| 1411. |
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| 1412. |
- Söderberg, Hans
(författare)
-
Growth and characterization of TiN/SiNx multilayer thin films
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demands from industry for higher cutting speeds, feeding rates, and reduction of the use of cooling agents during turning and milling operations are increasing. Consequently the requirements on the cutting inserts are increasing and new advanced coatings that can withstand the higher temperatures and larger loads are highly sought after. Throughout the last decade a large amount of publications regarding the Ti-Si-N system have been published. The majority of publications treat nanocomposites, exhibiting high mechanical properties, i.e. hardness. There are even reports of ultrahard nanocomposites reaching hardness values of ~100 GPa. When these nanocomposites are grown under conditions for optimal mechanical properties they have been described to consist of TiN nanocrystallites encapsulated by a thin layer (1-2 monolayers) of amorphous Si3N4. Due to the small crystallite size, a large part of nanocomposite coatings macroscopic properties will be controlled by the vast amount of interfaces between the crystallites. Despite the large amount of research done on these types of nanocomposites, the interfacial structure is still largely unexplored due to the complex 3-dimensional microstructure. Therefore, within this thesis, multilayers have been used as model systems. The layered structure provides a 2-dimensional geometry more suited for electron microscopy observations. Furthermore, a multilayer model system also allows for a precise control of the 2-dimensional geometry. Additional scientific importance can be found in the layered structure itself. Publications on multilayers deposited from various material systems all show similar results, i.e. hardness increase as the layer thicknesses are decreased. Hardening effects have been discussed to arise due to e.g. decreasing crystallite sizes, more interfaces, coherency strains, and differences in elastic shear modulus between the layers (Koehler hardening). In this work monolithic, trilayer, and multilayer/superlattice coatings have been grown by dual reactive magnetron sputtering. The films have subsequently been characterized and tested by a number of analytical tools such as x-ray reflection (XRR) and diffraction (XRD), in situ reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM), and nanoindentation. When depositing TiN on Si wafers, which have a native oxide layer on the surface, the TiN films grow polycrystalline. With the addition of periodic SiNx layers the columnar polycrystalline growth is maintained as long as the SiNx layers are grown thin. This indicates that the SiNx interlayers transmit the crystal structure and act as a template for each successive TiN layer. I.e. at small SiNx layers a crystalline structure is formed, and not an amorphous one. Similar epitaxial stabilization of non- equilibrium phases are observed in several other material systems and their formation are made possible due to the non-equilibrium conditions during deposition. However with thicker SiNx layers the columnar growth is lost and instead equiaxed TiN crystals are grown within each TiN layer, layers which are separated by amorphous SiNx. Changing the substrate to MgO, which exhibit a good lattice match with TiN, epitaxial growth of single crystal TiN films is possible. The deposition of thin (
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| 1413. |
- Söderfjäll, Markus, 1985-
(författare)
-
Friction in Piston Ring - Cylinder Liner Contacts
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With today’s striving towards reduction of fuel consumption it is moreimportant than ever to understand the function of different componentsin the internal combustion engine. There is a need to develop and usetools to investigate and predict the result of specific design changesmade on the components. In this work, the mechanics and the tribologyof the power cylinder unit and more specifically the operation of thepiston rings was investigated both numerically and experimentally. Theobjectives of the numerical part of this thesis were to develop simulationtools that can be used to quantify design changes to the TLOCR andthe cylinder liner. Such as the dimensions of the ring itself but also ringtension, running land profile, out of roundness of the cylinder liner andsurface texture of dimple type applied on the cylinder liner. Numericalsimulation models were developed and used to investigate operation of atwin land oil control ring (TLOCR). TLOCR are typically used in heavyduty diesel engines (HDDE). The TLOCR plays a very important role inthe engine since it is supposed to distribute the correct amount of oil onthe liner to lubricate the other rings. It is important that the TLOCRdoes not leave too much oil on the liner for the two top rings since itcould lead too high oil consumption. In a HDDE the piston assemblyis the largest contributor to frictional losses where the piston ring packaccounts for the major part of this. The oil control ring is the largestcontributor to frictional losses in the piston ring pack therefore makingit very interesting to study from a fuel consumption perspective. One ofthe models developed in this work accounts for the tribological interfaceof the TLOCR against the cylinder liner and piston ring groove as wellas the elastic deformation of the ring and the ring dynamics within thepiston ring groove. The actual ring cross