Existing wave energy converters are only based on a few ways to produce electricity from ocean waves. All of them suffer from low cost-efficiency so the proposal of new technologies is still up to date. This is a preliminary study to an innovative concept, based on wave-induced currents. As waves propagate into shallow water and break over a barrier, they dissipate their energy. The latter can be partly transformed in a hydraulic potential through the wave set-up behind the barrier and the cross-shore mass transport from waves. Electricity can then be produced by the mean of a water turbine.This study estimates qualitatively this energy potential. The 2D set-up is analyzed by the model of Calabrese et al. (2008) and is adapted to 3D for a regulated net cross-shore discharge. The 3D model of Bellotti (2004) is also used. Experiments have been carried out on a simplified lab-scale model to check qualitatively the applicability of the models, determine experimentally their calibration parameters and find the optimal combination flow rate/pressure head which gives the highest hydraulic potential. Two different barrier profiles are tested: a breakwater-like barrier with a steep seaward slope and a sandbar-like barrier with a mild slope. Despite a significant uncertainty, experimental and analytical results correlate well.The conclusions on the future of this technology are not thorough. Experimental conditions applied to full scale show a quite low efficiency compared to the main competitors, but much more perspectives of optimization are conceivable. Some of them have been studied from an analytical point of view.

A MATLAB script has been developed to investigate dynamics in the blades of a 10 MW downstream wind turbine, with both a tubular- and a truss tower. The classical Beam element momentum method with additional correction factors are used to determine forces on the blade. Centrifugal loading have been applied by use of an iteration method. Blade dynamic response is investigated in terms of Modal analysis. In addition, the dynamic response of a blade with adjusted stiffness has been investigated. Three approaches to obtain the wind velocity field in the rotor plane are studied; averaged Blevins model with input from a study in ANSYS FLUENT, Wind files extracted from ANSYS FLUENT, and results from a small scale wind tunnel experiment. The three cases provide ambiguous results with regards to blade deflection and root flapwise bending moment. Results indicates that vortex shedding have large effect in a tubular tower configuration, but small effect in a truss tower configuration. Based the most the most trusted input, the wind tunnel case, the results indicates that a truss tower would provide more desired values in terms of root flapwise bending moment and fatigue loading.

The current residential building stock in Norway is organized in to groups, and sorted after number of building units. The criteria used for sorting, are criteria that affect the viability and rationality of various energy supply systems. The results from this survey forms a database where it is possible to go in and find the number of buildings sorted after region, building type, urbanity and year of construction.Based on findings from the survey and other factors affecting the applicability, a set of four energy supply systems are introduced and studied closer as possible solutions in ZEBs; District heating (DH) + PV, Bio energy (BIO) + PV, Heat pump (HP) + PV, Combined heat and power (CHP) + PV. The Zero Emission Building balance is calculated for each solution and pre-defined energy level, to determine the required on-site electricity generation from the PV’s. A model is then developed to study the potential of the proposed solutions in the Norwegian residential building stock. The analysis is performed on future scenarios, which represent different development of the building stock with regards to new buildings, refurbishment and demolition. The number of buildings that can be converted to ZEBs with the investigated energy supply systems and [available roof area/floor area] are quantified. Results show uptake potential for all of the technologies in buildings with energy demand lower than 94,5 kWh/m2year, but limitations occur as soon as [available roof area/floor area] decreases from the upper limit investigated in the study (1:2). The greatest potential is shown by CHP + PV, where ZEB conversion is possible in approximately 30% of the total residential stock in year 2050. It is also observed a relative growth in the potential of DH + PV and HP + PV in small houses after year 2025 due to the estimated upgrade of energy-efficiency in the stock. In multi dwelling buildings, it is only CHP + PV and BIO + PV that show potential in both current and future stock.

