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Flow hydrodynamics and scour around bridge pier during tsunami propagation in coastal rivers
Published in Wim Uijttewaal, Mário J. Franca, Daniel Valero, Victor Chavarrias, Clàudia Ylla Arbós, Ralph Schielen, Alessandra Crosato, River Flow 2020, 2020
Later, in the same setup, a 0.02m thick sediment bed around the pier models was prepared to investigate locations of maximum scour during bore propagation as shown in Figure 1b. The sediment used in the present study is uniformly graded marine sand with d50 = 0.28mm. With the given sediment size and flow conditions, the Shields parameter in the model was estimated to be 0.6, while the critical Shields parameter at which sediment starts to move is of the order 0.05 (Nielsen, 1992), so extensive sediment motion is expected. However, it is difficult to achieve the same Shields number in both prototype and the model since the availability of non-cohesive sediment of the size obtained from Shields number scaling is limited. The estimated Shields number in the prototype is 0.78. The sediment bed was initially levelled to be horizontal around the cylinder. A total of six consecutive bores were run during each test to represent a prototype condition where usually 3 to 11 waves were recorded during past tsunami events.
Coastal and offshore structures
Published in G.J.C.M. Hoffmans, H.J. Verheij, Scour Manual, 2017
G.J.C.M. Hoffmans, H.J. Verheij
For a pipeline originally placed on the seabed, the scour depth develops towards the full state through a transitional period. The Shields parameter can adequately describe the initiation of sediment transport and is generally applied to a horizontal or near horizontal longitudinal bed slope. Gravity is likely to affect the mobility of the bed particles significantly in scour holes with steep slopes. However, Chiew (1991) found that the critical bed shear-stress in the scour hole is approximately equal to the critical shear stress given by Shields (1936). Fredsøe et al. 1992 used experimental data to confirm that the time scale of the scour process below a pipeline is governed by the Shields parameter. The larger the Shields parameter, the larger the sediment transport due to scouring and, consequently, the shorter the time period during which a substantial change in the scour depth will occur. For both steady-current (0.35 < U< 1.0 m/s) and regular waves (0.15 <um<0.4 m/s) the maximum scour depth as function of time can be given by the following simple relation (Fredsøe et al. 1992): () ym=ym,e(1−e−t/TF)
Initiation of motion
Published in G.J.C.M. Hoffmans, H.J. Verheij, Scour Manual, 2021
G.J.C.M. Hoffmans, H.J. Verheij
The Shields parameter Ψ can be related to the dimensionless transport rate ϕ which is a function of the sediment transport. Paintal (1971) does this for small transports with Ψ values in the range of 0.04–0.06. Further information can be found in sediment transport manuals, for example Van Rijn (1993, 2007).
Embankment breaching at Indian Sundarban – an assessment on altered primary sediment index properties and fluvial flow parameters
Published in ISH Journal of Hydraulic Engineering, 2022
Susanta Chaudhuri, Vikas Kumar Das, Koustuv Debnath, Sunil Hansda
where is the grain Reynolds number, = kinematic viscosity of water, = density of water, = dry density of sediment and g = acceleration of gravity. According to Shields (1936) the Shields parameter is used as a dimensionless shear stress parameter to characterize the threshold value for the sediment transport. The results show the fluid induced shear stress to the wall is greater than the critical shear stress (erosion threshold) estimated based on grain diameter and grain Reynolds number in the cohesive sediment. The erodibility of a cohesive bed is expressed by the critical erosion threshold and the erosion rate (Thompson and Amos 2004). Ternat et al. (2008) stated that the erosion of a sediment layer appears, when the shear stress is greater than the erosion threshold of that sediment layer.
Simulating 2DH coastal morphodynamics with a Boussinesq-type model
Published in Coastal Engineering Journal, 2018
Georgios T. Klonaris, Constantine D. Memos, Nils K. Drønen, Rolf Deigaard
where the subscripts w and n correspond, respectively, to the wave direction and the direction normal to the waves, g is the gravitational acceleration, is the relative density between sediment (ρs) and water (ρ), αw, αn and b are empirical coefficients, the median grain size, and are the mean absolute and maximum Shields parameters due to wave-current interaction, respectively. The Shields parameter in the direction normal to the wave direction, , is only due to current. It has been experimentally observed that low sediment transport may take place even when the instantaneous Shields parameter is slightly lower than its critical value, . This result is considered through the last exponential term in Equations (1a) and (1b). The phase-lag effects during the sediment’s movement are taken into account through the net Shields parameter, . The presented bed load formula is one of the few formulae that consider the aforementioned unsteady effects. For more details, the reader is referred to Klonaris et al. (2017).
Numerical implementation of wave friction factor into the 1D tsunami shallow water equation model
Published in Coastal Engineering Journal, 2021
Nguyen Xuan Tinh, Hitoshi Tanaka, Xiping Yu, Guangwei Liu
In hydrodynamic and sediment transport studies, the Shields parameter is a fundamental dimensionless parameter representing the ratio between shear stress and buoyant sediment weight per unit area. Shields parameter is commonly used to determine initial sediment motion on the sea bottom. In fact, Shields parameter is the basic parameter for many empirical sediment transport formulas developed by Meyer-Peter and Müller (1948), Engelund and Hansen (1967), and Van Rijn (1984).