section was modelled in orderto account for the full three dimensional elastic deformation of the ring.By solving all of these problems as a coupled system, the entire operation of the oil control ring can be understood in a better way than earlierand this opens up new optimisation possibilities for the TLOCR. Sincethe cylinder liner in an engine will always have some deviation fromperfectly round this is important. The full ring is modelled in order toaccount for out of round cylinder liners. The model can therefore beused to investigate the effect on oil distribution by reduced ring tensionwhich will affect the frictional losses of the system. It was found that thereduction in tangential force on the TLOCR with kept sealing capability,enabled by reduced out-of-roundness, could result in friction reductionof 40 % at mid-stroke.Because of the complexity, a multi-physics model of this type introducesdifficulties with convergence. Especially when implementinga mass conserving cavitation model and solving for the reversal of thepiston ring. Implementation and numerical verification of a mass conservingcavitation model was therefore performed. A method for dealingwith the convergence problem close to reversal was implemented and discussed.A model considering texture, of dimple type, on the cylinder linerwas also developed to find dimple dimensions optimal for reduced fuelconsumption. Since the dimples are modelled in a deterministic manner,only a periodic section of one land of the TLOCR was considered. Themodel takes mixed lubrication and inertia of the ring into considerationand a mass conserving cavitation algorithm were implemented. Theresults from the model predict friction reduction of approximately 40 %at mid-stroke speeds.The objective of the experimental part of this thesis is to developa novel test method for evaluation of piston ring friction at realisticspeeds. The test-rig was designed and constructed during the first halfof the project. The rig was designed so that standard HDDE productionpiston rings and cylinder liners could be easily mounted, and so thatpiston ring friction could be measured without influence from pistonfriction. Both cylinder liner and oil tank were equipped with heaters,where the oil supply resembles that in an actual engine. Repeatabilityof the results was found to be good. Influence on friction by differentcylinder liner surface roughness and coatings were investigated. Variouspiston ring designs, ring tension and coatings were also investigated. Itwas found that friction of the TLOCR could be reduced with close to50 % with kept sealing capability by reduced ring tension and differentgeometry on the lands in contact with the cylinder liner. The numerical simulation model governing the full cross section of the TLOCR wasvalidated against measured piston ring friction data at a number ofdifferent speeds and excellent correlation was found.
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| 1414. |
- Söderholm, Kristina
(författare)
-
Tekniken som problem och lösning : föroreningsmotstånd och teknikval i 1900-talets svenska pappersmassaindustri
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the advent of environmental issues in the public debate, historians world-wide have shown an increased interest in studying environmental issues. In this field of study, phenomena such as industrialisation, as well as economic and technological progress, have often been understood solely as the causes of environmental degradation with few attempts to examine the more complex features of the technology-environment relationship. In the late 1990s, though, scholars in the fields of history of technology, environmental history and business history extended the focus of historical studies on the internal and external dynamic processes that shape industrial production technologies with severe impacts on the natural environment. This study analyzes the technology choices confronting business enterprises, which have been exposed to public concerns and legal claims concerning their polluting activities. The ‘company-focus’ of the study permits an in-depth analysis of the relationship between industrial production technology and the environment. In this study we analyze in particular the underlying motives that induce a company to implement environmentally benign production technologies, as well as the process of technology choice and development at the company level. The technology choice process must however not only be understood as an internal ‘businesshistory’, but also as a process heavily dependent on a large number of economic, social, technological, legal and scientific factors. The analysis in this study builds on Nathan Rosenberg’s conception of technology choice and development. Rosenberg argues that decisions about the design of the production technology are made under incomplete information about technical solutions and their costs. This implies that technology choices are often characterized by the search for knowledge that enables the company to implement existing but not yet developed technical potentials, rather than a choice between ready-made technical solutions. Empirically the study focuses on the technology choices of two Swedish pulp and paper mills, which both were subjects to conflicts concerning their pollution into water and air. These conflicts include the one concerning Örebro paper mill, 1904-1911, and the more recent Värö mill conflict, 1964-1972. A comparison of these conflicts – from two distinctly different time periods – permits an analysis of