Nonlinear Dynamic Analysis Of Rotor System With Misalignment-cracking Coupling Faults

Rotating machinery is one kind of mechanical equipments most widely used in the industrial department, its stable operation in the influences the development process of all the industry. As the core component of rotating machinery, the dynamics characteristics of the rotor system directly affect the structural safety and working performance of rotating machinery. Due to the harsh running environment of the rotor system, the rotor system occurs coupling faults is very common in the actual engineering work, therefore the coupling faults of rotor system is an important research direction in the field of rotor dynamics. Misalignment fault and cracking fault are common faults of rotor system, when the rotor system is running in misalignment fault state, it may cause large deflection and abrasion of the shaft, the possibility of the crack appearing or original small crack deepening on the shaft is greatly increased, and the deep crack rotor system can make the system response too large and lead to misalignment fault. Therefore, an aircraft engine low pressure rotor system is investigated in this paper, and the nonlinear dynamic characteristics of the rotor system with misalignment-cracking coupling faults is studied.First, the motion characteristics of gear coupling in misalignment state are analyzed and the coupling parallel and angular misalignment force is deduced. The advantages and disadvantages of the commonly used mathematical model of crack are compared and the most suitable crack model is selected. The motion and force of the ball-bearings are analyzed. And the dynamic differential equation of the rotor system with misalignment-cracking coupling faults is established by using the Lagrange method, and the dimensionless is carried out.Then, the numerical integration method of Rugge-Kutta is used to analyze the system and obtain the dynamic characteristics of misalignment fault and cracking fault and misalignment-cracking coupling faults. When the rotor system only has misalignment fault, the response of the system appeared 1-time and 2-time frequencies. And the resonance vibration of the rotor system is not only induced in the position of the critical speed, but also induced in the position of the half-critical-speed. When the rotor system only has crack fault, the response of the system appeared the frequencies 1-time, 2-time, 3-time, and so on. And the vibration peak appeared in the position of the critical speed, the 1/2 critical speed and the 1/3 critical speed, and the amplitude of the 1/2 critical speed and the 1/3 critical speed is close. When the rotor system is with misalignment-cracking coupling faults, the response of the system appeared the frequencies 1-time, 2-time, 3-time, and so on. And the vibration peak appeared in the position of the critical speed, the 1/2 critical speed and the 1/3 critical speed, and the amplitude of the 1/2 critical speed is much higher than the amplitude of the 1/3 critical speed.Finally, the effects of the system parameters on the rotor system response with misalignment-cracking coupling faults are also studied by using the bifurcation plots, three-dimensional waterfalls, the Poincare maps, time-domain waveform, the frequency spectrogram.