1,720,963 research outputs found
Wind Effects on Tension Leg Platforms
No full textDocumenti del Dipartimento di Ingegneria Aerospazial
Centrifugal compressors Diffuser Rotating Stall Deep Insight
No full textIn this work the numerical analysis of a small flow coefficient stage vaneless diffuser is described. The main purpose of this analysis is to go inside the rotating stall physics with particular attention to the onset of the rotating cells and their properties. The diffuser aspect ratio (width divided radial extension) is low (0.03) and the effect of the wall (hub and shroud boundary layers) cannot be neglected. For this reason the model is a 3D model including the hub, the shroud walls and the downstream 180° cross- over bend. The numerical analysis has been carried out using an incompressible, viscous, unsteady commercial solver. Radial and tangential typical velocity profiles as produced by a hypotetical upstream impeller have been applied as boundary conditions and they have been changed in time to simulate the actual throttling valve closure as it is done during a test. Under these circumstances a rotating phenomenon is found to exist similar to what is found experimentally on similar geometries. The instability starts as a complex 3D flow involving both hub-to-shroud flow pulsations as well as radial non-uniformities and it stabilizes in the form of four rotating cells
Experimental Investigation on the Flow-Induced Loads and Wake Characteristics on Finite Length Triangular Prisms
No full textCentrifugal Compressors Diffuser Rotating Stall: Vaneless Vs. Vaned
No full textDiffuser rotating stall (in both cases of a vaneless or a vaned configuration) is still one of the open questions which has never been fully understood because of the complexity of the phenomenon and the experimental difficulties to get reliable measurements in such a complex environment. Under this perspective, Computational Fluid Dynamics (CFD) is an interesting tool to "see" the flow and to provide a basic understanding of the associated physics. Several published work have shown that a simplified model of the diffuser without the upstream impeller and the downstream return channel with, some realistic boundary conditions entering the diffuser, can provide a qualitative analysis of the stall onset. Thanks to the simplified model it has been possible to change progressively the boundary conditions in such a way that the continuous reduction of flow in time, as it is the experimental procedure, has been fully simulated. Vaneless and vaned options have been compared in terms of loss coefficient and rotating stall onset characteristics
Dynamic characterization of a centrifugal compressor rotor by a laser scanning vibrometer
No full textThe dynamic behavior of a 3D impeller (1100 mm diameter) has been modelled by means of a standard FEM code (ANSYS) and experimentally validated using a laser scanning vibrometer based measurement technique. The theoretical finite element model has been previously developed. Attempts made by using classical measuring techniques has not allowed to obtain the low frequency cyclic modes calculated. Those modes have been obtained using a laser scanning vibrometer. Sine sweep to detect frequencies and sine excitation at resonance frequencies, in order to improve the accuracy of the modal shape, have been used. The keys of success was the ability of the laser vibrometer to detect very low vibration amplitudes (of the order of nanometers) with a high spatial resolution, inside an industrial environment, in very low testing time, all fundamentals for this application. The experimental and numerical activity presented in this work has been carried out from Nuovo Pignone together with the University of Ancona with the final purpose of establishing a new fast procedure to identify, in production industrial environment, the dynamic behavior of large dimensions impellers for centrifugal compressors
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
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