dc.description.abstract | We integrate the 3D NS-VOF model with Bingham Bi-viscous fluid model to investigate the scouring problems around the structures induced by tsunami bores or typhoon floods. In this model, the scour mechanism is modeled by two viscosities and a yield stress. In which is used to describe Newtonian viscosity of liquefied sediment, and is for the solid-state properties of the sediment, and is for presenting the yield stress induced by the current. Before implementing this model, benchmark tests are performed. For validating the model accuracy on predicting the free-surface kinematics, we designed a case in which a dam-break bore is impinging with a structure array. A high-speed camera is used to record the free-surface movement. Very good agreement between the model prediction and experimental data can be seen. For validating the Bingham Bi-viscous fluid model, we compare the result with the analytical solution derived by Bird et al.(1983). The comparison shows that the numerical result is almost identical to the analytical solution in terms of the velocity distribution. For validating the profile of scour hold, we simulate the case proposed by Dey and Barbhuiya (2005) in which the current is flowing around a circular pier. The result shows that our model is able to predict the maximum scouring hole and properly describe the scour mechanism and also the scour area around the cylinder. However, larger discrepancy can be found in the accumulation zone at the downstream direction. In this case, the present model can accurately present several phenomena, such as the bow wave, downword jet current, and horseshoe vortex around the cylinder.
After validating the model, we study the event of Shuangyuan bridge failure caused by 2009 Moarkot typhoon flood. We focus the discussion on the shape difference of the scour holes around the origional of bridge plies and the extended bridge piles. We also explore the suitability of using the empirical formula issued by the government (Ministry of transportation and communications R. O. C., 2009) We further study the the blocking effect from the drifting obstacles. Four scenarios are studied for understanding the effect from different stocking locations. The result shows no significant difference for difference stocking locations. However, adding the quantity of the drifting obstacles will increase the scouring rate and increase scour depth.
Overall speaking, Bingham Bi-viscous fluid model can be used to explore the development of scour hold, and avoid using too many empirical formulations and parameters. We also demonstrate that the present model can be widely used to predict the local scour depth induced by floods or tsunami bores.
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