| 1. |
- Hedström, Brita, et al.
(författare)
-
Visby Innerstad : En användningsplan
- 1973
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Rapport (populärvet., debatt m.m.)abstract
- Sedan lång tid föreligger i stort sett enighet om att bevara innerstadens bebyggelse och att anpassa eventuella nytillskott till det redan bestående. Med den inställningen har förändringsprocessen både dämpats och mildrats men ändå inte bragts att avstanna. Förändringar sker ständigt om det också huvudsakligen i smått: de många synbart så anspråkslösa byggnadsåtgärderna adderar efterhand ihop sig till något större och mer genomgripande. Långsamt, nästan omärkligt, ändrar innerstaden sitt ansikte.Ändå är det inte själva husen som förändrats mest utan användningen av dem. Ur funktionell synpunkt har 1950 - och 60-talen har varit något av en omstörtning i innerstadens historia: den har förlorat nästan hälften av de boende, en stor del av detaljhandeln och praktiskt taget helt sin gamla roll som skolcentrum. I gengäld har ytterstaden vuxit ut till ett sammanhängande kilometerbrett bälte. Till stor del av denna funktionella förändring en följd av beslutet att bevara innerstadens bebyggelse. Vad som inte fått plats inom den gamla ramen har etablerats utandör den.Föreliggande arbete vill ge en översiktlig bild av förändringsförloppen, sedda i ett långt tidsperspektiv men med tonvikt på dagsläget. Bebyggelsen tas upp till utförlig granskning men också användningen av den. Det är just samspelet mellan husen och de funtkioner, de fyller, som kan sägas utgöra bokens huvudtema. I de flesta fall är detta sammanhang hus-användning alldeles konfliktfritt och föranleder därför inte heller någon diskussion. Vad som behandlas är de relativt få problematiska fallen, hus som borde rustas upp för att fylla sin uppgift, hus som är olämpligt nyttjade eller inte använda alls. En serie sådana fall tas upp till systematisk genomgång; samtidigt berörs också de trafik - och miljömässiga konsekvenserna. Bokens syfte är alltså klart: den ger ett underlag av fakta för arbetet med att jämka samman byggnader och användningsformer. I den meningen kan skriften kallas en anvädningsplan för Visby innanför murarna.Arkitekturskolanas arbete har bedrivitis parallellt med den kommunala Innerstadskommitténs verksamhet. Något organiserat samarbete har inte förekommit med de informella kontakterna har varit både täta och goda. Att likheterna mellan Innerstadskommittén och Arkitekturskolans slutsatser blivit så pass stora, kan tillskrivas en gemensam helhetssyn.En av Arkitekturskolans elever, arkitekt Lars-Ingvar Larsson, har tidigare självständigt genomfört en undersökning av förändringar i innerstaden 1945-70- Denna studie publicerats separat och bör uppfattas som ett komplement till den hör föreliggande.Förutom de i innehållsförteckningen nämnda har ytterligare några aktivt medverkat i arbetet. Studiet av trafikfrågorna i innerstaden, i hamnen och öster om ringmuren leddes av Åke Claesson, I fältstudier och diskussioner medverkande Göran Månsson.Arkitekturskolan har fått god hjälp av ett antal initierade personer i Visby. Särskild tacksamhet är vi skyldiga byggnadsnämnden ordförande Henning Jacobson, kommunalrådet C B Stenström, stadsarkitekten Måns Hagbergm f. länsbostadsdorektören Åke Malmberg och landsantikvarien Gunnar Svahnström. I boken publiceringskostnaderna har ekonomiskt bidrag lämnats av Gotlands kommun och Riksantikvarieämbetet.Boken har redigerats av Sture Balgård och Ann Mari Westerlind med hjälp av Henrik O Andersson, Bo Ek, Göran Lindahl, Fredrik von Platen, John Sjöström Gunnar Westerlind och Hans Wetterfors.Skeppsholmen, Stockholm, sommaren 1973.Arkitekturskolans lärare och elever.
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| 2. |
- Reifarth, R., et al.
(författare)
-
Nuclear astrophysics with radioactive ions at FAIR
- 2016
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
-
Konferensbidrag (refereegranskat)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 3. |
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| 4. |
- Andersson, Anders G., et al.
(författare)
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Flow through a two-scale porosity material
- 2009
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Ingår i: Research Letters in Materials Science. - : Hindawi Limited. - 1687-6822 .- 1687-6830.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Flow through a two-scale porous medium is here investigated by a unique comparison between simulations performed with computational fluid dynamics and the boundary element method with microparticle image velocimetry in model geometries.
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| 5. |
- Andersson, Anders G., et al.
(författare)
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Fluid flow through porous media with dual scale porosity
- 2008
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Ingår i: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19). - : University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science.
-
Konferensbidrag (refereegranskat)abstract
- Flow in two scale porous media takes place in applications such as advanced composites manufacturing. Knowledge of this flow is of general importance and is crucial for filtration mechanisms when functional filler-particles are added to the liquid resin impregnating the fibrous preform. Means to model and experimentally visualise this flow is here investigated. In particular simulations performed with computational fluid dynamics and the boundary element method are compared to micro particle image velocimetry in a model geometry.
