1,721,098 research outputs found
Performance evaluation of MHD generators: the lumped parameter model and its validation
No full textThe authors present a stationary model of MagnetoHydroDynamic (MHD) linear and disk generators. The active region of the device has been modelled by a 3D lumped parameter network which takes into account both the electrical characteristics of ionized gas and the external load apparatus. The 3D equivalent electrical network of the generator has been realized by subdividing the plasma into many elementary volumes, each of which is modelled by composite branches placed along the axes of a suitable Cartesian or cylindrical inertial coordinate system. These branches simulate all local characteristics and physical phenomena which influence the plasma behaviour around the centre of gravity of each brick. Then, in order to complete the stationary model of the device, the equivalent electrical network of the external load apparatus is attached to the previously defined network. The proposed model has been validated comparing the results of the simulation both with experimental data coming from measurements on various test facilities and with numerical values obtained by other researchers using sophisticated analytical models. The main advantage in using this model comes both from its 3D nature, which allows an accurate simulation of the device, and from the circuit approach, which allows to attainment important information on generator behaviour with small computational resources
Application of 3D lumped parameter model in MHD generator design
No full textMagnetohydrodynamic (MHD) energy conversion consists of electrical energy generation directly from high enthalpy of ionized gas. MHD generators are devices having a channel in which ionized gas (plasma) is blown, where a high magnetic field is present. The interaction between the conductive gas and the magnetic field makes the conversion. To describe and to design the MHD plants, circuital models of MHD generators are advantageous for an easier investigation approach to the interface between generators and power plants; they become extremely useful when a 3-D analysis is necessary for easier computation taking into account 3-D effects due to spatial distribution of electromagnetic fields. In this paper we describe some design applications of the three-dimensional (3-D) lumped parameter model for MHD generators
Displacement eddy current computation in magnetic laminates
No full textThe paper presents an equivalent circuit model of small magnetic laminated objects. The responses in the frequency domain of these laminates are significantly influenced by eddy currents which can exist even if the thickness of the magnetic films is smaller than the skin depth. These currents can circulate within the laminates because of the capacitive coupling across the dielectric layers separating the magnetic films. Using this model the effective permeability of the thin multilayer films has been computed also taking into account the displacement eddy currents. The results presented are in agreement with numerical and experimental tests available in literature. The authors have developed this model using the circuit theory because this approach has the major advantage of being simple to understand and easy to implement with a calculation code
MHD linear generator modelling
No full textThe performance of typical magnetohydrodynamic (MHD) linear generators are evaluated as function of the excitation magnetic field profile. Using a three dimensional (3D) lumped parameter model, able to simulate all major physical MHD energy conversion phenomena, a parametric analysis has been pointed out for various saddle shaped superconducting (sc) coils. For each type of MHD linear generator (Faraday, Hall and diagonal connected generator) the output electrical power has been correlated to the magnetic field characteristics and it has been compared with an ideal flat magnetic field profile in order to quantify the decay of the energy conversion efficiency
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Power distribution network configuration applying the corridor method
No full textIn this paper, an optimization scheme based on the Corridor Method (CM) matheuristic is proposed for power distribution network configuration with the objective of client balancing between feeders. The problem is formulated as a mixed integer optimization problem (MIP) referring to a variant of the constrained spanning forest problem on a network. The problem is classified as NP-complete in its decision version, and the proposed matheuristic optimization approach is aimed to find high quality solutions in a short computational time on large real instances. According to the characteristics of the power distribution networks, suitable modeling solutions are adopted to retain a radial structure, satisfy power flow and voltage constraints, and reduce the reconfiguration efforts requiring a limited number of maneuvers on the electrical network. Computational experiments on different instances related to a real network have been conducted. The results demonstrated the soundness and the effectiveness of the proposed solution with respect to a baseline represented by a MIP formulation solved by a state-of-the-art commercial solver: the scalability towards large-size cases has been also considered. These results show that the proposed configuration method can effectively and efficiently solve the considered problem giving adequate support to the decision-makers
Optimization of a variable width inductor for Transverse Flux Heating of Non-Magnetic strips
No full textThe paper deals with an optimal design of a variable width
inductor for Transverse Flux Heating (TFH). A genetic algorithm
coupled with an “ad hoc” numerical code, able to predict the
temperature distribution along the transversal and longitudinal section
of the heating strip, will be used. The results will be compared both with
a numerical code based on FEM and with experimental tests
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