| 1. |
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| 2. |
- Duru, Kenneth, 1975-
(författare)
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Perfectly Matched Layers and High Order Difference Methods for Wave Equations
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The perfectly matched layer (PML) is a novel technique to simulate the absorption of waves in unbounded domains. The underlying equations are often a system of second order hyperbolic partial differential equations. In the numerical treatment, second order systems are often rewritten and solved as first order systems. There are several benefits with solving the equations in second order formulation, though. However, while the theory and numerical methods for first order hyperbolic systems are well developed, numerical techniques to solve second order hyperbolic systems are less complete.We construct a strongly well-posed PML for second order systems in two space dimensions, focusing on the equations of linear elasto-dynamics. In the continuous setting, the stability of both first order and second order formulations are linearly equivalent. We have found that if the so-called geometric stability condition is violated, approximating the first order PML with standard central differences leads to a high frequency instability at most resolutions. In the second order setting growth occurs only if growing modes are well resolved. We determine the number of grid points that can be used in the PML to ensure a discretely stable PML, for several anisotropic elastic materials.We study the stability of the PML for problems where physical boundaries are important. First, we consider the PML in a waveguide governed by the scalar wave equation. To ensure the accuracy and the stability of the discrete PML, we derived a set of equivalent boundary conditions. Second, we consider the PML for second order symmetric hyperbolic systems on a half-plane. For a class of stable boundary conditions, we derive transformed boundary conditions and prove the stability of the corresponding half-plane problem. Third, we extend the stability analysis to rectangular elastic waveguides, and demonstrate the stability of the discrete PML.Building on high order summation-by-parts operators, we derive high order accurate and strictly stable finite difference approximations for second order time-dependent hyperbolic systems on bounded domains. Natural and mixed boundary conditions are imposed weakly using the simultaneous approximation term method. Dirichlet boundary conditions are imposed strongly by injection. By constructing continuous strict energy estimates and analogous discrete strict energy estimates, we prove strict stability.
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| 3. |
- Dahlström, Karin
(författare)
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Värdeskapande produktutveckling i tjänsteintensiva företag : en kvalitativ och vardagsorienterad studie om produktutvecklingsarbete i en era när kunder i allt högre grad betalar för ogripbara, men ändå högst förnimbara och värdeskapande, aspekter
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Kunder betalar i allt högre grad för ogripbara, men ändå högst förnimbara och värdeskapande, aspekter. Viktiga sådana aspekter är tjänster och service, men även aspekter av sinnlig, emotionell, ekonomisk, upplevelsemässig, etisk, estetisk, miljömässig, kvalitetsmässig, identitetsstärkande, social och kulturell karaktär. Denna avhandling handlar om produktutvecklingsarbete i tjänsteintensiva företag där utveckling av sådana ogripbara och immateriella aspekter är en väsentlig del av arbetet. I avhandlingen lyfts värdeskapande produktutveckling fram som ett arbete som handlar om att generera produkt- och konceptidéer, formge och utveckla koncept och produkter bestående av tjänstedimensioner och fysiska produktdimensioner och andra värdeskapande dimensioner, samt att integrera dessa med företagets värdeskapande produktplattform. Målet är att ”helheten” skall upplevas som sömlös och värdeskapande i kunders sinnen, hjärnor och hjärtan. Begreppen produkt, erbjudande, produkterbjudande och kunderbjudande används synonymt. Även tjänster och service används synonymt och ses som en delmängd av produkt- och produktplattformsbegreppen. Avhandlingens syfte är att belysa, beskriva, tolka och reflektera kring produktutveckling i tjänsteintensiva företag. Teoretiskt och empiriskt underlag kommer från; litteraturstudier, fallstudier utförda i antropologisk fältstudiemetodanda, förförståelse för arbetsmiljön, samt egna vardagslivserfarenheter. Fältarbetet genomfördes under månader av vardaglig närvaro på Vingresor (resor) och Scandinavia Online (internet). Tre forskningsfrågor har väglett arbetet: • Hur går det till att utveckla värdeskapande produkter i tjänsteintensiva företag? • Vad är det egentligen för värdeskapande produkter och produktdimensioner som utvecklas? • Med fokus på aktörer, kunskap och meningar: Vilka deltar i produktutvecklingsarbetet? Avhandlingen söker ge en djup empirisk belysning av vardagens produktutvecklingsarbete i två tjänsteintensiva branscher som är föga studerade när det gäller produkt- och tjänsteutvecklingsarbete. Arbetet framträder som ett mångfasetterat och komplext arbete med mål att utveckla en ”helhet” som kommer att upplevas som värdeskapande och sömlös i kunders sinnen, hjärnor och hjärtan. Det diskuteras att kunder är de aktörer som har mandat att bestämma huruvida ett företags produkter är mer eller mindre värdeskapande och kunder fattar sina värderingsbeslut i vardagliga ”här-och-nu-stunder” utifrån hur de upplever sina interaktioner med företagets värdeskapande manifestationer. Sådana interaktioner uppstår och pågår både före och under köp likväl som före, under och efter användning av produkten. Avhandlingen lyfter även fram förmågan att integrera och samordna de många involverade aktörernas kunskaper, meningar och handlingar som en väsentlig aspekt i vardagens utvecklingsarbete. Ytterligare ett bidrag är fokuseringen av en mängd socialt konstruerade polariseringar som tycks frodas väl i tjänsteföretags produktutvecklingsmiljöer.
