| 1. |
- Anttila, Sara, et al.
(författare)
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Grid Forming inverters : A review of the state of the art of key elements for microgrid operation
- 2022
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:15
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Forskningsöversikt (refereegranskat)abstract
- In the past decade, inverter-integrated energy sources have experienced rapid growth, which leads to operating challenges associated with reduced system inertia and intermittent power generation, which can cause instability and performance issues of the power system. Improved control schemes for inverters are necessary to ensure the stability and resilience of the power system. Grid-forming inverters dampen frequency fluctuations in the power system, while grid-following inverters can aggravate frequency problems with increased penetration. This paper aims at reviewing the role of grid-forming inverters in the power system, including their topology, control strategies, challenges, sizing, and location. In order to facilitate continued research in this field, a comprehensive literature review and classification of the studies are conducted, followed by research gaps and suggestions for future studies.
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| 2. |
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| 3. |
- Anttila, Sara
(författare)
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Power control strategies for renewable energy systems : The inverter's role in future power systems
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Connecting more non-dispatchable renewable energy sources (RESs) will result in a higher power variability and a lower system inertia when the synchronous generators are replaced by inverter-connected RES. Inverter control can be divided in three categories: grid-following, grid-forming (GFM) and grid-supporting. A literature review of inverter control strategies identifies the GFM control as having an important role in maintaining system stability assuming near 100 % inverter-connected RES. Critical aspects of the inverter control are also identified; the control need to function autonomously, be able to remain connected during transient events and be insensitive to grid topology.Combining various RES is also shown to improve system stability. The combination of RES that has been investigated in most studies is wind, solar and wave power. Wave power is still a young technology compared to solar and wind power. It generates higher power fluctuations over short time periods with a significant difference between average and maximum power. Additionally, wave power parks (WPPs) are often connected via long cables which contribute reactive power to the grid. These challenges has to be considered to maintain system stability and power quality when connecting a WPP to the grid.In a Power Hardware-In-the-Loop study of how a WPP affects the power quality at the point of common coupling (PCC), it is found that the impact is highest for WPPs with fewer generators as the variability is reduced when several generators are excited at different times. Energy storage is also shown to have a significant impact on the power quality at the PCC with reduced flicker, total harmonic distortion and power and voltage variability. A simulation study also shows the positive impact of energy storage on power variability and the role of inverter control in reactive power compensation.
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| 4. |
- Axell, Cecilia, et al.
(författare)
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Facts for youngsters : Contextualised technology or fragmented artefacts? A study on portrayals of technology in picture books from a gender perspective
- 2015
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Ingår i: PATT 29 Plurality and Complementarity of Approaches in Design and Technology Education, Marseille, France, April 2015. - Marseille : Presses Universitaires de Provence. - 9782853999946 ; , s. 42-48
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Technology is a field with strong connections to the female/male dichotomy and children's gender stereotyping starts as early as the age of two (Berner, 2004; Nisbet, Pendergast & Reynolds, 1998; Turja, Endepohls-Ulpe & Chatoney, 2009). According to the Swedish Curriculum for the Preschool, the preschool should strive to ensure that children ”develop their ability to identify technology in everyday life, and explore how simple technology works” (Lpfö98/2010, p. 10). The preschool also has a goal to actively counteract traditional gender roles and patterns (Lpfö98/2010, p. 4). An important part of children's activities in preschool relates to picture books. A government investigation states that the preschool, through its activities (among them ”reading aloud”) is an arena where societal norms can either be preserved or challenged (SOU 2006:75). Books about cars, airplanes, boats etc. often serve as an introduction to human applications of technology. Based on these, children start to identify and categorize the technologies they encounter in everyday life.The aim of this study is consequently to investigate the technological content from a gender perspective in a selection of picture books, more specifically; how do the books content preserve or challenge preschool children's view of technology and gender? Preschools use books from libraries in their daily activities, therefore the empirical material in this study is derived from the library section ”facts for youngsters”. A thematic analysis was employed to discover the dominant themes within the books. The result of the study shows that there is a focus on how separate artefacts function but no detailed explanation on how these artefacts are connected or what kind of implications they have in a societal context. There also seems to be an emphasis on traditionally masculine coded technology. This study will serve as a basis for a comparative study between two preschools, one where gender and technology is a prioritised goal and one where it is not.
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| 5. |
- Axell, Cecilia, 1965-, et al.
(författare)
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Preschoolers’ Conceptions of Technological Artefacts and Gender in Picture Books
- 2016
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Ingår i: PATT-32 Proceedings Technology Education for 21st Century Skills. - : ITEEA. ; , s. 57-64
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Konferensbidrag (refereegranskat)abstract
- Picture books are a frequent element of daily preschool activities (Damber, Nilsson & Ohlsson, 2013; Simonsson, 2004; SOU 2006:75). They are important pedagogical tools that can help children acquire an understanding of the everyday technology they come in contact with, as well as the human application of technology (Axell, 2015; Axell & Boström, 2015). These are skills that are emphasised in the Swedish preschool curriculum. In the curriculum it is also stated that the preschool should counteract traditional gender patterns and gender roles (Skolverket, 2010). However, an investigation of a selection of picture books aimed at preschool children shows that the books content is somewhat problematic. Many of the picture books provide a focus on the function of separate artefacts without any sort of context or explanation of their implications in a societal context. There also tends to be an emphasis on traditional masculine-coded technology in the books. Building and making and working with machines is depicted as a male activity. The male stereotype is essentially connected with different kinds of vehicles like cars, airplanes, motorbikes, tractors etc. (Axell & Boström, 2015; See also Holbrok, 2008). Based on these previous findings, the aim of this pilot study was to obtain an initial concept about how children’s literature may influence preschool children’s view on technological artefacts. The study was conducted through semi-structured interviews with four five-year-olds, two girls and two boys. Through a thematic analysis (Braun & Clarke, 2006) three overarching themes were identified: The relationship between design and function, anthropomorphic animals as users of artefacts, and gender and artefacts. Some of the key findings were that the 5-year-olds did not know what “technology” is, but had good knowledge about tools. Additionally, they did not genderise any of the artefacts included in the study.
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| 6. |
- Axell, Cecilia, 1965-, et al.
