Multiscale Analysis and Size Effect Discussion Investigation for the Armor Layer of Flexible Risers Based on NIAH Method

Abstract

The armor layer is one of the core components of flexible risers. It provides essential mechanical properties such as tensile strength, pressure resistance, and torsional performance, which are necessary for operation in complex marine environments. However, due to the significant disparity between the cross-sectional dimensions of the armor wires and the overall riser size, severe computational costs are often incurred when a finite element (FE) model is employed for the performance analysis of an armor layer. To address this, an asymptotic homogenization method for flexible risers is established in the present study. In this method, the armor wires, modeled as beam elements, are equivalent to an anisotropic shell structure, and the equivalent elastic properties of the armor layer are obtained with unit-cell analysis. These properties are then used for the overall analysis of the flexible riser’s armor layer response, without considering the specific characteristics of the steel wires, thereby improving the efficiency of the performance analysis. The effectiveness of the proposed method is verified in a numerical example based on a comparison with a finite element (FE) model. Moreover, the effect of the unit cell size is investigated by introducing a size factor. A significant size effect is observed, unlike in the truss-based unit cell, for which an explanation based on the stiffness coefficient is given. The proposed method offers a new technique for efficient performance analysis of the armor layer of flexible risers.

Keywords

• armor layer
• flexible riser
• asymptotic homogenization
• equivalent elastic property
• size effect