WIND INDUCED VIBRATION OF A LONG SPAN BRIDGE USING COUPLED FIELD ANALYSIS

Abstract

Aeroelasticity involves the interaction between elastic forces, inertia forces and the aerodynamic forces. These interactions were not considered in the civil engineering community till the 1940 Tacoma Narrows bridge collapse when a bridge which was designed for a static wind speed of 100 miles per hour, had collapsed after violent oscillations at about 42 miles per hour, nearly half its design speed. The forces acting on a structure placed in a fluid medium depends on the displacement of the structure. A change in the displacement will produce a change in the force, which again changes the displacement. This makes an aeroelastic problem a typical fluid-structure interaction problem. In the past many numerical and experimental methods were suggested by various researchers for such problems. Most of the numerical methods were based on the quasisteady fluid dynamics approximation. which was later found to be invalid for bluftsectioris. where the forces produced depend on the vortices generated, which the quasi-steady theory failed to predict. The experimental methods mostly performed in the wind tunnels were expensive and time consuming. In the present work, one of the critical aeroelastic phenomena called flutter is studied using coupled field analysis performed using a commercial finite element package and a computational fluid dynamics package called Mechanical APDL and FLUENT respectively. The fluid and the structural solvers were coupled using a strong synchronous coupling algorithm of ANSYS 14.0. that manages the interpolation and mapping of data between the two solvers. The deformations being large a remeshing algorithm is used instead of the Arbitrary Langrangian Eulerian description of the mesh motion. The flutter velocity of a typical rectangular cantilever plate is developed in this study. The response of a suspension bridge to a simulated wind gust as well as its flutter velocity is obtained by performing a coupled field analysis. The results of a coupled field analysis always have to be validated. With the availability of higher computing powers along with the parallel processing capabilities of the new solvers, the numerical simulation using coupled field analysis along with suitable validation studies, can replace the wind tunnel testing to a great extent which can minimize the cost and the time for performing such experiments.