Rodrigo Provasi

Flexible Pipe Modeling Using Finite Macro-Elements

Modeling flexible pipes in the local level is not a trivial task and many authors have employed a great amount of time in such task. The non-triviality arises from the various layers and their interaction, which are pretty tough to correctly model. The possible approaches to solve the problem are divided in to major categories: analytical models and numerical models. The analytical ones rely on a great number of hypotheses and, after a great effort, result in a system of algebraic equations. The numerical ones can be further differentiated in the ones developed using commercial software and the other ones using proprietary models.The authors choose the second way to approach the problem and presented in previous works a group of elements called macro-elements, including a cylindrical element for orthotropic layers, a three dimensional curved beam for helical elements, a rigid connection and a contact element, both dealing with different node displacement natures. These elements take into account the physical and geometrical characteristics of the components. In this paper a pipe model, with a flexible internal core, two tensile armors and an external sheath, will be simulated and its the results will be checked against commercial software and commented.Copyright

A Finite Macro-Element for Cylindrical Layer Modeling

The offshore industry is in constant evolution due to the need of reach increasing water depths for new oil fields exploitation. In this scenario, not only new types of platforms are being designed, but also new types of risers, including flexible pipes and new umbilical cable configurations. The greatest difficulty to generate a new concept for a riser is to determine if it is viable or not. Flexible pipes and umbilical cables are complicated to model, due to the interactions between their layers and the large number of possible arrangements. To predict the behavior of flexible pipes and umbilical cables, adequate models are necessary. One can rely on finite element models, which show a great difficulty in mesh generation and convergence (specially due to the contact pairs). One can also rely on analytical models, which have many limitations due to simplifications (even though they are necessary). Another possible approach is to define macro elements, which represent a component, instead of classical finite elements (such as tetrahedric elements). Related to that approach, this paper presents a tubular element, which describes a cylinder with isotropic properties and can accept various sorts of loads. This element has its displacements and loads described using Fourier series and, for each term of the series, a solution is obtained. The effect is then superposed and the complete solution is obtained. This formulation is implemented and their results compared to those obtained by a classical finite element modeling tool, with good agreement.© 2010 ASME

CAD Software for Cable Design: A Three-Dimensional Visualization Tool

The concept and project of umbilical cables and flexible pipes are not simple tasks, due to the great variety of components and possible arrangements. The design of those elements is based on the functions they are intended to perform. Also, some structural characteristics determine which component will be selected, including electrical cables and hydraulic hoses, to control underwater equipment, protective sheaths, helically wounded tensile armors, anti-wear layers, interlocked carcasses; pressure armors and so on. The modeling process consists on defining the cable features and selecting the elements that will compose it. The process should take into account the desired structural characteristics, such as axial stiffness, and must respect some constraints, such as weight. To have an operational cable, one must follow a number of steps from definition to validation of the cable and any tool that provides a easier way to deal with this process is highly desired. In this scenario, Computer Aided Design software was conceived. It enables the definition of cable elements and set its relative arrangements in a cross-section view. Post-processing features are also part of the program, enabling users to visualize the geometry, determining possible interferences only visible in a three-dimensional visualization module. Although a solver is also available to determine stress and displacements and, as a sub-product, the cable weight and equivalent stiffness, the CAD software can be easily integrated to other solvers, to provide pre and post processing resources. This paper gives a general description of the whole CAD system but focus on the three-dimensional module. Through the paper, an overview of the software is shown, pointing out the system requirements. Next, the user interface is described, showing its features and, to conclude, modeled cables geometries and some results are shown.© 2010 ASME