Dynamic Response Research Of Submerged Floating Tunnel With Local Cable Breakage Event And Progressive Collapse Phenomenon

Submerged floating tunnel(SFT)is a new type of transportation structure that can span wide deep water and strong environmental capacity,SFT has a huge advantage in the form of conventional traffic structures,such as the original marine environment,and mechanics indicators(tube bending moment,torque,anchor cable force,etc.)and unit economic costs will not change as significant changes with the increase of the length of the strait.It is foreseeable that the impact of SFT in marine transportation sectors will be revolutionary and profound and will receive more and more attention and favors from the engineering community and academia.However,due to the specificity and novelty of its structural form,there is still a lot of understanding of its safety and stability,and there are still many problems in engineering practice,which has never become a reality.Once anchor cable breaks,once it happens,it will inevitably cause the power response of the SFT to change dramatically,and then cause heavy distribution,which may even result in the exposition of the overall structure.In order to avoid engineering disasters due to anchor assessment,this study conducted a series of numerical simulations and experimental research on the hydraulic behavior of SFT under the breaking of anchor cable.By simulating the cable breakage behavior and progressive collapse phenomenon,the different influencing factors for the overall dynamic response of SFT is analyzed,such as wave and current parameters,BWR and cable breakage ways,etc.To provide a scientific reference basis for practical engineering design.The main research results are as follows:(1)The finite element analysis software ANSYS/AQWA establishes SFT numerical model,and the simulation of the failure behavior and progressive collapse phenomenon is established based on the life and death unit function in ANSYS/AQWA.the dynamic response behavior of SFT under cable breakage event are studied.The results show that after the cable breakage event,the impact effect of remaining anchor cable is induced,and the cable transient amplitude is gradually decreasing with the increase in the distance of the breaking position,and the tension variation amplitude of the opposite-side anchor cable the magnitude of the force is significantly larger than the same-side anchor cable;due to the SFT is a limited stiffness system,the movement of the tube has a compliant,in different wave and current environments,the transient effect of SFT is not obvious under the cable breakage event;The dynamic response of floating tunnel caused by regular wave,uniform flow and anchor cable breaking has different characteristics:regular waves mainly cause periodic motion of the structure,uniform current mainly causes the low-frequency motion and a large deviation of the structure,and the cable breakage effect mainly produces impact effects and high-frequency vibrations on the structure.(2)a specially designed anchor cable breakage device is presented to simulate the cable breakage event and the subsequent progressive collapse of SFT.It can effectively control the triggering conditions of cable breakage behavior with force control and timing control;A boundary constraint simulation method based on the numerical tool is adopted to obtain the parameters values of boundary constraint.The experimental data are observed to conform well with the numerical calculation results used for validating the test with boundary constraint.It is deemed that the present test model is capable of providing a sufficiently accurate analysis for the hydrodynamic behaviors of the SFT.Therefore,in order to simplify the experimental result,the free boundary is adopted,and it can be used to regular exploration of hydraulic behavior of SFT under wave and current.(3)Based on the physical model test results,The dynamic performance of the SFT under cables breakage is comprehensively investigated based on varying effect factors,e.g.,wave period,current velocity,BWR,and cable breakage sequence.The results from the test indicate that response variation assessment,transient effect,redistribution of forces,and impact force for the SFT under cable breakage in different cases are key to determine probability of occurrence of instability and progressive collapse.In the case of combination of regular wave and current,due to combined effect of the wave-current coupling and impact induced by cable breakage,sway of tube is sharply increased.The motion curve becomes irregular and unstable,and the increased amplitude is obviously larger than the sum of other two loading states cases;After the progressive collapse,the tube motion trace is diverging and dramatically varied,and shows more random characteristics.The progressive collapse happens dramatically and rapidly,which is difficulty for engineering prediction and disposition.The presented study can be helpful to the design strategy of redundancy,progressive collapse resistance capacity,prevention and control hazard system under local cables breakage for mooring system of SFT.