# Experimental Study on the Dynamic Response of an Immersed Tunnel Element Moored inside the Harbor
## 2 Experiments  
### Model Design  
The model test was designed according to the gravity similarity criterion. The scale of the model was 1:50, and the scales of some important physical parameters are listed in Table 1. The experiment was carried out in a large hydrodynamic laboratory at the Tianjin Water Transport Engineering Research Institute. The test tank, 40 m long and 30 m wide, includes the whole Longxue Harbor and the nearby regions. The Longxue Harbor owns upright side walls, and the bottom elevations of the berths and adjacent working areas for the tunnel element are \(-12.5\) m, while the bottom elevations of other parts are \(-6.256\) m. A flat-type wavemaker is installed on the southeast and east sides of the test tank, and energy dissipation facilities filled with porous media are arranged along the offshore boundary. The layout of the model is shown in Figure 1. A series of probes were set to measure the wave height; probe GC0 is situated at the harbor gate, and probes GC1, GC2, and GC3 are situated at the center of element berths near the wharf and jetty, respectively. Two main types of tunnel elements were utilized in model tests the first type is a standard element, and the other type is a non-standard element. The heights of the two types of elements are both 10.6 m, but with different horizontal sizes. For the standard immersed element, its length is 165 m and its width is 46 m; for the non-standard immersed element E30, its length is 123.8 m, and its widths at the wider end and narrower ends are 53.50 m and 49.75 m, respectively; for the non-standard immersed element E32, its length is 123.8 m, and its widths at the wider end and narrower end are 55.46 m and 53.50 m, respectively. The shell of the immersed element model is made of high-strength \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Expression** & **Value** \\ \hline Length, Width, Depth, Wave Height & \(\lambda\) & 50 \\ Velocity, Wind Speed & \(\lambda^{1/2}\) & 7.07 \\ Time, Wave Period & \(\lambda^{1/2}\) & 7.07 \\ Force, Gravity, Volume & \(\lambda^{3}\) & 125,000 \\ Angle & \(\lambda^{0}\) & 1 \\ Inertia Moment & \(\lambda^{5}\) & 312,500,000 \\ Mooring Line Stiffness & \(\lambda^{2}\) & 2500 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The model scale of physical parameters in the experiment. Figure 1: Model layout. (**a**) Simplified plane view. (**b**) Real scenes. PVC hardboard, the end sealing door is made of transparent acrylic board, and the three holes inside the immersed element are made of light wood-plastic plate, with a minimal counterweight space between the shell and the inner wood-plastic plate. The counterweight of the element model is achieved by the high-density lead sheet. There are two pontoons with a rod-bone plane. The geometric dimensions of their external outlines in the prototype are 40.62 m \(\times\) 16 m \(\times\) 3.0 m. The main body of the pontoon is a rectangular shell structure; the model material is wood; and waterproof paint is used for external protection. The pontoon uses a cement block as a counterweight to satisfy the similarity criterion on the center of gravity and mass distribution. The structure of the survey tower is complex, but the weight is very small compared with that of the immersed element. The model of the survey tower structure is made of light aluminum, and the small lead sheet is used for counterweighting. The key to making the pontoon model is to ensure that its wind area, total weight, and center of gravity position are similar. The immersed element model after outfitting is shown in Figure 2.  
The immersed element is moored by 8 cables, among which the ones on the inshore side are nylon ones and the ones on the offshore side are steel ones. The plane layout and lengths of the mooring cables are shown in Figure 3. The cables situated in the middle of the immersed element are mainly used to restrain the longitudinal displacement, which can be called the longitudinal regulating cables (the corresponding number is 2# or 3#).