Hydrodynamic response of moored ships to seismic-induced harbor oscillations

Abstract

Free-surface oscillations induced by seismic waves were observed in many harbors. These free-surface fluctuations could lead to damage in a wide range of forms, such as breakage of mooring systems due to excessive ship motions. The damage to moored ships and mooring systems will remarkably reduce their emergency capability to incoming tsunamis, probably further leading to property losses and casualties. However, investigation of floating bodies under seismic-induced free-surface oscillations is rare. Particularly, the hydrodynamic response of moored ships to seismic-induced harbor oscillations has not yet been studied. In this article, the transient hydrodynamic characteristics of moored ships under seismic-induced harbor oscillations are investigated by a hybrid Boussinesq-panel model where the free-surface oscillations are modeled by a fully nonlinear Boussinesq wave model and are further used to drive the ship motions. Results reveal that seismic-induced harbor oscillations can trigger long-period movements of moored ships, consistent with the existing observations. The long-period ship motions consist of the natural modes of the mooring system and the forced modes relating to long-period harbor oscillations. Notably, the ship's maximum displacement can be amplified remarkably when the periods of natural modes coincide with those of the forced modes. The effects of modal shapes of seismic-induced multi-mode harbor oscillations on the ship motions are analyzed. Finally, a brief discussion on studying the countermeasures against ship motions triggered by seismic-induced harbor oscillations is presented. • The hydrodynamic response of moored ships to seismic-induced harbor oscillations is first investigated using a hybrid Boussinesq-panel model. • The capacity of seismic-induced harbor oscillations to trigger long-period movements of moored ships is revealed, especially reproducing a typical process of this phenomenon. • The transient hydrodynamic characteristics of moored ships under seismic-induced harbor oscillations are analyzed, especially considering the resonant case when the natural periods of the ship motions are close to that of harbor oscillations. • The effects of modal shapes of seismic-induced multi-mode harbor oscillations on the ship motions are examined.