Numerical simulation of loop formation in catenary risers on nonlinear uneven seabed. (1st February 2023)

• Record Type: Journal Article
• Authors: Jia, Jichuan; Gu, Jijun; Huang, Jun; Gao, Lei; Chen, Leilei; Wang, Shujiang
• Is Part Of: Ocean engineering. Volume 269(2023)
• Publication Date: 2023-02-01
• Subjects: Loop formation -- Uneven seabed -- Nonlinear seabed soil -- Case study; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2022.113480
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: During installation, catenary risers exhibit low tension in the touchdown zone (TDZ) of the seabed. Manufacturing deviations in the riser and the yaw rotation of the installation vessel may induce the unbalanced distribution of torsion. Combined with tension, loop formation may occur and lead to extreme damage. This study established a finite element model (FEM) for a steel catenary riser (SCR) using OrcaFlex software to analyze the effect of a nonlinear uneven seabed on loop formation. Four typical uneven seabed profiles, including a trench, an upheaval, a depression, and a slope, were constructed, while five key nonlinear seabed soil parameters, including mudline shear strength ( S um ), shear strength gradient ( ρ ), suction ratio ( f suc ), suction decay parameter ( λ suc ), and normalized maximum stiffness ( K max ) were proposed for parametric analysis to summarize the response rules of maximum tension, maximum compression and maximum bending moment of the riser loop. A specific sea area was selected for the case study to verify the applicability of the response rules. The case study also confirmed that the uneven seabed profile and nonlinear seabed soil properties had a combined effect on the riser loop, further preventing loop formation and reducing subsequent damage. Highlights: A finite element model for the catenary riser with loop formation in complex environment is established by using OrcaFlex. The influence of seabed morphology including four typical uneven seabed profiles on the loop formation is analyzed. The influence of nonlinear seabed soil properties including five key parameters on the loop formation is analyzed. The applicability of the response rules and the combined effect of seabed profiles and soil properties are verified.