| 1. |
- Marganiec, J., et al.
(författare)
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Coulomb breakup of 17Ne from the viewpoint of nuclear astrophysics
- 2012
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Ingår i: Proceedings of Science. - Proceedings of Science : Sissa. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- By the Coulomb breakup of 17Ne, the time-reversed reaction 15O(2p,γ)17Ne has been studied. This reaction might play an important role in the rp process, as a break-out reaction of the hot CNO cycle. The secondary 17Ne ion beam with an energy of 500 MeV/nucleon has been dissociated in a Pb target. The reaction products have been detected with the LAND-R3B experimental setup at GSI. The preliminary differential and integral Coulomb dissociation cross section sCoul has been determined, which then will be converted into a photo-absorption cross section sphoto, and a two-proton radiative capture cross section σcap. Additionally, information about the structure of the 17Ne, a potential two-proton halo nucleus, will be received. The analysis is in progress. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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| 2. |
- Roos, Håkan, 1967, et al.
(författare)
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Displacement Forces in Iliac Landing Zones and Stent Graft Interconnections in Endovascular Aortic Repair: An Experimental Study
- 2014
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 47:3, s. 262-267
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Stent graft migration influences the long-term durability of endovascular aortic repair. Flow-induced displacement forces acting on the attachment zones may contribute to migration. Proximal fixation of aortic stent grafts has been improved by using hooks, while distal fixation and stent graft interconnections depend on self-expansion forces only. We hypothesized that flow-induced displacement forces would be significant at the distal end, and would correlate with graft movements. Methods: As part of an experimental study, an iliac limb stent graft was inserted in a pulsatile flow model similar to aortic invivo conditions, and fixed-mounted at its proximal and distal ends to strain gauge load cells. Peak displacement forces at both ends and pulsatile graft movement were recorded at different graft angulations (0-90°), perfusion pressures (145/80, 170/90, or 195/100mmHg), and stroke frequencies (60-100b.p.m.). Results: Flow-induced forces were of the same magnitude at the proximal and distal end of the stent graft (peak 1.8N). Both the forces and graft movement increased with angulation and perfusion pressure, but not with stroke rate. Graft movement reached a maximum of 0.29±0.01mm per stroke despite fixed ends. There were strong correlations between proximal and distal displacement forces (r=0.97, p<.001), and between displacement forces and graft movement (r=0.98, p<.001). Conclusions: Pulsatile flow through a tubular untapered stent graft causes forces of similar magnitude at both ends and induces pulsatile graft movements in its unsupported mid-section. Peak forces are close to those previously reported to be required to extract a stent graft. The forces and movements increase with increasing graft angulation and perfusion pressure. Improved anchoring of the distal end of stent grafts may be considered. © 2013 European Society for Vascular Surgery.
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| 3. |
- Wamers, F., et al.
(författare)
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First Observation of the Unbound Nucleus Ne-15
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:13
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first observation of the unbound proton-rich nucleus Ne-15. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u Ne-17. The Ne-15 ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to O-13 with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2(-) and 1(-) states in F-14 is observed. The Ne-15 ground state is shown to have a strong configuration with two protons in the (sd) shell around O-13 with a 63(5)% (1s(1/2))(2) component.
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| 4. |
- Zhang, Renyun, et al.
(författare)
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Soap-film coating : High-speed deposition of multilayer nanofilms
- 2013
-
Ingår i: Scientific Reports. - Nature Publishing Group : Springer Science and Business Media LLC. - 2045-2322. ; 3, s. Art. no. 1477-
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Tidskriftsartikel (refereegranskat)abstract
- The coating of thin films is applied in numerous fields and many methods are employed for the deposition of these films. Some coating techniques may deposit films at high speed; for example, ordinary printing paper is coated with micrometre-thick layers of clay at a speed of tens of meters per second. However, to coat nanometre thin films at high speed, vacuum techniques are typically required, which increases the complexity of the process. Here, we report a simple wet chemical method for the high-speed coating of films with thicknesses at the nanometre level. This soap-film coating technique is based on forcing a substrate through a soap film that contains nanomaterials. Molecules and nanomaterials can be deposited at a thickness ranging from less than a monolayer to several layers at speeds up to meters per second. We believe that the soap-film coating method is potentially important for industrial-scale nanotechnology.
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| 5. |
- Aksouh, F., et al.
(författare)
-
STUDY OF THE O-15(2p,gamma)Ne-17 CROSS SECTION BY COULOMB DISSOCIATION OF Ne-17 FOR THE rp PROCESS OF NUCLEOSYNTHESIS
- 2014
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Ingår i: Acta Physica Polonica, Series B.. - 1509-5770 .- 0587-4254. ; 45:2, s. 229-234
-
Tidskriftsartikel (refereegranskat)abstract
- The O-15(2p, gamma)Ne-17 cross section has been studied by the inverse reaction, the Coulomb dissociation of Ne-17. The experiment has been performed at the GSI. The Ne-17 excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb dissociation cross sections (sigma(Coul)) have been extracted, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the Ne-17 nuclear structure will be obtained. The analysis is in progress.
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| 6. |
- Andric, Jelena, 1979, et al.
(författare)
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A particle-level rigid fiber model for high-Reynolds number flow, implemented in a general-purpose CFD code
- 2013
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Ingår i: 8th International Conference on Multiphase Flow ICMF 2013, Korea.
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Konferensbidrag (refereegranskat)abstract
- A particle-level rigid fiber model has been integrated into a general-purpose, open source computational fluid dynamics code to carry out detailed studies of fiber–flow interactions in realistic flow fields. The fibers are modeled as chains of cylindrical segments, and their translational and rotational degrees of freedom are considered. The equations of motion contain the contributions from hydrodynamic forces and torques, and the segment inertia is taken into account. The model is validated for the rotational motion of isolated fibers in simple shear flow, and the computed period of rotation is in good agreement with the one computed using Jeffery’s equation for a prolate spheroid with an equivalent aspect ratio. The model is applied by suspending a number of fibers in the swirling flow of a conical diffuser, resembling one stage in the dry-forming of pulp mats. The Reynolds-averaged Navier–Stokes equations with an eddy-viscosity turbulence model are employed to describe the fluid motion, and a one-way coupling between the fibers and the fluid phase is included. The dependence of the fiber motion on initial position and density is analyzed.
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| 7. |
- Andric, Jelena, 1979, et al.
(författare)
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A study of a flexible fiber model and its behavior in DNS of turbulent channel flow
- 2013
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Ingår i: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 224:10, s. 2359-2374
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particlelevel fiber model has been integrated into a general-purpose, open source Computational Fluid Dynamics (CFD) code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct Numerical Simulation (DNS) of the incompressible Navier–Stokes equations is used to describe the fluid flow in a plane channel and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation time-scales of fibers suspended in a turbulent flow field.
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| 8. |
- Andric, Jelena, 1979, et al.
(författare)
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Description and validation of a flexible fiber model, implemented in a general-purpose CFD code
- 2013
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Ingår i: Proceedings of the 8th International Conference on Multiphase Flow ICMF 2013, Korea.
