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  • Disputas: 2024-05-28 13:00 E632, Luleå
    Toromanovic, Jasmina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Monitoring and Modelling of Embankment Dams2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Modelling can be used as a tool for prediction of the behaviour of embankment dams as a part of the dam safety work. It is advantageous to predict the performance and compare to measurements done, to obtain more knowledge about the dam behaviour, as these structures are complex and potential failures are hazardous. The research presented in this thesis covers parameter identification by backanalysis, interpretation of dam measurements and numerical predictions of dam behaviour. The research highlights the role of numerical modelling as a supportive tool in dam engineering, ratherthan a standalone technique. Two embankment dams were analysed in the research: a 45 metres high existing hydropower dam and a four metres high experimental dam built during the project.

    The soil materials in an embankment dam vary significantly, as the zones in a dam have different functions. To create reliable numerical models, parameter values defining the stress-strain relationship of the materials are needed. Obtaining such information for existing embankment dams poses challenges, often due to limited available data and the potential risks associated with traditional field sampling methods. In previous research at Luleå University of Technology, inverse analysis was successfully applied to embankment dam calibration of finite element models against field measurements, by utilizing an optimisation code with a genetic algorithm for optimisation. Inverse analysis provides a non-destructive method for obtaining information about the stress-strain relationship of the material in a dam.

    First, applications of inverse analysis are exemplified on an existing embankment dam. The study investigates the impact on the inverse analysis methodology when errors occur in the field measurements. The employed genetic algorithm showed its robustness when dealing with errors, this is important since errors are likely to occur in field measurements. Thereafter, the study examined the usage of parameters identified through inverse analysis in predictions of deformations when a stabilising berm was constructed on the downstream shoulder. The predicted deformations were compared to deformations from inclinometer measurements. The trend of the measured deformations was replicated in the numerical model, and the magnitudes were in the right order. The study shows that predicting future dam behaviour based on results from inverse analysis can be done reasonably well in this case.

    Second, the mechanical behaviour of an experimental embankment dam is interpreted and modelled. Monitoring of pore pressure was done with transducers that were installed at different levels covering the whole core and parts of the filters. Measurements were performed continuously. The response of pore pressure in the core, during impoundment and operation, are focused on. A significant delay of the saturation front was observed, as the pore pressure in the bottom of the downstream part of the core was not building up as expected during impoundment and operation. Fully-coupled numerical analyses were performed, in order to better understand the conditions of the core in the experimental dam. The core was initially assumed to be homogeneous, but the numerical results showed poor agreement with the observed behaviour from field. By further analysing the measurements and modelling, the experimental dam was found to be non-homogeneous, even though it was built under very controlled conditions. Variations in the hydraulic conductivity in the dam core were therefore introduced in the numerical model. The hydraulic conductivity changed with height in the dam, was different in the vertical and horizontal direction and was also changing with time at specific places in the core. With these numerical adjustments better correlations against measurements were obtained, compared to the homogeneous case, indicating that homogeneous conditions are not suitable for the core. The study also showed that the values of parameters obtained from laboratory testing are not suitable for the whole core, as the conditions assumed in laboratory do not correspond to the prevailing field conditions.

    Measurements of the strain development in the bottom of the embankment dam was done by fibre optics. The settlements in the dam body after construction are captured, mainly as areas of higher lateral strain at the toes of the dam. The 1% sloping foundation towards the downstream side is captured. The measurements show that more shear is activated at the downstream side. Impoundment causes the largest strains, it can be observed that the strains vary in the different dam zones the bottom of the dam body.

    In summary, the research presented in this thesis has shown how numerical modelling can be used as support in dam engineering, when combined with monitoring data. Values of parameters that would have been difficult to retrieve otherwise are obtained by inverse analysis, making it possible to perform more reliable predictions. The modelling has also helped to explain unexpected behaviour from monitoring of pore pressure. When the experimental dam was built, it was expected that the core would be homogeneous. The monitoring of the dam and the numerical modelling revealed that the core was non-homogeneous. The experimental dam is small, and it was constructed under very controlled forms. Therefore, it is reasonable to assume that it would be difficult to construct a homogeneous core in a real, large embankment dams. This is an important finding in the thesis, which can influence both how dams should be numerically modelled as well as how dam safety assessments during first impoundment and the beginning of the operation phase should be done.

    Fulltekst (pdf)
  • Disputas: 2024-06-04 09:00 E632, Luleå
    Chen, Jun
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Optimizing Ice-Resistant Surfaces: Unifying Self-Healing, Durability, and Functional Design for Superior Anti-/De-Icing Performance2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Snow and ice accumulation on critical infrastructure such as wind power turbines and power lines cause significant challenges and safety hazards in cold climate regions during wintertime. Research into anti-/de-icing technologies has been divided into two main streams, i.e., active, and passive approaches. Active technologies, including electric thermal, photothermal technologies, etc, are widely used in anti-/de-icing fields. Passive technologies, including hydrophobic and slippery surfaces, have gained increasing interest due to their low energy consumption and sustainable profile, but these passive technologies are often limited by relatively short service life and poor mechanical durability. 

    A potential way of improving the anti-/de-icing performance would be to combine different technologies and create electric thermal superhydrophobic surfaces and/or photo-thermal superhydrophobic surfaces. Furthermore, the mechanical durability could be improved by developing self-healing superhydrophobic surfaces and wear-resistant electric thermal surfaces. However, some important studies of relevant mechanisms to achieve this are absent in the literature, such as the influence of self-healing on ice adhesion, and investigation on how to unify the durability and anti-/de-icing performances via molecular structure design. 

    This thesis addresses these questions by focusing on enhancing the wear resistance and anti-/de-icing efficiency of anti-/de-icing materials through innovative material design. We conducted ice-phobic tests in lab environment, and long-term ice-phobic field tests, which helped us to further understand and optimize the design of ice-phobic surfaces. 

    This thesis contributes to developing more durable, efficient, and sustainable anti-/de-icing solutions, addressing the critical need for reliable performance under adverse weather conditions. 

    The key findings were: 

    (1) A novel self-healing and low-ice adhesion poly silicon urea coating was developed, leveraging the intrinsic material structure for creating sufficient wear resistance and self-healing capabilities. The Poly silicon urea coating exhibits below 10kPa ice adhesion strength, which is far lower than the ice-phobic surface request(<100kPa). The molecular structure’s influence on self-healing and ice adhesion are specified in this work.

    (2) Inspired by the low-icing bonding properties of silicon urea, a graphene-enhanced siloxane urea multi-functional coating was designed, where the low-icing properties were combined with electric and thermal conductivity to achieve both active and passive anti-/de-icing effects. This graphene enhancement coating exhibits 10 minutes of removing all ice accretion under ~570W/m2 electric power on the lab scale test. The field tests, where a graphene enhancement coating surface can keep ice-free under ~310W/m2 during the whole winter in a harsh natural environment.  

    (3) To explore the influence of mechanical durability on ice-phobic, a composite coating which integrates wear resistance and thermal conductive was formulated. Graphene was proven as a suitable additive to enhance thermal conductivity and wear resistance. Compared with the blank control coating and a boron nitride composite coating, the thermal conductivity of a graphene composite coating increased around 3 times, and the anti-wear performance based on wear depth was increased around 1.5 times. The wear mechanism and wear influence on anti-/de-icing behaviour are investigated in this work. 

    (4) This work also explored the impact of surface functional groups on anti-/de-icing performance, uncovering that the force interactions and steric radius of these groups significantly influence surface element distribution and material strength, thereby affecting wettability and wear behaviour. The results show that the hydrophobicity of the groups is not the only factor to influence the surface properties. A smaller steric radius and strong interactions are beneficial for reducing the van der Waals' gap between groups which can inhibit the wetting of the water molecules. The influence of five different typical groups on mechanical durability and ice adhesion is investigated in this work.

