Effects of Water Waves on Wind Shear Stress for Current Modeling

H. K. Johnson Danish Hydraulic Institute, Hørsholm, Denmark

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H. J. Vested Danish Hydraulic Institute, Hørsholm, Denmark

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Abstract

With the goal of improving the formulation of the wind shear stress used in numerical current modeling, a new method for including the effect of water waves on sea roughness is presented. The method is a hybrid of earlier sea roughness models by Kitaigorodskii and Volkov and Donelan, with two distinctions: 1) the roughness height is assumed to be proportional to a wave height representing high-frequency waves (k>1.5kp) in the spectrum, and 2) the hybrid model is calibrated to give drag coefficients obtained by Smith and Banke for their site conditions and verified by comparisons with other independent datasets. In deep water, this model gives a sea roughness that increases with wave age (Cp/U*) in the early stages of wave growth (up to Cp/U*=5), after which the sea roughness decreases with wave age. This method yields wave-modified Cd values for several test cases and can be used directly in numerical current models.

Abstract

With the goal of improving the formulation of the wind shear stress used in numerical current modeling, a new method for including the effect of water waves on sea roughness is presented. The method is a hybrid of earlier sea roughness models by Kitaigorodskii and Volkov and Donelan, with two distinctions: 1) the roughness height is assumed to be proportional to a wave height representing high-frequency waves (k>1.5kp) in the spectrum, and 2) the hybrid model is calibrated to give drag coefficients obtained by Smith and Banke for their site conditions and verified by comparisons with other independent datasets. In deep water, this model gives a sea roughness that increases with wave age (Cp/U*) in the early stages of wave growth (up to Cp/U*=5), after which the sea roughness decreases with wave age. This method yields wave-modified Cd values for several test cases and can be used directly in numerical current models.

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