| Steel Catenary Risers (SCRs) are a preferred solution for deepwater wet-treeproduction, water/gas injection and oil/gas export, with one end connected withplatforms via flexible joints and the other end connected with wells, Thetouchdown zone, at which the SCR contacts the seabed, proves to be a criticallocation for fatigue damage of the SCR. The interaction between the SCR and theSeabed is extremely complicated, and it has great impacts on the dynamicresponse and the fatigue life of the riser. And studies show the fatigue damage issensitive to the stiffness of the seabed.Therefore, in this thesis, the stiffness characteristics of seabed are describedby realistic nonlinear load-deflection (p-y) curves, where P is the supporting forceof the seabed and y is the vertical penetration of the riser into the seabed, in thesimulation of the SCR-seabed interaction. This study extends an existing finiteelement numerical code for dynamic analysis of mooring lines and risers, knownas CABLE3D, which is based on a slender-body assumption, in order to considerthe support of the seabed with the described p-y curve.A Steel Catenary Riser under different amplitudes of surge motion of upperstructure and under different ranges of seabed soil is studied using the newversion of CABLE3D. The results show a more accurate estimate of the dynamicresponses and fatigue life of SCR at the touchdown zone. The results show thenodes at touch-down zone of the riser may undergo different process of theinteraction of seabed and riser. And as the amplitude of heave motion of the upperstructure increases, the max penetration of the rise also increases, so do the maxmoment and max stress. And as the amplitude of heave motion of the upperstructure and the strength of the seabed increase, the range of the momentincrease. And it leads to the fatigue damage increase. Therefore the fatiguedamages at the touch down zone of the riser are affected by the amplitude of motions of the upper structure and the strength of the seabed. |
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