    Fulltekst (pdf)
  • Disputas: 2024-06-05 09:00 E231, Luleå
    Choudhry, Jamal
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Numerical models for simulating wear and friction-induced heating in rough surface contacts2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The study of friction and wear is a crucial element in the effort to reduce carbon footprint in technology. It is evident that friction and wear are responsible for a significant amount of global energy losses, emphasizing the need for research on the topic. However, due to the complexities associated with multi-physics phenomena and surface roughness at the micro-scale, it can become challenging to understand the tribological processes involved. Apart from friction and wear, this interaction also gives rise to phenomena like frictional heating and the generation of third-body wear particles due to both adhesion and abrasion. These phenomena can lead to reductions in performance, efficiency and durability in mechanical systems. 

    The aim of present work is the development of advanced numerical tools with the purpose of studying friction and wear processes in detail. Wear, friction and the associated heating can be found in nearly all types of sliding mechanical systems. Typical examples include, but are not limited to, bearings, gears, shafts and cams. The numerical methods which exist currently are usually simplified, using idealized assumptions and non-realistic boundary conditions. For this reason, many of the models are not able to account for the various mechanisms involved in multi-asperity contacts. 

    This research presents a multi-scale and multi-asperity thermo-mechanical model to study the temperatures at the interface due to surface roughness, while accounting for wear with Archard’s wear law. Realizing that the thermo-mechanical behavior is influenced by the post-necking behaviour of stresses and their respective states, the subsequent work focuses on incorporating these in single asperity wear simulations. The research has provided valuable insights into the wear mechanisms, revealing various issues within classical models, such as Archard’s wear law and resulting in the development of more advanced tools. Specifically, in the context of asperity-to-asperity interaction, where non-linear effects are more prominent, a linear relation between the wear volume and load may no longer hold. To address this, the research introduces thermo-mechanical models that combine the Boundary Element Method with non-linear Finite Element methods to study temperatures, deformations and wear in asperity-to-asperity contacts.

    Key findings suggests that the average interface temperature is independent of roughness, unlike the maximum temperature which increases with increasing high frequency cut-off values and decreasing Hurst exponent values. Recognizing the significant influence of strain-softening and stress-states on the thermo-mechanical behavior, subsequent studies have been directed towards addressing this aspect, while focusing on single asperity collisions. The work presents an advanced three-dimensional Finite Element and a meshfree particle method to simulate large deformations and fracture in colliding asperities, accounting for stress triaxiality and lode parameters. It is shown that the maximum temperature rise and total wear volume are both affected by the triaxiality values and strain-softening. Simulations conducted with a model based on the meshfree particle method reveals a critical parameter that signals the transition from mild to severe wear, leading to the creation of a wear particle at the interface. More importantly, the findings have reveal the limitations in Archard’s wear law, serving as motivation for improvement and resulting in the final paper. In the final study, an improved wear coefficient is presented, resulting in more accurate wear predictions than the traditional Archard’s wear law. The improved wear coefficient is deduced from the contact area and the accumulation of crack energy along the direction of frictional force, resulting in a spatially varying and non-linear relation between wear volume and load. This model is coupled with the Boundary Element Method, which assumes that the surfaces are flat and semi-infinite and that the interacting surfaces are perfectly-plastic. This advancement eliminates the necessity of resorting to large, complex, and often time-consuming finite element based methods. The work also highlights deficiencies in the classical Archard’s wear model in correctly predicting the wear particle formation.

    Fulltekst (pdf)
  • Disputas: 2024-06-07 10:00 A109, Luleå
    Dahlberg, Moa
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, Samhällsvetenskap.
    Shared Authority – More Capacity: Hybrid Governance of National Parks in Southern Africa2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A state's ability to establish and enforce collective rules is central to its ability to govern. How states can increase their capacity to achieve this in areas where local actors – such as traditional authorities in Africa –are central structures is therefore occupying both researchers and practitioners. I contribute to this growing body of literature by focusing on the de facto interactions between state- and traditional authorities. Based on extensive fieldwork, I study how hybrid governance arrangements with traditional authorities influence the state's capacity to govern through the perceptions and experiences of park- and traditional authorities and local inhabitants in National Park governance in the Great Limpopo Transfrontier Park and Conservation Area. The findings align with previous scholarships, showing that states can increase their capacity by sharing authority with traditional authorities. I show that park authorities actively interact with traditional authorities to increase their capacity to establish and enforce conservation rules. Negotiations and informal practices harmonize rules, mitigate conflicts, and combine formal and customary enforcement systems, thus strengthening the state system. The thesis underlines that to understand the capacity of the modern African state, we need to include the informal governance practices with local actors in our analyses.

    Fulltekst (pdf)
  • Disputas: 2024-06-11 09:00 E632, Luleå
    Valizadeh, Ali
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Role of Surface Morphology on Bed Particle Layer Formation During Thermal Conversion of Woody Biomass in Fluidized Beds2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Bed particle layer formation is a crucial aspect of fluidized bed conversion of woody biomass, which can positively and negatively impact the process performance. The layer formation may lead to issues such as bed agglomeration and bed material deposition or reduced oxygen transport capacity of oxygen carriers. However, bed layer formation may positively affect the product gas composition in gasification. While extensive research has been conducted on the interactions between the ash-forming constituents from various wood-derived fuels and different bed materials, the influence of the bed particle surface properties on the bed layer characteristics remains largely unexplored in the existing literature.

    This thesis thoroughly studied the role of bed particle surface morphology on the bed layer formation and its characteristics across different bed particle types within various fluidized bed conversion processes of woody biomass. The bed particle samples were collected from different bench-scale, semi-industrialscale, and industrial-scale conversion units at different time intervals from the start-up to assess the bed particle layer formation process throughout the bed particle age in different conversion processes of woody biomass. Natural sand bed samples (consisting mainly of quartz and K-feldspar) were taken from a 30 MWth bubbling fluidized bed (BFB30) combustion unit and a 90 MWth circulating fluidized bed (CFB90) combustion unit. K-feldspar and olivine were obtained from a dual fluidized bed (DFB12-4) indirect gasification unit comprising a 12 MWth circulating fluidized bed combustor and a 2-4 MWth bubbling fluidized bed gasifier. Different types of ilmenite samples were taken from a 5 kWth bench-scale bubbling fluidized bed (BFB5) and a 12 MWth circulating fluidized bed (CFB12) combustion unit. Additionally, quartz and natural sand samples (comprising mainly quartz, K-feldspar, and Na-feldspar) were gathered from three different industrial fast pyrolysis plants. Bed particles found in the samples were subjected to different analysis methods. Scanning electron microscopy (SEM), coupled with energy dispersive spectroscopy (EDS), served as a primary tool for obtaining information regarding the morphology and elemental composition of different layers present on the surface of bed particles and inside the bed particle core. In instances where layers were too thin to be adequately examined via SEM/EDS, transmission electron microscopy (TEM) was employed as a complementary analysis method. X-ray microtomography (XMT) was also utilized to explore the distribution of bed particle layers on the particle surfaces. This method facilitated both qualitative and quantitative assessments, including observation of the surface morphology of the bed particles, analysis of the bed layer distribution on the bed particle surface, along with measurements of bed particle layer thickness and the volume fraction of various features throughout the bed particles.

    Comprehensive analysis of the results from different characterization techniques showed that for all studied bed particles, regardless of their chemical composition, the inner layer (i.e., the Ca-reaction layer) was thicker on convex areas and thinner or entirely missing in the concave regions. The outer layer, mainly consisting of Ca compounds (i.e., the ash-deposition layer), was more likely to be found on the convex areas of the bed particle surface. Overall, the total bed particle layer thickness (inner and outer layer) was larger on the convex areas compared to the concaves. Consequently, the concave regions can facilitate mass transfer to and from the bed particle core even after the full development of the Ca-rich inner layer. Therefore, in the case of using quartz and Na-feldspar particles where there was a high chemical potential to react with fuel-derived gaseous alkali, the inner-inner layer and the crack layers (together referred to as the K-reaction layers) were connected to concaves on the bed particle surface. For the studied oxygen carrier (i.e., ilmenite), where most of the convex regions at the bed particle surface were covered with the Ca-rich layer, Fe could still migrate to the bed particle surface through concaves.

