Simplified analysis for estimation of the behavior of a submerged floating tunnel in waves and experimental verification

• Tests with physical models in the wave flume to measure characteristics of SFT in waves.
• Response of SFT in single mooring described by a pendulum model.
• Inertia force is dominant in wave loads.
• Wave loads mainly depending on wave height.
• Slack depending on buoyancy weight ratio.

To achieve rational design in waves for a submerged floating tunnel which has emerged as a new offshore transportation infrastructure, it's necessary to understand its hydrodynamic behavior. For simple but accurate estimation of hydrodynamic forces, a theoretical method is proposed and the tests with physical models in a wave flume were carried out for verification. Morison's equation was used to estimate wave loads composed of inertia force and drag force. Forces calculated by applying the linear wave theory to Morison's equation coincided well with those measured by the tests. The test results showed that mooring systems played a significant role in the movement of the submerged floating tunnel in waves. A pendulum model could be used to describe the motion of the submerged floating tunnel with a single vertical mooring. Based on the verified relations, a simple slack condition which causes the submerged floating tunnel to be unstable was also proposed. The simplified approach proposed by this study proved to be useful in designing the submerged floating tunnel in the initial stage.