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| 4. |
- Mattsson, Hans-Åke, 1959-
(författare)
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Integrated Bridge Maintenance : Evaluation of a pilot project and future perspectives
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The trend in many countries is to outsource maintenance with competitive tendering. The design of the tender is then a crucial issue. A new type of tendering contract, called "Integrated Bridge Maintenance", was introduced in one experimental area in Sweden. In this case the preventive bridge maintenance is separated from the standard road maintenance contract. The ideas behind these changes are that the new approach can increase efficiency through a combination of increased specialization, economies of scale and through giving the private contractor a greater degree of freedom concerning exactly what to do and exactly when to do it. A pilot project has been running since 2004 for all bridges in Uppsala County with about 400 bridges and since 2007 for all bridges in Örebro County with about 700 bridges. The experiences and lessons from this pilot project are presented in this thesis together with guidelines on how to procure Integrated Bridge Maintenance in the future. An important feature of the contract was that it contained a combination of specific measures that the contractor should carry out and properties of the bridges that the contractor was responsible to maintain. This created a balance between predictability and flexibility for the contractor. The contractor could make long term planning for the work. The client was satisfied because of increased competence and a low price. The latter can partly be explained by the possibility for the specialised bridge crew to receive additional work from other clients. As information about old bridges always is incomplete a partnering structure needs to be built into the contract. Experience has also shown that a conscious policy to maintain long run competition is important. The general conclusion is that the project was seen as successful and as creating more "value for money". To manage a bridge stock optimally from a life cycle perspective is a very complex task, since the conditions for the individual bridge can vary greatly from place to place which the answers from the research questions indicate. Besides following-up and evaluating the Integrated Bridge Maintenance projects a number of research questions have been studied. Is Integrated Bridge Maintenance a successful method to increase the effectiveness and to increase the standard in bridge maintenance alternatively increasing the service life for the bridge stock at an optimal cost, i.e., will IBM lead to lower LCC? It is difficult to answer this question with exact numbers after so short time, but so far the opinion is that the effectiveness has increased. How can a bridge stock develop over a long time e.g. 15 years? Based on historical data one can calculate, for instance, new construction rate, demolition rate and average age for the bridge stock. This information could together with different future scenarios be a basis for different bridge management strategies for the actual bridge stock. What is the real service life for a bridge? Survival analysis for the different types of bridges in the actual bridge stock will give a good estimate of the different expected service life. Why and at which age are bridges demolished? Two main reasons were found in this study: deterioration process of the bridge had gone too far and/or load bearing capacity was too low, and road were rerouted. What is the real service life for a bridge edge beam, one of the most often repaired element of Swedish bridges? Survival analysis of edge beams located on different types of roads will give a good estimate of the different expected service life. How should a long-term contract for bridge maintenance and specially Integrated Bridge Maintenance be procured? The bridge manager should have a good understanding of the answers on the research questions above when the tender documents are to be prepared for the actual bridge stock. Thereafter the area that the contract should cover could be chosen, a good balance between properties and measures, defining the working cycle for properties, a flexible partnering structure in the contract and a suitable length of the contract (x years) inclusive an option (+ y years) and finally good incentives in the contract. To sum up, the main purpose with the doctoral project has been reached. A model for procurement of bridge maintenance has been developed; see the projects in Uppsala and Örebro. The contractor has developed more effective methods for bridge maintenance. The doctoral project has been a step closer to the end goal of reducing the society’s costs for bridge maintenance in the future. The bridges should be functional to the lowest possible cost during its expected service life (LCC). The doctoral project has also contributed with new knowledge in the area of bridge maintenance, the actual development of a bridge stock over time, real service life for road bridges in Sweden and survival analysis.
