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  • Public defence: 2017-12-18 10:00 F3, Stockholm
    Peng, Ivy Bo
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Data Movement on Emerging Large-Scale Parallel Systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Large-scale HPC systems are an important driver for solving computational problems in scientific communities. Next-generation HPC systems will not only grow in scale but also in heterogeneity. This increased system complexity entails more challenges to data movement in HPC applications. Data movement on emerging HPC systems requires asynchronous fine-grained communication and efficient data placement in the main memory. This thesis proposes an innovative programming model and algorithm to prepare HPC applications for the next computing era: (1) a data streaming model that supports emerging data-intensive applications on supercomputers, (2) a decoupling model that improves parallelism and mitigates the impact of imbalance in applications, (3) a new framework and methodology for predicting the impact of largescale heterogeneous memory systems on HPC applications, and (4) a data placement algorithm that uses a set of rules and a decision tree to determine the data-to-memory mapping in heterogeneous main memory.

    The proposed approaches in this thesis are evaluated on multiple supercomputers with different processors and interconnect networks. The evaluation uses a diverse set of applications that represent conventional scientific applications and emerging data-analytic workloads on HPC systems. The experimental results on the petascale testbed show that the approaches obtain increasing performance improvements as system scale increases and this trend supports the approaches as a valuable contribution towards future HPC systems.

  • Public defence: 2017-12-18 10:00 K1, Stockholm
    Lindberg, Jonas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Electrochemical Investigation of the Reaction Mechanism in Lithium-Oxygen Batteries2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges.

    Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium  mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased.

    Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one.

    Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface.

    During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed.

    The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium.

    During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence.

  • Public defence: 2017-12-18 10:00 Kollegiesal, Stockholm
    Armendáriz, Mikel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Cost-effective Communication and Control Architectures for Active Low Voltage Grids2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The monitoring and control of low voltage distribution grids has historically been disregarded due to the unidirectional flow of power. However, nowadays the massive integration of distributed energy resources into distribution grids, such as solar photovoltaics, distributed storage, electric vehicles and demand response programs, presents some challenges. For instance, the unidirectional top-down power flow is being replaced by power flows in any direction: top-down and bottom-up. This paradigm shift adds extra regulatory, economic, and technical complexity for the Distribution System Operators (DSO). Thus to overcome the possible operational constraints, thermal limits, or voltage problems in the grid, an update of the existing electricity infrastructures is required. In response to this new situation, this thesis investigates the cost-effective communication and control architectures that are required for active low voltage grid monitoring and control applications, considering the regulatory constraints and the efficient utilization of the assets from a DSO’s perspective. The solutions include: i) optimal sensor placement configuration to perform low voltage state estimation, ii) optimal metering infrastructure designs for active low voltage monitoring applications, iii) coordinated control strategies to allow the integration of microgrid-like structures into the distribution grids, iv) optimal placement of actuators for operating the control strategies, v) a multiagent-based control solution for self-healing and feeder reconfiguration applications, and vi) a framework model and simulations to assess the reliability of the ICT infrastructure that enables the monitoring and control applications. As concluding remark, since the deployment of technology at low voltage grids is restricted to assets owned by the DSO, the operability of the grid is limited. This condition makes it so that the required communication and control enhancement solutions shall prioritize cost-effectiveness over comprehensiveness and complexity. Thus, the results from the presented studies show that it is essential to perform thorough cost-benefit analyses of the potential improvement solutions for each grid, because this will allow deploying the right technology only at the necessary locations.

  • Public defence: 2017-12-19 10:00 Q2, Stockholm
    Talebi Mazraeh Shahi, Mohammad Sadegh
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Minimizing Regret in Combinatorial Bandits and Reinforcement Learning2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis investigates sequential decision making tasks that fall in the framework of reinforcement learning (RL). These tasks involve a decision maker repeatedly interacting with an environment modeled by an unknown finite Markov decision process (MDP), who wishes to maximize a notion of reward accumulated during her experience. Her performance can be measured through the notion of regret, which compares her accumulated expected reward against that achieved by an oracle algorithm always following an optimal behavior. In order to maximize her accumulated reward, or equivalently to minimize the regret, she needs to face a trade-off between exploration and exploitation.

