Near-wall effect on the coupled dynamics of the submerged tunnel installation system due to random waves

• The seabed proximity effects on the tunnel installation in random waves is experimentally investigated. • The noteworthy disparity in the dynamics of tunnel-barge system between the regular and irregular waves is highlighted. • The off-seabed clearance of the TE is governed by the coupled roll resonance superposed with the near-seabed effect. • The near-seabed effect contributes to an impressive growth in the total suspension tension and the barge mooring tension. During the near-seabed installation, the hydrodynamic responses of the submerged tunnel element and its installation system sustain prominent wall effect, which would introduce detrimental risks of grounding accidents and alignment errors. To provide a complementary insight of the wall effect and entitle for the practical engineering demands, the 1:60 scale 3D wave basin experiment is implemented to capture the full 18-DOF coupled dynamics of the tunnel-barge system under random waves, which lacks of thorough investigation in previous studies. Spatial effects like asymmetric wave loading and multi-body movements in beam waves are highlighted in both time domain and frequency domain. To the authors’ knowledge, this study is the first to systematically investigate near-seabed effects of three-dimensional multi-body system under random waves, capturing low-frequency resonance and multi-peak responses that are absent in regular wave tests. It is found that the off-seabed clearance of the TE is predominantly affected by the superposition of the coupled roll resonance and the near-seabed effect. Furthermore, the near-seabed effect contributes to a favorable diminish in the maximum single suspension tension but an impressive growth in the total suspension tension and the barge’s mooring tension.