To correctly model the structural behavior of a flexible pipe, the contribution of all the layers must be completely understood, among them the interlocked carcass. That carcass is a metallic layer designed to provide radial stiffness to a flexible pipe, mainly supporting pressure differentials and thus preventing failure modes such as collapse and crushing, but its behavior under other loads is worth of investigation. This paper contributes to understanding the carcass behavior under tension. Given its complex helical and interlocked geometry, modelling the carcass through the Finite Element Method is a challenging task, not only due to the large size of the models, but also due to the nonlinearities and convergence difficulties that arise from the self-contacts at the interlocking. For these reasons, most works developed over the past decades have adopted an equivalent layer approach, in which the carcass is replaced by an orthotropic cylindrical layer with equivalent mechanical properties. Although practical, this approach disregards the effects from the interlocking, such as stiffness variations and stress concentrations. Therefore, aiming a more realistic representation and a better understanding of the mechanical behavior of the interlocked carcass, this work presents four different carcass finite element models to analyze this layer under tension loads. The first one is a complete three-dimensional finite element model of an interlocked carcass discretized with second order isoparametric solid elements and surface-to-surface contact elements. The second model consists of a version of the first one with the addition of an inner polymeric sheath. As for the third and fourth models, it was adopted the simplifying ring hypothesis, that is, a carcass with 90 degree lay angle, thus allowing the axisymmetric modelling of the two previous configurations, representing a substantial computational gain by using two-dimensional meshes. The results of those models are then presented and compared, and the validity of the adopted simplifying hypothesis is verified.

Flexible pipes are structures composed by many layers varying in composition and shapes, in which the structural behavior is defined by the role it must play. Flexible pipes construction is such that layers are unbounded, allowing relative movement between them and modifying its behavior. Many approaches are used to model such cables, both analytical and numerical, such as the macroelements model. This sort of model consists in finite elements where geometrical characteristics are taken into account by the formulation and is under development by the authors. Previous works have shown in detail the modeled cylindrical and helical elements, as well node-to-node connection elements (bounded, frictionless and frictional), which have allowed simplified flexible pipe with bonded elements simulations. This article will focus on modeling a simplified cable consisting in an external sheath, two armor layers and a polymeric core, since recent advances in the contact formulation opens the possibility to incorporate friction between the layers. Taking into consideration accuracy, computational time and memory usage, results from macroelements are compared to commercial finite element software.

Due to the number of layers and their respective geometrical complexities, finite element analyzes of flexible pipes usually require large-scale schemes, with a high number of elements and degrees-of-freedom. If proper precautions are not taken, such as suitable algorithms and numerical methods, the computational costs of these analyzes may become unfeasible to the current computational standards. Finite macroelements are finite elements formulated for the solution of a specific problem considering and taking advantage of its particularities, such as geometry patterns, in order to obtain computational advantages, as reduced number of degrees-of-freedom and ease of problem description. The element-by-element method (EBE) also fits very well in this context, since it is characterized by the elimination of the global stiffness matrix and its memory consumption grows linearly with the number of elements, besides being highly parallelizable. Over the last decades, several works regarding the EBE method were published in the literature, but none of them directly applied to flexible pipes. Due to the contact elements between the layers, problems with flexible pipes are usually characterized by very large matrix-bandwidth, making the implementation of EBE method more challenging, so that its efficiency and scalability are not compromised. Therefore, this work presents a parallelized implementation of an element-by-element architecture for structural analysis of flexible pipes using finite macroelements, consisting of an extension of a previous work from the same authors. New synchronization algorithms were developed, with scalability improvements, the methodology was extended to other finite macroelements and comparisons were made with a well-stablished FEM software, with significant gains in simulation time and memory consumption.