(författare)
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Technology in children's picture books as an agent for reinforcing or challenging traditional gender stereotypes
- 2021
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Ingår i: International journal of technology and design education. - Switzerland : Springer. - 0957-7572 .- 1573-1804. ; 31, s. 27-39
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Tidskriftsartikel (refereegranskat)abstract
- Technology is a field with strong connections to the female/male dichotomy. Children start to stereotype everyday life regarding this dichotomy as early as the age of two. The preschool, through its activities—among them reading aloud from picture books—is an arena where societal norms can be either preserved or challenged. Books about different artefacts, e.g. cars, airplanes and boats, often serve as an introduction for children about the human application of technology and may influence how they identify and categorise the technology they encounter in everyday life. The aim of this study was to investigate the technological content in a selection of picture books from a gender perspective. Since preschools in Sweden often use books from libraries in their daily activities, the empirical material was derived from the library sections Facts for youngsters and Technology for youngsters, aimed at children aged 1–3 and 3–6. A thematic analysis was used to discover the dominant themes within the books. The results show that there is a focus on how separate artefacts function but no detailed explanation of how these artefacts are connected or what kind of implications they have in a societal context. There also seems to be an emphasis on traditionally masculine coded technology.
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| 7. |
- Axell, Cecilia, 1965-, et al.
(författare)
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Unveiling Biases: An Exploration of ChatGPT-3.5-generated ‘Technology Stories’
- 2023
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Ingår i: The 40th International Pupils’ Attitudes Towards Technology Conference Proceedings 2023. - : Liverpool John Moores University. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- A technology that is increasingly affecting our daily lives is artificial intelligence (AI). An example of such a technology is ChatGPT-3.5, which has received a lot of attention recently. ChatGPT-3.5 is a text generator that is developed on a large number of existing texts. Currently, there is a debate about negative consequences in education, for example, if students let the chatbot write texts for them. In this study, however, our point of departure is on how ChatGPT-3.5 and storytelling can be used as a tool in teacher education to develop students’ critical thinking in relation to technology.A main objective of technology as a school subject is to prepare pupils to act in a technology-intensive world, which includes critical thinking about technology and its impact on individuals, society, and nature. However, a critical aspect of technology education is that it easily becomes an unreflective doing without a meaningful context. A way to circumventing this problem is to use storytelling in technology teaching.This is a pre-study for a coming project aiming to let teacher students create stories using ChatGPT-3.5 and then critically analyse the technological content in the stories. In this pre-study, we gave ChatGPT-3.5 the instruction to generate ten shorter stories for children with a focus on technology. A qualitative content analysis shows that there are several dominant themes within the stories, and that the chatbot presents a view of technology that is mainly positive and without any critical reflection on its effects on individuals, nature and society. Furthermore, in the stories, high-tech male coded technology is a dominating theme. The pre-study highlights the importance of critical thinking and reflections when using AI tools in technology teacher education. It also indicates that stories generated by a chatbot can be a steppingstone to visualise technology bias and contribute to developing teacher students’ critical gaze.
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| 8. |
- Baudoin, Antoine, et al.
(författare)
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Assessment of Thermal Cycling in a Rectifier For WavePower Generation
- 2016
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Konferensbidrag (refereegranskat)abstract
- Natural convection allows for passive cooling which isused in many engineering applications. Placing dissipatingcomponents on a common vertical heatsink can be opti-mized to give the best possible cooling capacity. In thisstudy, a numerical model for three-dimensional conjugatedconvective and conductive heat transfer was used to evalu-ate the distribution of up to 36 ush-mounted rectangularheaters. The temperature proles and the heat uxes werecompared with experimental data for validation. The dis-sipated power was set as an input parameter and the op-timal distribution was selected as the one with the lowesttemperature elevation. Two dierent heuristicsa geo-metric parameter and an articial neural networkwereproposed and evaluated as alternatives to heavy CFD cal-culations.
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| 9. |
- Baudoin, Antoine
(författare)
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Cooling Strategies for Wave Power Conversion Systems
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Division for Electricity of Uppsala University is developing a wave power concept. The energy of the ocean waves is harvested with wave energy converters, consisting of one buoy and one linear generator. The units are connected in a submerged substation. The mechanical design is kept as simple as possible to ensure reliability.The submerged substation includes power electronics and different types of electrical power components. Due to the high cost of maintenance operations at sea, the reliability of electrical systems for offshore renewable energy is a major issue in the pursuit of making the electricity production economically viable. Therefore, proper thermal management is essential to avoid the components being damaged by excessive temperature increases.The chosen cooling strategy is fully passive, and includes no fans. It has been applied in the second substation prototype with curved heatsinks mounted on the inner wall of the pressurized vessel. This strategy has been evaluated with a thermal model for the completed substation. First of all, 3D-CFD models were implemented for selected components of the electrical conversion system. The results from these submodels were used to build a lumped parameter model at the system level.The comprehensive thermal study of the substation indicates that the rated power in the present configuration is around 170 kW. The critical components were identified. The transformers and the inverters are the limiting components for high DC-voltage and low DC-voltage respectively. The DC-voltage—an important parameter in the control strategy for the WEC—was shown to have the most significant effect on the temperature limitation.As power diodes are the first step of conversion, they are subject to large power fluctuations. Therefore, we studied thermal cycling for these components. The results indicated that the junction undergoes repeated temperature cycles, where the amplitude increased with the square root of the absorbed power.Finally, an array of generic heat sources was optimized. We designed an experimental setup to investigate conjugate natural convection on a vertical plate with flush-mounted heat sources. The influence of the heaters distribution was evaluated for different dissipated powers. Measurements were used for validation of a CFD model. We proposed optimal distributions for up to 36 heat sources. The cooling capacity was maximized while the used area was minimized.
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| 10. |
- Baudoin, Antoine, et al.
(författare)
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Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
- 2016
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two.
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| 11. |
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| 12. |
- Baudoin, Antoine, 1984-, et al.
(författare)
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Optimized distribution of a large number of power electronics components cooled by conjugate turbulent natural convection
- 2017
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 124, s. 975-985
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Tidskriftsartikel (refereegranskat)abstract
- Natural convection allows for passive cooling which is used in many engineering applications. Placing dissipating components on a common vertical heatsink can be optimized to give the best possible cooling capacity. In this study, a numerical model for three-dimensional conjugated convective and conductive heat transfer was used to evaluate the distribution of up to 36 flush-mounted rectangular heaters. The temperature profiles and the heat fluxes were compared with experimental data for validation. The dissipated power was set as an input parameter and the optimal distribution was selected as the one with the lowest temperature elevation. Two different heuristics-a geometric parameter and an artificial neural network-were proposed and evaluated as alternatives to heavy CFD calculations.
