Effects of extensible modelling on composite riser mechanical responses. (15th January 2021)

• Record Type: Journal Article
• Authors: Ragheb, Hossam; Sobey, Adam
• Is Part Of: Ocean engineering. Volume 220(2021)
• Publication Date: 2021-01-15
• Subjects: Composite risers -- Cable dynamics -- Time domain -- Benchmarking; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2020.108426
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: The change from steel risers to composites comes with uncertainties that led to large safety factors. One area of uncertainty is the predicted response and stresses derived from commercial packages that are based on formulations that assume in-extensible riser. However, composite pipes exhibit a lower axial stiffness and therefore the velocity of the axial waves will change with a corresponding change in dynamic response. To determine the effect of this assumption, this paper assesses the effect of extensibility on the time-domain response. It is found that the in-extensible model predicts 3 times the number of high frequency tension cycles in the 20 kN tension range. To determine the impact of this change on the stress, the accuracy of available composite pipe models is benchmarked using shell, continuum-shell and solid elements. The quadratic and continuum-shell elements provide a maximum percentage difference of 4% compared to solid elements but the continuum-shell is selected as it has a lower computational cost. The response from the extensible and in-extensible models are input into the pipe model, they provide similar Tsai-Wu failure factors, alleviating concerns when modelling the strength. However, the change in dynamics remains a concern for other applications such as machine-learning or digital-twins. Highlights: Extensible and in-extensible beam models are investigated with composite risers. In-extensibility causes spurious oscillations, affecting the riser predicted tension. Quadratic S8R, and continuum shell elements SC8R are optimum to model the composite pipe. A coupled in-extensible beam predicts failure factors higher than the extensible equivalent.