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Measurement and modeling of bed shear stress under solitary waves

DRS at CSIR-National Institute of Oceanography

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Title Measurement and modeling of bed shear stress under solitary waves
 
Creator Jayakumar, S.
Guard, P.A.
Baldock, T.E.
 
Subject Bed shear stress
Shear plate
Convolution integrals
Tsunami
 
Description Direct measurements of bed shear stresses (using a shear cell apparatus) generated by non-breaking solitary waves are presented. The measurements were carried out over a smooth bed in laminar and transitional flow regimes (~ 10 sup (4) < R sub (e) < ~ 10 sup (5)). Measurements were carried out where the wave height to water depth (h/d) ratio varied between 0.12 and 0.68; maximum near bed velocity varied between 0.16 m/s and 0.51 m/s and the maximum total shear stress (sum of skin shear stress and Froude–Krylov force) varied between 0.386 Pa and 2.06 Pa. The total stress is important in determining the stability of submarine sediment and in sheet flow regimes. Analytical modeling was carried out to predict total and skin shear stresses using convolution integration methods forced with the free stream velocity and incorporating a range of eddy viscosity models. Wave friction factors were estimated from skin shear stress at different instances over the wave (viz., time of maximum positive total shear stress, maximum skin shear stress and at the time of maximum velocity) using both the maximum velocity and the instantaneous velocity at that phase of the wave cycle. Similarly, force coefficients obtained from total stress were estimated at time of maximum positive and negative total stress and at maximum velocity. Maximum positive total shear stress was approximately 1.5 times larger than minimum negative total stress. Modeled and measured positive bed shear stresses are well correlated using the best convolution model, but the model underestimates the data by about 4%. Friction factors are dependent on the choice of normalizing using the maximum velocity, as is conventional, or the instantaneous velocity. These differ because the stress is not in phase with the velocity in general. Friction factors are consistent with previous data for monochromatic waves, and vary inversely with the square-root of the Reynolds number. The total shear stress leads the free stream fluid velocity by approximately 50 degree, whereas the skin friction shear stress leads by about 30 degree, which is similar to that reported by earlier researchers
 
Date 2011-07-29T07:26:56Z
2011-07-29T07:26:56Z
2011
 
Type Journal Article
 
Identifier Coastal Engineering, vol.58(9); 2011; 937-947
http://drs.nio.org/drs/handle/2264/3890
 
Language en
 
Rights An edited version of this paper was published by Elsevier. Copyright [2011] Elsevier
 
Publisher Elsevier