Investigation On Hydrodynamic Responseof Bridge Substructure Based On The Two-way Fluid-structures Interaction

With the rapid development of China's transportation industry,a large number of Cross-sea Bridges is fast increased.Due to the complexity and changeability of the marine environment,the Cross-sea Bridge is subjected tovarious loads such as the wave force and the current force with performing the traffic function.Moreover,the substructures of the bridge suffer fatigue loadingwhich may result incatastrophicdamage after long time.Therefore,it is of great importance to investigating the mechanical characteristics of the substructure of the Cross-sea Bridge with both theoretical and simulated analysis.In present study,a three-dimensional numerical wave flume model,a three-dimensional numerical currentflume model,and a three-dimensional numerical wave current flume model were developed,based on the related theory and combinedthe theoretical analysis and the numerical simulation method.The force characteristics of different forms of bridge piers and group pile-cap structures under the uniform current,the wave force,and the wave current force were analyzed in detail.Furthermore,the related laws of itsinfluence factors were summarized.The main research contents are given as follows:Firstly,taking the linear wave as incident wave and based on the potential flow theory and Shear Stress Transport k-?(SSTKW)turbulence model,a three-dimensional numerical wave flume model was established by accessing the user subroutine,adopting the VOF method,and applying the finite volume method,in order to accurately reflect the real situation.The related parameters of present model were determined by comparingthe differences between the theoretical and numerical wave faces.The validity and accuracy of the established model are verified by the classical flow around the cylinder.Accordingly,the variation law of the maximum horizontal wave forces and the maximum displacements of the structure are analyzed under the different structural size and water depthwith and without coupling interactions of the two-wayfluid-structure.Secondly,the results of the current force and the wave forcefor thesmall scale pier attained bypresent model match well with those predicted by Morison equation.The variation laws of pier wave force with flow velocity,wave height,and wave length aresummarized.In addition,detailed analysis iscarried outon round end pier and dumbbell type pier,which had no reference data in the specification.Furthermore,the region of C_D of theround end pier is given and the responses characteristic of the dumbbell type pier are obtained.In addition,based on the above method,numerical simulation is adopted to analyze the current action and wave action of pile row with l/D<4.Numerical results demonstrate that the interference effect and shielding effect are reflected well in the numerical simulation.Thirdly,According to the MacCamy diffraction theory,the wave force of the large scale round end pier and square end pierare analyzed.Using the numerical simulation method,the modified Morison equation is obtained and the wave diffraction coefficient is determined.In addition,the flow field of circular pier with fluid-solid coupling under the wave current force is analyzed;the formulation of the structural dynamic equation of wave flow coupling is obtained;and the wave current force characteristics are analyzed.In light of above,the influences of flow velocity,section size,section shape,and angle of wave flow on wave flow force are discussed in detail.Finally,the numerical model of group pile-cap structure under the action of current andwave is established.The influences of water flow velocity and wave height on the structureare investigated.The effects of submergence depth,wave inflow angle,cross section shape,and pile group number are analyzed.Combined with the results of the theoretical analysis and numerical simulation,the influence of the group pile arrangement is analyzed,and the differences between the simulated results and the experimental resultsare comparedaccording to the engineering examples.In view of the above analysis,some suggestions for the bridge substructure design are put forward.The present workreveals the response of cross-sea bridge pier under the action of wave and current,in which the changing rule of the bridge foundation is studiedwith group piles and cap changed under wave current force.Moreover,it provides a theoretical basis and guidancefor further research such as multi-field coupling and optimization design of actual engineering...