| 1. |
- Jakobsson, S, et al.
(författare)
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Combustion engine optimization: A multiobjective approach
- 2010
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Ingår i: Optimization & Engineering. - : Springer Science and Business Media LLC. - 1389-4420 .- 1573-2924. ; 11:4, s. 533-554
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Tidskriftsartikel (refereegranskat)abstract
- To simulate the physical and chemical processes inside combustion engines is possible by appropriate software and high performance computers. For combustion engines a good design is such that it combines a low fuel consumption with low emissions of soot and nitrogen oxides. These are however partly conflicting requirements. In this paper we approach this problem in a multi-criteria setting which has the advantage that it is possible to estimate the trade off between the different objectives and the decision of the optimal solution is postponed until all possibilities and limitations are known. The optimization algorithm is based on surrogate models and is here applied to optimize the design of a diesel combustion engine.
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| 2. |
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| 3. |
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| 4. |
- Magnusson, Anna, 1974, et al.
(författare)
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Dual fibre optical probe measurements of solids volume fraction in a circulating fluidized bed
- 2005
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 151:1-3, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of a dual fibre optical probe was experimentally investigated in a circulating fluidized bed. The particle volume fraction registered by the optical probe was compared to pressure drop measurements for a range of operating conditions. A theoretical calibration theory was applied to the probe signal to obtain the local and instantaneous particle volume fraction. It was found that glare points on the particles and the beam length from the probe to the particle determines the curvature of the calibration function to a large extent.
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| 5. |
- Mark, Andreas, 1980, et al.
(författare)
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Comparison Between Different Immersed Boundary Conditions for Simulation of Complex Fluid Flows
- 2011
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Ingår i: Fluid Dynamics and Materials Processing. - 1555-2578 .- 1555-256X. ; 7:3, s. 241-258
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Tidskriftsartikel (refereegranskat)abstract
- In the literature immersed boundary methods are employed tosimulate complex flows around moving arbitrary bodies without thenecessity of remeshing. These methods employ a regular Eulerian meshto simulate the fluid flow and a Lagrangian representation of theboundary of the bodies. The two representations can be coupled throughan immersed boundary condition constraining the fluid to exactlyfollow the boundary of the bodies (immersed boundaries). Typicallysuch methods suffer from accuracy problems, that arise from spuriousmass fluxes over the immersed boundary (IB), pressure boundaryconditions or high density ratios. The mirroring IB method Mark(2008); Mark and van Wachem (2008) resolves these problems by ensuringzero mass flux over the IB instead of employing a pressure boundarycondition. In this work the mirroring IB method together with a hybridIB condition are implemented and validated in IBOFLOW. IBOFLOW is anincompressible finite-volume based fluid flow solver. TheNavier-Stokes' equations are coupled with the SIMPLEC Doormaal andRaithby (1984) method and discretized on a Cartesian octree grid thatcan be dynamically refined and coarsened, enabling grid refinement tofollow moving bodies. The variables are stored in a co-locatedconfiguration and pressure weighted flux interpolation Rhie and Chow(1983) is employed to prevent pressure oscillations. In theimplemented IB method the immersed bodies are represented by ananalytical description or by a triangulation. The method models thepresence of the bodies inside the fluid by an implicitly formulated IBcondition, which constrains the fluid velocity to the boundaryvelocity with second-order accuracy. The original mirroring IBcondition mirrors the velocity field over the local IB and the hybridIB condition mirrors and extrapolates the fluid velocity onto the IB.These IB conditions generate a fictitious velocity field inside thebodies, which is excluded in the continuity equation to ensure zeromass flux over the boundary. The fluid flow over an immersed sphere issimulated to validate and compare the different IB conditions. Thesimulated drag force is compared to experimental findings withexcellent agreement and a detailed convergence study of the error ofthe fluid velocity integrated over the immersed boundary is performedto show the strictly second-order accuracy of the implemented IBconditions. It is shown that the error is reduced with the hybrid IBcondition compared to the original mirroring IB condition. Inaddition, a sedimenting sphere with a moving grid refinement issimulated to validate the hybrid method and show the potential of thedynamic octree grid.
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| 6. |
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| 7. |
- Mark, Andreas, 1980, et al.
