| 1. |
- Ainegren, Mats, 1963-
(författare)
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The rolling resistances of roller skis and their effects on human performance during treadmill roller skiing
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern ski-treadmills allow cross-country skiers, biathletes and ski-orienteers to test their physical performance in a laboratory environment using classical and freestyle techniques on roller skis. For elite athletes the differences in performance between test occasions are quite small, thus emphasising the importance of knowing the roller skis’ rolling resistance coefficient, µR, in order to allow correct comparisons between the results, as well as providing the opportunity to study work economy between different athletes, test occasions and core techniques.Thus, one of the aims of this thesis was to evaluate how roller skis’ µR is related to warm-up, mass, velocity and inclination of the treadmill. It was also necessary to investigate the methodological variability of the rolling resistance measurement system, RRMS, specially produced for the experiments, with a reproducibility study in order to indicate the validity and reliability of the results.The aim was also to study physiological responses to different µR during roller skiing with freestyle and classical roller skis and techniques on the treadmill as a case in which all measurements were carried out in stationary and comparable conditions.Finally, the aim was also to investigate the work economy of amateurs and female and male junior and senior cross-country skiers during treadmill roller skiing, i.e. as a function of skill, age and gender, including whether differences in body mass causes significant differences in external power per kg due to differences in the roller skis’ µR.The experiments showed that during a warm-up period of 30 minutes, µR decreased to about 60-65% and 70-75% of its initial value for freestyle and classical roller skis respectively. For another 30 minutes of rolling no significant change was found. Simultaneous measurements of roller ski temperature and mR showed that stabilized mR corresponds to a certain running temperature for a given normal force on the roller ski. The study of the influence on mR of normal force, velocity and inclination produced a significant influence of normal force on mR, while different velocities and inclinations of the treadmill only resulted in small changes in mR. The reproducibility study of the RRMS showed no significant differences between paired measurements with either classical or the freestyle roller skis.The study of the effects on physiological variables of ~50% change in µR,showed that during submaximal steady state exercise, external power, oxygen uptake, heart rate and blood lactate were significantly changed, while there were non significant or only small changes to cycle rate, cycle length and ratings of perceived exertion. Incremental maximal tests showed that time to exhaustion was significantly changed and this occurred without a significantly changed maximal power, maximal oxygen uptake, maximal heart rate and blood lactate, and that the influence on ratings of perceived exertion was non significant or small.The final part of the thesis, which focused on work economy, found no significant difference between the four groups of elite competitors, i.e. between the two genders and between the junior and senior elite athletes. It was only the male amateurs who significantly differed among the five studied groups. The study also showed that the external power per kg was significantly different between the two genders due to differences in body mass and mR, i.e. the lighter female testing groups were roller skiing with a relatively heavier rolling resistance coefficient compared to the heavier testing groups of male participants.
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| 3. |
- Carlsson, Per
(författare)
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Entrained flow black liquor gasification : detailed experiments and mathematical modelling
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Black liquor, a by-product from the Kraft pulping process is a highly viscous fluid consisting of approximately 30% water, 30 % alkali salts and 40 % combustible material. The alkali salts originating from the pulp making process need to be recovered in order for the pulp mill to be economical and to satisfy environmental regulation. Currently, the recovery takes place in a large boiler called Tomlinson recovery boiler named after its inventor. However, a more energy efficient way to recover the chemicals could be via gasification in a pressurized, entrained flow, high temperature gasifier. To demonstrate this technology a development plant (DP1) was built in 2005 by the technology vendor Chemrec. Since then, the plant has been running for more than 10 000 h and frequently been updated and optimized. As steps towards commercialization and scale–up different computational models of varying sophistication are used as design and optimization tools for the process. Still, the engineering tools can only provide sensible predictions if they are properly validated and verified. This licentiate thesis is concerned with validation of a comprehensive mathematical model based on Computational Fluid Dynamics (CFD) describing the gasification reactor and experimental investigations of the process characteristics in the DP1 gasifier. Paper A describes the system design and methodology for high temperature gas sampling during pressurized black liquor gasification. In this work a water-cooled gas sampling probe is installed in the hot part of the DP1 gasification reactor and several gas samples are withdrawn and analyzed. The experimentally obtained data in Paper A are then used as validation data for the CFD-model described in Paper B. In Paper C the obtained data from Paper A are thoroughly analyzed and the influence of reactor operation on producer gas composition is determined. In Paper D black liquor sprays from a gas assisted nozzle is experimentally investigated using high speed photography. Furthermore, the particle content in the cooled producer gas is measured using a particle sizing impactor. The obtained results in Paper D can be used to explain some of the observations in Paper A.
