Investigation of the dynamic behavior of the flow-structure system of submerged floating tunnels under wave and current actions

Submerged floating tunnels (SFT) are innovative deep-water transportation infrastructures for crossing water-ways. This study experimentally investigated the dynamic behavior of SFTs subjected to regular waves, uniform currents, and their combination. Binocular stereo vision and particle image velocimetry techniques were adopted to measure instantaneous characteristics of the fluid-structure system in a non-intrusive manner. The time-and frequency-domain characteristics of the dynamic response of SFT, vortex patterns in the wakefield and spatio-temporal evolution of the energy distribution were analyzed. The results show that under current action, the frequency of vortex shedding gradually dominates in dynamic response and the wake vortices are generated from asymmetrically to periodically and alternately with increase of current velocity. The presence of waves in the following and opposing currents weakens and enhances the amplitude of the model response, respectively. The effect of the primary and secondary relationship of wave and current on the frequency distribution of the response is summarized. For the fluid-structure system, the wake vortices exhibit various forms of shedding frequency and spatial distribution under different wave-current combinations. In the presence of waves, the upper and lower vortices are generated almost simultaneously when the sway reaches peak values. This experimental research provides an engineering basis for revealing the mechanism and control of the wave and current-induced vibration of SFTs.