Harbor resonance under typhoon-generated swells in eastern Taiwan: numerical simulations and laboratory experiments

Typhoon-generated swells pose substantial threats to the coastal environment along the eastern coast of Taiwan. Harbors constructed along this coastline are directly exposed to the Pacific Ocean and vulnerable to swell waves propagating into harbor entrances. These waves can excite long-period harbor oscillations, degrading harbor tranquility and operational safety. Hualien Harbor provides a representative case of an exposed harbor susceptible to long-period swell-induced resonance. In this study, a series of laboratory experiments was conducted in a wave basin to investigate the interaction between typhoon-generated swells and the harbor geometry of Hualien Harbor. A dense array of wave gauges was deployed throughout the harbor to measure spatial water-surface oscillations. To interpret the underlying physics and extend the analysis beyond the instrumented locations, a wave-resolving numerical model based on Boussinesq-type equations was applied to reproduce the experimental configuration. Special consideration was given to the wave-maker configuration to address the limitations imposed by the finite length of the wave generator. Based on the combined experimental–numerical results, the spatial amplification patterns and natural resonance modes of the harbor were examined, and their dependence on incident wave conditions, dispersive effects, and boundary reflections was evaluated. These results demonstrate how the interaction between incoming swell spectra and the intrinsic modal structure of the harbor governs the magnitude and spatial distribution of in-harbor oscillations. The results further reveal that localized amplification zones within the harbor basin act as hotspots for harbor oscillations. The findings thus establish a physical basis for designing wave-dissipating structures and modifying harbor geometry to mitigate long-period resonance in high-energy coastal environments.