| 1. |
- Kontos, Sofia, et al.
(author)
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An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines
- 2020
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In: Energies. - : MDPI. - 1996-1073. ; 13:21
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Journal article (peer-reviewed)abstract
- In this paper, hard magnetic materials for future use in electrical machines are discussed. Commercialized permanent magnets used today are presented and new magnets are reviewed shortly. Specifically, the magnetic MnAl compound is investigated as a potential material for future generator designs. Experimental results of synthesized MnAl, carbon-doped MnAl and calculated values for MnAl are compared regarding their energy products. The results show that the experimental energy products are far from the theoretically calculated values with ideal conditions due to microstructure-related reasons. The performance of MnAl in a future permanent magnet (PM) generator is investigated with COMSOL, assuming ideal conditions. Simplifications, such as using an ideal hysteresis loop based on measured and calculated saturation magnetization values were done for the COMSOL simulation. The results are compared to those for a ferrite magnet and an NdFeB magnet. For an ideal MnAl hysteresis loop, it would be possible to replace ferrite with MnAl, with a reduced weight compared to ferrite. In conclusion, future work for simulations with assumptions and results closer to reality is suggested.
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| 2. |
- Leijon, Jennifer, et al.
(author)
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Freshwater and Lithium from Desalination Powered by Marine Energy Sources
- 2020
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In: International Journal of Offshore and Polar Engineering. - : International Society of Offshore and Polar Engineers. - 1053-5381. ; 30:3, s. 283-285
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Journal article (peer-reviewed)abstract
- To our knowledge, this paper represents an initial study of a novel concept in freshwater and lithium extraction from desalination powered off-grid by marine renewable energy sources. The project's background is interest in the local supply of lithium for the growing numbers of electric vehicles. The desalination technologies investigated are reverse osmosis and electrodialysis. The collocation of the marine resources, possibly available and future technical solutions, and demands for freshwater and lithium suggest that the proposed system could be interesting to study further.
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| 3. |
- Leijon, Jennifer, 1990-, et al.
(author)
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Variable renewable energy sources for powering reverse osmosis desalination, with a case study of wave powered desalination for Kilifi, Kenya
- 2020
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In: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 494:114669
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Journal article (peer-reviewed)abstract
- An analysis of reverse osmosis powered by ocean wave power is provided. A commercially available desalination system is connected via a DC/AC converter to a variable DC source and the input voltage is altered to emulate the response of a renewable energy system. Specifically, wave data from Kilifi in Kenya during 2015 is used. The wave resource variations provide variations in estimated power output from a wave energy converter, as well as in estimated freshwater production from a wave powered desalination system. Up to three wave energy converters for desalination are investigated for Kilifi. Also, a hybrid system including solar and wave power is proposed. The experiments show that reverse osmosis desalination systems can function at power levels below the rated values, but with lower freshwater flowrates. It is concluded that wave power, or wave power combined with PV systems, may be considered as power sources for desalination, with or without battery storage.
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| 4. |
- Ekergård, Boel, 1985-, et al.
(author)
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Longitudinal end effects in a linear wave power generator
- 2020
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In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:2
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Journal article (peer-reviewed)abstract
- Even though the magnetic circuit of a linear electric machine is very similar to a rotating electric machine, they diverge in one fundamental property. The linear generator is open in both ends, i.e., the magnetic circuit is non-symmetric. This paper investigates and discusses the drawbacks of this non-symmetric design in a linear permanent magnet generator, installed in a wave energy conversion system. A two-dimensional geometry has been utilized for the numerical calculations in a finite element method simulation tool. The results present an increased cogging force and significant core losses in the translator as consequences of the longitudinal ends in the machine.
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| 5. |
- Leijon, Ingemar, 1942-, et al.
(author)
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God prognos för unga vuxna med mycket låg födelsevikt [Follow-up study of very low birthweight children in Sweden at the age of 27-28]
- 2020
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In: Läkartidningen. - Stockholm, Sweden : Sveriges Läkarförbund. - 0023-7205 .- 1652-7518. ; 117
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Journal article (peer-reviewed)abstract
- Studies show that very low birthweight can be an important risk factor for mental problems, disturbed fertility and neuroendocrine dysregulation. In a regional long-term study 56 of 86 adult individuals 27 to 28 years of age with a very low birthweight were compared with normal birthweight controls. Analyses of self-reported mental health, socio-demographic factors, sex hormone levels, and hair cortisol levels showed no significant differences between the groups. However, in order to analyse subgroups with different risk factors from the newborn period or children with a variety of social background factors, larger patient groups are needed.