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| 6. |
- Baart, Pieter, et al.
(författare)
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Contaminant particle migration in a double restriction seal
- 2013
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Ingår i: Proceedings of the STLE Annual Meeting and Exhibition 2013, Detroit MI, USA.. - : STLE. ; , s. 125-
-
Konferensbidrag (refereegranskat)abstract
- Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile.In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication
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| 7. |
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| 8. |
- Baart, Pieter, et al.
(författare)
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The influence of speed, grease type, and temperature on radial contaminant particle migration in a double restriction seal
- 2011
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 54:6, s. 867-877
-
Tidskriftsartikel (refereegranskat)abstract
- Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile. In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication.
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| 9. |
- Badala, A, et al.
(författare)
-
Subthreshold production of low momentum K+ in p+C at 1.2 GeV
- 1998
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Ingår i: PHYSICAL REVIEW LETTERS. - : AMERICAN PHYSICAL SOC. - 0031-9007. ; 80:22, s. 4863-4866
-
Tidskriftsartikel (refereegranskat)abstract
- The double differential cross section of low momentum kaons (less than or equal to 0.3 GeV/c) from p + C collisions at subthreshold bombarding energies has been for the first time measured by the use of the CLAMSUD magnetic spectrometer installed at the C
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| 10. |
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| 11. |
- Castro, Marley, et al.
(författare)
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Multi-Cubesat Mission For Auroral Acceleration Region Studies
- 2021
-
Ingår i: IAC 2021 Congress Proceedings, 72nd International Astronautical Congress (IAC), Dubai, United Arab Emirates. - : International Astronautical Federation (IAF).
-
Konferensbidrag (refereegranskat)abstract
- The Auroral Acceleration Region (AAR) is a key region in understanding the Magnetosphere-Ionosphere interaction. To understand the physical, spatial and temporal features of the region, multi-point measurements are required. Distributed small-satellite missions such as constellations of multiple nano satellites (for example multi-unit CubeSats) would enable such type of measurements. The capabilities of such a mission will highly depend on the number of satellites - one reason that makes low-cost platforms like CubeSats a very promising choice. In a previous study, the state-of-the-art of miniaturized payloads for AAR measurements was analyzed and evaluated and capabilities of different multi-CubeSat configurations equipped with such payloads in addressing different open questions in AAR were discussed. In this paper the mission analysis and possible mission design, as well as necessary technology developments of such multi-CubeSat mission are identified and presented.
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| 12. |
- Duenas Dobrowolski, Jan, et al.
(författare)
-
Experimental Study of Lubricating Grease Flow inside the Gap of a Labyrinth Seal Using Microparticle Image Velocimetry
- 2018
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 61:1, s. 31-40
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the flow of lubricating greases in a labyrinth seal geometry is studied using microparticle image velocimetry (µPIV). The aim is to evaluate the grease velocity distribution inside the gap of a labyrinth seal and to find a relationship between the grease consistency and the transferred speed from the rotating ring in order to choose the correct grease as a sealing medium. In addition, the grease flow characteristics are important for the understanding of fracture due to grease layer displacement. For these purposes, four greases with different rheological properties were used in µPIV experiments. It was found that the grease consistency plays a crucial role in speed development as well as the grease composition and presence of a slip effect at the grease–rotating wall interface.
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| 13. |
- Elmer, R, et al.
(författare)
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K+ emission in symmetric heavy ion reactions at subthreshold energies
- 1996
-
Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. ; 77:24, s. 4884-4886
-
Tidskriftsartikel (refereegranskat)abstract
- Subthreshold K+ production cross sections have been measured in symmetric Ne + NaF, Ni + Ni, and Au + Au collisions at 1.0A GeV. The mass dependence is strong, close to A(2). The angular distributions are nonisotropic in the center-of-mass system. Introdu
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| 14. |
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| 15. |
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| 16. |
- Farré-Lladós, Josep, et al.
(författare)
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New method for lubricating wind turbine pitch gears using embedded micro-nozzles
- 2017
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Ingår i: Journal of Mechanical Science and Technology. - : Springer. - 1738-494X .- 1976-3824. ; 31:2, s. 797-806
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Tidskriftsartikel (refereegranskat)abstract
- The increase of power generated by wind turbines has increased the stresses applied in all of its components, thereby causing premature failures. Particularly, pitch and yaw gears suffer from excessive wear mainly caused by inappropriate lubrication. This paper presents a novel method to automatically lubricate the wind turbine pitch gear during operation. A micro-nozzle to inject fresh grease continuously between the teeth in contact was designed, manufactured, and installed in a test bench of a 2 MW wind turbine pitch system. The test bench was used to characterize the fatigue behavior of the gear surface using conventional wind turbine greases under real cyclic loads. Measurements of wear evolution in a pitch gear with and without micro-nozzle show a decrease of 70 % of the wear coefficient after 2×104 cycles.
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| 17. |
- Farré-Lladós, Josep, et al.
(författare)
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New solution to preent excessive wear in wind turbine gears
- 2014
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Ingår i: Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2014. - : Society of Tribologists and Lubrication Engineers. - 9781634391351 ; , s. 548-550
-
Konferensbidrag (refereegranskat)
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| 18. |
- Farré-Lladós, Josep, et al.