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Konferensbidrag (refereegranskat)abstract
- A flexible fiber model has been implemented in a general purpose open-source computational fluid dynamics code. The fibers are modeled as chains of cylindrical segments. Each segment is tracked individually and their equations of motion account for the hydrodynamic forces and torques from the interaction with the fluid, the elastic bending and twisting torques, and the connectivity forces and moments that ensure the fiber integrity. The segment inertia is taken into account and a one-way coupling with the fluid phase is considered. The model is applied to the rotational motion of an isolated fiber in a low segment Reynolds number shear flow. In the case of a stiff fiber, the computed period of rotation is in good agreement with the one computed using Jeffery's equation for an equivalent spheroid aspect ratio. A qualitative comparison is made with experimental data for flexible fibers. These results show that the implemented model can reproduce the known dynamical behavior of rigid and flexible fibers successfully.
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| 9. |
- Andric, Jelena, 1979, et al.
(författare)
-
Numerical investigation of fiber flocculation in the air flow of an asymmetric diffuser
- 2014
-
Ingår i: Proceedings of the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting and 12th International Conference on Nanochannels, Microchannels and Minichannels, FEDSM 201, August 3-7, Chicago, Illinois, USA..
-
Konferensbidrag (refereegranskat)abstract
- A particle-level rigid fiber model is used to studyflocculation in an asymmetric planar diffuser with a turbulent Newtonian fluid flow, resembling one stage in dry-forming process of pulp mats. The fibers are modeled as chains of rigid cylindrical segments. The equations of motion incorporatehydrodynamic forces and torques from the interaction with thefluid, and the fiber inertia is taken into account. The flow isgoverned by the Reynolds-averaged Navier ̶ Stokes equationswith the standard k-omega turbulence model. A one-waycoupling between the fibers and the flow is considered. Astochastic model is employed for the flow fluctuations tocapture the fiber dispersion. The fibers are assumed to interactthrough short-range attractive forces, causing them to interlockas the fiber-fiber contacts occur during the flow. It is found thatthe formation of fiber flocs is driven by both the turbulenceinduceddispersion and the gradient of the averaged flow field
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| 10. |
- Andric, Jelena, 1979, et al.
(författare)
-
Rheological properties of dilute suspensions of rigid and flexible fibers
- 2014
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 212, s. 36-46
-
Tidskriftsartikel (refereegranskat)abstract
- Particle-level simulations are used to study the rheology of monodispersed suspensions of rigid and flexible fibers in a creeping, simple shear flow of a Newtonian fluid. We also investigate the influence of different equilibrium shapes (straight and curved) of the fibers on the behavior of the suspension. A parametric study of the impacts of fiber flexural rigidity and morphology on rheology quantifies the effects of these realistic fiber features on the experimentally accessible rheological properties. A fiber is modeled as a chain of rigid cylindrical segments, interacting through a two-way coupling with the fluid described by the incompressible three-dimensional Navier--Stokes equations. The initial fiber configuration is in the flow--gradient plane. We show that, when the shear rate is increased, straight flexible fibers undergo a buckling transition, leading to the development of finite first and second normal stress differences and a reduction of the viscosity. These effects, triggered by shape fluctuations, are dissimilar to the effects induced by the curvature of stiff, curved fibers, for which the viscosity increases with the curvature of the fiber. An analysis of the orbital drift of fibers initially oriented at an angle to the flow--gradient plane provides an estimate for the time-scale within which the prediction of the rheological behavior is valid. The information obtained in this work can be used in the experimental characterization of fiber morphology and mechanics through rheology.
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| 11. |
- Beaudoin, Martin, et al.
(författare)
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Evaluation of an improved mixing plane interface for OpenFOAM
- 2014
-
Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 22
-
Konferensbidrag (refereegranskat)abstract
- A mixing plane interface provides a circumferentially averaging rotor-statorcoupling interface, which is extremely useful in practical turbomachinery simulations. Itallows fundamentally transient problems to be studied in steady-state, using simplified meshcomponents having periodic properties, and with the help of a multiple reference frames(MRF) approach. An improved version of the mixing plane interface for the community-drivenversion of OpenFOAM is presented. This new version of the mixing plane introduces a perfield,user-selectable mixing option for the flow fields at the interface, including the possibilityto use a mass-flow averaging algorithm for the velocity field. We show that the quality of themass-flow transfer can be improved by a proper selection of the mixing options at theinterface. This paper focuses on the evaluation of the improved mixing plane interface forvarious steady-state simulations of incompressible flows, applied to a simple 2D validation testcase, and to more complex 3D turbomachinery cases.
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| 12. |
- Choquet, Isabelle, et al.
(författare)
-
Analysis of the Influence of the Composition of the Shielding Gas on Pressure Force and Heat Fluxes in Arc Welding
- 2014
-
Ingår i: Proceedings of The 6<sup>th</sup> International Swedish Production Symposium 2014. - 9789198097412 ; , s. 1-8
-
Konferensbidrag (refereegranskat)abstract
- A main problem raised by arc welding manufacturing is the determination ofthe optimal process parameters to ensure weld quality as well as resource efficient andsustainable production. To address this problem a better process understanding is required.In this study thermal magneto hydrodynamic modeling of a welding arc is used to reacha deeper insight into the influence of the composition of the shielding gas on the pressureforce and the heat fluxes to a workpiece. The model was implemented in the open sourcesimulation software OpenFOAM. Four different shielding gas mixtures combining argonand carbon dioxide were studied. When increasing the fraction of carbon dioxide the resultsshow a significant increase of the arc velocity and temperature with constriction of thetemperature field, a decrease of the pressure force and a significant increase of the heatfluxes on the base metal.
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| 13. |
- Choquet, Isabelle, et al.
(författare)
-
Electric welding arc modeling with the solver OpenFOAM - A comparison of different electromagnetic models
- 2011
-
Ingår i: International Institute of Welding Document No 212-1189-11, July 2011..
-
Konferensbidrag (refereegranskat)abstract
- This study focuses on the modeling of a plasma arc heat source in the context of electric arc welding. The model was implemented in the open source CFD software OpenFOAM-1.6.x, coupling thermal fluid mechanics in three dimensions with electro magnetics. Four different approaches were considered for modeling the electromagnetic fields: i) the three-dimensional approach, ii) the two-dimensional axi-symmetric approach, iii) the electric potential formulation, and iv) the magnetic field formulation as described by Ramírez et al. [1]. The underlying assumptions and the differences between these models are described in detail. Models i) to iii) reduce to the same quasi one-dimensional limit for an axi-symmetric configuration with negligible radial current density, contrary to model iv). Models ii) to iv) do not represent the same physics when the radial current density is significant, such as or an electrode with a conical tip. Models i) to iii) were retained for the numerical simulations. The corresponding results were validated against the analytic solution of an infinite electric rod. Perfect agreement was obtained for all the models tested. The results from the coupled solver (thermal fluid mechanics coupled with electromagnetics) were compared with experimental measurements for Gas Tungsten Arc Welding (GTAW). The shielding gas was argon, the arc was short (2mm), the electrode tip was conical, and the configuration was axi-symmetric. The boundary conditions were specified at the anode and cathode surfaces. Models i) and ii) lead to the same results, but not the model iii). Model iii) neglects the radial current density component, resulting in a poor estimation of the magnetic field, and in turn of the arc fluid velocity. The limitations of the coupled solver were investigated changing the gas composition, and using different boundary conditions. The boundary conditions, difficult to measure and to estimate a priori, significantly affect the simulation results.