    Bed particle layer characteristics observed in the fast pyrolysis plants were, to some extent, different compared to those in the combustion and gasification of woody biomass. In general, the layers were considerably thinner in the fast pyrolysis process, with a similar exposure time compared to combustion and gasification. Crack layers were not detected in quartz and Na-feldspar bed particles in any of the studied fast pyrolysis plants, and the inner layer had a lower Ca concentration than that in the combustion or gasification. Further, only the Ca-reaction layer was identified on feldspar bed particles. However, the distribution pattern of the bed particle layers at different morphologies on the bed particle surface resembled that in combustion and gasification.

    The findings indicated that apart from the chemical composition, the surface morphology of the bed particles plays a vital role in determining their performance throughout the fuel conversion process in the fluidized bed. Specifically, as the crack layer formation in quartz bed particles is linked to the concave-shaped areas on the bed particle surface, quartz bed particles characterized by fewer concaves experience less fragmentation during the conversion process. Conversely, when employing ilmenite as an oxygen carrier, the presence of concaves on the particle surface facilitates the outward migration of Fe over prolonged exposures, albeit potentially compromising the structural integrity of the bed materials. Thus, a trade-off exists between achieving a desired oxygen-carrying capacity and maintaining structural integrity over extended durations. Previous studies have suggested that the formation of a Ca-rich layer on bed particles can positively influence the composition of the product gas in the gasification process. Results from this work showed that the Ca-rich layer on bed particles intended for gasification, such as K-feldspar and olivine, is thicker and more evenly distributed on particles possessing a surface morphology featuring more frequent convex shapes.

    Fulltekst (pdf)
  • Disputas: 2024-06-12 10:00 E632, Luleå
    Bahaloo, Hassan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mechanics of Ice and Snow as a Granular Material2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, the mechanical properties of ice and dry snow as a class of granular materials are investigated through a series of experiments, analyses, and simulations. The primary focus is on understanding the intricate details of ice sintering, capillary bridge formation, and the behavior of snow under varying conditions.

    The investigation into ice sintering reveals a formulation of the sintering force, considering temperature, pressing force, contact duration, and particle size during the primary sintering stage. The results indicate a nearly linear increase in sintering force with external pressing force, while dependency on contact duration and particle size follows a nonlinear power-law relationship. The temperature dependence of the sintering force is nonlinear, aligning with the Arrhenius equation. The ultimate tensile strength of ice and the axial stress concentration factor are identified as crucial factors in determining the sintering force. Additionally, observations near the melting point reveal the formation of a liquid bridge between contacted ice particles.

    Moving on to capillary bridge formation, the experiments demonstrate the presence of a liquid bridge between an ice particle and a smooth (or rough) aluminum surface at controlled temperature conditions. The separation distance is found to be proportional to the cube root of the bridge volume, which decreases with decreasing temperature. Notably, for a rough surface, capillary bridge formation diminishes under the considered experimental conditions.

    The significance of snow in various contexts prompts an exploration of its mechanical properties. Utilizing micro-computed tomography imaging and quasi-static mechanical loading, a methodology for mapping the density-dependent material properties of manufactured snow is established. The study investigates structural parameter variations during loading, revealing insights into the three-dimensional structure, relative density, and mechanical behavior of snow. Results from Burger’s model show an increasing trend in modulus and viscosity terms with density. Digital volume correlation aids in calculating full-field strain distribution, highlighting particle characteristics and changes in specific surface areas during loading.

    Expanding the scope to natural snow, cutting-edge techniques like micro-tomography are integrated with traditional loading methods. Employing CT imaging and uniaxial compression tests, along with digital volume correlation, density-dependent material properties are analyzed. The study incorporates two snow samples, revealing density-dependent trends in modulus and viscosity terms. The results provide valuable insights into the non-homogeneous behavior of natural snow and contribute to fields such as glacier dynamics and avalanche prediction.

    Finally, the discrete element method with a variable bond model is used to simulate the behavior of granular materials, specifically focusing on snow. The model incorporates temperature dependent cohesion and effectively captures the angle of repose and stress-strain behavior of snow.

    In summary, this thesis presents an investigation into the mechanical properties of ice, capillary bridge formation, manufactured snow, natural snow, and granular materials, providing insights and contributing to the understanding of ice and snow in various environmental and engineering contexts.

    Fulltekst (pdf)
  • Disputas: 2024-06-13 10:00 A109, Luleå
    Fjellborg, Daniel
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, Samhällsvetenskap.
    Strategies and Actions in Swedish Mining Resistance: Mapping Anti-Extraction Movements and Exploring How Their Interpretations of Socio-Political Context Shape Mobilization Against Mining Projects2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Across the world, the demand for minerals is steadily increasing. In Europe, the push for mining coincides with rising public mobilization against extraction projects, and mining-related conflicts will likely be a feature of Europe’s foreseeable future. To understand the trajectories of mining conflicts, and to find just ways of handling them, it is important to understand the strategies and actions of the networks of actors that oppose extraction projects, that is, anti-extraction movements. 

    While previous research has primarily explored mining resistance in the Global South, our knowledge about mining resistance in Europe is lacking. I contribute to filling this gap by investigating anti-extraction movements in Sweden, a long-term producer of minerals. The aim of the thesis is thus to explore what strategies and actions anti-extraction movements in Sweden use and how and why they choose them. I use social movement theory and emphasize how choices of strategies and actions are shaped by the socio-political context in which movements are embedded. With the help of frame analysis and an interpretive research approach, I explore how movement actors’ interpretations of contextual opportunities and constraints shape their actions, thus contributing to the ongoing research debate about how surrounding societal actors and institutions influence movement agency. 

    In four papers, building on an extensive document analysis and interviews with movement actors, I systematically map and analyse anti-extraction movements in Sweden and provide in-depth studies of selected cases. I ask two research questions: 1. What anti-extraction movements are there in Sweden, in what socio-political contexts are they embedded, and what actions have they taken? 2. How do anti-extraction movements’ goals and interpretations of contextual opportunities and constraints shape their strategies and actions?

    The thesis presents the first comprehensive mapping of anti-extraction movements in Sweden and shows that mining resistance has increased across Sweden during the last two decades. My results reveal that movements use a wide range of actions, from civil disobedience and public demonstrations to litigation and political lobbying, and are composed of heterogeneous mixes of actors, including newly formed activist networks, organizations for farmers and Indigenous Sámi, and environmental organizations. Movements promote several visions for societal development, including environmental protection and sustainability, Sámi Indigenous rights and culture, and landowners’ rights and agriculture. In international comparison, the Swedish anti-extraction movements to a larger extent aim to influence political and legal actors and place less emphasis on project owners and corporate investors. 

    Regarding how socio-political context shapes strategies and actions, my results indicate that movement actors’ interpretations of contextual opportunities do not always align with researchers’ understandings of what an opportunity is, thus producing unexpected actions. Movement actors’ interpretations of opportunities and constraints are found to be influenced by their goals, their comparisons of available options, their previous experiences, and their role in relation to other actors in the movement. 

    My research shows that socio-political context often influences movement actors’ strategies and actions via their interpretations of opportunities and constraints for achieving goals. My results also suggest that socio-political context shapes movement actors’ strategies and actions by presenting them with appropriate ways to act in society. Lastly, my studies indicate that additional factors, including movement actors’ action traditions and identities, resources, and the diffusion of strategies, can influence movement actors’ interpretations of contextual opportunities and strategies and actions.

