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Research Papers: Materials Technology

A Finite Macro-Element for Orthotropic Cylindrical Layer Modeling

[+] Author and Article Information
Clóvis de Arruda Martins

University of São Paulo,
São Paulo 05508-900, Brazil

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received February 1, 2011; final manuscript received January 17, 2013; published online May 24, 2013. Assoc. Editor: Pingsha Dong.

J. Offshore Mech. Arct. Eng 135(3), 031401 (May 24, 2013) (9 pages) Paper No: OMAE-11-1008; doi: 10.1115/1.4023793 History: Received February 01, 2011; Revised January 17, 2013

The offshore industry is in constant evolution due to the need to reach increasing water depths for new oil fields exploitation. In this scenario, not only are new types of platforms being designed but also new types of risers, including new flexible pipes and 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 mechanical behavior of flexible pipes and umbilical cables, adequate models are necessary. One can rely on finite element models (FEM), which show a great difficulty in mesh generation and convergence (especially 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 ones). Related to that approach, this paper presents a tubular element to model a cylinder with orthotropic material properties. In the model, the displacement and the loads are described by means of Fourier series, making it possible to treat a broad class of loads. The formulation is presented in detail, giving special attention to surface loading modeling. The results obtained in case studies are compared to those of a classical finite element modeling tool with a good agreement.

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Figures

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Fig. 1

Cylindrical coordinate system

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Fig. 2

Cylinder section with associated displacements

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Fig. 3

Areas of an infinitesimal cylindrical element

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Fig. 4

ANSYS convergence for radial displacement

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Fig. 5

Comparison between radial displacement for model and ANSYS (case I)

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Fig. 6

Mesh divisions (diva is the number of axial divisions and divr is the number of radial divisions)

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Fig. 7

Radial displacements comparison for top surface

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Fig. 8

Radial displacements comparison for sheath side

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