Numerical study of ship induced bed shear stress

Vessel movement in waterway disturbs flow field around and beneath the vessel. It creates turbulence in water between vessel and river bed resulting in sediment suspension. Erosion of sediment from river bank and bed occur due to orbital motion of wave field, wave breaking, and propeller wash which causes change in river morphology. This phenomenon is more common and severe in shallow waters where movement of high draught vessel exists. Currents generated due to vessel movement carry the suspended sediment and may deposit at low velocity zones. Existing sediment transport models consider shear stress excess to estimate the sediment load. However, these models neglect the shear stress around the vessel. In the present study, wall shear stress due to vessel movement is estimated using STAR-CCM+ (CD-ADAPCO). Volume of fluid (VOF) discretization method is used to solve RANS equations and k-ω SST method to model flow turbulence closure. Vessel movement was simulated using Dynamic Fluid Body Interaction (DFBI) with one-dimension translation (x-direction). Shallow water conditions are studied by simulating h/T of 1.2, where, h is flow depth and T is vessel draft. Model results are compared with empirical equations to predict bed shear stress due to barge tow.