Coupled dynamic analysis for wave action on a tension leg-type submerged floating tunnel in the frequency domain

One of the essential issues in the design of the Submerged Floating Tunnel (SFT) is the evaluation of its hydrodynamic performance when subjected to wave actions. In this paper, an efficient and relatively accurate theoretical method in the frequency domain is proposed to analyze the dynamic response of the full-length SFT tube in a steady state under wave actions. The tube is treated as a simplified model called a beam on an elastic foundation (BOEF) with three degrees of freedom, and the new calculation formula of cable-constraint reaction on the BOEF model is proposed, which fully considers the coupling relationship between horizontal displacement and torsional angle of the SFT tube due to the constraint effect of the cable, and more suitable for the case where the SFT tube has relatively obvious horizontal displacement or torsional angle. Based on the Hamilton principle, the governing differential equations of the SFT tube are obtained. Then, with the help of the mode superposition method, the solution for the governing equation is obtained. A numerical approach based on potential flow theory and a higher-order boundary element method (BEM) was developed to calculate the wave force on the SFT tube. By direct comparison with previously published numerical data and the finite element model's simulation, the numerical solutions are successfully validated. On this foundation, an investigation is conducted to examine how environmental factors and structural characteristics influence the dynamic response of the SFT to wave actions. The results indicate that the theoretical hydrodynamic model that has been provided may properly and efficiently estimate the dynamic response of the SFT tube to wave actions. Furthermore, it is found that both the inclined angle and installation angle of the cable significantly impact the dynamic response of the SFT.