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| 6. |
- Leijon, Ingemar, 1942-, et al.
(author)
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Self-reported mental health and cortisol activity at 27-28 years of age in individuals born with very low birthweight
- 2020
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In: Acta Paediatrica. - : Wiley-Blackwell Publishing Inc.. - 0803-5253 .- 1651-2227. ; 109:5, s. 948-958
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Journal article (peer-reviewed)abstract
- AimTo assess mental health outcomes of very low birthweight (VLBW, <1500 g) subjects to adulthood and to examine salivary cortisol and hair cortisol levels and their relation to birth characteristics and mental health.MethodsA Swedish regional cohort of 56 VLBW subjects and 55 full‐term controls were assessed at the ages 27‐28 with adult self‐reported scales and the mean of 2 days diurnal salivary cortisol and hair cortisol. The cohorts had been assessed at 15 years of age with youth self‐reported scales.ResultsThere were no differences between the groups in youth self‐reported scales and adult self‐reported scores. The 24 participating VLBW girls scored lower on youth self‐reported scales externalising and total problem scores than the control girls. In adulthood, the 21 participating VLBW women had significantly higher morning concentrations of salivary cortisol than control women, P = .014. No significant associations were found between cortisol concentrations and adult self‐reported scales internalising, externalising and total scores.ConclusionSelf‐reported mental health in VLBW subjects was comparable with normal birthweight controls indicating a satisfying transition from adolescence to adulthood. VLBW females had higher morning salivary cortisol concentrations, suggesting a gender difference. We found no correlations between cortisol and mental health.
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| 7. |
- Sjölund, Jonathan, et al.
(author)
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End Effects and Geometric Compensation in a Linear Permanent Magnet Synchronous Generator with Buried Topology
- 2020
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In: 2020 International Conference on Electrical Machines (ICEM). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728199450 ; , s. 455-461
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Conference paper (peer-reviewed)abstract
- Electricity production from ocean waves with different design topologies is a topic of big research interest. Many of such topologies are based on submerged linear generators which inherently introduce end forces. In this paper, the detent force is investigated for two different winding patterns using Maxwell stress tensor in a finite element software. Induced voltage is also investigated for active stator area and the unequal contributions due to stator ends. Two ways of overcoming the end forces are further investigated: The first method reduces the magnetic flux difference when the translator is surrounded by stator and air, respectively. The second aims at countering the end forces at both ends for full active stator area. The first investigated end effect compensation decreased the end effects but increased the attraction forces. The second end effect compensation decreased the end forces during full active stator area with little effect on the attraction forces.
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| 8. |
- Sjölund, Jonathan, et al.
(author)
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Method for optimizing the magnetic circuit of a linear generator using FEM simulations
- 2020
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In: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 10:3
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Journal article (peer-reviewed)abstract
- Within the area of permanent magnet electrical machines, there is an ongoing focus on replacing the rare earth permanent magnets with alternatives. An option is hard ferrites, commonly used in other applications. The relatively low coercive field strength of the ferrite magnets makes irreversible demagnetization an area that should not be neglected. In this paper, a methodology is proposed for the optimization of a slow-moving linear generator simulated in a finite element environment. The no-load phase voltage is maximized while accounting for iron saturation and permanent magnet irreversible demagnetization. This demagnetization is considered when the translator is alongside either the stator or air. The inclination angle between magnetization and magnetic field strength is accounted for by adjusting the intrinsic coercivity for each element of the permanent magnets. Characteristics for the magnet grades Y30 and Y40 are used in the optimization process. The velocity of the translator is set to resemble a speed common to wave power applications. Commercial finite element software is used together with two optimization algorithms: the genetic algorithm and the particle swarm optimization. The results of these optimization algorithms reach similar optimal solutions for the considered objective function, assuring a result close to a global maximum. The results also show a great difference in the optimal geometry for the two magnet grades and highlight the need to account for irreversible demagnetization when designing generators with ferrite magnets.
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