    The first part of this thesis investigates combinatorial multi-armed bandit (MAB) problems, which are RL problems whose state-space is a singleton. It also addresses some applications that can be cast as combinatorial MAB problems. The number of arms in such problems generically grows exponentially with the number of basic actions, but the rewards of various arms are correlated. Hence, the challenge in such problems is to exploit the underlying combinatorial structure.For these problems, we derive asymptotic (i.e., when the time horizon grows large) lower bounds on the regret of any admissible algorithm and investigate how these bounds scale with the dimension of the underlying combinatorial structure. We then propose several algorithms and provide finite-time analyses of their regret. The proposed algorithms efficiently exploit the structure of the problem, provide better performance guarantees than existing algorithms, and significantly outperform these algorithms in practice.

    The second part of the thesis concerns RL in an unknown and discrete MDP under the average-reward criterion. We develop some variations of the transportation lemma that could serve as novel tools for the regret analysis of RL algorithms. Revisiting existing regret lower bounds allows us to derive alternative bounds, which motivate that the local variance of the bias function of the MDP, i.e., the variance with respect to next-state transition laws, could serve as a notion of problem complexity for regret minimization in RL. Leveraging these tools also allows us to report a novel regret analysis of the KL-UCRL algorithm for ergodic MDPs. The leading term in our regret bound depends on the local variance of the bias function, thus coinciding with observations obtained from our presented lower bounds. Numerical evaluations in some benchmark MDPs indicate that the leading term of the derived bound can provide an order of magnitude improvement over previously known results for this algorithm.

  • Public defence: 2017-12-19 12:00 Madrid
    Khan, Zarrar
    KTH, School of Electrical Engineering (EES). Universidad Pontificia Comillas.
    Integrating Water and Energy Systems for Long-Term Resource Management2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Availability of and access to water and energy are key ingredients for economic and social development. Predictions show that pressure on already limited water and energy resources is expected to increase in many parts of the world as a result of growing populations, rapid urbanization, increasing pollution and climate change impacts. The water and energy systems are highly interdependent and these interlinks provide important opportunities to improve resource security and prevent inefficient decisions which could exacerbate problems even further.

    This thesis explores the benefits to be gained from and the drawbacks of ignoring the various interlinks. A review of several existing water-energy integration modeling methodologies shows that the different physical, temporal and spatial characteristics of the water and energy systems present several hurdles in analyzing the two resources simultaneously. This thesis overcomes many of these issues by developing a fully integrated hard-linked water-energy linear optimization model. A case study from Spain is used to demonstrate the applications of the model for simultaneous analysis of water, energy and climate change adaptation strategies. An integrated approach is shown to have several benefits including lower total costs, better resource efficiency and improved robustness for a wide range of variations in several uncertain parameters.

  • Public defence: 2017-12-20 13:15 Kollegiesalen, Stockholm
    Wahlström, Johan
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Sensor Fusion for Smartphone-based Vehicle Telematics2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The fields of navigation and motion inference have rapidly been transformed by advances in computing, connectivity, and sensor design. As a result, unprecedented amounts of data are today being collected by cheap and small navigation sensors residing in our surroundings. Often, these sensors will be embedded into personal mobile devices such as smartphones and tablets. To transform the collected data into valuable information, one must typically formulate and solve a statistical inference problem.

    This thesis is concerned with inference problems that arise when trying to use smartphone sensors to extract information on driving behavior and traffic conditions. One of the fundamental differences between smartphone-based driver behavior profiling and traditional analysis based on vehicle-fixed sensors is that the former is based on measurements from sensors that are mobile with respect to the vehicle. Thus, the utility of data from smartphone-embedded sensors is diminished by not knowing the relative orientation and position of the smartphone and the vehicle.

    The problem of estimating the relative smartphone-to-vehicle orientation is solved by extending the state-space model of a global navigation satellite system-aided inertial navigation system. Specifically, the state vector is augmented to include the relative orientation, and the measurement vector is augmented with pseudo observations describing well-known characteristics of car dynamics. To estimate the relative positions of multiple smartphones, we exploit the kinematic relation between the accelerometer measurements from different smartphones. The characteristics of the estimation problem are examined using the Cramér-Rao bound, and the positioning method is evaluated in a field study using concurrent measurements from seven smartphones.

