This paper describes a proposed test plan for harvesting energy from waves with a linear machine that uses gas-springs. The linear machine “Prototype 2B” has been put into production and will be finished. The machine has been constructed to withstand 300 bars of gas pressure and the maximum speed of the rotor is set to 10 m/s due to the sealing. The model made in [5] uses the fundamental equations and describes the system behavior of a linear machine with gas springs. The model has been slightly improved and the input specifications for the “Prototype 2B” have been used. The simulations shows that one needs to feed electric energy in some parts of the cycle, but the whole cycle will yield a positive net contribution of electrical energy. The model is not optimized, and hence should be improved due to the time consuming simulations. Steel profiles have been proposed to use for the frame of the test-bench. The first draft of the drawing has been sent to NTNU and the workers have started to build the frame. To ensure the vibration energy to spread itself into the surroundings, isolators need to be selected and adapted. The natural frequency of the test bench with four chosen isolators was calculated to 18,17Hz. The chosen isolators are therefore most likely good enough since the lowest operating frequency of the machine was simulated to 55 Hz.Transferring the energy from the high-force-low-speed source (the wave) to the resonator has been discussed and some suggestions have been proposed. The energy transfer is done by raising pressure in a freestanding actuator with a hose connected to the gas spring. Hence, increasing the actuator pressure will increase the gas spring pressure and the force acting on the rotor will be significantly higher. A procedure to select the correct components are discussed and a Matlab script for analyzing the choice has been made. The high-force-low-speed source has been discussed. Two solutions where a hydraulic system is used have been further investigated, and some calculations and analysis have been performed. Simulations show that one need to apply a maximum force of 24115N at one actuator with a 32mm effective piston area. The regulation of the high-force-low-speed source could be crucial to obtain a good test result since the regulation of the wave must adapt itself to the resonating force of the rotor. The regulation must therefore be investigated further as it can have tremendous impact on the possibility of extracting energy from the machine.The electrical source and regulation control have been discussed. Timing of the electrical energy supplied is crucial and three operational simulations have been performed to investigate when the positive net contribution is at it`s highest. In order to extract the maximum possible net energy from the machine, the right electrical control is very important to implement. Two of the control systems have been proposed, where perhaps the simple proportional controller should be chosen to prove the concept. Later on a more sophisticated electrical controller should be applied since the efficiency of the wave energy converter could increase significantly.The non-linear compression event in the gas-springs is not proportional to the electrical extracted energy. Simulations show that when the pressure increases in the springs one could extract more energy, but the non-linear event could not be recognized. Simulations show that the efficiency of the system varies significantly with the controlling of the machine. If a simple proportional controller is adapted, the theoretical efficiency becomes 2,87% and with a more sophisticated controller one could get 10,02%. This means that there must be done more research on the electrical operating control system if energy harvesting could be profitable.

AbstractIn relation to new building directives and regulations there is much focus on energy efficiencyand reducing the use of electricity. There is therefore a need for ventilation systems with lowSpecific fan power (SFP) and to limit or avoid the need for mechanical cooling.At the same time questions are raised concerning whether increasingly complicatedventilation systems are the best way to achieve energy efficiency. They are more vulnerablefor poor design and maintenance which especially school buildings have suffered from.This has led to the development of several natural and hybrid ventilation concepts. One ofthese which has had success in school buildings the last 15 years in Sweden and Norway isthe so-called Swedish model. Characteristic of this solution is that sub terrain culverts areused for passive cooling and heating of the ventilation air which passes through double innerwalls and is supplied to the room high on the inner wall. The supply air falls towards the floormixing in the surrounding air and spreads along the floor as displacement flow with an outletin the ceiling. This works particularly well in classrooms where the high occupation densitycreates a cooling demand large parts of the year. These schools therefore have a very low SFPfactor and no mechanical cooling.In the following report a classroom model with the Swedish ventilation concept is studiedwith the aim of developing a method of dimensioning such air flow. CFD simulations areused to confirm expected behaviour and the resulting thermal comfort and air quality attypical winter, spring and summer scenarios. Finally a Guide for preliminary design andsizing for climatization of rooms with cooling needs using the Swedish model is presented.The most important results were that there was a good correspondence between the empiricalcalculations and CFD simulations. Adequate carbon dioxide levels and temperature can beachieved without use of primary energy for heating at for outdoor temperatures above 5 ºC.There was a substantial risk of draft unless a near zone of 2-3 m is used. However the CFDmodel was limited to a slice of the classroom and the accuracy of the results suffers somewhatfrom this.Guidelines are developed for preliminary design and sizing of supply air plumes based onempirical expressions of air flow by Eimund Skåret(2000) and can be found in the appendix.

