1,720,968 research outputs found
A modeling approach to study the fluid dynamic forces acting on the spool of a flow control valve
No full textThis paper introduces an approach to study a valve’s internal fluid dynamics. During operation, the flow causes forces on the spool. These forces must be correctly balanced. Since these forces cannot be measured, a three-dimensional (3D) computational fluid dynamic (CFD) modeling approach is needed. A case study has been undertaken to verify the approach on a two-way pressure compensated flow control valve. Since forces vary during operation, the analysis must be transient. From the initial zero spool position, the flow goes through the valve causing a spool shift inside the valve’s housing until the spool stops at its final position. Forces depend on the spring reaction, the inlet pressure force, the pressure force of the fluid inside the spool, and the spring holder volumes, and the balance of forces influences the outlet flow rate at the final spool position. First, the initial case geometry was modeled, prototyped, and tested, and this geometry was studied to verify the model accuracy compared to experimental data. The comparison shows good agreement with a maximum error of 3%. With the same approach, several other geometries were designed, but only the best geometry was prototyped and tested. The model was adopted to make several analyses of velocity contouring, streamlines trends, and pressure distribution in the fluid volume. The modeled and tested results achieved the expected performance confirming the effectiveness of the methodology
A Mathematical Model to Analyze the Torque Caused by Fluid-Solid Interaction on a Hydraulic Valve
No full textIn this paper, a three-dimensional (3D) computational fluid dynamics (CFD) methodology to improve the performance of hydraulic components will be shown, highlighting the importance that a study in the fluid mechanics field has for their optimization. As known, the valve internal geometry influences proportional spool valve hydraulic performance, axial flow forces, and spin effects on the spool. Axial flow forces and spin effects interact directly with the position control performance of a direct actuating closed-loop control valve, reducing its capability. The goal of this activity is the study of the torque on the spool induced by the flow and using a CFD 3D methodology to identify causes of this phenomenon and to find a general mathematical solution to minimize the spool spin effect. The baseline configuration and the new ones of the proportional four-way threeposition closed-loop control spool valve have been studied with a mathematical model. The models were also validated by the experimental data performed in the Hydraulic Lab of the University of Naples. In particular, the tests allowed to measure the torque on the spool varying the oil flow rate, using a dedicated test bench layout where the spool was directly connected to a torque meter. Several geometries have been analyzed to find the best one to minimize spool spin behavior while maintaining an acceptable pressure drop. The study results confirmed the significant improvement of overall component performance
Hydrostatic Transmission for Wind Power Generation RS-0008-09
No full textThe University of Minnesota is performing research on the application of continuously variable hydrostatic transmissions for wind turbines. By replacing the gearbox of traditional wind turbines with a continuously variable hydrostatic transmission (HST), the rotor speed could be controlled independent of the generator speed. This would allow the use of more conventional synchronous generators instead of higher cost variable speed permanent magnet generators, and eliminate the need for power electronics. The gearbox of traditional wind turbines is one of the primary sources of premature failure and maintenance. HSTs have been the dominant choice for propulsion in agricultural, construction, forestry, and mining vehicles for more than half a century. Thus, replacing the gearbox in a wind turbine with an HST should improve the reliability of the machine. The IREE seed funding will be used by the University of Minnesota to begin the process of building a lab scale (50 kW) test stand to perform research on applying HSTs to wind turbines. The research will initially focus on determining the best drivetrain hardware configuration as well as on optimizing the wind turbine’s control algorithm.Thul, Brenen; Dutta, Rahul; Stelson, Kim; Bohlmann, Brad; Gust, Mike; Kildegaard, Arne. (2010). Hydrostatic Transmission for Wind Power Generation RS-0008-09. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/101789
A Three-Dimensional CFD Methodology to Study Vane-Ring and Vane-Under-Vane Interactions of a Vane Pump Power Split Transmission
No full textThis paper presents a study of a novel vane pump power split transmission (VPPST). The transmission incorporates a new component, the Vane Power Split Unit (VPSU). The VPSU is a double-acting vane pump with a floating ring where the input shaft is connected to the engine and the floating ring is connected to the output shaft. The VPSU generates hydraulic oil flow at a rate proportional to the difference in angular velocities between the input and output shafts. This flow enters a hydraulic motor mounted to the output shaft. The vane pump power split transmission (VPPST) is a combination of the double-acting vane pump (VPSU) and the hydraulic motor directly connected to the pump. A CFD model of the VPSU has been created to better understand its performance. The model uses the threedimensional CFD commercial code PumpLinx®, developed by Simerics® Inc. Thanks to collaboration with the code developers, the model is able to predict the complex fluid dynamics in the pockets in the rotor into which the vanes retract. These pockets are referred to as under-vane volumes. The rotor of the vane pump, in fact, has several internal channels that connect the pumping chambers between the vanes to the under-vane volumes. The combination of the vanes and the internal ducts and volumes of the under-vanes have been modelled as dynamic “valves” that rotate with the rotor. In this way the radial movements of the vanes are computed as a part of the simulation, based on the pressures due to the compression of the volumes on the inner diameter side of the vanes.
The study is a result of collaboration between the University of Minnesota and the University of Naples “Federico II” research groups and the code developers of Simerics® Inc. The universities and Simerics® Inc. have all been involved in this project, working in close cooperation for the model building and simulations
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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