    The characteristics of smartphone data vary with the smartphone's placement in the vehicle. To investigate this, a large set of vehicle trip segments are clustered based on measurements from smartphone-embedded sensors and vehicle-fixed accelerometers. The clusters are interpreted as representing the smartphone being rigidly mounted on a cradle, placed on the passenger seat, held by hand, etc. Finally, the problem of fusing speed measurements from the on-board diagnostics system and a global navigation satellite system receiver is considered. Estimators of the vehicle’s speed and the scale factor of the wheel speed sensors are derived under the assumptions of synchronous and asynchronous samples.

  • Public defence: 2018-01-08 10:00 Kollegiesalen, Stockholm
    Dahlqvist, Johan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Cavity Purge Flows in High Pressure Turbines2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Turbomachinery forms the principal prime mover in the energy and aviation industries. Due to its size, improvements to this fleet of machines have the potential of significant impact on global emissions. Due to high gas temperatures in stationary gas turbines and jet engines, areas of flow mixing and cooling are identified to benefit from continued research. Here, sensitive areas are cooled through cold air injection, but with the cost of power to compress the coolant to appropriate pressure. Further, the injection itself reduces output due to mixing losses.A turbine testing facility is center to the study, allowing measurement of cooling impact on a rotating low degree of reaction high pressure axial turbine. General performance, flow details, and cooling performance is quantified by output torque, pneumatic probes, and gas concentration measurement respectively. The methodology of simultaneously investigating the beneficial cooling and the detrimental mixing is aimed at the cavity purge flow, used to purge the wheelspace upstream of the rotor from hot main flow gas.Results show the tradeoff between turbine efficiency and cooling performance, with an efficiency penalty of 1.2 %-points for each percentage point of massflow ratio of purge. The simultaneous cooling effectiveness increase is about 40 %-points, and local impact on flow parameters downstream of the rotor is of the order of 2° altered turning and a Mach number delta of 0.01. It has also been showed that flow bypassing the rotor blading may be beneficial for cooling downstream.The results may be used to design turbines with less cooling. Detrimental effects of the remaining cooling may be minimized with the flow field knowledge. Stage performance is then optimized aerodynamically, mixing losses are reduced, and the cycle output is maximized due to the reduced compression work. The combination may be used to provide a significant benefit to the turbomachinery industry and reduced associated emissions.

  • Public defence: 2018-01-09 10:00 Kollegiesalen, Stockholm
    Nejad Ghafar, Ali
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    An Experimental Study to Measure Grout Penetrability, Improve the Grout Spread, and Evaluate the Real Time Grouting Control Theory2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to the significant influence of the grout penetrability properties on spread of grout in rock fractures, this study aimed to investigate the grout penetrability from four different aspects. In Part (a), after review of all the existing methodologies developed to measure the grout penetrability, Filter-pump and Penetrability-meter were examined against Short-slot to figure out which one is more reliable. The study decisively considered Short-slot more reliable. In part (b), the so-called varying aperture long slot (VALS), an artificial fracture with apertures of 230-10 μm, was developed to study the gout penetrability more realistically. In part (c), a low-frequency rectangular pressure impulse was introduced to improve the grout spread by successive erosion of the produced filter cakes in consecutive cycles. The results showed considerable improvement in experiments using Short-slot. The dissipation of the pressure impulses was then investigated using VALS with noticeable remaining amplitudes after 2.0-2.7 m. In part (d), VALS was once more introduced to examine RTGC theory in a fracture with variable aperture. The study showed a relatively satisfactory agreement between the experimental results and the predictions of the grout propagation using the hydraulic aperture, whereas the predictions using the mean physical aperture showed considerably faster spread.

  • Public defence: 2018-01-09 13:00 F3, Stockholm
    Josefsson, Pernilla
    KTH, School of Computer Science and Communication (CSC).
    Higher education meets private use of social media technologies: An explorative study of students’ use2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work in this thesis sets out to explore how students perceive social media use in the context of higher education. More precisely, the focus is on students' use of, experience with, and attitudes toward the integration of social media into their learning environment. To complement this, teachers' incentives for including social media have been studied; to some extent their communication, attitudes, and online activity were also analyzed.

