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Sökning: L4X0:1402 1544 > (2015-2019) > (2016)

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61.
  • Sirkka, Marianne (författare)
  • Hållbart förbättringsarbete med fokus på arbetsterapi och team Möjligheter och utmaningar
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Hälso-och sjukvården (HoS) har skyldighet att bedriva en evidensbaserad verksamhet baserad på bästa tillgängliga vetenskapliga kunskap, professionens expertkunnande, patienternas erfarenheter och tillgängliga resurser. Förbättringsarbeten pågår för att uppnå bästa möjliga HoS men kunskapen om hur hållbara förbättringar uppnås är fortfarande begränsad. Det övergripande syftet med denna avhandling var att bidra till ökad kunskap om möjligheter och utmaningar vid långsiktigt förbättringsarbete med fokus på arbetsterapi och team. Avhandlingens fyra delarbeten baseras på studier av långsiktiga förbättringsarbeten vid två olika enheter. Studie I syftade till att beskriva utvecklingen av ett långsiktigt förbättringsarbete som baserades på en arbetsterapeutisk praxis modell, Occupational Therapy Intervention Process Model (OTIPM). Data utgjordes av olika typer av dokument (435sidor) från 2001-2013 som var relaterade till förbättringsarbetet och analyserades med mönsterjämförelser (pattern matching). I Studie II var syftet attutforska arbetsterapeuters erfarenheter av ett långsiktigt förbättringsarbete. Data utgjordes av semistrukturerade intervjuer med 19 arbetsterapeuter i tre fokusgrupper år 2006 och uppföljande fokusgruppsintervjuer år 2011. Materialet analyserades med kvalitativ innehållsanalys. Studie III syftade till att identifiera stödjande och hindrande element vid långsiktigt förbättringsarbete med stöd av det implementeringsteoretiska ramverket, Promotion Action on Research Implementation in Health Services (PARiSH). Data från fokusgruppintervjuer analyserades först med manifest innehållsanalys med ramverket som raster och vidare med en latent innehållsanalys. Studie IV syftade till att utforska ett tvärprofessionellt teams erfarenheter av att implementera en teamorienterad och evidensbaserad behandlingsmodell Mentaliseringsbaserad terapi (MBT). Data utgjordes av återkommande fokusgruppsintervjuer som analyserades med en metod för jämförelseav kvalitativ data, inspirerad av Grounded Theory. Resultatet av studie I visar på sju olika faser i det långsiktiga förbättringsarbetet. Faserna representerar tre huvudmönster i processen och beskriver olika tillvägagångssätt för omorientering, etablering och långsiktig hållbarhet. I studie II beskrivs det långsiktiga förbättringsarbetet som en resa mot en hållbar ochevidensbaserad praktik. Resultatet visar på en förändringsresa med tre sammanflätade perspektiv; 1) omvandla tankar och handlingar genom återkommande kollegial reflektion, 2) hantera den upplevda dubbelheten av förändring, 3) utveckla en ömsesidigt professionell kultur. I studie III framkommer att samtliga element i ramverket PARiSH (evidens, kontext och facilitering) hade övervägande höga värden vilket indikerar en lyckad implementering. Vidare framkommer att den nya professionsinriktade kunskapen ansågs ha hög evidens. Den starka kollegiala kulturenvärderades högt och underlättade fortsatt förbättringsarbete trots olika utmaningar och stressmoment över tid. Resultatet av Studie IV beskriver implementeringen av den evidensbaserade och teamorienterade modellen, MBT som en interdisciplinär process med teoretiska, praktiska, emotionella och reflekterande komponenter. Det interprofessionella teamarbetet identifierades som en drivkraft för hållbar implementering och den reflekterande komponenten framstod som avgörande för utvecklingen av det interdisciplinära teamarbetet. Avhandlingen som helhet visar att hållbart förbättringsarbete inom arbetsterapi och team förutsätter a) ett reflekterande kollegialt förhållningssätt som ökar förmågan att hantera utmaningar i förbättringsarbetet, b) en i vardagsarbetet integrerad struktur förlångsiktigt förbättringsarbete med regelbunden avsatt tid och allokeradfaciliteringsfunktion, c) rutiner för att kontinuerligt hantera professionell kunskap från vetenskap och beprövad erfarenhet, d) ett strategiskt ledarskap och en gemensam kultur som håller drivkraften att förbättra levande över tid.Nyckelord: arbetsterapi, evidensbaserad praktik, hållbart förbättringsarbete,implementeringsteorier, MBT, OTIPM, PARiSH. hållbart förbättringsarbete, implementeringsteorier, MBT, OTIPM, PARiSH.
