| 1. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Emborg, Mats, et al.
(författare)
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Temperatursprickor i betong p g a hydratationen för några vanliga typfall
- 1994
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I samråd mellan Vägverket, Div. Väg och Trafik, Sekt. Broteknik (VTb) och Luleå Tekniska Högskola, Avd. för Konstruktionsteknik har ett antal förekommande typfall vid gjutning av betong studerats med avseende på temperaturspänningar på grund av hydratationen. För de studerade typfallen har spänningsanalyser utförtss och diagram framtagits över sprickrisk vid olika förutsättningar t ex gjutförhållanden och dimensioner. Diagrammen ger underlag för mer säkra sprickriskbedömningar än diagraam enbart baserade på temperaturberäkningar. Rapporten är indelad i tre delar. Del A berör hur temperatursprickor kan uppkomma, vilka huvudfaktorer som inverkar på sprickrisken, vilka förhållanden som gäller för aktuella typfall samt hur sprickrisker kan beräknas. I Del B sker en redogörelse för vilka förutsättningar som gäller allmänt vid sprickriskberäkningar och speciellt vid beräkningarna för typfallen. I Del B kommenteras de diagram över sprickrisker som redovisas i Del C. Del B och Del C kan användas separat vid sprickriskbedömningar.
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| 6. |
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| 7. |
- Groth, Patrik, et al.
(författare)
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Air cooling of concrete by means of embedded cooling pipes—Part II: Application in design
- 1998
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Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 31:210, s. 387-392
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Tidskriftsartikel (refereegranskat)abstract
- This paper relates the second part of the investigation of air-cooling in concrete; the first part is presented in `Air cooling of concrete by means of embedded cooling pipes Part I: Laboratory tests and heat transfer coefficients'. Embedded cooling pipes are used to reduce the risk of thermal cracking in early age concrete. Traditionally, water has been used as a cooling medium, but air cooling has been shown to be advantageous for many applications. The experimentally-determined heat transfer coefficients of cooling pipes, have been used and verified in comparisons of in situ measurements at the Igelsta Bridge in Sodertalje, Sweden. The close agreement between measured and calculated temperatures of air-cooled sections seems to justify the use of the averaged heat transfer coefficients determined in [1]. Some exemplifying calculations are also shown, and the general behaviour of cooled structures is discussed. The principles of designing a cooling system for a general case are proposed. It is concluded that it is possible to design prismatic structures, such as a columns, by the use of existing models and measured heat transfer coefficients
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| 8. |
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| 9. |
- Groth, Patrik
(författare)
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Cracking in concrete : crack prevention with air-cooling and crack distribution with steel fibre reinforcement
- 1996
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate Thesis consists of four parts. The first two parts, paper A and B, deal with air-cooling by means of embedded pipes in order to reduce thermal cracking in concrete structures. These two papers are submitted for publication to RILEM Journal; ‘Materials and Structures'. The next part, paper C, treats fracture mechanics properties of steel fibre reinforced concrete, SFRC. Paper C has been published in the proceedings of a conference on utilisation of high performance concrete in Paris 1996, ‘BHP-96'. The last part, paper D, is a compilation of results and evaluations of tests performed after 1994 on SFRC at the Division of Structural Engineering at Luleå University of Technology.Paper A: Hedlund H., Groth P., (1996), ‘Air-cooling of concrete with embedded pipes. - Part I: Laboratory tests of heat transfer coefficients', RILEM Jour-nal: Materials and Structures, submitted for publication. Embedded cooling pipes may be used in order to reduce the temperature rise in massive structures as a measure against thermal cracking. A necessary parameter in a calculation of the risk for thermal cracking is the heat transfer coefficient of the cooling-pipe. In this paper this coefficient have been determined for two different types of pipes and for various pipe flows and temperature levels.Paper B: Groth P., Hedlund H., (1996), ‘Air-cooling of concrete with embedded pipes. - Part II: Applications in design', RILEM Journal: Materials and Structures, submitted for publication. The experimentally determined heat transfer coefficients of air cooling pipes, Pa-per A, have been used and verified in comparisons with in situ measurements at the Igelsta Bridge, Sweden. The close agreement between measured and calculated temperatures of air-cooled sections justifies the use of heat transfer coefficients determined as in Paper A. Some exemplifying calculations are also given. The general behaviour of cooled structures is