(författare)
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On the Flow Dynamics of Polymer Greases
- 2022
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Ingår i: Lubricants. - : MDPI. - 2075-4442. ; 10:4
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the flow dynamics of polymer greases was investigated using micro-particle image velocimetry. Polymer greases have a different thickener structure, compared to widely used lithium-based greases, and they have the well-known ability to release oil. How these properties affect grease deformation and its ability to flow is investigated and compared to the corresponding behavior of a lithium complex grease with the same consistency. Two main tests were carried out, where velocity profiles in a straight channel were measured and analyzed, and velocity evolution during the transition period from a no-flow to a fully-established flow was measured, respectively. It was found that the polymer grease flow dynamics is different from that of the lithium grease. This indicates that the internal structure of the grease and the grease ability to bleed oil have a strong influence on the deformation on a global scale, which in turn entails other lubricating abilities for the two grease types.
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| 19. |
- Farré-Lladós, Josep, et al.
(författare)
-
The use of Rapid Prototyping techniques (RPT) to manufacture micro channels suitable for high operation pressures and µPIV
- 2016
-
Ingår i: Rapid prototyping journal. - 1355-2546 .- 1758-7670. ; 22:1, s. 67-76
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose– This paper aims to present a new methodology to manufacture micro-channels suitable for high operating pressures and micro particle image velocimetry (μPIV) measurements using a rapid-prototyping high-resolution 3D printer. This methodology can fabricate channels down to 250 μm and withstand pressures of up to 5 ± 0.2 MPa. The manufacturing times are much shorter than in soft lithography processes. Design/methodology/approach– The novel manufacturing method developed takes advantage of the recently improved resolution in 3D printers to manufacture an rapid prototyping technique part that contains the hose connections and a micro-channel useful for microfluidics. A method to assemble one wall of the micro-channel using UV curable glue with a glass slide is presented – an operation required to prepare the channel for μPIV measurements. Once built, the micro-channel has been evaluated when working under pressure and the grease flow behavior in it has been measured using μPIV. Furthermore, the minimum achievable channels have been defined using a confocal microscopy study. Findings– This technique is much faster than previous micro-manufacturing techniques where different steps were needed to obtain the micro-machined parts. However, due to current 3D printers ' resolutions (around 50 μm) and according to the experimental results, channels smaller than 250-μm2 cross-section should not be used to characterize fluid flow behaviors, as inaccuracies in the channel boundaries can deeply affect the fluid flow behavior. Practical implications– The present methodology is developed due to the need to validate micro-channels using μPIV to lubricate critical components (bearings and gears) in wind turbines. Originality/value– This novel micro-manufacturing technique overcomes current techniques, as it requires less manufacturing steps and therefore it is faster and with less associated costs to manufacture micro-channels down to 250-μm2 cross-section that can withstand pressures higher than 5 MPa that can be used to characterize microfluidic flow behavior using μPIV.
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| 20. |
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| 21. |
- Giacomini, Enrico, et al.
(författare)
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A Survey on Drones for Planetary Exploration: Evolution and Challenges
- 2022
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Ingår i: 2022 30th Mediterranean Conference on Control and Automation (MED). - : IEEE. ; , s. 583-590
-
Konferensbidrag (refereegranskat)abstract
- During the last decade, the efforts in space exploration have increased massively and led to a need for new ways to examine planets and other celestial bodies. The modern tendency is to create spacecraft able to scout the surface from a higher point of view, where drones have shown to be most helpful. Even if the benefits brought by this type of technology are considerable, the challenges are still difficult to overcome. This article presents a comprehensive literature review on drone technologies for planetary exploration, focusing mainly on the difficulties encountered. Considerable complications derive from the unknown environment, affecting most of the design, the mathematical model of the body, its controllability, and overall levels of autonomy. Various solutions to these challenges are proposed based on past and future missions. Furthermore, a look into the future gives an idea of possible technological developments and ways to provide the most efficient aerial exploration of other planets.
