High concentrations of sediments is a serious problem for hydropower stations in the Himalayas and the Andes Mountains. For run-of-river power plants sediment causes heavy erosion even with settling basins. This leads to reduced operating hours and high maintenance cost. In addition, the original design experienced problem with heavy cavitation.The objective of this master thesis is to carry out new hydraulic design of the runner and guide vanes of the existing Francis turbines in La Higuera Power Plant with reduced velocity components. To achieve this the cause of the heavy cavitation, which made the turbine fail, has to be established.Results from numerical simulations indicates a low pressure zone causing heavy leading edge cavitation is the reason for the turbine failure. The off-design operation has made the cavitation even worse.To carry out a new design, the in-house design software Khoj was used. Some new parameters, like blade leaning, were included in the program. Blade leaning is an important tool for pressure balancing the runner blade. Further, a parameter study was carried out to investigate the effect of blade leaning, blade angle distribution and blade length. The numerical simulation indicates proper pressure balancing could have avoided the cavitation problems and a new design should have an X-blade shape. Because the power plant is already built, the number of variables is limited. The rotational speed, inlet and outlet diameter remained constant. This made it impossible to significantly reduce the relative velocities. Therefore, coating of all wet surfaces is proposed to reduce the effect of erosion.The main objective for this thesis has been to identify the cause of the turbine failure and develop a new design to fit in the existing power plant. Complete 3D-drawings of the design, including runner and guide vanes, has not been made due to lack of time.

The goal with this master thesis was to establish Hill diagrams and improve a Kaplan turbine intended for use in Afghanistan. The turbine efficiency has been tested in setting 1 and 2. Turbine efficiency in setting 3 and 4 could not be tested because the runner blades interfere with the housing making it impossible to rotate the turbine. The efficiency was tested with an effective pressure head ranging from 2 to 8 meters. Best efficiency point was not reached because of limitations in the test rig making it impossible to reach a lower effective head. The best efficiencies tested in the two different settings are presented in the table below together with the uncertainty in the actual test point. All tests are done according to the IEC standard for model testing of hydraulic turbines. The computational fluid dynamics (CFD) simulations done on the inlet bend indicates that the bend should be rounded and flow controllers should be extended over the entire bend. This should be considered to get a more even velocity distribution at the inlet of the guide vane. An alternative placement of the lower bearing was designed but is discarded because of the disadvantages the modification leads to. High wear due to sand erosion on the seals causing high maintenance and costly stops makes the solution not optimal for use in water with high sand content. The runner blade design is checked against the design procedure presented by Professor Hermod Brekke in Pumper og Turbiner and found to be satisfying. It is concluded that time should rather be spent on optimizing the inlet of the turbine. Fluctuations in the measurements make it necessary to change the measuring equipment or search for error in the existing equipment before further tests can be carried out. In order to be able to test in setting 3 and 4 the runner needs to be placed while the blades are fixed in setting 4.

The aim with this thesis was to investigate moulds for composite production. A set of requirements needs to be established for such moulds. The requirements will then be used to find the right material and production method concerning the desired result. Different production methods and materials that can be used for moulds are presented.Two different master moulds were made using two different types of materials, ytong and aluminium. On each of these master moulds, has two types of carbon fibre prepreg been used to make moulds. After cure has the dimensional accuracy of these moulds been measured and compared with the CAD models. The accuracy has been one of KONGSBERG's main requirements. One of the two shapes of moulds was used to make parts in. These two parts have been measured after cure.Abaqus has been used to carry out an FE-analysis with simulations of spring due to cooling after cure.The measurements and the analysis shows the spring-in, but with some difference in the results.The two types of mould materials indicates good results for the shape and size they were tested on. They fulfill many of their requirements.

