In the figure a sample of rotor and foundation is shown. As an example, let's consider that the rotor can be modelled by 5 elements, i.e. 6 nodes and the foundation has 2 modal components. The vector x of the generalised displacements of the complete system is actually a column vector composed by two sub-vectors: in the upper parts are the d.o.f. of the rotor alone xr, in the lower part those of the foundation xc.

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