| 31. |
- Andersson, Roger
(författare)
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Deformation characteristics of stainless steels
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the results of a theoretical and experimental investigation into the deformation characteristics of stainless steels. The title of the chapters is as follows; A new type of forming limit diagram for use with meta-stable stainless steels. A new equation to describe the microstructural transformation of meta- stable austenitic stainless steels during plastic deformation. FEM-simulation of the forming and impact behaviour of stainless steel automobile components. The development of high strain rate equations for stainless steels. The metallurgy and mechanical properties of laser welds between stainless and carbon steels.
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| 32. |
- Andersson, Urban
(författare)
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An experimental study of the flow in a sharp-heel Kaplan draft tube
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This research project was originally part of a package (Turbine-99 Draft Tube) that had a mutual goal, to improve the understanding of draft tube flow and establish Best Practise Guidelines for simulation of draft tube flow.The draft tube is situated after the runner in a Hydropower turbine to recover as much of the remaining head and kinetic energy as possible before the water leaves the turbine. The case is fully turbulent, and because of the adverse pressure gradient with risk for separation, periodic inlet conditions from the runner with different degrees of swirl causes the draft tube flow to be difficult to predict. Therefore, unambiguous design criterions are lacking, and the slightly contradicting recommendations indicate that the standard rules give conservative, rather than optimal, designs. This thesis gives some background on draft-tube flows in general and discusses the parameters and flow conditions relevant to the Turbine-99 draft tube in some detail. The main goal of the thesis is to provide extensive experimental data on a well-defined sharp-heel draft-tube flow. The data bank has served as validation data for the simulation challenge presented by the Turbine-99 workshops in Porjus (June 1999), Älvkarleby (June 2001) and Porjus (December 2005).The experimental data and some numerical results are also available as an application challenge in the Qnet database (managed by Ercoftac), as a validation case for flow simulations.The experimental data consists of visualisations, pressure measurements and velocity measurements. These methods give a good qualitative picture of the flow pattern in the draft tube with quantitative data at selected cross section that can be used to validate the flow simulations. The first two workshops focused on mean quantities of pressure and velocities; however, phase resolved measurements have been added to add value to the experimental data.In addition to the experimental validation case, there is one paper that deals with loads on the draft tube, which affect the construction lifetime. Since the hydropower stations are expected to have a long total technical lifetime with a number of refurbishments, these questions will grow in importance over the next decades.
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| 33. |
- Angantyr, Anders
(författare)
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Rotordynamic optimization of large turbo systems using genetic algorithms
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In engineering design, nature has often been the source of inspiration. It is easy to point out solutions in nature that are optimal in some sense. One example is the roughness of the surface of a shark's skin. This is designed by nature to minimize the resistance when the shark swims in the water. Another example is the shape of an egg shell. This is an optimal load carrying structure which often is found in engineering design applications. An even more fascinating question is how nature has found these optimal solutions? The answer to this question is evolution. Instead of just analyzing and copying optimal structures invented by nature it seems reasonable to mimic the process how nature has came up with these solutions. Research on how these ideas can be interpreted and used in engineering design started in the early seventies and has now become a large field known as Evolutionary Algorithms (EAs). During the past decade these methods have emerged as potent tools for engineering design optimization. Some of these methods are especially suited for problems which involve multiple objectives such as almost all real engineering design problems. Just until recently, these methods have seldom been used in the area of rotordynamical design. This thesis deals with the question how these methods can be adapted and applied in order to improve the design and design process of large rotor-bearing system. A hypothesis for this work is that EAs are suitable to use in the late design process of these systems. The aim of this work is to evaluate this hypothesis by studying real applications found in industry. This thesis comprises an introductory part and five appended papers. The introductory part is divided into four different chapters. In the second chapter the concept of engineering design optimization is introduced. In the third chapter Genetic Algorithms (GAs) is presented. Finally, the analysis and design of rotor-bearing systems are introduced and discussed. The purpose with the introductory part is to introduce and prepare the reader to the concepts presented in the papers. The introductory part may serve as a start point for newcomers interested in these areas. The appended papers deal with different rotor-bearing system optimization problems and how these can be formulated and solved with GAs. Paper A introduces a constraint handling technique based on concepts found in multiobjective GAs. In Paper B the multiobjective optimization of a generator is presented and discussed. In Paper C and Paper D the constraint handling technique introduced in Paper A is used for two different rotor- bearing system where the actual bearing geometry parameters are used as design variables in the optimizations. In Paper E the feasibility of site balancing rewinded turbo generators is investigated by the use of a multiobjective GA.
