Study On Hydrodynamic Characteristics Of Immersed Tunnel During Immersion Standby

The immersion standby for the sinking of immersed tunnel is an important procedure in the construction of large immersed tunnels under complex ocean environment conditions.This procedure is relevant to the stability of immersed tunnel mooring system and safety of construction.It is of great significance in engineering practice.The study is based on the Hong Kong-Zhuhai-Macao bridge island tunnel project.Applying AQWA module based on potential flow theory in ANSYS software,the numerical calculation model of the immersed tunnel and pontoon is established.The model is verified based on the physical model,and the reliability of the calculated results is proved.Firstly,applying the verified model,the influence of mooring patterns(mooring angle,cable lengths,and mooring patterns)on hydrodynamic response are studied and a feasible mooring pattern is proposed.Secondly,under the condition of a feasible mooring pattern,the motion response and mooring tension law of the immersed tunnel-pontoon system are analyzed when different dynamic elements(wave,current,combined action of wave and current)act from different directions.The numerical results indicate that the motion response in all directions varying with the incident angle is different and yaw reaches the peak when the incident wave angle is 45°.The variation of the maximum mooring tension with the incident wave angle is related to the spectral peak period.The motion response in sway direction is more sensitive to the mooring pattern than the motion response in other directions.Under the system natural period,sway,heave,and roll all reach the peak values as well as the mooring lines experience the maximum tension.The existence of current increases the motion response in sway and weakens the heave and roll motion of the immersed tunnel-pontoon system in a certain range.When the change of current direction is less than 15 °,the influence of the change in the current direction is limited.