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| 14. |
- Choquet, Isabelle, et al.
(författare)
-
Magnetic field models for high intensity arcs, applied to welding - A comparison between three different formulations
- 2013
-
Ingår i: 9th International Conference on Trends in Welding Research; Chicago, IL; United States; 4 June 2012 through 8 June 2012. - 9781627089982 ; , s. 876-885
-
Konferensbidrag (refereegranskat)abstract
- Most simulation studies done to deeper understand high-intensity welding arcs address axi-symmetric configurations and use the electric potential formulation. This formulation involves the assumption of a one-dimensional magnetic field. The assumption is justified in its original frame: rather long arcs (about 10 mm), and when the electrode tip is excluded from the computational domain. However, arcs applied to welding are shorter, and the electrode geometry is important to take into account. The present work questions the assumption of a one-dimensional magnetic field for simulating short welding arcs. We have compared three different approaches for modeling the magnetic field: three-dimensional, two-dimensional axi-symmetric, and the electric potential formulation. These models have been applied to water cooled anode Gas Tungsten Arc Welding (GTAW) test cases with truncated conical electrode tip (tip radius of 0.5 and 0.2 mm) and various arc lengths (2, 3 and 5 mm). For the axi-symmetric cases studied in the present work, the three- and two-dimensional models give exactly the same results. The one-dimensional simplification of the magnetic field turns out to have a significant unfavorable effect on the simulation results. For axi-symmetric welding applications, it is argued that the two-dimensional axi-symmetric formulation should be used.
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| 15. |
- Choquet, Isabelle, 1965-, et al.
(författare)
-
Modeling and simulation of a heat source in electric arc welding
- 2011
-
Ingår i: Proceedings from the 4th Swedish Production Symposium, Lund, Sweden. ; , s. 202-211, s. 201-211
-
Konferensbidrag (refereegranskat)abstract
- This study focused on the modeling and simulation of a plasma heat source applied toelectric arc welding. The heat source was modeled in three space dimensions couplingthermal fluid mechanics with electromagnetism. Two approaches were considered forcalculating the magnetic field: i) three-dimensional, and ii) axi-symmetric. The anodeand cathode were treated as boundary conditions. The model was implemented in theopen source CFD software OpenFOAM-1.6.x. The electromagnetic part of the solverwas tested against analytic solution for an infinite electric rod. Perfect agreement wasobtained. The complete solver was tested against experimental measurements for GasTungsten Arc Welding (GTAW) with an axi-symmetric configuration. The shielding gaswas argon with thermodynamic and transport properties covering a temperature rangefrom 200 to 30 000 K. The numerical solutions then depend greatly on the approachused for calculating the magnetic field. The axi-symmetric approach indeed neglectsthe radial current density component, mainly resulting in a poor estimation of the arcvelocity. Various boundary conditions were set on the anode and cathode. Theseconditions, difficult to measure and to estimate a priori, significantly affect the plasmaheat source simulation results. Solution of the temperature and electromagnetic fieldsin the electrodes will thus be included in the forthcoming developments.
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| 16. |
- Choquet, Isabelle, 1965-, et al.
(författare)
-
Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc
- 2011
-
Ingår i: IIW Commission XII / SG 212 Intermediate meeting, University West, Trollhättan, Sweden, 21 - 23 March 2011, IIW Doc. XII-2017-11. ; , s. 1-12
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly resulting in a poor estimation of the arc velocity. Plasma arc simulations were done for various Ar-x%CO2 shielding gas compositions: pure argon ( x =0), pure carbon dioxide ( x =100), and mixtures of these two gases with x =1 and 10% in mole. The simulation results clearly show that the presence of carbon dioxide results in thermal arc constriction, and increased maximum arc temperature and velocity. Various boundary conditions were set on the anode and cathode (using argon as shielding gas) to evaluate their influence on the plasma arc. These conditions, difficult to measure and to estimate a priori, significantly affect the heat source simulation results. Solution of the temperature and electromagnetic fields in the anode and cathode will thus be included in the forthcoming developments.
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| 17. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding
- 2012
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 45:20, s. 205203-
-
Tidskriftsartikel (refereegranskat)abstract
- Four different approaches were considered for modelling the electromagneticfields of high-intensity electric arcs: i) the three-dimensional model, ii) the twodimensionalaxi-symmetric model, iii) the electric potential formulation, and iv) themagnetic field formulation. The underlying assumptions and the differences betweenthese models are described in detail. Models i) to iii) reduce to the same limit for anaxi-symmetric configuration with negligible radial current density, contrary to modeliv). Models i) to iii) were retained and implemented in the open source CFD softwareOpenFOAM. The simulation results were first validated against the analytic solutionof an infinite electric rod. Perfect agreement was obtained for all the models tested.The electromagnetic models i) to iii) were then coupled with thermal fluid mechanicsin OpenFOAM, and applied to the calculation of an axi-symmetric Gas Tungsten ArcWelding (GTAW) test case with short arc (2mm) and truncated conical electrode tip.Models i) and ii) lead to the same simulation results, but not model iii). Model iii)is suited in the specific limit of long axi-symmetric arc, with negligible electrode tipeffect. For short axi-symmetric arc, the more general axi-symmetric formulation ofmodel ii) should instead be used.
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| 18. |
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| 19. |
- Hartono, Erwin Adi, 1986, et al.
(författare)
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A PIV Study of The Cooling Air Flow in An Electric Generator Model
- 2012
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- One factor that affects the performance of a hydro power generatoris temperature. The efficiency, the electric resistance, the cables, thewindings, etc, are temperature-dependent. These make controllingtemperature rise in a generator of high importance in order to minimizehot spots and material failure. In order to tackle the problem airis used as a cooling fluid, which circulates through the stator and rotorin the generator.A generator model has been specially designed to perform fluid flowmeasurement. 2D-2C PIV (Two Dimension - Two Component ParticleImage Velocimetry) was used to measure the fluid velocity inside thestator channels. Stereo PIV (2D-3C) was used to measure fluid velocityoutside of the stator body.The results show that the tangential velocity component dominatesthe flow outside the stator. Inside the stator channels the fluid movesradially with a large recirculation region (almost half of the channelwidth) behind the coil. The flow structure inside the channels is shownto be independent of the rotor pole position.
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| 20. |
- Hartono, Erwin Adi, 1986, et al.
