American Society of Civil Engineers


Fluctuations of Turbulent Bed Shear Stress


by Nian-Sheng Cheng, (corresponding author), (Asst. Prof., School of Civ. and Envir. Engrg., Nanyang Technol. Univ., Nanyang Ave., Singapore 639798 E-mail: cnscheng@ntu.edu.sg) and Adrian Wing-Keung Law, M.ASCE, (Assoc. Prof., School of Civ. and Envir. Engrg., Nanyang Technol. Univ., Nanyang Ave., Singapore 639798. E-mail: cwklaw@ntu.edu.sg)

Journal of Engineering Mechanics, Vol. 129, No. 1, January 2003, pp. 126-130, (doi:  http://dx.doi.org/10.1061/(ASCE)0733-9399(2003)129:1(126))

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Document type: Technical Note
Abstract: With the assumption that the bed shear stress fluctuates in a lognormal fashion, the probability density function (PDF) of the standardized bed shear stress is derived as a function of the relative shear stress intensity. The PDF is more skewed with larger relative intensities, but approaches a Gaussian function when the relative intensity is small. The computed PDF agrees well with the reported experimental data for flows over a smooth boundary. The higher-order moments of the bed shear stress, skewness, and kurtosis, are shown analytically to be also dependent on the relative intensity. The theoretical dependencies are then compared to a number of measurements available in the literature. The Reynolds number effect on the relative intensity is also discussed.


ASCE Subject Headings:
Shear stress
Skewness
Reynolds number