| 31. |
- Billstein, Mats
(författare)
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Influence of fractures and air bubbles on the pressure distribution embankment dams
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In some large embankment dams unexpected pore pressure distributions within the core have been observed. As an example, the piezometer pressures in WAC Bennett Dam, Canada, which rose for about four years after the reservoir was filled, were steady for two years and subsequently declined. One peak pressure head was as much as 60 m higher than the expected steady state pressure head of 40 m. However, the pressure head had dropped 55 m from the peak value 25 years later. Four hypotheses have already been proposed to explain the anomalous pore pressures within embankment dams. The objective of this study is to examine two of them, inhomogenities (e.g. fractures) in the core and trapped air bubbles, which can both be examined from a fluid mechanical point of view. The other two mechanisms, settlements and bleeding of fine material, must also be examined from a geotechnical aspect. This examination, based on results from two numerical models, is mainly theoretical. Results from numerical simulations of simplified homogeneous and inhomogeneous embankment dams are compared with analytical solutions and basic experiments. Results from numerical simulations, including the influence of air bubbles, are evaluated using a plug flow analysis and field measurements. A Hele-Shaw cell and a bed of packed glass beads, both a homogeneous and an inhomogeneous experimental set up, were used in the examination of how inhomogenities influence the pressure distribution. In the inhomogeneous case, a horizontal fracture extended from the upstream boundary to a point within the embankment. The fracture was shown to have a significant influence on the pressure distribution, discharge, seepage level, and free surface profile. The numerical model is based on a direct solution of the conservation equations (mass and momentum). In the numerical simulations, the flow resistance is determined from a laminar velocity profile in a slot with smooth walls (Hele-Shaw cell) and from the Forchheimer equation (bed of packed glass beads). The problem is considered to be two-dimensional. Since air bubbles are always initially present in the voids, that air is compressible, and that the amount of air that can go into solution increases with pressure, a mechanism that generates hydraulic blockage in the downstream part of the core can be anticipated. The blockage decreases the hydraulic conductivity in the flow direction resulting in a pressure increase. The numerical model for this case is based on a direct solution of the conservation equations (mass and momentum) and Darcy's, Boyle's, and Henry's law. It is a two-phase problem treated as one-dimensional. The main result of the study is the development of numerical models to simulate how inhomogenities and trapped air bubbles influence the pressure distribution. These models have a solid foundation, i.e. are based on conservation principles, physical laws, and the best available empirical relationships. The models have been validated through comparisons with analytical solutions, basic experiments, and field measurements and thus provide a good starting point in the development of tools that can be used in dam engineering.
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| 32. |
- Birk, Wolfgang
(författare)
-
Industry applications of multivariable control
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the face of environmental regulations, optimization of industrial processes becomes necessary. This doctoral thesis summarizes the results of three application-driven projects in automatic control that were aimed at process optimization in the steel industry. The objective of the projects was to apply advanced control strategies to two important processes in steel making, namely pulverized coal injection (PCI) in blast furnaces and LD converters. Firstly, an LQ multivariable controller with gas leakage detection system for PCI vessels is designed and analyzed. Secondly, a foam level control system for the LD converter process using an audio signal for measurement is designed. Thirdly, it is attempted to create a single line flow control system for PCI using a video camera. In the latter two cases the conservative approach of inferring unmeasurable physical quantities from the audio and video sources is used. Moreover, all the designs are tested through implementation or experiments at the industrial plant. The control and gas leakage detection system ended up as a full-scale industrial implementation, whereas the projects comprising audio and video information is still at an experimental stage. Work with implementation and experiments pays off in experiences and further insights in the application of control theory, and reveals weaknesses and gaps in the existing theory. Thus, application-driven projects lead to practical solutions and at the same time pose new theoretical challenges. Consequently, this chain of events is favorable to both practitioners and theoreticians, and in turn stimulates the collaboration of industry and academia. Unfortunately, in many research projects this sequence is reversed which complicates technology transfer into industry. As a spin-off effect from the multivariable control project of the PCI process two topics are addressed anew. In the problem of measurement/actuator pairs assignment for decentralized control, the geometrical background of Gramian-based interaction measures is clarified. It is shown that weighted Gramian-based interaction measures can be effectively used for control structure design. In control structure improvement of multivariable control systems, it is shown that improvement potentials can be deduced from coarse models of the closed-loop system. Finally, in the projects comprising audio and video signals in control applications, it is concluded that the theory is rather undeveloped and that these sources should be treated as a multivariable system.
