Numerical and experimental investigations on dynamic responses of quasi-elliptical and optimized pontoons under wave action

To reduce the wave-induced dynamic responses of deep-sea floating bridge pontoons, this study employs a three-dimensional Fourier series parameterization and a gradient-based optimization model, starting from a quasi-elliptical baseline, to minimize surge and pitch amplitudes under regular waves. Numerical simulations and experiments are combined to elucidate the mechanisms by which the optimized geometry reduces hydrodynamic responses. Compared with the quasi-elliptical pontoon, the optimized pontoon achieves maximum reductions of 58.39% in surge amplitude and 44.72% in pitch amplitude. The optimization suppresses both wave-frequency and low-frequency motion components, thereby reducing the local flow velocity and vorticity around the pontoon. Experiments further examine the effects of wave incidence angle and irregular waves. As the incident wave angle increases from 0° to 15°, the surge and pitch amplitudes of the quasi-elliptical pontoon decrease by 20.25% and 22.32%, respectively, whereas the optimized pontoon remains smaller and less sensitive to wave direction. Under irregular waves, the optimized pontoon suppresses both the low-frequency component at 0.25 Hz and the wave-frequency peak near 0.87 Hz, and exhibits a narrower probability density distribution, indicating a lower risk of extreme responses. This study proposes a pontoon geometry that combines response reduction with manufacturability, offering practical insights for engineering design.