62.
  • Sjöholm, Jennie (författare)
  • Heritagisation, re-heritagisation and de-heritagisation of built environments The urban transformation of Kiruna, Sweden
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This doctoral thesis presents research that aimed to contribute to the understanding of heritagisation in built environments and how heritagisation interacts with structural changes to an environment. The theoretical framework of the research was based on heritagisation, a concept defined by Harrison (2013) as the process through which objects, places and practices are turned into cultural heritage. The research was part of a single case study investigating conceptualisations of built heritage during the urban transformation of the town of Kiruna. Kiruna is a mining town in the northernmost part of Sweden that has plans to be relocated so that the mining company LKAB can continue mining the iron ore deposit that extends underneath the settlement. Kiruna is also a designated heritage site since the 1980s, and includes a large number of protected buildings. Hence, it is of interest how the built heritage is managed during the urban planning process. This is not only because the urban planning situation, which includes the relocation of an entire town, is special, but also because the town’s built heritage inevitably will change during the urban transformation. The research underlying this thesis has followed heritagisation during the urban transformation, from 2004, when the urban transformation was announced, until 2015. The empirical data used consist of planning documents, media reporting and observations, which together provide an overall view of the public discussions over the course of the urban planning process. Findings from the Kiruna case study show that the town’s officially recognised built heritage corresponds with the concept of an authorised heritage discourse (AHD). This heritage discourse was challenged by the urban transformation. Conservation goals are not clearly stated in the urban planning process and there are differing ideas for how to manage historic buildings during the urban transformation. These ideas shift both over time and between stakeholders, and the outcome of the urban planning process depends on a balance between the discourses of heritage conservation, urban development and architectural production. During the urban planning process some parts of the town’s official heritage have been reaffirmed as built heritage, while others have been dismissed. The concept of heritagisation was adopted and developed throughout the research presented in this thesis. This research also introduced the concepts of re-heritagisation and de-heritagisation, which refer to new heritagisation processes that occur when built heritage is contested and challenged during urban change. One of the main conclusions of the research was that the changes in meaning during the heritagisation process can be divided into four dimensions to analyse the complicated relationship between different interests and strategies in urban planning. Heritagisation can refer to: the addition of new heritage; reaffirmation of already designated heritage; re-interpretation of already designated heritage; rejection of previous designated heritage.
63.
  • Szentes, Henrik (författare)
  • Organizational tensions when managing interorganizational projects Applying a paradox perspective on large construction projects in Sweden
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Over the years, technological developments and societal changes have forced companies to modify their organizing practices. Companies operating in the construction sector are no exception, but due to their project-based structure, it is more difficult to coordinate change initiatives. Indeed, the construction sector is often described as conservative and unwilling to adopt change. However, there is a growing interest and ambition within the construction sector to develop and implement new ways of working. In addition, the need to adapt organizing practices of large construction projects due to societal changes is particularly strong because large construction projects are very dependent on a wide range of societal stakeholders.Changes in organizing practices as well as contextual changes often create new and intensify existing organizational tensions. Because most large construction projects span organizations, tensions can emerge and develop at several organizational interfaces. For instance, tensions related to control and flexibility can emerge between the client and the contractor, within each of these parties, but also between the project organization and societal stakeholders. Another type of tension relevant to construction projects is between the exploitation of current knowledge to perform efficiently today and the exploration of new knowledge in order to innovate for tomorrow’s demands. The abovementioned tensions have a paradoxical nature, meaning that although both elements in the tension make sense, they appear to be impossible to combine. Yet, applying a paradox perspective on organizational tensions recognizes that both elements are required when organizing. Moreover, prior research has shown that due to interdependencies between different organizing activities, responses to tensions may evolve into reinforcing cycles, substantially impacting performance. Therefore, the aim of this thesis is to create an improved understanding of the dependencies between tensions at