A Hydrodynamic Numerical Study On The Immersion Motion Of Tunnel Element With Mooring Lines

During the construction of the large-scale immersed tunnel engineering, the immersion of the tunnel elements is one of the most dangerous procedures in the process of immersed tunnel construction that needs high technical requirements. Especially under the ocean environment conditions, anchoring the tunnel elements to seabed with mooring lines will be helpful for the safe construction and accurate preliminary positioning. On the base of this consideration, the time-domain motion responses and mooring line tensions of the tunnel element with mooring lines under the wave actions are studied by numerical model in this paper.Based on the time-domain Green function that satisfies the free water surface condition in the finite water depth, the integral equation for potential function is established and solved by the boundary element method. And the components of the wave force and moment are obtained. The suspension cable tensions are modeled by Wilson formula. The mooring line tension equation is established according to the force balance principle and solved on the basis of the lumped-mass method. The time-domain motion equations of immerged tunnel element are solved by the fourth order Runge-Kutta method. Firstly, the motion responses and suspension cable tensions of immerged tunnel element without mooring lines are computed and the numerical results are in good agreement with the experiments. Afterwards, the motion response, suspension cable tensions and mooring line tensions of immerged tunnel element with mooring lines are computed in different wave direction, wave height, wave period and immerge depths. Also,different types of arrangement of mooring lines are computed. The numerical results indicate that the mooring lines have certain effect to reduce the motions of the immerged tunnel, especially under the condition of lower immerged depth and a long period wave.The effects of mooring line arrangements on the motions are discussed and the better mooring line arrangements are given in the paper.