discussed. The principles of designing cooling systems for the general case are proposed. It is further concluded that it is possible to design the cooling system of prismatic structures such as a columns with existing models for tem-perature and crack risk calculations by using the measured heat transfer coeffi-cients. Paper C: Groth P., Noghabai K. (1996), ‘Fracture Mechanics properties of steel-fibre reinforced high performance concrete.', Proceedings of 4th Interna-tional Symposium on Utilization of High Strength Concrete (BHP-96), Paris, 1996. The fracture mechanics properties of plain and steel-fibre reinforced high perform-ance concrete in Mode I have been obtained by means of uniaxial tension tests on cylinders. Considerations were taken in designing the notches. Four-point bend tests on small beams were also carried out. In all cases the ascending part of the structural responses was successfully monitored. This is valid for all tested speci-mens. The material data acquired, was used in an existent analytical model for splitting of a thick-walled concrete ring, in order to map the structural behaviour of the composite material. Good correspondence with the test results was observed. It was confirmed that even a moderate amount of steel fibres, drastically enhanced the ductility of the concrete. Paper D: Groth P. (1996), Steel fibre reinforced concrete - tests and evaluations Properties of various SFRC mixes have been determined by three types of tests; single fibre pullout, four-point bending and ring tests. The pullout tests were performed under closed-loop control on single-sided speci-mens using various combinations of concrete mixes and fibre types. Three different models for the interfacial bond between fibre and matrix have been applied on the results. Neither of the existing models seems to be fully able to reproduce the pull-out curves. However, qualitative comparisons can be made regarding the efficiency of the different types and dimensions of steel fibres tested. The four-point bend test, as regulated in ASTM C1018, are probably the most common method to characterise SFRC. The flexural toughness properties obtained by this method, as well as by the method regulated in JSCE SF-4, are compared for the different SFRC mixes tested. Some correlation with results from single fibre pullout tests has been found. By use of the Inner Softening Band-model encourag-ing results of simulation of bend tests have been obtained. The case of cracking due to restrained shrinkage and the ability of SFRC to dis-tribute cracks have been studied by ring tests. SFRC or plain concrete is cast around the perimeter of a steel ring. The shrinkage is caused by either drying, self-desiccation shrinkage or a combination of both. Due to the restraint, caused by the ring, cracking will occur. The length and width of cracks are measured over time and the results are compared for the different SFRC and plain mixes. Comparisons with results found in literature are also made.
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| 10. |
- Groth, Patrik, et al.
(författare)
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Fiberarmerad betong
- 1996
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Ingår i: Byggforskning : Byggforskningsrådets tidning för en bättre byggd miljö. - 1102-3686. ; :3, s. 41-
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 11. |
- Groth, Patrik
(författare)
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Fibre reinforced concrete : fracture mechanics methods applied on self-compacting concrete and energetically modified binders
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibre reinforced concrete (FRC) is a type of building material that is increasing in use. As new types on concrete develops the need to update the knowledge on the use of fibre reinforcement increases. This thesis covers test methods for FRC that ranges from standard beam tests to sophisticated uniaxial tension tests. The consequence of applying fibre reinforcement in concrete made using various modified cementitious binders has also been studied. The binders used in this study are energetically modified cements (EMC). They consist of a mix of ordinary cement and different fillers, which has been processed through a vibrating mill. The influence of fibre reinforcement in self-compacting concrete (SCC) has been studied with regard to its feasibility in full-scale production. The fibre reinforced SCC has been studied with regard to its ability to retain its workability after addition of fibres and on its toughness properties. Finally, early age concrete and its fracture mechanical properties have been modelled. FRC is often used in structures where its task is to distribute cracks originating from stresses caused by volume changes in combination with restraint. In these cases, the appearance of cracks is a time-dependent phenomenon that occurs mainly in early ages. In this study a finite element model for localisation of strains in discreete cracks, the Inner Softening Band model, has been adopted and implemented with a model for the visco-elastic behaviour of early age concrete.
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| 12. |
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| 13. |
- Groth, Patrik, et al.