different organizational interfaces in large construction projects by applying a paradox perspective. Empirical material was drawn from a qualitative study of seven large construction projects in Sweden, including three rounds of interviews during a four-year period, site visits, and reading of project documentation. All projects had an original contract sum of at least 50 million Euros and durations over several years; they included both transport infrastructure and building projects. An initial analysis of changes that project managers in large construction projects perceived in their role due to changing external and internal conditions provided a better understanding of the origin and nature of tensions in contemporary large construction projects, resulting in Paper I. Moreover, specific questions on the subject of exploration/exploitation during the first round of interviews provided input to Papers II and III. The two concluding rounds of interviews focused on dependencies between the tensions related to control/flexibility at different organizational interfaces and, analyzed using a paradox perspective, resulted in Papers IV and V. This thesis contributes to the construction management literature by showing that despite institutional barriers, substantial changes in the organizing practices of large construction projects have occurred over the years. However, the statements and attitudes exhibited by several interviewees indicate that the construction sector’s reputation for being conservative has become institutionalized, blocking creativity and favoring exploitation over exploration. This thesis also contributes to the literature on managing large construction projects by showing that distinguishing between interorganizational and intraorganizational aspects is essential to achieving a better understanding of the dependencies between organizing activities. For instance, analyses using a systemic paradox perspective showed that tensions related to control/flexibility coexist at both interorganizational and intraorganizational interfaces and that there are interdependencies between the two tensions, resulting in reinforcing cycles. For example, urges from client governance to their project manager to increase control of the contractor translated into an increase of control over the contractor project manager by his/her governance forum in order to retain the contractor’s flexibility. This triggered further controls by the client, and so on, in a vicious cycle of control. Similarly, this thesis demonstrates that in order to better understand how exploration and exploitation in large construction projects is dependent on intraorganizational strategies and decisions, it is fruitful to apply a systemic paradox perspective and simultaneously analyze both intraorganizational and interorganizational aspects.In addition, this thesis contributes to the literature on paradoxical tensions by identifying tensions and reinforcing cycles simultaneously nested across both inter- and intraorganizational interfaces, thus further calling for a systemic view of paradoxical tensions.For practitioners it is therefore essential to reflect not only which project managers to appoint in large construction projects, but also simultaneously thoughtfully chose members of each governance forum to avoid vicious cycles to occur.
64.
  • Thiery, Florian (författare)
  • Simplified models to evaluate nonlinear dynamics in hydropower rotors
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • In hydropower systems, it is essential to avoid catastrophic failures that lead to human and economic losses. Unfortunately, a hydropower rotor can behave abnormally since several nonlinear effects occur during start-up, shut-downs or when running at nominal speed. Weak nonlinear interaction in the bearings, electromagnetic interaction between the generator and rotor or fluid-structure interaction in turbines are typical nonlinear effects that may appear. Moreover, strong nonlinearities can also occur due to blade contacts and assembly errors. These types of nonlinearities can be dangerous in case of bad design of the rotor, and it could even lead to catastrophes in the worst case. In this thesis, simple models are used to describe the different types of nonlinearities, with focus on blade rubbing, bearings and electromagnetic interaction. These interactions are usually investigated on Jeffcott rotors or rigid rotors to reduce the dimension of the design space to a few important parameters only. The dynamics of the system are evaluated by using common tools such as Poincare sections, bifurcation diagrams, Maximum Lyapunov Exponent (MLE), Lyapunov spectrum and waterfall plots of the Fast Fourier Transform (FFT). The numerical results have been compared with experimental results to ensure that these models are satisfying in our range of study. Once these simple models have been verified, they can be used to simulate the full hydropower rotor by including all interaction types. A focus is made on the numerical methods to employ and reduction methods to gain computation time, as well as to know under which circumstances the nonlinear interactions have to be included in comparison with the linear analysis. As a result, this work intends to provide guidelines about the models to use to perform dynamic simulations on fullscale turbines and to know when a linear model can be sufficient to evaluate a machine at design stage or when changing any mechanical component in the hydropower rotor.
65.
