Stress analysis of riser control pipes
The primary objective of this project was to characterize the response of the Filler/control duct assembly when bent around a rigid tool. It was desired to quantify the interface contact pressure as well as the components’ relative movements at peak curvature.
- Three different Filler configurations were studied
- Highly complex geometry: use of three different construction planes for generation of the Filler geometry
- Analyses performed for most critical loading conditions using 6 different bending planes to assess contact pressure distribution at the interfaces
- Geometric Idealization: simplification of CAD geometry, for usage in numerical simulation, performed in ANSYS DesignModeler
- Hyperelastic and elasto-plastic material behaviors were utilized
- Large deflection effects included
- Five different non-linear contact interaction between components were utilized, including friction and separation
- Rigid/flexible and flexible/flexible contact interactions
- Utilization of joint elements to impart constant-curvature bending to assembly
- A complex simulation, which included material, contact, and large-deformation non-linearities, was executed directly in ANSYS WorkBench
Numerical Modeling Challenges Overcome
- Large bending of a 7.2-meter long riser structure up to a final curvature of 2.5 meters. Large strain capabilities and enhanced-strain element formulations were used to avoid element distortion and achieve a converged solution.
- Modeling of the Filler’s material (Finathene), a highly-nonlinear rubber-like material, through the use of a hyperelastic formulation. Reduced integration elements were used for the Filler bodies to account for its significantly softer mechanical response and to avoid distortion at large strains levels.
- Five contact pairs (frictional and frictionless) were utilized to simulate the interaction between the Filler, the control duct, the reference duct and the rigid tool. All flexible/flexible and rigid/flexible contact interactions were successfully resolved.
Simulation results show that the 2.5-m curvature was achieved with a constant bending moment along the Filler assembly. Relative sliding of the Fillers with respect to the control duct can also be observed.
Contact pressure between the Filler and the control duct were quantified along the length of the duct, at nine different locations.