1,720,956 research outputs found
Numerical Simulation of the Motion of A Floating Body with Partially Filled Tanks by A Pressure-Convection Particle Method
No full textNumerical Study on Sheet Cavitation Flow of Two Dimension Hydrofoil
No full text空化(Cavitation)現象在流體中是普遍存在的現象，在造船產業的應用上尤其有很多明顯的例子，如螺槳和噴射推進器等。空化現象除了會造成流體機械效率的衰減，同時並產生震動、噪音和侵蝕問題。對於高速船舶，空化現象一直是重要的研究主題。然而高速推進器如噴射推進器、超空化螺槳、穿水式螺槳等也皆面臨來自空化現象的挑戰，因此有必要對空化現象進行完整的研究。由於分析空化現象的複雜度與困難度高，大部分的研究多以實驗方式進行。目前因為計算流體力學技術的快速發展，對於空化現象的紊流模式計算似乎變得較為可行。為了模擬片狀空化流場，本篇研究擬以自行建立完成之二維黏性流計算方法出發，導入以流體體積法為觀念之二相流的數值模型，利用等效流體模型，考慮流場中每一個控制體積內的兩種流體的分佈，使計算方法得以考慮流場中兩種不同的流體，再利用壓力、速度和密度之間的偶合關係使流場之計算可趨於穩定，其中經由疊代方式進行計算，直到片狀空化流場的形狀穩定為止。本文是應用二相流法來模擬二維水翼之片狀空化流場，進而預測空化區大小、形狀以及空化水翼的升力和阻力係數衰減。Marine applications involving attached bubbles on propellers and underwater vehicles are obvious examples of cavitation phenomena. For naval architecture issues, cavitation is always a very important topic related to high-speed ships. However, high-speed propulsors, including water jet system, super-cavitating propeller and surface-piercing propeller, are facing critical challenge from cavitation problems. For this reason, it is necessary to make a thorough study of cavitation phenomena. Due to the complexities and difficulties of theoretical analysis of cavitation, most of the researches are based on experimental approaches. With the fast development of computational fluid dynamics techniques, computations of turbulent flow for cavitation problems seem to become popular. In order to simulate sheet cavitation flows, the present method started from a two-dimensional flow code capable of computing turbulent hydrofoil flows. In order to take cavitation region into account, a two-phase flow scheme was further implemented. The proposed approach treats gas and liquid phases as an effective fluid with density varied in space. The flow field was computed in both phases with vapor pressure recovered inside the cavitation cavity via a pressure-velocity-density coupling scheme. The computation is iteratively conducted, until the shape of the sheet cavitation become stable. This thesis is to simulate steady sheet cavitation flows of a two-dimensional hydrofoil using a two-phase approach. The size and shape of sheet cavitation, and the lift and drag coefficient of a cavitating hydrofoil are predicted.誌謝……………………………………………….…. 一
摘要……………………………………………….…. 二
Abstract……………………………………………… 三
目錄……………………………….………………... 四
圖例目錄……………………………………………. 七
表格目錄…………………………………………..... 九
符號說明………………………………..…………... 十
第一章 緒論
1-1 研究目的及方向…………………………………. 1
1-2 空化介紹…………………………………………. 3
1-3 本文架構…………………………………………. 4
第二章 理論基礎
2-1 統御方程式………………………………………. 6
2-1-1 Reynolds–Averaged Navier-Stokes 方程式. 6
2-1-2 連續方程式及體積比率方程式…. 6
2-2 型…………………………………………………. 7
2-3 紊流模型……………………………….………… 8
2-4 邊界條件……………………………….………… 9
2-4-1 入口條件…………………………. 9
2-4-2 出口條件…………………………. 10
2-4-3 壁面函數…………………………. 10
第三章 數值方法
3-1 有限體積法……………………………………… 11
3-1-1 交錯放置…………………………. 11
3-1-2 非交錯放置………………………. 12
3-1-3 有限體積法………………………. 13
3-2 壓力修正方程式…………………………………. 16
3-3 數值網格產生及流場邊界條件…………………. 17
3-4 流場求解流程及參數設定………………………. 20
3-4-1 流場求解流場……………………. 20
3-4-2 計算流程…………………………. 21
3-4-3 參數設定…………………………. 21
第四章 計算結果與討論
4-1 網格密度的比較…………………………………. 22
4-2 不同參和係
Numerical Simulation of Free Surface Flow by Applying Particle Method
No full textWith fast development of the computer science, substantive efforts have been made in the computational fluid dynamics (CFD). Particularly a strong interest is focused on a new numerical method, namely, the meshless method. Since there is no mesh to distort, the meshless method can cope with large deformation in a Lagrangian framework. As a meshless method, the MPS (Moving Particle Semi-implicit) method has proven robust in a wide variety of naval architecture and ocean engineering including free surface flows. The MPS method is capable of dealing with problems in free surface, moving interface and wave propagation. Despite its applicability in many fields, the MPS method suffers unphysical numerical fluctuation of pressure with high frequencies. It leads the MPS method can not obtain accurate impact pressures. By implementing a new kernel function and the source term of Poisson pressure equation, a modified MPS method is proposed to suppress the pressure oscillation and obtained precise results in impact pressure prediction. The improved performance of the modified MPS method is validated by simulating the wave impact problems, such as the dam break problem, the droplet and wedge impact problem. Based on the previous research, some naval applications including bow flare impact and a floating body rolling in waves are introduced. The analyses show special advantage in simulating free surface flows
Simulation of a Ship with Partially Filled Tanks Rolling in Waves by Applying Moving Particle Semi-Implicit Method
No full text
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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