Nonlinear analysis of flexible and steel catenary risers with internal flow and seabed interaction effects

Abstract

Flexible risers and steel catenary risers often provide unique riser solutions for today's deepwater field development. Accurate analysis of these slender structures, in which there are high-speed HP/HT internal flows, is critical to ensure personnel and asset safety. In this study, a special global coordinate-based FEM rod model was adopted to identify and quantify the effects of internal flow and hydrostatic pressure on both flexible and deepwater steel catenary risers, with emphasis on the latter. By incorporating internal flow induced forces into the model, it was found that the internal flow contributes a new term to the effective tension expression. For flexible risers in shallow water, internal flow and hydrostatic pressure made virtually no change to effective tension by merely altering the riser wall tension. In deep water the internal pressure wielded a dominant role in governing the riser effective tension and furthering the static configuration, while the effect of inflow velocity was negligible. With respect to the riser seabed interaction, both the seabed support and friction effect were considered, with the former modeled by a nonlinear quadratic spring, allowing for a consistent derivation of the tangent stiffness matrix. The presented application examples show that the nonlinear quadratic spring is, when using the catenary solution as an initial static profile, an efficient way to model the quasi-Winkler-type elastic seabed foundation in this finite element scheme.

Stability Analysis of Nonlocal Elastic Columns with Initial Imperfection

“…The first study of the deformation of an elastica under loading was probably due to James Bernoulli although it was Euler who established the basic theory [11,13]. By taking advantage of Euler's celebrated work, considerable efforts have been devoted to the theory with applications extended from classical fields to statistical mechanics (see [14] and the references therein), biomechanics [15], and ocean engineering [16,17]. Within the scope of most of these studies, linear constitutive relations are utilized.…”

Flexible Riser Installation Optimisation Based on Virtual Prototyping

“…Finite element method (FEM) is adopted as an effective method in dealing with nonlinearity and boundary conditions [8][9] [10] in the global analysis of flexible riser and has been used to verify the model based on rod theory [11] [12]. However, the efforts that have been made rarely focus on the mechanical analyses for a whole planned procedure but single step, which means the impact from the previous step on the next one is ignored.…”

A Coupled Rans-Vof and Finite Element Model for Wave Interaction With Highly Flexible Vegetation

“…A Reynolds Averaged Navier-Stokes solver with Volume of Fluid surface capturing scheme (RANS-VOF) is extended to include the effect of flexible vegetation on flow. The vegetation is assumed to behave like a slender rod, whose governing equations are solved by Finite Element Method (Garrett 1982;Chen et al 2011). There is no constraint with regard to the magnitude of the vegetation motion in this coupled model as with most previous wave-vegetation models.…”