Study on Applicability of FEMA Formula in Prediction of Impact Load by Tsunami Drifting Vessels on Coastal Zone Structures

In this study, we consider and evaluate the applicability of the FEMA’s formula which is one of the main simple formulas for calculating impact forces through the comparison with our proposed numerical simulation model. We investigated the situation of collision with a thin structure such as a pillar by numerical experiments based on the particle method, in particular, we focus on the case where the drifting speed is fast in targeting the quay of Shimizu Port, Shizuoka prefecture. We compared the results of numerical experiments obtained by detailed simulations with FEMA’s formula and evaluated the applicable range of FEMA s formula for huge vessels. As results, it was suggested that the overestimation was occurred with FEMA’s formula for large vessel using the inundation height and its velocity. FEMA’s formula calculates the impact force of large vessel on the safe side if the drifting vessel speed is used: the condition of added mass coefficient changes the results, but these indicate the safe side in this study. On the other hand, the results of safety sides are fluctuated depending on the height of the action point of force. Therefore, we confirmed that there is a need to examine the height of the impact point when using FEMA’s formula for large vessels.