During the time domain simulation of a marine riser under stochastic wave loads, the small time increment and long time duration require efficiency in the finite element modeling. It is expected that the riser system can be modeled by larger elements, or fewer degrees of freedom. In this presentation, higher-order beam elements are introduced, with their tensions treated as Lagrangian multipliers. Each element can have zero, one, or two mid-nodes with varying geometry. Relatively few high-order elements can produce the same accuracy as a large number of conventional beam elements. Normally, the constraints have to be imposed to the element nodes. When a large number of constraints are involved, such as in the multitube analyses, the higher-order elements alone cannot reduce the number of elements. In the present methodology, this difficulty is also circumvented. A constraint is allowed to be applied to any location within an element. Even it is possible to model a lateral constraint sliding along a riser. The cross-sectional forces and moments can be output at any location along the riser. They are continuous within and across the elements by a special interpolation technique. These techniques help to enhance computational efficiency in the riser analyses, especially for the long-duration time simulation of the riser motions.
Higher-order finite element modeling of material degradation due to cutting
