Internal solitary waves (ISWs) can impose significant hydrodynamic loads on offshore structures; however, their impulsive effects on piles remain insufficiently understood. In this study, an analytical framework based on a modified Morison equation is developed to estimate the impulses exerted by ISWs on a pile and the resulting oscillatory motion during the lowering process. Using temperature and current observations collected west of the Dongsha Atoll on 28 July 2016, the drag and inertial impulses induced by a depression ISW are quantified. The results show that the impulse is dominated by the drag component, while the inertial contribution is much smaller. The unit impulse exhibits pronounced vertical variations, with large values near the surface and bottom layers and near-zero values at intermediate depths. Sensitivity analysis indicates that the impulse depends on pile diameter as well as the hydrodynamic coefficients. Modeling the suspended pile as a simple pendulum further demonstrates that ISW-induced impulses generally produce small-amplitude oscillations under typical engineering conditions, with the pile velocity and swing angle being insensitive to pile length. The proposed framework provides a practical tool for estimating ISW-induced loads and assessing potential risks during offshore pile installation in regions affected by strong ISWs. • An analytical framework is developed to quantify cumulative ISW effects on piles. • Drag force dominates the impulse acting on piles during ISW passage. • ISW-induced impulses generate small-amplitude oscillations of piles. • Pile velocity and swing angle show weak sensitivity to pile length.
Xie et al. (Thu,) studied this question.