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  • 121201. Åström, Mats E.
    et al.
    Österholm, Peter
    Gustafsson, Jon Petter
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Nystrand, Miriam
    Peltola, Pasi
    Nordmyr, Linda
    Boman, Anton
    Attenuation of rare earth elements in a boreal estuary2012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 96, p. 105-119Article in journal (Refereed)
    Abstract [en]

    This study focuses on attenuation of rare earth elements (REE) when a boreal creek, acidified and loaded with REE and other metals as a result of wetland drainage, empties into a brackish-water estuary (salinity < 6 parts per thousand). Surface water was collected in a transect from the creek mouth to the outer estuary, and settling (particulate) material in sediment traps moored at selected locations in the estuary. Ultrafiltration, high-resolution ICP-MS and modeling were applied on the waters, and a variety of chemical reagents were used to extract metals from the settling material. Aluminium, Fe and REE transported by the acidic creek were extensively removed in the inner/central estuary where the acidic water was neutralised, whereas Mn was relatively persistent in solution and thus redistributed to particles and deposited further down the estuary. The REE removal was caused by several contemporary mechanisms: co-precipitation with oxyhydroxides (mainly Al but also Fe), complexation with flocculating humic substances and sorption to suspended particles. Down estuary the dissolved REE pool, remaining after removal, was fractionated: the < 1 kDa pool became depleted in the middle REE and the colloidal (0.45 mu m-1 kDa) pool depleted in the middle and heavy REE. This fractionation was controlled by the removal process, such that those REE with highest affinity for the settling particles became most depleted in the remaining dissolved pool. Modeling, based on Visual MINTEQ version 3.0 and the Stockholm Humic Model after revision and updating, predicted that the dissolved (< 0.45 mu m) REE pool in the estuary is bound almost entirely to humic substances. Acid sulphate soils, the source of the REE and other metals in the creek water, are widespread on coastal plains worldwide and therefore the REE attenuation patterns and mechanisms identified in the studied estuary are relevant for recognition of similar geochemical processes and conditions in a variety of coastal locations.

  • 121202.
    Åström, Oskar
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    House of Darkness2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To go straight to the point the theme of this thesis is about darkness and shadows. To be more precise the study aims to explore how they can be created and manipulated, and find ways to work with them in a building. For the purpose of applying these findings I have designed what I call a “House of Darkness”; a building that gives the visitor an architectural experience of the dark. The thesis question that follows is: How can geometry and light sources be utilised in the creation of a murky interior world of shadows that makes use of the rich associative character of darkness? 

    The project works with two modes of darkness; abstract interiors that deal more physically with light and shadow and those which play with the associative qualities of that. This division is visible in the two series of study models, and the two types of interiors of the building. In summary the aim of this thesis project has not only been to create the physical effect of darkness and shadows, but to make use of some of their associative richness to create suggestive interiors.

  • 121203.
    Åström, Oskar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Fröderberg, Max
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Kv. Draken: En studie i kostnadseffektivt byggande2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The housing policy conducted over the past two decades has resulted in an increasingly segregated city center in Stockholm. The abolishment of housing subsidies in the 90s led to a historic low rate of construction and an urban development unilaterally directed towards the wealthy.

    Parallel to this, much of the housing stock has been converted to condominiums which caused many relatively cheap rental apartments in older buildings to disappear from the stock. These are difficult to replace with new housing, as they are more expensive.

    The core issue is of course that it is expensive to build houses and assuming that the current housing policy will last, ​​it is highly relevant to develop cost-effective construction methods in order to make possible apartments with affordable rents that can help to combat segregation over time.

    Our proposal consists of a residential building in Stadshagen. The property is divided into two buildings that are linked together by a system of access balconies connected to a stairwell. The houses are constructed with volume elements stacked on a concrete base. The design of the elements is based on shipping containers which provides a rational construction process and a high degree of prefabrication. The base contains an underground entrance, a business premise and common areas for the residents. The apartments are available in three sizes whereof the larger apartments have two floors.

  • 121204.
    Åström Paulsson, Sofia
    et al.
    Uppsala Universitet.
    Schmidt, Lisa
    KTH, School of Technology and Health (STH), Health Systems Engineering, Ergonomics.
    Eriksson, Tomas
    Uppsala Universitet.
    Nyman, Teresia
    Uppsala Universitet.
    Parmsund, Marianne
    Torgén, Margareta
    Svartengren, Magnus
    Uppsala Universitet.
    Procurement and implementation processes for Occupational Health Services in SwedenIn: International Archives of Occupational and Environmental Health, E-ISSN 1432-1246Article in journal (Refereed)
    Abstract [en]

    Purpose: This study investigates how contracts with OHS-providers in Sweden are established and implemented  to explore i) the procurement process ii) contractual terms and conditions and iii) processes for implementing and evaluating the services provided.

    Methods: Review and analysis of 17 OHS contracts using both quantitative and qualitative approaches. Follow-up interviews were conducted with Human Resource managers, management, health and safety representatives and OHS professionals.

    Results: Contracts with OHS providers were mainly drawn up by HR departments. First-line managers or health and safety representatives were not involved. The contracts were not integrated with the companies’ occupational health and safety management. The organisations lacked knowledge on when or why to use services from their OHS provider, which promoted reactive rather than preventive interventions. Terms and conditions of contracts were found to be quite irrelevant to what services that were actually utilised.

    Conclusions: Important factors in creating conditions for a more preventive and group-oriented use of OHS expertise could be 1) the inclusion of first-line managers and health and safety representatives in needs analysis and implementation processes, 2) the definition of relevant, achievable and measurable goals regarding the collaboration and 3) the arrangement of regularly meetings with the OHS-provider.

  • 121205.
    Åström, Per
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Hespe, Tobias
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    The Effects of an Increased Traceability on Lead Times: A case study on a material replenishment system at a Swedish industrial tools manufacturer2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study investigates the relationship between an increased traceability and shortened lead times in the internal material replenishment system at a large Swedish industrial tools manufacturer. Traceability and its effects on uncertainty in the supply chain has been widely researched in academia, but there is a gap regarding how traceability affects lead times.

    The research investigates which factors drive the lead times in the material replenishment to lean assembly lines and determines how these factors relate to traceability. A case study was conducted in one of the case company’s factories. The study consists of both quantitative and qualitative data. The quantitative data was derived from the case company’s ERP-system while the qualitative data consists of interviews and empirically collected data.

    The results of the study show that waiting time is the primary driver of lead times in the current state of the factory. No indication that internal material replenishment lead times decrease as a result of an increased traceability was found. However, there are aspects with an increased traceability that indirectly facilitates reduction of lead times by making it easier to make well-informed decisions due to the increased availability of real-time data.

    Traceability is found to not contribute any value to the end customer on its own. However, it can play an important role in a company’s supply chain. Further, potential advantages with a high traceability were observed when implementing advanced protocols such as JIT and other lean principles. The study should be seen as a starting point to further studies into the relationship between increasing traceability and reduced internal lead times.

    For managers and companies, the study identifies a potential procedure to use for deter- mining which factors drive replenishment lead times to lean assembly lines. Furthermore, the study shows that companies can have great use for traceability when trying to remove waste from its processes.

  • 121206.
    Åström, Teodor
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Conic Intersections: Art Centre in Solna2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The cone in architecture has often been used to shape and generate space with a cellular structural logic. This project reconsiders the use of the cone for organizing space, in this case applied on an Art Centre in Solna, going beyond the mere repetitive logic of conic modules, to allow for a variety of scales and directions, ranging from large span horizontal conic spaces to more intimate smaller scaled vertical conic rooms.

