| 43651. |
- Kitaev, Sergey, 1975, et al.
(författare)
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The problem of the pawns
- 2003
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 43652. |
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| 43653. |
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| 43654. |
- Kitagawa, Wataru, et al.
(författare)
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Efficiency Analysis of 5MW Wind Turbine System in an All-DC Wind Park
- 2017
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Ingår i: 3rd IEEE International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017; Kaohsiung; Taiwan; 3 June 2017 through 7 June 2017. - 9781509051571 ; , s. 1542-1547
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Konferensbidrag (refereegranskat)abstract
- This article presents the efficiency analysis of a 5 MW wind turbine generating system in an all-DC wind park comprising of a permanent magnet assisted synchronous reluctance generator (PMaSynRG) system as well as an IGBT equipped forced-commutated inverter. In this article, the focus is on the NPC converter and DC-DC converter with an optimized high-frequency transformer. The total efficiency through the AD-DC converter to DC-DC converter was found to be 96.72 % as safed operation.
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| 43655. |
- Kitagawa, Wataru, 1997, et al.
(författare)
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Inverter Loss Analysis and Comparison for a 5 MW Wind Turbine System
- 2017
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Ingår i: 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe). ; 2017-January
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Konferensbidrag (refereegranskat)abstract
- This article presents the losses of a 5 MW wind turbine generating system comprising of a permanent magnet assisted synchronous reluctance generator (PMaSynRG) system as well as an IGBT equipped forced-commutated inverter. In this article, the focus is on the classical 2-level converter and the NPC converter. Their inverter losses using three types of modules were calculated and compared.
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| 43656. |
- Kitamura, Yasunori, et al.
(författare)
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Calculation of higher moments of the neutron multiplication process in a time-varying medium
- 2007
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 34:5, s. 385-395
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Tidskriftsartikel (refereegranskat)abstract
- The zero-power reactor noise theory in a steady neutron multiplying medium was extended recently to a medium randomly varying in time to bridge the fields of the zero-power and the power reactor noise. For a time-varying medium in which the transition probability randomly fluctuates, only the use of the probability generating function technique based on the forward master equation approach is practical. However, with the forward master equation approach, the treatment of the joint moments of the neutron number and the medium state leads to a closure problem. Recently, the capability of the moment calculation technique for such cases was extended such that the closure problem could be solved exactly. The present paper describes and demonstrates this closure-free moment calculation technique in a time-varying binary multiplying medium, in which the medium state has two possible realizations. In addition to the first two moments of the neutron number N alone (irrespective of the medium state η), the joint moments of Nn and ηm, i.e., , were also obtained in a compact form for n = 1, 2 and arbitrary values of m, without a closure assumption. It was found that, for even m values, the asymptotic values of Nn and ηm are uncorrelated, whereas, for odd m values, they are negatively correlated, namely, their covariance is less than zero. The first two moments of the neutron number theoretically obtained were verified by the Monte Carlo technique. A perfect agreement was found between the Monte Carlo and the theoretical solutions. The closure-free moment calculation technique demonstrated in the present paper is expected to be applicable to various other problems related to the birth-and-death process with fluctuations of the transition probability, in which a closure problem occurs.
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| 43657. |
- Kitamura, Yasunori, et al.
(författare)
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Calculation of the stochastic pulsed Rossi-alpha formula and its experimental verification
- 2006
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Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 48:1, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- The Rossi-alpha formula for subcritical systems driven by a pulsed neutron source was derived with a solution technique that can effectively take different shape functions of the pulsed neutron source into account. The result of derivation showed that the present formula consists of the correlated and uncorrelated terms and an oscillating term whose period was identical to that of the pulsed neutron source.To investigate the validity of the pulsed Rossi-alpha formula and its applicability for the evaluation of the prompt neutron decay constant alpha from measurements, an experiment was performed at the Kyoto University Critical Assembly with a pulsed D-T neutron source. Although it seemed that fitting the present formula to the experimental curves was not practical because of an infinite-series expansion structure of the oscillating term, it was possible to extract only the correlated term, that explicitly includes the alpha value, by a simple data handling procedure. It was found that the measured alpha values agreed with those obtained by the pulsed neutron source method very well. This finding means that the pulsed Rossi-alpha method will be an attractive candidate for the monitoring method of the subcritical reactivity of future accelerator driven systems.
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| 43658. |
- Kitamura, Yasunori, et al.
(författare)
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Derivation of pulsed Feynman- and Rossi-alpha formulae including delayed neutrons
- 2005
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Ingår i: Annals of Nuclear Energy. ; 32:7, s. 671-692
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Tidskriftsartikel (refereegranskat)abstract
- In previous works, the authors have developed an effective solution technique for calculating the pulsed Feynman- and Rossi-alpha formulae.Through derivation of these formulae, it was shown that the technique can easily handle various pulse shapes of the pulsed neutron source.Furthermore, it was also shown that both the deterministic (i.e.{} synchronizing with the pulsing of neutron source) and stochastic (non-synchronizing) Feynman-alpha formulae can be obtained with this solution technique.However, for mathematical simplicity and the sake of insight, the formal derivation was performed in a model without delayed neutrons.In this paper, to demonstrate the robustness of the technique, the pulsed Feynman- and Rossi-alpha formulae were re-derived by taking one group of delayed neutrons into account.The results show that the advantages of this technique are retained even by inclusion of the delayed neutrons.Compact explicit formulae are derived for the Feynman- and Rossi-alpha methods for various pulse shapes and pulsing methods.
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| 43659. |
- Kitamura, Yasunori, et al.
(författare)
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Determination of prompt neutron decay constant by time-domain fluctuation analyses of detector current signals
- 2018
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 120, s. 691-706
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Tidskriftsartikel (refereegranskat)abstract
- The conventional time-domain reactor noise techniques analyse the number of neutron detector pulse signals, so that they sometimes encounter serious difficulties owing to the count-loss effect due to the dead time of detector systems. To avoid all the difficulties coming from the count-loss effect, a novel time-domain technique was recently proposed (Pál and Pázsit, 2015). This technique analyses the auto-covariance function of continuous current signals arising from ionization chambers such as the fission chamber, so that it is inherently insensitive to the count-loss effect. In the present study, a different time-domain technique that analyses the integral values of current signals is proposed. With regard to these two techniques, the experimental conditions under which they successfully measure the subcriticality through determination of the prompt neutron decay constant are clarified.
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| 43660. |
- Kitamura, Yasunori, et al.
(författare)
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Some properties of zero power neutron noise in a time-varying medium with delayed neutrons
- 2008
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 35:9, s. 1621-1627
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Tidskriftsartikel (refereegranskat)abstract
- The temporal evolution of the distribution of the number ofneutrons in a time-varying multiplying system, producing only prompt neutrons, was treated recently with the master equation technique by some of the present authors. Such a treatment gives account of both the so-called zero power reactor noise and the power reactor noise simultaneously. In particular, the first two moments of the neutron number, as well as the concept of criticality for time-varying systems, were investigated and discussed. The present paper extends these investigations to the case when delayed neutrons are also taken into account. Due to thecomplexity of the description, only the expectation of the neutron number is calculated. The concept of criticality of a time-varying system is also generalized to systems with delayed neutrons. The temporal behaviour of the expectation of the number of neutrons and its asymptotic properties are displayed and discussed.
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