Wind-induced vibration of super-long-span bridges is a major concern for bridge designers. The wind can induce problematic vibration in two different ways. One way is the vibration induced by the periodic shedding of vortices that are enhanced by coupling with bridge motion; this is Vortex-Induced Vibration. The second way is the high-speed winds associated with severe storms; in this situation, flutter, among other fluid-structure interaction phenomena, is a major concern for its catastrophic nature. Thus there is a need to enhance the design technology through the development of improved computational capability that takes into account critical fluid mechanical phenomena that potentially induce problematical vibration of flexible bridges. A multi-disciplinary research effort devoted to advanced modeling of flexible long-span suspension bridges is planned. The research is targeted to the development, validation, and application of relatively sophisticated analysis tools to model highly unsteady flow over bridge decks associated with uniform and other important wind conditions and with the nonlinear flexible structures with torsional, bending, and axial modes excited. The main focus of this research is the development and application of new reduced-order models based on unsteady aerodynamic non-linear indicial functions to investigate long-span wind-induced bridge-structure vibration with two major outcomes: (i) the availability of powerful and affordable computational tools for aeroelastic predictions in bridges and (ii) an improved understanding of the aerodynamic instabilities, their triggering mechanisms and hints on how to prevent them.
With the development of advanced aeroelastic modeling and computational techniques, engineers will be able to examine the inherent structural flexibility of long-span bridges coupled with aerodynamic nonlinearities due to fluid-structure interactions. The broader understanding of how elastic structures respond to wind should lead to new design criteria and insights for new design paradigms for long span bridges, wind turbines, skyscrapers, only to name a few. The results of this research will advance the knowledge of nonlinear fluid-structure interaction modeling of long- and super-long-span bridges and many other flexible structural systems exposed to aerodynamic loading. The results will also be useful to the engineer interested in retrofitting existing bridges with passive and active flow controls and other modifications as well as help engineers interested in developing improved structural health monitoring strategies.
Wind-induced vibration of super-long-span bridges is a major concern for the bridge designer. There is a need to enhance the structural design technology, through improved computational capabilities, which is critical for a better understanding of fluid-flow physics that induces vibration and of fluid-structure dynamics of flexible bridges. This research targeted the development, validation, and application of relatively sophisticated analysis tools to model: (1) Highly unsteady flow over bridge decks associated with even uniform wind conditions. (2) Nonlinear flexible structures with torsional, bending and axial modes excited. Even with the currently available computational tools, it is prohibitive to perform detailed structural finite element analysis and complete flow field Computational Fluid Dynamics (CFD) simulations with the purpose of evaluating the dynamics of Fluid-Structure Interaction (FSI) of large complex systems. As an outcome of this project the team developed general purpose efficient Reduced-Order Models (ROMs) that have been specialized for super long-span bridge aeroelastic predictions. Under the support of the NSF grant # 1031036, innovative computational tools have been developed. In particular: - A fully nonlinear parametric model of suspension bridges has been derived and validated by analyses characterizing the static and modal characteristics of two existing bridges. Torsional divergence and flutter phenomena have been investigated. - The aerodynamics of typical deck cross sections have been fully described through CFD simulations by the use of a mesh-free discrete-vortex method implemented in DVMFLOW, including viscous effects and the flow separation characterizing sharped-edge boxed sections have been captured and included in the time- and frequency-domain description of the aeroelastic loads. - Nonuniform (in space and time) wind distributions have been modeled and the effects of the flow nonuniformity on the critical flutter condition have been highlighted. - The capability to assemble parametric frameworks accounting for structural and aerodynamic nonlinearities to study the post-critical aeroelastic behavior of slender structures and investigate the Limit Cycle Oscillations (LCOs) occurring in the post-flutter wind speed regimes has been demonstrated. - Computationally efficient ROMs have also been successfully developed to reduce aerodynamic and aeroelastic computational efforts. The project outcomes and findings in support of the NSF intellectual merit criteria are as follows. - The team developed advanced aeroelastic modeling and computational techniques, enabling engineers to examine the inherent structural flexibility of long-span bridges coupled with aerodynamic nonlinearities due to FSI. This work advances the nonlinear modeling of flexible structures. - The team applied advanced fluid dynamics computational modeling tools to study nature of the highly unsteady flows associated with wind-bridge-structure interaction and developed enhanced indicial models of the unsteady aerodynamic loads. - The team developed nonlinear unsteady aerodynamics ROMs and fully nonlinear flexible structure models using model-reduction tools, nonlinear state descriptions for fluid-structure dynamics, and nonlinear indicial formulation. The project outcomes and findings in support of the NSF broader impacts criteria are as follows. - The team provided a broader understanding of how elastic structures respond to wind which should lead to new design criteria and insights for new design paradigms for long span bridges, wind turbines, skyscrapers, only to name a few. - The project supports two MS students, two PhD student, and involves 9 undergraduates and one Junior High (k-9) student. A first-year graduate class in aeroelasticity of flexible structures and the art of constructing ROMs was developed and delivered during the Fall semester 2012. Several archival publications including Journal and Conference Proceedings, as a direct result of this project and related activities, currently 42, are used as the primary vehicle for dissemination of major findings and discoveries. Presentations were also made at national and international conferences, currently 15. The successful Clarkson Pipeline Programs has been tapped to ensure that women and underrepresented minorities were involved in this project, 5 female students have been involved in this project.
