Research Output
1 - 6 of 6
Publication
Applying Computational Fluid Dynamics Simulations for Aerodynamic Studies of Long-span Bridges
2022, Zhang, Yuxiang, 0000-0003-2044-1199
In the design of long-span bridges, estimating the wind effects is a critical requirement to evaluate and eliminate the risks of wind-induced problems on structural safety and serviceability. This thesis aims to validate the use of Computational Fluid Dynamics (CFD) simulations in bridge aerodynamic studies. A comprehensive review of the literature on the use of wind tunnel testing and CFD modelling for wind issues on long-span bridges was prepared. The lack of confidence of the bridge industry in applying CFD simulations within the design process due to insufficient validation and standardized guidance for use was noticed. Also, the need for a robust workflow for CFD modelling of wind effects for long-span bridge design and bridge operation was identified. Hence, a workflow using open-source software was proposed, which can be conveniently adopted to investigate bridge aerodynamics in bridge engineering practice. A general guidance was also formed where examples were provided to demonstrate specific features. A group of three-dimensional (3D) Reynolds-Averaged Navier-Stokes (RANS) simulations and Detached Eddy simulations (DESs) were performed on sectional bridge deck models at a scale of 1/50. These simulations replicated wind tunnel tests conducted during the design of the Rose Fitzgerald Kennedy bridge in Ireland. Sensitivity studies of the mesh, domain sizes, and turbulence models were conducted during the development of the CFD model, and showed that these factors have appreciable effects on the results of the CFD simulations. When comparing aerodynamic coefficients calculated by simulations and wind tunnel tests, a general agreement was achieved though some discrepancies were found. Similar levels of discrepancies were witnessed in the literature and was most likely due to the sensor interference during wind tunnel tests. In addition, the effects of secondary structures on the aerodynamic coefficients of bridge decks were investigated and shown to be significant. This emphasized the necessity to include these secondary structures when investigating bridge aerodynamics, while existing studies in this area often neglect them. A group of full-bridge simulations were performed at full scale, which was the first to include boundary conditions mapped from Weather Research and Forecasting (WRF) simulations, a high-precision terrain model, and a full-bridge geometry with all the secondary structures. The pseudo-transient time history of wind velocities determined by CFD simulations achieved an extraordinary agreement field measurement data from sensors at multiple locations on the bridge, which was also unprecedented in this area. Results of these full-bridge simulations are also used to initialise simulations at local regions of bridge deck segments. Validations of these local simulations were completed through comparisons of wind velocities predicted by local simulations, full-bridge simulations, and field measurement data. Aerodynamic forces are calculated from these local simulations and compared with results determined by wind tunnel coefficients with field measurement data, Eurocode equations with field measurement data, and Eurocode equations with estimated wind velocities. Aerodynamic forces predicted by CFD simulations were shown to align with the philosophy of sustainable design. Overall, this thesis provided unprecedented validations for the use of CFD simulations at multiple geometric scales. It demonstrated the great performance of CFD simulations in investigating wind effects under realistic wind conditions, which are often challenging for wind tunnel tests to incorporate. The outcome of this thesis is being presented to the NSAI National Committee on revision of the National Annex of the Eurocode on Wind (EN 1991-1-4). But most importantly, great confidence can be drawn from the outcome of this thesis, in using CFD simulations as a robust approach to estimate wind effects on long-span bridges.
Publication
Quantifying the impact of bridge geometry and surrounding terrain: wind effects on bridges
2023-05-15, Zhang, Yuxiang, Sweeney, Conor, Cardiff, Philip, Cahill, Fergal, Keenahan, Jennifer
The safety and serviceability of long-span bridges can be significantly impacted by wind effects and therefore it is crucial to accurately estimate them during bridge design. This study develops full-scale 3-Dimensional CFD (computational fluid dynamics) simulation models to replicate wind conditions at the Rose Fitzgerald Kennedy Bridge in Ireland. The neglection of bridge geometries and the use of small scales in previous studies are significant limitations, and both the bridge geometry and surrounding terrain are included here at full-scale. Input values for wind conditions are mapped from weather simulations that apply the Weather Research and Forecasting (WRF) model. Wind velocities at four different points calculated by CFD simulations are compared with corresponding data collected from SHM field measurements. The calculated time-averaged wind velocities at four different locations on the bridge are shown to have relative differences of less than 10% to the measured wind velocities by anemometers 90% of the time. The maximum relative difference among all comparisons was only 15%, shown to be partially due to the inclusion of the full bridge and terrain geometry.