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| 13. |
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| 14. |
- Baudoin, Antoine, et al.
(författare)
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Thermal modelling of a passively cooled inverter for wave power
- 2015
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 9:4, s. 389-395
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Tidskriftsartikel (refereegranskat)abstract
- Owing to very costly maintenance operations, the reliability of electrical systems for offshore renewable energy is a major issue to make electricity production economical. Therefore proper thermal management is essential in order to avoid the components from being damaged by excessive temperature increase. Both analytic and computational fluid dynamics (CFD) models were implemented to assess the temperature increase in the inverter installed in a submerged substation and during working conditions. It was shown that this inverter could transmit a total power of up to about 35 kW. This limit is dependent on a certain distance between the modules and a perfect thermal contact with the hull. The influence of several of such parameters as well as the efficiency of passive cooling were studied.
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| 15. |
- Baudoin, Antoine, 1984-, et al.
(författare)
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Thermal Rating of a Submerged Substation for Wave Power
- 2016
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Ingår i: IEEE Transactions on Sustainable Energy. - 1949-3029 .- 1949-3037. ; 7:1, s. 436-445
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Tidskriftsartikel (refereegranskat)abstract
- The costs of offshore maintenance operations put high reliability-requirements on offshore equipment for ocean energy, especially on submerged ones. Thermal management is thus essential in the design of the prototypes of a marine substation, developed at Uppsala University, for grid interface of wave power parks. The cooling system itself should be efficient as well as reliable. Therefore, the feasibility of a completely passive cooling strategy was evaluated. The studied substation includes various power components, which dissipate heat and are installed in one pressurized vessel. Thermal cross-coupling was investigated with 3-D submodels and a thermal network model. An electric circuit was coupled to determine the rated power of the substation. The results depend mainly on the dc-voltage, the seawater temperature, and the thermal contact between the components and the hull.
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| 16. |
- Baudoin, Antoine
(författare)
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Thermal Study of a Submerged Substation for Wave Power
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- At the Division of Electricity of Uppsala University, a wave power concept is being developed.It relies on wave energy converters, one buoy and one linear generator placed on the seabed, connected together to a submerged substation. The mechanical design is kept as simple as possible to ensure reliability. The submerged substation includes power electronics and different types of electric components. High reliability requirements on such subsea devices make thermal management a keyaspect in the design. Besides, no fans are used and the cooling strategy is fully-passive. The overall approach for thermal modelling of the substation is based on a thermal network atthe system level, and both analytic- and CFD- modelling at the component level. This work is focusing on the second prototype of substation developed at Uppsala University. In this thesis, this overall strategy is presented as well as a comprehensive temperature study for the inverterinstalled in the substation.In the present configuration, the inverters are limited to about 35 kW. The seawater temperature,the choice of material for the heat-sink, and the spacing of the component, were identified tohave an influence on this value. The importance of a good thermal contact between the heat-sink and the hull was also illustrated.
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| 17. |
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| 18. |
- Bjursell, Cecilia, 1970-, et al.
(författare)
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Intergenerational learning in a changing world : Knitting generations together
- 2023
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Ingår i: Ricerche di Pedagogia e Didattica. - : University of Bologna. - 1970-2221. ; 18:2, s. 51-65
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Tidskriftsartikel (refereegranskat)abstract
- In intergenerational projects, learning a craft is an activity that may be of interest to people of different ages. This paper focuses on knitting as a craft. In most Western societies, knitting is often considered a craft for women, but on Taquile Island, Peru, it is the men who knit. This paper discusses knitting from an intergenerational perspective whilst focusing on gender and culture. To this aim, we introduce an intrinsic case study to examine the role of gender and culture in intergenerational learning. The data used in this study was collected during a visit to Taquile Island. In summary, the study’s findings reveal that (i) on Taquile, members of the community invest in maintaining cultural traditions in opposition to being swept along by (con)temporary social changes; (ii) knitting on Taquile is approached as a practical technique in contrast to Western culture where knitting is connected to the concept of ‘well-being’; and (iii) whilst gender structures may set frames for performance, the Taquile case demonstrates that what is typically considered ‘male’ or ‘female’ may vary.
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| 19. |
- Björk, Mathilda, et al.
(författare)
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Inflammatory Arthritis and the Effect of Physical Activity on Quality of Life and Self-reported Function : A Systematic Review and Meta-analysis
- 2022
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Ingår i: Arthritis care & research. - : John Wiley & Sons. - 2151-464X .- 2151-4658. ; 74:1, s. 31-43
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Forskningsöversikt (refereegranskat)abstract
- OBJECTIVE: Although physical activity (PA) is an evidence-based intervention that reduces disease-related symptoms and comorbidity in rheumatoid arthritis (RA), PA's effect on self-reported function and Quality of Life (QoL) has not been analyzed. This study synthesizes the evidence for the effectiveness of PA on QoL and self-reported function in adults with RA, spondyloarthritis (SpA), and psoriatic arthritis (PsA).METHODS: The databases PubMed, Embase, CINAHL, and Cochrane Central Register of Controlled Trials (CENTRAL) were searched to identify relevant randomized controlled trials (RCTs). Screening, risk of bias assessment (using RoB 2.0 tool), and data extraction were independently performed by two or more of the authors. The meta-analyses were conducted with a random-effects model.RESULTS: The systematic review included 55 RCTs and the meta-analysis included 37 RCTs. In 55 studies included, 76% investigated RA, 20% investigated SpA, and 4% investigated PsA. In RA effects were found on QoL and function compared to inactive controls, effects not sustained in comparison to active controls. In SpA the effects of PA on QoL were in favor of the control group. Effects on function were found compared to inactive controls and sustained in fatigue and pain when compared to active controls. In PsA no effects on QoL were found but on function compared to inactive controls. The effect size was below 0.30 in the majority of the comparisons.CONCLUSION: PA may improve QoL and self-reported function in RA, SpA, and PsA. However, larger trials are needed, especially in SpA and PsA.
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| 20. |
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| 21. |
- Boström, Cecilia, et al.