    Fulltekst (pdf)
  • Disputas: 2024-06-13 10:00 E632, Luleå
    Petkov, Valeri Ivanov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Characterisation of thermally induced degradation of high-temperature polymers and composites2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This project aimed to broaden the knowledge of high-temperature polymers and composites when exposed to elevated temperatures and an oxygen-containing atmosphere. The main accent has been on thermosetting polyimide resins reinforced with carbon fibers. When subjected to harsh atmospheric conditions, such as elevated temperatures and oxygen, polymer resins can undergo thermo-oxidative degradation, often resulting in weight loss and a surface layer with altered properties. High-temperature composites could experience such environments during operation. Therefore, it is crucial to understand how exposure to it could affect their performance. To simulate such an environment in the lab, the materials are aged in a controlled manner in a furnace or other equipment. The ageing of polyimide composites in this project was often performed at temperatures at or above 288 degrees Celsius for extended periods of up to 1500 hours.

    The first part of the project, and the first article, delved into the effect of different layups and thicknesses of the carbon fiber bundles on the thermo-oxidative behaviour of two composite materials made with the same thermosetting polyimide. Modelling the desorption during the initial stages of the ageing, showed that it exhibited a Fickian behaviour. X-ray computed tomography experiments were used to investigate the ageing behaviour of the materials and revealed that the satin weave composite formed a network of cracks, voids, and delaminations, that progressed with the ageing time, while the damage in the material made of thin plies was in the form of delaminations at the edges. The analysis of the tomographic datasets was performed using Otsu’s thresholding method for semantic segmentation of the defects within the materials.

    In an attempt to counter the crack formation on the surface of the satin weave composite observed during the first study, a new polyimide formulation was developed by the manufacturer. The amount of internal crosslinkers was reduced, aiming to increase the toughness of the resin after curing. The second article compares neat resin samples of the original and newly developed formulations with the help of a three-point bending test, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments. Samples were aged up to 1500 hours in ambient air. The results showed that while there were hints of a slight increase in the fracture toughness of the new formulation, the glass transition temperature had decreased, compared to the original resin.

    The two formulations were further investigated and compared with the help of thermogravimetric analysis in the fourth paper. Experiments were performed in isothermal and non-isothermal conditions for more robust results. It was found that the thermal oxidation of the two materials follows an autocatalytic model. The study highlights the importance of using both isothermal and non-isothermal data in the pursuit of more precise and robust analysis and modelling of the thermal oxidation of high-temperature polymers. Based on the results, a diagram, predicting the weight loss at specific times and temperatures, was created for each material.

    An alternative way of studying crack formation within challenging polymer composite tomographic datasets was presented in the fourth article. Instead of using a thresholding method, such as the

    previously used Otsu’s in the first study, in this case, a deep learning model was applied to the datasets to follow the progressive micro-cracking within the composite during a series of thermo-mechanical loadings. In contrast to a global thresholding method, which segments all defects within the dataset, the deep learning model, Attention U-Net, made it possible to create a more straightforward and robust way of performing segmentation on transverse cracks. The model was compared to and outperformed both Otsu’s method and a conventional U-Net.

    The previously developed methodology for semantic segmentation and the obtained results on transverse cracks were applied in a practical case in the fifth article, where the developed damage prediction model assumes that transverse cracks in thick plies span through the whole width of the specimen. The tomography and deep learning methodology helped shed light on the nature of the cracks and showed that previous assumptions, based on edge observation with light optical microscopy, should be taken as a conservative estimation.

    Fulltekst (pdf)
    Fulltekst tilgjengelig fra 2024-11-30 12:00
  • Disputas: 2024-06-14 09:00 B192, Luleå
    Rondon, David
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Dynamic Models for Mechanical Analysis of Synchronous Hydropower Generators2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Hydropower generators are essential for providing electricity for daily human activities. For that reason, designing and building reliable generators contributes to a sustainable energy supply market. Many studies have sought to model the dynamics of hydropower generators, as providing a reliable model would lead to more cost-effective designs; these models need to consider both operational and faulty conditions. A generator comprises many parts that contribute to its dynamics: tilting-pad bearings, rotor-rim, and stator’s core, which are the ones focused on in this study. Modeling a hydropower generator is a complex endeavor that requires considerable computational resources and is time-consuming. Therefore, this thesis aims to propose models to study and predict the dynamics of hydropower generators, which would be beneficial for manufacturers and operators, reducing the complexity of the design without compromising accuracy. To accomplish this, each mentioned individual part is explored. It starts with characterizing eight-pad tilting-pad bearings on vertical rotors, proposing a model, and comparing the results to experiments. Then it continues by considering the rotor rim in a generator to be flexible and proposing a model for the generator with flexible rotor rims while the stator remains rigid; this is accomplished using Lagrange equations, considering the centrifugal and Coriolis effects, the electromagnetic interaction between rotor and stator, and static and dynamic eccentricities. Reducing the complexity of the rotor rim required assembling 2-D curved beam elements to reproduce its geometry and testing on a generator prototype, discussing the impact of the connecting plates and the magnetic forces on the natural frequencies and the effect of static eccentricity and unbalance. A 3-D Finite Element model of the generator was also proposed, and both simulations focused on the similarities and differences between both approaches.  Furthermore, linear and nonlinear models of the electromagnetic forces acting on the rotor are also considered and applied in the model to study whether the nonlinear behavior in a generator can affect its stability by employing Bifurcation diagrams and Poincaré maps. 

    Fulltekst (pdf)
  • Disputas: 2024-06-14 09:00 A117, Luleå
    Bagheri, Marzieh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Sewage Sludge Treatment Scenarios: Techno-Economic Analyses of Energy and Phosphorus Recovery Focusing on Implementation Challenges2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Managing sewage sludge, an inevitable by-product of wastewater treatment processes rich in both contaminants and valuable resources, presents a dual challenge: ensuring pollution prevention by immobilizing or destroying contaminants, and facilitating resource recovery. Balancing these objectives is critical given the growing volumes of sewage sludge and the imperative to both protect the environment and recover valuable resources. The unknown risks of land application of sludge, the currently most common disposal method, make thermal conversion a promising alternative, as it enables energy recovery, the breakdown of potentially harmful organic compounds, and the formation of volume-reduced, sanitized products. Despite the technical feasibility, the commercial development of advanced recovery technologies has been slow. 

    This thesis aims to expand knowledge on different sewage sludge treatment and disposal scenarios under varying conditions; thereby shedding light on implementation challenges, local opportunities, and the financial dynamics critical for phosphorus and energy recovery from the perspectives of wastewater treatment plants, investors, and policymakers. The aim is primarily addressed by performing techno-economic analysis of sewage sludge treatment scenarios, covering the entire sludge treatment process from sludge treatment to end products and disposal (Paper II-V). The techno-economic analysis is supplemented by a review of academic research on sewage sludge management from 1971 to 2019 (Paper I). 

    Results from the analysis of sewage sludge management research (Paper I) show a narrow-focused perspective that often misses the broader, interconnected aspects of sewage sludge management, leading to research that, while detailed, fails to capture the complexity of the field. The investment viability of a new mono-/co-combustion plant for sewage sludge (Paper II) is highly conditional on heat, electricity, and fertilizer prices, and external financial support is often a crucial requirement. Cocombustion of sludge (in low ratios) with K-rich agricultural biomass requirement in and energy demand of a thermal dryer, and by yielding ash that contains phosphorus in a plant-available form. Utilizing existing heat facility (Paper III) and co-combustion to mitigate investment costs and energy demand in sludge management showed the potential to offer a cost-effective alternative to land application. However, the viability of co-combustion hinges on both a high heat market price (Paper II) and the proximity of affordable biomass resources (Paper III). Without these conditions, co-combustion may increase the financial burden of sludge management on wastewater treatment plants and policymakers. 

    Retrofitting a wastewater treatment plant by integrating hydrothermal carbonization in sludge treatment (Paper IV), demonstrated good economic feasibility, primarily due to the avoided disposal costs, while also recovering phosphorus. However, integrating hydrothermal carbonization in a system designed for a thermal dryer may cause a significant reduction in electricity production.