    The four different studies included in this thesis incorporated three major types of social media technologies: a social networking service (Facebook), a collaborative editable webpage (Wikipedia), and a microblog (Twitter). The studies adopted different approaches to data collection and analysis, including both qualitative and quantitative methods. The specific methods for each study were chosen to accommodate the research questions, for reasons of access to information, and due to ethical considerations.

    While each study differs in starting point and scope and provide particular contributions to the research area, the main contributions of the work as a whole are connected to findings on attitude changes, the professional role in students' use of social media, their teacher-like actions, confusion regarding moving between the identified roles, and the implementation of social media in higher education.

    The findings presented here are appropriate for guiding a nuanced discussion regarding the implementation of social media technologies in higher education, an implementation that was found to be contingent on appropriate use and a suitable social context. The findings suggest that the inclusion of social media in non-private contexts generally needs to have a clear aim and strategy for achieving it. The roles defined in this work - in terms of both being a student and the private and professional roles - could also serve as the basis for further exploration in other areas with comparable hierarchies in which it is necessary to understand how the individual relates to self-presentation, technological constraints, and roles, such as the relation between an employer and employee.

  • Public defence: 2018-01-12 13:00 F3, Stockholm
    Miranda Carranza, Pablo
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Urban Design.
    Program Matters: From Drawing to Code2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Whether on paper, on site or mediating between both, means for reading and writing geometry have been central to architecture: the use of compasses and rulers, strings, pins, stakes or plumb-lines enabled the analysis and reproduction of congruent figures on different surfaces since antiquity, and from the renaissance onwards, the consistent planar representation of three-dimensional shapes by means of projective geometry. Tacitly through practice, or explicitly encoded in classical geometry, the operational syntaxes of drawing instruments, real or imaginary, have determined the geometric literacies regulating the production and instruction of architecture. But making marks on the surfaces of paper, stone or the ground has recently given way to the fundamentally different sequential operations of computers as the material basis of architectural inscription. Practices which have dominated architecture since antiquity make little sense in its current reading and writing systems. 

    This thesis examines technologies of digital inscription in a search for literacies equivalent to those of drawn geometry. It particularly looks at programming as a form of notation in close correspondence with its material basis as a technology, and its effects on architecture. It includes prototypes and experiments, graphics, algorithms and software, together with their descriptions and theoretical analyses. While the artefacts and texts respond to the different forms, styles, interests and objectives specific to the fields and contexts in which they have originated, their fundamental purpose is always to critique and propose ways of writing and reading architecture through programming, the rationale of the research and practice they stem from. 

  • Public defence: 2018-01-15 09:00 F3, Stockholm
    Fagerland, Jenny
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Synthesis of degradable aliphatic polyesters: strategies to tailor the polymer microstructure2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Key factors for successful tissue engineering are the synthesis and design of the scaffold materials. Aliphatic polyesters have been studied and often used as scaffold materials for tissue engineering. However, their lack of biological cues and degradation under high-temperature processing (e.g., 3D printing) are a limitation. In this thesis, different synthesis strategies are presented which has the potential to improve the performance of aliphatic polyesters as scaffolds for tissue regeneration.

    To stimulate interactions between exogenous materials and the surrounding tissue, two different strategies were applied. Either, by designing a two component system in which the different degradation profiles of the polymers allow for sequential release of growth factors. Or, by peptide functionalization of an aliphatic polyester chain using template-assisted chemo-enzymatic synthesis. The results from the studies were successful. A hierarchical system was obtained in which the poly(L-lactide-co-glycolide)-graft-poly(ethylene glycol) methyl ether (PLGA-g-MPEG), hydroxyapatite solution formed a gel around and within the pores of the poly(L-lactide-co-ε-caprolactone) scaffold at 37 ºC, within 1 min, that was stable for 3 weeks. The peptide functionalization was also successful where an aliphatic polyester of L-lactide was functionalized with different oligopeptides using a grafter (ethyl hept-6-enoylalaninate) and chemo-enzymatic synthesis.

