An application of a finite element analysis to the study of Marine Risers



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A solution procedure is developed for the analysis of variable tensioned beam columns, using a finite element analysis. A specific application of this solution technique is the analysis of marine drilling risers. The static response of the riser column is obtained for the following loading conditions: 1. Hydrodynamic drag forces resulting from a steady current. 2. Horizontal offset of the drilling vessel from the wellhead. 3. Forces caused by the drilling mud flowing inside the riser pipe. Consideration is given to the variation of several parameters of a riser system design and their effect upon the operational effectiveness of the marine riser is discussed. The parameters that are considered are: 1.Effective top tension. 2. Top offset. 3. Effective rotational spring constant at the ends of the riser column. 4. Added buoyancy. An error analysis is included so that the error involved in using different element sizes can be evaluated. This is of importance since the optimum element size allows for the maintenance of a designated accuracy while being as large as possible hence requiring a minimum number of elements. The beam element utilized in the analysis has a continuous mass distribution. Thus the axial force in the riser column is a continuous function of the length. The geometric stiffness matrix for the beam element is derived for an axial force that is a linear function of the length. A comparison is made between models of the riser column having a continuous mass distribution and a lumped mass distribution. The static stability of variable tensioned beam columns is investigated. Different solution techniques are compared and also the different beam elements are compared.