Measurement and modeling of bed shear stress under solitary waves

Seelam, Jaya Kumar, Guard, Paul A. and Baldock, Tom E. (2011) Measurement and modeling of bed shear stress under solitary waves. Coastal Engineering, 58 9: 937-947. doi:10.1016/j.coastaleng.2011.05.012


Author Seelam, Jaya Kumar
Guard, Paul A.
Baldock, Tom E.
Title Measurement and modeling of bed shear stress under solitary waves
Journal name Coastal Engineering   Check publisher's open access policy
ISSN 0378-3839
1872-7379
Publication date 2011-09
Sub-type Article (original research)
DOI 10.1016/j.coastaleng.2011.05.012
Volume 58
Issue 9
Start page 937
End page 947
Total pages 11
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2012
Language eng
Formatted abstract
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 (~ 104 < Re < ~ 105). 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°, whereas the skin friction shear stress leads by about 30°, which is similar to that reported by earlier researchers.
Keyword Tsunami
Bed shear stress
Shear plate
Friction factors
Convolution integrals
Solitary wave
Coherent structures
Boundary-layers
Bottom friction
Propagation
Flow
Motion
Water
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Civil Engineering Publications
Official 2012 Collection
 
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