(författare)
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PIV Measurement of Air Flow in a Hydro Power Generator Model
- 2012
-
Ingår i: 16th Int Symp on Applications of Laser Techniques to Fluid Mechanics.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Cooling of electrical generators is of high importance since an uncontrolled temperature rise can lead toformation of hot spots which can cause material failure. The efficiency of the machines in converting themechanical energy to electricity is also affected by temperature, as the electric resistances of the cables andwindings are temperature dependent. In order to tackle the problem, air is used as a cooling fluid, whichcirculates through the stator and rotor in the generator. Despite the fact that electrical generators have beenused for many years, the knowledge about the cooling air flow inside them is still limited. Understanding theair flow inside the generators leads us into better predictions of heat transfer. The knowledge is alsoimportant when modifying the stator and rotor shapes, or when innovating new air cooling systems.In this work, a generator model has been specially designed to perform fluid flow measurement. RapidPrototyping was used to build the model due to its capability to create complex geometries in good accuracyin a short time.Planar two-component Particle Image Velocimetry (2D-2C) was used to measure the fluid velocity insidethe stator channels. A section of the stator was built in fully transparent material, to give optimal opticalaccess. The flow path inside the channels was small and thus the optical view was prone to light scatteringand reflection from the walls. A marker paint was used to paint the channel walls black, leaving just onetransparent wall. A special dummy channel without coils and baffles was manufactured, for use whenmeasuring in the middle channel rows.Stereo PIV (2D-3C) was used to measure the fluid velocity outside the stator body. In total 15measurement planes were created to capture the overall picture of the flow. This data was then interpolatedto get an overview of the flow field around the stator body.The results show that the tangential velocity component dominates the flow outside the stator. The flowoutside is highly swirling and three-dimensional. Inside the stator channels the fluid moves radially withlarge recirculation region (almost half of the stator channel width) behind the coil. Phase-averagedmeasurements show that the flow structures inside the channels are independent of the rotor pole position.
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| 21. |
- Jamshidi, Hamed, 1983, et al.
(författare)
-
Experimental and numerical investigation of hydro power generator ventilation
- 2014
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Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 22, s. Art. no. 012007-
-
Konferensbidrag (refereegranskat)abstract
- Improvements in ventilation and cooling offer means to run hydro power generators at higher power output and at varying operating conditions. The electromagnetic, frictional and windage losses generate heat. The heat is removed by an air flow that is driven by fans and/or the rotor itself. The air flow goes through ventilation channels in the stator, to limit the electrical insulation temperatures. The temperature should be kept limited and uniform in both time and space, avoiding thermal stresses and hot-spots. For that purpose it is important that the flow of cooling air is distributed uniformly, and that flow separation and recirculation are minimized. Improvements of the air flow properties also lead to an improvement of the overall efficiency of the machine. A significant part of the windage losses occurs at the entrance of the stator ventilation channels, where the air flow turns abruptly from tangential to radial. The present work focuses exclusively on the air flow inside a generator model, and in particular on the flow inside the stator channels. The generator model design of the present work is based on a real generator that was previously studied. The model is manufactured taking into consideration the needs of both the experimental and numerical methodologies. Computational Fluid Dynamics (CFD) results have been used in the process of designing the experimental set-up. The rotor and stator are manufactured using rapid-prototyping and plexi-glass, yielding a high geometrical accuracy, and optical experimental access. A special inlet section is designed for accurate air flow rate and inlet velocity profile measurements. The experimental measurements include Particle Image Velocimetry (PIV) and total pressure measurements inside the generator. The CFD simulations are performed based on the OpenFOAM CFD toolbox, and the steady-state frozen rotor approach. Specific studies are performed, on the effect of adding “pick-up” to spacers, and the effects of the inlet fan blades on the flow rate through the model. The CFD results capture the experimental flow details to a reasonable level of accuracy.
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| 22. |
- Javadi, Ardalan, 1984, et al.
(författare)
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A comparative study of scale-adaptive and large-eddy simulations of highly swirling turbulent flow through an abrupt expansion
- 2014
-
Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 22
-
Konferensbidrag (refereegranskat)abstract
- The strongly swirling turbulent flow through an abrupt expansion is investigated using highly resolved LES and SAS, to shed more light on the stagnation region and the helical vortex breakdown. The vortex breakdown in an abrupt expansion resembles the so-called vortex rope occurring in hydro power draft tubes. It is known that the large-scale helical vortex structures can be captured by regular RANS turbulence models. However, the spurious suppression of the small-scale structures should be avoided using less diffusive methods. The present work compares LES and SAS results with the experimental measurement of Dellenback et al. (1988). The computations are conducted using a general non-orthogonal finite-volume method with a fully collocated storage available in the OpenFOAM-2.1.x CFD code. The dynamics of the flow is studied at two Reynolds numbers, Re=6.0×104 and Re=105 , at the almost constant high swirl numbers of Sr=1.16 and Sr=1.23, respectively. The time-averaged velocity and pressure fields and the root mean square of the velocity fluctuations, are captured and investigated qualitatively. The flow with the lower Reynolds number gives a much weaker outburst although the frequency of the structures seems to be constant for the plateau swirl number.
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| 23. |
- Javadi, Ardalan, 1984, et al.
(författare)
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Advanced numerical prediction of strongly swirling turbulent flows
- 2013
-
Ingår i: 5th International Workshop on Cavitation and Dynamic Problems in Hydraulic Machinery. ; 23
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The strongly swirling turbulent flow through an abrupt expansion is investigated using highly resolved LES and hybrid RANS-LES, to shed more light on the stagnation region and the helical vortex breakdown. The vortex breakdown in an abrupt expansion resembles the so-called vortex rope occurring in hydro power draft tubes. It is known that the large-scale helical vortex structures can be captured by regular RANS turbulence models. However, the spurious suppression of the small-scale structures should be avoided using less diffusive methods [1]. The present work compares LES and hybrid RANS-LES results with the experimental measurement of Dellenback [2]. The computations are conducted using a general non-orthogonal, block-structured, finite-volume method with a fully collocated storage available in the OpenFOAM CFD code. The dynamics of the flow is studied at two Reynolds numbers, Re=6.0×104 and Re=10.0×104 to study the effect of high Reynolds turbulent flow with almost constant high swirl number (Sr=1.16 and Sr=1.23, respectively). The delayed detached eddy simulation (DDES) Spalart-Allmaras model [3] and the dynamic one-equation LES model are used to predict the coarse (8.2×106 cells) and fine (12×106 cells) discretized computational domain. The averaged velocity field, pressure field and the root mean square of the velocity fluctuations are captured and investigated qualitatively. Fig. 1 shows the instantaneous pressure iso-surface for the two operating conditions. The flow with lower Reynolds number gives much weaker outburst although the frequency of the structures seems to be constant for the plateau swirl number.
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| 24. |
- Javadi, Ardalan, 1984, et al.
(författare)
-
Unsteady numerical simulation of the flow in the U9 Kaplan turbine model
- 2014
-
Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 22, s. Art. no. 022001-
-
Konferensbidrag (refereegranskat)abstract
- The Reynolds-averaged Navier-Stokes equations with the RNG k-ε turbulence model closure are utilized to simulate the unsteady turbulent flow throughout the whole flow passage of the U9 Kaplan turbine model. The U9 Kaplan turbine model comprises 20 stationary guide vanes and 6 rotating blades (700 RPM), working at full load (0.71 m3/s). The computations are conducted using a general finite volume method, using the OpenFOAM CFD code. A dynamic mesh is used together with a sliding GGI interface to include the effect of the rotating runner. The hub and tip clearances are included in the runner. An analysis is conducted of the unsteady behavior of the flow field, the pressure fluctuation in the draft tube, and the coherent structures of the flow. The tangential and axial velocity distributions at three sections in the draft tube are compared against LDV measurements. The numerical result is in reasonable agreement with the experimental data, and the important flow physics close to the hub in the draft tube is captured. The hub and tip vortices and an on-axis forced vortex are realistically captured. The numerical results show that the frequency of the forced vortex in 1/5 of the runner rotation.
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| 25. |
- Javadi, Ardalan, 1984, et al.
