Investigations of aerodynamic coefficients and flutter derivatives of bridge decks by using CFD Approach

• Main Authors: Hung-Yi Lin, 林紘毅
• Other Authors: 林堉溢
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/ucauvm

碩士 === 淡江大學 === 土木工程學系碩士班 === 106 === Duo to the improvement of bridge engineering technology, the bridge span is getting longer and the wind response is more significant. Therefore, the wind tunnel experiments of long-span bridges have become more important. But the time consuming and the high costing are the weak points of wind tunnel experiments. Contrary to wind tunnel experiments, CFD simulations can obtain full-field physical variables with time and be becoming one of the mainstreams in wind engineering. In this study, the main methodology is 2D CFD simulation associated with the wind tunnel experiments to investigate the aerodynamic behavior of bridge decks. The method of flutter derivatives identification is based on forced vibration. This study is divided into three parts, the first one is to use CFD simulation to analyze the wind force coefficients and the flutter derivatives of a rectangular cross-section with B/D=10. The second part is using the similar configurations of the B/D=10 to analyze the bridge decks with B/D=5 and B/D=20. The third part is adopting the similar parameters to analyze the Kao-Ping-Hsi cable-stayed bridge. In this study, we use the preprocessing software Pointwise to arrange the calculating domains and then generate the meshes and set up the boundary conditions. Then we use the Ansys Fluent to simulate flow fields around the bridge decks. Through the tests of the parameters in the case of B/D=10, the optima parameters are identified which are then used to analyze the force coefficients in B/D=5 and B/D=20. There are good agreements in angles of wind attack between 4 and -4 degrees, but with some error in the larger attack angles. The force coefficients of Kao-Ping-Hsi cable-stayed bridge have similar trends with the results of wind tunnel experiments. However the larger errors occur when the wind attack angles are more than 5°. The results of the flutter derivatives in the case of B/D=5 and B/D=20 show that the overall trends are fairly well. Compared to the experiments the flutter derivatives of the Kao-Ping-His Bridge have good agreements with the wind tunnel experiments in the direct flutter derivatives but have some discrepancies in the cross flutter derivatives. According to the above comparative results, this study provides a reliable CFD approach for 2D simulations of bridge decks. A rapid 2D CFD simulation can be as the preliminary assessment of aerodynamic coefficients and flutter derivatives before the wind tunnel experiments are performed.