Study On Hydrodynamic Of Compound Sft Anti-Vibration System

Submerged floating tunnel(SFT)is an innovative cross-sea traffic structure,which mainly relies on buoyancy and cable tension to maintain balance.In practical engineering,SFT has worked in a complex marine environment for a long time.Under waves and currents,the SFT tube body and its mooring system are prone to large vibrations,which not only makes the motion response of the SFT tube body exceed the allowable value of the specification(translational±0.3m,rotation ±0.5°),but also affects driving safety and comfort.So how to restrain the structural vibration of SFT is one of the scientific problems that affect its transformation from imagination to reality.Therefore,a compound SFT anti-vibration system is innovatively proposed in this paper.The hydrodynamic characteristics of the system are studied by numerical simulation and physical test respectively.The main research contents and conclusions are as follows:(1)Compound SFT anti-vibration system is composed of SFT and floating energy dissipation device.The SFT adopts a three-tube structure to increase the anti-rotation ability of the SFT.At the same time,a rigid truss is installed below the tube body to improve the anchorage stiffness of the SFT.The floating energy dissipation device is composed of a box type floating breakwater with ballast water and the PVC blocking medium under it.The ballast water and floating breakwater form a tuned liquid damper,which greatly reduces the movement of floating breakwater and increases the performance of wave dissipation.The PVC medium can effectively interfere with the flow field.(2)Based on coupled Euler-Lagrange method,the numerical model of compound SFT anti-vibration system without ballast water was established with ABAQUS/Explicit module,and the hydrodynamic characteristics of SFT under different wave heights and different wave periods were calculated.The numerical results show that the maximum motion response of the SFT is 0.167 m in translational motion and 0.0026° in rotation.It can be known that the motion response of the compound SFT anti-vibration system under general sea conditions is within the standard allowable value,which fully verifies the feasibility of the compound SFT anti-vibration system.(3)Physical model tests were carried out on four SFT structures containing compound SFT anti-vibration system.The results show that the compound SFT anti-vibration system has the best hydrodynamic characteristics.Under the condition of 48 mm high wave height,the maximum motion response values of the compound SFT anti-vibration system model in three degrees of freedom directions(swing,heave and roll)are 0.993 mm,0.108 mm and 0.052°,which are only 7.5%,9.3% and 1.65% of the traditional SFT model,respectively.The vibration suppression effect in the translational direction is more than 10 times.The vibration suppression effect of rotation direction is more than 60 times.(4)The influence of different draft depths of the buoyancy tank in the floating energy dissipation device is studied.The results show that the vibration suppression effect is the best when the ballast water which makes the draft of the buoyancy tank reach 1/2 of its height is added.When the wave height is48 mm,the vibration suppression effect of the model with 1/2 ballast water is 6.5times better than the model without ballast water.The vibration suppression effect increases with the decrease of the wave height,and can reach 27 times when the wave height is 18 mm.When the wave-current load acts at the same time,the PVC flow blocking structure can effectively inhibit the flow load,and the influence of the flow load on it will make the floating energy dissipation device further reduce the wave energy.