The possibilities for using CaNb2O6 as a photocatalyst in direct water splitting have been evaluated by investigating the electronic structure of the material. In addition the oxide was doped with nitrogen in order to modify the electronic structure and obtain visible light absorption. Experimental techniques such as electrochemical impedance spectroscopy (EIS), photocurrent, and diffuse reflectance spectroscopy (DRS) were combined with theoretical approaches to determine the bandgap, flatband potential and quasi-Fermi levels of the photocatalyst. CaNb2O6 was prepared by a sol-gel synthesis and doped with nitrogen by heat treatment of the oxide powder in an ammonia atmosphere. X-ray diffraction (XRD) confirmed phase pure orthorhombic CaNb2O6 for both pure and N-doped oxide and excluded a possible transformation of the oxide into an oxynitride. Upon illumination anodic photocurrents were observed implying that CaNb2O6 was an n-type semiconductor due to oxygen vacancies in the lattice. From the wavelength dependency of the photocurrent a direct bandgap of 3.7eV and an indirect bandgap of 3.4eV were determined for undoped CaNb2O6. Doping with nitrogen altered the optical properties of the oxide and shifted the absorption edge into the visible light region. Calculations using the density functional theory (DFT) attributed the change in absorption properties to the formation of narrow energy bands above the valence band of pure CaNb2O6. An alternative explanation could be a hybridization of N 2p and O 2p bands. Correspondingly a reduction of the bandgaps for N-doped CaNb2O6 with respect to the undoped oxide was identified. Impedance was applied to determine the flatband potential of CaNb2O6 from Mott-Schottky plots. However the obtained results seemed to be dominated by contributions from the electrode substrate. Theoretical investigations concluded that pinhole-free oxide layers creating an ohmic contact with the substrate are required in order to designate the observed impedance response to the space charge capacitance. Quasi-Fermi level measurements indicated a low photocatalytic activity of CaNb2O6 as no photocurrent could be detected. Further investigations are needed to identify the cause of the photocurrent limitations. Nevertheless probable explanations could be low conductivity in CaNb2O6, high concentrations of recombination centers or slow charge transfer kinetics. The latter was confirmed for porous oxide layers as the addition of a hole scavenger increased the measured photocurrent. Positive photocurrent transients were also observed for porous CaNb2O6 films and could be related to either the diffusion of electrons through the porous oxide layer or to a photoanodic decomposition of the photocatalyst.

Material models has been developed for anionic and/or cationic hydrogels, with a simulation framework implemented in MATLAB and the finite element software ABAQUS. The geometry of the simulations is a hemispheroidal hydrogel, divided into a core with a shell, covalently attached to an optical fiber. The material models have been used to estimate the chemical parameters of poly-acrylamide hydrogels containing anionic or cationic monomer groups. Simulations comparing free and constrained swelling has been conducted in order to determine the effect of the geometrical constriction to the optical fiber. Constrained hydrogel swelling featuring shells with different properties than the core was also investigated.The aim of the study was to validate the material models and examine the effects of geometrical constrictions together with shell-impregnation. The anionic material model was shown to reproduce experimental swelling data, while the cationic material model only reproduced the data for ionic strength greater than 100 mM. Restricting the hydrogel to an optical fiber resulted in decreased change in volume and an increase in the axial swelling. The model was able to reproduce reported reduction in the swelling for an impregnated anionic hydrogel by using a neutral shell in the simulations, but failed to recreate the shape of the swelling curve. With the reduction of swelling as a basis, a new method for estimating thin-layer properties has been developed.