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| 33. |
- Bodin, Anders
(författare)
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Improving the mobility performance of tracked vehicles in deep snow
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improving the mobility of tracked vehicles in deep snow requires an increase in the knowledge and understanding of the design parameters which influence the tractive performance. This relates particularly to the new vehicle requirements of increased payload to vehicle weight ratio, improved fuel economy and reduced life cycle costs. It has been the aim of the research presented in this thesis to improve the understanding of how different vehicle design parameters affect the tractive performance of tracked vehicles in deep snow. A new tracked vehicle was developed to enable experimental studies of different vehicle design parameters in deep snow. The vehicle was skid steered with a hydrostatic transmission and driven by a five-cylinder diesel engine. The vehicle design made it possible to vary several vehicle design parameters in the field, one at a time, without affecting the others. To be able to compare vehicle tests from different snow conditions and also to be able to simulate vehicle performance in snow, the strength properties of the snow are required. A bevameter was developed to characterise the pressure-sinkage relationship, the response to unloading- reloading and the shear stress-shear displacement of the snow. The idea of using the bevameter technique was to measure the terrain data under loading conditions similar to those encountered by an off-road vehicle. The bevameter developed consisted of a hydraulic cylinder with a piston of one metre stroke through the cylinder. A hydraulic motor with a planetary gear was attached to the upper end of the rod piston, which exerted the turning torque in the shear test. The cylinder exerted the normal force in both the pressure-sinkage and the shear test. The most important finding was that the drawbar pull strongly increased when the initial rear track angle was reduced. This was due to both an increased thrust between the tracks and the snow and to a reduced track motion resistance. The increased performance originated from a reduced load transfer from the last roadwheel to the others when the initial rear track angle was reduced. The tractive performance increased continuously with decreasing initial rear track angle. The tractive performance not only increased when the idler made contact with the snow, thus increasing the track contact length, but increased continuously with a decrease in the initial rear track angle prior to the idler contacting the snow. Another important finding was that the drawbar pull increased when the centre of gravity was moved forward, especially when the idler was in the elevated position. An increased belly ground clearance and a reduced initial angle of the vehicle belly both provided improved mobility performance of the vehicle. This was due to both increased thrust and reduced belly resistance, which in both cases, originated from a vertical load transfer from the rear of the belly to the tracks. The experimental tests of the influence of the initial rear track angle on the tractive performance were compared with corresponding simulations using the Nepean Tracked Vehicle Performance Model for Microsoft Windows, (NTVPMwin). The simulation also showed an increased drawbar pull when the initial rear track angle was reduced. However, there was difference in the absolute level of the drawbar pull with the simulation results showing a 6-10% higher drawbar pull.
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| 34. |
- Bodin, Ulf
(författare)
-
Quality issues in Internet packet forwarding
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses quality issues in Internet Protocol (IP) packet forwarding. In IP networks, queue mechanisms and scheduling can be used to construct multiple forwarding behaviors. Thereby, both relative and independent services can be offered to Internet users. Independent services offer forwarding qualities known beforehand. Users are assumed to explicitly request admission to an independent service from their network provider. With relative services, users switch between these services to find one that provides an appealing balance between forwarding quality and cost. The thesis makes contributions to three research areas related to forwarding quality in IP networks; differentiating forwarding mechanisms, admission control for differentiated services, and forwarding quality in