Mastergradsoppgaver i energi og miljø i nord
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Mastergradsoppgaver i energi og miljø i nord
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Haaland, Silje Sanderud (Master thesis; Mastergradsoppgave, Jun-2011)[+][-]
Abstract: Icing on wind turbines are known to lower their performance, but the exact relationship between wind, ice and power production is not known. In this thesis power loss due to icing on turbine blades at Aapua wind park is investigated for the winter season 2009-2010. The total loss is found to be 30%, whereof 25% is concluded being due to icing. Three different methods are presented to estimate a power output model P(V,I), based on empirical data of wind speed, ice load and power production from a wind turbine. The models estimate power output from wind speed and ice load observations. Their performance are compared using correlation and root mean square error (RMSE), and the kriging method, using a weighted mean to calculate power output, is found best. A comparison of the proposed kriging model to an existing model show a 10% increase in performance for the kriging method. Testing shows that kriging works well for low wind speeds and low ice loads, but tends to overestimate production during high ice loads. For the season as a whole, the modelled power output underestimates the power production with 1%. Time series of modelled, measured and expected power output, together with ice load and temperature measurements, are investigated. Results show that sublimation, shedding, melting and accretion processes on the turbine wings, are not fully captured by the model. Mismatch between ice loads on measuring equipment compared to turbine blades, together with insufficient number of observation data, are found to be the main reasons for inaccuracy in the model. URI: http://hdl.handle.net/10037/3814 File(s) in this item: 1
thesis.pdf (2.709Mb) -
Vevik, Kristine (Master thesis; Mastergradsoppgave, 15-Jun-2011)[+][-]
Abstract: A widespread bottom-simulating reflection (BSR) defining the base of the gas hydrate stability zone (BGHSZ) exists on seismic data from the western Svalbard margin, including the Vestnesa Ridge, which is a mounded and elongated sediment drift NW of Svalbard to the north of the Molloy Transform. The BSR stretches from the continental slope to within few km of the mid-oceanic ridge system thereby shoaling due to an increase in heat flow over the juvenile oceanic crust, which cools off in eastward direction. The interpretation of a BSR leads to the subdivision into three regions based on distribution and geological setting, namely the Vestnesa Ridge, the continental slope and the Molloy Transform Fault (MTF), where potential gas hydrate occurrences comprise an area of ~2700 km2. The BSR occurrence and inferred hydrate accumulation zone is bound by impermeable glacial debris-flow (GDF) deposits on the upper continental slope, the Knipovich Ridge and MTF to the south and the Molloy Ridge to the west. Enhanced reflections beneath the BSR indicate the presence of significant amounts of free gas. The crest of the Vestnesa Ridge at water depth between 1200-1500 m is pierced with fluid-flow features, but they are absent on the flanks of the ridge, where hydrate-bearing sediments effectively reduce the permeability of the sediments. Thus, fluids are forced to migrate laterally upwards along the GHSZ towards the crest in this topographically controlled system. The vigorous flow of fluids at the crest disrupts the BSR, causing it to shoal locally in vicinity of fluid-flow features. The fluid-flow features are often connected to deep-seated faults indicating a deep hydrocarbon gas supply, which is corroborated by hydrate-stability modeling suggesting a larger fraction of thermogenic hydrocarbons involved in hydrate formation. In addition to that, the combination of high heat flow, tectonic activity, a thick sedimentary cover and a shallow maturation window suggests that the free-gas/gas-hydrate system at the Vestnesa Ridge is more active and dynamic than elsewhere in the study area. Free-gas/gas-hydrate systems on the lower continental slope and at the MTF seem mostly in a steady state with gas predominantly originating from biogenic methanogenesis. URI: http://hdl.handle.net/10037/3474 File(s) in this item: 1
thesis.pdf (6.956Mb) -
Skrunes, Stine (Master thesis; Mastergradsoppgave, Feb-2011)[+][-]
