| 1. |
- Larsson, Bengt, et al.
(författare)
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Molecular oxygen in the rho Ophiuchi cloud
- 2007
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 466:3, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org
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| 2. |
- Lidenholm, Johan, et al.
(författare)
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Effects of including automatic excitation control in transient field simulations of hydrogenerators
- 2009
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Ingår i: Proceedings of the 44th International Universities Power Engineering Conference. - University of Strathclyde Glasgow.
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Konferensbidrag (refereegranskat)abstract
- This paper addresses effects of automatic excitation control in time-stepped finite element analysis of hydroelectric generators. A simple method to incorporate exciter and automatic voltage regulator models in a finite element software is presented and tested on a small hydropower generator connected to a three-phase power system equivalent. Three simulations are performed to demonstrate the impact of the controller and to compare the field voltage and the field current as two possible excitation source variables. It is shown that inclusion of the excitation system greatly enhances the damping of rotor-angle oscillations and that the field voltage should be chosen as source variable to include the transient field winding inductance in the field problem.
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| 3. |
- Lundin, Urban, 1972-, et al.
(författare)
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Method for modeling time-dependent nonuniform rotor/stator configurations in electrical machines
- 2009
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Ingår i: IEEE transactions on magnetics. - USA : IEEE. - 0018-9464 .- 1941-0069. ; 45:7, s. 2976-2980
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Tidskriftsartikel (refereegranskat)abstract
- Nonuniform air gaps in electrical machines cause problems with forces and noise. There are a number of analytical and numerical methods to calculate the response due to nonuniform air gaps. In this paper, we present an efficient method based on an effective air gap permeability. Our unified method enables all nonuniform rotor-stator configurations to be simulated. We provide some results from simulations of static and dynamic eccentricity as well as irregularity.
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| 4. |
- Ranlöf, Martin, et al.
(författare)
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Core Loss Prediction in Large Hydropower Generators : Influence of Rotational Fields
- 2009
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Ingår i: IEEE transactions on magnetics. - USA : IEEE. - 0018-9464 .- 1941-0069. ; 45:8, s. 3200-3206
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we discuss the accuracy of several core loss models as compared to experimental data obtained from measurements on commercial hydropower generators. Our aim in this paper is twofold. First, we emphasize the problem of total core loss prediction by comparing the core loss figures obtained by different loss prediction schemes with measured no-load losses. Second, we examine the predicted net effect of bidirectional flux, i.e., the rotational loss. We show that the average degree of rotation in the stator core, and hence the rotational loss, is closely related to the stator slot geometry.
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| 5. |
- Ranlöf, Martin, et al.
(författare)
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Finite Element Analysis of a Permanent Magnet Machine with Two Contra-rotating Rotors
- 2009
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Ingår i: Electric power components and systems. - : Taylor & Francis. - 1532-5008 .- 1532-5016. ; 37:12, s. 1334-1347
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Tidskriftsartikel (refereegranskat)abstract
- Electrical machines with contra-rotating rotors find applications in direct-drive energy conversion systems and in ship propulsion systems that employ hydraulic machinery with two contra-rotating stages. In this article, the operating characteristics of permanent magnet machines with two contra-rotating rotors moving on opposite sides of a common stator core are studied via two-dimensional finite element analysis. Particular attention is devoted to the special flux distortion patterns that arise in contra-rotating machine topologies. The study suggests that the introduction of a screening iron core between the rotors provides for negligible flux distortion levels during contra-rotating synchronous operation of the two rotors.
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