| 1. |
- Löfgren, Hans B., et al.
(författare)
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Damping mechanisms of perturbations in electromagnetically braked horizontal film flows
- 2000
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Ingår i: Fluid Dynamics Research. - 0169-5983 .- 1873-7005. ; 26:1, s. 53-68
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Tidskriftsartikel (refereegranskat)abstract
- The stability of shear and surface modes in an electromagnetically braked free surface liquid metal flow over a horizontally moving boundary is considered. The main objective is to investigate the stabilizing effect of a transverse magnetic field of the film flow appearing in connection with the horizontal belt strip casting. The flow is two-dimensional and the upper boundary is a free surface. In the stability analysis the film flow is approximated as parallel and is therefore based on the MHD-modified Orr-Sommerfeld equation. Numerical calculations present the linear growth rate for shear and surface mode instabilities. A transverse magnetic field is found to have two damping mechanisms. For low Hartmann numbers the main mechanism is due to the braking of the flow, reducing the shear stress. The other mechanism is due to dissipation by the Joule effect.
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| 2. |
- Löfgren, Hans B., et al.
(författare)
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Electromagnetic braking of the flow of a liquid metal with a free surface
- 1998
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Ingår i: Fluid Dynamics Research. - 0169-5983 .- 1873-7005. ; 23:1, s. 1-25
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Tidskriftsartikel (refereegranskat)abstract
- The electromagnetic braking of liquid metal flowing over a moving boundary is considered. The flow is two dimensional and the upper boundary is a free surface. The main interest of this flow originates from the application of horizontal belt strip casting. In this process, the liquid metal is fed onto a single endless horizontal belt that runs between two rollers. The bottom of the belt is cooled by water and the liquid is fed onto the belt through a slit. This results in a flow that can be modelled as a flat free jet impinging onto a horizontally moving boundary. The flow after the impingement region is analysed using the boundary layer equations. Here, the flow depends on the Reynolds number R, the Froude number F, the Hartman number M, and the ratio of the belt velocity to jet velocity, β. For βF-2/3, there is no hydraulic jump and the film thickness grows smoothly into the final state with constant thickness and uniform velocity. The braking length for the case without hydraulic jump is shown to be of order O(F2/3Ra/2) without magnetic field and of order O(M-2Ra/2) with magnetic field, where a is the jet width. Thus, the magnetic field decreases the braking distance considerably. This result is favourable for both the stability of the flow and for the solidification process in the horizontal belt strip casting process.
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| 3. |
- Löfgren, Hans B., et al.
(författare)
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Initial solidification in liquid metal film flow over a moving bondary
- 2001
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310 .- 1879-2189. ; 44:4, s. 837-842
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Tidskriftsartikel (refereegranskat)abstract
- The initial solidification problem of a two-dimensional liquid metal film flow over a heat extracting moving boundary is studied. Analytical solutions in the limit of large Peclet numbers are found. It is shown that the point of initial solidification depends on the Peclet number, the Biot number and the superheat. The initial growth of the solidified phase is found to have a quadratic dependence of the distance from the point of initial solidification. The results are applicable to continuous strip casters.
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| 4. |
- Löfgren, Hans B., et al.
(författare)
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The laminar stagnation-point flow against a solidifying moving shell
- 2000
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Ingår i: Acta Mechanica. - 0001-5970 .- 1619-6937. ; 142:1-4, s. 33-46
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the two-dimensional laminar stagnation-point flow due to a jet impinging onto a solidifying moving boundary. The flow is of interest in connection with the horizontal belt strip casting process. An exact solution to the Navier-Stokes equations is found that is shown to depend on a single ordinary differential equation. The solution is useful in the study of morphological and hydrodynamic instabilities within the impingement region. Solutions for the steady-state shape of the initial stages as well as the asymptotic behavior of the solidifying interface are also discussed in a perturbative manner.
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| 5. |
- Åkerstedt, Hans O., et al.
