Comparison of flow fields induced by fixed and oscillatory vertical cylinders in regular waves using 3D numerical model

The influences of a flexibly mounted cylinder and a fixed cylinder on the flow field in regular waves are studied numerically. Performances of the flexibly mounted cylinder oscillating freely in still water and in regular waves are first simulated. Then the in-line forces on the two cylinders in regular waves are compared to the theoretical results. All results indicate the present model is valid. Then the entire flow fields induced by the two cylinders are analyzed in detail. The windward and leeward regions of the cylinder are each divided into eight sections. Results of the windward side are complex because of the superposition of incoming and reflected waves. Results of the leeward side show that the sectional average wave height decreases as the wave frequency increases. In general, the flexibly mounted cylinder attenuates wave energy more effectively. Moreover, the wave frequency is a major factor influencing the flow field. When the incident wave frequency approaches the natural frequency of the cylinder, differences of the two data sets become significant. Distance between the section and the cylinder is another influential factor. The two sets of results become more similar as the distance increases, especially in cases of low incident wave frequencies.