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| 22. |
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| 23. |
- Giacomini, Enrico
(författare)
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Investigating Aerodynamic Challenges for Rotorcraft Airfoil in the Martian Athmosphere
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over the past decade, there has been a considerable increase in space exploration efforts, driving the need for new methods to examine planets and other celestial bodies. The current trend involves designing spacecraft capable of surveying surfaces from elevated positions, with drones proving to be more suited for the task. . The focus of space missions has primarily been on exploring Mars, as evidenced by the pioneering flight of the Ingenuity helicopter in 2021. The Martian environment poses significant aerodynamic challenges due to its thin atmosphere and low pressure, complicating drone flight. The generation of lift is problematic owing to the scant atmosphere and the restricted dimensions required for space missions, resulting in low-chord Reynolds number flows. Despite the reduction in skin friction drag due to lower viscosity, the decrease in airfoil efficiency is significantly compromised, with only a partial counterbalance by the reduced gravitational pull. Two main challenges must be addressed: low chord-based Reynolds number flows and Martian dust. The former results in the formation of Laminar Separation Bubbles (LSB), severely impairing the aerodynamic efficiency of the airfoil. Concurrently, the accumulation of dust particles on the airfoil’s surface significantly affects its performance, altering its geometry and surface roughness. Thus, it is crucial to accurately determine the presence and location of both separation bubbles and particle deposition to predict performance degradation. \\This thesis presents a comprehensive survey on drones for planetary exploration and an analysis conducted on a cambered plate with 6$\%$ camber and 1$\%$ thickness, ideal for the types of flows considered. The studies are carried out for Reynolds number flows, namely 20,000 and 50,000, to observe the effects of rotor and airfoil dimensions. The computational study is performed using ANSYS Fluent, utilising a two-dimensional CFD model with a C-type mesh and the gamma-Re ($\gamma-Re_{\theta}$) transition model, which aids in capturing the behaviour of these flow regimes. Additionally, for the dust study, two phases are created: a primary phase, the atmosphere, and a secondary phase, the dust particles. The volume fraction of particles is assumed to be small enough to imply that the primary phase influences the secondary, but not vice versa (one-way coupling). To assess particle adhesion, a deposition model has been developed to check for the deposition of dust particles, working in conjunction with the Discrete Phase Modelling (DPM), which simulates the trajectory of particles within the control volume. The deposition model comprises a particle transport model, which accounts for the forces acting on the particles, and a particle-wall interaction model, which determines the particles' rebound or adhesion. The results are presented and discussed at the end of the thesis, along with a brief discussion of future studies focusing on alternative assumptions for dust modelling.
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| 24. |
- Green, Torbjörn M., et al.
(författare)
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A new method to visualize grease flow in a double restriction seal using microparticle image velocimetry
- 2011
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 54, s. 784-792
-
Tidskriftsartikel (refereegranskat)abstract
- A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.
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| 25. |
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| 26. |
- Hai, Ling
(författare)
-
Hydrodynamic Modelling of Wave Power using Electrical Equivalent Circuit Theory
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ocean wave energy can be harnessed and converted into electric energy nowadays. This provides a possibility for populations that live on islands or along coastlines to utilize the renewable and safe power produced by ocean waves. Point absorbing wave energy converter (WEC) is one example of such devices for electrical power production from ocean waves. It is composed of a floating buoy on the water surface, and a linear generator that sits on seabed and is connected with the buoy via a line. Electricity is generated when the buoy moves up and down in the waves.The geometry and dimensions of the floating buoy have dominant influences on the energy absorption. This thesis introduces an equivalent electric circuit for modelling the hydrodynamic interaction between the wave and a cylindrical buoy. The model allows a rapid assessment of the velocity, force in the connection line and output power, by which the system design and optimization can be performed faster and easier.The electric circuit model is based on the WEC's dynamic force analysis, and the electric components' parameters are determined from analytical approximations of the hydrodynamic coefficients. The simulation results of the equivalent circuit for one typical wave climate in Lysekil has been presented, and the results indicate a good fitting with former experimental results.The thesis also includes a hydrodynamic study for a torus shaped buoy, which aims at applying a theoretical background for a force measurement experiment. A comparison has been conducted between the torus buoy and two similar cylindrical buoys. Preliminary WAMIT simulation results demonstrate that the force in the connection line will be 5% bigger by using the torus buoy. It is also found that the torus buoy is advantageous for its larger excitation force and smaller added mass. A brief introduction of the 500kN force measurement system and the communication test have been introduced as well.
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| 27. |
- Hamedi, Naser, et al.
(författare)
-
Modelling of Flexible Fibres in Viscous Fluid Flow
- 2019
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Konferensbidrag (refereegranskat)abstract
- The current study relates to the development of a multiphase model of flexible fibre suspensions. An understanding of the rheology and dynamics of the deformation of such suspension is desirable in order to be able to fully disclose the flow behaviour from very low to very high shear rates. We present an approach for numerically simulating the dynamics of flexible fibres employing a particle-level method. This is performed by investigating the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres [1-3] enabling the model to have all degrees of freedom (translation, rotation, bending and twisting). The three-dimensional Navier-Stokes equations which describes the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The simulations are performed using OpenFOAM and the numerical outcomes are validated against experimental data.The purpose of the modelling framework applied in this work is to enable the numerical model to be extended to a 4-way coupling model, capturing shear thinning, shear thickening and the yield stress properties of a fibrous fluid suspension.
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| 28. |
- Hamedi, Naser, et al.
(författare)
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On the deformation of fibrous suspensions
- 2019
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Konferensbidrag (refereegranskat)abstract
- An understanding of the rheology and dynamics of the deformation of fibrous suspension as a multiphase fluid is important in order to be able to fully disclose the flow behaviour from very low to very high shear rates. In this study, a flexible fibre model has been implemented in an open source Computational Fluid Dynamics code. The three-dimensional Navier-Stokes equations which describe the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The aim of this study is to investigate the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres1-3 enabling the model to have all degrees of freedom - translation, rotation, bending and twisting. The simulations are performed using the OpenFOAM open source software.
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| 29. |
- Hamedi, Naser, et al.
