This paper presents a method to predict the bending hysteretic behavior of unbonded flexible pipes using full layered numerical general finite element models with an implicit solver. A predefined stress fields method is proposed to simulate the initial contact pressure effect introduced by the fabrication process. Detailed finite element modeling techniques are illustrated based on system balance principles of a cantilever beam system. The models can capture the interactions (normal contact and tangential friction behavior) between and among layers adequately, thus giving reasonable stress predictions of tensile armor tendons in both longitudinal and transverse (radial and lateral) directions. The results show that the proposed method through prescribing a fixed initial hoop stress value in the outer sheath could give consistent bending moment-curvature relations for all test pressure levels and corresponding numerical results. The stress-curvature relations reveal that the tensile armor tendons slide in an interval between the loxodromic and geodesic curves as proved in the open literature. In addition, sensitivity studies including element types, boundary conditions, material properties, normal contact stiffness and friction coefficients are performed to validate the feasibility of the proposed models. Moreover, if plastic layers are modeled by solid elements, the friction moment will be larger than that of using shell elements due to Poisson’s effect on pipe elongation.

本文提出了一种使用带有隐式求解器的全层数值通用有限元模型来预测未粘结挠性管弯曲滞后行为的方法。提出了一种预定义的应力场方法来模拟制造过程中引入的初始接触压力效应。基于悬臂梁系统的系统平衡原理，阐述了详细的有限元建模技术。该模型可以充分捕获各层之间以及各层之间的相互作用（法向接触和切向摩擦行为），从而在纵向和横向（径向和横向）方向上给出抗拉铠装腱的合理应力预测。结果表明，该方法通过在外套管中规定固定的初始环向应力值，可以在所有测试压力水平下提供一致的弯矩-曲率关系，并提供相应的数值结果。应力-曲率关系表明，如公开文献所证明的，拉伸装甲腱在低渗曲线和测地曲线之间的间隔内滑动。此外，还进行了包括元素类型，边界条件，材料特性，法向接触刚度和摩擦系数在内的敏感性研究，以验证所提出模型的可行性。而且，如果塑料层是用实体单元建模的，则由于泊松对管道伸长的影响，摩擦力矩将比使用壳单元的摩擦力矩大。