    The spaces are created through an additive process of intersecting cones with planar elements added into the operation, thus allowing the coexistence of two spatial logics, leading towards a manifold and allowing architecture that can handle the requirements of the program and that reinforces the perception of the shape.

    The project also explores the possibilities of the cone as a single curved unfoldable surface and it’s implications on digital model making, drawing and physical construction.

  • 121207. Åström, T
    et al.
    Brown, N
    Wain, M
    Nielsen, K
    Potau, X
    Arnold, Erik
    Philosophy and History, KTH, School of Architecture and the Built Environment (ABE), Philosophy and History of Technology, History of Science, Technology and Environment.
    How can the EU Framework Programme for Research and Innovation increase the economic and societal impact of RDI funding in Finland?2018Report (Other academic)
  • 121208.
    Åsén, Per-Olov
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    A parallel code for direct numerical simulations of pipe Poiseuille flowManuscript (Other academic)
  • 121209.
    Åsén, Per-Olov
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    A proof of a resolvent estimate for plane flow by new analytical and numerical techniques2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis concerns stability of plane Couette flow in three space dimensions for the incompressible Navier-Stokes equations. We present new results for the resolvent corresponding to this flow. Previously, analytical bounds of the resolvent have been derived in parts of the unstable half-plane. In the remaining part, only bounds based on numerical computations in an infinite parameter domain are available. Due to the need for truncation of this infinite parameter domain, these results are mathematically insufficient.

    We obtain a new analytical bound of the resolvent at s = 0 in all but a compact subset of the parameter domain. This is done by deriving approximate solutions of the Orr-Sommerfeldt equation and bounding the errors made by the approximations. In the remaining compact set, we use standard numerical techniques to obtain a bound. Hence, this part of the proof is not rigorous in the mathematical sense.

    In the thesis, we present a way of making also the numerical part of the proof rigorous. By using analytical techniques, we reduce the remaining compact subset of the parameter domain to a finite set of parameter values. In this set, we need to compute bounds of the solution of a boundary value problem. By using a validated numerical method, such bounds can be obtained. In the last part of the thesis, we investigate a validated numerical method for enclosing the solutions of boundary value problems.

  • 121210.
    Åsén, Per-Olov
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Stability of plane Couette flow and pipe Poiseuille flow2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis concerns the stability of plane Couette flow and pipe Poiseuille flow in three space dimensions. The mathematical model for both flows is the incompressible Navier--Stokes equations. Both analytical and numerical techniques are used.

    We present new results for the resolvent corresponding to both flows. For plane Couette flow, analytical bounds on the resolvent have previously been derived in parts of the unstable half-plane. In the remaining part, only bounds based on numerical computations in an infinite parameter domain are available. Due to the need for truncation of this infinite parameter domain, these results are mathematically insufficient.

    We obtain a new analytical bound on the resolvent at s=0 in all but a compact subset of the parameter domain. This is done by deriving approximate solutions of the Orr--Sommerfeld equation and bounding the errors made by the approximations. In the remaining compact set, we use standard numerical techniques to obtain a bound. Hence, this part of the proof is not rigorous in the mathematical sense.

    In the thesis, we present a way of making also the numerical part of the proof rigorous. By using analytical techniques, we reduce the remaining compact subset of the parameter domain to a finite set of parameter values. In this set, we need to compute bounds on the solution of a boundary value problem. By using a validated numerical method, such bounds can be obtained. In the thesis, we investigate a validated numerical method for enclosing the solutions of boundary value problems.

    For pipe Poiseuille flow, only numerical bounds on the resolvent have previously been derived. We present analytical bounds in parts of the unstable half-plane. Also, we derive a bound on the resolvent for certain perturbations. Especially, the bound is valid for the perturbation which numerical computations indicate to be the perturbation which exhibits largest transient growth. The bound is valid in the entire unstable half-plane.

    We also investigate the stability of pipe Poiseuille flow by direct numerical simulations. Especially, we consider a disturbance which experiments have shown is efficient in triggering turbulence. The disturbance is in the form of blowing and suction in two small holes. Our results show the formation of hairpin vortices shortly after the disturbance. Initially, the hairpins form a localized packet of hairpins as they are advected downstream. After approximately $10$ pipe diameters from the disturbance origin, the flow becomes severely disordered. Our results show good agreement with the experimental results.

    In order to perform direct numerical simulations of disturbances which are highly localized in space, parallel computers must be used. Also, direct numerical simulations require the use of numerical methods of high order of accuracy. Many such methods have a global data dependency, making parallelization difficult. In this thesis, we also present the process of parallelizing a code for direct numerical simulations of pipe Poiseuille flow for a distributed memory computer.

  • 121211.
    Åsén, Per-Olov
    et al.
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Kreiss, Gunilla
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    On a Rigorous Resolvent Estimate for Plane Couette Flow2007In: Journal of Mathematical Fluid Mechanics, ISSN 1422-6928, E-ISSN 1422-6952, Vol. 9, no 2, p. 153-180Article in journal (Refereed)
    Abstract [en]

    We derive a rigorous bound of the solution of the resolvent equation for plane Couette flow in three space dimensions. We combine analytical techniques with numerical computations. Compared to earlier results, our analytical techniques cover a larger part of the parameter domain consisting of wave numbers in two space directions and the Reynolds number. Numerical computations are needed only in a compact subset of the parameter domain.

  • 121212.
    Åsén, Per-Olov
    et al.
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Kreiss, Gunilla
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Resolvent bounds for pipe Poiseuille flow2006In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 568, p. 451-471Article in journal (Refereed)
    Abstract [en]

    We derive an analytical bound on the resolvent of pipe Poiseuille flow in large parts of the unstable half-plane. We also consider the linearized equations, Fourier transformed in axial and azimuthal directions. For certain combinations of the wavenumbers and the Reynolds number, we derive an analytical bound on the resolvent of the Fourier transformed problem. In particular, this bound is valid for the perturbation which numerical computations indicate to be the perturbation that gives the largest transient growth. Our bound has the same dependence on the Reynolds number as given by the computations.

  • 121213.
    Åsén, Per-Olov
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kreiss, Gunilla
    Uppsala Univ, Dept Informat Technol..
    Rempfer, Dietmar
    IIT, Chicago.
    Direct numerical simulations of localized disturbances in pipe Poiseuille flow2010In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 39, no 6, p. 926-935Article in journal (Refereed)
    Abstract [en]

    We consider pipe Poiseuille flow subjected to a disturbance which is highly localized in space. Experiments by Peixinho and Mullin have shown this disturbance to be efficient in triggering turbulence, yielding a threshold dependence on the required amplitude as R-1.5 on the Reynolds number, R. The experiments also indicate an initial formation of hairpin vortices, with each hairpin having a length of approximately one pipe radius, independent of the Reynolds number in the range of R = 2000-3000. We perform direct numerical simulations for R = 5000. The results show a packet of hairpin vortices traveling downstream, each having a length of approximately one pipe radius. The perturbation remains highly localized in space while being advected downstream for approximately 10 pipe diameters. Beyond that distance from the disturbance origin, the flow becomes severely disordered.

