| 1. |
- Eklund, Petter, 1989-, et al.
(författare)
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Experimental Evaluation of a Rare Earth-Free Permanent Magnet Generator
- 2021
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Ingår i: IEEE Transactions on Energy Conversion. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0059 .- 0885-8969. ; 36:1, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- Low speed, high torque machines are used in wind turbines where the turbine rotor is directly connected to the generator. A permanent magnet synchronous generator using high-energy rare-earth permanent magnets (PMs) is one common choice for this application, but rare-earth PMs have supply insecurities and cost risks. A rare-earth free 32-pole PM generator, using ferrite PMs in a spoke-type rotor, for use in a 12 kW experimental wind turbine is built and tested. Voltages and currents at load and no load are measured, as well as the magnetic field in the end regions of the machine. The generator can deliver the required power at nominal speed and has low harmonic content in the output. The electrical measurements are compared to two-dimensional finite element design calculations and the experimental results are lower than expected from simulations. The measured voltage is lower than expected, requiring a higher current than calculated for the rated power. Three-dimensional magnetic field simulations show that there are leakage flux paths in the end-regions that the two-dimensional design calculations overlook, explaining the discrepancy between simulations and measurements.
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| 2. |
- Ottermo, Fredric, 1975-, et al.
(författare)
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Resonances and Aerodynamic Damping of a Vertical Axis Wind Turbine
- 2012
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Ingår i: Wind Engineering. - Essex, UK : Multi-Science Publishing. - 0309-524X .- 2048-402X. ; 3:36, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of a straight-bladed vertical axis wind turbine is investigated with respect to oscillations due to the elasticity of struts and shaft connecting to the hub. In particular, for the three-bladed turbine, a concept is proposed for dimensioning the turbine to maximize the size of the resonance free rpm range for operation. The effect of aerodynamic damping on the struts is also considered. The damping of these types of oscillations for a typical turbine is found to be good.
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| 3. |
- Magnusson, Thomas, 1970-, et al.
(författare)
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Sustainability transitions in tourism : on the transformation of a fragmented sector
- 2024
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Ingår i: Tourism Geographies. - Abingdon, Oxon : Routledge. - 1461-6688 .- 1470-1340.
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Tidskriftsartikel (refereegranskat)abstract
- This conceptual paper argues that there are unrealized benefits from a cross-fertilization between research on sustainable tourism and sustainability transitions studies. With the aim to stimulate such cross-fertilization, the paper identifies three contemporary streams in sustainability transitions studies that are particularly relevant for sustainable tourism: deep transitions, transitions in practice, and the geography of transitions. These three streams present complementary perspectives, which can help reach a more nuanced understanding of transition processes in the tourism sector. The paper concludes that while research on sustainable tourism can benefit from theories, concepts, and frameworks from research on sustainability transitions, research on sustainable tourism can support further conceptual developments in sustainability transitions studies.
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| 4. |
- Ottermo, Fredric, et al.
(författare)
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An upper size of vertical axis wind turbines
- 2014
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Ingår i: Wind Energy. - Chichester : Wiley. - 1095-4244 .- 1099-1824. ; 17:10, s. 1623-1629
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Tidskriftsartikel (refereegranskat)abstract
- The scaling behaviour of a straight-bladed vertical axis wind turbine is considered. A scaling scheme is described that, in the presence of a wind shear profile, aims at leaving the material stresses of the scaled construction unchanged. On the basis of a recent 200 kW three-bladed H-rotor design, a structural upper size of the turbine is proposed, this size being the scale at which the gravitational force starts to become important. As gravity has a much worse scaling behaviour than the aerodynamic and centrifugal forces, the construction work will become increasingly more difficult above this scale. The upper size is estimated to be around 30 MW.
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| 5. |
- Ottermo, Fredric, 1975-, et al.
(författare)
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Location of aerodynamic noise sources from a 200 kW vertical-axis wind turbine
- 2017
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Ingår i: Journal of Sound and Vibration. - London : Elsevier. - 0022-460X .- 1095-8568. ; 400, s. 154-166
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Tidskriftsartikel (refereegranskat)abstract
- Noise levels emitted from a 200 kW H-rotor vertical-axis wind turbine have been measured using a microphone array at four different positions, each at a hub-height distance from the tower. The microphone array, comprising 48 microphones in a spiral pattern, allows for directional mapping of the noise sources in the range of 500 Hz to 4 kHz. The produced images indicate that most of the noise is generated in a narrow azimuth-angle range, compatible with the location where increased turbulence is known to be present in the flow, as a result of the previous passage of a blade and its support arms. It is also shown that a semi-empirical model for inflow-turbulence noise seems to produce noise levels of the correct order of magnitude, based on the amount of turbulence that could be expected from power extraction considerations.
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| 6. |
- Ul-Abdin, Zain, 1975-, et al.
(författare)
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A Radar Signal Processing Case Study for Dataflow Programming of Manycores
- 2017
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Ingår i: Journal of Signal Processing Systems. - New York : Springer Science and Business Media LLC. - 1939-8018 .- 1939-8115. ; 87:1, s. 49-62
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Tidskriftsartikel (refereegranskat)abstract
- The successful realization of next generation radar systems have high performance demands on the signal processing chain. Among these are advanced Active Electronically Scanned Array (AESA) radars in which complex calculations are to be performed on huge sets of data in real-time. Manycore architectures are designed to provide flexibility and high performance essential for such streaming applications. This paper deals with the implementation of compute-intensive parts of AESA radar signal processing chain in a high-level dataflow language; CAL. We evaluate the approach by targeting a commercial manycore architecture, Epiphany, and present our findings in terms of performance and productivity gains achieved in this case study. The comparison of the performance results with the reference sequential implementations executing on a state-of-the-art embedded processor show that we are able to achieve a speedup of 1.6x to 4.4x by using only 10 cores of Epiphany.
