Acoupled fluid-structure interactionmodel is applied to a disastermitigation structurewithamovable crown to investigate the mechanism of crown motion and wave dissipation. The model is composed of an extended Navier-Stokes solver for computing air-water two-phase flow, a volume-of-fluid module for tracking airwater interface motion, and an immersed boundary module for calculating structure motion and resulting interaction with fluid flow. It is revealed that the modeling of a gap around the movable crown affects numerical results in terms of water surface fluctuation in front of the structure, wave overtopping discharge, and crown motion, thus demonstrating that it is essential to accurately model the gap to assess the performance of the structure for optimal design. It is also found that it is important to consider not only water flow but also air flow because the movable crown is raised by air pressure trapped inside the structure and the impact of water propagating into the structure. In addition, the structure is found to efficiently dissipate wave energy due to the formation of vortices around the crown and the motion of the crown.

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