(författare)
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Design proposal of electrical system for linear generator wave power plants
- 2009
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Ingår i: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS. - : IEEE. - 9781424446483 - 9781424446506 ; , s. 4180-4185
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Konferensbidrag (refereegranskat)abstract
- This paper describes an electrical system layout for a wave power plant connecting linear generators to the grid. The electrical power out from the wave energy converters must be converted before they can be connected to the grid. The conversion is carried out in marine substations that will be placed on the seabed.The paper presents experimental power data from a wave energy converter that has been in operation at the Lysekil research site since March 2006. Moreover, results and analyses from experiments and simulations from tests with the generator connected to a rectifier and filter are presented. A simulation is made to show the difference between having the generator connected to a linear load and a nonlinear load, which would be the case when the generator is connected to the grid.
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| 22. |
- Boström, Cecilia
(författare)
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Electrical System of a Wave Power Plant
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several techniques to convert the energy in the ocean waves into electric energy. The wave energy converter presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. By keeping the generator as simple as possible and minimizing the number of mechanical parts, the lifetime of the generator is believed to increase. To convert and interconnect the power from the generators, marine substations are used. The marine substation will be placed on the seabed and it will convert the AC with variable amplitude and variable frequency from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the conversion, the rectification and filtering. The purpose with the study was to investigate how the generator will operate when it is connected to a non-linear load and to obtain guidelines on how larger systems could be designed. Another aim with the experiment was to see to which extent the voltage and power out from the generator can be smoothened. Offshore experiments and simulations have been done on a full scale generator connected to a diode rectifier and filter. The results show that a smooth DC output voltage after the rectifier has small ripple content. The kind of load and value of load will have an impact on the generators ability to absorb and produce power. The highest amount of absorbed power is achieved at the highest damping of the system. However, the highest damping function does not necessarily coincide with the maximum produced power. In connection to the installation of two new wave energy converters on the Swedish west coast, a marine substation will be launched at the site. Laboratory tests have been done on the marine substation and it worked as expected and the experimental data had a good agreement with the simulated data.
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| 23. |
- Boström, Cecilia, 1982-
(författare)
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Electrical Systems for Wave Energy Conversion
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several technologies on how to convert the energy in the ocean waves into electric energy. The wave energy converter (WEC) presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power.To convert and interconnect the power from the generators, marine substations are used. The marine substations are placed on the seabed and convert the fluctuating AC from the generators into an AC suitable for grid connection.The work presented in the thesis focuses on the first steps in the electric energy conversion, converting the voltage out from the generators into DC, which have an impact on the WEC's ability to absorb and produce power. The purpose has been to investigate how the generator will operate when it is subjected to different load cases and to obtain guidelines on how future systems could be improved. Offshore experiments and simulations have been done on full scale generators connected to four different loads, i.e. one linear resistive load and three different non-linear loads representing different cases for grid connected WECs.The results show that the power can be controlled and optimized by choosing a suitable system for the WEC. It is not obvious which kind of system is the most preferable, since there are many different parameters that have an impact on the system performance, such as the size of the buoy, how the generator is designed, the number of WECs, the highest allowed complexity of the system, costs and so on. Therefore, the design of the electrical system should preferably be carried out in parallel with the design of the WEC in order to achieve an efficient system.
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| 24. |
- Boström, Cecilia, et al.
(författare)
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Experimental results from an offshore wave energy converter
- 2008
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Ingår i: Volume 6. ; , s. 653-657
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Konferensbidrag (refereegranskat)abstract
- Anoffshore wave energy converter (WEC) was successfully launched at theSwedish west coast in the middle of March 2006. TheWEC is based on a permanent magnet linear generator locatedon the ocean floor driven by a point absorber. Ameasuring station has been installed on a nearby island whereall measurements and experiments on the WEC have been carriedout. The output voltage from the generator fluctuates both inamplitude and frequency and must therefore be converted to enablegrid connection. In order to study the voltage conversion, themeasure station was fitted with a six pulse diode rectifierand a capacitive filter during the autumn of 2006. Theobject of this paper is to present a detailed descriptionof the existing wave energy system of the Islandsberg project.Special attention will be given to the power absorption bythe generator when it is connected to a non linearload
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| 25. |
- Boström, Cecilia, et al.
(författare)
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Experimental Results From an Offshore Wave Energy Converter
- 2010
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Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : ASME International. - 0892-7219 .- 1528-896X. ; 132:4, s. 041103-
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Tidskriftsartikel (refereegranskat)abstract
- An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.
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| 26. |
- Boström, Cecilia, et al.
(författare)
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Experimental results of rectification and filtration from an offshore wave energy system
- 2009
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 34:5, s. 1381-1387
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Tidskriftsartikel (refereegranskat)abstract
- The present paper presents results from a wave energy conversion that is based on a direct drive linear generator. The linear generator is placed on the seabed and connected to a buoy via a rope. Thereby, the natural wave motion is transferred to the translator by the buoy motion. When using direct drive generators, voltage and current output will have varying frequency and varying amplitude and the power must be converted before a grid connection. The electrical system is therefore an important part to study in the complete conversion system from wave energy to grid connected power. This paper will bring up the first steps in the conversion: rectification and filtration of the power. Both simulation studies and offshore experiments have been made. The results indicate that this kind of system works in a satisfactory way and a smooth DC power can be achieved with one linear generator.
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| 27. |
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| 28. |
- Boström, Cecilia, et al.
(författare)
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Linear Generator Connected to a Resonance-Rectifier Circuit
- 2013
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Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 38:2, s. 255-262
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a linear direct driven generator used for wave energy utilization. The generator is placed on the seabed and connected to a buoy on the ocean surface. Due to the reciprocating motion of the translator, an electrical conversion system is needed between the wave energy converter (WEC) and the grid. Depending on how the conversion system is designed, the generator will be subjected to different loads. A novel conversion system is presented in this paper where the voltage from the WEC is rectified in a resonance circuit. Both simulations and experiments are performed on the circuit. The results from the simulations show that a higher power absorption and power production can be achieved with the resonance circuit compared to a WEC connected to a passive rectifier. A WEC, L9, developed by Uppsala University (Uppsala, Sweden) was used in the experiment. Significantly higher power absorption was obtained for L9 compared to power data from the first installed WEC, L1, at the Lysekil research site.
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| 29. |
- Boström, Cecilia, et al.
