Many breakwaters were damaged by the Great East Japan Earthquake of March 11, 2011. The majority of the breakwaters were destroyed or deformed under tsunami overflow; however, the failure mechanism under tsunami overflow is not clear. Therefore, with the main objective of this report being to clarify the stability of breakwaters under tsunami overflow, hydraulic model experiments and numerical simulations were conducted with Kamaishi Bay breakwaters as the subject, and failure mechanisms of the trunk of the breakwaters were examined.

This study proposes analyzing tsunami generation and propagation of tsunamis, wave runup onto land, object drift, collision with other structures, deformation prediction of colliding and collided-with, and collision force estimation. To reduce calculation load in using the LS-DYNA collision model, we use a drift model using the immersed boundary (IB) method from wave generation to just before collision, and the collision model is used during the collision phase, in which numerical data calculated using the drift model are used as an initial condition of the collision model. Validity of the drift model for wave level, wave force, and drift behavior of a container were verified through comparison with experimental data measured in laboratory experiments. Collision model predictability was also confirmed in terms of drift collision force. Fluid-structure interaction (FSI) between the container and the runup wave is reproduced in numerical drift collision analysis. Through this analysis of a full-scale container based on the international standard with a concrete column, we confirmed the applicability of the collision analysis using the drift simulation as an initial condition for an actual field.

As the size of ships increases, the size and output power of their thrusters also increase. When a large ship berths or unberths, the jet flow produced from its thruster has an adverse effect on the stability of quay walls. In this study, we conducted a numerical analysis to examine the impact of the thruster jet flow of a 30,000 TEU container ship, which is expected to be built in the near future, on the stability of a quay wall. In the numerical simulation, we used the fluid–structure interaction analysis technique of LS-DYNA, which is calculated by the overlapping capability using an arbitrary Lagrangian Eulerian formulation and Euler–Lagrange coupling algorithm with an explicit finite element method. As the ship approached the quay wall and the vertical position of the thruster approached the mound of the quay wall, the jet flow directly affected the foot-protection blocks and armor stones. The movement and separation of the foot-protection blocks and armor stones were confirmed in the area affected directly by the thruster jet flow of the container ship. Therefore, the thruster jet flows of ultra-large ships must be considered when planning and designing ports. In addition, the stability of existing port structures must be evaluated.

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This study proposes a calculation scheme which enables us to estimate the collision time and force of a container drifted by run-up tsunami. Simulated behaviors of the drifted container by a run-up wave are found to be in good agreement with the laboratory experimental results.A set of these calculated values are used as the initial values of the fluid-structure interaction analysis which simulates the collision of the drifted container. It is confirmed from these simulations that the added mass (water mass at the rear of the container) plays an important role on the collision and predicted collision force and time reached equilibrium state as the model accounts for adequate volume of water in the rear of the drifting container. Moreover, the effect of the added mass on the collision force and time is verified in full scale collision simulation.