A. Bahtui

A Finite Element Analysis for Unbonded Flexible Risers Under Torsion

This paper presents a detailed finite-element analysis of unbonded flexible risers. The numerical results are compared to the analytical solutions for various load cases. In the finite-element model, all layers are modeled separately with contact interfaces between each layer. The finite-element model includes the main features of the riser geometry with very little simplifying assumptions made. The numerical model was solved using a fully explicit time-integration scheme implemented in a parallel environment on a 16-processor cluster. The very good agreement found from numerical and analytical comparisons validates the use of our numerical model to provide benchmark solutions against which further detailed investigation will be made.

Numerical and Analytical Modeling of Unbonded Flexible Risers

This paper presents an analytical formulation and a finite element analysis of the behavior of multilayer unbonded flexible risers. The finite element model accurately incorporates all the fine details of the riser that were previously considered to be important but too difficult to simulate due to the significant associated computational cost. All layers of the riser are separately modeled, and contact interaction between layers has been accounted for. The model includes geometric nonlinearity as well as frictional effects. The analysis considers the main modes of flexible riser loading, which include internal and external pressures, axial tension, torsion, and bending. Computations were performed by employing a fully explicit time integration scheme on a parallel 16-processor cluster of computers. Consistency of simulation results was demonstrated by comparison with those of the analytical model of an identical structure. The close agreement gives confidence in both approaches.

A Finite Element Analysis for Unbonded Flexible Risers Under Axial Tension

Recent developments on the numerical analysis of detailed finite element models of unbonded flexible risers using ABAQUS are presented. Several analytical methods are studied and combined together, and their results are compared with those obtained in the finite element model for two different tests, the second one involving cyclic loading. In the finite element model all layers are modeled separately and contact interfaces are placed between each layer. A fully explicit time-integration scheme was used on a 16-processor cluster. The very good agreement found from numerical and analytical comparisons validates the use of our numerical model to provide benchmark solutions against which further detailed investigation will be made.Copyright

A Multi-Scale Approach to the Analysis of Ultra Deepwater Unbonded Flexible Risers

The results of a detailed, non-linear finite-element analysis of a small-scale (i.e. 1.7m long) six-layer unbonded flexible riser, accounting for interlayer contact and frictional slip, are used to calibrate a novel, simplified constitutive model for a 3D, non-linear Euler-Bernoulli beam model suitable for large scale analyses (hundreds of meters in length where water depth is more than 1000m). The detailed finite element model contains all the layers, each modeled separately with contact interfaces between them. The finite element model includes the main features of the riser geometry with very little simplifying assumptions made. The detailed finite element model is formulated in the framework of a novel, multi-scale approach potentially suitable for ultra deepwater applications. A simple, three-dimensional Euler-Bernoulli beam element, suitable for large scale analyses, is developed based on a non-linear constitutive law for the beam cross-section relating bending curvatures to the conjugate stress resultants.Copyright

One Dimensional Moving Heat Source in Hollow FGM Cylinder

This paper presents the analytical solution of one-dimensional mechanical and thermal stresses for a hollow cylinder made of functionally graded material. The material properties vary continuously across the thickness, according to power functions of radial direction. Temperature distribution is symmetric, and transient. The thermal boundary conditions may include conduction, flux, and convection for inside or outside of hollow cylinder. Thermoelasticity equation is transient, including the moving heat source. The heat conduction and Navier equations are solved analytically, using the generalized Bessel function. A direct method of solution of Navier equation is presented.Copyright