| 81. |
- Abitew, Aymiro, et al.
(författare)
-
Hydraulic conductivity of tailings deposit used as dam construction material at Aitik mine in Sweden
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Distribution of vertical and horizontal hydraulic conductivity and their correlation to geotechnical parameters affecting the hydraulic conductivity of tailings deposit at Aitik mine have been determined. The investigation was carried out along three sections which cover approximately 3km2 of area and 4-5meters of thickness. 3-5 test pits have been excavated in each section and samples are collected from various levels. The horizontal hydraulic conductivity has been found to have a good relation with fraction of fine particles in the deposit and void ratio. However, similar to the results of Jantzer et al (2008) from the same mine, the vertical hydraulic conductivity did not correspond to void ratio. According to evaluation of existing empirical relations to estimate hydraulic conductivity from particle size analysis, Hazen formula (1911) gives 25 and 45 times the measured values of vertical and horizontal hydraulic conductivity respectively. On the other hand, Chapuis et al (2003) has not been succeeded for prediction of hydraulic conductivity of undisturbed samples from the investigated area. However, it gives comparatively good prediction of hydraulic conductivity for disturbed samples which are compacted to their field dry density.
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| 82. |
- Abitew, Aymiro, et al.
(författare)
-
Hydraulic conductivity of tailings sand used for dam construction at Aitik mine in Sweden
- 2012
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Ingår i: SWEMP 2012.
-
Konferensbidrag (refereegranskat)abstract
- Distribution of vertical and horizontal hydraulic conductivity and their correlation to geotechnical parameters affecting the hydraulic conductivity of tailings deposit at Aitik mine have been determined. The investigation was carried out along three sections which cover approximately 3km2 of area and 4-5meters of thickness. 3-5 test pits have been excavated in each section and samples are collected from various levels. The horizontal hydraulic conductivity has been found to have a good relation with fraction of fine particles in the deposit and void ratio. However, similar to the results of Jantzer et al (2008) from the same mine, the vertical hydraulic conductivity did not correspond to void ratio. According to evaluation of existing empirical relations to estimate hydraulic conductivity from particle size analysis, Hazen formula (1911) gives 25 and 45 times the measured values of vertical and horizontal hydraulic conductivity respectively. On the other hand, Chapuis et al (2003) has not been succeeded for prediction of hydraulic conductivity of undisturbed samples from the investigated area. However, it gives comparatively good prediction of hydraulic conductivity for disturbed samples which are compacted to their field dry density.
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| 83. |
- Abolmasoumi, Amirhossein, et al.
(författare)
-
Observer design for a class of nonlinear delayed systems with unknown inputs and Markovian jump parameters
- 2012
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Ingår i: ICCAS 2012. - 9781467322478 ; , s. 1848-1852
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Konferensbidrag (refereegranskat)abstract
- The problem of full-order observer design for a class of delayed nonlinear systems with unknown inputs and Markovian jumping parameters is considered. The design method is formulated as solving a set of linear matrix inequalities (LMI's). Extending the results of nonlinear observer design to Markovian jump systems with time-varying delays is the main advantages of this paper. The sufficient LMI conditions are dependent on both the upper and lower bounds of delay. The effectiveness of the proposed method is shown via an illustrative example.
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| 84. |
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| 85. |
- Abrahamsson, Lars, 1979-
(författare)
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AC cables strengthening low frequency AC railway with purely active power loads
- 2018
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Ingår i: 2018 IEEE Power & Energy Society General Meeting (PESGM). - : IEEE. - 9781538677032
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Konferensbidrag (refereegranskat)abstract
- Converter-fed railway power systems traditionally use high voltage AC overhead transmission lines in the railway grid for increased loadability. An increased resistance to overhead high voltage AC transmission lines, may motivate cables as one alternative for the future. The focus of this paper is to compare a non-strengthened system with two cable solutions for comparing loadability, voltages, and reactive powers for different levels of load scaling. The studies confirmed that the obstacle of reactive power produced in lowly utilized cables is, even if less significant for low frequency AC, still present. A simplified load model is used representing trains with VSC-converters and three-phase motors as purely active loads regardless of motoring or regenerating. A previous study has been done on thyristor-based trains. The voltage levels while regenerating are higher than in the thyristor-train case study. Besides that the loadability for motoring and regenerating is higher with modern VSC-trains.
