Mechanical modeling of deepwater flexible structures with large deformation based on absolute nodal coordinate formulation

In this paper, a mechanical analysis model is proposed on basis of the absolute nodal coordinate formulation (ANCF) and the theories of continuum mechanics and finite element method to accurately analyze the statics and dynamics of deepwater flexible structures with large deformation. In this model, the traditional angle coordinate is replaced with slope coordinate under the frame of overall coordinate system. The mapping relation of the parameters under current and reference configurations is established, and the method of describing the nonlinear geometric relationship of the element with the current configuration parameters is discussed. Then, based on the energy variation principle, the generalized elastic force and stiffness matrix of the element are derived, and the mass matrix and external load matrix of the element are combined to perform the element assembling using the finite element method, and the static and dynamic equilibrium equations are then formed. The calculation programs are compiled by FORTRAN language, whose reliability and accuracy are checked by the cases of beam model with theoretical solutions. Finally, a kind of steel lazy wave catenary riser is taken as an example, and its static and dynamic characteristics are analyzed systematically, which further verifies the effectiveness and practicability of the mechanical model.