(författare)
-
Operation analysis of a wave energy converter under different load conditions
- 2011
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 5:3, s. 245-250
-
Tidskriftsartikel (refereegranskat)abstract
- This study analyses the electrical behaviour of a direct-driven linear generator under different load conditions. The studied generator is used in a wave energy converter (WEC) that converts the energy in ocean waves into electric energy. To enable a grid connection of a WEC, the voltage must be converted, and thereby, the generator will be subjected to a non-linear damping. Depending on how the conversion system is designed, the damping will be different. In the case studied, the voltage is first rectified, and on the dc-side of the rectifier the voltage is kept constant by controlling the power through a converter. In order to study the electrical behaviour of the generator in this operation mode, a simulation model was made in MATLAB Simulink. The model of the generator was verified with experimental data from an offshore operating WEC. The result of the study shows that the model of the generator agrees with the real generator and can be used for analysing the electrical behaviour of the WEC. Moreover, the results show that the operation with a non-linear load will be different compared to a linear load case.
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| 30. |
- Boström, Cecilia, et al.
(författare)
-
Study of aWave Energy Converter Connected to a Nonlinear Load
- 2009
-
Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 34:2, s. 123-127
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents experimental results from a wave energy converter (WEC) that is based on a linear generator connected to a rectifier and filter components. The converter-filter system is installed onshore, while the linear wave generator operates offshore a few kilometers from the Swedish west coast. The power from the generator has been rectified with a diode bridge and then filtered using a capacitive filter. Performance of the whole conversion system was studied using resistive loads connected across the filter. The aim was to investigate the operational characteristics of the generator while supplying a nonlinear load. By changing the value of the resistive component of the load, the speed of the translator can be changed and so also the damping of the generator. The power absorbed by the generator was studied at different sea states as well. The observations presented in this paper could be beneficial for the design of efficient wave energy conversion systems.
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| 31. |
- Boström, Cecilia, et al.
(författare)
-
Temperature measurements in a linear generator and marine substation for wave power
- 2010
-
Ingår i: PROCEEDINGS OF THE ASME 29TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING 2010, VOL 3. - 9780791849118 ; , s. 545-552
-
Konferensbidrag (refereegranskat)abstract
- This paper analyzes temperature measurements acquired in offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common DC-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. First results of temperature measurements on substation components and on the stator of one of the linear generators are presented from operation in linear and in non-linear damping. Results indicate that there might be some convective heat transport in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel to avoid heating from neighbouring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding PVC cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the WEC could be enhanced. Another suggested alteration would be to lower the resistive losses by reducing the linear generator current density.
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| 32. |
- Boström, Cecilia, et al.
(författare)
-
Temperature measurements in a linear generator and marine substation for wave power
- 2012
-
Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : ASME International. - 0892-7219 .- 1528-896X. ; 134:2, s. 021901-
-
Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes temperature measurements acquired in the offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common dc-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. The first results of temperature measurements on substation components and on the stator of one of the linear generators are presented based on operation in linear and in nonlinear damping. The results indicate that there might be some convective heat transfer in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel in order to avoid heating from neighboring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding polyvinyl chloride cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the wave energy converter could be enhanced. Another suggested alteration is to lower the resistive losses by reducing the linear generator current density.
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| 33. |
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| 34. |
- Boström Cars, Maria, 1980-, et al.
(författare)
-
Mind the Gap! : Maritime education for gender-equal career advancement
- 2015. - 1
-
Ingår i: Maritime Women. - Berlin Heidelberg : Springer. - 9783662453841 ; , s. 143-154
-
Bokkapitel (refereegranskat)abstract
- Seafaring as an occupation, and the maritime community as a whole, is still a male-dominated industry. In order to encourage more women to engage in a career at sea, a number of campaigns have been launched by various stakeholders. Since gender gaps in education generally are larger in the developing world, while steadily closing in the developed countries, it is both understandable and appropriate that efforts largely have been directed towards enabling women in developing countries to engage in professional education and training, may it be maritime or other. However, is opening the door and encouraging women to participate in maritime training sufficient to keep and encourage women to embark on a maritime career?In this paper, we set out to examine how gender equality is addressed in the curricula of maritime education. A document analysis was performed, examining official study plans and curricula from eight maritime universities in Finland, Norway, Sweden and the Philippines; all nations ranked in the top five in the Global gender Gap Index. The results show that gender issues are not explicitly mentioned or addressed in these documents, indicating a lack of clear strategies for these matters. Educational institutions are important bearers of societal norms and values. Without effective gender-inclusive strategies and pedagogical and didactic approaches, there is a risk of reproducing inequality, instead of producing equality. Increasing numbers of female students will not alone close the gender gap in the maritime industry. Gender issues must be well defined, operationalised and included in educational policy and curricula-making at individual, structural as well as symbolical levels.
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| 35. |
- Boström Cars, Maria, 1978-, et al.
(författare)
-
Mind the gap! Maritime education for gender-equal career advancement
- 2014
-
Ingår i: Maritime Women: Global Leadership 2nd International Conference, Malmö, March 31 - April 1, 2014. - Malmö.
-
Konferensbidrag (refereegranskat)abstract
- Seafaring as an occupation and the maritime community as a whole is still a male-dominated industry. In order to encourage more women to engage in a career at sea, a number of campaigns have been launched by various stakeholders. Since gender gaps in education generally are larger in the developing world while steadily closing in the developed countries, it is both understandable and appropriate that efforts largely have been directed towards enabling women in developing countries to engage in professional education and training, may it be maritime or other. However, is opening the door and encouraging women to participate in maritime training sufficient to keep and encourage women to embark on a maritime career?In this paper, we set out to examine how gender equality is addressed in the curricula of maritime education. A document analysis was performed, examining official study plans and curricula from in all eight maritime universities in Finland, Norway, Sweden and the Philippines, all ranked in the top five in the Global gender Gap Index. The results show that gender issues are not explicitly mentioned or addressed in these documents, indicating a lack of clear strategies for these matters. Educational institutions are important bearers of societal norms and values. Without effective gender inclusive strategies and pedagogical and didactic approaches, there is a risk of reproducing inequality instead of producing equality. Increasing numbers of female students will not alone close the gender gap in the maritime industry. Gender issues must be well defined, operationalized and included in educational policy and curricula making at individual, structural as well as symbolical level.
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| 36. |
- Boström, Jannika, et al.
