Dynamic effects from the barge motion during davit lifting of offshore pipelines have been estimated through this study. In this paper a geometrically nonlinear finite cable element is presented to use in the modeling of davit lines. The cable element is derived directly from the compatibility equations and flexibility matrix of elastic catenary cable theory for the arbitrary plane loading and geometry. Also the generalized beam element derived on the basis of large deflection theory is used to model the pipeline and the elastic bi-linear spring element is utilized to model the seabed A computer program has been developed to perform the static or dynamic analysis of the offshore pipeline installation problems In the program Newmark- β method is used to obtain a time domain solution for the dynamic response of the pipeline and cable. Newton-Raphson" s iteration method is used to solve the nonlinear system of algebraic static or dynamic equations at each time step The barge motion can be directly considered as a support motion. Results from the static and dynamic analysis of a conventional davit lifting system of submarine pipeline by the computer program are summarized and presented.
In the installation of a conventional riser system a davit system may be mobilized to lift submarine pipeline to which riser section is weld-connected on a barge above seawater level. In such a case an exact evaluation of dynamic effects on stresses of pipeline and cable tensions of davit lines by an wave induced barge motion can be so essential and the evaluated results so significant In the actual projects of the offshore pipeline installation only the margin of 25 or 30 percent of SMYS against the dynamic amplifications during davit lifting is generally given to the static stress level of pipe without any detailed dynamic analysis.