how technology choice processes are affected by increased knowledge about the pollution problems as well as by advances in the production of technology. We find that given the industry’s collective interest in solving the pollution problems, the pulp and paper industry initiated a large number of cooperative research undertakings aimed at developing cleaner production methods during the 1950s and 1960s. Thus, while the Örebro paper mill was a pioneer in initiating cooperation with its competitors, the Värö mill could benefit from previous advances in knowledge and implement – more or less well established – technological solutions. The result of the study suggests therefore that industrial cooperation within the environmental field does not necessarily have to be initiated by public organizations and institutions, but can also emerge as the result of the initiatives of a single company. The fact that the Örebro and Värö mills both faced a negative public opinion concerning their polluting activities, imply that the respective technology choice processes were influenced by the interests and motives of the opinions. The complainants in the two conflicts legitimized their arguments and complaints by referring (implicitly or explicitly) to existing laws and regulations, and by engaging the relevant scientific expertise. The two companies also engaged scientific experts, largely in order to learn more about potential technical solutions to the pollution problem but also to confront the arguments of the complainants and their respective experts. In both cases this type of setting resulted in what the sociology of science literature calls ‘scienitific controversies’. The analysis in this study provides support for the notion that these types of controversies are characterized by arguments and deliberations that are largely based on values and attitudes rather than on (scientific) facts. The study also illustrates how the controversies motivated the complainants in the respective conflicts to reframe their arguments, and, for instance, express their concerns in more general and definitive terms. The technology choice processes of both mills are clear examples of the floating distinction between technology choice and technological development. The search for technical solutions was not cost-free, especially not for the Örebro mill, which even had to initiate basic scientific research to solve the problem of the sulphate odour. Both mills had in the past invested in a lot of technology-specific human and physical capital, and they therefore faced strong incentives to direct the environmental activities toward technical solutions that could make as much use of this capital as possible. For this reason, the actual measures implemented as a result of the conflicts (and the related legal verdicts) were largely ‘end-of-pipe’-oriented rather than characterized by ‘radical’ changes in the underlying pulp production processes. Interestingly, although 60 years lapsed between the two conflicts, the measures undertaken to combat the emissions at the two mills were remarkably similar.
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| 1415. |
- Söderholm, Peter
(författare)
-
Maintenance and continuous improvement of complex systems : linking stakeholder requirements to the use of built-in test systems
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The failure of a technical system represents two different kinds of change. One change is the degradation of system functions, while the other change is the increase in stakeholder requirements. Hence, information about both stakeholder requirements and system health are necessary in order to properly manage system failures. This management includes a combination of maintenance and improvement efforts. The combination is especially crucial when dealing with complex and critical systems, where a change may result in unwanted consequences with extensive losses. In this situation, maintenance and improvements can be supported by the use of Built-in Test systems, which aim at enhanced testability and maintainability performance of the technical system. The purpose of this research is to explore and describe the linking of changing stakeholder requirements to the use of Built-in Test systems, in order to facilitate maintenance and continuous improvement of complex and critical systems. To fulfil the stated purpose two case studies and one pilot study, supported by a continuous literature study have been made. The main case study and the pilot study focused on a modern combat aircraft, which is considered as a highly complex and safety critical system with stringent requirements on low life cycle cost. The second case study focused on maintenance-related requirements and risks during maintenance execution within a paper-mill, which is a complex system with stringent requirements for uninterrupted production. The research is presented in this thesis, which consists of an extended summary of five journal papers that are appended in full. The thesis includes examinations of important stakeholders and their requirements of critical system health information. Furthermore, the thesis includes studies and analyses of hazards related to health information retrieved through Built-in Test systems and combined with information from external test systems. The thesis also provides suggestions for how stakeholder requirements can be linked to the use of Built-in Test systems, so that they together with external test systems provide required health information and reduce related hazards.