This thesis presents an off-design simulation of offshore combined cycles. Offshore installations have a substantial power demand to facilitate the oil and gas production. To cover this need of power almost all the platforms use one or several gas turbines, often described as a simple cycle. However, because of high taxes on emissions, and increasing gas prices, more efficient technologies have been reviewed. One solution has been installing combined cycles (CC) offshore. Between 1999 and 2000 three combined cycles were installed on the Norwegian continental shelf and are still in operation. A combined plant may operate for prolonged time at off-design conditions, depending on power demand, ambient condition offshore. First, this thesis gives a description of combined cycles from a thermodynamic and technical point of view. A study of existing offshore combined cycles is performed, and some of the implications of using combined cycles offshore are discussed. In the study, also off-design performance regarding the gas turbine and steam cycle is presented. Further, the simulation tool GTPRO is used to model two CC plants, one designed for offshore installations, and one designed to achieve high efficiency. As part of the design process a sensitivity analysis is performed to find a good trade-off between efficiency and weight for the offshore plant. The model showed good agreements compared with the existing offshore plants, with a power output of 50.3MW, plant efficiency of 50.3%, and similar weight of the skids. The high efficient plant, based on the same gas turbine, and the same assumptions produced 53.1MW. This model gained 2.4MW more in power output, however with a penalty of 209 ton in extra weight.To review the plants performance and operability, off-design simulations were performed in GTMASTER. Both part load and changing ambient temperature were investigated. The results showed that both plants had similar behavior in performance at off-design, and that the GT strongly dictates the behavior of the steam cycle. At part load the relative SC efficiency increases, resulting in general high plant efficiency. At 60% GT load, the relative gas turbine efficiency is 81% compared to the relative plant efficiencies of about 90%. The difference in efficiency between the high efficient plant and the offshore plant remains constant at part load. The result from the simulations of ambient temperature is that none of plants will achieve higher plant gross efficiency at changing ambient temperature. The best plant efficiency occurs at design point. However, both plants have a long interval with approximately 100 % plant efficiency. From 15 to 0°C, the relative SC gross efficiency drops with 5 %, and the relative GT efficiency increase with 2%. However, the power output changes for both the GT and ST. From 28°C to about 0°C the power output increase almost linearly for the SC and GT.

The use of offshore wind turbines as a source of renewable energy is promising. However, many challenges have to be solved before they will be cost effective. The operation time, without any maintenance required, is desired to be as long as possible, because downtime and maintenance costs are high. Thus it is important that the rotating parts in the turbine have a long operational time. The harsh marine environment, combined with the desire for elongated operating times and little or no maintenance, give rise to many tribological challenges. It is important that the chosen materials and lubricants can withstand the marine environment, and the high loads. The effect of marine environment on lubricating properties of lubricants is not well understood. The objective of this thesis has been to investigate this effect. Two lubricants that are commonly used as gear lubricants in onshore wind turbines were tested in this work; polyalphaolefin and polyalkylene glycol. They were both contaminated with different amounts of artificial seawater in order to investigate the effect on the lubricating properties. The lubricants were tested in a rotating ball-on-disc tribometer, with self-mated stainless steel, and self-mated silicon carbide. Stainless steel was selected as it is commonly used in gear bearings, whereas silicon carbide was chosen due to its promising excellent properties. The results obtained from this work show that PAO has a very low saturation limit for water, and an emulsion will be formed even at low contamination levels. This made the lubricant unstable, and the measured COF were unstable. It was found that the amount of two-body abrasive wear increased as a function of seawater content. The PAG lubricant managed to dissolve much larger quantities of seawater that PAO. But even though the system was one-phased, the results for COF were unstable. Wear induced pitting was found for both clean and contaminated lubricant. It is believed that it is caused by the additive package of the lubricant. For dry tribological testing COF was found to be mush less for self-mated silicon carbide than for self-mated stainless steel. This is as expected, since silicon carbide has shown outstanding tribological properties in previous work.For self-mated silicon carbide testing only abrasive wear could be found for both dry contact, and lubricated. The results from PAO contaminated with seawater, showed a clear increase in COF as a function of seawater content. Further, the COF all stabilized after the running-in period. PAG showed no such trend with increasing amounts of seawater, but the standard deviation of the measurements increased.

