Numerical Modeling and Experiments of Wave Shoaling over Semi-buried Cylinders in Sandy Bottom

摘要

In this paper, we study the propagation of long periodic waves over semi-buried cylindrical objects in the bottom. We present a combination of laboratory wave tank experiments, with a sandy bottom, and numerical modeling, using a two-dimensional fully nonlinear potential flow model. Experiments provide wave elevation at gages and velocity fields measured around the semi-buried objects, using an Acoustic Doppler Velocimetry (ADV) method. The model is run for the same geometry and wave parameters as in the experiments. A numerical absorbing beach is used to both prevent waves from overturning and specify wave absorption in the model surfzone. Bottom friction in the shoaling region is specified as a corresponding energy loss in the model, by using an absorbing surface pressure. Without the semi-buried cylinder, the comparison between computed and experimental results is quite good for both surface elevation and near bottom velocities, even for waves near the breaking point. With the cylinder, the agreement of computed and measured velocities close to the cylinder is also good, except, just in front and behind the cylinder, likely due to vortex shedding. The model can thus be used to accurately provide background wave fields around the buried object, say, at one diameter away. Based on these, more refined hydrodynamic and sediment transport modeling can be performed in future studies.