- A three-dimensional potential flow numerical method was developed for the study of harbor resonance and the wave reflections and diffractions around a modular hybrid pier with two moored ships. The method solves the Laplace equation for unsteady body-wave problems using a chimera domain decomposition approach. In order to facilitate time-domain simulations of harbor oscillation problems, a separate wavemaker grid was used for concurrent computation of the incident wave field in the absence of the structures. An absorbing beach was placed in front of the wavemaker with appropriate damping functions to eliminate the wave reflections and diffractions from the structures and/or the irregular harbor shorelines. This enables us to maintain the same incident wave field for long-duration simulations over many wave periods. The method was employed first for time-domain simulation of the wave diffractions around a combined breakwater and floating platform configuration with two different wave headings. Calculations were then performed for the diffraction wave patterns around an integrated pier system with two ships moored alongside a modular hybrid pier. Finally, the method was extended for time-domain simulation of harbor resonance in the San Diego Bay. The numerical results clearly illustrated the effectiveness of the absorbing beach approach for harbor resonance problems involving complex structures and realistic harbor configurations. Copyright 2004 by The International Society of Offshore and Polar Engineers.