Session: 04-03-01: Rigid Risers

Submission Number: 157520

An Investigation on the Dynamic Compression of Steel Lazy-Wave Risers 

Deepwater exploration required another solution instead of steel catenary risers due to the high top tension levels displayed in operation. The alternative solution is to employ steel lazy-wave risers which reduce the top tension, due to its constructive characteristics. The configuration consists in adding buoyancy modules in order to alleviate the tension in the line. However, these buoyancy modules added to the steel lazy-wave risers may impose compressive loads and, consequently, trigger structural instability.

There are some studies on instability concerning steel catenary risers, but no conclusive study has been shown about steel lazy-wave risers. This article focuses on investigating the occurrence of dynamic compression in steel lazy-wave risers to assess if the analytical formulae for steel catenary risers available in the literature are applicable to lazy-wave risers.

The article presents the lazy-wave problem and its modelling using commercial software. Then, it assesses the dynamic solutions in order to determine when instability occurs when the steel lazy-wave riser is subjected to imposed heave motion with a set frequency. These results from dynamic simulations using commercial software are presented, discussed and compared against analytical formulation in order to obtain a criterion for critical load determination.

Keywords: lazy-wave, critical load, instability, steel lazy-wave risers, analytical formulation.

Presenting Author: Rodrigo Provasi University of São Paulo

Presenting Author Biography: Rodrigo Provasi is currently an assistant professor in the department of Structural and Geotechnical Engineering in University of São Paulo. His background is from a graduation course in Mechatronics Engineering and PhD in Computational Mechanics, in which he focused on developing methods and tools for Offshore flexible pipes and umbilical cables analysis.
He is also part of the LMO - Offshore Mechanics Laboratory, which is well-known in the offshore industry with more than 30 years working as partner of the largest offshore players.