Evaluation of Linear and Nonlinear Concepts of Hydraulic Resistance in Alluvial Channels
Camacho, Rodolfo
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https://hdl.handle.net/2142/69980
Description
Title
Evaluation of Linear and Nonlinear Concepts of Hydraulic Resistance in Alluvial Channels
Author(s)
Camacho, Rodolfo
Issue Date
1988
Doctoral Committee Chair(s)
Yen, Ben C.
Department of Study
Civil Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Abstract
In view of the state-of-the-art of research on hydraulic resistance in alluvial channels, a new set of equations has been proposed for the determination of the hydraulic resistance coefficient for alluvial channels with steady, reachwise uniform flow in equilibrium sediment transport. An analytical study based on dimensional analysis and fluid mechanics concepts has been conducted to determine the functional relationships of these equations. The functional relationships of these equations have been analyzed through stepwise regression analysis of a sediment data bank consisting of more than 7,000 records compiled in the last 80 years throughout the world. Nondimensional parameters have been defined and computed in a consistent manner.
The analysis is conducted following two different traditional concepts for the determination of the Weisbach resistance coefficient $f$, namely, linear superposition and nonlinear approaches. In the nonlinear approach, the Weisbach resistance coefficient $f$ is expressed directly as a nonlinear function of the following nondimensional parameters F, R, $d\sb{50}/R$ and $T\sp\*$. However, if nonequilibrium sediment transport condition is present, the sediment concentration $C\sb{s}$ may appear as an independent variable. In the linear superposition approach, $f$ is expressed as a function of the same nondimensional parameters and is linearly separated into two parts, i.e., the part due to surface grain roughness resistance $f\sp\prime$, and the additional part attributed to form drag and wave resistance $f\sp{\prime\prime}$. Various techniques have been proposed by previous investigators to calculate $f\sp\prime$. After a careful examination of these techniques in this study, the resistance coefficient due to surface grain roughness is computed by either a plane sediment bed equation or by the Churchill-Barr equation which is essentially a simpler alternative form of the Colebrook-White equation. The results of the linear superposition approach are significant compared to previous work such as Kennedy's. However, it has been found that the nonlinear approach offers a number of advantages over the linear superposition approach.
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