Modeling and Analysis of in Line and Cross Flow Vibration of Risers in Drill Ships

In the last few years, drilling activities took place in water depths of more than 3000m. In order to convey the hydrocarbon to the sea level and do drilling operations, a steal pipe is installed between the wellhead in the seabed and drill ships. A control system keeps the drill ship in a safe area above the wellhead. Since the diameter of the riser is much less than its length, it can be simplified into the beam model. The fluid dynamic forces are expressed in Morison formula by using short wave theory. It is assumed that the riser is connected to the drill ship by means of a heave compensator. This device provides a large static tensile force at the top of the riser. In addition, it reduces the longitudinal stress variation induced by the relative vertical motion of the drill ship and the riser. With these assumptions, the equations of motion governing the transverse displacement of the riser in two directions are obtained. These equations are solved by using the finite difference method and Runga-Kutta method. At the end, the effects of environmental and mechanical parameters on the dynamic behavior of the riser are discussed.