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| 4. |
- Carlsson, Per
(författare)
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Market and resource allocation algorithms with application to energy control
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The energy markets of today are markets with rather few active participants. The participants are, with few exceptions, large producers and distributors. The market mechanisms that are used are constructed with this kind of a market situation in mind. With an automatic or semiautomatic approach, the market mechanism would be able to incorporate a larger number of participants. Smaller producers, and even consumers, could take an active part in the market. The gain is in more efficient markets, and – due to smaller fluctuations in demand – better resource usage from an environmental perspective.The energy markets of the Nordic countries (as well as many others) were deregulated during the last few years. The change has been radical and the situation is still rather new. We believe that the market can be made more efficient with the help of the dynamics of the small actors.The idealised world of theory (of economics) often relies on assumptions such as continuous demand and supply curves. These assumptions are useful, and they do not introduce problems in the power market situation of today, with relatively few, large, participants. When consumers and small producers are introduced on the market, the situation is different. Then it is a drawback if the market mechanims cannot handle discontinuous supply and demand.The growth in accessibility to computational power and data communications that we have experienced in the last years (and are experiencing) could be utilised when constructing mechanisms for the energy markets of tomorrow.In this thesis we suggest a new market mechanism, ConFAst, that utilises the technological progress to make it possible to incorporate a large number of active participants on the market. The mechanism does not rely on the assumptions above. The gain is a more efficient market with less fluctuations in demand over the day.To make this possible there is a need for efficient algorithms, in particular this mechanism relies on an efficient aggregation algorithm. An algorithm for aggregation of objective functions is part of this thesis. The algorithm handles maximisation with nonconcave, even noisy, objective functions. Experimental results show that the approach, in practically relevant cases, is significantly faster than the standard algorithm.
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| 6. |
- Hultgren, Peter, 1970-
(författare)
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Sjukskrivningspraxis på vårdcentralen
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Den här undersökningen handlar om vårdcentralens läkare och deras sjukskrivningspraxis. Till vårdcentralen kommer patienter med olika sjukdomsbilder och ohälsoproblem. Det är läkarnas grannlaga uppgift att utfärda sjukintyg även om en stor del av de sjukdomsbilder som läkaren möter är oklara. I de fallen ska läkaren inte bara diagnostisera och försöka avhjälpa patientens medicinska problem, läkaren ska också bedöma i vilken mån patientens arbetsförmåga är nedsatt av sjukdom. Dessutom ska läkaren bedöma hur omfattande nedsättningen är och hur länge patienten kan förväntas behöva avstå arbete eller att stå till arbetsmarknadens förfogande.Hur går det till när läkare bedömer patienters sjukdomsgrundade arbetsoförmåga och hur går det till när de bedömningarna översätts till sjukintyg? I den här explorativa studien söks svaren på dessa frågor utifrån ett teoretiskt perspektiv som fokuserar på de olika och ofta motstridiga rollförväntningar som riktas på läkarna i deras sjukskrivningspraxis.Sammanfattningsvis ger undersökningen om sjukskrivningspraxis på vårdcentralen en bild av läkare som strävar mot att förena det goda terapeutiska arbetet med korrekt regeltillämpning och en patientanpassad service, men där logikerna för professionellt, byråkratiskt och marknadsorienterat arbete skapar spänningar. Läkarna tillgriper medicinska, sociala och tekniska strategier för att hantera de osäkerheter som är förbundna med att bedöma och intyga patienters sjukdoms grundade arbetsoförmåga och för att överbrygga de konflikter som uppstår i mötet mellan skilda arbetslogiker.
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| 7. |
- Johansson, Simon
(författare)
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Numerical modelling of swirling drying flow
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Waste hydrochloric acid (HCl) from the pickling process at SSAB EMEA in Borl¨ange, Sweden, is regenerated using a technique called spray roasting where waste HCl is sprayed into a hot reactor through four spray nozzles at the top of the reactor. The regeneration (drying) process is driven by four natural gas burners placed symmetrically along the periphery of the reactor and causes the water in the waste acid droplets to evaporate. Through chemical reactions the iron chloride is oxidized to form hematite and chloride gas; the latter to be used for manufacturing of new HCl which anew is used in the pickling process. The produced byproduct in form of hematite is sold and used in e.g. the electronic industry and as filling material for road constructions. A good quality of the hematite powder vouch for profit of the sold product, and hence an enhanced economy for the whole regeneration process which in turn motivates a continued regeneration rather than shipping away the waste acid and continuously buying new HCl.Due to the hostile environment inside the reactor, measurements and optical visualizations are difficult to perform. This limitation lead to a poor understanding of the dynamics inside the reactor as the process is a black box where waste acid is injected and hematite and chloride gas is collected; what happens in-between the two stages is not known to any larger extent. Here Computational Fluid Dynamics (CFD) is a useful tool for the modeling of the physics inside the reactor. In this licentiate thesis, the commercially available CFD software Ansys CFX has been used to model the gas flow and temperature inside the regeneration reactor as part of the main goal of modeling the whole regeneration process. As a first approach, the gas flow and temperature behavior are of certain interest as these quantities determine the dynamics of the injected droplets through their journey inside the reactor, and hence the regeneration process. The present work comprise two papers devoted to the actual application of HCl regeneration, and one paper which emphasize the importance of grid independency studies and the impact of grid element size in regions with high gradients. In the two application-focused papers (Paper A and C) the gas flow and temperature profile inside the reactor is resolved together with the particle (droplet) distribution. In Paper C the study is developed to also comprise the influence on theses quantities due to different locations and spray directions of the spray nozzles located at the top of the reactor.