SummaryThis Master Thesis is a conclusion on work done as part of the Resource Optimizationand recovery in the Materials industry project (Roma). This project is involved in thedevelopment of a new technology for power production from low temperature heat sourcesfor off gases from aluminum production cells. The technology is based on an transcriticalRankine cycle with CO2 as a working fluid, as the work recovery circuit. The center ofthe test facility is the expander, a prototype provided by Obrist Engineering . 81 testswere perfomed to investigate the behavoir of the expander cycle. Effect of three mainparameters were investigated:• Effect CO2 massflow rate• Effect of heat source temperature• Effect of CO2 condensation pressureFor each parameter combination, the high pressure side of the expander cycle was variedin order to find the maximum power output.This study clearly showed limitation of the turbine which cannot maintain large pressuredifference probably due to large internal leakages. As a result, turbine outlet is highlysuperheated. This superheat is lost energy for the power cycle, and is simply dumpedinto the heat sink. One possible improvement would be to include a recuperator thatrecovers superheat after the pump.The results also indicate that the fan of the air loop is too small: increasing the CO2 flowrate to limit superheat at turbine outlet leads to turbine inlet temperature reduction.Last, for large CO2 mass flow rate (3.5 kgmin) which is required for proper operation ofthe turbine, the power generated is too large for the generator installed on the loop. Itstemperature reached 120 °C for some conditions. A new solution should be seeked.Based on experimental results, a mode of the power cycle was implemented in Pro/IIand simulations were run in order to find an improved design. The main goal is to beable to run the cycle at high CO2 mass flow rate: 3.5 kgmin. It was found that the airloop fan should be able to deliver up to 1 260 m3h . The new generator or braking systemshould be able to absorb up to 297 W.

LCA of buildings has become a distinguished field of LCA, and a number of previous studies have found that low energy buildings generally have better life cycle performance than conventional buildings. However, there has been a lack of studies comparing low energy buildings against passive buildings. The present study evaluates life cycle performance of two passive and two low energy buildings that are all part of the housing cooperative Løvåshagen in Bergen. Construction of the housing cooperative was completed in 2009 and measured material and operational data was used in a comprehensive LCA of the whole life cycle from cradle to grave, for twelve midpoint impact categories. The functional unit is a lifetime of fifty years of one square meter BRA of a building block apartment. Heating for low energy apartments are provided by electric resistance heaters and heating cables in the bathroom floors, while hot water heating is provided by an electric water heater. Evacuated tube thermal collectors are located on the roofs and provide passive house room heating through hydronic radiators and hydronic floor heating. They also provide hot water heating for each apartment. When solar collector output is not sufficient, heating is supplied by electric resistance elements.The LCA results show practically no difference between the climate change performances of the house models, and this is largely the result of a particularly low passive house performance. In simulation-based LCA literature there appears to be a trend of over-estimating the operational performance of passive and low energy buildings, and Løvåshagen is no exception. The measured electricity consumption is high, both compared to estimations and to the results of other, simulation-based, studies. The high consumption appears to be a result of a particularly low outdoor temperature for the year of the measured data. It is recommended to monitor the electricity consumption over the next few years of operation, and if it is not significantly reduced there is reason to suspect faults in building construction or in the solar collector system. In the case of no direct defects there is reason to re-evaluate the effectiveness of solar collectors for the climatic conditions of Bergen.

Fred Olsen is currently testing their latest wave energy converter outside of Falmouth Bay in England, preparing it for commercial exploitation at the Wavehub-project. Previous studies have shown that this device has potential for increased power extraction using reactive control, but so far these investigations have focused on the hydrodynamics of the device and on reducing the peak-to-average power ratio while omitting the effect of the electric power take off system. This thesis shows the development of the hydrodynamic model of the device as well as a detailed model of the all-electric power take-off system consisting of a permanent magnet synchronous generator, inverter and DC-link. Vector Control is used to control the Permanent Magnet Synchronous Generator, and field weakening control of the generator is applied in order allow over-speed operation. Time domain wave-to-wire simulations are performed to evaluate the power take off capabilities of the modelled wave energy converter with different control parameters. When tuned according to approximate complex conjugate control the accumulated average generator losses become large, giving a very low overall system efficiency. Optimal control with respect to electrical output power is found to be with low added mass, and when compared to pure passive loading a 1% increase in annual energy production is achieved. The main factor that reduces the effect of reactive control is found to be the minimum load-force constraint of the device, which cannot be lower than 1 ton. Example simulations on a device with different force constraint are performed which verifies this characteristic.These results suggests that the Bolt2 has limited potential for increase in power extraction by implementing reactive control. The analysis in this thesis is nevertheless valuable, as it demonstrates how a wave-to-wire model can be used for power take-off investigations, annual energy production estimations and evaluations of different control techniques.