    The thermal properties of poly(L-lactide-co-hydroxybutyrate) were tailored (by modification of the microstructure) to potentially improve the processability of the aliphatic polyester.  The results showed that the yttrium salan catalyst was the most successful, yielding high molecular weight copolymers in shorter time. They also showed that the Tg could be tailored by varying the amount of rac-β-butyrolactone in the copolymer to better suit thermal processing techniques, such as 3D printing.

    The full text will be freely available from 2019-01-15 19:21
  • Public defence: 2018-01-19 10:00 F3, Stockholm
    Vikström, Hanna
    KTH, School of Architecture and the Built Environment (ABE), Philosophy and History.
    The Specter of Scarcity: Experiencing and Coping with Metal Shortages, 1870-20152017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In spite of an ever-growing supply of metals, actors have long feared metal shortages. This thesis – departing from an understanding that metals scarcity is not an objective geological fact, but an experience, a fear of a shortage – explores why business and state actors have experienced metals as scarce and how they coped with scarcity from 1870 to 2015.

    The underlying reasons for scarcity experiences originated in high prices, a lack of substitutes, domestic unavailability, limited infrastructure and increased demand. In the view of businesses and the state, a shortage of metals could hinder successful industrialization. Defining metals as scarce was a first step in their attempts to ensure access through exploration, recycling, substitution, and trade agreements.

    This dissertation presents five case studies which provide insights into three selected aspects of metals scarcity that have been overlooked in previous studies. First, while small countries experienced and coped with metals scarcity in a similar way to large nations, they were more vulnerable because of their dependence on transnational flows controlled by larger countries. Yet if they remained neutral in international conflicts, they could enjoy other opportunities to import resources than their larger rivals. Second, industries experienced metals scarcity before World War I; with the onset of the Second Industrial Revolution, at the very latest, new technologies were often dependent on metals which had never before been used commercially – there were not yet any extraction systems in place. However, once these metals began to circulate, state actors became aware of the international traffic and began to classify certain metals as critical. Thirdly, technological change has affected – and been affected by – metals scarcity. If a metal was scarce, manufacturers were likely to embark on a different path to production. Inversely, sometimes new technologies were able to alleviate perceptions of scarcity.

  • Public defence: 2018-01-19 14:00 F3, Stockholm
    Bore, Nils
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Object Instance Detection and Dynamics Modeling in a Long-Term Mobile Robot Context2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the last years, simple service robots such as autonomous vacuum cleaners and lawn mowers have become commercially available and increasingly common. The next generation of service robots should perform more advanced tasks, such as to clean up objects. Robots then need to learn to robustly navigate, and manipulate, cluttered environments, such as an untidy living room. In this thesis, we focus on representations for tasks such as general cleaning and fetching of objects. We discuss requirements for these specific tasks, and argue that solving them would be generally useful, because of their object-centric nature. We rely on two fundamental insights in our approach to understand environments on a fine-grained level. First, many of today's robot map representations are limited to the spatial domain, and ignore that there is a time axis that constrains how much an environment may change during a given period. We argue that it is of critical importance to also consider the temporal domain. By studying the motion of individual objects, we can enable tasks such as general cleaning and object fetching. The second insight comes from that mobile robots are becoming more robust. They can therefore collect large amounts of data from those environments. With more data, unsupervised learning of models becomes feasible, allowing the robot to adapt to changes in the environment, and to scenarios that the designer could not foresee. We view these capabilities as vital for robots to become truly autonomous. The combination of unsupervised learning and dynamics modelling creates an interesting symbiosis: the dynamics vary between different environments and between the objects in one environment, and learning can capture these variations. A major difficulty when modeling environment dynamics is that the whole environment can not be observed at one time, since the robot is moving between different places. We demonstrate how this can be dealt with in a principled manner, by modeling several modes of object movement. We also demonstrate methods for detection and learning of objects and structures in the static parts of the maps. Using the complete system, we can represent and learn many aspects of the full environment. In real-world experiments, we demonstrate that our system can keep track of varied objects in large and highly dynamic environments.​

