CFD Simulation of Flow Characteristics on Semi-Submersible Platforms

Abstract

In this paper we present the turbulent flow around a semi-submersible platform, modelled using Ansys Fluent. The computational domain is designed as a rectangular horizontal channel with the semi-submersible platform mounted inside the channel. The top, bottom, left and right walls of the channel are treated with no slip boundary condition. The front and back walls are specified with velocity inlet and pressure outlet boundary conditions. The semi-submersible platform is designed with of two pontoons, four square columns and two bracings. The problem is modelled as three dimensional, transient, incompressible flow and turbulence is modelled using Large eddy simulation (LES) turbulence model. The computational domain is meshed to 4,72,749 hexahedral mesh cells. Parametric study is performed by varying the Reynolds number (Re) in the range of 104 ≤ Re ≤ 106 and also the shape of the columns. The investigation is carried out by plotting stream function, velocity and pressure contours. We observe vortex shedding and flow separation between the front and back columns of the semi-submersible platform. As we increase the Reynolds number the intensity of flow separation also increases. The transient flow characteristics of the lift and drag forces are evaluated by plotting the coefficients of lift and drag for different Reynolds number and column shapes.