Tunnel-mooring-train coupled dynamic analysis for submerged floating tunnel under wave excitations

A submerged floating tunnel (SFT) is considered as an effective alternative to conventional bridges and underground/immersed tunnels for passing through deep water. In this study, a time-domain coupled hydroelastic dynamics model has been developed to solve the tunnel-mooring-train interaction under wave excitations. The equations of motion for a tunnel and mooring lines are based on the FE (finite element) rod theory with the Galerkin formulations. The tunnel is coupled with mooring lines through a specially devised connection method with linear and rotational springs. Wave-induced hydrodynamic loads are estimated by the Morison equation for a moving object. The train is modeled by using the multi-rigid-body dynamic method, in which a train element is composed of seven constituent rigid sub-bodies. The interaction between the tunnel and the train is taken into consideration based on the correspondence assumption and the simplified Kalker linear creep theory. Accordingly, the train-tunnel coupled dynamics formulas are derived. In the simple case of moving mass inside SFT in calm water, SFT's dynamic responses and mooring tensions agree well with those by a commercial program, OrcaFlex. For more complex coupling of SFT dynamics with multi-car trains in random waves, the presently developed simulation program is applied. It is seen that the influences of moving trains on the dynamic responses of the SFT are small. Under the given moderately rough wave conditions and track irregularity, the moving train also meets the safety and passenger-comfort criteria at high (80 m/s) train speed.