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| 8. |
- Karlsson, Niklas
(författare)
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Parametric model for astrophysical proton-proton interactions
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Observations of gamma-rays have been made from objects such as active galaxies and supernova remnants and also as diffuse emission from the Galactic ridge. The study of gamma-rays can provide information about production mechanisms and tell us about cosmic ray acceleration. In the high energy regime, the dominant mechanism for gamma-ray production is the decay of neutral pions produced in interactions of accelerated cosmic ray nuclei and interstellar matter. Having an accurate model for this is an integral part in the study of gamma-rays and the sources in which they are produced. We present here a parametric model for calculations of inclusive cross sections for stable secondary particles (gamma-rays, electrons, positrons, nue, anti nue, numu and anti numu) produced in proton-proton interactions. The model is based on the up-to-date proton-proton interaction model by Kamae et al., which includes the diffraction dissociation process, violation of the Feynman scaling law and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added to the model: one representing the Δ(1232) and the other multiple resonances with masses around 1600 MeV/c^2. The parametric model predicts the spectra for all secondary particles to be harder by about 0.05 in power-law index than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on Feynman scaling. The transverse momentum distributions for gamma-rays have also been calculated from the described proton-proton interaction model, showing the potential of also having a parametric model for the transverse momentum distributions.
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| 9. |
- Saarinen, Linn, 1980-
(författare)
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A hydropower perspective on flexibility demand and grid frequency control
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production and consumption of electricity on the power grid has to balance at all times. Slow balancing, over days and weeks, is governed by the electricity market and carried out through production planning. Fast balancing, within the operational hour, is carried out by hydropower plants operating in frequency control mode. The need of balancing power is expected to increase as more varying renewable energy production is connected to the grid, and the deregulated electricity market presents a challenge to the frequency control of the grid.The first part of this thesis suggests a method to quantify the need for balancing or energy storage induced by varying renewable energy sources. It is found that for high shares of wind and solar power in the system, the energy storage need over a two-week horizon is almost 20% of the production.The second and third part of the thesis focus on frequency control. In the second part, measurements from three Swedish hydropower plants are compared with the behaviour expected from commonly used power system analysis hydropower models. It is found that backlash in the guide vane and runner regulating mechanisms has a large impact on the frequency control performance of the plants.In the third part of the thesis, the parameters of the primary frequency control in the Nordic grid are optimised with respect to performance, robustness and actuator work. It is found that retuning of the controller parameters can improve the performance and robustness, with a reasonable increase of the actuator work. A floating deadband in the controller is also discussed as a means to improve performance without increasing the actuator work.
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| 10. |
- Sjödin, Carina, 1964-
(författare)
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User-involved service innovation : Three participating perspectives on co-creation
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The involvement of customers and other stakeholders in the innovation process is proposed to be a key success factor and something that makes companies more competitive. As a consequence, more and more organizations alter their innovation strategy accordingly. In order for a company to open up innovation processes, it is vital to foster a practice where there is openness for external ideas and knowledge. However, when external ideas meet internal innovation practices complex organizational situations appear. Creativity, for example, involves co-dependence of other persons’ strategies and actions. New roles for those involved affect hierarchies and knowledge sharing opportunities.This thesis involves three different perspectives of the same process provides an opportunity to study both individual and structural challenges. This research aims to identify on-going challenges for an organization during the transformational processes that adjustment from a traditional product innovation structure to an open service innovation culture implies. This qualitative case study involves two main cases and three supporting cases and aims to understand how users and other external parties, top management and middle managers experience open innovation processes. The results describe interactions between organizations and users or external stakeholders as well as internal interactions within the organization. Top management were dedicated to the idea of increased openness, but detected structural issues to deal with in order to implement user involved innovation. Among middle management, some individual aspects such as attitudes and relational issues matter, as well as organizational structures and practices. Users had mixed opinions about their participation in the process. Favorable experiences, such as benevolence and deepened relationships, were balanced by un-favorable experiences such as incapability and intrusion. Different dimensions of openness regarding open innovation practice are discussed. In this work a relational focus is emphasized. The findings assist managers in their work to create conditions for open innovation. Managers can benefit from this research by getting a better understanding of how different stakeholders’ experience co-creation of value. This is relevant for innovation managers in the process of redesigning innovation processes to understand different aspects of the interactions involved.
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