was made in the model as one scenario to generate better attraction water. This considerably increases the attraction water although it cannot compete with the flow from the tailrace tunnel.
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| 31. |
- Andersson, Anders G., et al.
(author)
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CFD-modell av turbinutloppet i Stornorrfors
- 2009
-
In: Svenska mekanikdagarna. - Stockholm : Svenska nationalkommittén för mekanik. ; , s. 106-
-
Conference paper (other academic/artistic)
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| 32. |
- Andersson, Anders G., et al.
(author)
-
CFD-modelling and validation of free surface flow during spilling of reservoir in down-scale model
- 2013
-
In: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 7:1, s. 159-167
-
Journal article (peer-reviewed)abstract
- Fully three dimensional modelling of the spilling from a reservoir with relatively complex geometry were performed and compared to experimental results from a physical scale model with the aim to advance the science of numerical modelling of free surface flow of real reservoirs. In the set-up in focus the water was spilled from the reservoir through three gates that could be manoeuvred separately. In the first case two of the gates were closed and the third gate was partly opened. In this experimental set-up the water surface in the reservoir was close to horizontal. Therefore it was here meaningful to compare a rigid lid modelling approximation to the more computational heavy method of Volume of Fluids. In the second case, all three gates were open, resulting in a nonhorizontal varied flow surface profile in the reservoir upstream critical sections at the spillway crests. This case was simulated with Volume of Fluids and the position of the air-water interface was derived for two turbulence models, the standard k-ε and SSG. Water levels, velocities and the shape of the water surface were compared to experiments. The simulation results capture qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments regardless of method used to simulate the free surface. In general, simulations with the standard k-ε and the more advanced SSG turbulence models give the same results with respect to the averaged quantities measured.
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| 33. |
- Andersson, Anders G., et al.
(author)
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Effect of spatial resolution of rough surfaces on numerically computed flow fields with application to hydraulic engineering
- 2014
-
In: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 8:3, s. 373-381
-
Journal article (peer-reviewed)abstract
- In numerical simulations of flow over rough surfaces, the roughness is often not resolved but represented by a numerical model. The validity of such an assumption is investigated in this paper by Reynolds-Averaged Navier-Stokes simulations of flow over a surface with a large roughness. The surface was created from a high-resolution laser scanning of a real rock blasted tunnel. By reducing the geometrical resolution of the roughness in two steps, the importance of an appropriate surface description could be examined. The flow fields obtained were compared to a set-up with a geometrical flat surface where the roughness was represented by a modified form of the Launder and Spalding wall-function. The flow field over the surface with the lowest resolution was substantially different from those of the two finer resolutions and rather close to the results from the set-up with the wall-function. The results also yield that the finer the resolution is the more vorticity is formed close to the rough surface and more turbulence is generated.
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| 34. |
- Andersson, Anders G., et al.
(author)
-
Flow through a two-scale porosity material
- 2009
-
In: Research Letters in Materials Science. - : Hindawi Limited. - 1687-6822 .- 1687-6830.
-
Journal article (other academic/artistic)abstract
- Flow through a two-scale porous medium is here investigated by a unique comparison between simulations performed with computational fluid dynamics and the boundary element method with microparticle image velocimetry in model geometries.
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| 35. |
- Andersson, Anders G., et al.
(author)
-
Fluid flow through porous media with dual scale porosity
- 2008
-
In: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19). - : University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science.
-
Conference paper (peer-reviewed)abstract
- Flow in two scale porous media takes place in applications such as advanced composites manufacturing. Knowledge of this flow is of general importance and is crucial for filtration mechanisms when functional filler-particles are added to the liquid resin impregnating the fibrous preform. Means to model and experimentally visualise this flow is here investigated. In particular simulations performed with computational fluid dynamics and the boundary element method are compared to micro particle image velocimetry in a model geometry.
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| 36. |
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| 37. |
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| 38. |
- Andersson, H.M., et al.