(författare)
-
Autumn migratory fuelling : a response to simulated magnetic displacement in juvenile wheatears, Oenathe oenathe
- 2010
-
Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 64:11, s. 1725-1732
-
Tidskriftsartikel (refereegranskat)abstract
- Recent experiments exposing migratory birds to altered magnetic fields simulating geographical displacements have shown that the geomagnetic field acts as an external cue affecting migratory fuelling behaviour. This is the first study investigating fuel deposition in relation to geomagnetic cues in long-distance migrants using the western passage of the Mediterranean region. Juvenile wheatears (Oenanthe oenanthe) were exposed to a magnetically simulated autumn migration from southern Sweden to West Africa. Birds displaced parallel to the west of their natural migration route, simulating an unnatural flight over the Atlantic Ocean, increased their fuel deposition compared to birds experiencing a simulated migration along the natural route. These birds, on the other hand, showed relatively low fuel loads in agreement with earlier data on wheatears trapped during stopover. The experimental displacement to the west, corresponding to novel sites in the Atlantic Ocean, led to a simulated longer distance to the wintering area, probably explaining the observed larger fuel loads. Our data verify previous results suggesting that migratory birds use geomagnetic cues for fuelling decisions and, for the first time, show that birds, on their first migration, can use geomagnetic cues to compensate for a displacement outside their normal migratory route, by adjusting fuel deposition.
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| 37. |
- Boström, Jannika, et al.
(författare)
-
Northern magnetic displacements trigger endogenous fuelling responses in a naive bird migrant
- 2012
-
Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 66:5, s. 819-821
-
Tidskriftsartikel (refereegranskat)abstract
- In a previous study, we found that juvenile northern wheatears (Oenanthe oenanthe) exposed to a magnetic displacement to the west of their natural migration route increased their body mass. The total intensity and inclination used for the western displacement may also have been interpreted as northern compared to the experimental site (stronger total field intensity and steeper inclination angle). In order to investigate whether the fuelling response was a response to an unexpected magnetic field or specific to the northern magnetic field, we conducted a new experiment. Juvenile wheatears from the same study population were magnetically displaced to southwestern magnetic fields, exposing the birds to unexpected magnetic combinations, but eliminating the possible effect of a northern magnetic field. A control group was kept in the local geomagnetic field in Sweden for comparison. There was no difference in body mass increase between treatments, suggesting that the fuelling response previously found was not a simple response to an unexpected magnetic field, but rather a specific response to the northern magnetic field. Juvenile wheatears may have developed a fuelling response to northern magnetic fields in order to enable a successful flight towards the migration goal.
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| 38. |
- Boström, Martina, et al.
(författare)
-
A role for endothelial cells in radiation-induced inflammation
- 2018
-
Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 94:3, s. 259-271
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: To unravel the role of the vasculature in radiation-induced brain tissue damage.Materials and methods: Postnatal day 14 mice received a single dose of 10Gy cranial irradiation and were sacrificed 6h, 24h or 7 days post-irradiation. Endothelial cells were isolated from the hippocampus and cerebellum using fluorescence-activated cell sorting, followed by cell cycle analysis and gene expression profiling.Results: Flow cytometric analysis revealed that irradiation increased the percentage of endothelial cells, relative to the whole cell population in both the hippocampus and the cerebellum. This change in cell distribution indicates that other cell types are more susceptible to irradiation-induced cell death, compared to endothelial cells. This was supported by data showing that genes involved in endothelial cell-specific apoptosis (e.g. Smpd1) were not induced at any time point investigated but that genes involved in cell-cycle arrest (e.g. Cdkn1a) were upregulated at all investigated time points, indicating endothelial cell repair. Inflammation-related genes, on the other hand, were strongly induced, such as Ccl2, Ccl11 and Il6.Conclusions: We conclude that endothelial cells are relatively resistant to ionizing radiation but that they play an active, hitherto unknown, role in the inflammatory response after irradiation. In the current study, this was shown in both the hippocampus, where neurogenesis and extensive cell death after irradiation occurs, and in the cerebellum, where neurogenesis no longer occurs at this developmental age.
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| 39. |
- Boström, Magnus, 1981-, et al.
(författare)
-
Creating Clarity and Crew Courage : Preventive and Promotive Measures for a Maritime Industry Without Bullying and Harassment
- 2022
-
Ingår i: Occupational Health Science. - : Springer Nature. - 2367-0134 .- 2367-0142. ; 6:4, s. 605-629
-
Tidskriftsartikel (refereegranskat)abstract
- Seafaring shares many characteristics with contemporary working life ashore. However, a major difference is that seafarers can spend up to 12 months aboard a ship that constitutes a work, living and recreational environment. Onboard work includes many stressors that can potentially contribute to workplace bullying and harassment, which in turn can affect safety critical operations. The aim of this study was to identify underlying causes in the organizational and social work environment that can cause workplace bullying and harassment at sea, and to suggest appropriate preventive and promotive strategies and measures. Data were collected mainly through World Cafe workshops with 56 participants from the Swedish maritime industry. Seafarer occupational health, safety, and wellbeing is largely determined by interdependent factors at micro, meso, and macro levels, where different stakeholders play various roles. Strategies and measures starting at the individual seafarer, and gradually expanding outwards toward the maritime industry are suggested. It is important that a victim of bullying or harassment receives adequate support. Creating crew courage enables employees to both recognize troubling situations and know how to act and respond to a situation. To bridge the gap between policy and practice, the legislative framework needs translating into practical procedures to make sense to the middle manager at the sharp end, with limited knowledge, time, resources, and decision latitude. Future research should evaluate the effectiveness of work environment interventions - what works, for whom, and under which circumstances.
