In this study, liquid-vapor vertical upflow has been research with the intent of finding an improved method of modelling the interphase friction in two-phase vertical flow in nuclear thermal-hydraulic codes. An improved method of modelling interphase friction should allow for better prediction of pressure gradient, void fraction and the phasic velocities. Data has been acquired from several available published resources and analyzed to determine the interphase friction using a force balance between the liquid and vapor phases. Using the Buckingham Pi Theorem, a dimensionless interphase friction force was tested and refined before being compared against seven other dimensionless parameters. Three correlations have been developed that establish a dimensionless interphase friction force as a function of the Weber number, the Froude number and the mixture Froude number. Statistical analysis of the three correlations shows that the mixture Froude number correlation should be the most accurate correlation. The correlations have a weakness that makes them ineffective mostly for bubbly flow and some slug flow scenarios, while they should perform significantly better for annular flow cases. Comparisons have been made against the interphase friction calculations published in the manuals of RELAP5/MOD2, RELAP5/MOD3.3, RELAP5-3D and TRACE. The findings have generally shown that the equations in the manuals provide very inaccurate approximations of the interphase friction compared to the interphase friction that was found via force balance. When analyzing the source code of RELAP5/MOD3.3, several differences were noticed between the source code and manual, which have been discussed. Calculations with the source code equations reveal that the source code provides a modestly improved prediction of the interphase friction force, but still has significant errors. Despite the fact that the manual and source code equations indicate that RELAP5/MOD3.3 should perform poorly in modelling interphase friction, actual RELAP5/MOD3.3 model runs perform very well in predicting pressure gradient, void fraction, the liquid and vapor velocities and the interphase friction force. This is largely due to RELAP5/MOD3.3 being able to adjust parameters to converge to a solution that fits within the boundary conditions established in the input file. Modifications to the RELAP5/MOD3.3 code were first made with the three correlations developed using dimensionless parameters, and were tested with data points that the RELAP5/MOD3.3 flow regime map had predicted would be annular flow. While the mixture Froude number correlation has been analyzed to be the most statistically accurate of the three correlations, it was found that the Weber number correlation performed best when implemented into RELAP5/MOD3.3. In a parametric study of the Weber number correlation, it performed optimally at 150% of the original correlation, improving upon the original RELAP model in almost every metric examined. Additional investigations were performed with individual annular flow correlations that model specific physical parameters. Results with the annular flow physical models were inconclusive as no particular model provided a significant improvement over the original RELAP5/MOD3.3 model, and there was no clear indication that combining the models would provide significant improvement. / Ph. D.

Steady and unsteady flow over a generic Suboff submarine model is studied. The skin-friction magnitudes are measured by using hot-film sensors each connected to a constant temperature anemometer. The local minima in the skin-friction magnitudes are used to obtain the separation locations. Steady static pressure measurements on the model surface are performed at 10° and 20° angles of attack. Steady and unsteady results are presented for two model configurations: barebody and sail-on-side case. The dynamic plunge-pitch-roll model mount (DyPPiR) is used to simulate the pitchup maneuvers. The pitchup maneuver is a linear ramp from 1° to 27° in 0.33 seconds. All the tests are conducted at ReL=5,500,000 with a nominal wind tunnel speed of 42.7±1 m/s. Steady results show that the flow structure on the leeward side of the barebody can be characterized by the crossflow separation. In the sail-on-side case, the separation pattern of the non-sail region follow the barebody separation trend closely. The flow on the sail side is strongly affected by the presence of the sail and the separation pattern is different from the crossflow separation. The flow in the vicinity of the sail-body junction is dominated by the horseshoe type separation. Unsteady results of the barebody and the non-sail region of the sail-on-side case show significant time lags between unsteady and steady crossflow separation locations. These effects produce the difference in separation topology between the unsteady and steady flowfields. A first-order time lag model approximates the unsteady separation locations reasonably well and time lags are obtained by fitting the model equation with the experimental data. The unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag and the unsteady separation structure is different from the unsteady crossflow separation topology observed for the barebody and the non-sail region of the sail-on-side case. / Master of Science

A steel frame structure of a few storey building is considered in European project FRAMEUP. Each column of the building is constructed from steel profiles connected by column-to-column connection, called column splice. In FRAMEUP project new type of column splice connection is designed to facilitate assembly. This connection consists of a plate, called finger plate with characteristic shape of holes, called long open slotted holes. A column splice with long open holes is a type of friction connection, where finger plate transfer load between bottom of one column and top of a second part and preloaded bolts are used to clamp segments together. In this work, the behaviour of the connection is investigated. Moreover, general information about column splices, friction connection and loss of pretension are introduced in literature review. A recommendations, for the preloaded bolts are investigated in accordance with European standard EN 1993-1-8. An experimental static compression tests are performed in order to observe the real behaviour of the column splice with long open slotted holes. Several number of numerical tests are performed to predict behaviour of the connection by use of Abaqus software. The Numerical model is validated against experimental results. Further tests are performed in order to check an influence of other important factors on the behaviour of connection system. An influence of connection geometry i.e. filler plate thickness, characteristic of the surface and the material properties are analyzed. The variation of bolt forces as well as slip factor and reduction factor ks are investigated. Finally, experimental test and finite element method analysis are discussed and conclusion are given. / <p>Validerat; 20140913 (global_studentproject_submitter)</p>

