Boundary Layer Effects in the Modeling of Semi-Submersible Columns

A common structural element encountered in semisubmersible designs is a rectangular vertical column with rounded corners. The time-averaged drag and oscillating lift and drag forces on such columns are strongly influenced by the location of the lines of flow separation on the column and hence the angle of attack of the incoming flow and the corner radius. In this paper we examine published wind tunnel data to illustrate these effects which include angle of attack and Reynolds number effects. This examination suggests that care must be exercised modeling flows around these elements. Also, the data suggest that Reynolds number effects and surface roughness effects may distort the results of scaled experiments. We use CFD simulations first to model the existing data and then to explore the possible changes in hydrodynamic properties due to Reynolds number and boundary layer effects. Recommendations are made regarding the physical and CFD modeling of the flow over these structures.