(författare)
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On the Interaction of Side-By-Side Circular Cylinders in Viscoplastic Fluids
- 2019
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Ingår i: Fluids. - : MDPI. - 2311-5521. ; 4:2
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the static interaction of a train of three cylinders in a Bingham fluid is studiednumerically using Computational Fluid Dynamics. The variation of drag forces for the cylinders inseveral configurations is investigated. Positions of the particles in relation to the reference particleare recognized by the separation distance between the cylinders. A steady state field is considered,with Bingham numbers between 5 and 150. Several separation distances (d) were considered, such that2.0D d 6.0D where D is the cylinder diameter. The Reynolds number was chosen in the range of5 Re 40. In particular, the eect of the separation distance, Reynolds number and Bingham numberon the shape and size of the unyielded regions was investigated. The functional dependence of thisregion and the drag coecient is explored. The present results reveal the significant influence of thegap between the cylinders on the drag force and the shape of the unyielded regions surrounding thecylinders. It was found that there are several configurations in which the drag forces over the first andthe third cylinders are almost equal depending on variation of the Bi, Re and the separation distance.
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| 30. |
- Hamedi, Naser, et al.
(författare)
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Simulation of Flexible Fibre Particle Interaction with a Single Cylinder
- 2021
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Ingår i: Processes. - : MDPI. - 2227-9717. ; 9:2
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, the flow of a fibre suspension in a channel containing a cylinder was numerically studied for a very low Reynolds number. Further, the model was validated against previous studies by observing the flexible fibres in the shear flow. The model was employed to simulate the rigid, semi-flexible, and fully flexible fibre particle in the flow past a single cylinder. Two different fibre lengths with various flexibilities were applied in the simulations, while the initial orientation angle to the flow direction was changed between 45° ≤ θ ≤ 75°. It was shown that the influence of the fibre orientation was more significant for the larger orientation angle. The results highlighted the influence of several factors affecting the fibre particle in the flow past the cylinder.
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| 31. |
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| 32. |
- Johansson, Simon, et al.
(författare)
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Characteristics of flow and temperature distribution in a Ruthner process
- 2010
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Ingår i: Proceedings of Modeling for Material Processing, 6th International Scientific Colloquium. - : University of Latvia Press. ; , s. 317-322
-
Konferensbidrag (refereegranskat)abstract
- This study is devoted to CFD modelling of the gas flow and particle dynamics inside the reactor of a furnace used for regeneration of hydrochloric acid from iron chloride - a rest product from the pickling process in the steel industry. The understanding of the dynamics inside the reactor has shown to be of great importance in order to optimize the process. So far the process has been a black box, where only the inflow conditions are known together with the quality of the final product. In this work the gas flow is resolved together with the thermal distribution and the particle trajectory for the injected acid molecules.
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| 33. |
- Johansson, Simon, et al.
(författare)
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Gas and particle flow in a spray roaster
- 2014
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Ingår i: Journal of Applied Fluid Mechanics. - 1735-3572 .- 1735-3645. ; 7:2, s. 187-196
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Tidskriftsartikel (refereegranskat)abstract
- In the steel industry, waste hydrochloric acid is produced through the process to pickle steel slabs for removal of corrosion. Regenerated hydrochloric acid is obtained by separating the chloride gas from the waste product through spray roasting. This process also produces a by-product in the form of iron oxide which is sold to different industries. The present study is a continuation of a study arising from the need to better understand the dynamics inside the regeneration reactor, which in turn will improve possibilities to optimize the regeneration process, which to date has been manually adjusted by trial and error. In this study the velocity and temperature distribution inside the reactor is numerically modelled together with the droplet motion through the reactor. The main objective is to investigate the influence of a changed spray nozzle position on the flow characteristics of the continuous and dispersed phase, and the relation between temperature and energy efficiency and the regeneration process. Numerical models of the type of flow present in the regeneration reactor are not represented to any major extent in the literature, making the present study relevant to the engineers and researchers active in the steel industry and the application in question.
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| 34. |
- Johansson, Simon, et al.
(författare)
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Simuleringar av dyspositionens inverkan på flöde och temperturdistribution i en ruthner process
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Saltsyra (HCl) används inom stålindustrin för att beta järnoxider (Fe2O3) efter varmvalsning av plåt innan den förädlas i produktionslinan. Stora mängder HCl förbrukas, vilket både är kostsamt och miljöfarlig om den inte återvinns. Återvinningen sker oftast på stålverken med en metod som kallas Ruthner process. Den kan illustreras av en cylindrisk ugn med konisk nedre del, där det strax ovanför den koniska delen sitter naturgasbrännare tangentiellt till ugnen. Den förbrukade saltsyran, som består av vatten (H2O) och järnklorid (FeCl2), tillförs genom en till fyra dysor i toppen av ugnen. Återvinningen sker - något förenklat - genom att H2O först förångas från dropparna, därefter reagerar FeCl2 med syre (O2) och H2O och bildar HCl och Fe2O3. HCl återförs till betningsprocessen och Fe2O3 kan exempelvis säljas till elektronikindustrin.Denna studie syftar till att öka förståelsen av processen så att det i framtiden är möjligt att säkerställa god kvalité av restprodukten Fe2O3. Simuleringar görs i Ansys CFX med en tvåvägskopplad Euler/Lagrange-ansats där Eulerfasen består av gas och dropparna av förbrukad HCl är på Lagrangeform. Produkten från naturgasbrännarna ges som randvillkor till inloppet. I modellen är det första steget i återvinningsprocessen då droppar förångas implementerad. Även lyftkraft p.g.a. olika gastemperaturer, energiförluster genom väggar, och dragkraft på partiklar är implementerade i modellen. Som turbulensmodell används k-ε.Ur Figur 2 ses att både temperaturfördelning och hastighetsprofil förändras med olika dyspositioner. En korrelation mellan bilderna finns; i områden med låg temperatur är hastigheten riktad nedåt. Med dysan placerad 3,5 m från centrum förskjuts dock området för negativ vertikal hastighet bort från väggen. Detta beroende på att den varma gasen från brännare stiger längs väggen. De stora skillnaderna i temperaturfördelning är att dysposition 0.5 m från centrum ger en hög utloppstemperatur samt att dysposition 0.5 m och 3.5 m ger en högre temperatur i botten. Tendensen i hastighetsprofilen är lika för de tre fallen med dysan närmast väggen. När dysan placeras i mitten blir det ett kallras i centrum. För att få en klarare bild av processen krävs det även att partiklar analyseras samt att i framtiden även implementera kemiska reaktioner.
