Aerodynamic simulation of the Bronx-Whitestone suspension bridge using computational fluid dynamics

Over the years, much research and many investigations have been pursued to{09} answer the question: Which mechanism is the main reason for the loss of stability of suspension bridges? Is motion-induced flutter or vortex-induced harmonic resonance the cause for structural instability? Flutter occurs at non-positive damping of the fluid-structure interaction system. Vortex-induced primary harmonic or lock-on happens when structural oscillations have the same frequency as the vortices of fluid flow.; The main topic of this thesis is to investigate critical stability conditions of the prototype Bronx-Whitestone Bridge in New York by way of three 1:60 physical section models that include the bridge's original form of 1939, its current state, and its future geometry after retrofitting. For this purpose, computational fluid dynamics (CFD) simulations are used to investigate the aerodynamic interaction of wind on suspension bridges. The computational results are compared with experiments performed at the wind tunnel laboratory of the University of Western Ontario, Canada.; Using AERO-F2D computer program developed by the Center for Aerospace Structures at CU-Boulder, the laminar CFD simulations based on Navier-Stokes equations provided the following observations: Simulations of the stationary section models did result in the comparable aerodynamic forces and similar Strouhal numbers. Aeroelastic simulations of three 2-DOF section models indicated that no vortex-induced primary harmonic instability developed in the form of lock-on. Instead flutter instability of the fluid-structure interaction system occurred: The flutter wind velocity was 132 mph for the retrofit section model. The CFD investigations did yield critical wind velocities which compare well with the experimental results from wind tunnel tests (144 mph for the retrofit section model).; At flutter velocity of the retrofit model, the following characteristics were revealed: Non-positive damping was developed in the fluid-structure interaction system. The motion-induced forcing frequency was the same as the structural motion frequency, and the vortex-induced forcing frequencies were fractional multiples of the structural motion frequency. The transverse motion frequency did coalesce with the torsional motion frequency.