Cross Sectional Mechanical Characteristics and Sensitivity Analysis of Unbonded Flexible Risers Under Torsional Loads

Abstract Unbonded flexible risers have complex structures and numerous structural parameters. The torsional loads carried by each structural layer lead to different levels of coupling deformations of layers. These deformations bring challenges to the structural design and mechanical characteristics analysis of flexible risers. This study establishes the theoretical model of flexible risers under the torsional loads according to the law of conservation of energy and the deformation geometry theory. Depending on the material properties and structural forms of each layer, this study divides the layers of flexible risers into three categories: cylindrical layer, metal spiral layer and polymer spiral layer, and derives the expressions of torsional loads and torsional stiffness. The calculation program in this study is compiled with MATLAB software to calculate the mechanical properties of flexible risers under clockwise and counterclockwise torsional loads. This study analyzes the influence of structural parameters on the torsional performance of flexible risers. Calculation and analysis of the influence of structural parameters on their mechanical properties can provide not only the further insight into the mechanical principles of each structural layer, but also the reference for structural design and optimization of flexible risers.