I dette prosjektet er en barnevugge blitt designet. Vuggen tar utgangspunkt i en vippemekanisme utviklet av Terje Rølvåg ved Institutt for Produktutvikling og Materialer på NTNU. Målet med prosjektet har vært å utforme en estetisk og funksjonell vugge tilpasset vippemekanismen. Mekanismen skal bidra til å roe barnet ved hjelp av vugging ved optimal frekvens.Det ble uført en enkel segmentanalyse hvor ulike brukergrupper og forretningsideer ble drøftet før et utvalgt konsept ble videreført. Dessuten ble det foretatt et litteratursøk for å underbygge tidligere undersøkelser som antydet en frekvens på 1-1,5 Hz som optimal vuggefrekvens for babyer.Basert på det valgte konseptet ble kundekrav og -interesser identifisert for å kunne lage en adekvat kravspesifikasjon. Forskjellige løsninger er presentert før ett av designene ble tatt videre og modellert i NX.Forskjellige sikkerhetsstandarder ble gjennomgått for å sikre optimal kvalitet på sluttproduktet. Det endelige designet er basert på gjeldende sikkerhetsstandarder for vugger samt funn fra brukeranalysen.Prosjektet resulterte i fire ulike designforslag. Det vil være opp til veileder eventuelt å føre et av disse designene videre.

Carbon composite materials and structures have low weight, high stiffness, high strength and chemical resistance. Throughout this master thesis a feasibility study to utilize carbon composites in tubes, designed to withstand high pressures, is undertaken both analytically and experimentally. The tube is meant to be used for well intervention, replacing the current solid carbon rod. In such operations is low weight, in addition to above mentioned properties, a critical factor for long reach. To extend the reach of the equipment the submerged weight of such a tube must be as low as possible.To enable a tube to withstand the high pressures, which can reach more than 1000bar, a thick walled tube is the only alternative to decrease the submerged weight compared to a solid rod. Work and literature on thick walled composite tubes with inner diameter to thickness ratios as low as 2 is minimal, if not absent.A two layered laminate structure was chosen for the tube. The inner layer existing of hoop winded fibers and the outer layer of longitudinal UD fibers. Such a layup will give both high radial strength and axial stiffness.Throughout the analysis it was found that the cause of failure would be instability. This conclusion was drawn as instability would occur before any of the chosen failure criterions were fulfilled. This implies that the strength of the material is utilized maximally.The experimental results had good coherency with the analytical results. Results from physical tests had a large scatter, but this was predicted as a result of a manual production process leading to uneven distribution of fibers and medium to large voids.Several parameters, both regarding load cases and necessary material properties, for the given requirements of the tube have not been assessed. However, results from conducted analytical and experimental work shows that thick walled composite tubes are able to withstand the given loading conditions, together with keeping the submerged weight sufficiently low.Future work based on the results in this thesis should include test results with statistical significance, analyses on the more complex load cases, optimal laminate design and identifying a suitable matrix material which can withstand the necessary temperature requirement.

An analysis incorporating different principles for determination of the electricity mix and the subsequent environmental characteristic.

