Study On Mooring Cable Pulling Force Of Submerged Floating Tunnel Based On Buoyancy Weight Ratio

In the progress of scientific and technological innovation in transportation,highway tunnels have overcome mountains on land.However,there is no perfect solution to construct highway tunnels in oceanic trench and deep seas.Therefore,Submerged Floating Tunnel(SFT),as a trans-deep-sea mode of transportation,have attracted much attention.The Submerged Floating Tunnel(SFT)with tension legs is constrained by mooring cable.However,the mechanical response of mooring cable under the action of waves and currents is still unclear.Supported by the Ministry of Transport’s scientific and technological project “Preliminary study on Key Technologies of deep-sea Submerged Floating Tunnel”,and based on tunnel design theory and fluid mechanics theory,the mooring cable tension of SFT under different floating weight ratios is studied comprehensively in this thesis through large-scale solid model test.Classical load calculation equation of SFT is adopted and the hydrodynamic numerical simulation model is also combined in this research.Specific research contents and results are as follows:(1)The tension calculation equation of SFT mooring cable suitable for different buoyancy weight ratio(BWR)is established.The reasonable calculation model is selected and the detailed calculation process is enumerated.According to SFT’ s own characteristics and boundary conditions,Airy wave theory is optimized and adjusted,and Morison equation is improved.Besides,a new Morison equation suitable for SFT stress calculation is given.The results show that the phase of tension curves of mooring cable on both sides is half a period different,and the tension amplitude of mooring cable on the wave-front side is 3.35 times of the tension amplitude of mooring cable on the back-wave current side.The amplitude of tension vibration of mooring cable increases uniformly with the increase of wave height,and the tension of mooring cable appears negative at 14.0 M wave height,resulting in tension relaxation.The tension of anchor cable appears negative when the buoyancy weight ratio(BWR)is 1.1,which proves that tension relaxation occurs.(2)The cable tension of the large scale(1:40)tension leg SFT model is studied.Wave-current coupling experiment,which is a very advanced technique at home and abroad is adopted in this research.The results show that the tension amplitude of anchor cable under irregular wave action decreases by 33.6% compared with that under regular wave action.Under the action of regular wave,the peak tension of anchor cable on the back wave side increases by 6.5% compared with that on the front wave side,while it increases by 4.1% under the action of irregular wave.The maximum tension of tension leg SFT under 18.0 cm wave height is 12.7% higher than that under irregular wave.(3)The numerical model of tension leg SFT pipe segment with 160 m length is established by using ANSYS platform.It is concluded that when the wave height is 12.0m and 14.0m,the tension appears zero and the tension relaxation occurs.Meanwhile,the SFT presents an unstable state.When the amplitude of tension is at 14.0m wave height,the jumping growth occurs with the result of “impact tension”.When BWR is 1.1,the phenomenon of “impact tension” appears.The phenomenon of “impact tension” appears when the angle of anchor cable is 0 degree.(4)Last,three reasonable mooring cable arrangements on cross section are designed,and three numerical simulation models are established.When BWR is 1.1,the “impact tension” phenomenon of mooring cable occurs under the three laying modes.Under the “W” type anchor cable,the change of tension is relatively stable,and the change of tension extremum and tension amplitude with the change of BWR is small,which indicates that the “W” type anchor cable has better restraint on SFT.