radio networks carrying Internet traffic. It contributes to the first research area with definitions of three recommendations related to offering loss-rate differentiation (i.e., multiple drop precedence levels). These recommendations are; (1) the total forwarding quality at congested links should not be degraded due to actions taken to create loss-rate differentiation, (2) traffic at high drop precedence levels should always be given a useful share of available forwarding resources, and (3) users should be able to predict the change in loss-rates when switching between drop precedence levels. We specify and evaluate properties of queue mechanisms following these recommendations. Also, as a contribution to the first research area, a new set of forwarding behaviors is specified and analyzed. These forwarding behaviors are suitable for rate-adaptive and delay-sensitive applications with limited loss-tolerance. Applications needing loss-free forwarding of specific packets can be said to have limited loss tolerance. We define and evaluate a scheduling mechanism creating these forwarding behaviors that can be implemented efficiently. The contribution to the second research area is a mechanism for admission control giving assurances on loss-rates to rate varying applications is defined. With this mechanism, dynamic per-link admission thresholds are used to limit committed aggregate rates. To allow for high link utilization through statistical multiplexing we specify a method to adjust these thresholds using low impact traffic monitoring mechanisms commonly available in legacy routers. In radio networks carrying IP traffic, radio transmissions can be scheduled differently to balance spectrum utilization and the forwarding quality provided. Also, parameters settings can be used to optimize the forwarding quality in radio networks for certain transport protocols and applications. This thesis analyses delay spikes experienced by IP traffic in cellular radio networks. We evaluate two different radio-block scheduling mechanisms’ impact on two versions of the Transmission Control Protocol (TCP) (i.e., TCP Sack and TCP Eifel). The evaluation contributes to the third research area by revealing basic dependencies between scheduling, interference, and congestion control mechanisms implemented by TCP. Finally, the thesis contributes to the third research area by proposing extensions to the Internet architecture for inter-layer communication. These extensions allow applications and transport protocols to exchange information with radio link layers. Such information exchange can be used to improve the forwarding quality and to customize data and transport features for current radio conditions.
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| 35. |
- Brekke, Mary
(författare)
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Lærerutdanning i nord : et historisk kasus gjennom tre tidsperioder
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Avhandlingen beskriver den historiske utviklingen av lærerutdanningen, med spesiell vekt på lærerutdanningsdidaktikk, ved en spesiell utdanningsinstitusjon i Nord-Norge i perioden 1826-1940. Studien er i hovedsak basert på arkivdokumenter som kildemateriale. Det studerte kasus er den eldste statlige lærerinstitusjonen i Norge. Som andrehåndskilder er brukt historisk forskning om norsk seminar-/lærerutdanning og norsk allmue-/folkeskole. Samtidige lærebøker og håndbøker, aviser og fagtidsskrift for lærere er brukt som supplerende kilder. Studien er delt inn i tre tidsperioder; 1826-1848, 1848-1902 og 1902-1940. Inndelingen er gjort på bakgrunn av sentrale hendelser, enten i institusjonens historie eller i nasjonal lærerutdanningshistorie, avhengig av hva som brakte de viktigste didaktiske endringene. Studien er gjort så induktiv som mulig. Funnene er derfor satt inn i en teoretisk ramme først mot slutten av avhandlingen. De teoretiske begrep som er benyttet er hentet fra didaktisk og sosiologisk teori. Selv om tilnærmingen er induktive, er det likevel foretatt en kontinuerlig tekst- og kildeanalyse med tilhørende tolkninger i forbindelse med kildearbeidet, datainnsamlingen og funnene underveis i studien. Studien viser at den lærerutdanningsdidaktiske utvikling har gått gjennom en stille revolusjon, fra en pedagogisk kode dominert av lærer, fag, kirke, kristne normer og strenge regler for atferd til en mer usynlig didaktisk/pedagogisk kode. Samtidig har utdanningen bevart sentrale grunnverdier, slik som troen på metodeoverføring, lærerutdanneren som yrkesmodell og praksiserfaringer som grunnleggende for danningen til lærer.