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| 34. |
- Barabady, Javad
(författare)
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Production assurance : concept, implementation and improvement
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dynamic business environment is characterized by short-term and long- term uncertainties in the business processes, combined with a short-term focus on meeting customers' and share-holders' requirements. Therefore, making correct decisions in a dynamic business environ-ment is a major challenge for production plant engineers and managers all over the world. Such a situation necessitates the successful application of tools and engineering solutions to minimize the total business risk and reduce uncertainties through assurance of world-class production plant performance, which can ensure that the right level of production can be ob- tained in order to meet customer demands. To meet these challenges, many approaches such as reliability analysis techniques have proved an effective solution during both design and operation of a production plant, and have been implemented by production engineers and managers. The main focus of reliability is on the process of ensuring a reliable product and/or system as well as reducing system uncer- tainty. However, these are not discussing the issues of production availability which are criti-cal for meeting customer requirements and market demands and may increase risk and uncer-tainties in decision-making. However, production assurance (PA) plays a significant role in supporting the decision-making process by production managers and engineers deal with the above mentioned challenges. The main focus of existing research on the area of PA is on the models and methodologies for data analysis and prediction of future system performance. Fur-thermore, existing models and methodologies supporting PA analysis and management have been primarily developed for the planning phases, specifically for the petroleum sector, but have not yet been sufficiently developed for general use. In many cases, the engineers and managers may face many problems in the process of implementing and executing the PA con-cept. The purpose of this research is to study, analyze and evaluate the application and implementa-tion of Production Assurance Programs (PAP) in production plants, and find some importance measures that show the criticality of the components or subsystems. To fulfill the stated pur- pose, an explorative literature study combined with a case study of a process plant has been performed. Various examples and data from the oil and gas industry are also used to support the thesis. In this study, firstly the concept of production assurance is discussed and Overall Production Assurance Effectiveness (OPaE) is suggested as a developed metrics for measuring the per-formance of a production plant which is considered internal effectiveness of production plant as well as external effectiveness as it considered customer requirement and demand. This thesis present and discusses a methodology that facilitates implementation of PAPs in a production plant. Such a methodology would support production engineers and managers in reducing or eliminating uncertainties and risks in their day to day operation and maintenance decisions. In this research study, some availability importance measures are defined. Thereafter, it a methodology is suggested to improve the production assurance effectiveness through im-provement of reliability, maintainability, and availability of production plant. In the method-ology, the concept of importance measures is used to prioritize the components or subsystems. This analysis of importance measures has helped to identify the critical and sensitive subsys-tems or components that need more attention for improvement. The research study shows that in order to measure the performance of a production plant, the PA provides a more comprehensive measure of a production plant's real performance com-pared to system availability performance as the production assurance provides information about the production plant's delivery capacity, production rate and ability to deliver according to design or customer demands. The study also indicates that availability importance measures can serve as a guideline for developing a strategy for improvement of production assurance.