A dynamic one-dimensional homogeneous model for a packed bed sorption-enhanced water-gas shift (SEWGS) reactor has been developed, describing the non-isothermal, non-adiabatic and non-isobaric operation of this type of reactor. The model was developed to describe a SEWGS reactor designed to work under operating conditions and syngas feeds encountered in a coal-fed Integrated Gasification Combined Cycle power plant utilizing an oxygen-fed gasifier. Different from previous integration designs reported in literature, the feasibility of leaving out the conventional high-temperature water-gas shift (WGS) reactor upstream of the SEWGS reactor has been investigated. The reactor was assumed to be packed with a mixture of K2CO3-promoted hydrotalcite CO2 adsorbent and commercial high-temperature FeCr-based water-gas shift catalyst pellets. Utilizing the reactor model, a mathematical modelling framework for the operation of eight SEWGS reactors in a SEWGS cycle has been developed. This system model accounts for all the necessary interactions between the reactors during the SEWGS cycle, including the exchange of mass in the feed, rinse, equalization and repressurization steps. In contrast to available open literature, the mathematical framework describes in detail how the necessary switches in the boundary conditions for the reactors have been realized.Simulations of several SEWGS cycles were carried out. The results were compared with experimental and modelling data from literature. Due to inconsistencies in the parameters and implementation of the model in the simulation software employed, results were in most aspects quantitatively not comparable to results from literature. However, the qualitative trends and physical mechanisms expected were observed and confirmed by the model. The temperatures in the reactors reached an unacceptable high level with respect to the tolerable operating conditions of the catalyst and adsorbent. It is planned to continue the work on the model, and implementing it within a full power plant model to investigate the effects of changes in the power production and thus the required amount of syngas to be treated.

Våtgasskompressorer er en ny teknologi, og kan være svaret på hvordan uprosessert gass kan transporteres til prosessanleggene. Lykkes industrien med dette kan det føre til store kostnadsbesparelser som vil gjøre marginale felt lønnsomme. I tillegg vil teknologien føre til økt gassutvinning på eksisterende felt. I denne oppgaven er diffusor- og spiralhusdesign til eksisterende kompressor i laben på NTNU optimalisert. Ved hjelp av CFD programmet ANSYS 13.0 har de nye designene blitt simulert og strømningsbildet, ytelseskarakteristikk og polytropisk virkningsgrad har blitt dokumentert. I tillegg har simuleringer med partikkelinjeksjon blitt gjort for å se på hvilke innvirkning dette har for strømningsbildet i kompressoren. I diffusoren har fire nye design blitt laget. To er laget med nye diffusorbredder, et hvor innløpet har blitt innsnevret og et hvor diffusorutløpet ikke er avrundet. I spiralhuset har to nye design med økt tverrsnittareal blitt laget. I tillegg har eksisterende CFD modell av kompressoren på NTNU blitt oppdatert for å gjøre modellen mer lik kompressoren. Denne modellen benyttes som et sammenligningsgrunnlag for de andre designene. Analyse av de nye designene har vist at designet med det største spiralhuset har høyest trykkgjenvinning og polytropisk virkningsgrad for alle volumstrømmer. Maksimalt trykkforhold er 1,35 og maksimal polytropisk virkningsgrad er 85,1 % ved 0,86 m3/s. Eksisterende design har maksimal trykkøkning på 1,33 ved 0,76 m3/s og maksimal virkningsgrad på 82,7 % ved 0,86 m3/s. Simuleringene viste stor grad av seperasjon i diffusoren med det store spiralhuset, og kompressorytelsen vil økes ytterligere ved forbedring av diffusoren. Innsnevring av diffusor har redusert seperasjon i diffusoren, og dette har økt ytelsen. I tillegg har et ikke-avrundet diffusorutløp redusert virvelstrømning i spiralhuset betydelig.Partikkelsimuleringene har vist at partiklene legger seg på høytrykksiden av impelleren og blir kastet tangentielt mot spiralhuset. Partikkelinjeksjon reduserte strømningsvinkelen til gassen, α, i sentrum og mot shroud i diffusoren, mens vinkelen økte ved hub. Reduksjon i strømningsvinkel forbedret trykkøkningen til kompressoren med 4 %.

