Low order radiation forces by analytic interpolation with degree constraint

The positive real modeling of a floating body is considered, whereas the main focus is on the radiation forces and moments. The radiation forces and moments describe the interaction of a floating body with the surrounding fluid. This type of mathematical model is of interest in among control and simulation of dynamical positioned vessels (i.e. ships and offshore platforms) and wave power plants. It has been proven that the radiation forces are passive, but very little attention have been drawn towards low order passive identification of these forces. Traditionally high order models have been obtained, and subsequently model order reduction have been applied to obtain low order models. Here, a direct approach for obtaining low order passive models using analytic interpolation with a degree constraint is applied. A case study involving a 3 degrees of freedom surface vessel is shown to illustrate the features of the proposed approach.