1,720,959 research outputs found
Determination of added mass for earthquake induced hydrodynamic loadings on vertical structures
No full textEarthquakes can induce severe hydrodynamic loadings on dams and their equipment. The dynamic dam-reservoir interaction is usually modelled by the so-called added mass. There are two theoretical approaches in the literature, employing either momentum or compressibility theory. Both assume zero pressures at the top of the structure, leading to comparatively low design pressures for control structures. A new theory was developed for a simple approximation for added mass and hydrodynamic pressures. The added mass is assumed to be uniform over the dam height. The added mass becomes a linear function of acceleration and water depth. Comparison with 'classic' theories showed good agreement for accelerations up to 0.3g, and higher pressures for higher accelerations
Hydropower converters with head differences below 2·5 m
Get PDFHydropower with very low head (VLH) differences constitutes a largely unused potential source of renewable energy. A literature review of hydropower converters for VLH differences covering the engineering literature from the 1830s onwards was conducted to assess the potential of historic, current and emerging technologies. The results showed that a large number of different interesting technologies were used/developed, and that several novel and promising concepts are currently under development. Technologies emerged for different market segments: water wheels for low flow rates, turbines for large flow volumes. To take account of increased ecological demands and the desire for cost reduction, further improvements of existing technologies and new converter technologies have been developed. Other concepts described in the literature were apparently never applied although they promise development potential. The information gathered allowed for a comparison of available technologies with respect to area of application, performance, ecological impact and cost level
Design of steel lined penstock of hydroelectric power plant
Get PDFDie Diplomarbeit "Variantenuntersuchung der Druckrohrleitung eines Speicherkraftwerkes an einem Stausee" untersucht das Konzept, die Varianten und die Konstruktion der Anlagen eienes geplannten Speicherkraftwerkes. Die vorgegebene Plannungsunterlage umfaßt gleichzeitig viele Lösungskonzepte. Die entsprechenden Anlagen über die ganze Trasse der Druckrohrleitung sind einen vertikalen Druckschacht, eine gepanzerte unterirdische Hochdruckstrecke und eine eingeerdete Druckrohrleitung. Die drei Anlagen wurden hydraulisch und statisch bemisst. Die hydraulische Bemessung wurde für die stationären und instationären Vorgänge durchgeführt, wobei die Untersuchung der stationären Zustände die Ermittlung der kontinuierlichen Verluste in der Druckrohrleitung infolge der Flüssigkeitsreibung (Wandreibungsverluste) und der örtlichen Widerstände wie z.B. Rohrverengungen oder - erweiterungen erfasst. Bei den instationären Strömungsvorgängen wurde die maximale Erhöhung des statischen Druckes infolge einer Druckstoßentwicklung untersucht. Die instationäre Berechnung wurde mit dem an der UACG erarbeitetes Berechnungsprogramm "HIUD" nach der Charakteristickenverfahren durchgeführt. Als Egebnis liefert das Programm die Werte von der Druckhöhe, Geschwindigkeit und dem Durchfluß in jedem Berechnungspunkt für jeden Zeitschritt. Diese Änderungen der drei Parameter für den konkreten Fall wurden tabelarisch und grafisch dargestellt.Danach wurde die statische Bemessung durchgeführt. Aufgrund der Berechnungsergebnisse wurden die notwendigen Stützkonstruktionen und Auskleidungen des vertikalen Druckschachtes und der geneigten gepanzerten Strecke bestimmt.Für den Druckstollen mit der gepanzerten Auskleidung wurde zusätzlich noch eine Beulberechnung durchgeführt. Zu diesem Ziel wurden die Berechnungsmethoden von Amstutz, Montel und Jacobsen verwendet und die entsprechenden Ergebnisse verglichen.Die statische Bemessung für die letzte eingegrabene Strecke von der Triebwasserleitung wurde nach den bulgarischen Normen und nach ÖNORM B5012 durchgeführt und einen Vergleich zwischen den Ergebnissen und den Grundlagen der beiden Standards gemacht.Im letzten Kapitel wurde eine Beschreibung der Bauverfahrenstechnik der Anlagen gemacht. Es wurden die verschiedenen Ausbruchsmethoden, die Felssicherungsarten, die notwendigen Baumaschinen und Baugeräte mit den einzelnen Arbeitsvorgänge dargestellt
Pumped-storage in Bulgaria – Developments, Current Situation and Some Perspectives
No full textAbstractThe objective approach requires that the hydropower development cannot be analyzed outside the economical and overall national development of a particular country during a considered time period. Yet the current presentation addresses exclusively the Hydropower development in Bulgaria, and moreover, concentrated only on the features of pumped-storage as a reliable and still highly competitive energy storage technology.The pumped-storage as part of the hydropower development in Bulgaria and the situation as in 1989 are introduced. The overall development in Bulgaria after November 1989 and its impact on both running and future hydropower and pumped-storage projects are shortly presented. Particular features of the current situation are outlined. Furthermore, special attention is paid to the national legislative environment in the frame of the crucial policies, strategies and directives of the European Union.Finally, some ideas and project possibilities for the use of the still available pumped-storage potential in Bulgaria are discussed in more detail. The work ends with conclusions on the Bulgarian hydropower development with respect of pumped-storage mainly after 1989. Needed research activities in particular fields are identified for a possible future pumped-storage development in Bulgaria as an EU member state in the sense of global electricity market conditions
Nichtlineare dynamische Untersuchung einer 70 Jahre alten Gewichtsstaumauer in Bulgarien
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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
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