Simulations on liquid loads and flow rates which the Taitel-Dukler model predicts to have multiple solutions have been performed with ANSYS Fluent and LedaFlow. Both steady state and transient results in one, two and three dimensional flows are reported in this work. The hypothesis that the holdup of a pipe operated in the multiple solution region will be determined by the downstream holdup is investigated. Some results indicate that the hypothesized interface level gradients effects are correct.The Fluent steady state simulations had mass imbalance issues in addition to being both grid and geometry dependent, but produced results consistent with the independent Fluent transient simulations. The one dimension LedaFlow solver illustrated the effect shear stress modeling have on the multivalued solution region. The solver chose the intermediate solution for some flow rates, which by physical arguments can be excluded. The novel solver LedaFlow Q3D produced transient results displaying the wavy surface of the high holdup solutions. The results from the different models are deviating, but it is hard to predict which results are most the accurate since no comparison with experimental results have been conducted.

Aluminium is often treated as a homogeneous material. However, when investigated on a microscopic scale, a granular structure is observed. The mechanical properties of the constituents, together with the distribution of stresses and strains, determines the fracture toughness of the material.The objective of this master thesis was to investigate strain localization and fracture in aluminium on a microscopic scale. Relevant literature regarding fracture mechanisms was studied in order to determine which parameters influence the fracture toughness of aluminium. The distribution of effective plastic strain together with the stress triaxiality ratio is thought to give a prediction of the initiation of ductile fracture.A study of the microstructure of aluminium has been carried out. The aim of this study was to gain understanding of the mechanisms leading to the formation of a precipitate free zone (PFZ) near the grain boundary. Also the relation between the mechanical properties of the PFZ and the grain interior was studied. The literature study uncovered that the PFZ is expected to have a low yield stress and a high work hardening rate compared to the grain interior. A simplified numerical model representing a heterogeneous microstructure was developed. The aim of this model was to investigate the effect of certain parameters on the distribution of stresses and strains. The yield stress and work hardening rate of the PFZ as well as the global stress triaxiality, were all variables in a parameter study. A clear tendency of strain concentration in the PFZ was observed, which is consistent with the literature. For low global stress triaxiality, the PFZ oriented at an angle with respect to the external load was found to be the most likely location for initiation of intergranular fracture. Increasing the yield stress and work hardening rate of the PFZ was found to favor transgranular fracture.Due to long computational time, avoiding crystal plasticity analyses is of interest. Whether a material model using isotropic plasticity is able to give the same results as the crystal plasticity model has been investigated. The difference between the average effective plastic strain in the grain interior and in the PFZ was found to be lower using crystal plasticity than when using isotropic plasticity. Using crystal plasticity, the maximum effective plastic strain was found to be dependent of the crystallographic orientations of the grains. However, a more extensive study is required before conclusions regarding the consistency of the results are drawn.

The main goal for this thesis has been to perform fatigue life predictions on large components.Dierent methods were to be chosen and reviwed critically. Experimental datafor girth welded pipes was assessed by means of a version of BS7910 which were modeledfrom scratch. This version was veried with results from CrackWise, and used to predictthe fatigue life for loade cases matching the selected experimental data. The fatigue assessmenttool P-FAT was used to predict the fatigue life for the same experimental data,and the results were compared. Except for some deviations recorded for embedded cracks,a generally good agreement was found between the two tools.Both the modeled BS7910 and P-FAT predicted conservative but accurate fatigue livesfor the experimental data that had signicant defects. They predicted non conservativeresults for specimens that did not have signicant defects, when the initial crack depthwas set to 0.1 mm. When the initial crack depth was set to 0.5 mm the modeled versionpredicted fatigue lives in agreement with the experimental results.Fatigue life predictions were also performed by assistance of S-N curves provided by DNVRP-C203.The results from these predictions were in agreement with the experimentaldata, except for four specimens. These four specimens had signicant aws, which reducedthe fatigue life signicantly.A review of a two-phase fatigue assessment model was made. This model uses a strainedbased approach to assess the fatigue crack initiation phase, and the fracture mechanicapproach suggested in the BS7910 to assess fatigue crack growth. This method haveshown promising results for fatigue assessment of llet welds in the literature, but themodel needs further investigation and calibration to be used to predict fatigue life ofgirth welded structures. A specic area to investigate is the proposed transition depth of0.1 mm. This depth is dubious based on the results

