Investigation On The Motion Of Tunnel Element With Barge Immersion Under Wave Actions

The immersion of tunnel element is one of the most important procedures of immersion tunnel construction, in the process of which it is not only to guarantee the accuracy of the immersion into the bottom slot, but also to ensure the safety. In the actual immersion process, tunnel element is influenced by wind, wave, flow of ocean and barge. That is a very complicated hydrodynamics problems. Until now, there are less researches on the influence of barge to motion response of the tunnel element. In this paper, it is carried out for motion response of tunnel immersion under barge and wave with experimental and numerical investigation.The experiment is used to study the immersion of tunnel with single barge under regular wave. It is consisted of motion response and cable tension characteristic with single barge, and analyzes the influence of immersed depth and wave factors to motion response and cable tension. The result shows it is close between wave frequency motion of tunnel element in sway direction with and without barge, but the low frequency motion of tunnel element in sway direction with barge is for greater than without barge. Motion responses of tunnel element in heave direction with barge are little than those without barge, cable tension with barge is also little than without barge, but the cable with barge is state of tension all the time.At the same time, the influence is discussed fcr heave and sway motion of barge to those of tunnel in the tunnel-barge system, in which motion amplitude of tunnel in heave direction with barge is much smaller than without barge, but motion amplitude of tunnel in sway direction with barge is much greater than without barge.The experiment is also used to study the immersion of tunnel with single barge under irregular wave. It is analyzed for the frequency spectrum characteristics of motion responses and cable tensions, which has been influenced by the immersing depth and wave parameters. Spectrum analysis results show that with the immersion of single barge, it is major for low frequency motion of the tunnel element in sway, heave and roll directions. For low frequency of the tunnel in sway, heave and roll directions, it is same as the corresponding free damping of the tunnel. It is for peak amplitudes of low frequency motions of the tunnel with the barge for greater than without the barge in sway direction, but those with the barge are less than without the barge in heave and roll directions. It is tested for frequency analysis of cable tension that motion response spectrum curve of cable tension with barge is very small. With the increasing of Hs and Ts, it increases for motion response spectrum of the cable tensions, which reduces with the increasing of d.It is satisfied with the free water surface condition in the finite water depth for the time-domain Green function, which could solve the wave force on the runnel element by the boundary element method. The fourth order Runge-Kutta method is used to solve the time-domain motion equation of the tunnel element. It is developed for the time-domain numerical models of the tunnel element without barge. It is well for the verification on the approximate calculation of the green's function memory in the numerical model. The results of the tunnel element in the numerical model are according with those of physical model tests. At the same time, it is also established for the numerical model of mooring barge, and there are in good agreement for results between physical model tests and numerical model.It is proposed for the algorithm on the position variation of the tunnel element caused by heave motion of the mooring barge. Combined with time-domain numerical models of mooring barge and tunnel element without barge, time-domain numerical models of the tunnel element are developed with forced heave motion of the mooring barge under the wave. Using actual barge size, chain and wave parameters, heave motion responses of the mooring barge are obtained with applying numerical model of the mooring barge. It has calculated the motion responses of the tunnel element with the model under different wave conditions.