Publication
A Numerical Study of the Effect of Wind Barriers on Traffic and the Bridge Deck
2020-08-28, Keenahan, Jennifer, Zhang, Yuxiang, Cardiff, Philip
Wind actions can have a great impact on both bridges and traffic on bridges. However, structures designed to shelter the traffic from wind can influence the aerodynamic performance of the bridge deck, especially for long-span bridges. This study compares the effect of non-perforated walls and perforated walls used as wind barriers for traffic by conducting Computational Fluid Dynamics (CFD) simulations on three-dimensional geometries of a four-lane bridge deck. Steady-state simulations employ the Reynolds-Averaged Navier Stokes (RANS) method with the k-epsilon turbulence model and all simulations use parallel computing. An open-sourced software OpenFOAM is used.
Publication
Assessing the Capability of Computational Fluid Dynamics Models in Replicating Wind Tunnel Test Results for the Rose Fitzgerald Kennedy Bridge
2021-12-19, Zhang, Yuxiang, Cardiff, Philip, Cahill, Fergal, Keenahan, Jennifer
Despite its wide acceptance in various industries, CFD is considered a secondary option to wind tunnel tests in bridge engineering due to a lack of confidence. To increase confidence and to advance the quality of simulations in bridge aerodynamic studies, this study performed three-dimensional RANS simulations and DESs to assess the bridge deck aerodynamics of the Rose Fitzgerald Kennedy Bridge and demonstrated detailed procedures of the verification and validation of the applied CFD model. The CFD simulations were developed in OpenFOAM, the results of which are compared to prior wind tunnel test results, where general agreements were achieved though differences were also found and analyzed. The CFD model was also applied to study the effect of fascia beams and handrails on the bridge deck aerodynamics, which were neglected in most research to-date. These secondary structures were found to increase drag coefficients and reduce lift and moment coefficients by up to 32%, 94.3%, and 52.2%, respectively, which emphasized the necessity of including these structures in evaluations of the aerodynamic performance of bridges in service. Details of the verification and validation in this study illustrate that CFD simulations can determine close results compared to wind tunnel tests.
Publication
A numerical study on the sheltering effects of the central wind barriers on the Rose Fitzgerald Kennedy Bridge
2022-08-26, Zhang, Yuxiang, Cardiff, Philip, Sweeney, Conor, Cahill, Fergal, Keenahan, Jennifer
This study aims to examine the sheltering effects of central wind barriers installed near the pylons of the Rose Fitzgerald Kennedy Bridge. A full-scale Computational Fluid Dynamics (CFD) model is developed, which includes high-precision geometries of the bridge and the terrain. Simulations using this model are performed at realistic wind conditions as boundary conditions are mapped from mesoscale Weather Research and Forecasting (WRF) simulations. Wind velocities at multiple locations on the bridge predicted by the CFD simulations are compared with field measurement data where a good agreement is reached. The validated model is then applied with bridge geometries with and without the central wind barriers at high wind conditions. Comparisons between these two groups of simulations show that the wind barriers can effectively reduce wind velocities on traffic lanes near the pylon, which validates the current design of the barriers on the bridge.
Publication
Wind-Induced Phenomena in Long-Span Cable-Supported Bridges: A Comparative Review of Wind Tunnel Tests and Computational Fluid Dynamics Modelling
2021-02-11, Zhang, Yuxiang, Cardiff, Philip, Keenahan, Jennifer
Engineers, architects, planners and designers must carefully consider the effects of wind in their work. Due to their slender and flexible nature, long-span bridges can often experience vibrations due to the wind, and so the careful analysis of wind effects is paramount. Traditionally, wind tunnel tests have been the preferred method of conducting bridge wind analysis. In recent times, owing to improved computational power, computational fluid dynamics simulations are coming to the fore as viable means of analysing wind effects on bridges. The focus of this paper is on long-span cable-supported bridges. Wind issues in long-span cable-supported bridges can include flutter, vortex-induced vibrations and rain–wind-induced vibrations. This paper presents a state-of-the-art review of research on the use of wind tunnel tests and computational fluid dynamics modelling of these wind issues on long-span bridges.