dc.description.abstract | The tsunami caused by an undersea earthquake often leads to coastal areas hit seriously, and the flood entrained by tsunami surges often brings local scour around the buildings. Moreover, the high concentrations of sediment flow formed by heavy rain, such as Mudflow or Mud flood, often causes live losses or damages on structures during typhoon season. The flood induced by heavy rainfalls may result in local scour around the bridge. In order to understand more about the movement characteristics of sediment, which are similar to ones of the Bingham fluid, we newly developed a rheology model for simulating the natural hazards of landslide and local scour induced by a tsunami or severe floods in this study. The model originated from the conventional Bingham constitution model included tamping effect, which exists in most of the mud or sediment problems and usually is caused by the settlement and compaction processes.
The tamping effect is crucial to the shape of the slip surface and scour profile in the landslide and local scour problems, respectively. However, the conventional Bingham model lacks the mechanism of describing this prenominal. Hence, we converted the Bingham model into the Bi-viscous model, adding additional parameters, Yield_solid and Gamma_yield, to present the tamping effect. Yield_solid indicated the yield stress of compacted material; Gamma_yield indicated the yield strain rate. Without the tamping effect, the Yield_solid went to the yield stress, and the model went back to the conventional Bingham model. While the tamping effect was taken into account, the Yield_solid increased and made the rheology curve discontinuous. The novel model is called Discontinuous Bi-viscous Model, shorten as DBM. It solves 3D Navier-Stokes equation and tracking the movement of fluid interface with Volume of the Fluid method. The provided parameters in the model are Bingham yield stress、Bingham viscosity and yield strain rate. However, there is no systematical method for determining these parameters and need to rely on rheometer. For this reason, the present study developing Rheological Parameter Determining Method (RPDM) by way of the empirical formula of Raudkivi (1998) . It can be inquired into reasonable rheological parameters after providing sediment grain size and proportion, and grasp the appropriate initial value. The traditional models do not investigate yield strain rate, in this paper, we can get the appropriate initial value by numerical method.
The present study carrying out three-dimensional Mudflow landslides and local scour simulation on the cylinder. In three-dimensional Mudflow landslides, we apply our model to simulate one real case, 1966 dam break of gypsum tailing in Texas. First, we use yield stress and viscosity analyzed by Jeyapalan (1983) to simulate, and discuss the influence of yield strain to the mechanisms of landslides. The results show that yield strain will change the time of dam break, the process of mobile, stacking patterns and inundation distance.
From the simulation results, we know that DBM is not only express the movement of the process and the accumulation of mud flow but also has a good consistency with observations. With the grain size and proportion of sediment which provided by Jeyapalan (1983) , we can obtain the rheological parameters through the rheological parameter determining a method to carry out the dynamic simulation of three-dimensional mudflow motions. To verify our methods with Jeyapalan (1983) . Simulation results show that the parameters calculated by the present study could express the motion of mudflow and accumulation phenomenon appropriately, and well compare with experimental results. Regarding the issue of local scour, we study on the Turbulent flow field in a scour hole at a semicircular abutment (Dey and Barbhuiya, 2005) . The simulation result shows that the parameters calculated by our study could also describe the seabed erosion and the final development of scouring pit, and the maximum depth of scouring pit of error less than 10%, in addition to the good comparison with scouring pit patterns. | en_US |