Performance comparison of stress-objective and fatigue-objective optimisation for steel lazy wave risers

ABSTRACT

The distribution of buoyancy modules is a combined factor defined by multiple design variables for steel lazy wave risers, such as the length of the buoyancy section and the module diameter. Understanding the influence trend under different optimal objectives is significant for riser design. The aim of this study was to investigate riser performance through a comparison of the optimum configurations with the initial design. Genetic algorithms were implemented to minimise the maximum stress and fatigue damage along the risers. The comparison results show that the stress-objective and fatigue-objective can lead to conflicting criteria regarding the choice of the best overall riser configuration. The buoyancy section should be as close to the seabed as possible for a lower fatigue damage. Moreover, the arch height in a nominal position can be an alternative optimal objective for minimising the fatigue damage, which can save considerable computation time.

KEYWORDS:

• Steel lazy wave riser
• genetic algorithm
• optimisation
• riser fatigue

ORCID

Shangmao Ai http://orcid.org/0000-0002-2415-6611

Additional information

Funding

This research is supported by “China Scholarship Council” [grant number 201606685001] and “the Fundamental Research Funds for the Central Universities” of Harbin Engineering University.