The fatigue problem associated with the Touchdown Pointrn(TDP) of a Steel Catenary Riser (SCR) may be less seriousrnthan is commonly understood, particularly for “soft” seafloorrnsediments typical of the Gulf of Mexico. For such softrnsediments, a SCR will dig for itself a trench having a curvedrnvertical profile that minimizes the shear forces in the SCR atrnthe TDP and consequently reduces the fatigue damage in thernvicinity of the TDP. In this paper this trench is modeled as arnrigid curved surface upon which the SCR lands.rnQuasi-static analysis predicts that the fatigue life of a SCRrnwith the TDP touching down on a rigid curved trench is muchrngreater than that of an SCR landing on a rigid flat seafloor.rnThe maximum fatigue damage either occurs within the trenchrnpast the TDP, where riser motions are small, or occurs up thernriser away from the TDP, where shear forces are small.rnDynamic analyses utilizing finite element computer modelsrnare less clear. One early FE analysis incorporating a rigidrncurved trench showed a fatigue life improvement factor ofrnabout 2.3, whereas other analyses were inconclusive. Therefore,rnit is too early to draw general conclusions about potentialrnfatigue life improvements until further research is done.
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