# Experimental Study on the Dynamic Response of an Immersed Tunnel Element Moored inside the Harbor
## 3 Results
### Dynamic Responses of the Two Elements  
#### 3.3.1. Mooring with a Large Spacing  
The mooring scheme for the simultaneous mooring of two immersed elements (a standard element moored at berth GC3 near the bank wharf and a non-standard element E32 moored at berth GC1 near the dike wharf) at a relatively long distance (slightly more than one time the length of the immersed element) is shown in Figure 13.  
Compared with the results of the mooring test of a single element, the cable tension force and motion extremums of the standard element under the two elements mooring simultaneously are slightly smaller overall, and the relative changes of the maximum cable tension force and motion extremums are shown in Table 9. The relative changes in maximum tension force in the transverse cables are greater than those in the longitudinal cables. Additionally, this corresponds well with the relative changes of the motion component (as listed in Table 10), in which changes in roll are more obvious. When the non-standard element E32 is moored at berth GC1 near the harbor gate, it has a shielding effect on the rear waters, similar to the floating breakwater. Therefore, the wave action on the standard element moored at berth GC3 in the rear water is weakened, resulting in a relatively smaller dynamic response amplitude. However, the reduction is very limited because the immersed element itself has no obvious influence on the short-period waves. Because  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Motion**} & \multicolumn{2}{c}{**No Load**} & \multicolumn{2}{c}{**Half Load**} & \multicolumn{2}{c}{**Heavy Load**} & \multicolumn{2}{c}{**Full Load**} \\ \cline{2-10}  & **Offshore** & **Inshore** & **Offshore** & **Inshore** & **Offshore** & **Inshore** & **Offshore** & **Inshore** \\  & **Wind** & **Wind** & **Wind** & **Wind** & **Wind** & **Wind** & **Wind** & **Wind** & **Wind** \\ \hline Surge (m) & 0.19 & 0.26 & 0.32 & 0.27 & 0.44 & 0.26 & 0.34 & 0.29 \\ Sway (m) & 4.25 & 2.17 & 2.98 & 1.66 & 2.14 & 1.02 & 2.59 & 1.39 \\ Heave (m) & 0.25 & 0.23 & 0.22 & 0.22 & 0.17 & 0.16 & 0.16 & 0.16 \\ Yaw (\({}^{\circ}\)) & 0.31 & 0.58 & 0.33 & 0.52 & 0.33 & 0.45 & 0.35 & 0.44 \\ Pitch (\({}^{\circ}\)) & 0.37 & 0.28 & 0.25 & 0.28 & 0.46 & 0.27 & 0.36 & 0.35 \\ Roll (\({}^{\circ}\)) & 1.77 & 1.51 & 1.19 & 1.13 & 1.01 & 1.02 & 1.13 & 1.11 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Motion extremums of a standard immersed element under wind and wave action (center of mass).  
Figure 12: Maximum tension force of mooring lines with a single immersed element moored under wind and wave action.  
of the randomness of irregular waves and the statistical uncertainty of test data, some dynamic responses of the element show slight increases, and that is reasonable. No obvious correlation is found between the relative changes in dynamic response and the load condition. The comparison of test results between a single-element mooring and a two-element mooring with a large spacing indicates that when two elements are berthed simultaneously, a distance of approximately one time the element's length is sufficient for mooring safety and there is no mutual interference, which would make mooring conditions worse.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Motion Component** & **Half Load** & **Heavy Load** & **Full Load** \\ \hline Surge (m) & \(-1.3\) & \(+0.9\) & \(-2.2\) \\ Sway (m) & \(-6.2\) & \(-5.4\) & \(-7.0\) \\ Heave (m) & \(-3.7\) & \(-2.2\) & \(-1.4\) \\ Yaw (\({}^{\circ}\)) & \(-2.1\) & \(-2.3\) & \(+1.3\) \\ Pitch (\({}^{\circ}\)) & \(+1.4\) & \(-2.6\) & \(-3.3\) \\ Roll (\({}^{\circ}\)) & \(-3.5\) & \(-4.0\) & \(-4.5\) \\ \hline \hline \end{tabular}
\end{table}
Table 10: Relative change of motion response of a standard element under two elements mooring simultaneously with a large spacing.  
Figure 13: Mooring scheme for a standard immersed element moored at berth GC3 near the wharf and a non-standard immersed element E32 moored at berth GC1 near the jetty.