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| 35. |
- Bark, Glenn
(författare)
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On the origin of the Fäboliden orogenic gold deposit, northern Sweden
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A new promising ore province, the Gold Line, southwest of the well- known Skellefte District, northern Sweden, is currently under exploration. This province hosts, so far, one operating mine, the Svartliden Au mine, and the recently closed Blaiken Zn-Pb-Au-Ag mine. The largest known gold deposit, the hypozonal Fäboliden orogenic gold deposit, in the area was recently granted mining permits. The deposit holds c. 54 Mt at 1.2 g/t Au, with a planned production of 4.6 Mt of ore/year. The mineralization at Fäboliden is commonly hosted in arsenopyrite-bearing quartz-veins, within a roughly N-S striking, steeply dipping shear zone in amphibolite facies volcano- sedimentary host rocks. The narrow belt of supracrustal rocks is surrounded by late- to post-orogenic Revsund granite. The gold is fine-grained (2-40 µm) and closely associated with arsenopyrite- löllingite and stibnite. Gold is found in fractures and as inclusions in the arsenopyrite-löllingite. Gold is also seen as free grains in the silicate matrix of the host rock. The hydrothermal mineral assemblage in the proximal alteration zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. This type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide. The lateral extent of the proximal alteration zone is estimated to 30-50 meters, and there is a good agreement between diopside- amphibole-biotite alteration, quartz veining, and gold mineralization. The mineral assemblage in the distal alteration zone is characterised by the presence of Ca- and Fe-Mg amphiboles, hedenbergite, biotite, and quartz. The transition from the distal alteration into the regional metamorphic assemblage is diffuse, and the only discernable feature appears to be a gradual decrease of amphibole away from the mineralization. The ductile gold-hosting fabric progresses laterally across the Revsund granite contact and then disappears after a few meters inside the granite, suggesting that at least the final stages of mineralization syn- to postdate the emplacement of the c. 1.81-1.77 Ga Revsund granite. Relationships between garnet-biotite and graphite geothermometry, together with these field relationships, indicate that the late stages of mineralization at Fäboliden post-date regional peak-metamorphism in the area, which is estimated at c. 1.80 Ga. The Fäboliden gold mineralization is hosted by a reverse, mainly dip-slip, high-angle shear zone with a relatively small horizontal shear movement. The mineralization constitutes two sets of mineralized quartz veins, one steep fault-fill vein system that is parallel to the regional foliation and one flat-lying extensional vein system. Both vein sets are suggested to have been generated from the same stress field, during E-W shortening at c. 1.80 Ga. At least two types of ore shoot are present at Fäboliden, intersections between the fault-fill vein set and the extensional vein set and bends in the shear zone system both show elevated gold content, similar to many gold- quartz vein deposits globally. The fluids involved in the precipitation of gold at Fäboliden shows characteristics similar to other hypozonal orogenic gold deposits, such as a CO2-CH4-H2S fluid composition and pressure-temperature conditions of c. 4 kbar and 520-560°C. Sulphur isotope data ranges between -1.5 and +3.6‰. Oxygen and hydrogen isotope data ranges between +10.6 and 13.1‰, and -120 to -67‰, respectively. The hydrothermal fluids at Fäboliden are interpreted to have originate from a crustally contaminated magmatic source. The potential for future orogenic gold discovery in the Fennoscandian Shield is considered good. From this PhD study it is suggested that interesting targets, concerning exploration for orogenic gold in at least the Gold Line, would be areas associated with roughly N-S striking tectonic zones that were active at around 1.80 Ga.