(författare)
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Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
- 2011
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Ingår i: Paper360. - 1933-3684. ; 10:11, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Paper forming is the first step in the paper machine where a fibersuspension leaves the headbox and flows through a forming fabric.Complex physical phenomena occur during paper forming due to theinteraction between fibers, fillers and fines as well as chemicalsadded to the suspension. Understanding this process is important forthe development of improved paper products because the configurationof the fibers during this step has a large influence on the finalpaper quality. Since the effective paper properties depend on themicro-structure of the fiber web, a continuum model is inadequate andthe properties of each fiber need to be accounted for in thesimulations.In the present work, a framework for microstructure simulation ofearly paper forming has been developed. The simulation frameworkincludes a Navier-Stokes solver and immersed boundary methods are usedto resolve the flow around the fibers. The fibers are modeled with afinite element discretization of the Euler-Bernoulli beam equation ina co-rotational formulation. The contact model is based on a penaltymethod and includes friction as well as elastic and inelasticcollisions.The fiber model and the contact model are validated against demandingtest cases from the literature with excellent results. Thefluid-structure interaction in the model is examined by simulating anelastic beam oscillating in a cross flow. Finally, a simulation ofearly paper forming is performed to demonstrate the potential of theproposed framework. The unique modeling approach can be used toincrease the fundamental understanding of paper forming and supportprocess optimization.
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| 8. |
- Mark, Andreas, 1980, et al.
(författare)
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Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 283-290
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Konferensbidrag (refereegranskat)abstract
- Paper forming is the first step in the paper machinewhere a fiber suspension leaves the headbox and flowsthrough a forming fabric. Understanding this processis important for the development of improved paperproducts because the configuration of the fibers duringthis step has a large influence on the final paperquality.The simulation framework includes IBOFlow, a stateof-the-art Navier-Stokes solver, and PaperGeo, the virtualpaper structure generator in GeoDict. ImmersedBoundary Methods are used to resolve the flow aroundthe fibers. The fibers are modeled with a finite elementdiscretization of the Euler-Bernoulli beam equationin a co-rotational formulation. The contact modelis based on a penalty method and includes friction aswell as elastic and inelastic collisions.The fiber model and the contact model are validatedagainst demanding test problems from the literaturewith excellent result. The fluid-structure interaction inthe model is examined by simulating an elastic beamoscillating in a cross flow. Finally, a simulation of initialpaper forming is performed, which demonstratesthe capabilities of the simulation framework.
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| 9. |
- Palm, Stig, 1964, et al.
(författare)
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Microdosimetry of astatine-211 single-cell irradiation: role of daughter polonium-211 diffusion.
- 2004
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 31:2, s. 218-25
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Tidskriftsartikel (refereegranskat)abstract
- A microdosimetric analysis of previously published data on 211At-albumin, free 211At, and 211At-C215 irradiation of Colo-205 cells in a slowly rotating single-cell suspension is presented. A custom-built computer program based on the Monte Carlo method was used to simulate the irradiation and the energy deposition in individual cell nuclei. Separate simulations were made for the assumption that the 211Po atom stays in the position where it is created, and that it diffuses away. The mean event number at which 37% of all cells survived, n37, and the frequency mean specific energy per event, zF, were estimated. The Poisson distribution of events and simulated single and multievent distributions of specific energy were used to find the single-cell specific energy at which the probability of survival is reduced to 37%, z37. The calculated single-cell radiosensitivity values show that 211Po atoms, created on a cell surface by the decay of 211At atoms, will diffuse from the cell during its life-span. The increasing distance to the cell nucleus will drastically decrease the probability of the emitted alpha particle to hit the nucleus. This will result in fewer alpha-particle events in the cell nucleus. For dispersed cells, the diffusion of 211Po atoms will reduce the total dose from cell-bound 211At by a factor of 2.