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| 36. |
- Broman, Olof
(författare)
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Means to measure the aesthetic properties of wood
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood is a biological material with inherent aesthetic properties which can give the final product a competitive advantage over other materials. In this thesis, people’s feelings and preferences for Scots pine (Pinus sylvestris) wood surfaces have been examined. The main objectives of this thesis are to develop methods for measuring people’s preferences toward different looks of wood and to connect the subjective preference data with objective measurements of wood features. It comprises both qualitative and quantitative methods for collecting preference data. Two projection methods, PCA and PLS, were used to analyze the quantitative studies. Interviews made clear that people prefer different blends of wood features. There are two qualitative differences that are of importance for people's impressions and valuations of wood: The overall blend of wood features and divergent features that mismatch in a surface. It was found that divergent features are more important than the overall mixture of features. But if there are no defects that mismatch, the overall mixture will then be the key to a person's appreciation of a wood surface. Wood surfaces should stimulate people's interest and be fresh looking. A clear surface is naturally rather harmonious, elegant and easy to look at. On the other hand, a clear surface should be stimulating to look at, should be exciting and it should not look like an imitation. Knotty surfaces usually are less harmonious. Therefore, questions about harmony, easiness to look at and balance are of importance. Just as for clear surfaces, a knotty surface should also stimulate people's interest, have a fresh look, be exciting and stimulating to look at. The quantitative studies show that it is possible to measure people’s preferences toward wood by a questionnaire technique. The results also show that there are differences in people’s judgments for surfaces with knots and for those without knots. There are stronger connections between questions regarding the overall impression and the final assessment than there are for detailed questions regarding certain wood features. Thirteen questions were pointed out as relevant to use with interviews. Two interview methods were compared. The first method used wood surfaces and the second used computer images with the same wood surfaces applied to an example product, a kitchen cabinet. The results show that the two methods are comparable and useful. It was shown that it is possible to some extent to connect subjective preference data with objective wood feature measurements. Results show that a lot of wood feature measurements are needed and that it is a multivariate problem. Concerning the measurements, it seems easier to find features that negatively affect people’s liking than to find the opposite. Among the most important variables were those that detect different kinds of feature distribution over a wood surface, and especially those variables that detect a deviation in center of gravity. Increased knowledge about people’s preferences for the aesthetic properties of wood will lead to a better understanding of which wood features should be measured and controlled in the future.
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| 37. |
- Brännström, Oskar
(författare)
-
Market offer development : industrial experiences in a business-to-business context
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A company’s competitive advantage is best understood in its ability to fill its relationships with a unique and meaningful value. Especially in business-to-business relationships value is complex and abstract, so complex that the product alone is not a meaningful representation of that value. Rather, the complete set of values represented by the company’s market offer needs to be considered. A market offer could be seen as the carrier of all values in a relationship. It contains both products and services but its essence is far more complex and multi dimensional than simply the combination thereof. While marketing scholars especially within the fields of service and relationship marketing have discussed the need for new or alternative product constructs, or conceptualisations, to embody this set of values, they have not addressed the issue from the point of view of actually develop a market offer. And while scholars within the field of product development research have been concerned with understanding how to practically manage product development – also presenting a number of best practice models – they have been limited by the context of the product as a physical artefact. There is an apparent gap between these two fields of research. Drawing on the knowledge on both these fields this work contributes to the filling of this gap by means of answering two main research questions: 1. How can a market offer be conceptualised to support its development? 2. What constitutes a market offer development process? In addition this work has also addressed how the product as such is affected by being part of larger solution and examined the possibility of expanding the product platform concept to include the complete market offer. To answer these questions four studies have been carried out during a period of three and a half years between April 2000 and June 2003. The first was an explorative survey covering 8 companies with the purpose of sharpening the problem formulation and to get a broad industrial view of the problem area. The second was a case study where the phenomenon was studied more in-depth based on the models of the first study. On this followed two participative studies at two different companies, each for a period of six months. In both these studies I was a fully participating member of a project team. On the second occasion, I also initiated the project and had a coordinating function. Both research questions have been answered by means of different models. Each model is a graphical framework with a description. These models are also verified in practice by means of implementation in the final participating research project. On research question one an important finding is that the current conceptualisation, made from a marketing perspective, is not detailed enough to support the management of developing market offers. Instead a model with three layers has been developed. These three layers are: the product & service layer; the business solutions layer; and the customer interaction layer. Between these layers different types of relationships have been identified. On research question two this project presents the first description of a market offer development process and clarify its relationship to currently published product as well as service development processes. Verifying findings of current marketing research it is found to be a continuous process rather than a process with a clearly defined start or end. It is found to be the continuous management of: the customer portfolio; products and services; commercial logic and business solutions; customer interaction; the resource structure; internal marketing efforts to facilitate internal change and overcome political and cultural boundaries; business analysis and follow-up to ensure profitability.