    Given the high moisture content of sludge and the low market prices for fertilizer, the potential revenue from energy and phosphorus recovery is inadequate to solely drive investment in advanced sewage sludge treatment technologies (Papers II-V). This issue is exacerbated by the fact that most wastewater treatment plants are small in scale. Collaborative sludge management across neighboring wastewater treatment plants (Paper V) increases phosphorus recovery capacity and leverages economies of scale, fostering investment in advanced technology. This strategy presents a significant opportunity to lower the treatment costs and offers a competitive alternative to land application, while encompassing energy and phosphorus recovery into the sludge treatment.

    In conclusion, resource recovery and pollution prevention in sludge management is a complex task that necessitates simultaneous consideration of technical aspects, product quality, site-specific conditions, and profitability to ensure a comprehensive and viable approach. Leveraging local infrastructure and resources in sewage sludge management is crucial, highlighting the ecessity for strategies to be tailored to the local opportunities and limitations. Such an approach outperforms mono-combustion by eliminating the investment ensures that solutions are not only environmentally sustainable but also economically viable and socially acceptable. 

    Fulltekst (pdf)
  • Disputas: 2024-06-14 09:30 E231, Luleå
    Loudoun, Fiona M.
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Hälsa, medicin och rehabilitering. University College Cork, Cork, Ireland.
    Play Occupations in Digital Spaces: Children’s Experiences Throughout Childhood2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Play is enshrined as a right for all children and is characterised by its autotelic and intrinsic nature.  As such, play is recognised as the primary occupation of children and best understood in terms of the multiple meanings it holds for individuals. The spaces in which children choose to play are considered to facilitate and limit opportunities and experiences for play reflecting a dynamic and complex interconnection between individuals, spaces, and occupations.    Despite the exponential growth of gaming technologies and digital devices offering children spaces for a plethora of novel, captivating and diverse play experiences, there remains a limited understanding of how these spaces afford or constrain play, especially from the perspective of the main protagonist, the child.  Exploring children’s perspectives of their play in such digital spaces can uncover the multifaceted dimensions highlighting the purposeful and meaningful nature of such occupations in children’s everyday life. Such understanding challenge current social discourses and support how such play experiences contribute to children’s wellbeing and active participation in society.   

    The overall aim of this thesis was to generate a deeper understanding of children’s perceptions of their play occupations in digital spaces throughout the trajectory of childhood. This thesis was informed by four, qualitative research studies.  

    Study I, a scoping review, aimed to identify and map the current literature examining children’s perspectives of play in digital spaces by exploring how the daily relevance, personal and ecological significance, and methods were approached in the research.  The review identified thirty-one articles from the past fifteen years with data extracted inspired by theories of play, ecology, and occupation.  The review highlighted a significant lack of empirical research focusing specifically on children’s autotelic play and which demonstrated a relevance to their everyday life.  Additionally, we found that methods did not consistently involve the active participation of children.  The findings from this review provided a clear rationale for the design of the subsequent three studies.

    Choice making reflects a key aspect of how children experience their play, therefore, study II explored children’s experiences of their choice making in play within digital spaces.  Eight participants were recruited who were aged between 6 and 7 years old.  Using a focus group design and a plethora of data generation tools, the findings indicate that children enjoyed the flexibility and variety of choices offered by their play in digital spaces yet were constrained in their possibilities for play.  Further, findings highlight how children negotiate play experiences as a tension between choice making and their desire for mastery.  

    Study III explored the play value of digital spaces, specifically how the digital space affords play from the perspective of the child.  The study was conducted using focus groups and comic strips to elicit data from eight children aged 11 years old.  Findings indicate that children value the endless opportunities for play that were not necessarily available to them in real world spaces.  Children discussed the play value associated with continually exploring new tasks, roles, and arenas, a space to be and do together, and to develop and learn. 

    Study IV explored and identified how the meaning of playing video games is situated in adolescents’ everyday life.  The study utilised narrative methodologies to generate data from five participants aged 16 – 17 years.  The findings reflect how they engage in processes negotiating and balancing between occupations in both the physical and digital space with play integrated across their everyday lives. 

    These studies reveal the richness and depth of perspectives children hold with regard their play in digital spaces and uncovers a unique and diverse number of characteristics that contributes to our understanding of the meaning children hold of this key occupation of childhood. This thesis articulates how children consider the primacy of play in their everyday lives in their negotiations between play in physical and digital spaces and how the, often overlooked, social dimensions of such play experiences throughout the course of childhood serves to enhance their connections with others and promote a sense of belonging. Additionally, the perception of competence in their play fostered their sense of self whilst embodying other roles and identities reflect a progression towards a future self.  

    This enhanced understanding of the play occupations in digital spaces can be used to promote, offer, and design play occupations that reflect the experiences of children themselves thus recognising how and where play in digital spaces is integrated in relation to everyday life.  To further explore play occupations in digital spaces, it may be fruitful for future research to be designed with children in mind to further enhance understanding.  

    Fulltekst (pdf)
    Fulltekst tilgjengelig fra 2025-11-30 12:00
  • Disputas: 2024-06-14 10:00 A109, Luleå
    Rydström, Klara
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, Människa och teknik.
    Unpacking Online Retailing: The Organization of Warehouse Work and Inequality2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This dissertation studies the organization of warehouse work and inequality in Swedish online retailing. Online retailing relocates the work of providing service to individual customers, usually performed by frontline workers in retail stores, to warehouses backstage. In line with the on-demand characteristics of online retail warehousing, where a fast and smooth goods handling process becomes a competitive advantage for the companies, the manual warehouse work has been shown to be associated with routinization, and a high work tempo and monotony for workers performing it. Little is known about these issues in Sweden. Union reports and news media have shown that online retail warehousing involves a generally poor work environment and low wages. Research-based findings from other geographical contexts explain that the workforce mainly consists of those who cannot find a job elsewhere and whose subordinated position limits their possibilities for resistance against the working conditions. Herein, inequality appears. Inequality is understood in the dissertation as a consequence of the practices that organize the work, which tend to be shaped by gendered and racialized processes. The inequality as such often, but not always, take the form of class relations (Acker 2006).


    Based on an ethnographic study of five online retail warehouses in Sweden – Homeware, Electronic, Recreational, Pharmacy, and Grocery – the dissertation aims to explore and understand how practices and processes to organize online retail warehouse work relate to inequality, and it aims to contribute with knowledge in this regard. As part of this, the dissertation also aims to make visible the work, workplaces, and workers that online retail warehousing brings about. The methods and materials include interviews with managers, workers, and union and health and safety representatives (n=30); focus groups with workers and pharmacists (n=15 groups, a total of 49 participants); and ethnographic observations (a total of eleven weeks). The dissertation also comprises material from a systematic literature review of 21 articles focused on warehouse working conditions and inequality, and employment data from Statistics Sweden divided into occupations groupings. My ambitions with the dissertation have been empirical – in how I have worked to contribute with knowledge about online retail warehousing, in particular in with regards to the Swedish context – and theoretical – in how I have strived to contribute with perspectives on how we can analytically approach inequality.


    The results show that the warehouse work was organized in relation to the ‘on-demand’ element of online retailing, wherein flexibility becomes a necessity for online retail warehouses in the strive to fulfil the (over time fluctuating levels of) customer orders on time. While Homeware, Electronic, Recreational, Pharmacy, and Grocery all strived for profit by making warehouse workers provide a fast and satisfactory service for customers, the differences between them with regards to how the warehouse work was organized meant that there were variations in the shape and the degree of the inequality (cf. Acker 2006). This is exemplified in the dissertation with the practices and processes of the division of work tasks, the monitoring of workers’ performance through productivity data, and a Swedish language policy. In addition to inequality expressed in gendered and racialized class relations between managers and warehouses workers, and other groups of employees, the dissertation also found inequality produced by class and shaped by gender and race/ethnicity between groups of warehouse workers. The variations of the inequality seemed to be associated with the differences in the size and spatiality of the online retail warehouses, the size of the workforce, and the extent of technology applied in the goods handling process. Furthermore, the dissertation suggests that there are three analytical points of entry to from where to approach inequality – the workplace level, the field of work level and the worker level – which together help us understand its manifoldness, how the severity of inequality varies and the lived and embodied realities of it.

