Coupled pitch and roll control of floating bridges using corner-distributed pendulum dampers

Ensuring the dynamic stability of floating bridges in deep-water environments presents a complex fluid–structure interaction challenge, particularly concerning coupled pitch and roll motions. This study proposes a decentralized vibration control strategy utilizing External Pendulum-type Tuned Mass Dampers (E-PTMDs) distributed at the four corner nodes of the pontoon. By leveraging the geometric extremities, this configuration strategically transforms vertical inertial forces into substantial rotational restoring moments. A comprehensive fluid–structure-damper coupled numerical framework is established, integrating frequency-dependent boundary element method (BEM) hydrodynamic coefficients into a time-domain Cummins’ equation under stochastic JONSWAP wave spectra. Simulations reveal that the E-PTMD system reduces the pitch root-mean-square (RMS) response by 44.3% under head sea conditions (0°). Under quartering sea conditions (45°), the spatial distribution of the dampers inherently induces phase delays across the diagonal wave field, successfully mitigating strongly coupled pitch and roll responses by 42.9% and 75.6%, respectively. The analytical results demonstrate that corner-distributed mass dampers kinematically replicate the multidirectional rotational stability typical of Tension Leg Platform (TLP) mooring systems. This ”mooring-free” stabilization mechanism offers a robust and cost-effective alternative for deep-water offshore infrastructure, circumventing the exponential weight penalties and subsea installation costs associated with physical tendons.