| 摘要(英) |
In recent years, the number of natural disasters have increased due to the global warming. The typhoon struck Taiwan and brought heavy rain, which caused the the flow rate and water level rise in a short time and destroy the bridge. This study used Computational Fluid Dynamics (CFD) model to investigate the hydrodynamic forces on rectangular section, fully submerged bridge decks. The turbulent flow and pressure distribution around the deck were computed by the Large Eddy Simulation (LES) model with the Volume of fluid (VOF) method to handle the water surface. The experimental results of Chang (1988), Malavasi & Guadagnini (2007), and Bruno et al. (2010) were compared with the simulation results to verify the numerical results.
Then the verified LES model was utilized to examine the influences of Reynolds number, submergence ratio, blockage ratio and proximity ratio on the drag and lift coefficients. The simulation results demonstrated that the drag coefficient remain a constant increased as the blockage ratio increased. This can be explained by the velocity and pressure around the deck increased due to the blockage effect. In addition, the proximity effect was examined by changing the distance between the deck and channel bed while keeping other parameters constant. When proximity ratio 5.0 ? Pr > 2.0, the results indicated that the lift coefficient increased as the proximity ratio decreased. This is because the velocity beneath the deck is smaller than the velocity above the deck. According to Bernoulli equation that the pressure on the lower side of the deck is larger than the pressure above the deck, and produce a positive lift force.
Keywords: Drag coefficient, Lift coefficient, Submergence ratio, Blockage effect, Proximity effect.
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| 參考文獻 |
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