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| 35. |
- Karami, Fatemeh, et al.
(författare)
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Nano-fluid flow in a catheterized tapered artery : Consistent couple stress-theory and wall slip
- 2019
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer. - 1388-6150 .- 1588-2926. ; 137:1, s. 327-342
-
Tidskriftsartikel (refereegranskat)abstract
- This study was conducted with the aim of investigating the Newtonian nanofluid flow in a catheterized tapered artery through using a completely consistent couple stress theory. In the process of carrying out this study, the slip condition at the arterial wall and the catheter, as well as, the permeability was taken into account. Further, the velocity, temperature, and concentration profiles were analytically modeled and the effect of the length scale on these profiles was well presented through the way it influences small-scale flows. The effect of the slip condition at the artery and catheter walls on the velocity was also investigated and revealed that any increase in the velocity leads to an increase in the slip velocity. Furthermore, the effect of other parameters such as the catheter diameter, shape, and height of the stenosis on these profiles was explored for all three artery geometries, i.e., diverging tapered artery, converging tapered artery, and non-tapered artery, respectively. The findings suggested that any increase in the catheter diameter and stenosis height can decrease the velocity and nanoparticle concentration profiles, while the temperature profile increases. It was also found that by increasing the stenosis shape parameter the velocity and concentration profiles increase and temperature decreases.
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| 36. |
- Kluge, Jimmy Nils Erik, et al.
(författare)
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Modelling heat transfer inside an autoclave: Effect of radiation
- 2016
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Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 35:14, s. 1126-1142
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, computational fluid dynamics simulations are performed to predict the temperature distribution on a part during an autoclave run. Data from an experimental study are used as input to the simulations and also for comparison with the numerical results. A conjugate heat transfer approach was used for the simulations, where best agreement with experiments was obtained from the simulation that included thermal radiation and utilized an experimentally obtained velocity profile as inlet velocity. A yet more detailed inlet velocity profile and more advanced turbulent model could result in an even better agreement.
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| 37. |
- Kluge, N. E. Jimmy, et al.
(författare)
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An Experimental Study of Temperature Distribution in an Autoclave
- 2016
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Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 35:7, s. 566-578
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the temperature distribution on an industrial mold tool is monitored during autoclave runs with three settings. In one of the settings, the temperature and pressure follow a scheme used in real moldings, while in the other two cases, the temperature is increased as fast as possible with and without an applied pressure. The temperature difference over the tool is relatively large and varies between 29℃ and 76℃ validating a detailed investigation of the temperature at different points. Two results of this are that positions on the up-stream side of the tool are heated faster than positions down-stream and the heating over the tool is symmetric while that within is asymmetric. Roughly estimated heat transfer coefficients reveal that the temperature ramping has no significant effect on the local heat transfer coefficients while the applied pressure more than doubled them. In addition flow field measurements with particle image velocimetry are performed, revealing a very slow flow near the roof of the autoclave and a velocity peak near the floor of it, indicating that the flow profile within the autoclave and variation in heat transfer coefficients should be considered in autoclave simulations.
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| 38. |
- Kluge, NE Jimmy, et al.
(författare)
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Compression moulding of sheet moulding compound : Modelling with computational fluid dynamics and validation
- 2015
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Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 34:6, s. 479-492
-
Tidskriftsartikel (refereegranskat)abstract
- Compression moulding experiments of sheet moulding compound, visual observations of a vacuum test with prepregs and numerical models with two main approaches for computational fluid dynamics simulations of the mould filling phase are presen ed. One assumes that there are layers near the mould surfaces with much less viscosity and the other only use one viscosity model. The numerical experiments showed that the pressure could be accurately predicted with both approaches. The property ne essary to predict correct pressure with altered mould closing velocities was that the bulk material had to obey shear-thinni g effects. Preheating effects before compression were neglected, but altering the heating time until the prepreg was assumed to start flow had a significant effect. The experiments confirmed that the pressure is predominantly affected by the mould c osing velocity. Regardless of the considered process settings, a first pressure top always appeared approximately at the logarithmic strain 0.25. A second top was associated with a slowdown of the press. The location of this was affected by the velocity and the vacuum, the latter indicating that vacuum assistance prevents a build-up of back pressure. Furthermore, heated prepreg above a critical temperature is observed to swell immediately as vacuum assistance is applied.