Formålet med masteroppgaven har vært å studere opp og utladninger knyttet til ulike HVDC kabel isolasjonsmaterialer. Eksperimentelle forsøk ble gjennomført for å beskrive disse fenomene for en 450 kV HVDC massekabel, og en 12 kV PEX kabel.Litteraturstudier tilsier at den dominerende polarisasjonsmekanismen for en massekabel er grenseflatepolarisasjon. Ledningsevnen til denne kabeltypen kan estimeres ved å bruke:σ = σ0e(αT+βE)Polarisasjonsstrømmen kan beskrives med:i(t) = Ke-t/τ + U/R0 Denne formelen kan brukes til å estimere relaksjonstiden, , til polarisasjonsmekanismene i massekabelen.Litteraturstudier for PEX kabelen viser at dipol polarisasjon, pga grenseflatepolarisasjon mellom to flater, er den dominerende polarisasjonsmekanismen. Det vil i denne rapporten bli brukt samme forenklinger for begge kablene for å finne ledningsevne og relaksjonstid.For å kunne gjennomføre de nødvendige forsøkene, ble det laget en datastyrt målekrets. Denne bestod i all enkelhet av en spenningskilde, en bryter, et måleinstrument og testobjektet. Kretsen ble styrt, og resultatene logget, av et dataprogram laget i LabVIEW.Resultatene fra forsøkene viste at polarisasjonsstrømmen i massekabelen kunne uttrykke som:i(t) = K1e-t/τ1 + K2e-t/τ2 + U/R0 Hvor er relaksjonstiden til oljen(10,388-56,163 s), mens (53,345-1114,1 s) er relaksjonstiden til papiret. Det siste leddet representerer DC-strømmen i isolasjonen.Polarisasjonsstrømmen til PEX: i(t) = Ke-t/τ + U/R0Hvor er relaksjonstiden i PEX(59,406-3,103 s). Ledningsevnen og relaksjontiden ble estimert som funksjon av elektrisk felt og temperatur, og ut fra disse resultatene kan man trekke følgende konklusjoner:•Ledningsevnen er størst i massekabelen (8*10-16-6,2*10-14 Ω-1m-1 mot 7,2*10-18-3,2*10-16 Ω-1m-1 for PEX)•Ledningsevnen er temperaturavhengig for begge kablene.•Ledningsevnen er kun felt avhengig ved de høyeste temperaturene, for PEX kabelen. •Relaksjonstiden reduseres med økende spenning og temperatur, for massekabelen.•Relaksjonstiden PEX lavere enn for massekabel.

The principles of the object oriented slug tracking schemes at EPT (Department of Energy and Process Engineering, NTNU) have been developed and discussed in some detail.Simple bench-mark testing revealed that the LASSI code suffers form a pipe inclination-dependant lack of mass conservation, the cause of which is presently unidentified.Comparing simplified and non-simplified SLUGGIT simulations with experimental data published by Taitel <i>et al.</i> mostly indicate a reasonable correspondence, though the precision is somewhat imprecise. In particular, obtaining stable riser flow (free of significant pressure oscillations) at low liquid flow rates was not managed without excessive gas rates.This is possibly a consequence of the method's intrinsic slug flow approximation to dispersed regimes, but further investigation showed that the methods stability response altered with recent code versions in which alterations to management procedures was identified as the main differences, indicating that the SLUGGIT method's riser stability properties are quite sensitive to intuition-based section management routines. Further developing the models to better accommodate vertical flow regimes is advised.Supplementary testing was afforded through the development of a steady-state unit-cell type model for phase fractions in the riser. Excellent accordance with simulation data was found, confirming that the SLUGGIT model is capable of reproducing stable, expanding bubble flow. Coarse resolution served to disturb this process as bubbles becomes longer and are affected by riser entrance and exit effects. It was also found that pressure oscillations caused by such entrance and exit effects display the typical characteristics of terrain slugging and may be mistaken as such.With basis in the P50 Girassol pipeline, a systematic investigation into operational instability phenomena has been carried out using the available boundary conditions. Instabilities rooted in gas accumulation in jumpers, possibly also influenced by the U-bend, were found when studying the fixed pressure open inlet condition. The character of these instabilities were of a frequency and intermittency uncongenial to the field data. Most instability phenomena captured in these simulations were sensitive to changes in geometry, inlet condition and management parameters. Severe slugging was initially found to dominate the flow picture with a fixed flow closed inlet condition. Also this type of operational instability had too high a frequency to be a match with the field data. Nor does the well-know `shark fin' pressure profile of the terrain slugging liquid build-up and blow-out precesses match the sinusoidal character of the field data.It was recently found that the supplied field data needed adjustment for phase transition at the inlet state, amounting to a considerable reduction in gas flow. This produced predictions of more stable production compatible with those generated by external participant, though significant pressure fluctuations were still observed. These fluctuations were found to originate from slugging in the U-bend and entrance effects as large Taylor bubbles formed through coalescence and penetrated into the riser.This latter cause is believed to be a feature of the limited, non-dispersed flow objects available in the EPT models.A production index type boundary condition was implemented to better accommodate the well production response. Even so, the conditions under which the Girassol field instability data was recorded could not be recreated satisfactorily without gas lift and PVT support implemented. Simulations including the productivity index inlet indicated, for the most part, that without the presence of a gas lift system, the pipeline is likely to come to a complete stand-still; unless the liquid in riser and well are strongly aerated at all times, the well head will not be sufficient to overcome the total system liquid column weight.