    Fulltekst (pdf)
  • Disputas: 2024-06-14 11:00 E632, Luleå
    Hussamadin, Raafat
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriellt och hållbart byggande.
    Development of Adaptable Information Structures for House-Building Reusability2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The house-building industry is increasingly recognizing the importance of information, viewing it as key for driving sustainable construction. This acknowledgment highlights that informed decision-making, based on the effective use of information, can enhance all phases of house-building. Sustainable house-building demands an integration of diverse information, technologies, and standards, necessitating the increased use of information to support decision-making. In response, the industry is focusing more on the capture, management, and storage of information. Despite significant investments in these areas, the full potential of this information is not yet realized due to the lack of and poor use of structured information systems. Furthermore, the information produced is often tailored for specific segments, leading to the creation of information silos that isolate data, making it difficult to collaborate across different stakeholder groups. While the benefits of structured information are widely acknowledged, the integration of structured data and information technologies in house building is impeded by unintuitive and fragmented information management practices. Additionally, many current information systems in the industry still emulate paper-based document structures, continuing the use of unstructured and non-standardized data. To address these challenges, this thesis explores the development of information structures that facilitate reusability across house-building projects and explores the integration of visualization techniques into these development methodologies. By employing cross-case analysis as the scientific method, this study evaluates findings from multiple cases to identify common themes and patterns, thereby enhancing the understanding of the observed phenomena by effectively comparing and contrasting findings from individual case studies.

    The findings of this thesis underscores the delicate balance required in information structures to effectively blend standardization with project-specific flexibility. Effective reuse in house-building necessitates an equilibrium between these approaches to achieve both widespread applicability and project-specific relevance. The case studies analyzed illustrate how navigating this balance can enhance communication, foster collaboration, and ensure adherence to established procedures. This balance is crucial because information visualization can falter when skewed too far towards either extreme of this spectrum. Over-standardization can hinder the application to specific project nuances, while excessive customization may complicate data collection and visualization, requiring substantial resources to format and prepare. Therefore, developing reusable information structures depends on achieving a middle ground that is neither overly standardized nor excessively tailored.

    Fulltekst (pdf)
  • Disputas: 2024-06-18 09:00 B192, Luleå
    Benti, Gudeta Berhanu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Rotordynamic Modeling and Characterization of Support Elements in Vertical Machines2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The dynamic properties of rotating machines are highly influenced by supporting elements, such as bearings, seals, damping elements or housings. They play a significant role in regulating the characteristics of the interaction between the rotating and stationary parts of machines. Over the past few years, numerous research studies have been published focusing on the dynamics of such devices across a wide range of applications. The advancement of the research has significantly contributed to enhancing their performance and ensuring the smooth operation of rotating machinery by minimizing excessive vibrations that can lead to catastrophic failure. The research work in this thesis explores the dynamics of supporting elements in vertical rotating machinery, with a particular focus on hydropower applications. In fact, some of the concepts are generic and can be applied to horizontal rotors or any other types of rotating machines. Using numerical simulation and actual measurements, their contribution to the system’s overall performance was investigated. These include the self-induced vibration in vertical application tilting pad journal bearings, and vibration issues observed on a hydropower unit attributed to large bearing clearance. Also, particular attention was given to the influence of the squeeze film damper on the rotor-stator contact dynamics of hydropower units, using tools such as Poincaré maps and bifurcation diagrams.

    Moreover, achieving optimal design of such devices requires, among other key aspects, accurate and reliable simulation models to facilitate the prediction and evaluation of their characteristics at any stage in the product development process. In rotordynamic simulations, a common approach for incorporating bearing forces in the system equation is by representing them with stiffness and damping coefficients. For a small vibrational amplitude about a static position, linearized bearing coefficient assumptions can be valid. This is especially applicable for operation under a large radial static load, such as in horizontal rotors, due to the dead weight of the rotor. For vertical rotors, however, the weight of the rotor acts axially, and the radial bearing load is usually low. The bearing coefficients show nonlinearity, making them dependent on the trajectory of the rotor. Therefore, the linear bearing assumption, which is valid for horizontal rotors, does not hold true for vertical rotors. This makes the simulation of a vertical machine more complicated as it typically involves solving the fluid film lubrication model. The classical numerical models can sometimes be computationally demanding and require impractically long computational time. An efficient and fast numerical simulation method which does not significantly affect the accuracy of the result is critical to facilitating the simulation processes effectively. This thesis details the suggested simplifications employed on the bearing models and transformation matrices in the numerical integration procedure. The results from these models were validated using experiments to ensure their reliability.

    Fulltekst (pdf)
  • Disputas: 2024-06-18 09:00 E632, Luleå
    Shiraghaee, Shahab
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental Investigation and Mitigation of Part-load Pressure Pulsations in Hydro Turbines Using Solid-body Protrusion inside the Draft Tube2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The global demand for electricity generation has been increasing over the recent decades and is expected to grow steadily. Therefore, activating new energy sources to improve the present capacity of electricity production is inevitable. In addition, the reduction of greenhouse gas emissions is another growing concern that is increasingly promoted. Consequently, the integration of clean sources of energy into the electrical grid is a necessity. Renewable energy sources such as wind and solar appear as practical and easy-to-harvest solutions that are clean and sustainable. Thus, their penetration into the electrical grid is both encouraged and pursued on a global scale. However, these sources are intermittent and have a slow regulation response, and an electric network predominantly comprising such sources faces challenges in adapting to the market’s fluctuating demand. As a result, a rapid-response auxiliary source is required in such networks to balance the grid output and guarantee a stable supply of electricity. Hydropower is an ideal and clean alternative that can adopt this regulation role due to its short response time. The shift in hydropower implementation towards this new role requires a broader range of operations with more frequent transitions between the design and off-design conditions. However, current hydro turbines are designed to operate at a limited range of the highest efficiency, termed the best efficiency point (BEP). When operating away from the BEP, hydro turbines confront adverse flow-induced phenomena such as vortex breakdown that can induce pressure pulsations and periodic loadings. These oscillations can cause power swings and aggravated wear rates on turbine compartments through increased fatigue. Part-load (PL) turbine operation is a condition where the precession of a rotating vortex rope (RVR) in the turbine diffuser induces harmful oscillations. With prolonged turbine PL operations, these machines are expected to face a shortened life span and increased repair cycles. Therefore, the need for practical flow control methods to reduce the pressure pulsations under PL is growing.

    The present thesis aims to introduce and investigate the concept of protrusion-based methods to mitigate PL pressure pulsations. The latter is attempted by perturbing the flow in the turbine with the radial insertion of solid bodies into the draft tube. The proposed geometries include cylindrical rods and flat plates. The impact of cylindrical rods has been examined on multiple scales of axial turbines, including a downscaled model turbine, a model turbine, and a prototype. These effects were observed with different measurement tools depending on the investigated turbine. The obtained resultspresented in this work for rod protrusion experiments include turbine operation parameters, timeresolved pressure data, strain data, flow visualization, and efficiency. As an improvement to the rod protrusion concept, the flat plates were tested on the downscaled model turbine. The results from these measurements consist of turbine operation parameters, time-resolved pressure data from the draft tube and vaneless space, and efficiency.