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| 40. |
- Boström, Magnus, 1981-
(författare)
-
Creating clarity and managing complexity through co-operation and communication : The case of Swedish icebreaker operations
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sea transportation is vital for the global economy, and the amount of seaborne trade is expected to increase in the future. In some areas, icebreakers are necessary for maintaining open shipping lanes all-year round and ensuring safe navigation. Vessels operating in ice are exposed to harsh environmental factors such as severe weather and heavy ice, and when external forces become too strong vessels will depend on icebreaker assistance. However, successful icebreaker operations require the icebreaker to operate in close vicinity to the assisted vessel to break the ice, which in turn increases the risk of collision.There are many factors which make icebreaker operations complex. The aim of this thesis is to use work organization, operational safety, and interpersonal communication as three lenses to describe and analyse the complexity of icebreaker operations, and its implications for practice. To thoroughly investigate this complexity, data are drawn from numerous sources; semi-structured interviews, a questionnaire, and a substantial amount of recorded authentic communication all provide complementary insights.The results show that the icebreaker performs a multitude of tasks directly concerned with icebreaking, e.g. directing and physically assisting other vessels, but that these tasks indirectly rely on interpersonal interaction and communication. A number of conflicting constraints add to the complexity. For example, harsh winter conditions impede vessels’ independent navigation in ice, while offering icebreaker crews opportunities to practice and maintain important skills. Furthermore, it was shown that language skills and communication play an important role in upholding the operational safety. However, closed-loop communication is not always used as intended, a deviation from intended communication protocol with potential to increase the risk of misunderstandings.This thesis suggests that safety and efficiency of winter navigation can be enhanced by making better use of existing technology and data; by examining the past track of other vessels, e.g. via AIS, finding suitable ice tracks will be made easier. Another implication concerning communication is that training institutes should emphasize the logic behind standardized communication protocols rather than focusing on standard phrases, i.e. facilitating means for advanced English speakers to adapt their communication style. That way, novice and advanced speakers could find common ground.
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| 41. |
- Boström, Magnus, et al.
(författare)
-
Improving operational safety during icebreaker operations
- 2017
-
Ingår i: WMU Journal of Maritime Affairs (JoMA). - : Springer. - 1651-436X .- 1654-1642. ; 16:1, s. 73-88
-
Tidskriftsartikel (refereegranskat)abstract
- The study presented in this paper aims at investigating what safety measures that can be taken to improve the operational safety during icebreaker operations in the Baltic Sea. During icebreaker operations, the icebreaker and the assisted vessel operate in close proximity to each other, a distance which can be even smaller if weather and ice conditions are severe. This poses a severe threat to the operation, since the extremely short distance between the vessels leaves no room for error. The results, which are based on data collected through individual interviews and questionnaires, indicate several possible improvements. Firstly, on a regulatory level, the introduction of an ice navigation certificate for deck officers would set a minimal level of formal competency. Secondly, on a knowledge level, more ice navigation training and better language skills work in favour for the safety. Thirdly, on a technical level, having an electronic chart with target tracking capability increases the efficiency and safety of the passage through ice. In addition to these results, this study shows a need to further research the communication and language situation during icebreaker operations.
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| 42. |
- Bull, Cecilia, 1977, et al.
(författare)
-
A novel mouse model of radiation-induced cancer survivorship diseases of the gut
- 2017
-
Ingår i: American journal of physiology. Gastrointestinal and liver physiology. - : American Physiological Society. - 1522-1547 .- 0193-1857. ; 313:5, s. G456-G466
-
Tidskriftsartikel (refereegranskat)abstract
- A deeper understanding of the radiation-induced pathophysiological processes that develop in the gut is imperative to prevent, alleviate, or eliminate cancer survivorship diseases after radiotherapy to the pelvic area. Most rodent models of high-dose gastrointestinal radiation injury are limited by high mortality. We therefore established a model that allows for the delivering of radiation in fractions at high doses while maintaining long-term survival. Adult male C57/BL6 mice were exposed to small-field irradiation, restricted to 1.5 cm of the colorectum using a linear accelerator. Each mouse received 6 or 8 Gy, two times daily in 12-h intervals in two, three, or four fractions. Acute cell death was examined at 4.5 h postirradiation and histological changes at 6 wk postirradiation. Another group was given four fractions of 8 Gy and followed over time for development of visible symptoms. Irradiation caused immediate cell death, mainly limited to the colorectum. At 6 wk postirradiation, several crypts displayed signs of radiation-induced degeneration. The degenerating crypts were seen alongside crypts that appeared perfectly healthy. Crypt survival was reduced after the fourth fraction regardless of dose, whereas the number of macrophages increased. Angiogenesis was induced, likely as a compensatory mechanism for hypoxia. Four months postirradiation, mice began to show radiation-induced symptoms, and histological examination revealed an extensive crypt loss and fibrosis. Our model is uniquely suitable for studying the long-term trajectory and underlying mechanisms of radiation-induced gastrointestinal injury. NEW & NOTEWORTHY A novel mouse model for studying the long-term trajectory of radiation-induced gut injury. The method allows for the use of high doses and multiple fractions, with minor impact on animal health for at least 3 mo. Crypt loss and a slow progression of fibrosis is observed. Crypt degeneration is a process restricted to isolated crypts. Crypt degeneration is presented as a convenient proxy endpoint for long-term radiation-induced gut injury.
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| 43. |
- Danyang, Cui, et al.
(författare)
-
Design of Spoke Type Traction Motor with Ferrite Material for EV Application
- 2022
-
Ingår i: 2022 International Conference on Electrical Machines (ICEM). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 315-320
-
Konferensbidrag (refereegranskat)abstract
- Motor design for electric vehicle application using non-rare-earth permanent magnetic materials has become a research hotspot due to cost reduction and environmental issues. Among different motor topologies, permanent magnet synchronous motor (PMSM) with spoke-type ferrite magnets has great potential because of its competitive performance. In this paper, a novel design of a spoke-type synchronous motor using ferrite Y40 and non-magnetic steel material is presented, with optimizations on the overall structure and considerations on the effects of pole numbers. The performance of the designed motor verified with magnetic simulations shows that it has a high probability to be a candidate for replacing the conventional PMSM with rare-earth materials in Electric Vehicles (EV) application. © 2022 IEEE.
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| 44. |
- Döhler, Jéssica S., et al.
(författare)
-
An application of four-wire grid-forming power inverter in unbalanced distribution network
- 2023
-
Ingår i: IET Generation, Transmission & Distribution. - : Institution of Engineering and Technology. - 1751-8687 .- 1751-8695. ; 17:2, s. 324-336
-
Tidskriftsartikel (refereegranskat)abstract
- The modelling of a three-phase four-leg four-wire grid-forming inverter in a low voltage distribution system 18-bus European Cigre under unbalanced conditions in an autonomous distribution network is presented. The case study has two types of inverters control strategy: (i) grid-forming to supply all the system demand in the interval of the intentional supply interruption and (ii) grid-following to integrate photovoltaic renewable energy resources into power systems. The model suggests a control scheme with two loops: An inner current loop with a proportional-integral controller and an outer voltage loop with a proportional controller, both in the synchronous reference frame (dq0), in which dq-axis are decomposed in positive and negative sequences. Simulation results, carried out using the PSCAD software, showed the effectiveness of the suggested control strategy with smooth synchronization where the grid-forming inverter was able to form a network with an unbalanced degree lower than 2%, sinusoidal voltage and frequency within standard limits 49.5-50.5 Hz.
