Nonlinear Dynamics in Immersed Tunnel Installation Under Regular Waves

Immersed tunnel technique has been developed and successfully applied to the installation of immersed tunnel. During the installation, the tunnel is connected to the dual pontoon floating structures (DPFS) by cables and lowered slowly to the tunnel trench. Such installations generally involve multi-body dynamics with wave-induced motions and nonlinear constraints. This paper establishes a time domain model for the immersed tunnel installation based on a linear potential flow approach. The mooring lines are simplified as linear undamped springs with constant stiffness. More attention has been paid to simulate the marine cables, which are modelled by the lumped mass method as well as by bilinear undamped spring. The effects of cable model on the wave-induced dynamics of the given system are discussed. In the numerical simulation, the slack phenomena and snap load of cables are observed and reveal the rich and complex dynamical behaviors of the immersed tunnel installation.