# A Mesh-Free Particle Method for Simulation of Mobile-Bed Behavior Induced by Dam Break
## 4 Conclusions  
Since the multi-phase flow has more interface than single-phase flows, multi-phase particle interaction models are required to be employed in order to achieve an accuracy of numerical simulation and avoid the numerical error. The newly employed multi-phase model, including self-buoyancy and surface tension models, was introduced in this study. The dam break problem with erodible beds was simulated by developing the MPS method with the multi-phase particle interaction models, and then comparing the well to the corresponding experimental results including a single-phase dam break, dam break with erodible beds, and the swash uprush problem in the inclined tank.  
In order to validate the developed MPS program, a single-phase dam break, which is a classical problem of the particle method, was simulated. The single-phase problem does not activate multi-phase particle interaction models. However, it is necessary for being validated. By comparing snapshots between experiments and numerical simulation, both results show good agreement. Regarding the pressure calculation, the time history of pressure was well matched with visual results by taking pressure peaks. Moreover, the initial particle distance, which is the same as the grid size in a conventional CFD method, also investigated the initial particle distance, which was selected by a numerical test.  
For the erodible beds problem, the PEO solution was used as a bed property. The PEO solution is not exactly a solid object. However, by considering the liquefaction of erodible beds, the PEO solution was an appropriate model. The water captured by the gate on the left side of the tank and erodible PEO solution beds was located beyond the gate with various thicknesses corresponding to experimental conditions. When the gate opened, the captured water collapsed and ran toward erodible beds. In the case of a relatively thin layer of the soil bed that was 0.015 m in thickness, the collapsed water runs over the beds, while in other cases such as 0.030 m, 0.058 m, and 0.070 m, the water dug into the erodible beds and lifted the beds. This is because the weight of the bed layer affected the flow development that was observed in both experiments and numerical simulations.  
Figure 12: Time history of change of height and velocity from (**a**) experiment and (**b**) numerical simulation.  
The swash uprush problem was also investigated by the newly developed multi-phase MPS method. For the swash uprush problem, the tilted tank, which contained the water and the PEO solution divided by the gate, was considered. The tilting angle was 2.87\({}^{\circ}\), which is the same as the corresponding experiment. Upon comparing the wave height and maximum velocity at the certain measuring point between the experiment and numerical simulation, it was found that have satisfactory agreement. There were several irregular data points in both the wave height and maximum velocity history, but these were related to the fragmented particle by a splash, which did not affect all of the results.  
These observations cannot fully explain the effects of the soil bed downstream of the collapsed fluid, because PEO is also regarded as a fluid particle. Moreover, the physical characteristics of PEO solution are similar to a water particle. However, in the most realistic situation, the soil bed contains a fluid. Therefore, it can be assumed to be a fluid due to liquefaction. Despite stated flaws in this simulation, the agreement between numerical simulation and the experiment may help to understand the phenomena of soil behavior due to very violent forces induced by large-scale flows. It can be used to design wave prevention technology to avoid massive disasters.  
This Research was funded by the Tongmyong University Research Grants 2017 (2017A001).  
This Research was supported by the Tongmyong University Research Grants.  
The author declares no conflict of interest.