Structural optimization model of confined polyhedral composite subsea pipelines under pressure and thermal fields

Abstract

This paper investigates the structural optimization of a polyhedral composite subsea pipeline (cylinder) under pressure and thermal fields. The pipeline is confined tightly and deforms inward when it is subjected to external loadings. The interface is frictionless between the pipeline and its surrounding medium. Based on the above assumptions, thin-walled shell principles, and an admissible displacement function, the potential energy of a pipeline per unit length is obtained explicitly by simplifying the radius and bending rigidity. After taking the first derivative of the potential energy, two equilibrium equations are obtained. By combining these two equations, the critical buckling pressure of the polyhedral pipeline is expressed analytically with the inclusion of the temperature effects. Then, the present analytical study is compared with other numerical and experimental results, and excellent agreements are reached. A configuration factor is defined as the buckling pressure between the polyhedral and circular pipeline. Finally, parametric studies show the configuration factor decreases with the increase of thickness-to-radius ratio, the increase of the number of sides, and the increase of the temperature variation, respectively. Therefore, a polyhedral pipeline with a low thickness-to-radius ratio is recommended in engineering practices since it may reduce the material cost.