(författare)
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Velocity and pressure fluctuations induced by the precessing helical vortex in a conical diffuser
- 2014
-
Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 22, s. Art. no. 032009-
-
Konferensbidrag (refereegranskat)abstract
- The flow unsteadiness generated in the draft tube cone of hydraulic turbines affects the turbine operation. Therefore, several swirling flow configurations are investigated using a swirling apparatus in order to explore the unsteady phenomena. The swirl apparatus has two parts: the swirl generator and the test section. The swirl generator includes two blade rows being designed such that the exit velocity profile resembles that of a turbine with fixed pitch. The test section includes a divergent part similar to the draft tube cone of a Francis turbine. A new control method based on a magneto rheological brake is used in order to produce several swirling flow configurations. As a result, the investigations are performed for six operating regimes in order to quantify the flow from part load operation, corresponding to runaway speed, to overload operation, corresponding to minimum speed, at constant guide vane opening. The part load operation corresponds to 0.7 times the best efficiency discharge, while the overload operation corresponds to 1.54 times the best efficiency discharge. LDV measurements are performed along three survey axes in the test section. The first survey axis is located just downstream the runner in order to check the velocity field at the swirl generator exit, while the next two survey axes are located at the inlet and at the outlet of the draft tube cone. Two velocity components are simultaneously measured on each survey axis. The measured unsteady velocity components are used to validate the results of unsteady numerical simulations, conducted using the OpenFOAM CFD code. The computational domain covers the entire swirling apparatus, including strouts, guide vanes, runner, and the conical diffuser. A dynamic mesh is used together with sliding GGI interfaces to include the effect of the rotating runner. The Reynolds averaged Navier–Stokes equations coupled with the RNG k–ε turbulence model are utilized to simulate the unsteady turbulent flow throughout the swirl generator.
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| 26. |
- Javidi Shirvan, Alireza, et al.
(författare)
-
Modelling of electrode-arc coupling in electric arc welding
- 2014
-
Ingår i: Proceedings of The 6<sup>th</sup> International Swedish Production Symposium 2014 16-18 September 2014. - 9789198097412 ; , s. 1-8
-
Konferensbidrag (refereegranskat)abstract
- Modelling of the arc in electric arc welding is significant to achieve a better pro-cess understanding, thus gain better weld quality and a more efficient production process.It requires knowing the conditions at the surfaces of the anode and cathode. These condi-tions are very difficult to set from measurements and should be calculated. This requiresmodelling the complex physics of the electrode layer coupling electrode and arc. Thispaper presents a self-consistent electrode layer model that 1) is suited to welding applica-tions, 2) accounts for the known physics taking place, and 3) satisfies the basic conservationrequirements. The model is tested for different conditions. Its potentiality for welding ap-plications is shown through calculations coupling plasma arc, electrode and cathode layermodels. The calculations are done for both tungsten and thoriated tungsten electrode.
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| 27. |
- Javidi-Shirvan, Alireza, 1978, et al.
(författare)
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Numerical modelling of shielding gas flow and heat transfer in laser welding process
- 2012
-
Ingår i: Proceedings of The 5th International Swedish Production Symposium, Linköping, Sweden. - 9789175197524 ; , s. 269-276
-
Konferensbidrag (refereegranskat)abstract
- In the present study a three-dimensional model has been developed to study shieldinggas in a laser welding process using computational fluid dynamics. Laser heatingof titanium alloy Ti6Al4V was done by imposing a volumetric laser heat source. Themodel was implemented in the open source software OpenFOAM and applied to theinvestigation of the shielding gas behaviour over the base metal.Three different cases regarding the outlet shape of the shielding pipe were studied. Insome laser welding processes a shielding plate is used to help protecting the weldedarea. The plate injects the additional shielding gas screen during the welding process.This plate is also considered in the modelling as the fourth case.The influence of the shape of the pipe outlet is discussed.The simulation results confirmedthat the shielding plate can protect the welded area by covering the welding pathwith shielding gas. However, the simulation showed that the shielding gas leaving theplate flows towards the keyhole. It can thus bring some fumes over the keyhole whichis not desired since it can make it difficult to track the welding with optical method.
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| 28. |
- Johansson, Håkan T, 1977, et al.
(författare)
-
The unbound isotopes He-9,He-10
- 2010
-
Ingår i: Nuclear Physics A. - Elsevier : Elsevier BV. - 0375-9474 .- 1873-1554. ; 842:1-4, s. 15-32
-
Tidskriftsartikel (refereegranskat)abstract
- The unbound nuclei He-9 and He-10 have been produced in proton-knockout reactions from a 280 MeV/u Li-11 beam impinging on a liquid hydrogen target at the ALADIN-LAND setup at GSI. Information on their nuclear structure has been obtained from the relative-energy spectra, He-8 + n and He-8 + 2n, employing reaction models incorporating the structure of Li-11. The (8H)e + n relative-energy spectrum is dominated by a strong peak-like structure at low energy, which may be interpreted within the effective-range approximation as the result of an s-wave interaction with a neutron scattering length of -3.17(66) fm. This spectrum also shows evidence for resonance states at 1.33(8) MeV and at 2.4 MeV above the He-8 + n threshold. It is argued that the s-state might not be the He-9 ground state. For He-8 + n + n, the analysis of the relative-energy spectrum gives two alternative possibilities for an interpretation: either a narrow resonance at 1.42(10) MeV (Gamma = 1.11(76) MeV) superimposed on a correlated background, or two overlapping resonances, a ground state at 1.54(11) MeV (Gamma = 1.91(41) MeV) together with an excited state at 3.99(26) MeV (Gamma = 1.64(89) MeV). The two possible interpretations are discussed. (C) 2010 Elsevier B.V. All rights reserved.
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| 29. |
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| 30. |
- Marganiec, C., et al.
(författare)
-
Coulomb breakup of 17Ne from the viewpoint of nuclear astrophysics
- 2013
-
Ingår i: Proceedings of Science.
-
Konferensbidrag (refereegranskat)abstract
- By the Coulomb breakup of 17Ne, the time-reversed reaction 15O(2p,γ)17Ne has been studied. This reaction might play an important role in the rp process, as a break-out reaction of the hot CNO cycle. The secondary 17Ne ion beam with an energy of 500 MeV/nucleon has been dissociated in a Pb target. The reaction products have been detected with the LAND-R3B experimental setup at GSI. The preliminary differential and integral Coulomb dissociation cross section sCoul has been determined, which then will be converted into a photo-absorption cross section sphot o, and a two-proton radiative capture cross section σcap. Additionally, information about the structure of the 17Ne, a potential two-proton halo nucleus, will be received. The analysis is in progress.
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| 31. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
A PARAMETRIC STUDY OF THE AIR FLOW IN AN ELECTRIC GENERATOR THROUGH STEPWISE GEOMETRY MODIFICATIONS
- 2011
-
Ingår i: An ECCOMAS Thematic Conference, CFD and OPTIMIZATION. - 9786056142741
-
Konferensbidrag (refereegranskat)abstract
- The air flow through an electric generator has been numerically investigated to give a better understanding of the flow for cooling purposes. A simple generator design has been chosen to start with, and stepwise modifications have been imposed to the design of the rotor and the stator. The flow properties for all cases have been compared to each other to investigate the effect of each parameter change on the flow inside the machine.The flow is predicted with the OpenFOAM solver MRFSimpleFOAM, which is a steady-state solver that uses the Frozen Rotor concept for the rotor-stator interaction.This means that there is no actual mesh movement in this study, but instead, the rotating regions in the domain are provided with source terms that account for rotation. The flow through the machine is not explicitly specified. Instead, it is the effect of the rotating regions that drive the flow through the machine. The reason for this is the lack of knowledge of the flow rate and inlet velocity distribution, which requires an approach without inlet and outlet. The flow is thus recirculating in the computational domain.