  • 121214.
    Åteg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Aktiviteter och lärande för attraktivt arbete.: Utvecklingsprocesser inom verkstadsindustrin2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [sv]

    Avhandlingsarbetet utgår från ett nätverk av mindre verkstadsföretag som under mer än fem års tid varit engagerade i utvecklingsprocesser för att skapa mer attraktiva arbeten. Arbetet har genomförts inom ramen för att…-projektet i samverkan mellan Högskolan Dalarna och Arbetslivsinstitutet. Det övergripande syftet är att utveckla kunskap om och förståelse för utvecklingsprocesser med utgångspunkt i att skapa mer attraktivt arbete. Särskilt intresse ägnas åt hur dynamiken i utvecklingsprocesserna kan analyseras utifrån ett lärandeperspektiv. Ett resonemang förs om utvecklingsprocessernas karaktär och om egenskaper i arbetets attraktivitet. Ansatsen kan beskrivas som interaktiv forskning med tät interaktion med praktiker i verkstadsföretag och i lokalt utvecklingsarbete. Metodansatsen är aktions-, och processorienterad. Attraktivt arbete ses som ett processuellt begrepp, dvs ett strävansmål utifrån individers upplevelser, vilka är stadda under förändring. En distinktion görs mellan en skalbetonad (tilldragande) och en innehållsbetonad (behållande) egenskap. Avhandlingen baseras på fyra delstudier.

    Utifrån tidigare forskning och eget material skapas en analysram över utvecklingsprocessers dynamik avseende aktivitetsnivåer och lärdimensioner. Processer kan ut¬ifrån ramen karaktäriseras som ställföreträdande förändring, skalförändrande utveckling, temporärt förändrande utveckling eller reflektiv utveckling. Faktaunderlag och diskussioner har i en spegelmetod utgjort grund för företagens reflektion om interna och externa förhållanden. Aktiviteter för att skapa attraktiva arbeten har skett på diagnos-, intentions-, och handlingsnivå. Analysramen tillämpas på dels utvecklingsprocesser inom fem verkstadsföretag, dels lokalt utvecklingsarbetet för mer attraktiv industriutbildning.

  • 121215.
    Åteg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Attraktiv industriutbildning på gymnasiet: Ett deltagandeperspektiv på lokalt utvecklingsarbete2005In: Arbetsliv i omvandling, ISSN 1404-8426, Vol. 2, p. 1-110Article in journal (Refereed)
    Abstract [sv]

    Studiens syfte var att skapa förståelse för hur lokalt utvecklingsarbete kan öka industriprogrammetsattraktivitet för ungdomar i valet av gymnasieutbildning, och för att programmet ska vara attraktivt förelever som studerar på programmet.Ett särskilt intresse ägnas åt samverkan mellan gymnasieskola och lokala verkstadsföretag, samt åtinsatser med betoning på utveckling av den arbetsplatsförlagda utbildningen – APU.Under ett flertal år har antalet elever på industriprogrammet i Sverige minskat kraftigt. Samtidigt sermånga industriföretag en brist på utbildad arbetskraft som ett stort hinder för framtiden.Sökandetrycket, mätt i antalet förstahandssökande, har minskat med mer än tre fjärdedelar sedan slutetav 1980-talet.År 2001 sökte två elever till industriprogrammet i Avesta. Insatser för att öka industriprogrammetsattraktivitet fick ett överväldigande resultat – totalt 63 elever sökte till industriprogrammet 2002.Tjugonio elever sökte programmet i första hand.Undersökningar har gjorts av hur ungdomar som sökt och studerar på industriprogrammet sett på sittgymnasieval, på utbildningen, på APU samt på ett framtida industriarbete. Ett särskilt fokus har varit omeleverna gett uttryck av att vara vilseledda och inlurade på utbildningen genom insatser för ett merattraktivt industriprogram.Information om industriprogrammet, om branschen och om industriarbete har visat sig vara av stortvärde för att öka utbildningens attraktivitet. Vikten av en ärlig bild poängteras: det är bättre att visa upprealistiska arbetsmiljöer och arbetsinnehåll, än att peka på en alltför ”modern” bild som branschen intekan leva upp till.Tidigare litteratur har visat att elever har känt sig utnyttjade då de ingått i den ordinarie produktionen påAPU. I denna studie har eleverna istället ansett detta vara något positivt. Det har gett en känsla av att fåarbeta ”på riktigt”, samtidigt som det gett större acceptans för det som varit tråkigare eller mindreintressant. Eleverna som fått arbeta i produktionen har förmedlat en känsla av att ha blivit behandladesom de anställdas jämlikar.

  • 121216.
    Åteg, Mattias
    et al.
    Högskolan i Dalarna.
    Andersson, Ing-Marie
    Högskolan i Dalarna.
    Rosén, Gunnar
    Högskolan i Dalarna.
    Change Processes for Attractive Work in Small Manufacturing Companies2009In: Human Factors and Ergonomics in Manufacturing, ISSN 1090-8471, E-ISSN 1520-6564, Vol. 19, no 1, p. 35-63Article in journal (Refereed)
    Abstract [en]

    The article originates from research in interaction between researchers and companies in a network,which has led to an increasing awareness among managers on issues such as reasons behind difficultiesin attracting competent labor. Particularly, attention has been directed toward the importance ofwork environment improvements that increase the attractivity of industrial work. To deal with suchchallenges, for more than 5 years a number of small engineering companies, with research support,have been engaged in change processes based on the concept of attractive work. The purpose of thearticle is to develop knowledge and understanding for how small engineering companies can createmore attractive work. One goal is to make it possible to draw conclusions about the employees’ experiencesof changes in the attractivity of industrial work. Efforts in this direction have been conductedthrough work environment assessments (before and after the changes) and through administration ofa questionnaire. The results show that it is possible to analyze how employees experience changes inthe attractivity of work. This is most interesting from the perspective that the results can be used forassisting further improvements.

  • 121217.
    Åteg, Mattias
    et al.
    KTH, Superseded Departments, Industrial Economics and Management.
    Hedlund, Ann
    KTH, Superseded Departments, Industrial Economics and Management.
    Pontén, Bengt
    Attraktiv arbete: från anställdas uttalanden till skapandet av en modell2004In: Arbetsliv i omvandling, ISSN 1404-8426, Vol. 1, p. 63-Article in journal (Refereed)
    Abstract [en]

    The purpose of the study was to create a deeper knowledge and understanding ofwhat makes work attractive, and to create a model and to test the possibility togeneralize the model. The study had a qualitative approach, with a starting pointin a mapping method.The results of the study are put in relation to prior research, constituted bytheories on organization and motivation, and in relation to literature on attractivework and adjacent concepts. An establishment was that the prior literature onattractive work is not adequate to give an understanding for what makes workattractive, due to unsuitable starting points.Three different categories have been identified in the analyses of the empiricalmaterial. Attractive work contents include dimensions that deal with what andhow the employee is doing during the performance of the job. Examples areworking speed, freedom of action and variation. Work satisfaction includesdimensions that deal with what the employee think he or she gets out of doing thejob. Examples are acknowledgement, status and stimulation. Attractive workingconditions deal with dimensions that are common for every employee within acompany or organization. These dimensions are not dependent on the specificwork tasks of how the employee thinks about what he or she gets out of doing thejob. Examples are working hours, physical work environment and leadership.The model of attractive work represents an overall picture about what makeswork attractive and it can form a base for continued research or developmentwork. The contents of the model corresponds to what prior research has shown isimportant. But at the same time there is a need to de-learn some of the old structuresof thought, since they include features that in some cases constitutes theopposite to an attractive work.