I denne oppgaven beskrives de aerodynamiske ustabilitetene kalt stall og surge. Oppgaven består hovedsakelig av tre deler. I første del gjennomgås noe fundamental teori på aerodynamikken i sentrifugalkompressorer, før funn gjort i tidligere eksperiment på ustabilitetene presenteres. I litteraturen er det bevist at stall og surge forekommer i flere former og med flere karakteristikker. Med tørrgass som arbeidsmedium kan disse karakteristikkene identifiseres ved hjelp av trykksensorer. Karakteristikkene har vist seg å være svært avhengig av kompressorens geometri.Visualiseringsmetoder som tidligere har vist seg å fungere godt på turbomaskineri gjennomgåes og det diskuteres rundt applikasjonen med våtgass. Laser Doppler Velocimetry ble prøvet ut, men det viste seg at denne måleteknikken er for ømfintelig til at den kan brukes med våtgasstrømning. En spesialløsning med pitot-prober er en mulig metode for fremtidige visualiseringsforsøk. Til slutt presenteres et eget eksperiment hvor en industriell kompressor utsettes for tørr- og våtgass. Formålet med eksperimentet var å dokumentere ustabiliteter, med hovedfokus på frekvens og størrelse. Karakteristikken til tørrgassustabilitetene ble kartlagt ved hjelp av dynamiske trykksensorer plassert i diffusoren. Resultatene ble sammenligning med resultat fra tidliger eksperiment funnet i litteraturen. Funnene stemte godt med tidligere forsøk gjort med tørrgass. Karakteristikken til våtgass lot seg ikke identifisere like lett. De dynamiske sensorene plukket ikke opp noen stallfrekvenser eller størrelser, selv om ustabiliteter var observert visuelt ved testkjøring. Det ble heller ikke funnet noe bevis på at maskinen gikk i surge.

Denne masteroppgaven evaluerer svingningene is sugerørsstrømingen til en Francis turbinved dellast. Bakgrunnen for dette studiet er delvis på grunn av verdens økende energibehov. Med varierende energipriser og vannivåer i magasinene opererer vannturbiner på varierende last. Operasjon ved fullast og dellast skaper trykkpulsasjoner i turbinen, hvor en av årsakene er ustabil strømning i sugerøret. Hovedmålet med denne oppgaven er å gjennomføre en CFD-analyse av løpehjulet og sugerøret i en Francis turbin ved dellast.Resultatene fra CFD-analysen stemmer godt overens med modelltesten gjennomført i Vannkraftlaboratoriet. Ved bestpunktet er sugerørsstrømingen symmetrisk og stabil både i CFD-analysen og i laboratoriet.Ved fullast er søgerørsstrømningne også symmetrisk og stabil, men det er et stort lavtrykksområde under løpehjulets boss. I laboratoriet kaviterte vannetpå grunn av det lave trykket. Ved dellast blir sugerørsstrømingen ustabil, og trykkpulsasjoner ble målt. En sugerørsvirvel formet som en korketrekker oppstod i sugerørskonusen i laboratoriet. CFD analysen er en-fase, uten mulighet for å kavitere, men en trykkoverflate viser en tilsvarende virvelform i sugerørskonusen.Frekvensen på trykkpulsasjonene målt ved dellast stemmer godt med den teoretiskefrekvensen ved det samme operasjonspunktet.

A dense gas released into the atmosphere will have a flow development that can be described by a large range of physical scales and quantities. An instantaneous release will slump towards the ground unaffcted by the wind, before it is gradually and increasingly diluted by the turbulence in the surrounding flow. Therefore, when the gas is far from the release point, its movement is determined by that of the wind.The wind's turbulence characteristics varies with the atmospheric stability. An unstably stratified boundary layer will have turbulence production by negative density gradients, regardless of free stream velocity. A stable stratification, however, requires a wind velocity and shear to produce turbulence. The wind profile's velocity and turbulence characteristics can be described by similarity models, which may further be used as initial and boundary conditions in a turbulence model.The ke~model is a second order turbulence closure that has proved succesful in describing several turbulent flow scenarios. The version of the model used in the software package Kameleon FireEx has here been tested for dense gas releases, with a focus on far field development. Wind modeling is an area where the standard k-[epsilon] model is known to have problems, as it gives an unrealistic, inhomogoneous flow field.Three alterations to the k-[epsilon] model were tested in the work on this thesis. The first was a model constant varying with the local turbulence parameters, the second was a modification to the turbulence Schmidt number and, finally, a correctional production was added to the transport equations for k and [epsilon]. Of the three approaches, the last one gave the most encouraging results.There are still problems left regarding the k-[epsilon] model's handling of buoyancy-affected diffusivity. The Schmidt number modification dampens the dense gas' ability to diffuse also in the lateral directions, not only in the vertical, an effect that should be investigated further.

