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Dynamic analysis of a marine riser Guo, Yongzhi

Abstract

The problem of the dynamic analysis of a marine riser is considered in this thesis. The equations of motion for a marine riser undergoing large three dimensional deflections and rotations are derived using modal discretization approach. The nonlinear expressions for the bending and torsional deformations are obtained for a beam undergoing finite rotations. The elastic strain energy is expressed in terms of these deformations and the Lagrange equations are used to derive the equations of motion valid for large deformations. The three dimensional shear effect based on nonlinear elastic theory is included in the formulation. The dynamic response of a typical marine riser system due to excitations of the ocean waves, current and surface vessel motion is studied. The hydrodynamic loading on the riser is represented by a general form of the Morison equation. The nonlinearity of structure and drag force are completely retained and a numerical procedure in the time domain is developed. The effects of structural and hydrodynamic parameters on motion amplitude in two dimensional case are evaluated. Alternatively, the dynamic response of the simplified riser system is studied by an analytical approach based on Butenin's method. The Butenin's method involves less computational effort and the solution based on this method matches the numerical solutions well when the nonlinearities are small.

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