Investigation of the friction coefficient in smooth open channel flows [Serbest Yuzeyli Puruzsuz Kanallarda Yuk Kayip Katsayisinin Incelenmesi]

In practical engineering, the friction coefficient formulations developed for circular pipes are usually assumed to be valid for open channels and used in derivation of mathematical formulation. However, with the advent of more accurate measurement devices, it is now clear that such formulations cannot be used in open channels without modifications. The phenomena such as free surface, different wet surfaces with irregular shear stresses and secondary flows, make open channel flows more complicated than circular pipe flows. A new formulation for the friction coefficient is developed depending on the Reynolds Number (Re) and W/h, which is the ratio of channel width to its height. It is found that there is a 10 % difference in the friction coefficient in circular pipe flow and open channel flow under the same conditions. The new correlation agrees satisfactorily with those in the literature. The relation between ? and Re in circular pipe flow is found to be deviate in open channel flows. In this research a formulation similar to the Blasius equation is proposed for rectangular channels.In practical engineering, the friction coefficient formulations developed for circular pipes are usually assumed to be valid for open channels and used in derivation of mathematical formulation. However, with the advent of more accurate measurement devices, it is now clear that such formulations cannot be used in open channels without modifications. The phenomena such as free surface, different wet surfaces with irregular shear stresses and secondary flows, make open channel flows more complicated than circular pipe flows. A new formulation for the friction coefficient is developed depending on the Reynolds Number (Re) and W/h, which is the ratio of channel width to its height. It is found that there is a 10% difference in the friction coefficient in circular pipe flow and open channel flow under the same conditions. The new correlation agrees satisfactorily with those in the literature. The relation between ? and Re in circular pipe flow is found to be deviate in open channel flows. In this research a formulation similar to the Blasius equation is proposed for rectangular channels

Investigation of flow resisstance in polish rectangular open channels

Günümüzde borular için elde edilen sürtünme faktörlerinin açık kanal akımları içinde geçerli olduğu kabul edilmekte ve kurulan matematiksel denklemler bu doğrultuda olmaktadır. Ancak daha hassas deney ölçü aletlerinin gelişmesi neticesinde açık kanallar üzerinde yapılan çalışmalar, borular için elde edilen denklemlerin kanallar için kullanılamayacağım ortaya koymaktadır. Açık kanallarda; serbest yüzey gerilimi, düzensiz kayma gerilmeleri, farklı yüzeyler, sekonder akımlar gibi bir çok faktörler problemi daha kompleks duruma getirmektedir. Direnç faktörü açık kanallar için Reynolds sayısı ve W/h oranı ile belirlenmiştir. Dikdörtgen kanallar ve borular için hesaplanan sürtünme faktörleri arasındaki farkın yaklaşık %7 civarında olduğu gözlenmiştir. Diğer çalışmalarla karşılaştırıldığı zaman genelde uyum olduğu ve $\sqrt{f}-Re\sqrt{f}$ ilişkisinin boru akımlarına göre farklılaştığı gözlenmiştir. Fakat bu farklılık bir sabit olarak belirlenememiştir. Açık kanallar için ölçülen deneysel veriler, Prandtl'ın ilişkisine göre incelendiği taktirde kesin bir sonuca varılamamaktadır.The friction factors correlations obtained for pipes are generally assumed to be valid in the open channels. However, with the advent of more accurate measuring equipments, the studies on open channels are showed that the use of mathematical formulations developed for pipes in channels may lead significant errors in open channels. Some of the phenomena such as surface tension, heterogeneous shear, stresses, different surfaces, secondary flowsmakes channel flows extremely complex over the pipe flows. The friction factor in channel flow is found to be depend on Reynolds number and w/h ratio. It is found that the value of friction factor obtained for pipe flow may result up to %7 error in channel flow. The results are found to agree satisfactorily with those of literature. It is also found that $\sqrt{f}-Re\sqrt{f}$ relation in channels flow significantly deviates from that of in pipe flow. The prandtl formulation is found to fail to analyse the measures data

Estimation of slump value and Bingham parameters of fresh concrete mixture composition with artificial neural network modelling

High performance is the most important expectation from concrete which is commonly used in today's construction technology. To form a high performance concrete "HPC", two fundamental properties are required. These properties are optimization of the materials used to form the concrete and the workability of fresh concrete during shaping. Many scientists have used rheological properties in conjunction with Bingham model to determine the workability of fresh concrete. Bingham model is represented by two parameters: yield stress and plastic viscosity. Even though, many models are developed to explain rheological properties, there is no acceptable easy to use method. In this study, artificial neural network "ANN" is used to determine the rheological properties of fresh concrete. Ferraris and de Larrard's experimental slump, yield stress and viscosity data from different composed concretes is used in this study. Slump, yield stress and viscosity are estimated with respect to mixture design parameters. Obtained results from this study indicates that ANN is a utilizable method to determine the rheological proporties (Bingham model) of fresh concrete. © 2011 Academic Journals

Correlation and distribution of shear stress for turbulent flow in a smooth rectangular open channel

