Measurement and modeling of bed shear stress under solitary waves (original) (raw)
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Comparison of Bed Shear Under Non- Breaking and Breaking Solitary Waves
New experimental measurements of bed shear under solitary waves and solitary bores that represent tsunamis are presented. The total bed shear stress was measured directly using a shear cell apparatus. The solitary wave characteristics were measured using ultrasonic wave gauges and free stream velocities were measured using an Acoustic Doppler Velocimeter. The measurements were carried out in laminar and transitional flow regimes (¡«104 < Re < ¡«105). This sort of data is sparsely available in literature. In the absence of direct measurements, shear stress is indirectly estimated using velocity profiles or is inferred using standard friction factors. However, this indirect method has its limitations, e.g., under unsteady hydrodynamic conditions and relatively large roughness the assumptions of both approaches are no longer valid. More than 168 experimental runs comprising solitary waves and bores were carried out over a smooth flat bed with wave height to water depth ratio varying between 0.12 and 0.69. Analytical modeling was carried out to predict shear stresses using Fourier and convolution integration methods. This paper presents comparison of the measured and predicted bed shear stress or skin friction stress, together with estimates of traditional wave friction factors. Overall, the models can predict the bed shear stress with a satisfactory degree of accuracy.
28th IAHR Biennal Congress, Graz, Austria, 1999
Waters flowing in natural streams and rivers have the ability to scour and to deposit materials, hence to change the bed topography. It is recognised that undular flows have great potential for sediment dispersion. In the present study, a fixed-bed model was used to investigate the spatial variations of boundary shear stress under standing waves (i.e. undular flow). The results (Fig. 5) highlight the threedimensionality of the boundary shear stress distributions. Maximum boundary shear stress are observed under the wave crests and minimum shear stress under the wave troughs. The experimental findings suggest the formation of three-dimensional standing waves bed forms below undular flows. Overall the study emphasises the existence of large boundary shear stress variations below free-surface undulations.
Boundary shear stress measurements in undular flows: Application to standing wave bed forms
WATER RESOURCES RESEARCH, 2000
Waters flowing in natural streams and rivers have the ability to scour and to deposit materials, hence to change the bed topography. It is recognized that undular flows have great potential for sediment transport. In the present study, a fixed-bed model was used to investigate the spatial variations of boundary shear stress under standing waves (i.e., undular flow). The results (Figure 8) highlight the nonuniformity of the boundary shear stress distributions. Minimum boundary shear stress is observed under the wave crests, and maximum shear stress is observed under the wave troughs. The experimental findings suggest the formation of three-dimensional standing waves bed forms. Overall, the study highlights large variations of boundary shear stress in response to free-surface undulations.
On the Wave Bottom Shear Stress in Shallow Depths: The Role of Wave Period and Bed Roughness
Water
Lagoons and coastal semi-enclosed basins morphologically evolve depending on local waves, currents, and tidal conditions. In very shallow water depths, typical of tidal flats and mudflats, the bed shear stress due to the wind waves is a key factor governing sediment resuspension. A current line of research focuses on the distribution of wave shear stress with depth, this being a very important aspect related to the dynamic equilibrium of transitional areas. In this work a relevant contribution to this study is provided, by means of the comparison between experimental growth curves which predict the finite depth wave characteristics and the numerical results obtained by means a spectral model. In particular, the dominant role of the bottom friction dissipation is underlined, especially in the presence of irregular and heterogeneous sea beds. The effects of this energy loss on the wave field is investigated, highlighting that both the variability of the wave period and the relative bo...