  • Tsandzana, Afonso Fernando, 1969- (författare)
  • Homogenization of some new mathematical models in lubrication theory
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • We consider mathematical modeling of thin film flow between two rough surfaces which are in relative motion. For example such flows take place in different kinds of bearings and gears when a lubricant is used to reduce friction and wear between the surfaces. The mathematical foundations of lubrication theory is given by the Navier--Stokes equation, which describes the motion of viscous fluids. In thin domains several approximations are possible which lead to the so called Reynolds equation. This equation is crucial to describe the pressure in the lubricant film. When the pressure is found it is possible to predict vorous important physical quantities such as friction (stresses on the bounding surfaces), load carrying capacity and velocity field.In hydrodynamic lubrication the effect of surface roughness is not negligible, because in practical situations the amplitude of the surface roughness are of the same order as the film thickness. Moreover, a perfectly smooth surface does not exist in reality due to imperfections in the manufacturing process. Therefore, any realistic lubrication model should account for the effects of surface roughness. This implies that the mathematical modeling leads to partial differential equations with coefficients that will oscillate rapidly in space and time. A direct numerical computation is therefore very difficult, since an extremely dense mesh is needed to resolve the oscillations due to the surface roughness. A natural approach is to do some type of averaging.In this PhD thesis we use and develop modern homogenization theory to be able to handle the questions above. Especially, we use, develop and apply the method based on the multiple scale expansions and two-scale convergence. The thesis is based on five papers (A-E), with an appendix to paper A, and an extensive introduction, which puts these publications in a larger context.In Paper A the connection between the Stokes equation and the Reynolds equation is investigated. More precisely, the asymptotic behavior as both the film thickness <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cepsilon" /> and wavelength <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmu" /> of the roughness tend to zero is analyzed and described. Three different limit equations are derived. Time-dependent equations of Reynolds type are obtained in all three cases (Stokes roughness, Reynolds roughness and high frequency roughness regime). In paper C we extend the work done in Paper A where we compare the roughness regimes by numeric computations for the stationary case.In paper B we present a mathematical model that takes into account cavitation, surfaces roughness and compressibility of the fluid. We compute the homogenized coefficients in the case of unidirectional roughness.In the paper D we derive a mathematical model of thin film flow between two close rough surfaces, which takes into account cavitation, surface roughness and pressure dependent density. Moreover, we use two-scale convergence to homogenize the model. Finally, in paper E we prove the existence of solutions to a frequently used mathematical model of thin film flow, which takes cavitation into account.
66.
  • Wallström, Peter (författare)
  • On Value and Waste
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Value and waste are concepts that are used in improvement projects. In lean the concepts are fairly simple. Reduce the waste and the value has increased. However, value is both multidimensional and differs over time. If the concepts value and waste are to be used, the concepts must be clearly defined and measured. Otherwise, value can be reduced for the customer/user and the cost increased for the producer/seller. The purpose in this thesis is to investigate how value and waste are perceived by different stakeholders, how value and waste are related, and how value and waste are measured. The focus of the study is the improvement of production and services. The study does not investigate the product/service development. The conclusions are based on a number of cases and research from different fields such as resource-based view and marketing. The study use mix of qualitative and quantitative methods. Measures of forecasting accuracy and their relations where explored with different statistical tools in order to understand the influence of measures and dimensions. The view of value concerning energy efficiency was examined in a statistical analysis of a survey concerning stakeholders’ view of a specific value, energy efficiency, as well as their influence on the value creation process. A multiple qualitative case study explores the relation between value and waste in different settings and the consequences of waste focus. The findings in the multiple case study are confirmed and elaborated further by an additional case study, both qualitative and quantitative, of value stream mapping.Value and waste are analysed with the use of order winners and qualifiers. Also, a model to clarify the consequences of mixing value creation and value exchange for customer/user and producer/seller have been defined and used in the analysis.Depending on the stakeholder there is a difference between whether value can be regarded as a use value, exchange value or both. Even if exchange value is related to a specific moment in time, use value is not. The view of value differs among stakeholders which increase the risk of sub-optimisation in production.Value and waste have multi-dimensional properties and there are links between the different dimensions. The relationships depend upon the situation in question. The lean seven types of waste are not independent dimensions. Also, the concept of waste as anti-value is too simplistic. In all cases studied the focus is on waste, not value. Also, it is often the symptoms of waste that are of interest in measures taken not the root causes. Reduction of waste without considering the value can create new waste. Since waste is a dependent variable, it should not be measured without considering value. Another complication is that value and waste often occurs at different points in time and in different settings.Single measures are sensitive to its environment. Several measures are more robust. Measures distort and influence the perception and thereby the decision of the studied phenomena. Also, the notion of value and waste becomes harder to define and trace as the resolution and detailing of the studied process increases.
67.
