1,720,965 research outputs found
The Investigation Of Aerodynamic Drags For Truck And Truck Trailer Combinations
No full textBu çalışmada, rüzgâr tüneli içine yerleştirilmiş 1/32 ölçekli çekici ve römorktan oluşan bir ağır vasıta aracın modeli üzerinde 6 farklı hızda yüzey basıncı ve kuvvet ölçümü gerçekleştirilmiştir. Çekicinin rüzgar tüneli testleri 59 000 - 317 000 Reynolds sayılarında yapılmıştır. Çekici römork kombinasyonunun rüzgâr tüneli testleri ise 156 000 - 844 000 Reynolds sayılarında yapılmıştır. Çekici ve römork üzerindeki basınç katsayısı (CP) dağılımı ve aerodinamik direnç katsayıları (CD) deneysel olarak tespit edilmiştir. Yapılan deneysel çalışmalarda kinematik benzerlik sağlanmış ve blokaj etkileri ihmal edilmiştir. Deneysel çalışmalarda dinamik benzerlik şartında Reynolds sayısı bağımsızlığı kullanılmıştır. Çekiciye römork ilavesinin aerodinamik direnç katsayısına etkisi belirlenmiştir. Yüzey basıncı ve kuvvet ölçümleri aynı deney şartlarında Fluent® programında sayısal olarak yapılmış ve çekici römork etrafındaki akış görüntülemeleri elde edilmiştir. Çekici ve çekici römork kombinasyonun aerodinamik direnç katsayıları (CD) sayısal olarak hesaplanmıştır. Deneysel çalışma sonuçları sayısal çalışma sonuçları ile karşılaştırılarak sayısal çalışma sonuçları doğrulanmıştır. Basınç katsayısı dağılımları ve akış görüntülemeleri sonucunda çekici römork üzerinde aerodinamik direnç oluşturan bölgeler tespit edilmiş ve pasif akış kontrolü yöntemleri ile aerodinamik iyileşme elde edilmiştir. Model 1 aracında spoiler yapısı iyileştirilerek % 11,37, model 2 aracında spoiler ile birlikte römork arka uzantısı eklenerek % 12,88, model 3 aracında spoiler ve römork arka uzantısı ile birlikte yan rüzgâr kırıcı eklenerek % 20,11 oranında aerodinamik iyileşme elde edilmiştir. Model 4 aracında ise model 2 aracının çekici römork arası körükle kapatılarak toplam % 23,85 oranında aerodinamik iyileşme elde edilmiştir.In this study, at 6 different speed surface pressure and force measurement were measured on a heavy vehicle model consisted of truck and in 1/32 scale trailer placed wind tunnel. The wind tunnel tests were made for trailer on 59 000 - 317 000 Reynolds numbers. The wind tunnel tests of truck trailer combination were made on 156 000 - 844 000 Reynolds numbers. The pressure coefficient (CP) distribution and aerodynamic drag coefficient (CD) on truck and trailer were experimentally determined. In experimental studies, kinematic similarity was provided and blocking effects were neglected. In the dynamic similarity condition, the independence of Reynolds number was used in the experimental studies. The effect of the addition of trailer to the truck on aerodynamic drag coefficient was determined. The surface pressure and force measurements were performed as numerically in the same experimental conditions at Fluent® software, and the flow visualization around of the truck and the trailer was obtained. The aerodynamic drag coefficients of the combination of the truck and the truck trailer were numerically calculated. Numerical study results were verified as experimental study results were being compared with experimental study results. The pressure coefficient distributions and the regions forming aerodynamic resistance on the truck trailer at the end of the flow visualization were determined and aerodynamic improvement was obtained with passive flow control methods. As the structure of spoilers was being improved on model 1 truck trailer, % 11,37 aerodynamic improvements, adding trailer rear extension with spoiler on model 2 truck trailer, % 12,88 aerodynamic improvements and trailer spoiler with trailer rear extension by adding side wind breaker on model 3 truck trailer, % 20,11 aerodynamic improvements were obtained. As between truck and trailer of model 2 was being closed with articulated, totally % 23,85 improvements were obtained on model 4 truck trailer
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
Enhancement performance and exhaust emissions of rapeseed methyl ester by using n-hexadecane and n-hexane fuel additives
