This work presents the application of a reduced time integration method to the nonlinear dynamic analysis of compliant structures for deepwater oil exploration and production. The main features of the method are outlined, by observing the results of the case studies - a tension-leg platform (TLP) and a guyed tower.


The expression for the reduced equations of motion (I) will have a drastically smaller number of unknowns whenever the transformation matrix's is able to provide an accurate dynamic response with m « n. In these cases, reduced integration methods can perform remarkably better than the standard direct time integration procedure; this will be true in linear analyses of large-scale structural systems presenting an inertial behavior, under medium to long-duration loadings and/or periodic loadings. In linear problems the matrix "l" and the reduced matrices of eq (I) can be determined only once, prior to the time integration process, and the associated computational costs are amortized by the economy obtained along the integration of the reduced equations. In problems with mild nonlinearities or with localized nonlinear effects, that can be efficiently treated by the Pseudo-Force technique, reduction techniques have also been successfully employed [Landau, 1983; Bathe and Gracewski, 1981; Shah et aI., 1979; Lukkunaprasit et aI., 1980; Lima et aI., 1985]: the stiffness matrix is not reevaluated, and the reduced matrices can again be determined only once. The potential benefits of the application of a reduced integration method to problems presenting more severe nonlinear effects are, however, apparently smaller. In the analysis of such problems, that include compliant structures for deepwater oil exploration and production, an incremental iterative (i-I) formulation is required [Bathe, 1982; Batlle and Cimento, 1980], and the transformation matrix should, in principle, be updated at every step of the time integration process.

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