Many offshore installations are dependent on power generated by gas turbines and a critical issue is that these experience performance deterioration over time. Performance deterioration causes reduced plant efficiency and power output as well as increased environmental emissions. It is therefore of highest importance to detect and control recoverable losses in order to reduce their effect. This thesis project was therefore initiated to evaluate parameters for detecting performance deterioration in addition to document different aspects of gas turbine degradation and performance recovery. Compressor fouling is the largest contributor to performance deterioration. Investigating fouling was therefore the main focus of this study.In the present study the deterioration rates of four different gas turbines were evaluated. When choosing gas turbines it was emphasised to select gas turbines operating under equal conditions but with different washing procedures. In addition to offline washing two of the gas turbines had daily online washing routines and one of the gas turbines run idle wash every 1000 hour between each offline wash. Data was extracted from the monitoring software, TurboWatch, and loaded into Excel files. MATLAB scripts were created to handle the large amount of data and visualize performance trends. Series of two parameters were plotted against each other and the graphs were evaluated.The evaluation showed that an overall trend was that the gas turbine that had been running with online washing continuously over a long period of time had higher performance than the reference engine. For the second gas turbine a daily online washing procedure has recently started. The advantage with the evaluation of this gas turbine was that a good reference engine was available. The two engines were operating under quite similar conditions at the same location in addition to having equal filter systems. Some deterioration trends were possible to detect. For the first period both engines seemed to have quite equal deterioration trends. During the second period no clear trends were seen in corrected CDP and corrected EGT when evaluated for constant GG speed. The compressor efficiency had decreasing trends for both engines during the second period as well, but the compressor efficiency for machine 1 was overall higher during the period with online washing than the previous period. The borescope pictures taken after the first period with online washing showed good visual results. However, it is too premature to make a final decision regarding the exact performance gain of online washing. At the time the study was performed the engine had only been running online washing for one operating interval, and more investigation over longer time is recommended. For the engine running with idle wash it was not possible to conclude on the basis of the collected data. No clear deterioration trends were detected and investigations over longer time and several operating intervals are recommended. It is also important to be aware of the fact that the performance gain of idle wash needs to be much higher than for online washing in order for idle wash to be economically profitable. There are several uncertainties related to performance trends. These include inaccuracy in instrumentation, monitoring software, calibration etc. Due to the fact that all the gas turbines evaluated in this study only have standard instrumentation it caused additional uncertainty in the performance trends. One suggestion for further study is to initiate a test instrumented gas turbine into operation with sensors for measuring inlet pressure depression

Målet for prosjektet var å finne virkningsgradkurve for en turbin ved hjelp av Winter-Kennedy målinger og CFD-analyser. Det ble derfor laget en CAD-modell av gjennomstrømningsvolumet i spiraltromma på NTNUs vannkraftlaboratorium basert på en eksakt modell av spiraltromma. På denne modellen ble det så gjort CFD-analyser med et visst antall volumstrømmer for å finne kalibreringskonstantene til Winter-Kennedy målingene.I laboratoriet ble så Francis-turbinen kjørt i et passende område rundt det optimale driftspunkt, mens det ble utført absolutte volumstrømsmålinger og Winter-Kennedy-målinger på turbinen. Trykkmålingene ble utført ved både automatisk logging med differensialtrykktransducer og optisk avlesning av vannsøylemanometerVed hjelp av kalibreringen fra CFD-resultatene ble det utarbeidet virkningsgradskurver og Hill-diagram for både de relative og de absolutte målingene.Differensialtrykk simulert med CFD stemte godt overens med, og var i gjennomsnitt 0,3 % høyere enn, målingene fra vannsøylemanometeret. Målingene med transduceren ser ut til å være heftet med systematiske feil, og ligger gjennomsnittlig 40 Pa over vannsøylemanometermålingene. Det lot seg gjøre å opprette virkningsgradsdiagram med relative målinger. Formen på Hill-diagrammet basert på Winter-Kennedy-målingene med vannsøylemanometer stemte godt overens med de absolutte, mens målingene med trykktransducer ble forstyrret av systematiske måleavvik. Beste virkningsgrad målt med absolutte målinger var omtrent 0,2 % lavere enn hva som tidligere er blitt målt på samme turbin. Virkningsgraden fra relative målinger kalibrert med CFD var ca. 0,3 % lavere enn de absolutte målingene. Kalibrering med CFD ga totalt sett kun en liten økning (0,16 %) i forventet avvik av volumstrømmåling med Winter-Kennedy-metoden.

Boiling two-phase flow is found in many industrial applications such as boiling water reactors, two-phase flow heat exchangers and refrigeration systems. The physics of two-phase gas-liquid flow may lead to undesirable system instabilities, and in the literature density wave oscillations (DWO) is reported to be the most commonly observed instability phenomenon. However, the literature alsoprovides two opposing views on what the fundamental mechanism of DWO is. The so-called classical description of DWO focuses on the variation in mixture density as the governing mechanism, and the oscillation period will consequently be about one to two times the channel residence time. The findings presented in citet{Rizwan-Uddin1994} show that it is the variation in mixture velocity that hasthe dominating effect, and the oscillation period was reported to be closer to four times the channel residence time. citet{Ambrosini2000} united the two opposing views by stating that the governing mechanismdepends on the level of system subcooling. The classical description of DWO is based on a lower level of subcooling, while citet{Rizwan-Uddin1994} considered higher subcooling. Here, the fundamental mechanisms of DWO and the effect of system subcooling is investigated further by performing a numerical analysis using a one dimensional homogenous equilibrium flow model. The modeled system consists of a horizontal uniformlyheated boiling channel with an inlet- and exit restriction. The system is exposed to constant externally imposed pressure drop. The effect of system subcooling is investigated by comparing the self-sustained periodicoscillations which make out the modeled stability threshold. The flow model is validated by observing the above mentioned effects of subcooling on DWO. Further, it is found that the change from a density dominated exit restriction towards a velocity dominated exit restriction is a smooth transition for increased subcooling. The amplitude of the variations in exit mixture velocity increases continuously with subcooling, anddue to the squared relationship between the exit restriction pressure drop and the exit mixture velocity, velocity becomes the governing mechanism at high subcooling.The modeled stability threshold approaches a straight line at high subcooling. This line represents operating conditions which have the same mean boiling boundary location. However, the amplitude of the variations about this mean limit grows exponentially at high subcooling. The oscillation period of the observed DWO grows continuously with higher subcooling, and the period increases exponentially at high subcooling. In contrast, the mean boiling channel residence time approaches an upper mean limit at high subcooling. It is postulated that it is the transition towards a more mixture velocity dominated system that causes the oscillation period to evolve as it does with respect to the level of subcooling.