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| 36. |
- Bask, Michael
(författare)
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Dynamic threshold generators for robust fault detection
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Detection of faults, such as clogged valves, broken bearings or biased sensors, has been brought more and more into focus during the last few decades. There are two main reasons why faults are important to detect at an early stage. Firstly, faults in safety critical applications, such as aircraft, nuclear reactors, cars and trains, may create risks of personal injuries. Secondly, faults in the manufacturing or process industry, e.g. flotation processes and steel plants, may cause decrease in quality or interruptions of production. A fault detection algorithm consists of two parts, the residual generator, which generates a residual, and the residual evaluator, which compares the residual, or a function of it, with a threshold to determine if a fault is present. The residual generation contains a process model and the residual can be described as a filtered difference between the measured and estimated process outputs. When no fault is present, the residual will be nonzero due to residual disturbances, i.e. measurement disturbances, process disturbances and model uncertainties. Therefore, the residual evaluation must be robust against these disturbances to avoid false alarms. Due to the model uncertainties, the residual is affected by the known input signals, which are, in general, time varying. To achieve a threshold that is as tight to the residual as possible, the threshold should also depend on the known input signals. To make this possible, parametric uncertainty in the process model is considered in this thesis. The dynamic threshold generator is introduced, a dynamic system whose output is the threshold and the inputs are the known process inputs. A dynamic threshold generator is developed for full-state measurement systems, assuming that the residual disturbances are constant and unknown but bounded. This dynamic threshold generator is then generalized to non-full state measurement systems with time-varying but bounded residual disturbances. Both generators depend on the unknown upper bounds of the residual disturbances. These upper bounds are replaced by design parameters, which are determined by minimizing the threshold for a set of fault free data. A nonlinear optimization solution is discussed. It is also shown that the residual generator state vector can always be parameterized such that the designing of the parameters can be done by linear optimization. A part of the generalized dynamic threshold generator is a system whose impulse response is an upper bound to another impulse response. Automatic methods to find realizable upper bounds are derived. To validate the methods in this thesis, two applications have been considered, detection of clogging in the valves of a flotation process and detection of faults in the compressor inlet temperature sensor of a jet engine.
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| 37. |
- Beeri, Guy
(författare)
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Some mathematical, numerical and engineering aspects of composite structures and perforated solids
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this doctoral thesis in engineering mathematics we present some new modeling, numerical and engineering aspects and results concerning composite structures and perforated solids.The thesis consists of five papers, which are divided into three parts. Part A functions as an introduction where we look into some of the mathematical, numerical and engineering aspects of the effective in-plane elastic properties of periodic structures. We focus on one- and two-component composites and, in particular, we discuss locally anisotropic perforated structures. Moreover, we describe how the elastic properties of such and more general structures can be calculated. Finally, we present bounds and relations between different effective moduli.In Part B we study twelve of the simplest structures belonging to the class of one-component structures with holes and which, in addition, are three-fold rotational symmetric. We look into the effective elastic in-plane properties such as effective bulk and shear moduli and the so-called Vigdergauz constants. A comparative overview of all of these properties is given. Furthermore, we derive low-density asymptotics and present numerical data from finite element calculations. We also show that several of the studied structures have optimal elastic properties in the limit when the volume fraction of the connected material goes to zero. Finally, some remarks on the manufacturability of the structures are made.In Part C, which is divided into three papers, we continue to explore the effective properties of periodic structures. In paper [C1] we introduce a new model for estimating the elastic effective properties of regular hexagonal honeycombs. In contrast to previous cases, with this model we introduce a new formula, which match and complement the results obtained by Vigdergauz in 1999 in an essential way. Furthermore, by comparing some of the results with numerical finite element computations we find an improved formulae which enable us to estimate the effective properties with an accuracy better than one percent. In paper [C2] we study the effective elastic properties of regular triangular honeycombs. In particular, we obtain some simple approximate formulae for the corresponding Vigdergauz constants with accuracy better than one percent for all densities. In paper [C3] we study a scale of two-component composite structures of equal proportions with infinitely many microlevels. The structures are obtained recursively and we find that their effective conductivities are power means of the local conductivities.
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| 38. |
- Bengtsson, Fredrik
(författare)
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Algorithms for aggregate information extraction from sequences
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, we propose efficient algorithms for aggregate information extraction from sequences and multidimensional arrays. The algorithms proposed are applicable in several important areas, including large databases and DNA sequence segmentation. We first study the problem of efficiently computing, for a given range, the range-sum in a multidimensional array as well as computing the k maximum values, called the top-k values. We design two efficient data structures for these problems. For the range-sum problem, our structure supports fast update while preserving low complexity of range-sum query. The proposed top-k structure provides fast query computation in linear time proportional to the sum of the sizes of a two-dimensional query region. We also study the k maximum sum subsequences problem and develop several efficient algorithms. In this problem, the k subsegments of consecutive elements with largest sum are to be found. The segments can potentially overlap, which allows for a large number of possible candidate segments. Moreover, we design an optimal algorithm for ranking the k maximum sum subsequences. Our solution does not require the value of k to be known a priori. Furthermore, an optimal linear-time algorithm is developed for the maximum cover problem of finding k subsequences of consecutive elements of maximum total element sum.
