It is based on logarithmic law in the form that captures the unknown flow friction factor λ in a way that it cannot be extracted analytically.
The 80 year-old empirical Colebrook function ξ, widely used as an informal standard for hydraulic resistance, relates implicitly the unknown flow friction factor λ, with the known Reynolds number Re and the known relative roughness of a pipe inner surface ε* λ=ξ(Re,ε*,λ). K E Y W O R D S bed roughness predictor, educational module, Excel and VBA, open channel flow, resistance equation Finally, as the VBA codes are presented in detail, they can be modified by users in accordance with their priorities for both educational and practical purposes. This computer application can help students in open-channel engineering courses not only to become familiar with modified BRPs but also to acknowledge the merit of the Excel spreadsheet for estimating flow resistance coefficients.
On the basis of different groups of input and output data, each BRP is implemented into an Excel spreadsheet and VBA codes are presented for BRPs incorporating both grain and form roughness. For this purpose, the problem statement is first revisited to accomplish a better understanding in light of proper problem classification. This study presents an Excel VBA-based educational estimator to address the gap. Also, each BRP is tailored to solve a distinct type of problem however, a proper definition of a problem statement helps shedding light on this application. A rigorous analysis of available BRPs for estimating grain and form roughness coefficients delineates that most of them are comprised of a scheme rather than a single equation. There can be various reasons for not using new bed roughness predictors (BRPs), one of which is the absence of teaching BRPs.
Despite many equations and methods recommended for estimating roughness coefficients, only two standard resistance equations (original Manning's and Keulegan's equations) have been widely taught and utilized in practice. Estimation of flow resistance coefficients plays an inevitable role in open-channel flows in hydraulic modeling and water resources engineering.
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