Riser-Soil Interaction: Local Dynamics at TDP and a Discussion on the Eigenvalue and the VIV Problems

Abstract

The eigenvalue problem of risers is of utmost importance, particularly if vortex-induced vibration (VIV) is concerned. Design procedures rely on the determination of eigenvalues and eigenmodes. Natural frequencies are not too sensitive to the proper consideration of boundary condition, within a certain extent where dynamics at the touchdown area (TDA) may be modeled as dominated by the dynamics of the suspended part. However, eigenmodes may be strongly affected in this region because, strictly speaking, this is a nonlinear one-side (contact-type) boundary condition. Actually, we shall consider a nonlinear eigenvalue problem. Locally, at TDA, riser flexural rigidity and soil interaction play important roles and may affect the dynamic curvature. Extending and merging former analytical solutions on touchdown point (TDP) dynamics and on the eigenvalue problem, obtained through asymptotic and perturbation methods, the present work critically address soil and bending stiffness effects a little further. As far as linear soil stiffness and planar dynamics hypotheses may be considered valid, it is shown that penetration in the soil is small and that its effect does not change significantly the bending loading that is mainly caused by the cyclic excursion of the TDP and corresponding dynamic tension. A comparison of the analytical results with a full nonlinear time-domain simulation shows a remarkable agreement for a typical steel catenary riser. The WKB approximation for the eigenvalue problem gives good estimates for TDP excursion. As the dynamic tension caused solely by VIV is very small, the merged analytical solution may be used as a first estimate of the curvature variation at TDP in the cases of current perpendicular to the "riser plane."

The 3D Nonlinear Dynamics of Catenary Slender Structures for Marine Applications

“…Indicative examples are the seafloor interaction, buckling-like effects, "compression loading" and heave induced out-of-plane motions. For the formulation of the seafloor interaction, various approaches have been proposed and it appears that the associated effects continue to attract the attention of the research community (Leira et al, 2004;Aubeny et al, 2006;Pesce et al, 2006;Clukey et al, 2008). "Compression loading" has been studied mainly in 2D (Passano & Larsen, 2006& 2007Chatjigeorgiou et al, 2007;Chatjigeorgiou, 2008), while buckling-like effects and possible destabilizations are mainly considered for completely vertical structures (Kuiper & Mertikine, 2005;Gadagi & Benaroya, 2006;Chandrasekaran et al, 2006;Kuiper et al, 2008).…”

Uma formulação em elementos finitos para a análise dinâmica e estática não linear de risers incluindo o contato com o leito do mar

“…Segundo Pesce et al (2006) a aproximação com fundações elásticas lineares pode ser uma alternativa válida, pelo menos, para solos relativamente rígidos.…”

“…Pesce et al (1998) avaliam o efeito da rigidez do solo sobre a configuração estática de um riser. Pesce et al (2006) consideram um solo linear para a análise dinâmica da estrutura.…”

Experimental analysis of fluid-structure interaction phenomena on a vertical flexible cylinder: modal coeficients and parametric resonance.

“…This is an usual and classical approach; further acknowledgment might be seen on Pesce and Martins (2005), Huera-Huarte (2006), Pesce et al (2006b), Silveira et al (2007), Rustad et al (2008), Tsukada (2011), Takafuji andMartins (2012), Mainçon andBernardo-Viljoen (2013) &Prado et al (2013). Numerical models that consider large rotations have shown to be a good approach for some stability investigations; see Gay Neto and Martins (2013).…”

“…• The analytical treatment of riser dynamics, see Pesce (1997), Aranha et al (1997), Pesce and Fujarra (1997), Fujarra et al (1997), Pesce et al (1998), Pesce et al (1999), Ramos Jr. andPesce (2003), Pesce et al (2006a) and Silveira et al (2007). ;…”