ABSTRACT
One of the crucial factors governing the vibration characteristics of rotating machinery is the effective rotor dynamic parameters (stiffness and damping) of the supports and similar components as seen by the rotor. The dynamic stiffness of the support is determined by the combined effects of flexibility of the bearing, the bearing pedestal assembly (bearing housing), and the foundations on which the pedestal is mounted. For the case of turbo-generator rotors mounted on oil-film bearings, the bearings might be three times more flexible as compared to pedestals and foundations. In Chapter 3, various kinds of bearings, dampers, and seals were described and the main focus of the chapter is to outline theoretical methods of calculation of rotor dynamic parameters for bearings, dampers, and seals. Practical limitations of such procedures are outlined, subsequently. In the present chapter, the focus is the same: obtaining the rotor dynamic parameters of bearings, dampers, and seals; however, methods involve experimental estimation based on the force-response information of rotor systems. These methods are broadly classified based on the force given to the system, i.e. the static and dynamic forces. The static method can be used for obtaining stiffness coefficients only; however, dynamic methods can be used to obtain both the stiffness and damping coefficients. Initially, these methods are described for rigid rotors mounted on flexible bearings. Subsequently, literature surveys are presented for the methods extended for real rotors by considering shaft and bearings both as flexible and by a more general modeling technique, i.e. the finite-element method (FEM). Various methods are compared for their merits and demerits in terms of the simplicity of applications, accuracy, consistency, robustness, and versatility. Experimental considerations for designing the test rig, types of vibration measurements, suitable conditions at which measurements of vibration signals are to be taken, and processing of raw vibration signals are also addressed (some of these will be covered in Chapters 15 and 16).
