A Numerical Simulation Scheme for Dynamics of Flexible Riser and Its Validation by Forced Oscillation Experiments

摘要

This paper presents a numerical simulation scheme for the dynamics of a highly flexible riser, and the validation of the scheme by forced oscillation experiments. Governing equations of motion for riser dynamics are derived using Hamilton's principle, and nonlinear terms of a small-order magnitude in the derived equations are neglected by using appropriate assumptions. The Galerkin and Newmark-β methods are used for spatial and time integration of the governing equations. Sinusoidal modal functions are adopted for the description of the variables. Inertia and drag coefficients used in the numerical scheme depend on the Keulegan-Carpenter number. A series of model experiments with 2 different boundary conditions is executed for the purpose of validating the developed simulation scheme. A highly flexible riser model is used, and the boundary conditions are either simple or fixed at the top end of the riser and free at the bottom. Three-dimensional riser motion is measured using 10 to 12 CCD cameras, and force/moment are obtained by using a 5-component load cell. The results of the numerical simulation and experiment are compared in various ways. They showed quite good agreement and confirmed the good performance of the developed numerical simulation scheme.