Comparative study between various reduced model and modal analysis of viscoelastic rotors

Abstract

The present work includes the study of dynamic characteristics on a flexible rotor shaft system. This arises due to the internal material damping of rotor bearing system, which produces a tangential force on a rotor and increasing with the rotor spin speed. Due to these dynamic characteristics of rotor is influence which destabilizes the rotor shaft system. Under this dynamic behaviour of rotor shaft system is studied to get the dynamic nature of rotor shaft system. This can be estimated in terms of Campbell diagram, modal damping factor, mode shape and directional frequency response function. These plots are obtained by using the matlab software by solving a eigenvalues problem. finite element approach plays a significant role in modelling continuum system after discretizing it into some finite number of element. More number of elements or enhancing the mesh size give better accuracy in results. But discretizing the system into infinite elements inherits the swelling size of system matrices. Substantial increment of the system matrices sometime causes very high mathematical complications and takes an unwanted computational time. Model reduction is techniques for reducing the degree of freedom from the full system model to produce a reduced model but its dynamic characteristics is maintain. System equivalent reduction process, Improved reduced system, Guyan reduction are used to reduce the large system of equation of motion to fewer degree of freedom. The full system model also includes internal and external damping and gyroscopic effect. Since it is not practical to measure all degree of freedom, so the model is reduced using model reduction techniques. The reduced model is used to plot Campbell diagram, unbalance response using MATLAB software and comparison is done with original system to show its effectiveness.