First of all we consider the unbalance. It is modelled by force which is applied in a node of the system and depends on the square of the rotating speed.
Then we consider a bow, in particular a thermal bow or a permanent bow. We give to this fault also the name of extended bow. This fault can be represented by means of a couple. It has a constant module but rotates with the rotor.
Then we consider another kind of bow that we call local bow.
This bow can be induced f.i. by rub. You can see that the couple is applied on one element of the system.
Also in this case the amplitude of the couple is constant and the couple is rotating with the rotor.