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| 32. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
CFD of Air Flow in Hydro Power Generators for Convective Cooling, using OpenFOAM
- 2010
-
Ingår i: 5th European Conference on Computational Fluid Dynamics, ECCOMAS CFD 2010. - 9789899677807 ; , s. 556-
-
Konferensbidrag (refereegranskat)abstract
- Hydroelectric power generation plays an important role in the total electric power generation in Sweden. Almost half of the electric power in Sweden is generated by hydro electric power plants and any modifications and improvements of the system would lead to a significant contribution to the total electric energy production. Two large sources of losses in the electric generators are the thermal and ventilation losses. The electric resistance in the generator system causes heat generation in windings and coils, which decreases the total efficiency of the stator in delivering power and causes material through thermal stresses in components. The generators are thus cooled by air flowing through the rotor and stator.This paper will focus on ventilation of axially air-cooled generators through the stator cooling channels in the stator wall. The name axial suggests that the air movement in the gap between rotor and stator is along the rotors axis of rotation. It is important to have a good understanding of the complicated flow field in the air passages in the generator in order to be able to design the cooling of the system. The air flow is driven by the rotational movement of the rotor and its appended poles, which will act as a fan, into the radially extended stator channels. The air thus cools the stator body and the stator coils.The flow in the generator here is in the present work modeled with a multiple-reference-frame method, which includes source terms for rotation. This ensures that Coriolis effects are taken into account in the simulations. The flow is simulated employing a low-Reynolds number turbulence model where the fluid flow is solved throughout the boundary layer. The computational domain is generated without inlets and outlets so that the volume rate of flow through the generator is determined by the solution, rather than by an imposed inlet volume flow rate. Some parts of the surrounding environment are thus included in the simulation to allow for recirculation of air in the domain. The establishment of the flow depends on the pressure distribution in the domain. The development of the pressure distribution has been validated for the laminar flow between two concentric circular cylinders where the inner cylinder rotates and the outer is at rest. The numerical results for both pressure and velocity distributions have been in agree with analytical results, which will also be presented in the paper.
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| 33. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THE COOLING AIR FLOW IN AN ELECTRIC GENERATOR
- 2011
-
Ingår i: HEFAT2011, 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics. ; , s. 242-249
-
Konferensbidrag (refereegranskat)abstract
- The cooling air flow in a small-scale electric generator has been investigated experimentally and numerically, and the results have been compared to each other. The studies have been made in cold conditions, without heat transfer. The velocity profiles at the inlet of the generator have been measured by means of a 5-hole probe, traversed in the axial direction to give the axial distribution of the radial velocities at the inlet of the generator. The outlet velocity distribution has been measured by means of a total-pressure rake, consisting of a number of total pressure probes, which gives the horizontal distribution of the velocity magnitudes, aligned with the stator channels at the outlet of the generator. Smoke visualization of the flow has been performed at the inlet of the generator and the flow pattern has been visualized.The numerical study has been performed using the OpenFOAM open source CFD software. The corresponding numerical velocity profiles at the inlet and the outlet of the generator have been extracted and compared with the experimental profiles. The velocity vectors at the inlet of the generator have been compared to the flow pattern obtained by the smoke visualization.Because of geometrical dissimilarities between the experimental rig and the numerical computational domain, there are unavoidable differences in the results. This yields a qualitative comparison, although the comparisons still show a relatively good quantitative agreement between the experiments and the numerical simulations. (Note: Figure 13 and its description updated)
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| 34. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
EXPERIMENTAL AND NUMERICAL STUDY OF COOLING AIR FLOW IN A HYDROELECTRIC GENERATOR
- 2012
-
Ingår i: European Research Comunnity On Flow, Turbulence and Combustion, ETMM9.
-
Konferensbidrag (refereegranskat)abstract
- The cooling air flow inside an electric generator has been numerically simulated and validated with experimental measurements. The numerical studies are performed using OpenFOAM in a quasi-steady mode at three rotor speeds. The numerical and experimental results show similar flow distributions.
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| 35. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
Experimental assessment of a fully predictive CFD approach, for flow of cooling air in an electric generator
- 2014
-
Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 124, s. 223-230
-
Tidskriftsartikel (refereegranskat)abstract
- A fully predictive computational fluid dynamics approach is assessed for the flow of cooling air in an axially cooled electric generator. The flow is driven solely by the rotation of the rotor, as in the real application. A part of the space outside the generator is included in the computational domain to allow for the flow of air into and out of the machine. This yields a flow prediction that is determined without the input of any experimental data. Two different choices of ‘surrounding’ outer boundary conditions are studied, and the mesh sensitivity is discussed.The numerically predicted flow is compared with experimental data. Flow visualizations are performed at the inlet. The inlet velocity distribution is determined using 5-hole and total pressure probes. The outlet velocity distribution is determined using a total pressure rake.It is found that the numerical approach qualitatively, and to a large extent quantitatively, predicts the same velocity distributions as in the experiment. The numerically predicted flow rates are however lower than that estimated from the experimental data. The differences are considered small, given the many uncertainties in both the numerical and experimental studies, and that they are performed completely independently.
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| 36. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
Flow of cooling air in an electric generator model - An experimental and numerical study
- 2014
-
Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 114, s. 644-653
-
Tidskriftsartikel (refereegranskat)abstract
- The need for electric power is continuously increasing. The power output of existing electric generators is forced to its limit, and the new intermittent electric energy sources increase the variations of the operating conditions of the electric generators in the power system. This requires better cooling of the heat that is generated by the electric losses in generators. New experimental and numerical techniques need to be developed and validated, to increase the knowledge of the cooling processes and to improve the accuracy of the design tools. The present work focuses on the flow of air through electric generators, as a necessary and important first step towards future accurate and detailed convective heat transfer analysis.A half-scale model of an electric generator is designed and manufactured specifically for detailed experimental and numerical studies of the flow of cooling air through the machine. The model is slightly simplified compared to the original geometry, to benefit from the use of geometry parameterization, and with numerical mesh quality in mind already at the design of the experimental set-up. Special care is taken to provide optical access for accurate and detailed Particle Image Velocimetry (PIV) measurements inside the machine.The experimental measurements include PIV measurements at the inlet and inside the machine, and total pressure measurements at the outlet of the stator channels.Computational Fluid Dynamics (CFD) simulations are performed using two approaches. In one approach the inlet flow rate is specified from the experimental data, as is commonly done in the literature. In the other approach the flow rate is determined from the numerical simulation, independently of the experimental results, yielding predictions differing by 2-7% compared to the experimentally estimated values. The results of both approaches capture the experimental flow details to a high level of accuracy. Mesh sensitivity studies highlight the need of a specific resolution of the baffle edges.
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| 37. |
- Moradnia, Pirooz, 1982, et al.
