Hydrodynamic response of a submerged tunnel element suspended from a twin-barge under random waves

It is possible that the excessive dynamic responses of tunnel elements could jeopardize the safety and accuracy of installation procedures used during subsea tunnel construction. To investigate the motion characteristics of the tunnel element, experimental measurements of a moored tunnel element suspended from a twin-barge were conducted in a wave flume at a geometric scale of 1:50. A corresponding numerical model was developed to simulate the dynamic response of the tunnel-barge system in realistic sea conditions, using hydrodynamic parameters from a radiation/diffraction potential model. Multiple linear wave conditions and three immersion depths were tested. The results indicate that the motion response of the tunnel element increases with decreasing immersion depth, and the natural periods of the tunnel, barge and combined tunnel-barge system play key roles in the influence of wave conditions on the motions of the tunnel. It was found that the low frequency motion of the tunnel element is large in small wave periods. The mooring system under such conditions needs to be considered carefully during system design in order to safely control the motions of the tunnel-barge system in energetic ocean environments.