Armor pots are mechanical devices employed in the offshore oil production to anchor armor wires/steel tubes of an umbilical cable. In epoxy-based armor pots, this anchoring is obtained through the interaction between the resin and the tensile armors/steel tubes and also through the capstan effect from geometric variations, such as radius and lay angle changes. In this context, friction plays a fundamental role in the anchoring capacity and is mainly affected, among other factors, by the intensity of resin thermal contraction, which generates positive pressure at the contact interfaces, and also by the friction coefficient. Therefore, this works presents an extensive parametric analysis of the resin thermal contraction and of the friction coefficient performed through the finite element method with the objective of understanding their qualitative and quantitative influence at the anchoring capacity of a steel-tube umbilical armor pot. In recent years, the authors published fully three-dimensional finite element models of armor pots. In order to accomplish the present work, several enhancements were performed in the aforementioned models. The main development is an innovative methodology for the resin mesh generation, ensuring mapped elements at the interfaces with steel tubes, resulting in a smoother contact representation. At the same time, this methodology is computationally advantageous by allowing larger element sizes at the remaining resin volume without loss of quality in the representation.

The armor pots on an umbilical system are critical accessories that are subjected to high tensile loads. To ensure tensile resistance to an umbilical cable connection, its structural elements must be properly anchored to the armor pot. One way to provide that connection is the use of the adhesive properties of an epoxy resin. When designing this type of ancillary, it is important to determine the stress and strain distributions along the structural anchored components and thus ensure that they can withstand the loads. In this context, three-dimensional fully parameterized finite element models with bonded contact have already been developed, consisting of a good alternative to evaluate the critical delamination load. However, for a more complete understanding of the anchoring phenomenon, it is also important to analyze the effects caused by the sliding of the tendons and tubes inside the resin: friction gives additional axial resistance and bending-torsion effects can occur while these elements are being pulled out. Therefore, in this article three-dimensional anchoring models are presented with standard contact, which enables normal and unilateral tangential gap formations and considers the effects of friction, allowing the reproduction of the desired phenomenon.

The connectors on an umbilical system are critical components that are subjected to high tensile loads. To ensure tension resistance to an umbilical cable connection, its structural elements must be properly anchored to the armor pot. One way to provide that connection is the use of the adhesive properties of an epoxy resin. In that context, it is necessary to perform a series of pull out tests in order to verify if the resin is capable of withstanding the tensile loads transmitted by the tensile armor layers or the steel tubes. For that purpose, a series of tridimensional finite element models are being developed to represent, as realistic as possible, the interaction between metallic layer and resin. These models allow a fully helical tensile armor to interact with a resin substrate. For this article, an early stage model considering bonded contacts is presented and the adhesion of the tensile armor tendons is evaluated in terms of the shear stresses in the contact regions.

Flexible pipes are employed to transport oil and natural gas from the seabed to the floating units, and vice versa. These pipes are made of concentric layers of different geometries, materials and structural functions in order to withstand a series of static and dynamic loads from its adverse operating environment. The local analysis is an important stage in the design of a flexible pipe and consists in determining the stresses and strains distributions along its layers. Multipurpose finite element packages, such as ANSYS and ABAQUS, are commonly used in this task, but present many limitations for their generic nature, varying from the absence of specific tools for model creation to heavy restrictions of the number of degrees-of-freedom to make computational processing feasible. Over the past years, several macro finite elements were formulated by PROVASI & MARTINS specifically for modeling a flexible pipe, allowing a reduction in the total number of degrees-of-freedom. However, until the present moment, there is no parallel processing software that efficiently implements these elements for large model applications. Aiming greater computational performance, the macro elements can be combined with the element-by-element (EBE) method, which is characterized by the global stiffness matrix elimination, is highly parallelizable, scalable and shows a memory consumption that grows linearly with the number of elements in the model. In this context, a parallelized architecture for structural analysis of flexible pipes that explores the EBE method and macro finite elements has been developed, being of great interest for design applications in the industry.

The modelling of flexible pipe interlocked carcasses is complicated when considering all the geometric complexity of their profile. A possible approach is to model them as cylindrical equivalent layers. To follow this path several alternatives can be considered in changing the geometrical and material properties. However, the thickness and the mean radius of those layers must not be changed to not interfere with the diameter of the other flexible pipe layers. In this paper, a model of an orthotropic cylindrical layer, with the same thickness and mean diameter of the original carcass layer is constructed and its material parameters are adjusted for axial loads using a finite element model of the real carcass profile.