Buoyancy forces and the 2D finite element analysis of flexible offshore pipes and risers

Abstract

SUMMARYMany analysts use simple lower-order beam elements for the non-linear analysis of curved beam and arch structures. The aim of the present paper is to indicate how one may add the e ects of buoyancy, steady-state current loading and riser top-tension to such an idealization so that it may be used for the analysis of o shore pipes and risers. The current work is restricted to static two-dimensional modelling but it paves the way for further work in three dimensions, which will include dynamics.

Non-linear finite element analysis of flexible risers in presence of buoyancy force and seabed interaction boundary condition

“…Also, the pipe material properties are as; modulus of elasticity, 2.0 GPa and Poisson's ratio 0.25. Yazdchi and Crisfield [6] used a two-dimensional model to analyze this problem. The purpose of the analysis is to find the final configuration of the beam under gravity combined with external and buoyancy loads.…”

“…They adopted a simplified model by replacing the seabed surface with an elastic foundation with independent elastic springs having an arbitrary thickness which maybe critically damped. Yazdchi and Crisfield [6] used a simple two-dimensional lower-order beam element formulation for nonlinear analysis of riser structures. They included in their formulation the effects of buoyancy, steady-state current loading and riser top-tension, but they did not consider sea-bed effects.…”

Buoyancy potential conserving technique for dynamic analysis of offshore pipes and risers

“…The coefficients k A and k B have been defined in our previous papers [1,24]. The stiffness matrix due to these buoyancy forces can be calculated by applying variations to the corresponding buoyancy forces and for the sake of the brevity, they are not explained here.…”

Non‐linear dynamic behaviour of flexible marine pipes and risers

“…In contrast, in the current work we directly relate equivalent forces to the rotational degrees of freedom at the nodes. We have demonstrated this procedure for a two-dimensional modelling in Reference [37] and in the current work, we both extend the approach to 3D and introduce dynamics.…”

“…In the present work, we ÿnd that our tangent sti ness matrix is non-symmetric, although only weakly so, with the non-symmetry vanishing as the mesh is reÿned. It was postulated in Reference [37] that the non-symmetry was a consequence of the way in which we moved from a continuum to a beam. Indeed, current work by the authors for 3D analysis starts with a potential and leads to a fully symmetric tangent [43].…”