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| 1416. |
- Söderholm, Patrik
(författare)
-
Two studies on fuel choice in power generation
- 1997
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation consists of two studies, both related to the impacts of economic and political factors on fuel choice in electric power generation. The primary purpose of the first study is to estimate the degree of price-induced interfuel substitution between three fossil fuels in West European power generation. The problem is studied within two restricted flexible cost functions, a translog model and a Generalized Leontief model. The results show that both models generate reasonable short-run responses to changes in relative fossil fuel prices. In general the degree of short-run interfuel substitution is found to be substantial, a result that is partly explained by the large share of multi-fuel plants in West European power generation. In addition, by deriving the shadow price of capital from the Generalized Leontief cost function the long-run own- and cross-price elasticities of fossil fuel demand are presented. Overall, however, this approach is not able to produce empirically reliable long-run estimates. Finally, the empirical investigation also indicates that public policies and changes in system load factors have had significant impacts on fossil fuel choices in West European power generation. The main purpose of the second study is to explore what factors have been the most important in determining the choices between different electricity supply alternatives in Zimbabwe since 1980. In a first step the economic costs of the available electricity supply options are estimated and secondly these costs are contrasted with the actual choices made by the electricity authorities. It is shown that in the early 1980s the electricity supply choices in Zimbabwe were dictated by a self-sufficiency policy, and accordingly least-cost alternatives were rejected. Due to a new political environment, financial problems and pressures from the World Bank, the step towards least-cost choices was substantial in the 1980s and the 1990s, although not complete. This and the ongoing trend towards higher discount rates imply that thermal power, be it coal- or gas-fired power, probably will dominate future electric power investments in Zimbabwe.
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| 1417. |
- Söderlund, Anders
(författare)
-
Det långa mötet - IT och skolan : om spridning och anammande av IT i den svenska skolan
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Avhandlingen syftar till att beskriva och förstå hur IT spridits och anammats i den svenska skolan. Den vetenskapliga frågeställningen är om det är möjligt att att förstå IT-utvecklingen på skolområdet i termer av teknikspridning. Avhandlingen vilar på det ontologiska antagandet att teknikspridning är en komplicerad process där beslut på olika nivåer i samhället om att använda teknik finns med i bilden när IT betraktas som en social konstruktion. Avhandlingen bygger på Giddens samhällsteoretiska arbeten, särksilt viktigt är begreppet strukturering som avser en social process av ömsesidig interaktion mellan mänskliga aktörer och organisationsstruktur. Inspirerad av Giddens har Orlikowski utvecklat en modell för samspelet mellan människa, teknik och organisation som används i avhandlingen. Avhandlingen begränsar teknikbegreppet och spridningen av teknik till att gälla innovationer som innebär eller syftar till förändring. Innovationer med tekniskt innehåll har två aspekter, den "hårda" som rör de materiella artefakterna som representrar tekniken, och de mjuka som rör t.ex. olika antaganden om hur tekniken ska användas och av vilka, som kopplats till tekniken. Objeketet för studierna är uppfattningar om IT som fenomen och dess introduktion i det svenska skolsystemet. Objektet rör alltså en implementation av en innovation. Innovationen är till synes en materiell artefakt men som dessutom är ett viktigt stöd för lärandet genom att den skapar möjlighet att fästa tankarna i text, ljud och bild, bevara dessa och kommunicera