Submerged floating tunnel (SFT) is a new type of transportation infrastructure for crossing sea straits in relatively deeper water. Compared with the fixed tunnel, the main challenge in designing a SFT is the stability maintaining in a complex hydrodynamic environment, especially for the wave-induced dynamic load. In this study, a series of systematic experiments were conducted to investigate the 2D motion characteristics (i.e., heave, sway and roll) of the SFT exposed to regular waves. The movement of the SFT model is measured by the image processing method which is a noncontact measurement. The experimental observation of SFT motion during the process of wave and SFT interaction is described in detail, and the influence of several governing parameters is thoroughly analyzed, including the wave height and period, submergence depth, buoyancy to weight ratio (BWR), and the mooring line angle. The results show that the motion amplitudes of SFT increase with the wave height increasing. The effect of wave period is related to the natural period of the structure. The sway, heave and roll of the SFT submerged beneath the water surface are much smaller than that of the SFT on the water surface. With the increase of BWR, the motion of SFT decreases. The motion amplitude increases with mooring line angle increasing. Finally, empirical equations are proposed to estimate the motion characteristics of the SFT.

A 2D numerical model was established to investigate vortex induced vibration (VIV) for submerged floating tunnel (SFT) by solving incompressible viscous Reynolds average Navier-Stokes equations in the frame of Abitrary Lagrangian Eulerian (ALE). The numerical model was closed by solving SST k-ω turbulence model. The present numerical model was firstly validated by comparing with published experimental data, and the comparison shows that good achievement is obtained. Then, the numerical model is used to investigate VIV for SFT under current. In the simulation, the SFT was allowed to oscillate in cross flow direction only under the constraint of spring and damping. The force coefficients and motion of SFT were obtained under different reduced velocity. Further research showed that Reynolds number has not only a great influence on the vibration amplitude and ‘lock-in’ region, but also on the force coefficients on of the SFT. A large Reynolds number results in a relatively small ‘lock-in’ region and force coefficient.

Based on the open-source code DualSPHysics, a numerical model was conducted to simulate the regular wave transformation on the slope breakwater with artificial block, and the simulation results were verified according to the measured data from the physical experiment. The deviation between the numerical model and the measured data was less than 6% and 9% in wave run-up and overtopping, respectively, which demonstrated the model can reliably capture the wave evolution on the breakwater with an artificial block. Based on this verified model, the size of the artificial block was adjusted to obtain optimal wave-damping effects. Once obtained, the hydrodynamic characteristics of the optimized new artificial block TB-CUBE were further studied, and the effects of the breakwater slope, water depth in front of the breakwater, incident wave period, and the height on wave run-up were all analyzed. Finally, an empirical formula for wave run-up on this type of article block was suggested through data-fitting, for which the correlation coefficient is 0.981.

Lifetimes of Ag/AgCl electrodes determine whether it is possible to monitor the concentration of chloride ions in marine concrete structures. A novel manufacturing method, pulse current electrodeposition at a low current density, was proposed to prepare the long-lifetime Ag/AgCl electrode. Influences of electrodeposition duration were investigated on the Nernst response, exchange current density, and lifetime of Ag/AgCl electrodes, and the properties were also compared to those of the ones electrodeposited by applying constant currents. Ag/AgCl electrodes prepared with the pulse current exhibited a wider potential response, a higher exchange current density, and a longer lifetime than those prepared by the constant current under the same equivalent charge transfer conditions. AgCl film on the electrode prepared with the pulse current displayed a thicker layer, a lower density of micropores, a higher Cl/O ratio, and a lower Ag/Cl ratio than those of its counterpart electrodeposited by applying the constant current. The lifetime of the Ag/AgCl electrode was mainly determined by the thickness of AgCl films in the concrete environment. The lifetimes of the Ag/AgCl electrode, which was prepared with a 0.1 mA cm⁻² pulse current for 15 h, were 420 h in pore solution and more than 3500 h in mortar, respectively. In addition, the potential of this Ag/AgCl electrode did not show any significant decrease after 3500 h in the mortar without Cl⁻. The results suggest that pulse current electrodeposition is an effective method to improve the lifetimes of Ag/AgCl electrodes in concrete.

The erosion of the seabed around offshore structures has emerged as a critical factor impeding the operational safety of offshore engineering facilities. Prompt and precise identification and monitoring of the water–soil interface hold significant importance in mitigating the seabed erosion challenges facing offshore structures. To tackle this issue, a monitoring framework for the water–soil interface is proposed, grounded in heat transport theory. This framework exploits the thermodynamic variances between seawater and the seabed soil to examine the temperature changes in linear heat sources in water and soil under a constant power. In this study, a typical metallic material—iron (Fe)—and non-metallic material—polyvinyl chloride (PVC)—are considered the linear heat sources, and their temperature variations are analyzed within this framework. The findings reveal that the temperature of the linear heat sources rapidly stabilizes, with the ultimate temperature exhibiting a logarithmic correlation with the convective heat transfer coefficient. To further test the practicability of the framework, an indoor test is conducted. The errors between the theoretical calculation results and the experimental results are less than 14% in water and 19% in soil. The results of the framework and the indoor test have a high degree of coincidence. This framework has proved that it can be used in practical engineering.