# Experimental Study on the Dynamic Response of an Immersed Tunnel Element Moored inside the Harbor
## 3 Results
### Dynamic Responses of a Single Element
#### 3.2.1 Under Wind Conditions  
The wind not only acts directly on the freeboard of the immersed element but also indirectly on the immersed element in the form of wind-generated surface waves. The immersed element moves under the action of the wind, and the mooring system will produce a reverse restraining force to restrict this displacement. As the cables are long and have a very small initial tension, all the cables show a catenary state (no obvious tensioning) in the initial state. When the immersed element begins to displace, first the catenary shape of the cable changes while the tension deformation of the cable itself is small; that is, the tension force of each cable along the cable axis does not change significantly, but the direction of cable force at the mooring point of the immersed element changes with the increase in displacement. With the continuous increase in displacement, the catenary form  
Figure 8: Mooring scheme for a standard immersed element moored at berth GC3 near the wharf.  
of the cable will no longer change significantly when the cable is significantly tensioned, and the continuous increase in displacement will be reflected in the tension deformation of the cable itself, resulting in an increase in cable tension force. In general, the tension force-deformation curve of a mooring cable shows the following characteristics. As the displacement gradually increases, the cable tension force does not obviously change at the beginning until the catenary shape of the cable no longer changes significantly. Then, with the continuous increase in displacement, the cable tension force presents its own characteristics of force with deformation.  
The maximum tension force of each cable under wind action is shown in Figure 9. The test results show that the cable on the leeward side has no force, and the wind force is borne by the windward cables. For various load conditions, the wind force on the immersed element is the largest under a no-load condition. The maximum tension force of the nylon cable reaches 635 kN, and the maximum tension of the steel cable reaches 765 kN. The order of the cable tension force under different load conditions is no-load > half-load > full-load > heavy-load. The wind force acting on the pontoons and the survey towers is relatively significant. The cable tension force under a full-load condition is generally about two times that as compared to a heavy-load condition.  
Under the action of wind, the immersed element moves toward the leeward side, and a net displacement exists, accompanied by a small amplitude oscillation that is a result of the wind-generated surface wave. The maximum values of the immersed element motion components are listed in Table 6. The sway under offshore wind action is obviously greater than that under inshore wind action, which is closely related to the different compositions of the cable material on the leeward and windward sides. The maximum sway is 3.42 m under a no-load condition with offshore wind action.  
Figure 9: Maximum tension force of mooring lines with a single immersed element moored under wind action.