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| 39. |
- Bergfors, Markus
(författare)
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Designing R&D organisations in process industry : essays on context, process, and structure
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis reports on a research project in R&D organisational design carried out at Promote - the Centre for Management of Innovation and Technology in Process Industry. The thesis itself consists of six appended papers and an extended summary covering the background of the project, the theoretical frameworks and methodologies used in studying R&D organisations in process industry, as well as a discussion of the research findings. This project aims at furthering the understanding of how intrafirm industrial R&D is organised in process industry through studying the context of innovation process industry and the organisation of innovation strategy formulation processes and intrafirm organisational structures for product and process innovation. The research project employed several different methodological approaches - including case studies in Swedish process industry firms, an industry wide survey, and a workshop survey consisting of a select group of R&D managers and industry experts. In studying the issue of context, a ranking of critical management of technology issues was composed through a survey of industry experts. The ranking proposes that the top issue is involvement of manufacturing in new product development and issues concerning integration of manufacturing in product development. Discrepancies concerning critical issues in regard to other manufacturing industries are also noted. In response to the issue of strategy formulation processes two opposing methodologies for innovation strategy formulation were studied. Findings from case studies suggest that the level of diversification, the characteristics of industry boundaries, customers, and competitors, and the role and organisation of R&D are key contingencies for choosing between innovation strategy processes either focusing on positions in the market or on internal resources. In response to the third question two different studies were carried out. One case study focuses on the centralisation versus decentralisation of product and process innovation. It suggests that a distinction between product and process innovation should be made and that the organisation of these depend on how the firm views these activities. The second study, an industry survey, looks closer at the organisational affiliation of process innovation. It determines that the degree of newness is a key determinant and that radical innovation will be organised in R&D while incremental innovation will be organised in production. Pros and cons concerning organisational choices are also discussed in light of these findings. Overall, the research project and the thesis stress the importance of context and how strategic choices should be reflected in the design of R&D organisations. Implications for management and academia are discussed and some avenues for further research are proposed.
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| 40. |
- Bergmark, Ulrika
(författare)
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Building an ethical learning community in schools
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of this thesis was to explore the school as a site for ethical practice. Specific objectives were to elucidate, encourage understanding for, and discuss: (i) teachers' and students' lived experience of ethical situations in school, (ii) teachers' and students' working together to promote learning in subjects and also to develop an ethical attitude towards society and the way people interact, and (iii) teachers' and students' working together to create an appreciative and positive climate in school. The research was conducted in a secondary school in Northern Sweden, which participated in a school improvement process, entitled Full of Value. The process has aimed at promoting learning through the development of an ethical attitude. This involves both the psycho-social and the physical community of the school.The research was inspired by life-world phenomenology. A total of 45 teachers and 45 students participated in the study. To create empirical data, the following methods have been used: written reflection, interview, close observation, and photo documentation. Through empirical findings during the research process, some parts of the research were inspired by participatory and appreciative action research (PAAR).The thesis consists of five part studies, published in international pedagogical journals. The findings show essential values for teachers and students in school, such as: openness, communication, trust, respect, care, empathy, truth, justice, appreciation, participation, and mutual learning.Teachers' and students' experiences of school as a site for ethical practice imply the value of: striving for ethical awareness, building ethical relationships, and encouraging ethical actions. The findings in this thesis suggest that the schools' mission to integrate ethics into the curriculum can be viewed as a process whereby, together with students in different educational settings, an ethical learning community can be created and sustained.
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