Abstract
Steel risers are widely used in offshore oil and gas industry. However, the production capacity and depths are limited due to their extreme weight and poor fatigue and corrosion resistance. Nowadays, it is confirmed that fiber reinforced polymer (FRP) composite risers have apparent advantages over steel risers. However, the study of vortex induced vibration (VIV) for composite risers is rarely involved. Three different risers (one steel riser and two composite risers) were compared for their VIV characteristics. The effects of 2D and 3D models and fluid–structure interaction (FSI) were considered. The models of composite risers are established by effective modulus method (EMM) and layered-structure method (LSM). It is found that 2D model are only suitable for ideal condition, while, for real situation, 3D model with FSI has to be considered. The results show that the displacements of the FRP composite risers are significantly larger than those of the steel riser, while the stresses are reversed. In addition, the distributions of the displacements and stresses depend on the geometries, material properties, top-tension force, constraints, etc. In addition, it is obvious that EMM are suitable to study the global working condition while LSM can be utilized to obtain the results in every single composite layer.
Highlights
The exploitation and utilization of marine resources, such as oil and gas, lead to the development of offshore structures
The material properties listed in the table were utilized for steel riser directly, as well as composite risers with layered-structure method (LSM)
When the vortex shedding frequency becomes close to the natural frequency of the riser, the phenomenon of “lock-in” happens, which results in large and damaging vibrations leading to the fatigue failure of the riser
Summary
The exploitation and utilization of marine resources, such as oil and gas, lead to the development of offshore structures. More tests, including field tests and optimized designs of composite risers, were conducted by different research institutes and global enterprises [5,6,7,8,9,10,11,12,13]. These prototypes prove that FRP composite risers have significant benefits in weight saving compared to steel risers. Huang and Chen et al compared the dynamic performance of composite and steel risers using ABQUS and SHEAR7 [32,33] These studies normally employed empirical models and no fluid–structure interaction (FSI) was included. The VIV responses, such as coefficient of drag (CD ), coefficient of lift (CL ), displacement and stress under VIV, were obtained and compared for all the three risers with different modeling methods
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