  • 121218. Åvitsland, G.A.
    et al.
    Sterner, M.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Ödberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    AKD sizing of TCP and ECF bleached birch pulp characterized by peroxide edge wicking index2006In: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 21, no 2, p. 237-244Article in journal (Refereed)
    Abstract [en]

    To study the impact of extractable materials and xylan on the sizing efficiency of totally chlorine-free (TCF) bleached birch pulp and elemental-chlorine-free (ECF) bleached birch pulp, several pulps with different amounts of extractable material were studied. The content of extractable material in the pulp was shown to be detrimental for sizing efficiency, measured both as Cobb60 values and edge penetration in a model liquid packaging board, and a higher content of extractable material causes a reduced sizing efficiency for a given pulp. No significant difference was observed between extracted TCF and ECF bleached birch pulps, while unextracted pulps containing the same amount of extractable material yielded different sizing efficiencies. The TCF bleached birch pulp had a lower sizing efficiency than did the ECF bleached birch, probably because of differences in the fatty acid composition. A greater amount of extractable material also resulted in a smaller fraction of non-extractable alkyl ketene dimers (AKD) relative to the total amount of AKD in the sheet. Enzymatic removal of xylan and thus the reduction of the surface charge had no measurable effect on sizing efficiency. Extracted TCF and ECF bleached pulps only need a content of 0.05 kg/ton non-extractable AKD or 0.08 kg/ton total AKD in the sheets produced to achieve a good sizing effect.

  • 121219.
    Åvitsland, Grete
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Impact of heat treatment on hygroexpansion, absorption and pore structrure of paper and boardManuscript (Other academic)
  • 121220.
    Åvitsland, Grete A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edgewise liquid penetration in paper: influence of surface chemistry and paper structure2005Licentiate thesis, comprehensive summary (Other scientific)
  • 121221. Åvitsland, Grete
    et al.
    Sterner, Mirjam
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ödberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    AKD sizing of TCF and ECF bleached birch pulp characterized by peroxide edge wicking2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 237-241Article in journal (Refereed)
    Abstract [en]

    To study the impact of extractable materials and xylan on the sizing efficiency of totally chlorine-free (TCF) bleached birch pulp and elemental-chlorine-free (ECF) bleached birch pulp, several pulps with different amounts of extractable material were studied. The content of extractable material in the pulp was shown to be detrimental for sizing efficiency, measured both as Cobb. values and edge penetration in a model liquid packaging board, and a higher content of extractable material causes a reduced sizing efficiency for a given pulp. No significant difference was observed between extracted TCF and ECF bleached birch pulps, while unextracted pulps containing the same amount of extractable material yielded different sizing efficiencies. The TCF bleached birch pulp had a lower sizing efficiency than did the ECF bleached birch, probably because of differences in the fatty acid composition. A greater amount of extractable material also resulted in a smaller fraction of non-extractable alkyl ketene dimers (AKD) relative to the total amount of AKD in the sheet. Enzymatic removal of xylan and thus the reduction of the surface charge had no measurable effect on sizing efficiency. Extracted TCF and ECF bleached pulps only need a content of 0.05 kg/ton non-extractable AKD or 0.08 kg/ton total AKD in the sheets produced to achieve a good sizing effect.

  • 121222.
    Åvitsland, Grete
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Billerud Skärblacka AB, Sweden.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Flow resistance of wet and dry sheets used for preparation of liquid packaging board2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 3, p. 345-353Article in journal (Refereed)
    Abstract [en]

    The present work has shown that an evaluation of the flow resistance of wet and dry sheets can be used to identify how to improve the resistance against edgewise liquid penetration in liquid packaging board. By application of liquid extrusion measurements it was possible to determine the wet and dry structure of liquid packaging board made from CTMP and chemical pulps typically used in the production of packaging board. The expansion of the papers upon wetting induces a large difference between the dry and wet sheet structure, and the wet pore volume is three to four times the dry pore volume. Sheets made from kraft pulps only expand moderately, whereas sheets made from CTMP expand to a higher extent. Both porosities and flow resistances, calculated from pore volumes, display a large impact of both the wet and dry sheet density. From these results it is clear that CTMP sheets resist flow much less than sheets based on kraft pulps, and even considerably reducing the porosity of CTMP sheets only gives a small effect in the magnitude of the flow resistance. Finally at high levels of sizing it will be difficult to compensate changes in sheet structure with an additional size addition in order to prevent liquid penetration.

  • 121223. Çakir, S.
    et al.
    Eriksson, Magnus
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Koning, C. E.
    Multiblock copolymers of polyamide 6 and diepoxy propylene adipate obtained by solid state polymerization2016In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 79, p. 13-22Article in journal (Refereed)
    Abstract [en]

    Polyesteramide multiblock copolymers based on polyamide 6 and diepoxy propylene adipate blocks were synthesized. For this purpose a carboxyl-terminated polyamide 6 (Mn = 2400 g/mol, Tm = 205.5 °C) and diepoxy propylene adipate (Mn = 450 g/mol) were separately synthesized and characterized. The incorporation of the oligoester into the polyamide 6 backbone was performed by solid state polymerization (SSP) well below the melting temperature of the polyamide (80-140 °C) so that the physical and thermal properties of the original polyamide 6 block were retained. Formation of the multiblock structure was confirmed by following the increase in molecular weight by SEC, reaction of the end groups by 1H NMR and by following the maintained melting temperature after the copolymerization. These segmented copolymers have molecular weights up to 10 kg/mol, thermal stability of 325 °C at 5% weight loss and a melting temperature of 205 °C.

  • 121224.
    Çelaj, Ilir
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Rusu, Lazar
    IT Outsourcing Relationships in Swedish Public Organizations2014In: PERSPECTIVES IN BUSINESS INFORMATICS RESEARCH, BIR 2014 / [ed] Johansson, B; Andersson, B; Holmberg, N, 2014, Vol. 194, p. 15-29Conference paper (Refereed)
    Abstract [en]

    Information technology (IT) is not only beneficial for the private sector but has a lot to offer for the public sector as well. However, most of the studies in IT outsourcing relationships consider only the private sector and do not pay attention to the public sector. In this context, the research has looked to determine the influential factors in IT outsourcing relationships in Swedish public organizations like are Swedish municipalities and classified them according to the importance. The research methodology used has included a survey among IT outsourcing decision makers from Swedish municipalities and a case study in a Swedish municipality. The survey has revealed that trust, cooperation, commitment, communication, and flexibility are the top five most important factors which are influencing the provider-recipient IT outsourcing relationship in Swedish municipalities. While the case study has revealed that all the factors that were identified during the literature review are influencing the provider-recipient IT outsourcing relationship in Swedish municipalities plus the identification of two new factors which are legislation and economy/money.

  • 121225.
    Çinar, O.Y.
    et al.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden. Gebze Institute of Technology, Department of Mathematics, Turkey.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Çinar, G.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden. Gebze Institute of Technology, Department of Mathematics, Turkey.
    Nilsson, B.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden.
    Jet pipe reflections - Influence of geometrical and flow exit conditions2010In: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010, p. 2010-4013-Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the influence of the exit conditions on the acoustic reflections at a jet pipe opening. For the flow exit conditions, the model of Munt assuming a vortex sheet at the exit of a semi-infinite jet pipe is improved by considering more general coupling conditions. We focus on modelling the acoustic properties at the shear layer in general and the stability properties in particular. Experimental methods are used for studying primarily the geometric exit conditions. Both theoretical and experimental results are presented and discussed. Numerical results related to the theory show that the thickness of the shear layer causes an expected increase in the magnitude of the reflection coefficient compared to the original infinitely thin shear layer in the Munt model. The experimental results, on the other hand, show that there are additional effects due to the presence of thick walls at the exit of the straight pipes used in the experiments. These effects are observed to be more dominant than the effects due to the shape of the edges. Based on the discussions, further theoretical and experimental investigations are proposed.

  • 121226.
    ÇÖMLEKÇİOĞLU, İNCİ
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Entrepreneurship and innovation.
    IDEA MINING: Can Business Intelligence be an alternativeidea generation method in service companies?2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Enabled by the increased amount of digital data storage, business intelligence (BI) became a powerful  method  to  improve  business  decision  making  since  1990s.  It  yields  competitive advantage for firms and helps solving business problems faster especially in service business. Despite near real time market analysis, customer segmentation or prediction capabilities of BI, its role in stimulating the innovation is not clearly described.

