Researches On Modeling And Dynamic Properties Of Rotor-SFD System Subjected To Basic Excitation

Rotor system is the core part of rotating machinery,it is usually fixed on the base or supporting structures.The dynamics of rotor system are influenced by base excitations including the overall maneuver and slight vibration of base.For example,the aero engine is meditative by the vibration of base when the aircraft is maneuvering;For submarines,the changing of density and earthquake produce impact load or random excitation to rotor system.The vibration resulted from rough ground can transmit to rotating system.In addition,there are several vibration sources in complicated turbo machineries,the vibration is transmitted to rotor system through supporting system,and produce a significant influence on the performance and stability.This dissertation investigates the modeling method,dynamic performance of rotor-bearing-squeeze film damper system through theoretical analysis,numerical simulation and practical experiments.1.The paper proposed a combined numerical modeling method.The influences of nonlinear bearing force,oil film force,seal force,squeeze film damper,crack,rubbing,misalignment and looseness are generally investigated based on Jeffcott model.This model can simulate the nonlinearities.However,the model is raised with many simplifications,and the interaction inside the shaft and the gyro moment cannot be considered.Finite element method is a way that can cover the shortages of Jeffcott model.It subdivides a large problem into smaller,simpler parts that are called finite elements.The simple equations that model these finite elements are then assembled into a larger system of equations that models the entire problem.In addition,this method can modify the rotary matrix of shaft,and add gyro moment parameters,so the dynamics of rotor system is analyzed more meticulously.Implicit nonlinear forces cannot be calculated at the same time due to the limitation of iteration format.Typical finite element rotor software,such as ANSYS/Dynamic rotor、NASTRAN/rotor dynamics、SAMCEF/For rotor and so on,simplify complicated force into main stiffness and damping,cross-couple stiffness and damping.This dissertation uses both finite element and discrete element methods,and discretizes the shaft and disk into finite elements,specific shape function of elements can simulate stress state better.The supporting part is discretized into several particles and nonlinear forces.The combined numerical method is proved to be efficient and can get a better result both considering FEM and nonlinearities.2.The dynamics of rotor system passing flight maneuvers are studied.The transient response and sub-harmonic response during maneuvering process are analyzed.The results show that large transient vibration happens at the beginning and end based excitation.This kind of vibration may leads to rubbing.Transient vibration amplitude decreases when the aircraft does rolling maneuvering.Squeeze film damper depresses the vibration,and the damping effect increases during maneuvering process.In addition,the stiffness of squirrel cage affects the damping effect of squeeze film damper,which should be carefully considered.For sub-harmonic and super-harmonic resonance during maneuvering process,the moments when they occurs are given,and the effect of squeeze film damper for depressing sub and super harmonic resonance is analyzed.3.The dynamics of rotor system under sine and random excitations is studied The Duhamel integral method is used to modeling of based excitation.The results show that the energy of based excitation transmits to rotor system with some kind of regular pattern.If vibration isolation is not considered,the damping effectiveness of squeeze film damper is weakened by sine-based excitation,which becomes more serious when the based excitation frequency approaches the working frequency or the doubling of working frequency.For random vibration,the squeeze film dampers can suppress the vibration of rotor system.The SFD will only suppress the energy of rotational rotor or the same frequency in Sine component when Sine and random excitation working at the same time.4.The experimental study on rotor system subjected to Sine and random basic excitations is given in the paper.A rotor test rig with two disks and rolling bearings and SFD is built.The contents of experiment including two parts: 1)the efficiency of hybrid numerical modeling method is verified by experiment.2)the conclusions from numerical analysis of rotor system subjected to basic excitations are proved by experiment.Overall,the dissertation estiablishes a rotor model with nonlinear support using finite element method.The dynamics o f a rotor system with two disks under large and small-based excitations are investigated,and validated by practical experiments.The results are valuable for solving rotor problems.