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| 39. |
- Li, Jinxia, et al.
(författare)
-
Design of test rig for visualizations of cylindrical shear and pressure driven Couette flow using μPIV
- 2014
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Konferensbidrag (refereegranskat)abstract
- Couette flow is often encountered in concentric cylinder application such as rheometers etc. Being able to visualize such flows is of interest both from a fundamental point of view to understand the dynamics of complex fluids, but also in specific applications such as lubricants flowing through seal geometries. In this study a concentric cylinder test rig has been designed to visualize Couette flow in both radial and axial direction using micro Particle Image Velocimetry. The rig allows for control of the flow motion; the rotating inner cylinder creates a peripheral flow and an applied pressure in the axial direction creates a pressure driven flow. Thus, a single flow direction or a combination of directions can be analyzed. To demonstrate the technique a flow of a non-Newtonian shear thinning fluid in the form of lubricating grease was investigated and discussed. It is found that it is possible to capture the yield behavior of the grease, with regions of fully and partially yielded flow visible. The influence of temperature creep flow is also presented. Grease with both high and low yield stress are measured and compared could be measured and compared in a pocket with variable size. Furthermore, non-homogeneous effects such as shear banding and wall slip can be visualized. The test rig has thus a high potential to investigate the influence of wall material and wettability between fluids and the housing on the flow and wall slip behavior as long as the fluid is optically transparent.
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| 40. |
- Li, Jinxia, et al.
(författare)
-
Experimental study of free surface grease flow subjected to centrifugal forces
- 2014
-
Konferensbidrag (refereegranskat)abstract
- In order to improve the understanding of grease flow in various applications such as gears, seals and rolling bearings, the free surface flow of different greases under different running conditions has been investigated. A rotating disc has been used to study grease flow as the grease was subjected to a centrifugal force. The grease flow and mass loss was measured for greases with different rheology on different surfaces and with surface textures. It is shown that the speed at which grease starts to move is mostly determined by grease type and yield stress, while the impact of the surface material and roughness is less pronounced. The mass loss is shown to be influenced both by the rheology of the grease and the surface material
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| 41. |
- Li, Jinxia, et al.
(författare)
-
Grease free surface flow on a rotating plate
- 2014
-
Konferensbidrag (refereegranskat)abstract
- In order to improve the understanding of grease flow in various applications such as gears, seals and rolling element bearings, free surface flow of different greases under different running conditions has been investigated. A rotating disc has been used to study grease flow as the grease is subjected to a centrifugal force. The adhesion and mass loss was detected for greases with different rheology on different surfaces and surface textures. It is shown that the speed at which grease starts to move is mostly determined by grease type, yield stress and bleeding properties rather than surface material. Also, the surface adhesion is shown to be influenced both by the rheology of the grease and the surface material.
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| 42. |
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| 43. |
- Li, Jinxia, et al.
(författare)
-
Lubricating Grease Shear Flow and Boundary Layers in a Concentric Cylinder Configuration
- 2015
-
Konferensbidrag (refereegranskat)abstract
- Grease is extensively used to lubricate various machine elements such as rolling bearings, seals, and gears. Understanding the flow dynamics of grease is relevant for the prediction of grease distribution for optimum lubrication and for the migration of wear and contaminant particles. In this study, grease flow is visualized using micro Particle Image Velocimetry (μPIV). The experimental setup includes a concentric cylinder configuration with a rotating shaft to simulate the grease flow in a double restriction seal geometry with two different grease pocket sizes. It is shown that the grease is partially yielded in the large grease pocket geometry and fully yielded in the small grease pocket. For the small grease pocket, it is shown that three distinct grease flow layers are present: a high shear rate region close to the stationary wall, a bulk flow layer, and a high shear rate boundary region near the rotating shaft. The grease shear thinning behavior and its wall slip effects have been identified. The μPIV experimental results have been compared with a numerical model for both the large and small gap size. It is shown that the flow is close to one-dimensional in the center of the small pocket. A one-dimensional analytical model based on the Herschel-Bulkley rheology model has been developed, showing good agreement with the measured velocity profiles in the small grease pocket. Furthermore, wall slip effects and shear banding are observed, where the latter imply that using the assumption of uniform shear in conventional concentric cylinder rheometers may result in erroneous rheological results.
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| 44. |
- Li, Jinxia, et al.
(författare)
-
Lubricating grease shear flow and boundary layers in a concentric cylinder configuration
- 2013
-
Ingår i: Proceedings of the 3rd International Tribology Symposium of IFoMM (International Federation for the Promotion of Mechanism and Machine Science), Luleå, March 19-21, 2013.