There is a growing demand for increased electricity transfer capacities between the countries surrounding the North Sea. The increased capacities will enable easier integration of intermittent renewable energy sources, decrease the need for balancing power, increase power trade and competition, and increase security of supply across the region. Interregional offshore grid connections are required if large scale deployment of deep sea, far from shore offshore wind energy in the North Sea is to take place. The WINDSPEED research project has resulted in proposals of realistic scenarios for large scale deployment of offshore grid and wind energy in the North Sea. In this study the environmental impacts of an interregional meshed offshore grid as proposed by WINDSPEED have been assessed. Environmental impacts of the offshore wind farms, which may be connected to the grid, have been included in the assessment as well, completing the system boundaries.The methods used to quantify the environmental impacts are process-based life cycle assessment (LCA), input-output assessment (IOA) and tiered hybrid LCA, with main focus on the results of the latter. Four offshore grid scenarios have been assessed, with and without offshore wind farms connected. The offshore grid is primarily composed of 450 kV HVDC technology for long distance transmission, based on the HVDC cables used in the NorNed connection. Wind farms are deployed far from shore (requiring much sea transport and long distance grid connections) and at an average of 43.9 meters depth (requiring large bottom-mounted foundations for the wind turbines). These requirements make the environmental impacts of deep sea, far from shore offshore wind energy substantially higher than for both close to shore offshore wind energy and onshore wind energy.The environmental assessment of the interregional meshed offshore grid found that the largest contribution to environmental impacts is from manufacturing and installation of HVDC cables. Sea transport required for installation of components and operation and maintenance contributes between 5 and 25 percent to most impact categories. The electrical equipment (converters, breakers and switchgear) required by the grid has a quite varying contribution, from almost none to some impact categories to about 35 percent to climate change impact. The environmental assessment of the deep sea, far from shore offshore wind energy, finds that the largest contributors to environmental impacts are the wind turbines. But the other components required – deep sea foundations, offshore grid and sea transport for installation, operation and maintenance – makes the environmental impacts caused by it around twice as high as for onshore wind energy installations. Total climate change impacts were found to be 42.9 g CO2-Eq/kWh; the grid is responsible for 11, foundations 31 and sea transport 9 percent of that. The largest impacts of deep sea, far from shore offshore wind energy as compared to other relevant energy sources are to the impact categories freshwater ecotoxicity, human toxicity and metal depletion. The impacts to these categories are many times larger, up to almost 20 times, compared to other relevant fossil fueled energy sources. The impacts to the other impact categories are substantially lower.The results indicate that the environmental impacts caused by an interregional meshed offshore grid in the North Sea are substantial; it needs to be considered an important part of an environmental assessment of deep sea, far from shore offshore wind energy. On the other hand, the environmental costs are probably not so high that they outweigh the potential benefits of such offshore grid connections. It may in fact lead to net environmental gains because of a decreased demand for fossil balance power. As for large scale deployment of deep sea, far from shore offshore wind energy the environmental benefits as opposed to relevant fossil alternatives are obvious, but, including the significant disadvantages of intermittent energy supply and high monetary costs, overall gain to society is harder to predict.

This work involves the study of heating systems that combine solar collectors, geothermal heat pumps and thermal energy storage in the ground. Solar collectors can reduce the electricity use in these systems by reducing the operation time of the geothermal heat pump and by increasing the ground source temperature. These systems can be designed in many ways, consequently the complexity is high. The purpose of this study has been to develop simulation models to study the behavior of these systems, with emphasis on the thermal energy storage in the ground. A simulation tool with several models has been developed in the simulation software TRNSYS based on the proposed heating system at the GEL under the metrological conditions of Shanghai. The program was used for an intensive simulation study, in which the interaction with the borehole heat exchanger, the geothermal heat pump, the evacuated tube collector and the load requirements could be analyzed. A base case was developed to make it possible to vary and compare the design parameters of interest, such as the ground storage volume, the flow rate of the solar collector and the solar collector area. The base case was based on the design parameters of the GEL. The GEL was used as reference building and was simulated in TRNBuild with the thermal characteristics of the building material. From the simulations the heating demand of the building could be obtained and the building model could later on be used as a heat load for the other simulation models. The results showed that the there were heating demand from November to March. The four operation modes of the proposed heating system at the GEL were presented. All of the operation modes were simulated in TRNSYS. The four operation modes were solar thermal ground storage, solar direct heating, direct heat exchange with the ground storage and geothermal heat pump. The operation modes worked in two different seasons, storage season and heating season. The ground storage mode was studied thoroughly by varying the parameters of interest. To test the significance of the borehole configuration, the storage volume was kept constant and the number of boreholes and the borehole spacing were varied. It was found that a compact pattern with a high number of boreholes and small borehole spacing is favorable for borehole thermal energy storages. The performance of a ground storage is directly linked to the storage size. The solar collector efficiency is highly dependent on the return temperature of the storage. It was decided to continue to work with a compact pattern of the storage, rather than the base case of the GEL. This is because this kind of storage showed the most promising storage efficiency and also reached a high ground temperature during storage season.Simulations of the heating modes showed that the solar direct heating mode, the direct heat exchange with ground storage mode and the geothermal heat pump mode can each cover 37%, 25% and 38% of the heating demand respectively. For the simulations of the geothermal heat pump it was shown that the borehole depth is a very important factor for the system performance. Too short borehole depth will cause unstable and too low temperatures at the inlet of the evaporator. To compare the electricity use of a geothermal heat pump system with and without solar collectors there were also performed simulations for a traditional geothermal heat pump system. Results showed that 26.1% of the electricity consumption could be saved. The savings was mostly due to the reduced operation time of the heat pump, since other heating modes could be used. The studies showed that due to the complexity of such systems it is very important to perform simulations to optimize the performance. There are many factors that play an important role since there are so many components involved. The simulations showed that sizing of the system is critical for the system performance.

