| dc.description.abstract | This study uses a Large Eddy Simulation (LES) model and the Volume of Fluid (VOF) method to examine the wave/turbulence interactions and hydrodynamic loadings on submerged bridge decks. The flow condition includes periodic waves, solitary waves, and wave-current combined flows. The surface waves in the numerical model were generated by an internal source function. The simulated wave heights and surface pressures on the rectangular deck are compared with the experimental results to validate the accuracy of the present numerical model. The numerical model was then used to examine the wave loads of different wave conditions.
For periodic wave flows, the influences of wave height, submergence ratio, scale ratio, and blockage ratio on the wave loads of the submerged deck are studied. The simulation results point out that the drag, lift, and pitching moment on the deck are linearly proportional to the wave height H. The dimensionless force coefficients are functions of submergence depth S, but are independent of Reynolds number of the bridge deck. The maximum force coefficients occur when the deck is near the water surface (submergence ratio S/D = 0 ~ 1.0) and decrease with the increasing submergence ratio. This results from the wave-induced pressure being the largest close to the water surfaces. Moreover, the turbulence induced by the wave breaking affects the leeward pressures and hydrodynamic forces on the bridge deck.
For wave-current combined flows, the influences of current velocity, wave height, deck length, and blockage ratio on the wave loads are examined. The simulation results concluded that the wave loads are linearly proportional to wave height H when H 0.4h, h is the water depth. The hydrodynamic load mainly comes from the surface pressures on the upper side of the decks due to the deck length being much larger than the deck thickness. A modified Morison equation is proposed to predict the hydrodynamic loadings on the deck. By adopting the reference velocity Ur = (gH)1/2 for wave-induced flow, the hydrodynamic loads can be separated into a steady term (current-induced force) and an acceleration term (wave-induced force). Furthermore, the drag coefficient is independent of the wave height H, aspect ratio L/D, and the Keulegan-Carpenter (KC) number, while the lift coefficient depends on the submergence ratio S/D. The maximum drag coefficient CD = 2.73 for a rectangular deck, drag coefficient CD = 2.51 for a girder deck, lift coefficient CL = -2.05, the inertia coefficients CMx = 0.95 and CMz = 2.53 could be used to design bridge decks against wave-current combined flows.
For solitary wave flows, the influences of current velocity, wave height, deck length, and blockage ratio on the wave loads of a rectangular deck are investigated. The simulation results indicate that the wave loads of solitary waves are larger than those of the periodic waves of the same wave amplitude. In addition, the resulting force coefficients are independent of the wave heights when the reference velocity Ur = [gA(A+h)/h]1/2 is used to normalize the hydrodynamic loads, and A is the amplitude of the solitary wave. Nonetheless, the drag and lift coefficients increase nonlinearly with increasing the aspect ratio and blockage ratio. For coastal engineers, the maximum drag coefficient CD = 1.40 and -0.95, and the lift coefficient CL = 0.57 and -0.86 can be utilized to compute the wave loads of solitary waves.
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