AbstractIn order to utilize the fossil resources on the Norwegian continental shelf, technology and expertise have proven to be of great importance and hence, essential for further exploration and development of new resources. A key element in this matter is the subsea wet gas compression technology which enables the transport of well stream directly to a land based treatment system, or more remote processing facilities offshore. Compression of gas at the seabed is a significant technology advance no one has previously made. The technology of subsea gas compression is one of the most important measures to deliver increased volumes from existing gas fields as well as developing resources in more remote and vulnerable areas.Due to the need of expertise and development of subsea installations, in order to meet the demand for fossil fuels and be competitive in a constantly increasing market, the Norwegian University of Science and Technology (NTNU) has built an experimental rig to test a wet gas compressor. The rig is unique and important to analyze the basic mechanisms and occurrence of instabilities related to wet gas compression. Both the literature review and the experimental work presented here are performed in order to visualize and document instabilities related to the phenomena surge and stall. Experimental data in this master thesis are obtained from a one- stage wet gas centrifugal compressor with an axial direct inlet. The stage involves a shrouded impeller, a vaneless diffuser and a volute. The compressor is a part of an open loop facility that is located at NTNU in Trondheim. The test rig is designed to operate with different amounts of liquid in the gas with gas volume fractions (GVF) and gas mass fractions (GMF) down to correspondingly 0.95 and 0.5. Applications in LabView were made and designed to analyze the raw data from the pressure sensors and pitot tubes in order to post-process and represent the data in a graphical manner. Log files from a total of seven scientific experiments with dry- and wet gas were documented and analyzed to identify the impeller outlet angle and achieving a more precise identification of wet gas surge initiation and instability precursor. The steady state flow angle experiments revealed a stringent increase in flow angle with decreasing volume flow, for both the dry gas test of 10000 and 9000 rpm, with maximum corresponding flow angles of 81.5 and 86 degrees. A sudden rise in flow angle gradient was found to occur at a volume flow of 0.95 m3/s and 0.8 m3/s for 10000 rpm and 9000 rpm, respectively, due to the volute causing a shift change from deceleration to acceleration performance, at the respective volume flows. Flow angle measurements of dry gas were further validated and compared with Matlab and CFD simulation revealing coincident trends. The performed wet gas tests were associated with a greater uncertainty than dry gas, due to the influence of liquid. However, the wet gas curves showed distinct trends with lower discharge angles across the spectrum compared to the case for dry gas measurements.The transient surge identification test was conducted on 7500 rpm with alternating GMF in the range from 0.6 to 0.42. The pressure characteristic revealed the first sign of intermittent behavior at a volume flow of 0.26 m3/s prevailing sudden stringent static pressure fluctuations. The corresponding frequency spectrum for dynamic pressure sensors shows that the critical disturbance occurs, and is enhanced at low frequencies causing the initiation of surge at a volume flow of 0.27 m3/s. A pitot tube set-up for identification of surge onset was evaluated and compared to the measurements conducted by a static pressure-, a differential pressure- and a high responsive dynamic pressure sensor. The detection tube indicated a possible precursor to surge by prevailing change and high fluctuations in the stagnation pressure.Observation through the impeller inlet showed that an annular backflow ring was formed with decreasing volume flow. The first observation of the ring shape was done for a volume flow of 0.3 m3/s, followed by larger developments and a chaotic flow path with complete backflow for volume flow lower than 0.25 m3/s.