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- Alnersson, Gustaf, et al.
(författare)
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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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Ingår i: Functional Composite Materials. - : Springer Nature. - 2522-5774. ; 4
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Tidskriftsartikel (refereegranskat)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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- Alnersson, Gustaf, et al.
(författare)
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Review of the Numerical Modeling of Compression Molding of Sheet Molding Compound
- 2020
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Ingår i: Processes. - : MDPI. - 2227-9717. ; 8:2
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Forskningsöversikt (refereegranskat)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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- Alnersson, Gustaf
(författare)
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Towards 3D modelling of Compression Moulding of SMC
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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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- Barestrand, Henrik A., et al.
(författare)
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Modeling Convective Heat Transfer of Air in a Data Center Using OpenFOAM : Evaluation of the Boussinesq Buoyancy Approximation
- 2023
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Ingår i: OpenFOAM® Journal. - : OpenCFD Ltd. - 2753-8168. ; 3, s. 146-158
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Tidskriftsartikel (refereegranskat)abstract
- Achieving energy and cooling efficiency in data center convective air flow and heat transfer can be a challenging task. Among different numerical methods to work with such issues is the Finite Volume Method in Computational Fluid Dynamics. This work evaluates the performance of two such solvers provided by OpenFOAM® in solving this type of convective heat-transfer problem, namely BuoyantBoussinesqPimpleFOAM and BuoyantPimpleFOAM. This is done for two different flow configurations of significantly different Richardson number. To sufficiently resolve the flow, grid sizing effects are elucidated by way of the kernel density estimate. It determines the volume distribution of the temperature in the data center configuration. For the k-epsilon turbulence model used here, it was found that the compressible solver performs faster and requires less grid resolution for both flow configurations. This is attributed to the nature of the boundary conditions which are set such that the mass flow conservation per server rack and cooling unit is achieved. Transient solutions are found to provide better iterative convergence for cases that involves buoyancy, compressibility and flow separation. This is, in comparison to steady-state solutions where artificial numerical pressure drop is found, to depend on the momentum relaxation factors for the convective case with a higher Richardson number.
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- Darbandi, Tayebeh
(författare)
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Development of flue gas treatment for small-scale boilers with a focus on particulate matters purification
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Small-scale boilers significantly contribute to particle matter (PM) emissions, which adversely affect health and global warming. According to World Health Organization, particulate matter was ranked as the fifth significant parameter in premature death in 2015. Based on the Clean airpolicy package, which was established in 2013 by the European Commission, it is aimed to mitigate the emission from the combustion of energy sources to half by 2030. In Europe, small-scale biofuel boilers and domestic heating systems release 25% of total particulate matter annually. Thus, finding an economical method for small-scale cleaning flue gas is necessary.This research aims to obtain an efficient system to clean the flue gas from a small-scale biomass boiler. For this purpose, a setup has been built at Luleå University. The setup consists of a boiler (20kW), three heat exchangers, and a generator. The flue gas from combustion, which heats the water in the boiler, flows through the absorber and generator. In the absorber (packed bed wet scrubber), the flue gas is in contact with an absorption solution, and at the same time, particulate matter is cleaned from the flue gas. The solution is passed through a filter and is purified. A part of the solution flows through the generator, absorbed water is evaporated, and concentrated solution returns to the absorber. During this study, the stability of the solution in particulate matter collection was tested in the long-term running of the system (8 months), which did not show any deterioration in the solution ability for particle collection. The system efficiency in particulate matter size D50 (0.8-10 μm) collection efficiency was 42%. Also, the heat recovery of the system was improved by 18%.The effect of different forces on particulate matter in a wet scrubber was simulated by Ansys Fluent 19. 2 under different operation conditions. The governing forces on the particulate matter were studied, and the results showed that the concentration gradient has the highest effect on the collection of particulate matter. The effect of concentration gradient is explained as diffusiophoresis phenomenon. On the other hand, the temperature gradient (thermophoresis) did not strongly affect particulate matter collection. The influence of diffusiophoresis and thermophoresis on different particulate matter (PM) sizes under different flue gas velocities, temperatures, and water vapor mass fractions were simulated. Results demonstrated that increasing the flue gas velocity and particle size reduces the particle collection efficiency. The simulation result was validated against previous empirical models.In the next step, the effect of operation conditions on the PM collection efficiency was investigated. Based on the simulation results, the effect of water vapor concentration gradient, temperature gradient, and various heights of packed bed material in the absorber was studied experimentally. The measurements demonstrated that the water vapor concentration gradient greatly affects system PM collection efficiency. To improve the system’s efficiency, it is suggested to keep the temperature of the solution as low as possible and the absorption solution concentration at the highest applicable concentration. The obtained results showed that the absorber with a fully packed bed material has a better performance in particle collection.The obtained data can be used to build an efficient setup to clean the particulate matter released by small-scale boilers and would be interesting for companies that want to develop further the technology to be commercial for the market.
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