1,721,054 research outputs found
Coupling of CFD and SYS TH codes in BEPU approach, Case study : two-phase PTS scenario
No full textBEPU (Best Estimate Plus Uncertainty) is a new modern approach for nuclear reactor safety and used in accident analysis. In this area, BEPU implies the application of standard and qualified procedures to survey the effect of each phenomenon on safety margin. System TH and CFD codes are the main tools in this way utilizing appropriate model for each phenomenon. However, models and simplifications employed in each code limit the application of them. As a part of BEPU, identification and selection of the best tool for investigation of a phenomena have effects on safety margin. But some TH scenarios and industrial concerns are beyond the ability of individual category of codes, and code coupling should be considered as main strategy for capturing all features of those scenarios. For different nodalization and models considered in system TH and CDF codes, correct coupling of them requires more attention about preparing suitable boundary condition for each type. TH step of Two-Phase PTS scenario is one of those events: the coupling of system TH and CFD codes is needed to predict imposed temperature profile on the downcomer. The maturity of system codes such as RELAP is sufficient to obtain plant response to the initial event. On the other hand, produce necessary input data for structural mechanical analyses may include 3D effects and local phenomena which are outside the capabilities of systems codes. Therefore, CFD codes should be employed to bridge the gaps. The results of RELAP simulation before injection point of ECCS is considered as input of CFD part. CFD codes is employed for mixing and stratification zone of cold leg needing 3D nodalization for prediction of temperature profile. In these zones, calculation of interfacial heat transfer, based on turbulence kinetic energy and dissipation rate, plays a significate role to predict temperature profile. But, traditional eddy viscosity model need special treatment near the free surface for prediction of turbulence characteristics. In this paper, a new model for turbulence based on source function of turbulence kinetic energy and eddy frequency was employed to investigate the effects of improvement CFD turbulence models on safety margin as main goal of BEPU for two-phase PTS. The result of this coupling platform is compared with whole simulation of RELAP code for demonstration of coupling effect and improvement of turbulence prediction in stratified zone
Application of new turbulence modeling in stratified flow of PTS
No full textHigh neutron flux in core of a nuclear reactor can affect the material of Reactor Pressure Vessel (RPV). The neutron radiation has a detrimental impact on the mechanical properties of the RPV material such as hardening (or embrittlement) while neutrons are absorbed by the material. A major concern in embrittled RPVs is propagation of critical flaw which may cause through-wall cracks. Some transients leading to overcooling of RPV intensify the propagation of the cracks and known as Pressurized Thermal Shock (PTS). Such situation could be created in case of Emergency Core Cooling System (ECCS) actuation which leads to injection of cold water into the cold leg of the primary loop in some accidents, e.g. Loss Of Coolant Accident (LOCA). The investigation of PTS is performed throughout three steps including Probabilistic Safety Assessment (PSA); thermal-hydraulics and structural mechanics i.e. fracture mechanics. The final goal of the thermal-hydraulics analysis step is the prediction of the imposed temperature gradient on the downcomer as a result of single-phase and two-phase phenomena. Depending on the leak size, its location and the operation condition of the plant after LOCA, water in the cold leg can be in single-phase or two-phase condition. Two-phase PTS will occur when steam and water are in the cold leg during the injection of ECCS water. The ECCS water enters the hot steam flow environment in the cold leg and two phase stratified flow propagates in the cold leg by means of density difference between water and steam. Condensation of steam and mass transfer between two phases is the only heat source in this zone and the accurate modeling of DCC plays a significant role to predict temperature profile in downcomer. The interfacial heat transfer coefficient is defined according to eddy contact time with both steam and water at interface which is a function of turbulence characteristics. The high gradient of velocity generates too high turbulence when differential eddy viscosity models are used and some modifications should be considered in turbulence models at the interface. Implementation of turbulence damping function in turbulence eddy frequency transport equation is one of this modification. Although the new source function improves velocity profile of smooth stratified flow, but significant deviations reveal when the vertical motion of the interface is considerable. Also, the value of turbulence kinetic energy decreases substantially by employment of damping function without the other modification. The reduction of turbulence kinetic energy at the interface changes the value of heat transfer coefficient. In this paper, the other source function of turbulence is proposed by consideration of different boundary condition at the interface and the effect of turbulence characteristics on condensation rate is demonstrated. The results show that implementation of damping function, without any special treatment of turbulence kinetic energy, leads to a considerable overestimation of condensation rate which would be improved with employment of proposed turbulence source function at the interface. then, the new turbulence model is used for stratified flow zone in PTS scenario in VVER-1000 RPV to find the effect of interfacial heat transfer coefficient on temperature profile in the cold leg. For this purpose, the plant response to LOCA is simulated by RELAP system code until the injection of ECCS water. The results of RELAP simulation before injection point of ECCS is considered as input of CFD part. CFX code is employed for mixing and stratification zone of cold leg needing 3D nodalization for prediction of temperature profile
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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