  • Wenngren, Johan (författare)
  • Team activities in concept development Addressing open-ended problems
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The concept development stage is a fundamental part of the development process; in this early stage, teams define what constitutes the problem and find direction for the subsequent problem-solving activities. Concept development that searches for innovative results starts from a problem formulation, or design brief, that should not be too precise; keeping parts open for interpretation and alternatives is important for allowing for the possibility to create new solutions. However, handling such open-ended development problems is a challenge as they do not point to a specific solution from the start. The difficulties that the development team encounters in order to find a way forward are the focus of this thesis. Thus, the purpose of this thesis is to identify, describe and discuss how teams explore and define open-ended problems in concept development. Fundamentally, teams have to explore and define open-ended problems in order to retrieve answers needed to undertake purposeful actions. The exploration and definition procedure creates stepwise understanding of sub-problems as open-ended problems typically have interdependencies. This implies that the team must suggest a number of representations before they can propose corresponding alternative solutions. The failure to adopt such a procedure leads to a risk of fixation and prematurely closing the definition of what constitutes the core issues of the design problem. This study specifically shows that confronting the design brief or task is an essential activity in the resolution of open-ended problems. Moreover, a number of practical steps for iteratively managing open-ended problem resolution are proposed. The study in this thesis is based on an explorative approach utilising experiments and observations as methods for data collection. The empirical data come from a workshop format (i.e., an innovation contest), teams on student projects and, to some extent, companies. The contribution from this thesis to engineering design relates mainly to the social and participatory aspects of innovation in concept development. The contribution to practice is mainly the formulation of iterative steps; these could be applicable to different types of open-ended problem resolution. One additional area of application may be a more modern type of product development in the manufacturing industry — namely, where product logics and service logics are interlinked.
68.
69.
  • Ye, Pengcheng (författare)
  • Zeolite Membrane Separation at Low Temperature
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The energy consumption of separation processes accounts for a large part of the total energy consumption in chemical industry. Membrane separation processes require much less energy than the currently used thermally driven separation processes and could therefore reduce energy consumption in industry considerably. Today, most commercially available membranes are organic polymeric membranes. Inorganic zeolite membranes have several superiorities over polymeric membranes, e.g., higher flux and selectivity, higher chemical and thermal stability, and thus have great potential for a variety of gas and liquid separations. Whereas there have been extensive studies on zeolite membrane separation at high temperature during the past decades, scientific reports on the low temperature applications of zeolite membranes is extremely scarce and there are no reports at cryogenic temperature. This work is pioneering research on investigation of the performance of zeolite membranes for separation of various gas mixtures at unprecedentedly low temperature, down to cryogenic temperature. In the present work, zeolite membranes were, for the first time, evaluated for gas separation at cryogenic temperature. Air separation by ultra-thin MFI membranes was carried out at a feed pressure ranging from 100 mbar to 5 bar over the temperature range of 62–110 K. The membranes were found to be oxygen selective at all the conditions investigated. The observed results were well above the upper bound in the 2008 Robeson selectivity-permeability plot when the feed pressure was less than or equal to 1 bar. The O2/N2 separation factor reached 5.0 at 67 K and 100 mbar, with a high O2 permeance of 8.6 × 10-7 mol m-2 s-1 Pa-1. The performance of our membranes (in terms of selectivity) was comparable to that recently reported for promising polymeric membranes, but 100 times higher in terms of permeance and flux. The membrane selectivity was found to increase with decreasing temperature and feed pressure. The present work has therefore indicated the optimum conditions for air separation using MFI membranes, namely low feed pressures and cryogenic temperatures. A mathematical model showed that the selectivity to O2 emanated from O2/N2 adsorption selectivity. N2/He separation is essential for helium recovery from natural gas and helium reclamation for airships and submarines. Zeolite membranes were evaluated for this separation over the temperature range of 85–260 K, possessing high N2-selectivity at all the conditions investigated. When the feed pressure was 5 bar and the permeate pressure was 0.5 bar, a highest N2/He separation factor of 62 was observed at 124 K. The N2 permeance was rather high, up to 39 ×10−7 mol m−2 s−1 Pa−1. The separation was attributed to adsorption selectivity of the membranes to N2, effectively suppressing the transport of He in the zeolite pores and this effect was more significant at cryogenic temperature. A mathematical model showed that the largest difference of adsorbed loading over the film at ca. 120 K was probably the main reason for the observed maximum selectivity at this temperature. The model also indicated that the selectivity could even be increased by 2–3 times if the membrane