    Investigated under different PL conditions, the rods could effectively mitigate the RVR-induced pressure pulsations at upper and lower PL conditions. The obtained mitigation rates under these conditions reached as high as 80%. In addition, this method proved effective in reducing flow induced fatigue at lower PL and even speed-no-load (SNL) conditions. However, rod protrusion entailed mixed results under the PL conditions where the RVR induced the strongest periodic oscillations. Moreover, the rods caused a maximum efficiency drop of approximately 3% of the BEP efficiency. More importantly, for all the investigated scales, under the conditions where the rods appeared effective, an optimum protrusion length was found where the most significant mitigation occurred. On the other hand, the investigation of plates on the downscaled model showed complete mitigation of the RVR-induced pressure pulsations under the entire turbine PL range, and the turbine efficiency was even improved under lower PL conditions.

    The investigation of both protrusion-based methods verified the need for an adjustable mitigation technique that can adapt to variable flow conditions under different PL ranges. Protrusion-based flow control systems can be incorporated as a new degree of freedom in the existing turbines and modify their operational maps. Thus, depending on the turbine operating condition, the solid bodies can be protruded at a given length or retracted completely to reduce the flow-induced adverse effects with marginal efficiency penalties. Hence, the turbine can operate at an extended range with fewer consequences, which will be a key requirement for hydropower in the future.

    Fulltekst tilgjengelig fra 2024-05-28 09:00
  • Disputas: 2024-06-18 10:00 F1031, Luleå
    Kothari, Ankit
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Low Portland cement content concretes at freezing and subfreezing temperatures2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Concrete is the most used building material. With the increasing growth of industries and urbanization globally; the demand for concrete is increasing significantly. Ordinary Portland Cement (PC) is the binder used to produce typical concrete. Unfortunately, for every ton of manufactured cement about 0.61-ton CO2 is emitted into the earth’s atmosphere. As a result, several solutions have been implemented to reduce the usage of this material in the production of concrete. This includes its partial or full replacement with supplementary cementitious materials (SCMs) or alternative binders. Some of these combinations could be problematic to be used in cold climates due to a lower developed hydration heat, slower setting, or worse frost durability.

    In winter the immediate exposure of fresh concrete to freezing temperatures results in pore ice formation and could delay or completely stop the hydration process. This is commonly prevented by using an additional heating system installed in concrete or the formwork. Unfortunately, usually, it adds complexity, increases the price, and depending on the used power source, could increase the CO2 footprint. Another potentially simpler and more sustainable solution is to modify the concrete itself by adjusting the mix design, by using certain chemical admixtures and special cementitious binders.

    This research aimed to better understand how partial replacement of Portland cement with GGBFS and/or CSA cement affects the properties of concretes exposed to freezing and subfreezing temperatures in a fresh state and at a young age. The secondary aim was to evaluate a possible application of UHPC to protect new and existing concrete structures from frost damage.

    The research included a literature review of methods used to produce concrete structures at zero and subzero temperatures. A special emphasis was on the application of chemical and mineral admixtures that could eliminate the need to use heat treatments. The output of this analysis enabled to narrow the scope of the research.

    The experimental program focused on the optimization, testing, and analysis of mixes containing various combinations of chemical admixtures, CSA cement, and Portland cement. Tests included exposure to freezing and subfreezing temperatures. The aim was to lower the freezing point of water and promote faster hydration and strength gain. Fresh and hardened properties were determined for all produced concretes. The phase transition of pore water into ice, the ice-forming temperature, and their effects on the binder matrix were studied using differential scanning calorimetry (DSC). Other tests included ultrasonic pulse velocity measurements (UPV), bond test (pull-off), scanning electron microscope (SEM) for analysis of the microstructure and phase composition, frost durability evaluation with Båras test, semi-adiabatic calorimetry to study hydration processes, compressive strength measurements.

    Fulltekst tilgjengelig fra 2024-05-28 09:00
    Fulltekst tilgjengelig fra 2024-05-28 09:00
  • Disputas: 2024-06-20 10:00 A109, Luleå
    Tossavainen, Anne
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Pedagogik, språk och ämnesdidaktik.
    Characterizing Prospective Elementary Teachers' Mathematical Knowledge for Teaching Fractions2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Although research has delved into the challenges faced by mathematics teachers and students across various educational levels when working with fractions, these challenges persist. Fractions are an important but difficult content area in elementary school mathematics, and many future elementary teachers enter teacher education with limited knowledge of fractions. This lack of prior knowledge, combined with diverse experiences and attitudes toward the teaching and learning of mathematics, presents a challenge for teacher education programs aiming at enhancing prospective teachers’ knowledge to enable them to teach fractions effectively. Teacher education is a crucial time to attain a comprehensive pedagogical knowledge of mathematics, and this thesis characterizes prospective elementary teachers’ (n = 61) knowledge for teaching fractions as an outcome of Swedish teacher education. Through four empirical studies, the thesis also addresses the concept of mathematical identity and investigates the topic in light of the Mathematical Knowledge for Teaching framework.

    The findings highlight substantial differences between the participants in the subject matter and pedagogical content knowledge domain of fractions, revealing difficulties in both their procedural and conceptual knowledge. Challenges also arise in analyzing different fraction solutions and combining knowledge of fraction content with knowledge about elementary students, teaching, and the national curriculum document. This difficulty can be a hindrance for the quality teaching of fractions. Moreover, incoherent fraction knowledge occurs across the different knowledge categories included in the Mathematical Knowledge for Teaching framework. The findings also reveal uncertainty in relation to work with fractions and prospective teachers’ mathematical identities. A new framework for the analysis of different aspects of fractions is also presented in the thesis, and the findings are discussed considering the context of Swedish teacher education and the Mathematical Knowledge for Teaching framework. 

  • Disputas: 2024-08-30 08:30 A 193, Skellefteå
    Alizadeh, Morteza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Architectural Aspects of Identification in Decentralized Systems2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-09-19 10:00 E632, Luleå
    Saback, Vanessa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Digital Twins for Asset Management of Civil Structures: Can we close the gap between perceived potential and practical applications?2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-09-20 09:00 E632, Luleå
    Johansson, Gunilla
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Omvårdnad och medicinsk teknik.
    Nature-based interventions to promote health in people with stress-related illness2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Stress-related illness is increasing and is a common cause of sick leave in Sweden. Spending time in nature reduces stress and promotes health and well-being. Consequently, nature-based interventions (NBI) for people with stress-related illness have been developed, implemented and studied in southern Scandinavia. However, such interventions are uncommon in the Circumpolar North with a different climate which affect conditions for outdoor activities. 

    The overall aim of this doctoral thesis was to explore NBIs to promote health in people with stress-related illness from the perspectives of previous research, people with stress-related illness, healthcare professionals and entrepreneurs offering NBIs with a specific focus on northern natural conditions.

    The thesis includes four studies. An integrative literature review (I) identified and summarised scientific studies of NBIs for people with stress-related illness. Studies using both qualitative and quantitative designs were included. Study II explored key stakeholders’ perceptions of the value of NBIs in promoting health in people with stress-related illness. Semi-structured interviews were conducted with people with stress-related illness experience, healthcare professionals, and entrepreneurs offering NBI and data were analysed through qualitative content analysis. In study III people with stress-related illness experiences of participating in an NBI program in a northern natural setting were explored. A longitudinal case study design was used, and data were collected through repeated semi-structured interviews, diary entries and self-assessment questionnaires. Qualitative content analysis was used to analyse interviews and reflections from diaries and data from self-assessing questionnaires were presented descriptively. Study IV explored people with stress-related illness experiences of nature prescription. Data were collected through interviews with open-ended questions and analysed with a phenomenological-hermeneutic method.

    Findings show that natural environments offer unique qualities for individualised, meaningful activities and interactions with others in a non-demanding atmosphere. In NBI people with stress-related illness find a source for recovery, joy, and well-being. Spending time in nature is perceived as calming and facilitates being in the present. NBIs improve health and strengthen self-efficacy and work ability. Time in nature provides new perspectives, supports existential reflections, and empowers people with stress-related illness to find opportunities for change to achieve balance in everyday life. NBIs can be helpful for people with stress-related illness to overcome barriers to going out in nature or to find their way back to nature. 

