A study on the interaction between circular or elliptical cross-section submerged floating tunnels and elevation internal solitary waves

Recently, submerged floating tunnels (SFTs) have been widely studied around the world, as it is viewed as one of the alternatives to sea bridges and underwater tunnels for wide and deep sea-crossings. Being submerged in the water, SFTs face the potential safety risk from the internal waves, which contain huge amounts of energy and span across a substantial portion of the water column. To better understand the nonlinear interaction between elevation internal solitary waves (ISWs) and SFTs with different cross-sections in stratified fluids, a numerical model based on the Navier-Stokes equations and density transport equation has been developed. The accuracy of this numerical model is then confirmed through comparisons with both theoretical and experimental results. By applying this model, a comparative study focusing on the three wave forces acting on fixed circular and elliptical SFTs, including horizontal wave force, vertical wave force variation and moment, has been conducted with the consideration of different submergences, incident wave amplitudes and density ratios. Subsequently, a typical tether-constrained SFT system under the wave forces of elevation ISW is studied. The results show motion responses of sway, heave and roll are relatively small compared to the size for both circular and elliptical SFTs, which implies that the elevation ISW-SFT interaction can be effectively limited by the mooring lines. Nevertheless, the motion responses under mooring line constraint are close to the allowable deflection limit for floating bridges. Therefore, the potential for fatigue failure should still be carefully considered, particularly when the SFT encounters internal soliton trains.