was totally defect-free. This work demonstrates that a zeolite membrane process could be rather competitive for N2/He separation. Synthesis gas generated from biomass is a valuable, renewable resource that can be used for production of clean energy and various chemicals. It is mainly a mixture of CO, CO2, and H2. CO2 is an undesired component in the syngas and should, therefore, be removed. In this work, CO2 separation from H2 and CO using zeolite membranes was studied for at low temperatures, down to 235 K and at a feed pressure of 9 bar. The membrane performance in terms of both selectivity and flux was superior to that reported for the state-of-the-art polymeric and inorganic membranes. The highest separation factor was 202 for CO2/H2 separation at 235 K and 21 for CO2/CO separation at 258 K, significantly higher than that at room temperature. The observed CO2 flux was very high, i.e., 300-420 kg m-2 h-1, in the entire temperature range of 235–310 K. Initial cost estimation revealed that high flux zeolite membranes were economically competitive with the present commercial polymeric membranes. Moreover, the process relying on our zeolite membranes was shown to be appreciably more space-efficient. Efficient light olefins/N2 separation technologies are of great interest to recover monomers from N2 purge gas in polymer plants. C3H6/N2 and C2H4/ N2 separation were investigated using zeolite membranes in a temperature range of 258–356 K. The membranes were rather selective towards the hydrocarbons. For C3H6/N2 separation, a maximum separation factor of 43 was observed at room temperature with a C3H6 permeance of 22×10-7 mol m-2 s-1 Pa-1. For C2H4/N2 separation, the maximum separation factor was 6 at 277 K with a C2H4 permeance of 57×10-7 mol m-2 s-1 Pa-1. The findings reveal that zeolite membranes are promising candidates for light olefins/N2 separation in petrochemical processes. The adsorption properties dominate separation performance for systems studied in the present work. The high selectivity emanates from competitive adsorption, e.g., the strongly adsorbing components hinder the permeances of the weakly adsorbing ones and the effect was stronger at low temperature. In addition, gas permeances through zeolite membranes tend to decrease at low temperature most likely due to decreasing diffusivity, especially at cryogenic temperature. However, the permeances of our membranes even at low temperature were still one to two orders of magnitude higher than those reported for inorganic and polymeric membranes. Thus, the high-flux membranes have great superiority in this case. The fairly high permeance even at low temperatures was ascribed to the ultra-thin (&lt; 1µm) film and highly permeable support used. We provide here a promising candidate, ultra-thin zeolite membranes, with high permeance and excellent selectivity for gas separation application at low temperature.
70.
  • Zhang, Liangwei (författare)
  • Big Data Analytics for Fault Detection and its Application in Maintenance
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Big Data analytics has attracted intense interest recently for its attempt to extract information, knowledge and wisdom from Big Data. In industry, with the development of sensor technology and Information &amp; Communication Technologies (ICT), reams of high-dimensional, streaming, and nonlinear data are being collected and curated to support decision-making. The detection of faults in these data is an important application in eMaintenance solutions, as it can facilitate maintenance decision-making. Early discovery of system faults may ensure the reliability and safety of industrial systems and reduce the risk of unplanned breakdowns.Complexities in the data, including high dimensionality, fast-flowing data streams, and high nonlinearity, impose stringent challenges on fault detection applications. From the data modelling perspective, high dimensionality may cause the notorious “curse of dimensionality” and lead to deterioration in the accuracy of fault detection algorithms. Fast-flowing data streams require algorithms to give real-time or near real-time responses upon the arrival of new samples. High nonlinearity requires fault detection approaches to have sufficiently expressive power and to avoid overfitting or underfitting problems.Most existing fault detection approaches work in relatively low-dimensional spaces. Theoretical studies on high-dimensional fault detection mainly focus on detecting anomalies on subspace projections. However, these models are either arbitrary in selecting subspaces or computationally intensive. To meet the requirements of fast-flowing data streams, several strategies have been proposed to adapt existing models to an online mode to make them applicable in stream data mining. But few studies have simultaneously tackled the challenges associated with high dimensionality and data streams. Existing nonlinear fault detection approaches cannot provide satisfactory performance in terms of smoothness, effectiveness, robustness and interpretability. New approaches are needed to address this issue.This research develops an Angle-based Subspace Anomaly Detection (ABSAD) approach to fault detection in high-dimensional data. The efficacy of the approach is demonstrated in analytical studies and numerical illustrations. Based on the sliding window strategy, the approach is extended to an online mode to detect faults in high-dimensional data streams. Experiments on synthetic datasets show the online extension can adapt to the time-varying behaviour of the monitored system and, hence, is applicable to dynamic fault detection. To deal with highly nonlinear data, the research proposes an Adaptive Kernel Density-based (Adaptive-KD) anomaly detection approach. Numerical illustrations show the approach’s superiority in terms of smoothness, effectiveness and robustness.
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