Development of a Simulation System for Estimating the Impact Force of Tsunami Drift Using the Explicit MPS Method

When a large-scale tsunami occurs, structures in the coastal area will be destroyed by the impact of tsunami drifts. In the design of tsunami evacuation facilities and petroleum complexes, it is necessary to estimate the impact force of tsunami drift, which varies in size, shape and mass. Although some design equations have been proposed to estimate the impact force of tsunami drift, the impact force varies depending on various conditions such as the draft of the tsunami drifts, the attitude of the collision, the condition of the surrounding flow field, and the rigidity of the structure, etc. No reasonable design equation has been developed yet to meet all these conditions. Therefore, it is necessary to estimate the impact force of tsunami drift by water tank experiments and numerical simulations. In order to simulate the impact of a tsunami drift on a structure by numerical simulation, it is necessary to solve the coupling of fluid, floating object and structure. In this study, we have developed a simulation system that can simulate the impact force of a tsunami drift with the MPS method, which is a kind of particle method. This simulation system introduces an explicit method for pressure calculation, which allows for relatively large scale numerical calculations. In addition, the system is able to reproduce the deformation of structures as an elastic body due to the impact of tsunami drift. In particular, we have introduced an analytical method that allows us to set the computational time step that satisfy the CFL conditions for elastic and fluid particles, respectively, for stable simulation even when there is a large difference between the velocity of fluid particles and the velocity of structural particles caused by elastic waves. As a result of the comparison of the impact force on the cantilevered beam of the tsunami drift with the simulation and the water tank test, the deformation of the structure at the time of impact was reproduced with more than 90% accuracy.