  • Public defence: 2018-01-25 13:00 Stockholm
    Ghafoori Roozbahany, Ehsan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Flow behavior of asphalt mixtures under compaction2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Asphalt compaction is one of the most important phases of road construction, being the decisive phase when the structure of the asphalt pavement layer is formed. In spite of its importance, the knowledge about this construction phase is still based on empirical and technological background and therefore surprisingly limited. This lack of knowledge is also due to the fact that the existing laboratory scale compaction devices for mix design are not fully capable of simulating the field compaction. The simulation of asphalt compaction in the laboratory is normally focused on the vertical rearrangements of asphalt particles whereas the flow behavior of these particles in other directions is mostly neglected. However, existing literature suggests that the neglected flow is one of the most important factors for the quality of the road construction, particularly in special cases such as asphalt joints. Therefore, building up a better understanding of the flow behavior of asphalt mixtures subjected to compaction loads is needed for improving the quality of the pavements.

    In this study, a new test setup, the so called Compaction Flow Test (CFT), was developed to simulate the flow behavior of asphalt mixtures at early stages of compaction. In the first step, feasibility tests were performed, substituting asphalt mixtures by model materials with simple geometries and less complex properties. X-ray Computed Tomography (CT) was utilized for capturing 2D radiography images of the flow patterns in the model material during the test. Results of the CFT showed the capability of the new test setup to clearly distinguish between model mixtures with different characteristics. Hence, in the next step, the CFT was applied to real asphalt mixtures and the obtained results were found to support the findings of the feasibility tests with the model materials.

    The results from the feasibility tests encouraged examining the possible use of an ultrasonic sensor as alternative to the complex and costly X-ray imaging for flow measurements during the CFT. Hence, the CFT was used along with a distance measuring ultrasonic sensor for testing asphalt mixtures with different characteristics. The test results confirmed that an ultrasonic sensor could be effective for capturing the differences of the flow behavior of asphalt mixtures tested by the CFT. 

    In addition, a parametric study with the X-ray setup was carried out to examine the capability of the CFT in reflecting the possible changes of the flow behavior in asphalt mixtures due to the change of construction parameters such as lift thickness, bottom roughness and compaction modes. The results obtained also confirmed the capability of the CFT in showing the possible differences in the flow behavior of the mixtures under the chosen conditions.

    The encouraging results suggested that the CFT may have potential to become a simple but effective tool for assessing compactability of the mixtures on-site, right after production in an asphalt plant or before placing the mixture on the road. Hence, discrete element method (DEM) was utilized to understand both the influence of selected boundaries of the CFT and the effect of its design on the results.

    As one specific example of application, an investigation was carried out using the CFT to find the most suitable tracking method for flow measurements in the field. Based on the literature review and feasibility tests, a tracking method with the highest potential for conducting flow measurements during field compaction was introduced. X-ray radiography confirmed the validity of the results obtained with the suggested method.

    The overall results obtained from this study suggest that the recommended CFT along with the suggested field tracking method may be helpful in building up a comprehensive basis of knowledge on the flow and compaction behavior of asphalt mixtures thus helping to close the gap between the field and laboratory.

  • Public defence: 2018-01-26 09:00 Kollegiesalen, Stockholm
    Jerpdal, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Processing of self-reinforced poly(ethylene terephthalate) composites for automotive applications2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The vehicles of the future must have less negative environmental impact during their use phase than the vehicles of today in order to avoid major climate change on earth. Consequently electric vehicles are currently under development with the purpose of reducing CO2 emissions when the vehicle is

    driven. There are also efforts put in to reducing the weight of vehicles in order to reduce the demand for energy to drive them. One important aspect of weight reduction is that new materials and technologies are developed. Plastic materials have low a density and can therefore be used to reduce the weight of vehicle components and with composite materials there is further potential for weight reduction. Self-reinforced thermoplastic composite materials are materials in which both reinforcement and matrix are thermoplastic materials and thanks to their low density and relatively good mechanical properties, these materials may be used for weight reduction of vehicle components.