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| 10. |
- Rundqvist, Robert, 1974
(författare)
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Disperson and Flocculation in a Dry Mat-Forming Process
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The absorption cores in disposable nappies, incontinence pads and female hygiene products are manufactured by a dry mat-forming process. Cellulose fibers and super-absorbing particles are suspended in air and blown onto a forming wheel on which the cores are formed. It is vital for the quality of the product that the fibres and particles are evenly distributed in the suspension. The purpose of this project has been to establish a platform of scientific knowledge from which the fluid mechanics aspect of the manufacturing process can be understood. To better understand the problems relevant to the process, air/particle flows and air/fiber flows have been studied separately. A two-fluid model with a modified κ-ε model for the gas phase has been used to simulate a horizontal air/particle flow. An optical probe and a calibration procedure for measuring the local particle volume fraction have been developed and used to verify the models. The probe uses two optical fibres, to emit infrared light and detect light reflected by the particles. The calibration procedure is based on the assumption that light paths including reflections on more than one particle do not make a significant contribution to the probe signal. Measurements of a horizontal air/particle flow have been made to verify the simulations. The agreement between simulations and experiments is good. For the air/fiber flow, it is suggested that a two-fluid model be used together with a turbulence model for the gas phase and a transport equation for a floc characterizing scalar. This scalar may be either flocculation intensity or floc size. A technique for characterizing the flow using optical probes has been developed. Measurements of floc velocity and size distributions have been made in a production-scale facility for process research. The shape of the measured floc size distribution indicates that the mechanism for aggregating fibres into flocs is strong compared to the mechanism for breaking up flocs.
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| 12. |
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| 13. |
- Rundqvist, Robert, 1974, et al.
(författare)
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Modeling and Simulation of Sealing Spray Application Using Smoothed Particle Hydrodynamics
- 2011
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Ingår i: Fluid Dynamics and Materials Processing. - 1555-2578 .- 1555-256X. ; 7:3, s. 259-278
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Tidskriftsartikel (refereegranskat)abstract
- Multiphase flow simulation using Smoothed Particle Hydrodynamics (SPH)has gained interest during recent years, mostly due to the inherentflexibility of the method and the physically rather intuitiveformulation of extra constitutive equations needed when dealing withfor instance non-Newtonian flows. In the work presented here,simulations based on an SPH model implemented in the flow solverIBOFlow has been used for simulation of robotic application of sealingmaterial on a car body. Application of sealing materials is done inorder to prevent water leakage into cavities of the body, and toreduce noise. In off-line programming of the robots in the automotivepaintshop it is of great interest to predict shape and appearance ofsealing material without having to resort to trial and errorprocedures.The flow of sealing material in the air between applicator and target(car body) is relatively uncomplicated, as the material mostly movesat constant velocity until impact on target. The flow of the materialon the target is however more complex, applied material flows at thetarget surface due to inertia, gravity and pressure and in order topredict the appearance of the applied material, flow equations for anon-Newtonian fluid with an open surface needs to be solved. Thesealing material is both thixotropic and viscoelastic; the material isshear thinning but needs to be sheared for some time before thestructure of the material is broken down. Conversely, the regain ofstructure of the material, and thereby also the increase of viscositywhen shearing is stopped or reduced, is also connected to a delaytime. In the model used, the local viscosity is considered obeying afirst order differential equation where the stationary limit isdetermined by a Bingham relation.The simulation model was built by comparing simulations andexperiments at three different stages of complexity. In the mostfundamental stage the material properties were determined. Using arotational rheometer, yield stress, plastic viscosity and thixotropytime constant was determined and implemented in the simulation model.To verify the numerical behaviour of the rheology, simulated rheometerexperiments were carried out and compared with the physicalexperiments. In the second stage, simulation of application of sealingmaterial with a stationary hollowcone nozzle was carried out. Toverify the simulations, the resulting thickness, width and shape ofapplied material as a function of time were compared to experiments.In the third stage a moving applicator of the same type wasconsidered, here thickness width and shape of applied material as afunction of applicator to target distances were compared betweenexperiments and simulation. At all three stages the number of SPHparticles, /i.e./ grid points, in the simulations was varied in orderto verify that the simulations were resolution independent.Results of the simulations show good agreement between experiments andsimulations in all stages using no artificial tuning of the models,that is, all parameters used in the models are based on physicalconsiderations. Furthermore, simulation time on a desktop computerindicate that computational power required for industrially relevantcases is not prohibitively large, for the most complex cases in thiswork simulation time did not exceed six hours.
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| 14. |
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| 15. |
- Rundqvist, Robert, 1974, et al.
(författare)
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Simulation of Spray Painting in Automotive Industry
- 2010
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Ingår i: Numerical Mathematics and Advanced Applications 2009 (Proceedings of ENUMATH 2009, the 8th European Conference on Numerical Mathematics and Advanced Applications, Uppsala, July 2009). - Berlin, Heidelberg : Springer Berlin Heidelberg. ; Part 2, s. 769-777
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Konferensbidrag (refereegranskat)
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| 16. |
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