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Sökning: LAR1:uu > Högskolan i Halmstad > Licentiatavhandling

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1.
  • Möllerström, Erik (författare)
  • Vertical Axis Wind Turbines : Tower Dynamics and Noise
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research.The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires.This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied.  The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied.The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.
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2.
  • Thelin, Mikael, 1971- (författare)
  • Elevers val av gymnasieskola : En experimentell studie om elevers geografiska, akademiska och sociala preferenser
  • 2014
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Increased possibilitiesof choosing one’s school of preference hasbeen raised as a key factor in many countries to promote equal opportunitiesand higher quality of education. This has been endorsed by policymakers whoassume that students make well-informed rational choices and that students only stress academic quality whendeciding which school to attend. If this is true, it will benefit schools ofhigh academic quality, rendering improved school quality overall. To date,little research has examined the validity of these assumptions despite theprofound effects they have had for changing the school systems in manycountries. This study employs an experimental approach to investigate therelative importance of attributes in school choice. Specifically the study isbased on experimental data from 587 prospective high school students inHalmstad, Sweden. The purpose is to contrast the principal school qualityattributes behind the policy change (academic reputation and programfeasibility), with the presence of friends and geographical attributes such asdistance, location and accessibility, while controlling for individualcharacteristics. The results are disturbing as they reveal flaws in theassumptions that motivated the school choice policy reform. The study presents evidence of differencesin preferences and that grades are the most important background characteristic for this difference. The study also shows that all studentsare not rational to the same extent as theory predicts. Hence theSwedish school reforms have been based on a slightly biased theory. Finally, the study indicates that differentgeographic contexts (e.g. where the studentslive) affect students' preferences.
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