Every year in the Nordic countries we are affected by winter road conditions. The roadsbecome unpredictable and many traffic accidents occur. This report aims to study thefriction on snow and ice and see how it is affected by different temperatures and surfaces.The friction will also be compared between tests made on outdoor tracks against tests onindoor tracks, and how the friction is affected after a studded tire passes and drives up thesurface. For this, several tests have been performed on Arctic Falls indoor and outdoortracks, where measurement data has been collected using two different ViaFriction carts.The data has then been analyzed in the program Matlab and compiled into several graphsand tables. The results show that there is a clear correlation between a varying temperature and howthe coefficient of friction is affected by it. Indoor tracks do not differ significantly fromoutdoor tracks, but more tests or time may be required to make a completely safeconclusion. Finally, one can clearly see a big difference in the friction/surface when astudded tire has passed, in some cases up to a halved coefficient of friction for the drivensurface.

Refill friction stir spot welding (RFSSW) is an emerging technology, capable of joining thin sheets of aluminum alloys. The present thesis comprises two studies which were conducted to address two challenges faced by RFSSW: the long cycle time traditionally associated with welding and the poor life of existing RFFSW tools. In the first study, welds were made in AA5052-H36, at various cycle times and with various process parameters. It was shown that RPM, cycle time, and material thickness, all have an effect on the machine response. Decreasing RPM or weld duration leads to increased force and torque response during welding. Welds with cycle times below one second were successfully made without severely impacting joint quality, suggesting that prior work may have been limited by machine capabilities rather than by phenomena inherent to the process. On average, the sub-one second welds caused a peak probe force of 9.81 kN, a plunge torque of 26.3 N*m, and showed average lap-shear strengths of 7.0kN; compared to a peak probe force of 5.14 kN, a plunge torque of 17.3 N*m, and lap-shear strength of 6.89kN for a more traditional four-second welding condition. In the second study, the life of a steel toolset was quantified as consecutive welds were made in AA5052-H36 until the toolset seized from material accumulation/growth. At a one-second welding condition, the toolset was only capable of producing 53 welds before seizure. At a two-second welding condition, the toolset was only capable of producing 48 welds. In subsequent temperature experiments, thermocouples were embedded into welding coupons at various locations near weld center, allowing novel temperature data to be collected for welds with varying cycle times and parameters. The collected temperature data shows that as cycle time increases, so does weld temperature. At weld center, temperatures in excess of 500°C were observed in welds with 4 second durations. At these temperatures, Fe-Al intermetallic growth is anticipated as a mechanism limiting the tool life observed. The results suggest that steel is not an appropriate choice for RFSSW tools, and future evaluation of other materials is merited.

Denna rapport undersöker olika metoder för estimering av friktion på snö och is. Det finns i dagsläget flera olika metoder för att estimera friktion. I det här arbetet analyseras skillnaderna i resultatet mellan de olika metoderna samtidigt som orsaken till dessa skillnader försöker förklaras. Att uppskatta en korrekt friktionskoefficient kan vara av yttersta vikt för att minimera olycksrisken och för att öka säkerheten på vägarna. För att kunna jämföra de olika systemen mot varandra genomfördes friktionstester på snö och is, dels i en inomhushall i Piteå, dels utomhus i Arjeplog. De system som användes under testerna var två ViaFriction-vagnar, Coralba µ/3, VBOX 3i samt NIRAs system TGI. Resultaten visar att det finns tydliga skillnader gällande uppskattad friktionskoefficient mellan de olika testmetoderna. Analysen visar att NIRAs system genomgående estimerar en hög friktionskoefficient oavsett underlag medan den uppskattade friktionen för VBOX varierar kraftigt beroende på underlag. Det går även att konstatera att ViaFriction 1233 estimerar den lägsta friktionen på snö men att ViaFritcion 1203 får den lägsta friktionen på is. Detta trots att vagnarna är kalibrerade mot varandra. En av de största orsakerna till skillnaderna mellan de olika metoderna är att olika däck användes för de olika metoderna. / This report investigates different methods for estimating friction on snow and ice. Today there are several different methods for friction estimation. In this work the differences between the  methods will be analysed and, an attempt to explain these differences will be made. To estimate an accurate coefficient of friction can be crucial to minimize the risk of accidents and increase the safety on the roads. To be able to compare the different systems to each other, friction testing on snow and ice were executed. The testing took place partly indoor in Piteå but also outside in Arjeplog. The systems used during the tests were two ViaFriction systems, Coralba µ/3, VBOX 3i and NIRAs system TGI. The results shows that there are significant differences for the estimated friction between the different methods. The analysis shows that NIRAs system constantly estimates a high coefficient of friction regardless of road conditions whilst the friction for VBOX varies heavily depending on road conditions. We also noticed that ViaFriction 1233 estimates the lowest friction on snow whilst ViaFriction 1203 estimates the lowest friction on ice, even though the systems are calibrated against each other. One of the main reasons to the differences between the methods are that different tires were used for each method.