Even though venture capital trade sale exits are the most common and successful exit vehicle, historically most academic attention has been given to IPO exits. This thesis takes the first steps towards opening the black box that is trade sale exits. The thesis is paper-based, and the main academic contributions belong to the four papers appended. This document opens with an introduction to the field of study as well as overall reflections in order to offer the reader a contextual background. Paper one is based on a literature review, while paper two through four are based on an inductive multiple-case study covering 19 venture capital trade sale exits from Norway and the U.S. Paper one conducts an extensive literature review of venture capital exits in general, leading up to the development of a model denoted “The Road to Venture Capital Exit”. This model identifies the variables that influence the exit process in the different phases, and describes how these variables influence the exit process.Paper two explores the relation between pre-planned exit strategies and value-adding, and suggests the existence of two different venture capitalist mindsets; the Tailor and the Architect. The Tailor uses exit possibilities as an addition to traditional deal evaluation criteria, has a pre-planned exit strategy, and adds value with exit in mind. The Architect does not use exit possibilities as an evaluation criteria, and adds value in a more general manner.Paper three examines the relationship between the venture capitalist and the entrepreneur during the trade sale exit process, finding that this relationship is characterized more by consensus and cooperation than by conflict and defection. Further, it is found that four factors influence the relationship during the exit process, and are determining for the conflict level. These factors are: pre-investment alignment, strategic hurdles and personal motives faced by the entrepreneur, the reputation and connectedness of the venture capitalist, and the probability for entrepreneurial recycling.Paper four explores the role of financial advisors in trade sale exits, by looking closer at why advisors are utilized, as well as by examining the factors determining the choice of a specific advisor. It is found that advisors are considered especially useful in bargaining situations, through playing the role of bad cops, and also by letting venture capitalists and entrepreneurs focus on their primary tasks. With regards to selection criteria, venture capitalists emphasize industry experience, prior relations and the size of the advisory firm. Finally, the findings are integrated in a framework explaining the role of financial advisors in venture capital trade sale exits.

Increased knowledge of the degassing process in separation of gas from oil is important in connection with development of subsea separation and boosting units for heavy oil fields. The focus in the thesis is on theory and equipment design for two-phase separation of oil and gas. A review of gravitational separators and compact separation technology with a focus on subsea installations is given first. An extensive literature review related to theory governing the degassing process is further presented. The effectiveness of the degassing process depends on the gas’ ability to migrate out of the oil. Bubble dynamics theory, especially correlations for calculation of a bubbles velocity in a liquid is therefore examined. Bubble size, fluid properties, especially liquid viscosity, and gas volume fraction in the liquid is decisive factors for the bubble velocity. A comparison of several correlations obtained in various literature is made to determine the best available for modeling degassing. Most of the correlations have a limited range of validity in terms of bubble size and Reynolds number. It is verified that they are highly inaccurate outside this range. A correlation developed to be valid for a large range of bubble sizes seems to predict bubble velocities reasonably well. Because of its large range of validity, this is chosen to be used in the development of a separator model. Some experimental work is performed on two liquids with different viscosity. It is verified that separation of gas in viscous liquids requires significantly more retention time for the smallest bubbles reach the liquid surface. Occasional deviations from the examined theory are observed, especially for the more viscous liquid. Based the chosen correlation for bubble velocity a simplified model for horizontal and vertical gravity separators is developed. Separator size, fluid properties, flow rate and distribution of bubbles are input parameters. The model calculates how much of the initial gas volume fraction that remains in the liquid after separation. Consequence of high liquid viscosity and distribution of bubble size and bubble distribution in the liquid are evaluated by use of the model. When the oil becomes very viscous is it important that separator and internals are designed to optimize the conditions for degassing. This implies among others an inlet device which provides an ability to control the bubble distribution and keep the size of bubbles as large as possible. Methods are suggested for increased effectiveness in degassing of heavy oils, by reducing viscosity, increase the coalescence rate and affecting the flow pattern. Separation of other phases and undesirable components is also important and may make it difficult to optimize the design for the degassing process. However, a separator should be efficient in all respects, making knowledge of the degassing process anyhow important. The thesis gives an overview of important parameters in the degassing process. Much work still remains to develop correlations and models which can give a more exact description of real systems. Continuous development in separator components and not at least compact separation technology is important to effectively be able to produce heavy oil, especially in terms of subsea installations.