WOS: 000229849000009Calculation of shear stresses in open channel flow is very important in civil engineering applications such as structural design, determination of velocity distribution and sediment transport. It is argued in literature that the velocity distribution equations for pipe flow may be used in open-channel flow analysis. However, due to irregular boundary sheer stress, this claim seems to be unreasonable and the irregularities should be taken into consideration. In this study, wall shear stresses for turbulent flow in rectangular open channel are investigated. Using mean velocity measurements and assuming validity of the logarithmic velocity distribution perpendicular to wetted perimeter, dimensionless shear stresses in the unified velocity distribution are determined. A semi-theoretical method is applied for the solutions of non-linear equations. A shear stress distribution equation is proposed to calculate irregular boundary shear stresses on the wall and bed in smooth rectangular channels

A numerical approach to determine viscosity-dependent segregation in fresh concrete

WOS: 000226859900019In this study, the mechanism of segregation during the filling of fresh concrete into formwork is numerically investigated. A mathematical model, which considers fresh concrete as a non-Newtonian fluid, is developed. The aggregates are considered as Lagrangian particles whose trajectories determine segregation. Aggregate segregation is partially affected due to concrete viscosity. The study presented here will show the relationship between viscosity and segregation during fill of fresh concrete in formwork. The relationship in between aggregate segregation and viscosity during the fill of fresh concrete for both MC concrete mixture and MCS concrete mixture is investigated. MCS concrete mixture includes superplasticizers for the same composition of MC. Cylindrical formwork (30 cm by 150 cm) is employed. It is found that MC concrete mixture has an aggregate segregation level of 50%, while it reduces to a level of 20% for MCS concrete mixture. The use of superplasticizer reduces aggregate segregation. (C) 2004 Elsevier Inc. All rights reserved

Investigation of flow resistance homogenity in open channels using the manning's formula

Açık kanal akımlarında enerji kayıplarını belirlemek için deneysel ve teorik çalışmalar yapılmıştır. Çalışmada 0,21x0,50x9,00 metre boyutlarındaki pürüzsüz açık kanal modeli üzerinde Pitot tüpü kullanılarak kanalın orta kısmında ve tam türbülanslı bölgede 8 farklı kesit ile 34 farklı eğimdeki en kesitte hız ölçümleri yapılmıştır. Ölçülen lokal hızlar ile ıslak çevreye dik kesitlerde logaritmik hız dağılımının geçerliliği kabul edilmiş, düzgün hız dağılımındaki boyutsuz cidar kayma gerilmeleri hesaplanmıştır. Hesaplamada, lineer olmayan denklem sistemlerinin çözümü için yan teorik bir metot kullanılmıştır. Farklı W/h oram ve cidar kayma gerilmelerine göre Manning denkleminde kullanılmak üzere yeni bir sürtünme katsayısı önerilmiştir. Yapılan bu çalışma ile açık kanatlardaki akım direncinin boyutsal homojenliği daha iyi temsil edilebileceği gösterilmiştir.In this paper on the flow of smooth open channel experimental and theoric studies have been done for the determination of enrgy losses. In the study, in a smooth open channel model which has dimensions of 0,21x0,50x9,00 m. velocity measurement was made by using a Pitot tube in the middle of channel and in full turbulenced region at 8 diffirent sections with 34 diffirent slopes. Assuming the validity of logarithmic velocity distribution along perpendiculars to the wetter perimeter, dimentionless shear stress have been calculated by using these measuretd local velocities. In the calculations, a semi-theorical method is applied for the solutions of non-linear equations. In this process for different W/h ratio and for shear stress anew fraction factor has been suggested in the Manning formula. As a result of this study the dimensionel homogenity on the open channel flow has been represented better

Investigation of flow resistance in smooth open channels using artificial neural networks

WOS: 000261005700013An accurate prediction of the friction coefficient is very important in hydraulic engineering since it directly affects the design of water structures, the calculation of velocity distribution, and an accurate determination of energy losses. However, conventional approaches that are profoundly based on empirical methods lack in providing high accuracy for the prediction of the friction coefficient. Consequently, new and accurate techniques are still highly demanded. This study introduces an efficient approach to estimate the friction coefficient via an artificial neural network, which is a promising computational tool in civil engineering. The estimated value of the friction coefficient is used in Manning Equation to predict the open channel flows in order to carry out a comparison between the proposed neural networks based approach and the conventional ones. Results show that the proposed approach is in good agreement with the experimental results when compared to the conventional ones. (C) 2008 Elsevier Ltd. All rights reserved

Treatment of multi-dimensional data to enhance neural network estimators in regression problems

WOS: 000242979100033This paper proposes and explains a data treatment technique to improve the accuracy of a neural network estimator in regression problems, where multi-dimensional input data set is highly skewed and non-normally distributed. The proposed treatment modifies the distribution characteristics of the data set. The prediction of the suspended sediment, which is an important problem in river engineering applications, will be considered as a case study. Conventional approaches lack in providing high accuracy due to the inherently employed simplicity in order to obtain empirical formulae. On the other hand, artificial neural networks are able to model the non-linear characteristics of the mechanism of the sediment transport and have a growing body of applications in diverse applications in civil engineering. It will be shown that a significant enhancement and superior score in accuracy, compared with the classical approaches, are obtainable when the proposed treatment is employed. The proposed technique is an extension to the understanding of the practical aspects of neural computing applications. Therefore the outcome of the present study is important as it is applicable to any scenario where neural network approaches are involved. (C) 2006 Elsevier Ltd. All rights reserved