1,720,956 research outputs found
Development and simulation of a 3D printed liquid oxygen/liquid natural gas aerospike
Full text linkOne of the most difficult aspects to solve, in the development of an aerospike engine, is the cooling of the throat and base regions. This issue is addressed nowadays by relying on new capabilities offered by additive manufacturing techniques together with novel powder materials, that allow to design complex shapes while keeping the prototyping cost low. The following work shows the design and manufacturing process of DemoP1, an aerospike engine demonstrator developed by Pangea Aerospace, that applies the new capabilities offered by additive manufacturing. To validate the development, the engine has been tested at the P8.2 test stand of the Germany Space Agency (Deutsches Zentrum für Luft-und Raumfahrt, DLR) in Lampoldshausen. Finally, a numerical strategy has been implemented and validated to simulate the engine flowfield, therefore obtaining relevant information that would be impractical to measure during tests, such as the pressure distribution along the plug and in the plume and the estimation of the heat flux on the throat and spike walls to be used to guide and validate the design process
Validation of a numerical strategy to simulate the expansion around a plug nozzle
No full textRocket engines currently use traditional bell-shaped nozzles that have a fixed area ratio and can only operate at maximum efficiency at a given altitude. Plug nozzles have been proposed as an alternative solution to achieve higher performance over a larger altitude range. Unlike bell nozzles, the flow is free to expand along the plug, as it is no longer surrounded by solid boundaries. Therefore, plug nozzles can adapt to different altitudes by expanding the flow to ambient pressure, resulting in continuous altitude adaptation. Due to the high surface area that needs to be cooled, one of the main challenges of plug nozzle design is thermal management. However, the introduction of aerospike geometry, which is essentially a truncated plug nozzle, has helped mitigate this issue. Simulating an aerospike engine is challenging due to the interaction between the plume and the external flow, which is necessary to accurately predict thrust. In this work, a numerical strategy for predicting the performance of an aerospike engine, during a static fire, was developed and validated
Particle migration modeling in solid propellants
No full textThis work presents the development of an OpenFOAM solver to predict the migration of solid particles in concentrated suspensions under non-uniform shear flow. The solver modifies the pimpleFoam solver by implementing the conservation equation for particle volume fraction. It adapts the equation of motion for non-Newtonian flows and establishes a model for the viscous field using Krieger's correlation. The code is successfully validated by the experimental results from literature
Effects of inclusions on the performance of a solid rocket motor
Full text linkSome of the most common defects that can be generated during the production of solid propellant are voids and porosity, usually associated with the casting process, and cracks and debonding, typically initiated by the high stresses caused by the curing process. This paper presents the development of an algorithm capable of evaluating the burning surface regression of a solid rocket booster when inclusions are present within the grain. The effects produced by the cavities are evaluated both in terms of performance (i.e., comparison with the behavior of the nominal combustion surface), and in terms of safety (i.e., evaluation of the thermal protection increased exposure). The paper also documents the influence of uncertainties in the knowledge of the real dimension and position of the inclusions detected within the motor. The radiography inspection of the motor is able to detect the presence of cavities within a certain level of accuracy, and the worst combination of these uncertainties has to be determined in order to guarantee, even under such circumstances, the safe and successful firing of the motor. The methodology developed in the paper is adapted in order to identify the worst uncertainty combination, and to subsequently determine the corresponding performance deviation
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
- …
