Hydrodynamic loads of the bridge decks in wave-current combined flows

This work uses a Large Eddy Simulation (LES) model and the Volume of Fluid (VOF) scheme to investigate the hydrodynamic loads on submerged rectangular decks in wave-current combined flows. The influences of current velocity, wave height, deck length, and blockage ratio on the wave loads are examined, and a modified Morison equation is used to predict the hydrodynamic forces on the deck. The simulation results demonstrate that the wave loads are linearly proportional to wave height H when H <= 0.4h, h is the water depth. By setting the reference velocity as Ur = (gH)1/2 for wave-induced flow, the hydrodynamic loads can be separated into a steady term (current-induced load) and an acceleration term (wave-induced load). The crucial hydrodynamic load comes from the surface pressures on the upper side of the decks, owing to the deck length being much larger than the deck thickness. In addition, the drag coefficient is independent of the wave height H, aspect ratio L/D, and the Keulegan-Carpenter number KC; while the lift coefficient depends on the submergence ratio S/D. Bridge engi-neers could easily use the modified Morison equation and the maximum drag coefficient CD = 2.73, lift coeffi-cient CL =-2.05, the inertia coefficients CMx = 0.95 and CMz = 2.53 to compute the maximum loads against wave-current combined flows.