    In conclusion, NBIs seem to be beneficial in promoting health in people with stress-related illness. Different stakeholders have similar perceptions of the value of NBIs, indicating that it could be a valuable complement to health care. NBIs in a northern natural setting seems to have similar health promoting qualities as those seen in studies of NBIs in other natural settings.

  • Disputas: 2024-09-20 12:00 C305, Luleå
    Paulsen Thoresen, Petter
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Structure and property oriented organosolv lignin extraction2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this Thesis, organosolv fractionation of softwood (spruce), hardwood (birch and beech), and herbaceous crops (wheat straw) was performed by applying various organosolv process conditions. Among these were a novel steam-explosion/organosolv hybrid mode, and two ternary solvent systems utilizing water/ethanol/acetone, and water/acetone/acetic acid. In addition, the effect of using inorganic acidic catalyst (H2SO4) was investigated for all raw material classes. Also, alkaline catalyst (NaOH) was investigated for wheat straw due to its reported high content of inorganics which presence adds additional structural complexity to the lignocellulosic recalcitrance. Following the organosolv fractionation, structural characterization was performed (content of cellulose, hemicellulose, lignin) in the isolated product fractions. Additionally, in-depth characterization of the isolated lignins was performed by combining Pyrolysis-Gas Chromatography Mass Spectroscopy (Pyr-GC/MS), Gel Permeation Chromatography (GPC), and different modes of Nuclear Magnetic Resonance (NMR; 13C, 1H-13C, 31P). Complementary analytics, such as content of monomeric/oligomeric sugars, dehydration products, total phenolics, and Size-Exclusion Chromatography (SEC) of the isolated product liquor, were performed to provide a comprehensive understanding of the process. Special attention was given the lignin structural changes occurring throughout the organosolv process. This was done as the use of lignin for higher-value application is considered crucial for the economic viability and development of a modern biorefinery. For this reason, significant focus was given to study how the lignin characteristics translate into physical properties such as solubility. The latter property was measured through solubility trials in binary aqueous acetone solutions, as well as solvent-based fractionation (acetone-water system). A coherent picture was aimed for, where structural motifs and lignin characteristics were correlated to reductions/enhancements in solubility at various water contents. To finally bridge this with a potential down-stream application, DPPH radical scavenging was performed in DMSO with and without intercalating Lithium Bromide (LiBr) for a selection of organosolv lignins, as well as their acetone/water fractionated lignins. This was complemented with a UV absorption study of the lignin solutions.The results provide a descriptive span of chemical characteristics related to organosolv lignins, where they range between highly native, to non-native. Whereas the former lignins are largely comprised of inter-unit motifs such as β-O-4’, β-β’ and β-5’, the non-native lignins are instead better characterized by a high content of oxidized sidechains, biaryls and bifurans, as well as showing strong indications of having quaternary cross-linkers originating from ketone functionalities. The ketones are also found to undergo aldol condensation with aldehydes formed throughout the process. Interestingly, these two extremes in lignin characteristics yield highly varying physical properties, where the predominantly native and non-native lignins for example display low and high solubility in pure acetone, respectively. Simultaneously, the latter is more prone towards water-induced precipitation, whereas the former instead require water to display complete (~100%) solubility at specific concentrations. These properties and findings are eventually consistent with recent literature where lignin aggregates also dominate their dissolved state, and the interunit motifs dictate the affinity on forming such aggregates which are important for both their dissolution, precipitation, but also their display of functionality such as antioxidant activity.                    

  • Disputas: 2024-09-26 09:00 C305, Luleå
    Hruzova, Katerina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Potential of Organosolv Lignin Nanoparticles as a Sustainable Flotation Reagent: Towards a Low-Carbon Footprint Mining Industry2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The green transition is driving a steep increase in the demand for minerals, which has put the focus on more responsible and sustainable mining practices as there is a growing pressure on mining operations to minimise their environmental footprint, mitigate risks in neighbouring communities, and decrease the consumption of natural resources. In 2022, mineral froth flotation was used to recover 18 million tonnes of copper from copper ore, accounting for 80% of total copper mine output. The mineral froth flotation process can be made more sustainable through the use of bio-based and biodegradable flotation reagents. Currently, xanthates are used as collectors for the recovery of copper-bearing sulfide minerals from sulfide ores. However, xanthates are fossil-based and pose significant risks, particularly to aquatic life and ecosystems. Additionally, a significant part of xanthates is currently obtained from production sites in Asia, which can lead to supply dependency and delays, as evident during the global pandemic.

    The aim of this thesis was to develop an efficient, sustainable, and environmentally friendly mineral froth flotation process based on total or partial replacement of xanthates with bio-based, biodegradable, and low-carbon footprint organosolv lignin particles (OLP). The lignin was obtained through organosolv fractionation of residual forest biomass, i.e. spruce and birch. The particles were produced via solvent exchange method from the homogenized lignin solution. As a result, 4 different particle types were produced: birch nanoparticles (BN), birch microparticles (BM), spruce nanoparticles (SN), and spruce microparticles (SM). At first, the characterization and surface chemistry study of the OLP was carried out to deepen the understanding of interaction mechanism between the OLP and mineral surfaces. The lignin was characterized by gel permeation chromatography and nuclear magnetic resonance for its molecular size and content of functional groups. While morphology, surface charge and stability in dispersion of the particles was determined using scanning electron microscopy, ζ-potential, and Turbiscan. All 4 particles were spherical with the diameter around 100 nm for nanoparticles and 1μm for microparticles. The ζ-potential measurement showed the surface variation caused by the difference in size and content of functional groups. Spruce particles, SN and SM, had higher negative charge due to higher content of carboxylic and total phenolic groups. Under alkali conditions, the ζ-potential below -20mV for all particles, with the lowest at −55.1 mV for SM. Finaly, the interaction of OLP with mineral surfaces was examined using quartz crystal microbalance. While the attachment of all OLP was very rigid for both, chalcopyrite and pyrite surfaces, the affinity for attachment was notably greater in the case of pyrite compared to chalcopyrite.

    The OLP was tested in proof-of-concept study on three different ore samples, and improvements in the flotation performance was observed, including better selectivity and increased recovery. The further evaluation of the OLP as flotation reagent was conducted with copper ore samples. The flotation trials were carried out with 600 g of ore sample in laboratory flotation cell. Starting with the dosage study, the results were confirmed in rougher-cleaner flotation tests. However, the OLP could not be used as a sole collector, it was shown that significant part of xanthate in the flotation mix could be replaced by OLP resulting in improved copper recovery and selectivity. Additionally, a synergy was observed when the OLP and xanthate mixture was used as combined reagents performed better than each of them separately at the same dosage. The copper recovery was increased from 82.2% to 88.7% in a semi-pilot rougher flotation when 50% of xanthate was replaced by OLP compared to the xanthate alone. Significant depression of iron recovery was observed when the OLP was utilized, even in absence of lime. Thus, the OLP reagents eliminated the need for lime, which is required on an industrial scale. Further positive effect of OLP application was indicated recovery of other valuable elements in the concentrates, such as cobalt and molybdenum, while there was no increase in penalty elements. The amount of OLP needed was up to 10 g/ton of ore, which is very small amount, and it is roughly 10 times less compared to any other modifier used in such a process. Therefore, this thesis demonstrates the potential of OLP as flotation reagent. If implemented, the proposed flotation system would lead to better resource efficiency and lower environmental impact.

  • Disputas: 2024-10-15 09:00 E632, Luleå
    Savolainen, Eva
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Hälsa, medicin och rehabilitering.
    The road towards making the active choice the easy choice: Facilitating and feasibility aspects of children’s active transportation2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-10-17 13:00 Multistudion A1123, Luleå
    Eronen, Minna
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, Människa och teknik.
    Maps for The layered Gaps: Tools for affording situational awareness in human inclusive place design2024Doktoravhandling, med artikler (Annet vitenskapelig)