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| 7. |
- Alkhabbas, Fahed, et al.
(författare)
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ASSERT : A Blockchain-Based Architectural Approach for Engineering Secure Self-Adaptive IoT Systems
- 2022
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Ingår i: Sensors. - basel : MDPI. - 1424-8220. ; 22:18
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Tidskriftsartikel (refereegranskat)abstract
- Internet of Things (IoT) systems are complex systems that can manage mission-critical, costly operations or the collection, storage, and processing of sensitive data. Therefore, security represents a primary concern that should be considered when engineering IoT systems. Additionally, several challenges need to be addressed, including the following ones. IoT systems’ environments are dynamic and uncertain. For instance, IoT devices can be mobile or might run out of batteries, so they can become suddenly unavailable. To cope with such environments, IoT systems can be engineered as goal-driven and self-adaptive systems. A goal-driven IoT system is composed of a dynamic set of IoT devices and services that temporarily connect and cooperate to achieve a specific goal. Several approaches have been proposed to engineer goal-driven and self-adaptive IoT systems. However, none of the existing approaches enable goal-driven IoT systems to automatically detect security threats and autonomously adapt to mitigate them. Toward bridging these gaps, this paper proposes a distributed architectural Approach for engineering goal-driven IoT Systems that can autonomously SElf-adapt to secuRity Threats in their environments (ASSERT). ASSERT exploits techniques and adopts notions, such as agents, federated learning, feedback loops, and blockchain, for maintaining the systems’ security and enhancing the trustworthiness of the adaptations they perform. The results of the experiments that we conducted to validate the approach’s feasibility show that it performs and scales well when detecting security threats, performing autonomous security adaptations to mitigate the threats and enabling systems’ constituents to learn about security threats in their environments collaboratively. © 2022 by the authors.
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| 8. |
- Araujo, Hugo, et al.
(författare)
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Sound conformance testing for cyber-physical systems : Theory and implementation
- 2018
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Ingår i: Science of Computer Programming. - Amsterdam : ELSEVIER SCIENCE BV. - 0167-6423 .- 1872-7964. ; 162, s. 35-54
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Tidskriftsartikel (refereegranskat)abstract
- Conformance testing is a formal and structured approach to verifying system correctness. We propose a conformance testing algorithm for cyber-physical systems, based on the notion of hybrid conformance by Abbas and Fainekos. We show how the dynamics of system specification and the sampling rate play an essential role in making sound verdicts. We specify and prove error bounds that lead to sound test-suites for a given specification and a given sampling rate. We use reachability analysis to find such bounds and implement the proposed approach using the CORA toolbox in Matlab. We apply the implemented approach on a case study from the automotive domain.
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| 9. |
- Blomgren, Bo, et al.
(författare)
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A computerised, unbiased method for epithelial measurement
- 2004
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Ingår i: Micron. - Amsterdam : Elsevier. - 0968-4328 .- 1878-4291. ; 35, s. 319-329
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Tidskriftsartikel (refereegranskat)abstract
- ObjectiveTo develop and evaluate a standardised method for unbiased measurements of epithelial thickness taking the variability of the dermal papillae in consideration.MethodsA computer-assisted measurement program suitable for haematoxylin and eosin routine stained specimens has been developed.ResultsThe developed program was designed to measure four different distance parameters, taking the number, height and width of dermal papillae into account. The measurement program gave very accurate results compared with manual measurements. The measurement results can be presented as tables or star graphs, and the results can be further processed by multivariate analysis.ConclusionThe computer-assisted measurement program is considered to be a valuable and reliable tool for measurements of epithelial thickness, irrespectively of the variability of the epithelial morphology. Since length, size and number of the papillae may change with certain pathological conditions, age and also under hormonal influence, this method can be a helpful diagnostic tool.
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| 10. |
- Eriksson, Sandra, 1979-, et al.
(författare)
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Effect of magnetic properties on performance of electrical machines with ferrite magnets
- 2021
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Ingår i: Journal of Physics D. - Bristol : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 54:5
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Tidskriftsartikel (refereegranskat)abstract
- The increased focus on ferrite magnets makes it interesting to investigate their suitability in electrical machines such as generators for wind power and motors for electric cars. Efforts are currently being made to improve the magnetic properties of ferrites. A simulation method is used to investigate how different magnetic properties such as remanence, coercivity and intrinsic coercivity affect the performance of electrical machines, here quantified as output torque. It is also ensured that the magnet is not partly demagnetized during a short-circuit event. Simulations are performed through a two-dimensional finite-element-based simulation method. Not all combinations of magnetic properties will render a usable design and it is therefore investigated how high the required values are for different magnetic properties as well as how high an output torque can be achieved. It is concluded that increasing the remanence or the coercivity can be quantified as an improved energy product, whereas improvement of the intrinsic coercivity enables the magnet to have a more optimal shape and thereby have a working point where the energy product is maximized. In addition it is found that for a fixed available magnetic energy, the performance does not change significantly with increasing remanence.
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