Different concepts for Enhanced Geothermal Systems (EGS) are presented and evaluated according to their potential for medium to large scale power production in Norwegian conditions. Potential locations for geothermal energy in Norway are identified. A fractured EGS with multiple wells situated in a low to medium temperature granitic basement was found to be the concept best suited for medium to large scale power production in Norway. An Organic Rankine Cycle (ORC) is typically used as the heat conversion cycle in low to medium temperatures. The ORC yields a better thermal performance in these temperatures, compared to flash cycles and Stirling engines. It is also a mature technology and commercially available. Thermal efficiency of the ORC was found to decrease drastically when operated at lower than design temperature. A numerical model of a fractured EGS was developed using Matlab. The model was able to capture the long term thermal behavior of a EGS. Based on this model was a sensitivity analysis conducted in order to see how responsive the thermal output is to different parameters. Typical ranges of fractured EGS parameters was found in existing literature regarding EGS. Thermo physical properties, such as thermal conductivity and specific heat, are highly dependent on mineral composition and temperature. They can therefore vary several factors between sites. Typical fracture apertures were found to be between 0.2 mm to 3 mm, and dependent on local geological conditions. The thermal output from the fractured EGS was found to be highly sensitive to changes in parameters like fracture aperture, fracture length and fracture spacing. Geothermal energy is marginal at best, consequently is it vital to extract as much geothermal energy as possible. A typical fractured EGS is therefore designed with a temperature drop of about $10^0C-15^0C$. The result is that the system is highly sensitive to variations in reservoir parameters. It is therefore critical to obtain accurate estimates and models of the fractured reservoir, and to control the fracture development during stimulation and operation. A system consisting of a fractured EGS and ORC was found to be extremely sensitive to variations in geothermal temperature. A temperature decrease of 10% yielded a 25% decrease in net work output.In order to reduce the risk related to the uncertainty of the geothermal temperature over the life time of the EGS is it advisable to combine geothermal energy with an alternative energy source. A hybridization of geothermal energy and a waste combustion plant was found to yield a stable power output regardless of geothermal temperature, and also offered a higher thermal efficiency than a standalone ORC. Geothermal energy could either by used as pre-heat in the waste combustion cycle or a ORC bottoming cycle could be used.

The stochastically forced Burgers equation shares some of the same characteristics as the three-dimensional Navier-Stokes equations. Because of this it is sometimes used as a model equation for turbulence. Simulating the stochastically forced Burgers equation with low resolution can be considered as a one dimensional model of a three-dimensional large eddy simulation, and can be used to evaluate subgrid models. Modified versions of subgrid models using the fractal interpolation technique are presented here and tested in low resolution simulations of the stochastically forced Burgers equations. The results are compared with high resolution simulations, then low resolution simulations first using the dynamic Smagorinsky model and then using no subgrid model other than the numerical dissipation of the convective flux discretisation scheme. The fractal models perform reasonably well and most of the large scale features from the high resolution simulations are reproduced by corresponding simulations with low resolution. The performance of the fractal models is not, however, better than the performance of the dynamic Smagorinsky model. Therefore one might say that although the fractal models give promising results, it is not obvious that they are in any way superior to the traditional models. Also the low resolution simulation with the dissipative convective scheme performs well, suggesting that numerical dissipation can be sufficient as a subgrid model in one dimension.The solutions to the stochastically forced Burgers equation follow a k^(-5/3) energy spectrum, but high order statistics are not similar to real turbulence, due to the complete domination of shocks. Thus the stochastically forced Burgers equation might not be a suitable model for turbulence. It is not likely that the complexity of three-dimensional subgrid modelling is sufficiently represented by the one-dimensional case either.