(författare)
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Influence of steel fibre reinforcement on the workability of self-compacting concrete
- 2000
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Ingår i: Concrete Science and Engineering. - 1295-2826. ; 2:6, s. 65-70
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Tidskriftsartikel (refereegranskat)abstract
- This study consists of results of workability tests for concrete mixes using various amounts and types of steel fibres. The mixes are proportioned using the addition of filler and superplasticizer in order to obtain Self-Compacting Concrete (SCC) before addition of fibres. The test methods that have been used are the slump flow test and a modified L-box test. The results show the general correlation between the measured workability parameters and fibre volume and shape. The results show that the type of concrete mix used clearly affects the relative behaviour of using various types and amounts of steel fibres. In some of the mixes the influence of fibres can be detected by a decrease in flowability as the fibre amount or fibre aspect ratio increase. However, in the case of well-proportioned SCC the workability is not influenced by the steel fibres added within realistic amounts, i.e. 60 kg/m exp 3 for a fibre aspect ratio up to 100. The tests imply therefore, that it is quite feasible to use fibres in combination with SCC for structural applications.
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| 14. |
- Groth, Patrik, et al.
(författare)
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Jämförelse mellan uppmätta och beräknande temperaturer vid kringgjutning av Ölandsbrons pelare
- 1993
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I många sammanhang är det av stort intresse att teoretiskt kunna bestämma temperaturutvecklingen i nygjutna betongkonstruktioner. Temperaturutvecklingen påverkas i huvudsak av hur mycket värme som bildas vid hydrationen och hur mycket värme som avges till omgivningen. Denna rapport syftar till att jämföra beräknade temperaturer med uppmätta i en konstruktion med i huvudsak två-dimensionell värmeströmning. Temperaturberäkningarna har här utförts med datorprogrammet HETT2D och resultat av fältmätningar har hämtats ur ett examensarbete från Chalmers Tekniska Högskola. Mätningarna utfördes vid Ölandsbron. De befintliga pelarna kringgjuts med ny betong som åtskiljs av ett glidskikt som skall ta upp temperaturrörelserna. Beräkningsmodellen i HETT2D beaktar värmeflöden i två dimensioner och beräknar värmeutvecklingeen över valda tvärsnitt i en betongkonstruktion. Avslutningsvis kan man konstatera att: Man med HETT2D kan beräkna temperaturutvecklingen i ung betong med god noggrannhet. eftersom de parametrar som styr betongens värmeutveckling har en naturlig variation behöver de aktuella parametrarna antingen vara framtagna genom laboratorieförsök eller behöver temperaturutvecklingen vara uppmätt i något jämförelsesnitt för att erhålla högsta beräkningsnoggrannhet.
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| 15. |
- Groth, Patrik, et al.
(författare)
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Luftkylning av betong med ingjutna kylrör
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rapporten inleds med en sammanfattande genomgång av tidigare genomfört arbete inom detta projekt vilket redovisas i kapitel 2. Kapitel 3 innefattar en redovisning av de fältmätningar som utförts inför denna del av projektet på Igelstabrons enkelspårspelare. Som en uppföljning till fältmätningarna har även laboratorieförsök utförts i syfte att finna värmeövergångstal för kylrör, dessa återfinns i kapitel 4. Till sist har ett antal beräkningar avseende temperaturer och temperaturspänningar genomförts vilka visar en jämförelse mellan uppmätta och beräknade resultat och en del exempelfall vilket finns i kapitel 5. Bilaga A och B innehåller samtliga mätresultat från fältundersökningen och bilaga C innehåller en redovisning av de beräkningsverktyg, HETT2D och TEMPSTRE, som använts. Bilaga D innehåller samtliga resultat från laboratorieförsöken och i bilaga E redovisas de parametrar som använts i exempelberäkningarna.
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| 16. |
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| 17. |
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| 18. |
- Hedlund, Hans, et al.
(författare)
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Air cooling of concrete by means of embedded cooling pipes-Part I: Laboratory tests of heat transfer coefficients
- 1998
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Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 31:5, s. 329-334
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Tidskriftsartikel (refereegranskat)abstract
- Embedded cooling pipes can be used to reduce the temperature rise in massive structures as a measure against thermal cracking. When air is used as a cooling medium, relatively large diameters with profiles causing friction losses along the pipe are preferred. In this paper, heat transfer coefficients for two different types of cooling pipes have been determined for different pipe flows in combination with various temperature levels. This paper relates to the first part of the investigation dealing with the laboratory tests of heat transfer coefficients. The second part, dealing with application in design, is presented in "Air cooling of concrete by means of embedded cooling pipes-Part II: Applications in design"
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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