| In the coastal area, the main factor which forces the movement of sediment is the wave. When waves enter into the shallow area, they will reflect, metamorphose, or break up. Constructions at the sea are most built at the coastal lines, such as pipe lines, small scale pile, large scale cylinder, groyne, manpower land, etc. The existing of these constructions will influence the flow nearby, accrete the velocity shear stress, sediment transportation, and result in local scour. If the scour is serious, it will induce the instability of the foundation. So local scour under the wave action is more and more important for coastal engineering design.Large scale cylinder is one of constructions that being usually used. Many researches focus on its local scour, but only a few have studied the flow field. A bedding cylinder is a kind of structure which has broad foreground application but few researches have studied on it. Now it has used as the foundation of the wind power generation at the sea. Bi-influence of the bedding and pole makes local scour and flow field different from the single cylinder.Flume experiment and numerical flume model simulate the whole progress about wave from depth water, enter into shallow water then reflect, metamorphose, sediment movement, local scour around large scale cylinder and bedding cylinder. Accord these limited data this paper tries to analysis the scour character, flow field character and discuss local scour mechanism.On the flume experiment, Wave Height Sensor is used to measure the wave height and period at different locations. NDV is used to measure the scour depth real time and three dimensional instantaneous velocities. Topographic instrument is used to measure the landform at 15 min and 60 min after wave generated. Using numerical camera to take pictures 60 min after wave generated. Base on these data, this paper uses different means to analysis the wave metamorphose and its effect to local scour, scour character, flow field character and scour mechanism.Wave mathematical model based on Boussinesq equation is used to calculate the wave height at different locations and instantaneous flow field, average shear stress and average eddy field around cylinder. Comparing calculated data with the measured data, they have a nice coherence. |