    This research presents methods for generating new service ideas that a company can use, and

    determines the role of business intelligence in today’s innovation ideation process based on an empirical study on biggest four Turkish Telecommunication firms. Among various methods for idea  generation,  business  intelligence  has  not  developed  enough  to  provide  an  alternative ideation method yet. However, it can be a complimentary method which covers drawbacks of other methods.

  • 121227.
    ÓLAFSDÓTTIR, VERA SÓLVEIG
    KTH, School of Chemical Science and Engineering (CHE).
    Fällning av kisel från avloppsvatten vid Hellisheidarvirkjun - experimentell studie2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report is about the experiments with mixing of the separated water and the vacuum pump seal water at Hellisheiði power plant. This is done to prevent silica scaling and clogging in pipes and reinjection wells as well as eliminating vacuum pump seal water from the plant. The experiments were done in four stages: the first stage comprised of tests with different flows of separated water at 70°C, the second stage was carried out by mixing the separated water at 70°C and the seal water with different amounts of the seal water, the third and the fourth stages were like the first and second but with the separated water at 120°C. The results show that this method is good if the mixture is around 50/50 separated water and seal water, to control the silica scaling in the separated water and to be able to reinject the seal water with the separated water. This does not eliminate the silica scaling in all of the separated water because the amount of separated water is much more than the amount of seal water that comes from the plant.

     

  • 121228.
    Ólafsdóttír, Ásdís
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Bus service performance analysis.: Case study: Bus line 1 in Stockholm, Sweden2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Transit reliability is one of the key factors in running a successful transit system from both

    passengers’ and operators’ perspective. To improve the reliability of a transit service a

    performance analysis is necessary. There are several service measures that can be applied to

    evaluate the performance of a transit service, both in relation to service punctuality and

    service regularity. Punctuality can be considered of higher importance on low frequency

    lines and regularity on high frequency lines. Bunching is used to describe how vehicles

    occupying the same bus route tend to bunch up and consequently the reliability decreases.

    For improving reliability several holding control strategies can be applied such as schedulebased

    holding, where early vehicles are held at time points, and headway

    ‐based holding,

    where vehicles are held to retrieve even headways between consecutive vehicles.

    This thesis provides an overview of several different performance measures that can

    be analyzed using

    Automatic Vehicle Location data (AVL) and Automatic Passenger Counters

    data (APC) collected from bus vehicles. As a case study, bus line 1 in Stockholm was

    analyzed. The line is a high frequency, inner city bus line, where schedule based holding is

    the current holding control strategy.

    The performance analysis included an analysis of service regularity, service

    punctuality, dwell times, passenger boarding/alighting and load, and run times. A linear

    regression analysis was applied to evaluate the effects of passenger activity on the dwell

    times.

    The results showed that the overall service performance decreased along the line for

    both directions. Vehicle trajectories revealed increased bunching along the line. The drivers’

    compliance to holding analysis showed that there was room for improvement. Overall, the

    analysis showed that the current holding control strategy does not retrieve headway

    regularity and that the schedule for vehicle run times was too tight and needs revision.

    Furthermore, switching to headway

    ‐based holding was suggested.

  • 121229.
    Ólafsson, Páll
    KTH, Superseded Departments, Materials Science and Engineering.
    Modelling properties of aluminium alloys1997Doctoral thesis, comprehensive summary (Other scientific)
  • 121230.
    Óskarsdóttir, Arna
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Finite Element Analysis of Infant Skull Trauma using CT Images2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Some cases of infant skull fracture fall under the category of forensic study where it is not obvious whether the head trauma happened due to an accident or abuse. To be able to determine the cause of the head trauma with sufficient accuracy, biomechanical analysis using finite element modeling of the infant cranium has been established. By simulating the trauma, one may be able to obtain the fracture propagation of the skull and from it determine if the scenario narrative is plausible. Geometry of skull, sutures, scalp and brain of a 2 month old infant head was obtained using CT images and meshed using voxel hexahedral meshing. Simulation of an impact to the head from a fall of 0.82 m height, to a rigid floor, was carried out in the non-linear finite element program LS-Dyna. Two scenarios were simulated: an impact to the occipitalparietal bones and an impact to the right parietal bone. The fracture propagation was obtained using the Chang-Chang Composite Failure Model as a constitutive model for the skull bones. The amount of material parameters gathered in the present study to predict fracture of the infant skull has not been obtained before, to the best knowledge of author.

    Validation of the models’ ability to show relatively correct fracture propagation was carried out by comparing the obtained fracture pattern from the parietal-occipital impact against published fracture patterns of infant PMHS skulls from a free fall onto a hard surface. The fracture pattern was found to be in good compliance with the published data. The fracture pattern in the parietal bone from the impact was compared against a fracture pattern from a previously constructed model at STH. The patterns of the models show some similarities but improvements to the model and further validations need to be carried out.

  • 121231.
    Óskarsson, Einar
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Redistribution of bending moments in concrete slabs in the SLS2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The finite element method (FEM) is commonly used to design the reinforcement in concrete slabs. In order to simplify the analysis and to be able to utilize the superposition principle for evaluating the effect of load combinations, a linear analysis is generally adopted although concrete slabs normally have a pronounced non-linear response. This type of simplification in the modeling procedure will generally lead to unrealistic concentrations of cross-sectional moments and shear forces. Concrete cracks already at service loads, which leads to redistribution of moments and forces. The moment- and force-peaks, obtained through linear finite element analysis, can be redistributed to achieve a distribution more similar to what is seen in reality. The topic of redistribution is however poorly documented and design codes, such as the Eurocode for concrete structures, do not give descriptions of how to perform this in practice.

    In 2012, guidelines for finite element analysis for the design of reinforced concrete slabs were published in a joint effort between KTH Royal Institute of Technology, Chalmers University of Technology and ELU consulting engineers, which was financially supported by the Swedish Transport Administration. These guidelines aim to include the non-linear response of reinforced concrete into a linear analysis.

    In this thesis, the guidelines mentioned above are followed to obtain reinforcement plans based on crack control, for a fictitious case study bridge by means of a 3D finite element model. New models were then constructed for non-linear analyses, where the reinforcement plans were implemented into the models by means of both shell elements as well as a mixture of shell and solid elements. The results from the non-linear analyses have been compared to the assumptions given in the guidelines.

    The results from the non-linear analyses indicate that the recommendations given in the aforementioned guidelines are indeed reasonable when considering crack width control. The shell models yield crack widths equal to approximately half the design value. The solid models, however, yielded cracks widths that were 15 - 20$\%$ lower than the design value. The results show that many factors attribute to the structural behavior during cracking, most noticeably the fracture energy, a parameter not featured in the Eurocode for concrete structures.

    Some limitations of the models used in this thesis are mentioned as well as areas for further improvement.

  • 121232.
    Ótão Pereira, Pedro Miguel
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Geometric Control of Thrust Propelled Systems2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis was motivated and inspired by the AEROWORKS project, a European research project, whose main goal was to deploy multiple heterogeneous unmanned aerial vehicles in environments where human intervention is restricted.In particular, this thesis focuses on control of aerial vehicles for the purposes of cargo transportation, an application of interest, for example, in inspection and maintenance of aging infrastructures.

