Hydroelastic Response of Submerged Floating Tunnel

This research investigation addresses the analysis and numerical simulation of dynamic response of submerged floating tunnels (SFTs) under the influence of surface waves. As an innovative technical solution for waterway crossings, an SFT is usually considered as a slender structure restrained by cable system due to its large aspect ratio, i.e. ratio of length to diameter. Although an SFT is usually placed at a certain depth under the water surface, it is still susceptible to wave field due to its slenderness. In this research study, a three-dimensional finite element solving technique, using both Morison’s equation and modal analysis, is formulated to construct a hydroelastic model of an SFT and to determine its deformation considering the fluid-structure interactions. Two preliminary tunnel models for China and Japan, respectively, were studied by implementing the proposed methodology. In the first case study, a three-dimensional finite element model of the SFT prototype in Qiandao Lake (China) was built in Matlab and subsequently analyzed using mode decomposition to determine its natural frequencies and mode shapes. For each mode shape, Morison’s equation was employed to calculate fluid forces at each cross section along the tunnel for given surface wave conditions. Then in the frequency domain, a complex equation of motion was solved iteratively to address the convergence of the stiffness of the cable system. The total dynamic response of SFT was the sum of contributions from each mode component. Results obtained from Matlab were compared with findings from previous publications and numerical simulations in ABAQUS. Next, a generic pedestrian-aimed SFT proposed for Otaru Crossing in Japan was studied. Parametric studies were performed to evaluate the influence of configuration scheme of cable system and tunnel submerged depth on the dynamic response of SFT. Results show the importance of fundamental structural parameters in the SFT global performance and several key conclusions regarding parameter selections were drawn for engineering practices in design phase