Journal of Waterway, Port, Coastal, and Ocean Engineering

Low rock structures have been constructed on some beaches to reduce storm-induced damage to backshore areas, but no method is available to design such structures. Four test series were conducted in a wave flume with a sand beach and a berm to compare the effectiveness of a narrow dune and a rock (stone) seawall placed on the foreshore in reducing wave overtopping and sand overwash. The incident irregular waves were kept approximately the same. The water level was raised to increase wave overtopping. The dune was effective in eliminating or reducing wave overtopping compared with the corresponding berm with no dune, but the narrow dune was destroyed easily as the water level was increased. The stone seawall reduced wave overtopping even after its deformation. A stone seawall buried inside a dune functioned like the dune initially and like the seawall after the sand on and inside the porous seawall was eroded by overtopping waves. An existing numerical model was extended to predict sand transport on and inside the porous structure in the swash zone.

The results of an experimental study on combined wave and current flow around a partially submerged cylinder with a large Reynolds number ($R$ = 5.96 × 10⁴) are reported. The measured instantaneous velocity time-series data were analyzed to acquire insight into the first-, second-, third-, and fourth-order statistical moments. It was observed that turbulence generated because of the surface wave plays a significant role in the occurrence of vortex lock-on, which in turn alters the excitation frequency. For the vortex lock-on case in which the shedding frequency is the same as the natural shedding frequency, the recirculation zone is significantly reduced. However, for higher wave frequencies, the shedding frequency was modulated and the recirculation was somewhat enlarged. The comparative study between only current flow (OCF) and combined wave-current flow (WCF) showed that the intermittency in turbulence was larger for the OCF case (without a cylinder) than for the WCF case. The surface-wave-generated vortices induced around the cylinder interacted with the vorticity shear layers at the side of the cylinder and at the wake region, resulting in the formation of new induced wake vortices. These induced wake vortices controlled the recirculation region behind the cylinder.

Natural channels are seldom straight and commonly take sinuous patterns with turbulent and strongly three-dimensional (3D) flows in the bends. A 3D hydrodynamic model [Reynolds-averaged Navier-Stokes (RANS)] with major 3D flow features and different turbulence submodels was developed in a curvilinear, nonorthogonal coordinate system. A typical consecutive bend experiment was chosen as the verification case. A bend flow characteristic model with two turbulence submodels (k-ε and shear-stress transport model) was developed using different grid mesh systems. A comparative assessment of the models was performed. The model verification was conducted by comparing the simulated velocity distribution, flow structure, and secondary current development with the experimental measurements. Differences between the simulations and measurements were observed when the secondary current or separation layer occurred. This indicates that the simulation accuracy in the high-sinuosity bends decreases with the development of channel bends. Comparison of the results obtained by the 3D RANS model with experimental and field data, and numerical predictions, validates that the k-ε model with the fine-grid system is capable of simulating flow fields in curved open channels with reasonable accuracy.