dessa. Avhandlingen har en undersökningsmatris som används som ett raster genom vilket utvecklingen betraktas på makro- och mesonivå. Studierna avgränsas i tiden till efter 1970. Tyngdpunkten ligger på 1980- och 1990-talen då flera omfattande skolreformer ägde rum och då ansträngningarna att sprida IT och dess användning i skolan ägde rum. På makronivån studeras offentliga texter. På mesonivån görs en omfattand eempirisk undersökning i Sandvikens kommun. Valet av kommun motiveras att Sandviken som första kommun i landet bestämde sig för att på bred front introducera IT som pedagogiskt verktyg i skolan. Ansatsen är inspirerad av etnografisk metod och använder sig av textanalyser, observationer vid fältbesök, intervjuer, fältanteckningar och enkäter. Resultaten visar att IT-frågorna redan från början på makronivån kopplades samman med näringslivets konkurrenskraft. Därmed följer man en tradition från folkskolans tillkomst 1842 som skulle förändra bildningsnivån hos medborgarna så att de kunde kvalificeras för industrisamhället. Resultaten presenteras i grafer och figurer som visar hur IT snabbt spridits i samhället under den studerade tiden. IT:s möte med skolan had dock varit en mer långsam och utdragen process med en viss slagsida mot de tekniska aspekterna av IT på bekostnad av de pedagogiska. Studien på mesonivå där Sandviken satt lärandet i fokus kontrasteras mot detta. En omfattande utbildningsverksamhet med studiecirklar, ledda av pedagoger som utbildats till piloter resulterade i att udner den studerade perioden från 1994-1998 1141 pedagoger genomgick studiecirklar och att mer än 450 IT-pedaogiska projekt genomfördes. Avhandlingen visar att mesonivåns starka betoning av lärandet fick stor betydelse för implementeringen coh anammandet av IT-användningen. Resultaten diskuteras mot de teoretiska utgånspunkterna. En diskussion förs om makronivåns satsningar i förhållande till skolans legitimitetskris under 1980-talet. Det konstateras också att en del av del allra senaste satsningarna från makronivån går stick i stäv mot de resultat som avhandlingen lägger fram från mesonivån. Avhandlingen pekar också på att det på makronivån under de aktuella decennierna finns vissa personalunioner mellan olika initiativ som kan ha bidragit till implementeringens utformning.
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| 1418. |
- Sörensson, Anna
(författare)
-
Energy absorption and transmission in the hand and arm during high frequency vibration and impact
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There has been discussion in international literature as to whether vibration containing impact and high frequencies, i.e. above 1000 Hz could make a special contribution to injuries in the hand and arm. The aim of this thesis was to investigate the effect of impact and high frequency vibration on the absorption and transmission of energy to the hand and arm system. The results show that the transmission of acceleration magnitude or energy to different parts of the hand and arm decreases with the distance from the source and are highly dependent in the vibration frequency. There are also differences in the energy transmission due to different types of exposure, random or sinusoidal vibrations. Furthermore, the results show that a great amount of energy was absorbed in the human hand and arm within the freequency range 20 to 5000 Hz. Moreover, was found that there were also differences in energy absorption due to gender; females absorbed less energy than males. Vibration containing impact had a significant influence on both the energy absorption and the hand forces compared to vibration without impact. There were differences in the amount of absorbed energy in the hand and arm between the four investigated vibrating tools. The vibration level also has a strong effect on the quantity of absorbed energy in present studies. If the assumption that higher amount of absorbed energy in the hand and arm represent and increased risk for injury, it can be concluded from the results in this thesis that high frequency vibration and impacts increase the risk for injury.