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| 38. |
- Burman, Jörgen
(författare)
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Geometry parameterisation and response surface-based shape optimisation of aero-engine compressors
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main goal in jet engine design is to achieve light, compact and highly efficient systems while reducing the cost and design times. Traditionally, the design has been based on trial-and-error procedures, which count on the skills and experience of the designer to suggest design improvements. In step with recent advances in efficient and robust computational algorithms and the fast development in computer resources, computational fluid dynamics (CFD) has matured to a stage where it provides substantial insight into the physical processes involved in engineering flows. The CFD solvers do, however, not indicate which geometry modifications are required to improve performance. Even if it is possible to investigate a very large number of design alternatives it is difficult to find the optimum only by trial-and- error and it can also be very time consuming. The search for an improved design can be aided by the integration of a numerical optimisation algorithm with the CFD code. Before this can be done several decisions have to be taken. The first is how to make a parameterisation of the geometry to describe allowable shape variations in the design. The second decision is to define problem constraints. Finally, the performance parameters to be used in the definition of the objective function have to be identified. The main objective of this work has been to develop and implement methods for shape optimisation of compressor blades. A large part of the work has been devoted to the development of a compressor blade design system. The geometry description is based on Non-Uniform Rational B-Splines (NURBS), which are used by modern computer aided design tools and have suitable mathematical properties for parameterisation of fluid flow domains. The problem with the NURBS parameters is that they do not coincide with the traditional design parameters used by the aerospace engineers. However, keeping the traditional parameters as design variables will help the designer to chose fewer but more relevant design parameters for the problem. A separate optimisation algorithm has thus been integrated in the blade design system to optimise the NURBS parameters to achieve the desired traditional design parameters, also called implicit design parameters. A second method to reduce the total number of design parameters is to introduce B-spline mapping curves that interpolates shape modifications of a starting blade in the spanwise (radial) direction. This method allows the designer to arbitrary select the number of degrees of freedom depending on his/her needs. The blade design system has been used to optimise a compressor blade geometry via construction of response surface approximations. Optimisation both with and without implicit design variables has shown that using implicit design variables can substantially reduce the number of CFD simulations. The response surface method has shown to be efficient in filtering numerical noise intrinsic to the numerical data produced by the CFD code. The method is also capable of handling multi-criterion optimisation problems in a straightforward manner by building a composite response surface from individual response surfaces.
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| 39. |
- Bylund, Nicklas
(författare)
-
Simulation driven product development applied to car body design
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the development of complex mechanical structures, from concept to detail design, as applied to car bodies. Efforts have been made to clarify how computer tools and analysis methods are used in product development in industry today. It has been found that the design and the analysis activities are separated, leading to product development that is simulation-verified rather than simulation-driven. This calls for better integration of computer support and analysis in the development process. Based on the above findings, a framework for car bodies is proposed, extending from concept to detail design. A property based model (PBM)/concept model, consisting of the following three sub- systems: beams, joints and panels, has been made to break down the requirements to sub-system level according to the design areas of the design engineers. Analysis tools have been developed and implemented, tailor-made according to the requirements at sub-system level. It has been shown that by providing design engineers with requirements according to their design area, and with corresponding analysis tools, it is possible for the design engineer to do preliminary analysis on their design in parallel with their normal design activity, leaving complete-vehicle a posteori simulation to the analysis experts. This increases the use of simulation in product development so that more solution alternatives are evaluated, leading to better design. The findings are corroborated by industrial studies, both at pilot level and full-scale. The implementation of simulation-driven design by designers is ongoing and increasing in projects at VCC. The implementation of the framework and tools has resulted in depended knowledge regarding interaction with industry and a contribution regarding how improvement of product development can be made.
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| 40. |
- Byström, Johan
(författare)
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Some mathematical and engineering aspects of the homogenization theory
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to some problems connected to the theory of homogenization of partial differential operators. The thesis consists of an elementary introduction and five different parts, A-E. In the introduction we give an elementary presentation of the basic ideas in the homogenization theory. Moreover, the introduction also serves as an overview of the field and points out where the results contained in this thesis fit in. The first part, Part A, consists of two papers with a complementary appendix and deals some purely theoretical parts of homogenization theory. Part B consists of one paper dealing with bounds of the homogenized operator. The third part, Part C, consists of two papers concerning some computational aspects of homogenization. Part D consists of two papers which show how the theoretical results from the homogenization theory can be practically used in composites engineering. Finally, Part E consists of two papers presented at international conferences, which consider some further mathematical and engineering aspects of the homogenization method.
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