    This thesis also focuses on control of multi-agent systems, where agents are required to accomplish some common goal, such as collaborating on transporting a common cargo. In the first part of this thesis, we focus on control of thrust-propelled systems.A thrust-propelled system is similar to a multi-rotor system, where a thrust input is available along some direction, which we can rotate by means of a torque input.In a first step, we develop controllers for the thrust-propelled system, by application of nonlinear control techniques.In a second and final step, we convert a physical system, by means of an appropriate change of coordinates, into the thrust-propelled system form, at which point we are able to leverage the controllers designed in the first step.Among the physical systems considered in this thesis, we highlight slung-load transportation, where a point-mass cargo is tethered to a single aerial vehicle, and slung-bar transportation, where a bar cargo is tethered to two aerial vehicles.Another key idea, exploited throughout this thesis, is that of geometric control, where one attempts to design controllers that are independent of the user choices.For example, when performing an experiment, a user picks a reference frame, and the application of a geometric controller is insensitive to that choice.On the contrary, a non-geometric controller yields different results depending on which frame is chosen.Experiments and simulations illustrate the performance of the proposed control strategies.

    In the second part of this thesis, we focus on global stabilization of mechanical systems, in contrast with the first part, where almost global and/or local stabilization sufficed.However, for non-contractible sets, which are pervasive throughout this thesis, a globally asymptotically stable equilibrium point does not exist under a continuous control law.In particular, we consider a rigid-body pendulum, which we wish to globally stabilize at some desired configuration.To accomplish the latter, we create a graph between several stabilizing continuous control laws, and switch among them so as to provide the desired equilibrium with a global region of attraction, which we validate in simulations.

    In the final part of this thesis, we consider a multi-agent system composed of rotation matrices, and we design controllers that guarantee asymptotic incomplete synchronization.In particular, we develop decentralized torque controllers for the agents, and when the directions to be synchronized are principal axes, we are able to propose torque control laws that do not require torque input in all bodies directions, but rather only in the body directions orthogonal to the respective principal axis.Simulations are then presented which illustrate the performance of the proposed control strategy.

  • 121233.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES).
    Collaborative Transportation of a Bar by Two Aerial Vehicles with Attitude Inner Loop and Experimental Validation2017In: 2017 IEEE 56TH ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2017, p. 1815-1820Conference paper (Refereed)
    Abstract [en]

    We propose a control law for stabilization of a bar tethered to two aerial vehicles, and provide conditions on the control law's gains that guarantee exponential stability of the equilibrium. Given the proposed control law, we analyze the stability of the equilibrium for two cases, specifically, for a bar of known and unknown mass. We provide lower bounds on the attitude gains of the UAVs' attitude inner loop that guarantee exponential stability of the equilibrium. We also include an integral action term in the control law, so as to compensate for battery drainage and model mismatches, and we provide a lower bound on the integral gain that guarantees stability of the equilibrium. We present an experiment that demonstrates the stabilization and that validates the robustness of the proposed control law.

  • 121234.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES).
    Control Framework for Slung Load Transportation with Two Aerial Vehicles2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 4254-4259Conference paper (Refereed)
    Abstract [en]

    We model a point mass load tethered to two aerial vehicles, and propose a control strategy that guarantees that the load tracks a desired position trajectory. Our framework consists in designing an input and a state transformation which converts the quadrotors-load system into three decoupled subsystems: one concerning the position of the load, with dynamics similar to those of an under-actuated aerial vehicle; one concerning the angle between the cables, with double integrator dynamics; and another concerning the yaw motion of the plane formed by the cables, also with double integrator dynamics. Once the decoupling is done, controllers from the literature can be leveraged, which we take advantage of when controlling the subsystem with dynamics similar to those of an under-actuated aerial vehicle. Simulations are presented which validate the proposed algorithm.

  • 121235.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH Royal Inst Technol, Sch Elect Engn, SE-10044 Stockholm, Sweden..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH Royal Inst Technol, Sch Elect Engn, SE-10044 Stockholm, Sweden..
    Lyapunov-based Generic Controller Design for Thrust-Propelled Underactuated Systems2016In: 2016 EUROPEAN CONTROL CONFERENCE (ECC), IEEE , 2016, p. 594-599Conference paper (Refereed)
    Abstract [en]

    We present a controller for an underactuated system which is driven by a one dimensional linear acceleration/thrust along a direction vector, by a time-varying gravity, and by the angular acceleration of the direction vector. We propose state and time-dependent control laws for the linear and angular accelerations that guarantee that the position of the system is steered to the origin. The proposed control law depends on (i) a bounded control law for a double integrator system; and (ii) on a Lyapunov function that guarantees asymptotic stability of the origin for the double integrator system when controlled with the previous bounded control law. As such, the control law forms a family of control laws depending on (i) and (ii). The complete state space of the system, under the proposed control laws, has two equilibria, and by proper control design, a trajectory of the system is guaranteed to converge to only one of those. The overall design provides a common framework for controlling different systems, such as quadrotors and slung load transportation systems.

  • 121236.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES).
    Nonlinear Pose Tracking Controller for Bar Tethered to Two Aerial Vehicles with Bounded Linear and Angular Accelerations2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 4260-4265Conference paper (Refereed)
    Abstract [en]

    We consider a system composed of a bar tethered to two aerial vehicles, and develop a controller for pose tracking of the bar, i.e., a controller for position and attitude tracking. Our first control step is to provide an input and a state transformations which convert the system vector field into one that highlights the cascaded structure of the problem. We then design a controller for the transformed system by exploring that cascaded structure. There are three main contributions: i) we provide bounds on the linear and angular acceleration of the bar that guarantee well-posedness of the controller, and such bounds can be used when selecting the gains and saturations of bounded controllers for both three dimensional and unit vector double integrators; ii) the proposed control law includes a degree of freedom which can be used to regulate the relative position between the aerial vehicles; and iii) the proposed control law for the throttle guarantees that the cascaded structure of the problem is preserved. Simulations are presented which validate the proposed algorithm.

  • 121237.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Stability of load lifting by a quadrotor under attitude control delay2017In: Proceedings - IEEE International Conference on Robotics and Automation, Institute of Electrical and Electronics Engineers Inc. , 2017, p. 3287-3292Conference paper (Refereed)
    Abstract [en]

    We propose a control law for stabilization of a quadrotor-load system, and provide conditions on the control law's gains that guarantee exponential stability of the equilibrium. The system is composed of a load and an unmanned aerial vehicle (UAV) attached to each other by a cable of fixed length, which behaves as a rigid link under tensile forces; and the control input is composed of a three dimensional force requested to the UAV, which the UAV provides with or without delay. Given the proposed control law, we analyze the stability of the equilibrium in two separate parts. In the first, the system is modeled assuming that the UAV provides the requested control input without delay, and we verify that the equilibrium is exponentially stable. In the second part, the UAV is modeled as possessing an attitude inner loop, and we provide a lower bound on the attitude gain for which exponential stability of the equilibrium is preserved. An integral action term is also included in the control law, which compensates for battery drainage or model mismatches, such as an unknown load mass. We present experiments for different scenarios that demonstrate and validate the robustness of the proposed control law.

  • 121238.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dimarogonas, Dino V.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Family of controllers for attitude synchronization in S22016In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, p. 6761-6766Conference paper (Refereed)
    Abstract [en]

    In this paper we study a family of controllers that guarantees attitude synchronization for a network of elements in the unit sphere domain, i.e., S2. We propose distributed continuous controllers for elements whose dynamics are controllable (i.e., control with torque as command), and which can be implemented by each individual agent without the need of a common global orientation frame among the network, i.e., it requires only local information that can be measured by each individual agent from its own orientation frame. The controllers are specified according to arbitrary distance functions in S2, and we provide conditions on those distance functions that guarantee that i) a synchronized network of agents is locally asymptotically stable for an arbitrary connected network topology; ii) a synchronized network can be achieved for almost all initial conditions in a tree graph network. We also study the equilibria configurations that come with specific types of network graphs. The proposed strategies can be used in attitude synchronization of swarms of fully actuated rigid bodies, such as satellites.