(author)
-
Application of digital speckle photography to measure thickness variations in the vacuum infusion process
- 2003
-
In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 24:3, s. 448-455
-
Journal article (peer-reviewed)abstract
- A new method to measure the movement of the flexible bag used in vacuum infusion is presented. The method is based on an in-house developed stereoscopic digital speckle photography system (DSP). The advantage with this optical method, which is based on cross-correlation, is that the deflection of a large area can be continuously measured with a great accuracy (down to 10 μm. The method is at this stage most suited for research but can in the long run also be adopted in production control and optimization. By use of the method it was confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. The existence of the ditch demonstrates that the stiffness of the reinforcement can be considerably reduced when it is wetted. Hence, the maximum fiber volume fraction can be larger than predicted from dry measurements of preform elasticity. It is likely that the overall thickness reduction after complete filling emanates from lubrication of the fibers combined with an outflow of the resin. Besides, the cross-linking starts and the polymer shrinks. Hence, the alteration in height will continue until complete cross-linking is reached.
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| 39. |
- Andersson, L. Robin, et al.
(author)
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Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations
- 2018
-
In: Engineering. - : Scientific Research Publishing. - 1947-3931 .- 1947-394X. ; 10, s. 399-416
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Journal article (peer-reviewed)abstract
- High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.
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| 40. |
- Andersson, Magnus, et al.
(author)
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Computational fluid dynamics applied to the vacuum infusion process
- 2005
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In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 26:2, s. 231-239
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Journal article (peer-reviewed)abstract
- An all-purpose computational fluid dynamics software is used for simulations of the vacuum infusion process. The study comprises simulations of a full three-dimensional two-phase flow through a porous medium. The medium that has an anisotropic, spatial- and time-dependent permeability is located in a complex mold with moving boundaries. With this generalization, different material combinations, processing conditions, and even other manufacturing techniques can be evaluated. The strength of the presented approach is exemplified by simulations of mold filling of a real part, using a typical vacuum infusion set-up. In addition to the overall development of the model, a number of specific aspects and phenomena are investigated and evaluated. Local lead of the flow front and a minor influence in overall flow front lead-lag, with no influence on the fill time, is the result of simulations of edge effects due to poor preform fitting.
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| 41. |
- Andersson, Magnus, et al.
(author)
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Development of guidelines for the vacuum infusion process
- 2000
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In: Proceedings of the 8th International Conference on Fibre Reinforced Composites, FRC 2000. - Cambridge : Woodhead Publishing Materials. - 1855735504 ; , s. 113-120
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Conference paper (peer-reviewed)abstract
- The current trend towards increased use of vacuum infusion moulding for large surface area parts has increased the interest for an advanced modelling of the process. This paper presents a detailed experimental investigation of laminate thickness and out-of-plane flow front shape during impregnation of high permeability reinforcement on top of a non-crimp fabric reinforcement lay-up. The goal with the experiments is to increase the understanding of the process and to provide accurate data that can later be used for validation of numerical models. The laminate thickness was measured during impregnation with a stereoscopic digital speckle photography system and the flow front shape was determined by tracking of colour marks in the stacking. The laminate lay-ups studied are different combinations of non-crimp fabrics and flow layers while the resin used was a polyester developed specifically for vacuum infusion moulding. Results are presented both for the instantaneous thickness and the flow front shape for several different material combinations. It was found that the skewness of the flow front became more pronounced with increasing number of flow layers when the number of non-crimp fabric layers was kept constant. As a first step towards a complete numerical model of the impregnation process a simplified model for the compressibility and a proven model for permeability was implemented in a commercial CFD package that can handle moving boundaries and moving flow fronts. Only a qualitative comparison with experiments was done but the conclusion was that the overall behaviour of the model was encouraging. A validation of the numerical model based on the measurements in this paper is under development.
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| 42. |
- Andersson, Magnus, et al.
(author)
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Flow-enhancing layers in the vacuum infusion process
- 2002
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In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 23:5, s. 895-901
-
Journal article (peer-reviewed)abstract
- The current trend towards increased use of vacuum infusion molding for large surface-area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow-enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through-thickness flow front was observed by making a number of color marks on the glass-mats forming the reinforcing stack, which became visible when the resin reached their position. The in-plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill-time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead-lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead-lag has a miximum close to the inlet.
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| 43. |
- Andersson, Magnus, et al.