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| 5. |
- Mattsson, Ken, 1970-
(författare)
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Summation-by-Parts Operators for High Order Finite Difference Methods
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High order accurate finite difference methods for hyperbolic and parabolic initial boundary value problems (IBVPs) are considered. Particular focus is on time dependent wave propagating problems in complex domains. Typical applications are acoustic and electromagnetic wave propagation and fluid dynamics. To solve such problems efficiently a strictly stable, high order accurate method is required.Our recipe to obtain such schemes is to: i) Approximate the (first and second) derivatives of the IBVPs with central finite difference operators, that satisfy a summation by parts (SBP) formula. ii) Use specific procedures for implementation of boundary conditions, that preserve the SBP property. iii) Add artificial dissipation. iv) Employ a multi block structure.Stable schemes for weakly nonlinear IBVPs require artificial dissipation to absorb the energy of the unresolved modes. This led to the construction of accurate and efficient artificial dissipation operators of SBP type, that preserve the energy and error estimate of the original problem.To solve problems on complex geometries, the computational domain is broken up into a number of smooth and structured meshes, in a multi block fashion. A stable and high order accurate approximation is obtained by discretizing each subdomain using SBP operators and using the Simultaneous Approximation Term (SAT) procedure for both the (external) boundary and the (internal) interface conditions.Steady and transient aerodynamic calculations around an airfoil were performed, where the first derivative SBP operators and the new artificial dissipation operators were combined to construct high order accurate upwind schemes. The computations showed that for time dependent problems and fine structures, high order methods are necessary to accurately compute the solution, on reasonably fine grids.The construction of high order accurate SBP operators for the second derivative is one of the considerations in this thesis. It was shown that the second derivative operators could be closed with two order less accuracy at the boundaries and still yield design order of accuracy, if an energy estimate could be obtained.
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| 6. |
- Do, Tan Manh
(författare)
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Excess pore water pressure generation in crushed and fine granular materials under cyclic traffic loads
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Excess pore water pressure can develop in subgrades of railway and pavement substructures due to cyclic loading from heavy traffic, leading to the migration of fine particles into upper layers. This migration can clog pores and diminish the drainage capacity of upper layers,negatively impacting the long-term performance of sub-structures and service life, ultimately risking failure. Therefore, understanding the mechanisms behind the accumulation of excess pore water pressures and the migration of fine particles under cyclic loading is essential for efficient and cost-effective maintenance methods. The main objectives of this research include (1) investigating excess pore water pressure generation in crushed and fine granular materials under cyclic loading, (2) evaluating the migration of these materials into upper layers under cyclic loading, and (3) simulating a practical application using an advanced model to provide valuable insights into the operation of structures subjected to cyclic traffic loads while considering real-world factors from the field.A series of cyclic triaxial tests were conducted to investigate the generation of excess pore water pressure in fine granular materials. Two types of fine granular materials, tailings (a crushed material) and railway sand (a fine granular material) were selected for this investigation. The cyclic characteristics of these materials, including cyclic axial strain and excess pore water pressure, were evaluated in terms of number of cycles and applied cyclics tress ratios (CSR). As a result, the cyclic axial strain and excess pore water pressure were observed to accumulate over time due to cyclic loading. However, the extent of accumulation was found to be significantly dependent on CSR values and material types. In addition, a relationship between excess pore water pressure and cyclic axial strain of the fine granular materials was established and proposed based on the results from the undrained cyclic triaxial tests (including both tailings and railway sand samples).To assess the migration of fine granular materials into overlying layers under cyclic loading, a modified large-scale triaxial system was employed as a physical model test. A quantitative analysis of material migration was based on the mass percentage and grain size of migrated materials collected at the gravel layer. Additionally, cyclic responses (strain and excess pore water pressure) were evaluated. As a result, the total migration rate of the tailing sample was significantly higher than that of the railway sand sample. The migration analysis on tailings also revealed that finer tailings particles exhibited a greater tendency to migrate into the upper gravel layer compared to coarser tailings particles under cyclic loading. This migration could be attributed to significant increases in excess pore water pressure during the final cycles of the physical model test. The findings from this research could make