Full text linkA lot of studies were conducted in recent years to improve of biodiesel performance. It has been stated that the addition of additives in biodiesel reduces emissions of unburned hydrocarbon (HC), carbon monoxide (CO) and particulate matter (PM). It makes a significant improvement in thermal efficiency (BTE) and heat dissipation rate (HRR). The additives are attractive in automotive applications due to their excellent phase stability and clean combustion ability. Engine performance and exhaust emissions are mainly based on air-fuel ratio, cetane number, oxygen content of fuel, fuel atomization and the other features. In this study, two different additives were added to the biodiesel to change the number of cetane. In addition, engine performance and emission changes were investigated experimentally. The viscosity and density of fuels were reduced by additives. Compared to R0 fuel, torque increased by 9.74% and 7.22% in RHD20 and RHX20 fuels respectively. While specific fuel consumption decreased by 9.58% and 6.50% respectively. The ignition delay and combustion times decreased due to combustion quality. Maximum cylinder pressure and heat release rate values increased after additives adding in fuels. With the increase of the additive rate, HC (RHD20 23.68%, RHX20 21.05%), CO (RHD20 16.89%, RHX20 15.81%), and soot (RHD20 34.35%, RHX20 26.19%) emissions reduced while NOx (RHD20 2.26%, RHX20 3.21%) emissions increased. (C) 2020 Elsevier Ltd. All rights reserved
The improving of affecting aerodynamic drag force to a vehicle with rear deck spoiler
Full text linkBu çalışmada, 1/15 ölçekli bir minibüs modeline etki eden sürükleme kuvveti spoiler uygulaması ile iyileştirilmiştir. Model minibüse ait çizim datası Solid Works® Programında oluşturulmuş ve bir bagaj üstü spoileri geliştirilmiştir. Spoiler minibüs bagajı üstüne 10 mm (L/H=0.065) ve 15 mm (L/H=0.1) mesafelerinde konumlandırılmıştır. Bu spoiler kullanımı ile minibüsün arka bölümünde oluşan negatif basınç alanının azaltılması amaçlanmıştır. Geliştirilen spoiler ile kara taşıtlarının toplam aerodinamik direnç katsayılarının büyük bir kısmını oluşturan negatif basınç kaynaklı sürükleme kuvveti azaltılmıştır. Minibüs modeline etki eden sürükleme kuvvetleri Fluent© programında 5 değişik serbest akış hızı ve Reynolds sayısında belirlenmiştir. Aerodinamik direnç katsayısı sırası ile ortalama (CD) % 4.96 ve %5.27 azaltılmıştır. Model minibüs etrafındaki akış yapısı ve taşıt gövdesi üzerindeki basınç dağılımına ait akış görüntülemeleri yapılmıştır.In this study, the drag force which affecting on a 1/15 scaled minibus model was improved by rear deck spoiler. The drawing data of the model minibus was created in the Solid Works® Program and a rear deck spoiler was designed. The spoiler was mounted on rear deck in 10 mm (L/H=0.065) and 15 mm (L/H=0.1) distances. It was aimed to decrease of negative pressure area where the back of the minibus by using of this spoiler. The negative pressure-based drag force which forms a large part of the total aerodynamic drag coefficients of land vehicles was decreased with this method. The drag forces which effect on the minibus model was determined in 5 different free flow velocities and Reynolds numbers in Fluent© program. Aerodynamic drag coefficient (CD) was decreased average 4.96% and 5.27% respectively. The flow visualizations of flow structure around model minibus and pressure distribution on vehicle body were carried out
The effects of the use of different catalyst in the cotton seed methyl esters production on the engine emissions performance
Full text linkIn this study the effect of mixture of cottonseed oil methyl ester-diesel, which is one of renewable energy resource, on exhaust emission and the effect of utilizing different catalyst in production of biodiesel on exhaust emission are investigated experimentally. Utilizing KOH as catalyst has increased HC emissions 54,58% and CO emissions 18,10% in spite of decreasing CO2 emissions 15,45%, NOx emissions 28,45% on average comparing to NaOH. 93% of CO2 emissions of pollutants in the atmosphere, 57% of HC, 39% of NOx and 1% of SO2 is vehicle sourced. Most important polluter are particulate matter emissions (PM) and NOx for diesel engines. It has been observed that use of cotton seed methyl ester as engine fuel is decreased to NO emission in our study
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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