Hydrodynamic Investigation on a Submerged Tunnel Suspended From Two Pontoons Under Various Immersion Depths

In this paper, the hydrodynamic responses of a tunnel element suspended from two immersion pontoons have been studied by physical model tests in wave basin. A wide range of irregular waves is conducted on the tunnel immersing from the depth near the free surface to the depth near seabed. During each test, the six-DOF motion of the tunnel element and the immersion barge are measured in a simultaneous manner with two receiving terminals of an electromagnetic motion tracking system. Based on the measured data of scale 1:60, response spectra analysis is conducted to examine the coupled motion characteristics of the tunnel element for various immersion depths. Furthermore, to explore the coupled resonant properties of the tunnel immersion system, the coupled motion equation of the whole system is solved and the eigen modes and natural frequencies are obtained. The results showed that the mode frequencies of the coupled tunnel-barge system have a good corresponding relationship with the peak frequencies in the motion spectra. This demonstrates that the coupling mechanism between the tunnel element and immersion barges plays an important role in the motion responses of the tunnel. The increasing immersion depth have a significant effect on the coupling effects, and thus on the motion characteristics of the tunnel element.