a valuable contribution to the existing literature concerning the accumulation of excess pore water pressure and its effects on the migration of fine particles under cyclic loading.A numerical study was conducted to simulate the complex interactions between tailings materials and cyclic traffic loads on the piers of tailings dams. The integration of experimental data and advanced constitutive models enabled a comprehensive understanding of the behavior of tailings under these loading conditions. The findings focused on the build-up of excess pore water pressures in tailings subjected to cyclic traffic loads while taking into account the effects of truck loads, velocities, and truck resting times. As a result, excess pore water pressures in tailings progressively increased with the number of passing trucks, indicating a cumulative effect of loading cycles. In addition, the effect of truck loads and truck velocities on the excess pore pressure build-up was discovered, with higher truck loads and lower truck velocities leading to increased excess pore pressures, posing a greater risk. Furthermore, through anoptimization process involving variations in truck loads, velocities, and resting times, it was revealed that a combination of increased truck velocity, reduced truck load, and extended truck resting time could effectively minimize the build-up of excess pore water pressures in tailings beneath the pier. These findings offer valuable guidance for optimizing transportation operations on tailings dam piers, enhancing efficiency and safety.
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| 7. |
- Kellgren, Jan, 1967-
(författare)
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Mål och metoder vid tolkning av skattelag : Med särskild inriktning på användning av förarbeten
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis is the interpretation of tax legislation, particularly the use ofpreparatory works. The purpose of the thesis is to devise appropriate principles for theinterpretation of tax legislation in general and principles for the use of preparatoryworks in particular.The author discusses the different goals involved in interpreting tax legislation, such as achieving predictability, uniformity and facilitating reasonable courtdecisions. In this context, the effect. of the EC-membership on the use of Swedishpreparatory works in the interpretation of tax legislation is analysed.Subsequently, the use of preparatory works in the interpretation of tax legislationin the Swedish Supreme Administrative Court is examined, from the viewpoint of thegoals for the interpretation of tax legislation.Thereafter, the author discusses German doctrine on the sources of law and theuse of preparatory works in the highest German court of law for tax cases (Bundes-finanzhof). The focus is put on the question of whether any of the distinctive featuresof the German doctrine on the sources of law could contribute toattaining the goals ofthe interpretation of Swedish tax legislation.In the last chapter, the prerequisites of putting forward principles for theinterpretation of tax legislation are discussed and a proposal for an overall structurefor the interpretation of tax legislation is presented. This structure is based on analysisat two different levels. The first level consists of a prima facie analysis of basicprinciples governing the interpretation of tax legislation. The result of the prima facieanalysis is supplemented and tested against the goals of the interpretation of taxlegislation.
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| 8. |
- Ljungberg, Anders, 1964-
(författare)
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Lokal kollektivtrafik på samhällsekonomisk grundval
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Förutom i Stockholm uppvisar den lokala kollektivtrafiken en nedåtgående trend i trafikutvecklingen, trots en årlig subvention om 10 miljarder kronor. Drift av lokal kollektivtrafik i mindre och medelstora städer baserat på samhällsekonomiska kriterier skulle bl a medföra en prispolitik som kräver en subvention om drygt 50%. Att detta ungefär motsvarar rådande subventioneringsgrad är dock inte ett tecken på att kollektivtrafiken bedrivs på samhällsekonomisk grundval, eftersom det visar sig att prisstrukturen är grovt suboptimal. Vad gäller investeringspolitik framgår det dessutom av en enkätundersökning att trafikhuvudmännen inte använder samhällsekonomisk kalkyl (CBA) vid planering och drift av lokal kollektivtrafik, så syftet med avhandlingen är att visa på de möjligheter till förbättringar av den lokala kollektivtrafiken som skulle uppstå om den bedrevs på samhällsekonomisk grundval.Operationaliseringen av teorin kräver först att några grundfrågor för en tillämpning av allmän välfärdsekonomisk teori på bedrivande av lokal kollektivtrafik benas upp. Det är väsentligt att göra en åtskillnad av utbudet av kollektiva transporttjänster mellan ett grundläggande utbud som är att betrakta som ”merit goods” och övrigt utbud där nyttan på normalt sätt mäts genom konsumenternas betalningsvilja.I en omfattande fallstudie av den lokala kollektivtrafiken i Linköping exemplifieras vad effekten blir, dels av vissa utbudsförändringar, som har sållats fram i strävan mot systemoptimum, dels av ändamålsenlig efterfrågestyrning, och med CBA beräknas vad nettoresultatet kan tänkas bli. Om förbättringar som ger lika stor nettonytta som i Linköping kan göras hos flertalet andra trafikhuvudmän med en samhällsekonomisk ansats, skulle den totala nettonyttan aggregerad över hela Sverige vara betydligt större än vad vissa av de omskrivna jätteprojekten inom kollektivtrafiksektorn kan prestera.
