| Summary: | 碩士 === 國立中央大學 === 土木工程學系 === 102 === In recent years, the numbers of floods have increased due to the global warming. The bridge engineers used the historical flood levels to design, so it may underestimate the water level during the future flood. This study focuses on the interaction between the free surface flow and a submerged cylinder with rectangular cross-section. The turbulent flow and pressure distribution around the cylinder were computed by the Large Eddy Simulation (LES) model with the Volume of fluid (VOF) method to track the water surface. The experimental results of Malavasi &; Guadagnini (2007) and water-surface measured in this study 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, Froude number, blockage ratio and submergence ratio on the drag and lift coefficients. The simulation results demonstrated that the drag coefficient is dependent on the Froude number, rather than the Reynolds number. For sub-critical flow (deck Froude number FrD < 0.52), due to the blockage effect, the drag coefficient increases as the blockage ratio increases. For trans-critical flow (FrD 0.78), because of the wave-induced drag, the drag coefficient is larger than that in sub-critical flow with the same blockage ratio. On the other hand, the lift coefficient is a function of the deck Froude number and the submergence ratio h*. The separation shear flow on the upper side of the cylinder was constrained by the water surface when h* = 2.0, and resulted in an asymmetric pressure distribution on the upper and lower sides of the cylinder, subsequently generate a downward force on the cylinder.
|
|---|
