Study On Nonlinear Dynamics Of Rotor Bearing System With Crack Fault

Rotary machinery is one of the most important mechanical equipment.However,due to its high speed,high load and bad working environment,faults such as cracks and rubbing often occur,which pose a great threat to its safe,stable and effective operation.At the same time,the non-linear oil film force will generate complex external excitation,which further aggravates the instability of the rotor operation.Therefore,this paper establishes a dynamic model of a cracked double disk rotor system and analyses its dynamic characteristics under the action of non-linear oil film force and rub-impact force,in order to provide some reference for improving the design parameters of the rotor.Firstly,the dynamic model of a two-disk rotor system with rubbing force and crack force is established.The dynamic differential equation of the system is listed by Newton's second law of motion,and the dimensionless treatment is carried out.The equation is solved numerically by compiling the C language program of the fourth-order Runge-Kutta method.The bifurcation diagram,phase diagram,Poincare section diagram,axis trajectory diagram and time history diagram are used to analyze the dynamic characteristics of the rotor system.In order to study the influence of parameters of a single rotor system on its dynamic behavior in detail,five parameters,including stator stiffness kc,rotor eccentricity u1 damping coefficient c1,clearance delta between stator and rotor friction coefficient f,are selected as the research objects.The periodic motion,quasi-periodic motion,chaotic motion,doubling bifurcation,inverse doubling bifurcation and Hopf bifurcation under different parameters are discussed.General bifurcation and other dynamic behaviors.Through the analysis,the following conclusions are drawn:stator stiffness kc,rotor eccentricity u1,damping coefficient c1,clearance delta between stator and rotor ? have a greater impact on the system,while friction coefficient f has a smaller impact on the system.At the same time,the smaller the stator stiffness kc,the better the stability of the rotorthe overall stator stiffness should be less than 3.0 × 107N/m.The larger the damping coefficient c1,the delayed appearance,reduction or even disappearance of the chaotic region of the system,and the overall damping coefficient should be greater than 1600N s/m.The larger the eccentricity of the rotor u1,the greater the dynamic behavior of the system,and more chaotic motions will occur,and the amount should be less than 0.03mm.The smaller the clearance delta between the stator and the rotor ?,the greater the chance of rubbing between the rotor and the stator,and the occurrence of rubbing Serious rubbing should be avoided.Secondly,the dynamic model of a two-disk rotor system with rub-impact force and crack force under the action of non-linear oil film force is established.The dynamic differential equation of the system is listed by Newton's second law of motion,and the dimensionless treatment is carried out.The equation is solved numerically by compiling the C language program of the fourth-order Runge-Kutta method.The bifurcation diagram,phase diagram,Poincare section diagram,axis trajectory diagram and time history diagram are used to analyze the dynamic characteristics of the rotor system.By establishing the stator stiffness kc,eccentricity u2,damping coefficient c2 and equivalent lumped mass m1 at the axis as reference parameters and stiffness variation of cracked rotor Ak.The influence of single rotor system parameters on rotor dynamic behavior is studied.Through the analysis,the following conclusions are drawn:when the non-linear oil film force acts on the rotor,it is necessary to work at high speed(greater than 2500(rad/s)).Then the selected stator stiffness should be less than 3.0 X 107N/m,the eccentricity less than 0.04mm,and the damping coefficient greater than 2500N·s/m.It is necessary to work at medium speed(more than 1000(rad/s)and less than 2500(rad/s)).The selected stator stiffness should be less than 1.0 X 107N/m,the eccentricity should be about 0.06mm,the damping coefficient should be more than 4000N s/m,and the equivalent concentrated mass of the rotor at the bearing should be more than 6kg,which can make the rotor system in a more stable one-cycle motion state.At low speed(less than 1000(rad/s)),or when the rotor is started,the rotor will become more stable with small eccentricity and small equivalent concentrated mass of the rotor at the bearing.For cracks,it is absolutely necessary to avoid them,especially to control the crack stiffness ratio below 0.3.