(author)
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Numerical model for vacuum infusion manufacturing of polymer composites
- 2003
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In: International journal of numerical methods for heat & fluid flow. - : Emerald. - 0961-5539 .- 1758-6585. ; 13:3, s. 383-394
-
Journal article (peer-reviewed)abstract
- The focus is set on the development and evaluation of a numerical mgodel describing the impregnation stage of a method to manufacture fibre reinforced polymer composites, namely the vacuum infusion process. Examples of items made with this process are hulls to sailing yachts and containers for the transportation industry. The impregnation is characterised by a full 3D flow in a porous medium having an anisotropic, spatial- and time-dependent permeability. The numerical model has been implemented in a general and commercial computational fluid dynamic software through custom written subroutines that: couple the flow equations to the equations describing the stiffness of the fibre reinforcement; modify the momentum equations to account for the porous medium flow; remesh the computational domain in each time step to account for the deformation by pressure change. The verification of the code showed excellent agreement with analytical solutions and very good agreement with experiments. The numerical model can easily be extended to more complex geometry and to other constitutive equations for the permeability and the compressibility of the reinforcement.
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| 44. |
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| 45. |
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| 46. |
- Andersson, Robin, 1987-, et al.
(author)
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Gävunda case study
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Other publication (other academic/artistic)
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| 47. |
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| 48. |
- Andersson, Robin, 1987-, et al.
(author)
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Numerical investigation of a hydropower tunnel : Estimating localised head-loss using the manning equation
- 2019
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In: Water. - : MDPI. - 2073-4441. ; 11:8
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Journal article (peer-reviewed)abstract
- The fluid dynamics within a water tunnel is investigated numerically using a RANS approach with the k-ε turbulence model. The computational model is based on a laser scan of a hydropower tunnel located in Gävunda, Sweden. The tunnel has a typical height of 6.9 m and a width of 7.2 m. While the average cross-sectional shape of the tunnel is smooth the local deviations are significant, where some roughness elements may be in the size of 5 m implying a large variation of the hydraulic radius. The results indicate that the Manning equation can successfully be used to study the localised pressure variations by taking into account the varying hydraulic radius and cross-sectional area of the tunnel. This indicates a dominant effect of the tunnel roughness in connection with the flow, which has the potential to be used in the future evaluation of tunnel durability. ANSYS-CFX was used for the simulations along with ICEM-CFD for building the mesh.
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| 49. |
- Asplund, Kjell, et al.
(author)
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End of life after stroke : a nationwide study of 42,502 deaths occurring within a year after stroke
- 2018
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In: European Stroke Journal. - : Sage Publications. - 2396-9873 .- 2396-9881. ; 3:1, s. 74-81
-
Journal article (peer-reviewed)abstract
- Introduction: In the scientific literature, there is very limited empirical information on end-of-life issues after stroke in the scientific literature. The present nationwide study describes the circumstances surrounding deaths that occur within a year after a stroke. Patients and methods: Datasets from three nationwide Swedish registers (on stroke, palliative care and cause of death) were linked. Basic information was available for 42,502 unselected cases of death that occurred within a year after a stroke and more detailed information was available for 16,408 deaths. Odds ratios for characteristics of end-of-life care were calculated by logistic regression. Results: In the late phase after stroke (three months to one year), 46% of patients died in a nursing home, whereas 37% of patients died in a hospital after readmission and 10% of patients died at home. Eleven per cent of deaths were reported as being unexpected. A next of kin was present at 49% of deaths. The frequency of unattended deaths (neither next of kin nor staff were present at the time of death) ranged from 5% at home with specialised home care to 25% in hospitals. Discussion: This is, by far, the largest study published on end-of-life issues after stroke. Major differences between countries in healthcare, community services, family structure and culture may limit direct transfer of the present results to other settings. Conclusion: There is considerable discordance between presumed good death' late after stroke (dying at home surrounded by family members) and the actual circumstances at the end of life.
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| 50. |
- Baart, Pieter, et al.
(author)
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Contaminant particle migration in a double restriction seal
- 2013
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In: Proceedings of the STLE Annual Meeting and Exhibition 2013, Detroit MI, USA.. - : STLE. ; , s. 125-
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Conference paper (peer-reviewed)abstract
- Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile.In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication
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