Numerical Study On Nonlinear Aerodynamic Forces On Typical Bridge Decks

Large-span flexible bridges got rapidly development these years, of which stiffness and damping are lower than that of small bridges, highlighting the problem of nonlinear aerodynamic forces with large scale wind-induced vibration. CFD technology obtained widely application in bridge wind-resistance area these years as a consequence of complement of computational fluid dynamics and rapidly development of computer property. This paper conducted 2D static and dynamic simulations of flow fields around two typical bridge deck sections by means of CFD, then studied the aerodynamic nonlinearity under different cases, main works are as follows:(1) Summarized the state of art of aerodynamic forces on bridge deck sections and application of CFD in bridge wind-resistance area;(2) Introduced the basis theory of wind effects on bridge structures and CFD;(3) 2D flow simulations are conducted over thin plate, streamlined bridge deck and bluff bridge deck, respectively, variations of aerostatic coefficients and surface pressure distribution of deck sections are studied with different attack angles and fillet radius of bottom plate;(4) Identification method of flutter derivatives are introduced, vertical and torsional forced vibration are performed on thin plate and the two typical bridge decks, the influence of reduced velocity, initial attack angle and vibration amplitude on flutter derivatives are studied combined with the surface pressure distribution and flow field visualization.(5) Analyzed the nonlinearity of aerodynamic forces on typical bridge decks, indicated the existence of remarkable high-order components in case of large amplitude vibration, then deduced the nonlinear aerodynamic force expression based on Taylor expansion at equilibrious position both under 1 Degree-Of-Freedom (DOF) and 2 DOF vibration. Combined with the Fast Fourier Transformation and the least square method, identified the nonlinear parameters of aerodynamic forces obtained in numerical simulation, the reliability of the nonlinear aerodynamic force expression was validated by reproducing the aerodynamic forces by those nonlinear parameters, which were much more closed to the initial values than that obtained by flutter derivatives.