Search

This study presents a system based on passively controlled leading- and trailing-edge flaps that is designed to suppress wind-induced instabilities such as flutter and torsional divergence. The utility of the approach is demonstrated on a three-dimensional bridge model. Particular emphasis is placed on the early stages of the deck erection process when the bridge is particularly vulnerable to flutter. The flaps are activated by the deck's movements though passive phase-compensating mechanisms comprising of springs, dampers and inerters. It is demonstrated that optimised compensator parameters, and optimum hinge locations, result in a substantially improved deck aerodynamic performance. Particular importance is given to ensuring that the controlled system has good closed-loop ‘robustness’ properties, or in other words, that the controlled system has a high tolerance to parameter variations and uncertainties in the system dynamics. The practical use of a nonlinear optimisation algorithm with a FE bridge aeroelastic model, which includes the flap dynamics, necessitates the use of reduced-order models. A novel model reduction procedure that is based on the retention of dominant poles is introduced into the aeroelastic modelling framework. Multimodal interactions are observed at the various erection stages and conclusions are drawn with regard to the contributions of various modes of vibration to aeroelastic instabilities. The main advantage of this approach lies on the passive system's simplicity and its ability to simultaneously increase the flutter and torsional divergence boundaries. The Humber Bridge in the U.K. is chosen as a study example for numerical simulations. [ABSTRACT FROM AUTHOR]

This paper describes experiments relating to the buffet response and control of a section of a long-span suspension bridge deck elastically mounted as part of a wind tunnel experiment. The bridge section is subject to grid generated flow turbulence. Two grids are used — one is a standard biplanar grid, while the second is a new design that provides larger turbulence length scales. The buffet response results are compared with admittances calculated using unsteady, three-dimensional, lifting-surface theory that extends standard two-dimensional Sears׳ theory. The bridge deck heave and pitch responses are predicted with comparisons made with wind tunnel measurements. In order to suppress buffeting, and increase the deck׳s critical flutter speed, the deck model is fitted with controllable leading- and trailing-edge flaps. Two sets of passive controllers, which use the flap angles as the control inputs, are demonstrated and evaluated for their capability to suppress the buffet response of the deck and increase its critical flutter speed. The first set of controllers sense the deck׳s position (pitch angle and heave, or pitch angle alone), whilst the second set (which are mechanical controllers) sense the vertical velocity of the flap hinge points. The control system design problem is solved as a mixed H 2 / H ∞ optimisation problem. The wind tunnel experiments show that these control systems can reduce considerably the deck׳s buffet response, whilst simultaneously increasing its critical flutter speed. [ABSTRACT FROM AUTHOR]

The aeroelastic behavior of suspension bridges under generic temporal and space wind distributions is studied employing a parametric one-dimensional structural model coupled with a strip-based indicial representation of the unsteady aerodynamic loads. The aeroelastic response to spatially nonuniform gusts is also investigated. The equations of motion linearized about the prestressed aerostatic equilibrium are expressed in terms of incremental kinematic variables. The aerodynamic loading characteristics of the deck cross sections of the Runyang Suspension Bridge (over the Yangtze river in China) are evaluated by means of computational fluid dynamics simulations performed to extract the aeroelastic derivatives from which the indicial aerodynamic representation is obtained. The aeroelastic equations of motion are then reduced to the state-space ordinary differential form by using the Faedo–Galerkin approach. The reduced-order bridge dynamics and the description of the aerodynamic loading via the added aerodynamic states are solved simultaneously by using a time-integration numerical scheme. Dependence of the flutter condition and the transient response to gusts is shown through systematic parametric studies. [ABSTRACT FROM AUTHOR]

Two vortex-induced vibration (VIV) events of the main girder of long-span bridges successively happened on the Yingwuzhou suspension bridge and Humen suspension bridge in China, 2020, and drew public attention. Especially for the Humen suspension bridge, the amplitude of VIV was so notable that the traffic was closed for 10 days. Generally, VIV is sensitive to the structural and ambient issues and large-amplitude VIV is unacceptable for engineering structures as it could result in potential fatigue failure of some key joint components. Therefore, it is of great significance to explore the excitation mechanism of VIV and develop effective methods to mitigate excessive vibration of main-girders. From the perspective of vortex dynamics, we present a selective review of recent progress on the mechanism of VIV occurred in long-span bridges and aerodynamic countermeasures to attenuate the VIV amplitude. Notwithstanding the VIV mechanism of girders has not been thoroughly clarified, it is generally accepted that VIV rises from the unsteady vortex shedding from the main girder. Besides, the flow control methods, which are proposed to manipulate the surrounding flow patterns around the girder, are also focused in this review. Some perspectives are finally presented for future studies in fluid–structure interaction and aerodynamic vibration mitigation of long-span bridges. [ABSTRACT FROM AUTHOR]

The complex wake-induced vibrations (WIVs) of four aligned hangers behind a bridge tower were numerically simulated. The aligned hangers were simplified to two-dimensional spring–mass–damperdynamic models, and the hanger collisions were described with a rigid impact model. The Newmark - β method was employed to calculate the hanger oscillations with the user-defined function embedded in the numerical Computational Fluid Dynamics (CFD) simulations. The flow fields around the bridge tower for various yaw angles were simulated first to analyse the wake velocities at the hanger point. Subsequently, the characteristics of the hanger vibrations and the correlations between the hanger vibrations and tower wake were studied. The mechanism of the hanger collisions was revealed by analysing the differences between the aerodynamic coefficients of the hangers. Finally, the changes in the characteristic size of the tower and incoming wind speed were investigated to explain the occurrence of the violent WIVs of the hangers behind the bridge tower. [ABSTRACT FROM AUTHOR]