(författare)
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Free surface magnetohydrodynamic flow with solidification
- 2003
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Ingår i: European journal of mechanics. B, Fluids. - : Elsevier BV. - 0997-7546 .- 1873-7390. ; 22:6, s. 581-601
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Tidskriftsartikel (refereegranskat)abstract
- The paper considers an analysis of a liquid metal flow, occurring in the horizontal belt strip casting process. The liquid metal flows over a moving copper belt with a growing solidifying phase beneath the melt. The effect of applying a transverse magnetic field is investigated. A set of three-dimensional shallow water equations is derived. Supercritical flow is assumed and the shallow water equations are solved numerically using a shock-capturing method, which automatically takes care of the possibility of oblique hydraulic jumps.It is shown that non-uniform conditions introduced in the feeding region give a pattern of steady hydraulic jumps, which propagate downstream and are reflected at the sidewalls. The effect of the magnetic field is to brake the flow and damp the standing hydraulic jump pattern. Different feeding methods are compared and it is shown that the magnetic field erases the initial differences in liquid distribution using different feeding techniques.
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| 6. |
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| 7. |
- Axberg, Stefan, et al.
(författare)
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Lärobok i Militärteknik, vol. 9 : Teori och metod
- 2013. - 1
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Ämnet militärteknik utgår från att tekniska system är officerens arbetsredskap och att en förståelse för och kunskap om dessa verktyg är central för att kunna utöva professionen framgångsrikt. Denna nionde volym av Lärobok i Militärteknik, benämnd Teori och Metod, behandlar centrala begrepp, teorier och postulat samt metoder för värdering av teknik och består av ett antal texter författade av 16 forskare och lärare vid den militärtekniska avdelningen. Volymen riktar sig främst till de som inlett sin officersutbildning och utgörs till stora delar av ett kompilat av publicerade och opublicerade militärtekniska texter och kan sägas utgöra militärteknikens ”state of the art”.
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| 8. |
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| 9. |
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| 10. |
- Bååth, Lars, 1948-, et al.
(författare)
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Ny teknik för avisning av vindkraftsvingar
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This is a pilot study to investigate icing on wings of wind power turbines. In this report we present and discuss various ways and means to either heat water droplets or melt ice when formed on the wings of wind turbines. The situation is different from icing on wings of airplanes in that (1) the wings of wind turbines spend all of their time in the atmosphere where the risk of icing is highest and (2) the speed of wing to air varies over the wing where it is constant for an airplane. The form of the wind turbine wings also varies from tip to centre, to compensate for the varying relative air speed.We have concentrated on icing conditions at temperatures -10°C – 0°C and droplet sizes of 1-10 μm. Icing occurs also at much lower temperatures, but this will probably be because of direct freezing of water vapour to ice. This is presently outside the scope of our pilot project report.We conclude thatThe form of the wing, especially on the contact area may be crucial to the icing problem.Also the nano-metric structure of the wing surface can probably be designed so that the water droplets have a minimized contact area to the wing.Our pilot investigation also suggests the following:Microwaves are much too inefficient to heat water or melt ice. Direct microwave devices should therefore not be developed. Indirect heating with microwaves is possible.Millimeter waves are sufficiently efficient, but the generation is most probably too inefficient to be of any practical use.Infrared waves are very efficient to heat water and melt ice and should be investigated.Heat conduction is also efficient and should be pursued. Using microwaves to heat the wing surface which then conduct heat to the water/ice is a very efficient and robust method.Our pre-study suggests that the solution to avoid icing or de-ice wings of wind turbines most probably is not one single technology. The form and surface structure of the wings play important role for icing conditions. Both variables have to be modified depending on the latitude and atmospheric climate. The surface structure also has to be designed to vary over the wing, both along and across to be optimized for the mean conditions at the site. In addition, heating of the impact area, or at least the possibility to heat this, may be important to avoid loss of energy output due to ice.Further research is required. We strongly suggest investigating the water droplet flow over the wing as function of the cross section form, and the contact with the wing surface as function of the surface structure (e.g. Lotus effect).The present report is the result of a pre-study project. We will now continue with a deeper project which will concentrate on the form and surface structure suggestions which results from our analysis and flow simulations.
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