<p> An experimental study of forced convection heat transfer and friction in water flowing in a vertical tube is reported in this thesis. The study investigates the effect of coiled wire turbulence promotors of various pitch to diameter ratios (ranging from 1.00 to 5.50) upon the Nusselt Prandtl modulus Nu/Pr^1/3 and Fanning friction factor f. The investigation is carried out for three different wire sizes, 0.052 in., 0.063 in., 0.072 in. respectively.</p> <p> Analysis of the various dimensionless numbers computed from the measurements of the present study indicates that the heat transfer increases by as much as 250% for low values of pitch to diameter ratio, though at the cost of a much larger increase in pressure drop. Consequently, the tubes using coiled wire turbulence promotors can be employed with advantage for cases where pumping power is not the dominating factor and reduction in weight and size of the equipment are more important.</p> <p> The experimental data are empirically correlated in terms of the ratio of Nusselt numbers for the tubes with turbulence promoters to the empty tube as a function of Reynolds number and pitch to diameter ratio. Nu/Nuo = K(Re)^a (H/D)^-0.3 </p> <p> To evaluate the net effect of coiled wire turbulence promotors, the ratio j/f = [Nu/RePr^1/3]/f is plotted against Reynolds number. The curves for the coiled wire turbulence promotors fell below the theoretical curve for the empty tube indicating that coiled wire turbulence promotors are not advantageous in terms of heat transfer per unit pressure drop.</p> / Thesis / Master of Engineering (MEngr)

Automotive brake systems are source of particulate matter (PM) emissions, particularly in the urban areas. Several human ill-health are related with this kind of pollution. Along tire wear, road wear and dust from resuspension, the brake wear comprises the most relevant non-exhaust source of road traffic related emissions. Aiming at studying the PM brake emissions, this thesis is composed of an introductory part containing the main concepts and the state of art of the main subjects; and the experimental part, which comprehends three investigations. Chapters 2, 3, 4 and 5 are dedicated to the introduction part. Chapter 2 provides a brief description of the friction and wear, as well as the fundamental principles of braking by contact. Chapter 3 discuss the disc braking system, with particular attention to the pad friction materials. Chapter 4 is dedicated to friction layer: the layer usually developing at the disc/pad interface, affecting the performances of the tribological system. Finally, Chapter 5 provides an extensive discussion of the issues related to the particulate matter originated from disc brake systems. The experimental part is presented in the Chapters 6, 7, 8 and 9. Chapter 6 describes the methodology applied in all the investigations. Chapter 7 investigates the PM emissions behavior and its interaction with the friction and wear, aiming to identify the mechanism of generation the PM emissions. A copper-containing and a copper-free commercial friction materials were used, with particular emphasis on the effect of the scorching treatment. The Chapter 8 is dedicated at investigating the tribological behavior and the corresponding PM emissions in two Cu-free commercial friction materials, aiming to a better understanding the effect of abrasive ingredients on the emissions generation. Finally, the Chapter 9 investigated the addition of natural ingredient rice husk in a new eco-friendly Cu-free brake friction material composition, focusing the attention on the tribological and emissions behavior. All tests were carried out using a pin-on-disc tribometer equipped with an enclosure, especially designed for investigating the tribological properties, as well as the airborne particles generated by contact. Low-metallic friction materials, both commercial and laboratory-produced, were tested against cast iron discs. The tests parameters used correspond to mild sliding conditions resembling those faced in real braking. Such conditions are characteristic of driving in urban areas, where the expose to traffic PM is concentrated. A specific methodology of analysis was developed, based on SEM/EDXS techniques. Using this methodology, comparative investigations between the elemental composition of the virgin friction materials, the worn surfaces of the friction materials and the airborne particles collected during the tribological tests were carried out. The results point out the triboxidative wear as the main mechanism of the PM brake emissions generation. Moreover, particles produced by abrasive wear can be also directly emitted to the environment.

No description available.

No description available.