An investigation of how different levels of turbulence modelling tackle the effects of system rotation has been performed. Ranging from simple one-equation models to large-eddy simulations, different approaches have been considered by means of a literature study and numerical calculations of turbulent flow over a backward-facing step subjected to spanwise rotation. The computed results were compared with results from direct numerical simulations.The literature study revealed that simple linear eddy-viscosity turbulence models are unable to predict any effects on the turbulence field due to system rotation. Eddy-viscosity models may be sensitised to rotation, but this has been done with a varying degree of success. The Reynolds stress equation models inherently respond well to system rotation, but a more costly eddy simulation will yield the most accurate result.Numerical calculations confirmed what was found in the literature. A linear eddy-viscosity model was unaffected by system rotation, while the sensitised model exhibited some effects on the mean flow field. The Reynolds stress model managed to predict all essential effects related to system rotation, although one separation bubble was oversized. This defect was attributed to a flaw in the modelling of the Reynolds stress redistribution process.

Målet med denne masteroppgaven er å undersøke dynamisk drift av RSW-anlegg med CO<sub>2</sub> for å optimalisere kapasitet og redusere energibruk. Ulike faktorer som spiller inn på den dynamiske driften for et RSW-anlegg, ble først kartlagt. At prosessen kan drives gunstig i subkritisk drift ble vurdert som mest avgjørende på grunn av generelt lav sjøvannstemperatur i Norge. Fire ulike løsninger som er utviklet av SINTEF Energi for RSW-anlegg ble drøftet i denne rapporten. Simuleringer i Csim viste at alle systemløsningene klarte å kjøle vannet i tanken på de 12 timer som maksimalt er disponibelt. Et system med tørr fordamper og gasskjøler ga best COP i subkritisk drift. En kontrollstrategi for minimal energibruk ble videre foreslått for subkritisk drift. I samarbeid med SINTEF og NTNU ble det skrevet en artikkel om dette temaet til den internasjonale kjølekonferansen ”ICR2011” i Praha. Simuleringer viste 50 % reduksjon i kompressorarbeid. Resultatene fra eksperimenter i laboratoriet viste at kompressorarbeidet kan reduseres ved bruk av kontrollstrategien, men at reduksjonen i energiforbruk vil variere med anleggets spesifikasjoner. Denne driftsmåten gjør at sirkulasjonspumpene må drives lengre, og hvilke energibesparelser som kan oppnås, avhenger av pumpevirkningsgrad, trykktap og muligheten for regulering av kompressorturtall og kondenseringstrykk. Det er nødvendig med et komplekst reguleringssystem for å oppnå de største energibesparelser. Dagens RSW-modell i Dymola manglet en rørkjelvarmeveksler, og dette ble implementert i løpet av denne oppgaven i samarbeid med SINTEF. Resultatene fra simuleringer ble sammenlignet med stasjonære simuleringer av det samme anlegget i Csim, da denne modellen er mer verifisert. Modellen i Dymola ga til slutt kun 3 % avvik i nedkjølingstid fra Csim.For å oppnå en kontrollstrategi for minimal energibruk i transkritisk drift er det gunstig med en direktekoblet høytrykksoptimalisator. Et nytt reguleringssystem basert på maksimalverdisøking ble vurdert, og en modell med utgangspunkt i denne kontrollstrategien ble utviklet i Dymola i løpet av denne masteroppgaven. Simuleringer av RSW-anlegg viste at denne maksimalverdisøkeren fant det høytrykket som ga best COP selv i dynamisk drift av komplekse system. Da RSW-anlegget i hovedsak drives subkritisk, vil høytrykksoptimalisatoren ha større potensial for energisparing ved bruk i andre CO<sub>2</sub>-anlegg, som oftere drives transkritisk. Dette kan for eksempel være varmepumper for varmtvannsberedning.