(författare)
-
Transient and steady-state air flow simulations in generators using OpenFOAM
- 2012
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The flow of air in two generator geometries has been simulated with OpenFOAM-1.6-ext and the results compared against CFX. The effect of the different simulation strategies as well as numerical methods, turbulence models, matrix linear solvers, matrix solver preconditioners, mesh resolutions, rotor-stator interface locations and boundary conditions on the flow has been examined. The convergence, computational time, flow field, axial torque on the rotor and windage losses have been observed and conclusions have been drawn.
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| 38. |
- Muntean, S., et al.
(författare)
-
Mathematical, numerical and experimental analysis of the swirling flow at a Kaplan runner outlet
- 2012
-
Ingår i: 26th IAHR Symposium on Hydraulic Machinery and Systems. - : IOP Publishing Ltd. ; 15:Part 3, s. Art. no. 032001-
-
Konferensbidrag (refereegranskat)abstract
- The paper presents a novel mathematical model for a-priori computation of the swirling flow at Kaplan runners outlet. The model is an extension of the initial version developed by Susan-Resiga et al [1], to include the contributions of non-negligible radial velocity and of the variable rothalpy. Simple analytical expressions are derived for these additional data from three-dimensional numerical simulations of the Kaplan turbine. The final results, i.e. velocity components profiles, are validated against experimental data at two operating points, with the same Kaplan runner blades opening, but variable discharge
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| 39. |
- Nilsson, Håkan, 1971, et al.
(författare)
-
Effects of inlet boundary conditions, on the computed flow in the Turbine-99 draft tube, using OpenFOAM and CFX
- 2012
-
Ingår i: 26th IAHR Symposium on Hydraulic Machinery and Systems. - : IOP Publishing Ltd. ; 15:PART 3, s. Art. no. 032002-
-
Konferensbidrag (refereegranskat)abstract
- The flow in the Turbine-99 Kaplan draft tube was thoroughly investigated at three workshops (1999, 2001, 2005), which aimed at determining the state of the art of draft tube simulations. The flow is challenging due to the different flow phenomena appearing simultaneously such as unsteadiness, separation, swirl, turbulence, and a strong adverse pressure gradient. The geometry and the experimentally determined inlet boundary conditions were provided to the Turbine-99 workshop participants. At the final workshop, angular resolved inlet velocity boundary conditions were provided. The rotating non-axi-symmetry of the inlet flow due to the runner blades was thus included. The effect of the rotating angular resolution was however not fully investigated at that workshop. The first purpose of this work is to further investigate this effect. Several different inlet boundary conditions are applied – the angular resolved experimental data distributed at the Turbine-99 workshop, the angular resolved results of a runner simulation with interpolated values using different resolution in the tangential and radial directions, and an axi-symmetric variant of the same numerical data. The second purpose of this work is to compare the results from the OpenFOAM and CFX CFD codes, using as similar settings as possible. The present results suggest that the experimental angular inlet boundary conditions proposed to the workshop are not adequate to simulate accurately the flow in the T-99 draft tube. The reason for this is that the experimental phase-averaged data has some important differences compared to the previously measured time-averaged data. Using the interpolated data from the runner simulation as inlet boundary condition however gives good results as long as the resolution of that data is sufficient. It is shown that the difference between the results using the angular-resolved and the corresponding symmetric inlet data is very small, suggesting that the importance of the angular resolution is small. The results from OpenFOAM and CFX are very similar as long as the inlet data resolution is fine enough. CFX seems to be more sensitive to that resolution.
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| 40. |
- Nilsson, Håkan, 1971, et al.
(författare)
-
Implementation of a 3D solver for electric arc welding, coupling fluid mechanics with electromagentics
- 2011
-
Ingår i: 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics. HEFAT2011. ; , s. 614-620
-
Konferensbidrag (refereegranskat)abstract
- This paper describes the implementation of a 3D numerical solver for electric arc welding, where the fluid mechanics of the shielding gas is strongly influenced by the electromagnetic fields. The implementation is done in the OpenFOAM-1.6.x OpenSource Computational Fluid Dynamics (CFD) tool (www.openfoam.com). OpenFOAM is basically a general library of C++ classes for numerical simulation of continuum mechanic problems, but it is mainly used in CFD. The basics of high-level programming in OpenFOAM is described briefly, while the main components of the implementation done in the present work are described in high detail. The implementation is validated against an analytical solution of the electromagnetic field of an infinite electrically conducting rod, and against an experimental study of GTAW (Gas Tungsten Arc Welding). The numerical results agree very well with both the analytical and experimental results. A grid-dependency study has been made for the GTAW case, showing that the main features of the presented solutions are independent of the mesh size.
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| 41. |
- Nilsson, Håkan, 1971
(författare)
-
Simulations of the vortex in the Dellenback abrupt expansion, resembling a hydro turbine draft tube operating at part-load
- 2012
-
Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 15, s. Art. no. 022016-
-
Konferensbidrag (refereegranskat)abstract
- This work presents an OpenFOAM case-study, based on the experimental studies of the swirling flow in the abrupt expansion by Dellenback et al.[1]. The case yields similar flow conditions as those of a helical vortex rope in a hydro turbine draft tube working at part-load. The case-study is set up similar to the ERCOFTAC Conical Diffuser and Centrifugal Pump OpenFOAM case-studies [2,3], making all the files available and the results fully reproducable using OpenSource software. The mesh generation is done using m4 scripting and the OpenFOAM built-in blockMesh mesh generator. The swirling inlet boundary condition is specified as an axi-symmetric profile. The outlet boundary condition uses the zeroGradient condition for all variables except for the pressure, which uses the fixed mean value boundary condition. The wall static pressure is probed at a number of locations during the simulations, and post-processing of the time-averaged solution is done using the OpenFOAM sample utility. Gnuplot scripts are provided for plotting the results. The computational results are compared to one of the operating conditions studied by Dellenback, and measurements for all the experimentally studied operating conditions are available in the case-study.Results from five cases are here presented, based on the kEpsilon model, the kOmegaSST model, and a filtered version of the same kOmegaSST model, named kOmegaSSTF [4,5]. Two different inlet boundary conditions are evaluated. It is shown that kEpsilon and kOmegaSST give steady solutions, while kOmegaSSTF gives a highly unsteady solution. The time-averaged solution of the kOmegaSSTF model is much more accurate than the other models. The kEpsilon and kOmegaSST models are thus unable to accurately model the effect of the large-scale unsteadiness, while kOmegaSSTF resolves those scales and models only the smaller scales. The use of two different boundary conditions shows that the boundary conditions are more important than the choice between kEpsilon and kOmegaSST, for the results just after the abrupt expansion.
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| 42. |
- Petit, Olivier, 1980, et al.
(författare)
-
A swirl generator case study for OpenFOAM
- 2010
-
Ingår i: 25th IAHR Symposium on Hydraulic Machinery and Systems.
-
Konferensbidrag (refereegranskat)abstract
- This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-epsilon model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against designed velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and designed profiles. This case study was presented at the 5th OpenFOAM Workshop, held in Gothenburg, Sweden, as a tutorial on how to treat turbomachinery applications in OpenFOAM.
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| 43. |
- Petit, Olivier, 1980, et al.