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| 9. |
- Lättman, Håkan, 1958-
(författare)
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Studies on spatial and temporal distributions of epiphytic lichens
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lichens are an important group of organisms in terms of environmental issues, conservation biology and biodiversity, principally due to their sensitivity to changes in their environment. Therefore it is important that we develop our understanding of the factors that affect lichen distribution. In this thesis, both spatial and temporal distributions of epiphytic lichens at different scales have been studied in southern Sweden.Generation time of the red-listed lichen Cliostomum corrugatum was examined using Bjärka-Säby as the study site. The results showed that the average age of an individual of C. corrugatum is 25–30 years at the onset of spore production.The rarity of C. corrugatum was also examined. DNA analysis of an intron from 85 samples, collected at five sites in Östergötland, yielded 11 haplotypes. Results from coalescent analysis, mantel test and AMOVA indicated that C. corrugatum have a high ability to disperse. The study concluded that its rarity is most likely connected with the low amount of available habitat, old Quercus robur.The changes in the distribution of epiphytic lichens in southern Sweden, between 1986 and 2003, were also compared. For each year a centroid was calculated on all combinations of tree and lichen species. The three significant cases showed that the centroid movement pointed toward a north-east or north-north-east direction.Finally differences in species richness and cover of lichens on large Q. robur were examined between urban and rural environment. The results demonstrated that species number and percent cover was significantly higher on oaks standing rural compared to oaks standing urban. Effects of urban sprawl showed a decline in species richness and cover with increasing age of the surrounding buildings.
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| 10. |
- Peterson, Anders, 1976-
(författare)
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The Origin-Destination Matrix Estimation Problem : Analysis and Computations
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For most kind of analyses in the field of traffic planning, there is a need for origin--destination (OD) matrices, which specify the travel demands between the origin and destination nodes in the network. This thesis concerns the OD-matrix estimation problem, that is, the calculation of OD-matrices using observed link flows. Both time-independent and time-dependent models are considered, and we also study the placement of link flow detectors.Many methods have been suggested for OD-matrix estimation in time-independent models, which describe an average traffic situation. We assume a user equilibrium to hold for the link flows in the network and recognize a bilevel structure of the estimation problem. A descent heuristic is proposed, in which special attention is given to the issue of calculating the change of a link flow with respect to a change of the travel demand in a certain pair of origin and destination nodes.When a time-dimension is considered, the estimation problem becomes more complex. Besides the problem of distributing the travel demand onto routes, the flow propagation in time and space must also be handled. The time-dependent OD-matrix estimation problem is the subject for two studies. The first is a case study, where the conventional estimation technique is improved through introducing pre-adjustment schemes, which exploit the structure of the information contained in the OD-matrix and the link flow observations. In the second study, an algorithm for time-independent estimation is extended to the time-dependent case and tested for a network from Stockholm, Sweden.Finally, we study the underlying problem of finding those links where traffic flow observations are to be performed, in order to ensure the best possible quality of the estimated OD-matrix. There are different ways of quantifying a common goal to cover as much traffic as possible, and we create an experimental framework in which they can be evaluated. Presupposing that consistent flow observations from all the links in the network yields the best estimate of the OD-matrix, the lack of observations from some links results in a relaxation of the estimation problem, and a poorer estimate. We formulate the problem to place link flow detectors as to achieve the least relaxation with a limited number of detectors.
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