-
Konferensbidrag (refereegranskat)abstract
- Grease is extensively used to lubricate various machine elements such as rollingbearings, seals, and gears. Understanding the flow dynamics of grease is relevant forthe prediction of the grease distribution for optimum lubrication and the migration ofwear- and contaminant particles. In this study grease flow is visualized using themethod of micro Particle Image Velocimetry; the experimental setup comprises aconcentric cylinder with rotating shaft to simulate the grease flow in a DoubleRestriction Seal (DRS) geometry with two different grease pocket heights. It is shownthat grease may be partially yielded in the large grease pocket geometry and fullyyielded in the small grease pocket geometry. For the small grease pocket geometry, itis shown that three distinct grease flow layers are present: a high shear rate regionclose to the stationary wall, a bulk flow layer, and a high shear rate boundary regionnear the rotating shaft. The grease shear thinning behaviour and its wall slip effectshave been detected and discussed.
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| 45. |
- Li, Jinxia, et al.
(författare)
-
Lubricating grease shear flow and boundary layers in a concentric cylinder configuration
- 2014
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 57:6, s. 1106-1115
-
Tidskriftsartikel (refereegranskat)abstract
- Grease is extensively used to lubricate various machine elements such as rolling bearings, seals, and gears. Understanding the flow dynamics of grease is relevant for the prediction of grease distribution for optimum lubrication and for the migration of wear and contaminant particles. In this study, grease flow is visualized using microparticle image velocimetry (μPIV). The experimental setup includes a concentric cylinder configuration with a rotating shaft to simulate the grease flow in a double restriction seal geometry with two different grease pocket sizes. It is shown that the grease is partially yielded in the large grease pocket geometry and fully yielded in the small grease pocket. For the small grease pocket, it is shown that three distinct grease flow layers are present: a high shear rate region close to the stationary wall, a bulk flow layer, and a high shear rate boundary region near the rotating shaft. The grease shear thinning behavior and its wall slip effects have been identified. The μPIV experimental results have been compared with a numerical model for both the large and small gap size. It is shown that the flow is close to one-dimensional in the center of the small pocket. A one-dimensional analytical model based on the Herschel-Bulkley rheology model has been developed, showing good agreement with the measured velocity profiles in the small grease pocket. Furthermore, wall slip effects and shear banding are observed, where the latter imply that using the assumption of uniform shear in conventional concentric cylinder rheometers may result in erroneous rheological results.
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| 46. |
- Li, Jinxia, et al.
(författare)
-
Measurements of grease flow in channels with restrictions using μPIV
- 2010
-
Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
-
Konferensbidrag (refereegranskat)abstract
- Grease is commonly used to lubricate various machine components such as rolling element bearings, open gears etc. Better understanding of the flow properties of grease will contribute to understanding the lubrication mechanism in bearings and flow in lubrication systems. In an earlier paper Micro Particle Image Velocimetry (μPIV) techniques were used to study the flow in a rectangular channel. The present paper is an extension of this work where restrictions were applied in such a channel, which creates a much more complex velocity field. The grease is seeded with fluorescent particles, which are illuminated by a double-pulsed laser. The test geometries that are used in this study are a channel with one flat restriction and one with two flow restrictions in a similar channel. The stationary grease mass-flow and the two dimensional velocity fields have been monitored for different pressure drops. For the channel with one flat restriction, the flow was measured to be symmetric at the inlet and outlet, and the distance for the flow to fully develop is comparable with the height of the channel; Slow motion was followed near the step corner at the inlet. For the channel with two flow restrictions, the vector profiles show that the maximum velocity appears at the restrictions; In-between the two restrictions, a part of the grease is not moving. This particularly applies to cases with low-pressure drop and where high consistency grease was used.
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| 47. |
- Li, Jinxia, et al.
(författare)
-
µPIV measurement of grease velocity profiles in channels with two different types of flow restrictions
- 2012
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 54, s. 94-99
-
Tidskriftsartikel (refereegranskat)abstract
- Grease is commonly used to lubricate various machine components such as rolling bearings and seals. In this paper the flow of lubricating grease passing restrictions is described. Such flow occurs in rolling bearings during relubrication events where the grease is flowing in the transverse (axial) direction through the bearing and is hindered by guide rings, flanges et cetera, as well as in seals where transverse flow occurs, for example during so-called breathing caused by temperature fluctuations in the bearing. This study uses a 2D flow model geometry consisting of a wide channel with rectangular cross-section and two different types of restrictions to measure the grease velocity vector field, using the method of Micro Particle Image Velocimetry. In the case of a single restriction, the horizontal distance required for the velocity profile to fully develop is approximately the same as the height of the channel. In the corner before and after the restriction, the velocities are very low and part of the grease is stationary. For the channel with two flow restrictions, this effect is even more pronounced in the “pocket” between the restrictions. Clearly, a large part of the grease is not moving. This condition particularly applies to the cases with a low-pressure drop and where high consistency grease is used. In practice this means that grease is not replaced in such “corners” and that some aged/contaminated grease will remain in seal pockets.
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| 48. |
- Li, Jinxia, et al.
(författare)
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Rheology of Lubricating Grease
- 2015
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Ingår i: Lube Magazine. - 1744-5418. ; 126, s. 12-18
-
Tidskriftsartikel (refereegranskat)
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| 49. |
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| 50. |
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