Research On Extreme Wave Force On Coastal Bridge Based On Space-time Finite Element Method

With the vigorous development of transportation industry and the development of coastal engineering,coastal bridges are an important part of the “21st Century Maritime Silk Road”.More and more coastal bridges are being built and developed in the outer seas and deep seas.However,the marine environment in which coastal bridges are located is extremely complex and will be greatly threatened by complex extreme disasters such as typhoons and tsunamis.At present,the interaction of the extreme waves and large-scale coastal bridges has not been effectively solved at home and abroad.Most of the research in this area is in the initial stage,lacking systemicity and integrity,which has restricted the safety construction of coastal bridges.This paper mainly studies the two-phase flow-structure coupling problem based on the space-time finite element method:(1)The fluid mechanics governing equations are briefly introduced firstly.The mechanism of the time-space finite element method using the streamlined upwind Petrov–Galerkin method to solve the numerical oscillation problem in fluid field calculation and the variational multi-scale method for turbulence problems are introduced in detail.The space-time finite element variational formula of fluid control equations is deduced in detail,and a parallel iterative solution program is written for the two-dimensional hydrodynamics problem.The validity and accuracy of the program are verified by the simulation of the cavity and the dam break cases.(2)The gap between the traditional bridge design and the finite element analysis of the bridge structure will complicate the design and analysis process.To realize the integration of computer-aided design and structural finite element analysis in area of the costal bridge,NURBS is constructed as basic function of an isogeometric analysis framework.It also provides an accurate and simple way to construct and analyze complex structures.(3)In the wave forces problem of coastal bridges,the simulation of waves involves fluids with both air and water characteristics.This paper introduces the use of the space-time finite element method to solve the coupling formula of fluid control equation and Level Set equation to realize the interface capture of two-phase flow field problem,and verified with many classical examples.(4)Using the combination of experiment and numerical simulation to study the fluid-structure coupling problem in the actual coastal bridge engineering and use the experimental data to test the numerical method proposed in the paper.The study of the extreme wave forces on the deck with box girder of coastal bridge are carried out by experimental measurements and numerical simulations.The results show that the space-time finite element algorithm and the Level Set method can accurately simulate the wave generation,propagation and breaking,and accurately calculate the wave forces on the bridge.When the superstructure of the coastal bridge is higher than the still water level,the impact wave force cannot be ignored.In the horizontal direction,the total wave forces can reach twice the quasi-static forces;there have differences on the wave force between the superstructure of the box girder and the T-type girder.The study of the wave force on the box girder section has great significance for the construction of China’s coastal bridge.Based on the experimental and numerical results,the estimation formula of the wave forces on the superstructure can provide some references for the design of the coastal bridge.