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| 1419. |
- Tabatabaei, Narges
(författare)
-
Impact of Icing on Wind Turbines Aerodynamic
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wind energy covered 11.6% of Europe electricity demand in 2017. Region with cold climates represent a strong potential for wind energy companies because of their sparse population and proper wind conditions. The global wind energy installations in cold climate regions is forecasted to reach a capacity of 186 GW by the end of 2020. But wind turbines installed in cold climate regions are prone to the risks of ice accumulation which affects their aerodynamics behavior, as well as the safety, and structural loads.The aerodynamic forces on wind turbine can be affected in two main ways: ice accretion changes the blade profile, and thus the flow path curvature, and the surface roughness. The importance of these two parameters depend on the ice type. The target ice type for this thesis is the smooth leading-edge glaze ice with horn shape. The aerodynamic consequences of the blade profile change because of the mentioned ice type are studied in detail. The findings of this thesis are classified in five main sections. The first section considers the methodology to model the performance of a wind turbine. The wake behind the turbine is also explored. Different aspects of the simulation methods with computational fluid dynamics using the Reynolds-averaged Navier-Stokes equations are investigated in both steady state and transient. In the second section, the time-dependent effects of icing are studied, exploring the moving vortices created by the irregularity of the ice and their frequencies and amplitudes. The main frequency modes of the flow dynamics were analyzed. In the third section, three-dimensional simulation of icing is implemented and the fluid flow arrangement through the rotor is investigated. Two well-recognized approaches are applied and compared, which are Blade Element Momentum (BEM) and CFD. An automated setup is programmed and launched to implement multiple CFD simulations to provide the aerodynamic data for structural analysis in the fourth section. The developed methodology is illustrated on a large-scale wind turbine. In section five, the effects of the uncertain level of ice-accretion is studied through an uncertainty quantification method. The aerodynamic losses are statistically discussed. Then, a scenario study is conducted according to the obtained polynomial chaos expansion, in which the probability distribution of wind power loss due to icing is inspected.The achievements of this thesis can be used in to design of a wind turbine which is supposed to work in a cold climate, as well as assess the economics of a predesigned wind turbine working in a cold region.
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| 1420. |
- Tadaros, Marduch
(författare)
-
Models and Metaheuristics for Real-World Applications of Location and Vehicle Routing Problems
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The supply chain's underlying infrastructure affects the efficiency and design of distribution routes. As such infrastructure is associated with substantial capital investments, it is crucial to consider the network design and the location of various facilities. The supply chain network design in this context encompasses two major problem classes; the vehicle routing problem aiming to find optimal routes to serve a set of customers by a fleet of vehicles from various facilities, and the facility location problem aiming to find the optimal location for various facilities. Moreover, these problems are interconnected as the facilities affect the demand fulfillment and the vehicle routing. Such problems are often solved with optimization techniques within the field of Operations Research, which is concerned with the mathematical modeling and algorithmic solution of decision-making problems. In response to changes of the conditions of supply chains, researchers have directed their attention to extending and introducing new problem variants. These extensions and variants address real-life aspects of transportation systems, but also elevate operational complexity, making them harder to solve.The objective of this thesis is to contribute to the advancement of the field of supply chain network design, by;exploring and identifying opportunities and needs for modeling and solution approaches that address the increased complexity of real-life industrial applications in facility location and distribution systems of goods, andto propose new modeling approaches and solution methods that address such opportunities and needs.The thesis is based on five appended papers. Paper A presents a network design modeling approach for a reverse supply chain of spent lithium-ion batteries in Sweden and addresses the difficulties in demand estimations. Paper B is a literature review covering multi-objective location-routing problems; these are strategic models aiming to determine the location of facilities considering aspects of tour planning and multi-stop routes. An annotated review is presented based on the application area of the various models and an analysis of objectives and solution approaches used. Paper C introduces the Hierarchical Multi-Switch Multi-Echelon VRP (HMSME-VRP), which is a new variant of the vehicle routing problem based on a real-life operational problem originating from the policies of a Nordic distribution company. A mixed-integer formulation of the problem is proposed, and its relations to other previously stated VRP variants are analyzed and discussed. As only small instances can be solved using a commercial solver, Paper D presents two different General Variable Neighborhood Search procedures in order to solve realistic-sized instances and instances of real-world size. Paper E extends the HMSME-VRP by considering service times and thus incorporates more real-life aspects. A Hybrid Clustered Ant Colony Optimization algorithm, incorporating two local search schemes based on Variable Neighborhood Descent, is proposed to solve the problem with the increased complexity that the service times entail.
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