High cost and a short lifetime are the two main reasons why the PEM fuel cell is yet to be commercialized. The bipolar plate in a PEM fuel cell is alone responsible for about 45% of the cost and 85% of the total weight of a single cell. stainless steel has been suggested as material for the bipolar plate because of its good mechanical properties, easy manufacturing and relatively low price. A problem with stainless steel is the Chromium oxide film formed on the surface which causes a high contact resistance. In order to prevent this oxide formation, the stainless steel can be coated. Gold has been suggested as coating, but it is too expensive to be considered a viable alternative. The objective of this thesis was to investigate stainless steel as bipolar plate material for PEM fuel cells. In cooperation with SINTEF polarization tests were done on stainless steel bipolar plates with and without two different coatings; gold and Coating A. The tests were performed in H2SO4 electrolytes with different molarities and additives. Before and after each polarization test Interfacial Contact Resistance (ICR) measurements where done to see how the oxide layer on the stainless steel surface changed during polarization. Gold coated stainless steel was chosen as standard for both the polarization tests and the ICR measurements because of its corrosion resistance.The results obtained from both polarization tests and corresponding ICR measurements showed that the reproducibility was not as good as one had hoped, but this can be explained by low absolute values of the current densities. Gold coated steel proved to be a good standard for the ICR measurements, but due to pitting corrosion the corresponding polarization results were not as promising. The pH in an operating fuel cell was found to be approximately 3.5, and the tests done at different molarities showed that at a lower pH the oxide layer seemed to be thinner and the stainless steel surface thus became more exposed to corrosion. Additions of fluoride and chloride in the amounts expected in an operating fuel cell did not seem to cause any changes for neither the polarization results nor the contact resistance measurements. Stainless steel plates with Coating A showed very small changes in contact resistance after being put trough the polarization tests, but at low potentials the current densities in the polarization test were very high, indicating that components in the coating either catalyzed hydrogen evolution or were reduced themselves. Out of all the ICR measurements, gold coated stainless steel was the only plate satisfying US department Of Energy’s (DOE) resistance requirement for bipolar plates of less than 10 mΩ cm2. The stainless steel plates with Coating A were close to DOE’s requirements for both corrosion current and contact resistance. Non-coated stainless steel was ruled out as bipolar plate material due to high contact resistance measurements.

A study of the influence of artificial ageing temperature on the precipitation behaviour in three distinct direct chill casted and extruded Al-Mg-Si alloys has been carried out. The total amount of alloying elements is approximately the same in these alloys, but the difference is the ratio between these elements. The master thesis is a continuation of the work reported in Characterization of precipitates at maximum hardness in Al-Mg-Si alloys which was written in connection to the course TMT4500 Materials Technology, Specialization Project. The primary objective of this work was to identify the value of maximum hardness, and at what time it is obtained for these alloys after they have been artificially aged, one set at 200 °C and another at 250 °C, i.e. six cases in total. The aim in the master thesis has been to investigate which type and relative amount of needle shaped precipitates that are present, and what size, number density and volume fraction that is responsible for these conditions by using transmission electron microscopy (TEM). In addition, all three alloys have been shown to obtain a local hardness maximum at overaged conditions in the 200 °C case. These conditions have also been analysed by comparing with an overaged condition for KK5 for an ageing time shorter than the one were the local maximum appears. Therefore, ten different conditions have been investigated in total.One sample has been selected from each case based on the hardness curves in the project work, and prepared for analysis in two different TEM instruments. A number of general trends between alloy composition, heat treatment, and the resulting microstructure and hardness that already have been reported, have been verified during the master thesis. The maximum hardness conditions after artificial ageing at 200 °C have been found to be quite different for KK5, KK6 and KK7 in terms of type and relative amount of precipitates, and precipitate size and number density. Artificial ageing at 250 °C has been observed to give very similar values of maximum hardness for the three alloys primarily due to the size and number density of the precipitates. The local maximum hardness peaks observed at overaged conditions after artificial ageing at 200 °C have been seen to be purely due to precipitate size and number density, but the reason for their appearance has not been clarified. The observed differences between the three alloys in each condition and the differences between the conditions themselves for each alloy have been seen to be reflected in both type and relative amount of precipitates, and precipitate size and number density.