1,721,009 research outputs found
Numerical assessment of simplified formulas for electrostatic simulation and design of Micro-Electro-Mechanical Systems (MEMS)
No full textThe design procedures of micro-electro-mechanical systems (MEMS) can be strongly dependent on the accurate evaluation of global quantities related to the electrostatic fields. In particular, the capacitance and the electrostatic force play often an important role in the design of micro-machines. In order to accelerate the design process, it is customary to adopt simplified formulas which have been proposed for simple geometries. Nevertheless, in many cases it is necessary to improve the accuracy of computations. This paper intends to provide some new investigations on the numerical evaluations of electrostatic quantities by means of the Finite Element Method (FEM), presenting some numerical results on realistic examples and comparing them to experimental outcomes
Experimental characterization of vaneless diffuser rotating stall. Part V: Influence of diffuser geometry on stall inception and performance (3 rd impeller tested)
No full textVaneless diffuser rotating stall is a serious problem for centrifugal compressors, since it limits their working range. In the literature some good correlations can be found for predicting stall inception but they have limited coverage of last stage configuration case, especially for very low blade-outlet-width-to-impeller-radius-ratio impellers typically used in high-pressure applications. In addition, stall inception is strictly bounded to diffuser geometry (for example, diffuser width and diffusion ratio). As a part of a wide range activity on rotating stall, a stage with a blade-outlet-width- to-impeller-radius-ratio of 0.1 has been tested. The stage configuration is made up by a 1:1 geometrical scale stage with a return channel upstream, a 2D impeller with a vaneless diffuser and a volute with a constant cross sectional area downstream. Diffusers with three different widths and two diffusion ratios were tested in order to find their influence on stage stability and performance. Results obtained for impellers with lower blade-outlet-width-to-impeller- radius-ratios have been published in previous papers. The purpose of this paper is to comment the obtained results and increase the amount of experimental data available on vaneless diffuser rotating stall behaviour
A coupled experimental/numerical analysis for low solidity vaned diffusers performance optimization
No full textThe impact of low solidity vaned diffusers (LSVDs) on rotating stall and performance was investigated in an industrial centrifugal stage initially designed with a vaneless diffuser. The activity was based on the coupled use of advanced measurement techniques and 3D fully-viscous computations. Experimental data at the impeller inlet was used as boundary conditions in 3D computations, in order to reproduce actual test working conditions. In previous studies the effectiveness of LSVDs for stall control was shown. In this work attention was focused on the effects of LSVDs on the performance curve. Three diffusers were designed and tested in order to achieve a stage performance curve close to the vaneless one or even better. The parameters changed are incidence at design point and blade deflection (blade exit angle compared with free vortex stream line at design point). The main results of this activity are presented and discussed
On the Numerical Evaluation of Capacitance and Electrostatic Forces in MEMS
No full textThis paper deals with the problem of accurate evaluation of global quantities related to the electrostatic fields in micro-electromechanical systems (MEMS). In particular, the capacitance and the electrostatic force play often an important role in the design of micro-machines. In spite of the fact that some simplified formulas have been proposed so far, in many cases it is necessary to improve the accuracy of computations. This paper intends to provide some new investigations on the numerical evaluations of electrostatic quantities by the Finite Element Method (FEM), presenting some numerical results on realistic examples and comparing them to experimental outcomes
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
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