This paper is a master thesis written at NTNU for the Co-Patch project. The Co-Patch project is an EU-funded consortium of 15 organizations from 8 different countries, developing a standard for composite patch repair of steel structures in fire hazard areas. The standard includes methods for dimensioning against delamination. This thesis looks at the fatigue properties in delamination of patches from their substrates. By testing Double Cantilever Beam and End-Notched Flexure specimens in fatigue loading, G-N curves were made for Mode I and Mode II fatigue fracture. This gives an indication of the lifetime of a patch given a specific cyclic load condition and a pre-existing crack. The longest cycle life recorded was 4.35E5 cycles at 104 J/m2 for Mode I and 1.23E5 cycles at 122 J/m2 for Mode II.Furthermore, a relation for crack propagation rate and energy release rate in Mode I was found for low cycle life estimation. From this relation, the crack front position may be estimated for a given set of cycles through calculations using Paris’ law. Based on the quasi-static data of a previous report, and the fatigue data found in this thesis, a numerical simulation procedure for crack propagation was proposed. Using direct cyclic fatigue analysis and Virtual Crack Closure Technique based on linear elastic fracture modelling, the crack propagation may be estimated for patches exposed to combined conditions, such as plane strain/plane stress and different fracture modes, as well as on advanced geometries. The procedure was validated as a viable simulation, but more work needs to be done on the model for accurate estimates. 

An experimental study of Carbon Nanotube (CNT) growth has been performed by using radio frequency plasma enhanced chemical vapour deposition with methane (CH4) as the hydrocarbon source. The experimental results have been compared towards earlier experiments and theories that exist. A study of the effect by changing parameters during thermal- and plasma- pretreatment has been conducted which have led to successful yield of vertically aligned CNTs forests. Different growth conditions have been conducted in order to see the influence of the following: Methane (CH4) flow, plasma power, growth time, temperature, methane (CH4)/ammonia (NH3) mixtures during growth, no barrier layer, thermal- versus plasma-pretreatment and oxidizing pretreatment. The conclusion from this experiment is that oxidizing pretreatment seems yields the tallest vertically aligned CNTs with the narrowest diameter.

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Sediment erosion in Francis turbines is a big problem in hydropower plants in and around the Himalayas. The sediment composition in the rivers contains high levels of the hard mineral quarts. When the sediments enter the turbine they cause erosive damage to exposed parts such as covers, guide vanes and runner. The sediment concentration is at its highest during the monsoon period. During this period some turbines are stopped when the sediment consentration reaches certain levels to reduce the damage. Jhimruk power plant in the mid-western part of Nepal is a good example of how the sediment erosion affects the operation of a power plant. During the monsoon period the turbines can be eroded to an almost unrepairable state. The turbines have to go through substantial annually maintenance. A result of this is reduced power output and high maintenance costs. It is therefore of interest to design a new Francis turbine that can better withstand the sediment erosion. A cooperation project between Kathmandu University and The Norwegian University of Science and Technology was started as a part of the RenewableNepal project which aims to develop and start manufacturing of erosion resistant Francis turbines.A parameter study of different blade designs have been performed to find a more erosion resistant design. In this thesis FSI analyses have been performed on three different designs to verify their structural integrity. The designs transfers the hydraulic energy from the water to the blade in different sections. The results showed a stress distribution which coincided with the energy transfer along the blade. The reference design was analyzed with two different blade thickness. For all the designs the stress was relatively low compared to the criteria for hydraulic turbines.

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.

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.