  • 121239.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Herzog, M.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dimarogonas, Dimos
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Slung load transportation with a single aerial vehicle and disturbance removal2016In: 24th Mediterranean Conference on Control and Automation, MED 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 671-676Conference paper (Refereed)
    Abstract [en]

    We present a trajectory tracking controller for a quadrotor-load system, composed of a single load and a single unmanned aerial vehicle connected by a cable or rope. The load is modeled as a point mass while the aerial vehicle is assumed to be fully actuated, with thrust and attitude of the quadrotor as inputs to the system quadrotor-load. We assume there is a constant input disturbance at the thrust input, and a disturbance estimator is presented that guarantees that asymptotic tracking is guaranteed in the presence of such a disturbance. The load and the aerial vehicle are connected by a cable of fixed length that behaves as a rigid link under tensile forces, and as a non-rigid link when under compressive forces. The proposed controller guarantees that the cable is always under tensile forces, provided that the position trajectory to be tracked satisfies some mild conditions. The system quadrotor-load can be transformed into a form that resembles that of systems describing underactuated aerial vehicles, and for which a variety of control strategies have been proposed. In particular, we propose a controller based on a backstepping procedure in conjunction with a bounded double integrator controller. We present simulations validating the proposed control algorithm, and some preliminary experimental results are also presented.

  • 121240.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    V. Dimarogonas, Dimos
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Technical Report:: Attitude Synchronization in S2Manuscript (preprint) (Other academic)
    Abstract [en]

    In this paper we study a family of controllers that guarantees attitude synchronization for a network of elements in the unit sphere domain, i.e. S<sup>2</sup>. We propose distributed continuous controllers for elements whose dynamics are controllable (i.e. control with torque as command), and which can be implemented by each individual agent without the need of a common global orientation frame among the network, i.e. it requires only local information that can be measured by each individual agent from its own orientation frame. The controllers are specified according to arbitrary distance functions in S<sup>2</sup>, and we provide conditions on those distance functions that guarantee that i) a synchronized network of agents is locally asymptotically stable for an arbitrary network topology; ii) a synchronized network can be achieved for almost all initial conditions in a tree graph network. We also study the equilibria configurations that come with specific types of network graphs. The proposed strategies can be used in attitude synchronization of swarms of fully actuated rigid bodies, such as satellites.

  • 121241.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zanella, Riccardo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Decoupled Design of Controllers for Aerial Manipulation with Quadrotors2016In: 2016 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS 2016), 2016, p. 4849-4855Conference paper (Refereed)
    Abstract [en]

    In this paper, we model an aerial vehicle, specifically a quadrotor, and a load attached to each other by a rigid link. We assume a torque input at the joint between the aerial vehicle and the rigid link is available. After modeling, we decouple the system dynamics in two separate subsystems, one concerning the position of the center of mass, which we control independently from the chosen torque input; and a second subsystem, concerning the attitude of the rigid link, which we control by appropriately designing a torque control law. Differential flatness is used to show that controlling these two separate systems is equivalent to controlling the complete system. We design control laws for the quadrotor thrust, the quadrotor angular velocity and the torque input, and provide convergence proofs that guarantee that the quadrotor follows asymptotically a desired position trajectory while the manipulator follows a desired orientation. Simulation and experimental works are presented which validate the proposed algorithms.

  • 121242.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH Royal Inst Technol, Sch Elect Engn, SE-10044 Stockholm, Sweden..
    Roque, Pedro
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH Royal Inst Technol, Sch Elect Engn, SE-10044 Stockholm, Sweden..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH Royal Inst Technol, Sch Elect Engn, SE-10044 Stockholm, Sweden..
    Asymmetric Collaborative Bar Stabilization Tethered to Two Heterogeneous Aerial Vehicles2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION (ICRA), IEEE Computer Society, 2018, p. 5247-5253Conference paper (Refereed)
    Abstract [en]

    We consider a system composed of a bar tethered to two unmanned aerial vehicles (UAVs), where the cables behave as rigid links under tensile forces, and with the control objective of stabilizing the bar's pose around a desired pose. Each UAV is equipped with a PID control law, and we verify that the bar's motion is decomposable into three decoupled motions, namely a longitudinal, a lateral and a vertical. We then provide relations between the UAVs' gains, which, if satisfied, allows us to decompose each of those motions into two cascaded motions; the latter relations between the UAVs' gains are found so as to counteract the system asymmetries, such as the different cable lengths and the different UAVs' weights. Finally, we provide conditions, based on the system's physical parameters, that describe good and bad types of asymmetries. We present experiments that demonstrate the stabilization of the bar's pose.

  • 121243.
    Öberg, Christian
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. 8912104273.
    Thermal Cycling, Creep- and Tensile Testing of Cast Exhaust Materials at Elevated Temperatures2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    An exhaust manifold of a truck engine is subjected to tough conditions. As the truck is started, operated and shut down, it becomes subjected to thermal cycling up to around 800°C. At such high temperatures, corrosion, fatigue and creep are active degradation mechanisms. As can be imagined, the interplay between the three complicates materials selection. It is desired to have a versatile grade of high durability which is not too expensive. At the moment, a ferritic, ductile cast iron designated SiMo51 is used for the application. However, due to the rough conditions, it is considered to be on the verge of its operational limit. As a consequence, there is an ongoing search for candidate materials. In this study, the ductile cast irons SiMo51, SiMo1000, D5S and the cast steel HK30 have been included.

    In the past, there have been several studies describing corrosion and fatigue of the cast materials used for exhaust manifolds. However, on the subject of creep of cast materials, little is known. The present study aims to reveal creep tendencies of cast materials and to do it in several ways. More precisely, three creep-testing methods were employed: the conventional constant-load creep-test, the “Sequential tensile test (STT)” and “Stress relaxations with thermal cycling (SRTC)”. The first one is the traditional one. It is tedious, usually lasting months or years. The second one is a tensile test in which the strain rate is changed in sequences as specimen deformation proceeds. Here, the idea is that a slow tensile test is not different from a conventional creep test. In the third one, stress relaxations are provoked as a specimen is thermally cycled in a locked state. Since stress relaxations are a consequence of creep deformation, the relaxation data gathered from isothermal holds can be directly compared to results from the isothermal constant-load creep-test and STT. When thermally cycled in a locked state, the materials display a loop character in σ, ε and T which provides extensive information about the mechanical properties over the selected temperature interval.

    In a logarithmic Norton plot, the creep strain rate is plotted as a function of stress. By plotting STT-data in such Norton plots, it was shown that the creep behaviour of the included materials is well represented by Norton’s law. Furthermore, it was found that the creep strain rates and stress relaxations, measured during isothermal holds in SRTC, in several cases show perfect coincidence with tensile test data obtained through STT. At 700°C, data from all three tests were inserted in the same Norton plot. At higher stress levels, the SRTC-curve follows the STT-curve and at lower stresses, when the creep regime is entered, it bends down and unites with data obtained by the constant-load creep tests. Additionally, it was seen that a relatively high degree of pre-deformation can give a critical stress below which creep deformation stops completely.