In this diploma thesis, the possibilities to enhance the process production and energy efficiencyas well as the energy recovery potential of PFA 2 at Hydro-Sunndalsøra have been determined.To identify the potentials for energy recovery, it has been conducted energy balances. The resultsfrom the balances give an overview of the waste heat sources and their total energy content, togetherwith the temperatures at which they are available. The total energy in the waste heatsources for PFA 2 was found to be 17.8 GWh/year. The largest waste heat sources were localisedin connection to the cooling agent of the casting ingot machine. Here disappears 12.32GWh/year through cooling water within a temperature range of 10 to 30°C as well as convectionand radiation to surrounding. The cooling water section one was determined as the most promisingheat recovery potential with 7.47 GWh/year. Furthermore the initialisation of liquid aluminiumalloy was revealed as a waste heat source with 5.48 GWh/year. Here disappears 3.34GWh/year through the flue gas of the furnace within a temperature range of 288 to 1,100°C andcreates the most promising heat recovery potential at the furnace.The energy saving potential is divided into three groups: energy saving by existing equipment,optimising of equipment and waste heat recovery. Here energy saving by existing equipmentreveals 26.4 MWh/year for an improved control quality of the melt temperature. The greatestpotential for energy saving by optimisation of the equipment was found to be 1.98 GWh/year forthe implementation of regenerative burner. Furthermore effects an installation of a furnace pressurecontrol system 689.14 MWh/year less energy consumption due to the avoided false air. Thegreatest energy saving potential for waste heat recovery was estimated to 1.65 GWh/year for thepreheating of charged metals to 300°C, instead of 20°C. The preheating also leads to improvedsafety, because of the elimination of moist metal in the furnaces, and increases the process production,as a consequence of larger melt capacity. Furthermore, heat to power solutions revealedthe use of favourable electricity production by the generation of waste heat. Here the greatestgeneration potential was found to be in the flue gas from the furnace. A common Rankine cycle,with a direct heat recovery design and water as working fluid, was estimated with a recoverypotential of 1.1 GWh/year. With the use of an organic Rankine cycle the potential can be recoveredto 489.8 MWh/year for an indirect heat recovery design and pentane as working fluid. Thereare still some challenges associated with flue gas heat exchangers (dust) and operation of suchpower generation plants at alternating heat loads, but the technology is under rapid development.The waste heat generation potential for the casting ingot machine was determined with 411.3MWh/year for an ideal organic Rankine cycle heat recovery design, within a temperature rangeof 58 to 90°C and R 134a as working fluid. An alternative ideal organic flash cycle layout revealed253.4 MWh/year (expander = 0.6) respectively 416.5 MWh/year (expander = 0.6), within atemperature range of 36 to 90°C and butane as working fluid. These considerations have lowerefficiencies compared to the furnace layouts caused by the low application temperatures (TBoiler <90°C).