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| 45. |
- Ekergård, Boel, et al.
(författare)
-
Experimental results from a linear wave power generator connected to a resonance circuit
- 2012
-
Ingår i: Wiley Interdisciplinary Reviews. - : Wiley. - 2041-8396 .- 2041-840X. ; 2:4, s. 456-464
-
Tidskriftsartikel (refereegranskat)abstract
- The output voltage from a direct-driven permanent magnet linear generator installed in a wave power plant varies both in amplitude and frequency. Electrical conversion is therefore necessary before grid connection can be achieved. The aim of this paper is to present an electrical conversion system based on the electric resonance phenomena. As one of the first steps in the development, and to gain further knowledge and understanding of the proposed resonance circuit, experimental tests with a single-phase permanent magnet linear generator connected to a resonance circuit were performed. The experimental results presented in this paper indicated that a successful resonance between the generator and external circuit was achieved. The research regarding the wave energy converters lies within The Lysekil Wave Power Project at Uppsala University and has been ongoing since 2002.
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| 46. |
|
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| 47. |
- Ekström, Rickard, et al.
(författare)
-
Evaluating Constant DC-Link Operation of Wave Energy Converter
- 2012
-
Ingår i: Proceedings of the 31st ASME International Conference on Ocean, Offshore and Arctic Engineering, vol. 7. - 9780791844946 ; , s. 269-276
-
Konferensbidrag (refereegranskat)abstract
- A Wave Energy Converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common DC-bus. The DC voltage level seen by the generator is directly linked to the electromagnetic damping of the generator A lower DC-level results in a higher damping factor and is important for increased absorption of the wave power The drawback is increased losses in generator windings and cable resistance. There will be an optimal DC-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the DC-level seen by the generator influence the power output. The results indicate that higher DC-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which DC-level is chosen.
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| 48. |
- Ekström, Rickard, et al.
(författare)
-
Evaluating Constant DC-Link Operation of Wave Energy Converter
- 2014
-
Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 136:1, s. 014501-
-
Tidskriftsartikel (refereegranskat)abstract
- A wave energy converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common dc-bus. The dc voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower dc-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal dc-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the dc-level seen by the generator influence the power output. The results indicate that higher dc-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which dc-level is chosen.
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| 49. |
- Francisco, Francisco, 1985-, et al.
(författare)
-
Wave Power as Solution for Off-Grid Water Desalination Systems : Resource Characterization for Kilifi-Kenya
- 2018
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 11:4
-
Tidskriftsartikel (refereegranskat)abstract
- Freshwater scarcity is one of humanity's reoccurring problems that hamper socio-economic development in many regions across the globe. In coastal areas, seawater can be desalinated through reverse osmosis (RO) and transformed into freshwater for human use. Desalination requires large amounts of energy, mostly in the form of a reliable electricity supply, which in many cases is supplied by diesel generators. The objective of this work is to analyze the wave power resource availability in Kilifi-Kenya and evaluate the possible use of wave power converter (WEC) to power desalination plants. A particular focus is given use of WECs developed by Uppsala University (UU-WEC). The results here presented were achieved using reanalysis-wave data revealed that the local wave climate has an approximate annual mean of 7 kW/m and mode of 5 kW/m. Significant wave height and wave mean period are within 0.8-2 m and 7-8 s respectively, with a predominant wave mean direction from southeast. The seasonal cycle appeared to be the most relevant for energy conversion, having the highest difference of 6 kW/m, in which April is the lowest (3.8 kW/m) and August is the peak (10.5 kW/m). In such mild wave climates, the UU-WEC and similar devices can be suitable for ocean energy harvesting for water desalination systems. Technically, with a capacity factor of 30% and energy consumption of 3 kWh/m(3), a coastal community of about five thousand inhabitants can be provided of freshwater by only ten WECs with installed capacity of 20 kW.
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| 50. |
- Frisendahl, Nathalie, et al.
(författare)
-
Predictive Performance of the FIF Screening Tool in 2 Cohorts of Community-Living Older Adults
- 2020
-
Ingår i: Journal of the American Medical Directors Association. - : Elsevier. - 1525-8610 .- 1538-9375. ; 21:12, s. 1900-1905
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: The First-time Injurious Fall (FIF) screening tool was created to identify fall risk in communityliving older adults who may benefit from primary preventive interventions. The aim of this study was to evaluate the predictive performance of the FIF tool in 2 cohorts of older adults. Design: Longitudinal cohort study. Setting and Participants: The Swedish National Study on Aging and Care in Skane (SNAC-S) and Blekinge (SNAC-B), Sweden. Community-living people aged >= 60 years (n = 2766). Methods: Nurses and physicians collected data in the 2 cohorts through interviews and testing. Data on injurious falls were collected from register data and were defined as receipt of care after a fall. The FIF tool, consisting of 3 questions and 1 balance test, was examined in relation to injurious falls for up to 5 years of follow-up using Cox proportional hazards models. The predictive performance of the FIF tool was further explored using Harrell C statistic and Youden cut-off for sensitivity and specificity. Results: The hazard ratios (HRs) of an injurious fall in the high-risk group for women and men were 3.80 (95% confidence interval [CI] 2.53, 5.73) and 5.10 (95% CI 2.57, 10.12) in SNAC-S and 4.45 (95% CI 1.86, 10.61) and 32.58 (95% CI 4.30, 247.05) in SNAC-B compared with those in the low risk group. The sensitivity and specificity of the Youden cut-off point (3 or higher for high-risk) were 0.64 and 0.69 for women and 0.68 and 0.69 for men in SNAC-S, and 0.64 and 0.74 for women and 0.94 and 0.68 for men in SNAC-B. The predictive values (Harrell C statistic) for the scores for women and men were 0.73 and 0.74 in SNAC-S and 0.72 and 0.89 in SNAC-B. Conclusions and Implications: Our results suggest that the FIF tool is a valid tool to use for prediction of first-time injurious falls in community-living older adults. (C) 2020 AMDA - The Society for Post-Acute and Long-Term Care Medicine.
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