Abstract: In this thesis, marine targets in Synthetic Aperture Radar (SAR) imagery are studied. The appearance of different marine targets in different polarization channels, their scattering behaviour, and their contrast measures and geometric properties are investigated. RADARSAT-2 data containing ships, oil rigs and icebergs in ocean and/or sea ice background are evaluated. To be able to detect a target in a SAR image, a significant contrast between target and background is needed. In this thesis, peak-to-background ratios (PBR) and target-to-background ratios (TBR) are used to evaluate the contrasts for different target types and background classes. The relations between contrast measures and incidence angle, target size and weather conditions are addressed. In order to track, identify or classify targets, reasonable features for discrimination must be chosen. In this project, Hu's 1st geometric moment is used as a geometric feature to investigate the elongatedness of the targets. It is found that cross-polarization (HV and VH) gives better contrast than co-polarization (HH and VV), especially at low incidence angles. Where quad-polarimetric data is available, enhanced contrast can be obtained through polarimetric decompositions. For man-made targets, the contrasts are seen to be dominated by the volume scattering and double bounce components, i.e. HV+VH and HH-VV. For man-made targets in ocean, contrasts for co-polarization channels are seen to increase with incidence angle, while cross-polarization contrasts decrease. The contrast measures are also seen to increase with target size, and to decrease with increased wind in the case of ocean background. Comparison of contrasts for different target types shows that PBR is larger for man-made targets in sea ice than in ocean areas, while the opposite is seen for TBR. Comparison of man-made targets versus icebergs shows that the latter has highest mean PBR while man-made targets have highest mean TBR. Ships in sea ice have higher contrasts than icebergs in both PBR and TBR. More data would provide more reliable results and a more accurate comparison. It is seen that Hu's 1st moment may be a useful feature for distinguishing between small and large ships, or between larger ships and other target types. URI: http://hdl.handle.net/10037/3358 File(s) in this item: 1
thesis.pdf (27.55Mb) -
Mjøen, Håvard Uv (Master thesis; Mastergradsoppgave, Jun-2008)[+][-]
Abstract: Information about snow covered area is important for several purposes, and this information can be found by detecting reflection of optical waves using optical sensors or by using active radars such as SAR. This thesis is explaining how information from the measurements are used to make snow maps. Optival sensors cannot detect snow when the area is covered by clouds, and this is a problem in the melting season in Norway. Microwaves can penetrate clouds, and detect wet snow. It cannot detect dry snow, but we will make snow maps based on the probability of dry snow. When we combine snow maps made from an optical instrument (MODIS) and a SAR (ENVISAT ASAR) we are able to get improved snow cover maps in times when the optical instrument cannot see the surface because of clouds. We will study a moving average filter and the Kalman filter. These filters are used to be able to filter the information about the snow cover to get an estimate of the snow covered area for each day. When comparing the results from the moving average filter with the Kalman filter, the results indicate that the Kalman filter gives a better estimation based on the measurements. We will also study relation between measured snow cover and the topography, and also if there are any relation between land cover and snow cover. The results indicate that the data from the optical sensors is underestimating the snow cover in northern slopes. The results also indicates that the melting of snow is correlated to the elevation. URI: http://hdl.handle.net/10037/1869 File(s) in this item: 1
thesis.pdf (2.200Mb) -
Moumets, Heike (Master thesis; Mastergradsoppgave, 15-Dec-2008)[+][-]
Abstract: The Fugløy area is located on the south-western Barents Sea shelf, in northern Norway. Multibeam echosounder bathymetry data, backscatter data and high-resolution seismic profiles were used to identify cold-water coral reefs. Together 12 cold-water coral reefs were mapped. Coral reefs have the highest density of up to 1.39 reefs per km² on top of ridges of morainic origin and they occur in areas where the seafloor is represented by hard bottom sediments. Moraine ridges are often cut by erosional channels; those probably have a positive influence on the transport and concentration of food particles. Numerous pockmarks were observed in the sedimentary basin in the northeast from the main coral reef concentration. The data suggest that the development and lateral distribution of reefs in the Fugløy area is characterized by an interaction between biological growth processes and factors like seepage of fluid from pockmarks, local topography, hard substrate and current regime. The vertical distribution is most likely controlled by physical oceanographic conditions like temperature, salinity and density. This study shows that high-resolution multibeam data together with backscatter and seismic data are effective tools to cold-water coral reef distributions in relation to the geological and oceanographic environment. URI: http://hdl.handle.net/10037/1795 File(s) in this item: 1
thesis.pdf (5.249Mb)
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