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| 86. |
- Abrahamsson, Lars
(författare)
-
AC cables strengthening railway low frequency AC power supply systems : a deepened study
- 2017
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Konferensbidrag (refereegranskat)abstract
- n railway power supply systems using ACfrequencies lower than the public grids of 50/60 Hz,high voltage AC overhead transmission lines in railwaygrid frequency are used as one measure of strengthen-ing the systems. An increased resistance to overheadhigh voltage AC transmission lines, may motivate ca-bles for future railway power systems.With the frequency of 50/60 Hz, reactive powerproduced in lowly utilized cables imposes an obstacle.For low frequency AC, this issue is less significant.Moreover, in converter-fed railways, no reactive powerwill leak into the feeding public grid.This paper studies AC cables in low-frequency ACrailway. Two reinforcement cable solutions are com-pared with no reinforcement. A simplified load model oftrains, with thyristor bridges and DC motors, is used
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| 87. |
- Abrahamsson, Lars, et al.
(författare)
-
AC cables strengthening railway low frequency AC power supplysystems
- 2017
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Ingår i: ASME/IEEE 2017 Joint Rail Conference. - : ASME Press. - 9780791850718
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Konferensbidrag (refereegranskat)abstract
- In present-day railway power supply systems using an AC frequency lower than the one in the public power system of 50/60 Hz, high voltage overhead transmission lines are used as one measure of strengthening the railway power supply system grids. This option may be economically beneficial, compared to strengthening the grid purely by increasing the density of converter stations or increasing the cross section areas of the overhead catenary wires. High voltage AC transmission lines in the railway power supply system allow larger distances between converter stations than would otherwise be possible for a given amount of train traffic. Moreover, the introduction of AC transmission lines implies reduced line losses and reduced voltage level fluctuations at the catenary for a given amount of train traffic. However, due to the increased public and government resistance for additional overhead high voltage AC transmission lines in general, different alternatives will be needed for the future improvements and strengthening of railway power systems. For a more sustainable transport sector, the share and amount of railway traffic needs to increase, in which case such a strengthening becomes inevitable. Earlier, usage of VSC-HVDC transmission cables has been proposed as one alternative to overhead AC transmission lines. One of the main benefits with VSC-HVDC transmission is that control of power flows in the railway power systems is easier and that less converter capacity may be needed. Technically, VSC-HVDC transmission for railway power systems is a competitive solution as it offers a large variety of control options. However, there might be other more economical alternatives reducing the overall impedance in the railway power system. In public power systems with the frequency of 50/60 Hz, an excess of reactive power production in lowly utilized cables imposes an obstacle in replacing overhead transmission lines with cables. In low frequency AC railway power system, the capacitive properties are less significant allowing longer cables compared to 50/60 Hz power systems. Moreover, in converter-fed railways, some kind of reactive compensation will automatically be applied during low-load. At each converter station, voltage control is already present following the railway operation tradition. Therefore, in this paper, we propose AC cables as a measure of strengthening low-frequency AC railway power systems. The paper compares the electrical performances of two alternative reinforcement cable solutions with the base case of no reinforcement. The options of disconnecting or toggling the cables at low load as well as the automatic reactive compensation by converter voltage control are considered. Losses and voltage levels are compared for the different solutions. Investment costs and other relevant issues are discussed.
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| 88. |
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| 89. |
- Abrahamsson, Lena, et al.
(författare)
-
Avslutning
- 2013
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Ingår i: Lean i arbetslivet. - Stockholm : College of Liberal Arts and Sciences. - 9789147105601 ; , s. 317-325
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 90. |
- Abrahamsson, Lena
(författare)
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Bevara bredden i svensk arbetslivsforskning
- 2015
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Ingår i: Arbetsmarknad & Arbetsliv. - 1400-9692 .- 2002-343X. ; 21:2, s. 74-80
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Det finns positiva tecken på att något ska hända med arbetslivsforskningensvillkor. Mer bekymmersamt är att facket och arbetsgivarna vill återskapaett nationellt centrum för arbetslivsforskning i Stockholm. Vi börinte fortsätta att reproducera bilden av att svensk arbetslivsforskningförsvann när Arbetslivsinstitutet lades ned. Det finns många starkaforskargrupper på universiteten ute i landet. Nu är det viktigt att vi ser tillatt de positiva signalerna blir verklighet på ett klokt sätt så att bredden iarbetslivsforskningen säkras.
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