     

    The aim of this thesis is to study selected process parameters for component manufacturing with self-reinforced poly(ethylene terephthalate) (SrPET) in order to increase knowledge and thereby advance the field of self-reinforced PET composites. This thesis shows that stretching the material in the manufacturing process increases the mechanical performance of the material due to increased orientation of the amorphous phase in the PET reinforcement. However, stretching introduces stresses in the material that give rise to negative shape distortions in the formed component. The degree of stretching during forming must therefore be controlled in order to achieve a robust serial production. The concept of a SrPET component over-moulded for integration of stiffeners and attachments has been evaluated in a life-cycle-assessment. This evaluation shows that the component weight can be reduced compared to technology currently in use and thereby contribute to increased sustainability of transport.

  • Public defence: 2018-01-26 10:00 F3, Stockholm
    Saffar Shamshirgar, Davood
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Fast methods for electrostatic calculations in molecular dynamics simulations2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with fast and efficient methods for electrostatic calculations with application in molecular dynamics simulations. The electrostatic calculations are often the most expensive part of MD simulations of charged particles. Therefore, fast and efficient algorithms are required to accelerate these calculations. In this thesis, two types of methods have been considered: FFT-based methods and fast multipole methods (FMM).

    The major part of this thesis deals with fast N.log(N) and spectrally accurate methods for accelerating the computation of pairwise interactions with arbitrary periodicity. These methods are based on the Ewald decomposition and have been previously introduced for triply and doubly periodic problems under the name of Spectral Ewald (SE) method. We extend the method for problems with singly periodic boundary conditions, in which one of three dimensions is periodic. By introducing an adaptive fast Fourier transform, we reduce the cost of upsampling in the non periodic directions and show that the total cost of computation is comparable with the triply periodic counterpart. Using an FFT-based technique for solving free-space harmonic problems, we are able to unify the treatment of zero and nonzero Fourier modes for the doubly and singly periodic problems. Applying the same technique, we extend the SE method for cases with free-space boundary conditions, i.e. without any periodicity.

    This thesis is also concerned with the fast multipole method (FMM) for electrostatic calculations. The FMM is very efficient for parallel processing but it introduces irregularities in the electrostatic potential and force, which can cause an energy drift in MD simulations. In this part of the thesis we introduce a regularized version of the FMM, useful for MD simulations, which approximately conserves energy over a long time period and even for low accuracy requirements. The method introduces a smooth transition over the boundary of boxes in the FMM tree and therefore it removes the discontinuity at the error level inherent in the FMM.

  • Public defence: 2018-01-26 13:00 Kollegiesalen, Stockholm
    Tsaknaki, Vasiliki
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Making Preciousness: Interaction Design Through Studio Crafts2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation explores value-creation in interaction design through practical collaborations with studio craftspersons. A focus is on the meaning of “preciousness” from a design perspective – what I refer to as Making Preciousness –  which highlights aspects of material properties, design processes, and the attitude to the design space. Theoretically, the work takes inspiration from the Japanese philosophy of Wabi-Sabi, which is based on the fact that things are impermanent, incomplete, and imperfect. This reflects a view of preciousness beyond notions of practical use, luxury or monetary cost. In addition to theoretical studies, I engaged in practice-based research at the intersection of interaction design and studio crafts, in the domains of leather, silversmith and textile crafting. Through an approach that blends these practices with the making of interactive artefacts, preciousness for interaction design was explored.

    Through this work, I extract three qualities, all of which are closely linked to attributes and values ​​embedded in the craft practices examined. I refer to these as resourceful composition, material sensuality and the aiming for mattering artefacts. Resourceful composition refers to approaching a design space “resourcefully”, meaning that the designer actively values and uses the specific qualities of materials and tools consciously, for what they are suitable for. Material sensuality is about appreciating the sensory experience of interacting with materials, arriving through particular material qualities, such as texture, temperature or smell, but also interactive qualities. Aiming for mattering artefacts involves actively designing for impermanence, incompleteness and imperfection, and through that contributing to notions of preciousness through use, care, ownership and interaction between users and artefacts over time.

    The attitude of making preciousness can be seen as tying together materials and making with user experiences of computational artefacts. For interaction design, this points towards making processes in which computation and material knowledge, craftsmanship and aesthetic intentions are placed at the core. These values ​​relate to cultural, but also sensual experiences, which can be seen as under-explored in the design of interactive products.