  • 121244.
    Öberg, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM). 8912104273.
    Tjernberg, Anders
    Scania CV.
    Rablbauer, Ralf
    Volkswagen.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM).
    Monotonic and Cyclic Creep of Exhaust Manifold Materials and their effects on Predicted Thermo-mechanical Fatigue LifeManuscript (preprint) (Other academic)
    Abstract [en]

    Creep properties of SiMo51, SiMo1000, Ni-resist D5S and HK30, materials used for exhaust manifolds in heavy-duty diesel-engines, are examined by three methods; sequential tensile tests at high temperature, varying the strain rate; relaxation of stresses and strains during isothermal holds of thermal cycling with fixed grips; and traditional creep testing. The results for tensile tests and relaxations coincide while the creep tests show values, one order of magnitude lower.

    The creep can be modelled by Norton’s law and the cyclic influence, including strain reversals, is low. Simulations with/without taking creep into account show that predicted fatigue life for an exhaust manifold, subjected to engine tests with cycling between hot and cold gases, generally increase, with a few exceptions in some points, and that critical spots of low fatigue life are removed because of reduced mean stresses.

  • 121245.
    Öberg, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhu, B. H.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Plastic deformation and creep of two ductile cast irons, simo51 and simo1000, during thermal cycling with large strains2018In: 11th International Symposium on the Science and Processing of Cast Iron, SPCI-XI 2017, Trans Tech Publications, 2018, Vol. 925, p. 361-368Conference paper (Refereed)
    Abstract [en]

    Cyclic deformations of two ferritic, ductile cast irons, SiMo51 and SiMo1000, were studied in air and Ar using a new method, SRTC (stress relaxation with thermal cycling). Locked specimens were thermally cycled up to 800 °C with isothermal holds, varying temperature interval, heating/cooling rates and hold times. A description of the mechanical response to thermal cycling of a locked specimen is given.

  • 121246.
    Öberg, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. 8912104273.
    Zhu, Baohua
    Scania CV.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Plastic deformation and creep of two ductile cast irons, SiMo51 and SiMo1000, during thermal cycling with large strainsIn: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752Article in journal (Refereed)
    Abstract [en]

    Cyclic deformations of two ferritic, ductile cast irons, SiMo51 and SiMo1000, were studied in air and Ar using a new method, SRTC (stress relaxation with thermal cycling). Locked specimens were thermally cycled up to 800 °C with isothermal holds, varying temperature interval, heating/cooling rates and hold times. A description of the mechanical response to thermal cycling of a locked specimen is given.

  • 121247.
    Öberg, Emma
    KTH, School of Chemical Science and Engineering (CHE).
    Investigation of mineral oils as a compatibilizer between metallocene polyolefins and rosin resins in hot melt adhesives2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Limning är en gammal fogningsteknik som har många olika användningsområden. Marknaden för limmer växer, smältlim förväntas ha stor tillväxt även med hårdare miljölagstiftning då appliceringen av limmet sker utan lösningsmedel.

    För att ta fram och tillverka lim används idag polymerer i stor utsträckning. Metallocen polyolefin (mPO) är en typ av polymer som används i limmer på grund av dess utmärkta prestanda som uppnås genom en smal molekylviktsdistribution (MWD). Detta gör det lätt att tillverka limmer med önskade egenskaper. Den här typen av polymerer tenderar dock att vara opolära vilket gör att de är inkompatibla med tallhartser, som ger klibbighet till limmet, eftersom tallhartserna har en högre poläritet.

    Mineraloljor används i limmer som mjukgörare, men används också i vissa fall för att öka kompabiliteten i olika typer av limmer. Därför har det undersökts om de kan användas i limmer med mPO och tallharts för att öka kompabiliteten.

    ”Cloud point”-tester och reologistudier har utförts för att undersöka om kompabiliteten påverkades av tillsatt mineral olja. Peel tester har också utförts för att mäta limegenskaperna för formuleringarna av smältlim.

    Resultaten visar att även om formuleringarna av smältlim har relativt låg peel styrka, så ökade kompabiliteten signifikant mellan mPO och tallhartser vid användning av mineraloljor.

  • 121248.
    Öberg, Fredrik
    et al.
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Askenfelt, Anders
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Acoustical and perceptual influence of duplex stringing in grand pianos2012In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 131, no 1, p. 856-871Article in journal (Refereed)
    Abstract [en]

    This study investigates the acoustical and perceptual influence of the string parts outside the speaking length in grand pianos (front and rear duplex strings). Acoustical measurements on a grand piano in concert condition were conducted, measuring the fundamental frequencies of all main and duplex strings in the four octaves D4-C8. Considerable deviations from the nominal harmonic relations between the rear duplex and main string frequencies, as described by the manufacturer in a patent, were observed. Generally the rear duplex strings were tuned higher than the nominal harmonic relations with average and median deviations approaching _50 cent. Single keys reached +190 and -100 cent. The spread in deviation from harmonic relations within trichords was also substantial with average and median values around 25 cent, occasionally reaching 60 cent. Contributions from both front and rear duplex strings were observed in the bridge motion and sound. The audibility of the duplex strings was studied in an ABX listening test. Complete dampening of the front duplex was clearly perceptible both for an experiment group consisting of musicians and a control group with naive subjects. The contribution from the rear duplex could also be perceived, but less pronounced.

  • 121249.
    Öberg, Gustav
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Erfarenhetsåterföring: En väg till bättre anbud2013Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis has been done in collaboration with JM Entreprenad, a wholly owned subsidiary of JM AB. JM AB is one of Sweden's largest construction companies. The task has been to assist JM Entreprenad Region Hus with an investigation concerning how the experience feedback between Calculus Department and Production is working and to make suggestions for improvements.

    Experience feedback comprises collecting and reusing the experience and knowledge which comes from different parts of the organization and to use this knowledge as a basis for improvement of future work.

    There is currently no established procedures for how this experience feedback shall be carried out which is a shortcoming in the organization. To change this, the company should strive to become a learning organization and establish clear procedures for how this work shall be organized.

  • 121250.
    Öberg Hed, Kim
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Advanced polymeric scaffolds for functional materials in biomedical applications2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Advancements in the biomedical field are driven by the design of novel materials with controlled physical and bio-interactive properties. To develop such materials, researchers rely on the use of highly efficient reactions for the assembly of advanced polymeric scaffolds that meet the demands of a functional biomaterial. In this thesis two main strategies for such materials have been explored; these include the use of off-stoichiometric thiol-ene networks and dendritic polymer scaffolds. In the first case, the highly efficient UV-induced thiol-ene coupling (TEC) reaction was used to create crosslinked polymeric networks with a predetermined and tunable excess of thiol or ene functionality. These materials rely on the use of readily available commercial monomers. By adopting standard molding techniques and simple TEC surface modifications, patterned surfaces with tunable hydrophobicity could be obtained. Moreover, these materials are shown to have great potential for rapid prototyping of microfluidic devices. In the second case, dendritic polymer scaffolds were evaluated for their ability to increase surface interactions and produce functional 3D networks. More specifically, a self-assembled dendritic monolayer approach was explored for producing highly functional dendronized surfaces with specific interactions towards pathogenic E. coli bacteria. Furthermore, a library of heterofunctional dendritic scaffolds, with a controllable and exact number of dual-purpose azide and ene functional groups, has been synthesized. These scaffolds were explored for the production of cell interactive hydrogels and primers for bone adhesive implants. Dendritic hydrogels decorated with a selection of bio-relevant moieties and with Young’s moduli in the same range as several body tissues could be produced by facile UV-induced TEC crosslinking. These gels showed low cytotoxic response and relatively rapid rates of degradation when cultured with normal human dermal fibroblast cells. When used as primers for bone adhesive patches, heterofunctional dendrimers with high azide-group content led to a significant increase in the adhesion between a UV-cured hydrophobic matrix and the wet bone surface (compared to patches without primers).

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