(författare)
-
Comparison of numerical and experimental results of the flow in the U9 Kaplan turbine model
- 2010
-
Ingår i: 25th IAHR Symposium on Hydraulic Machinery and Systems. - London : IOP Publishing Ltd. ; , s. 12024-
-
Konferensbidrag (refereegranskat)abstract
- The present work compares simulations made using the OpenFOAM CFD code with experimental measurements of the flow in the U9 Kaplan turbine model. Comparisons of the velocity profiles in the spiral casing and in the draft tube are presented. The U9 Kaplan turbine prototype located in Porjus and its model, located in Älvkarleby, Sweden, have curved inlet pipes that lead the flow to the spiral casing. Nowadays, this curved pipe and its effect on the flow in the turbine is not taken into account when numerical simulations are performed at design stage. To study the impact of the inlet pipe curvature on the flow in the turbine, and to get a better overview of the flow of the whole system, measurements were made on the 1:3.1 model of the U9 turbine. Previously published measurements were taken at the inlet of the spiral casing and just before the guide vanes, using the laser Doppler anemometry (LDA) technique. In the draft tube, a number of velocity profiles were measured using the LDA techniques. The present work extends the experimental investigation with a horizontal section at the inlet of the draft tube. The experimental results are used to specify the inlet boundary condition for the numerical simulations in the draft tube, and to validate the computational results in both the spiral casing and the draft tube. The numerical simulations were realized using the standard k-e model and a block-structured hexahedral wall function mesh.
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| 44. |
- Petit, Olivier, 1980, et al.
(författare)
-
Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser
- 2013
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; Volume 2013
-
Tidskriftsartikel (refereegranskat)abstract
- Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTACcentrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test caseconsists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number ofmeasurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numericalmethods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and fourdifferent turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses afully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadinessof the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flowcomputations.The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for acrude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.
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| 45. |
- Petit, Olivier, 1980, et al.
(författare)
-
Unsteady Simulations of the Flow in a Swirl Generator, using OpenFOAM
- 2011
-
Ingår i: International Journal of Fluid Machinery and Systems. - 1882-9554. ; 4:1, s. pp.199-208
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Tidskriftsartikel (refereegranskat)abstract
- This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-ε model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against design velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and design profiles. The unsteady pressure fluctuations at four different positions in the draft tube is recorded. A Fourier analysis of the numerical results is compared whit that of the experimental values. The amplitude and frequency predicted by the numerical simulation are comparable to those given by the experimental results, though slightly over estimated.
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| 46. |
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| 47. |
- Svensson, Mats, 1960, et al.
(författare)
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Simulation of Venous Plexus Blood Flow during Rapid Spinal Bending
- 2010
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Ingår i: Proc. 6th World Congress of Biomechanics, Singapore, 1-6 August 2010.
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Konferensbidrag (refereegranskat)abstract
- The Spinal Venous Plexus has special properties compared to the veins in most other regions of the body. The plexus has one part situated inside the spinal canal, embedded in the epidural fat, and one part surrounding the spine. These two parts are connected to each other via the intervertebral vein bridges at each spinal level. These vein vessels, unlike most other veins in the body, have no valves so the blood can flow in both directions in every vessel section. The abundance of vein vessels in the spinal region cannot be explained by exceptional nutritional needs and there is no corresponding abundance of arteries. Svensson et al. (1989) hypothesized that the venous plexus is shaped like this in order to facilitate the change of the spinal canal inner volume that takes place during spinal sagittal bending. During sagittal bending the spinal canal becomes longer in extension and shorter in flexion while its diameter remains almost constant. This leads to a very significant change in the inner volume of the spinal canal during this motion. In the cervical section a volume change in the order of 25% will take place between maximum flexion and maximum extension. Since the contents of the canal are virtually incompressible a mechanism to exchange volume between the inside and the outside of the spinal canal must exist to allow for spinal sagittal bending motion. In the spinal canal there is only one fluid system that allows for a rapid exchange of volume between the inside and the outside of the spinal canal, namely the inner venous plexus and its many connection points to the external vein system.Svensson et al. (2000) summarized findings of transient pressure changes during experimental rapid neck bending exposures (extension, flexion and lateral whiplash motion). The pressure transients were hypothesized to result from rapid vein blood flow changes. These results were accompanied by findings of spinal ganglion nerve cell membrane dysfunction that potentially was caused by pressure loading in the intervertebral canals. The present work aims at explaining the flow pattern in the spinal venous plexus during rapid spinal bending. One particular focus is whiplash motion in the neck during a car accident. Recent versions of Computational Fluid Dynamics (CFD) modeling software such as Fluent and Open Foam have been utilized to model the internal venous plexus and its intervertebral vein bridges. The spinal canal length change during experimental and simulated whiplash motion has been used as input to the CFD models. The results indicate complex flow phenomena with rapid flow accelerations that correlate to local pressure transients. The pressure profiles are sensitive to changes in neck motion input such as direction and acceleration magnitude.References: MY Svensson, et al. (1989): A Theoretical Model for and a Pilot Study Regarding Transient Pressure Changes in the Spinal Canal under Whip-lash Motion. Chalmers University of Technology, Injury Prevention, Sweden, R 005 MY Svensson et al. (2000): NECK INJURIES IN CAR COLLISIONS. Accident Analysis and Prevention, 32 (2000) 167-175
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| 48. |
- Vallier, Aurelia, et al.
(författare)
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Mass transfer cavitation model with variable density of nuclei
- 2010
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Ingår i: 7th International Conference on Multiphase Flow, ICMF 2010, Tampa, USA, May 31-June 4, 2010.
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Konferensbidrag (refereegranskat)abstract
- The performance of the mass transfer cavitation model of Sauer is investigated using a varying nuclei concentration. The Sauer model assumes a uniform nuclei distribution despite measurement of the non-homogeneous nucleus population. Here the nuclei density is studied and a non-homogeneous nuclei distribution in a modified Sauer model is implemented. It is used to study how the increased cavitation nuclei density in regions of low pressure affects the inception of cavitation. The interface between the water and the water vapor is tracked using a volume of fluid method and vaporization and condensation are described by the modified Sauer¿s mass transfer model. The nuclei in the liquid phase are modeled with a Lagrangian Particle Tracking method. The LPT computations yield to a non uniform nuclei distribution which consists of nuclei accumulation close to the leading edge and no nuclei on average in the boundary layer of the hydrofoil. The sensitivity of the modified Sauer model to nuclei distribution is proven. The shape of the sheet cavity and the volume of vapour are affected by the nuclei content.
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| 49. |
- Vallier, Aurelia, et al.
(författare)
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Procedure for the break-up of cavitation sheet
- 2011
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Ingår i: 4-th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, October, 26-28, 2011, Belgrade, Serbia. - 9788670837409 ; , s. 77-85
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The actual mass transfer cavitation models are limited by the grid size dependency of the Volume-Of-Fluid method. A new multi-scale approach is developed which can model the presence of bubbles smaller than the grid size. Using this method for simulations of cavitating hydrofoil will lead to a better modelling of the mixture of vapor and liquid in the transition region between the attached cavity and the shedding cloud. The principle of this approach is to complement the VOF method with a two-way coupling Lagrangian particle tracking method. The VOF-LPT coupling model is tested on simplified configurations for the breakup of an attached cavity. The results show that the model successfully displays the formation of small structures and gives a better description of the liquid/gas mixture.
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