Research On Synchronous Operation Stability Of Rotating Machinery With Multi-unit Shaft

Starting with the production of small Chinese air separation plant of30m3/h in1950s, it has been developed for supper-large plant, such as model110000m3/h. According to the current investigation state of the domestic air separation plant, there are some deficiencies of less reliability, frequent malfunctions, and its continuous operation periodic is only1/2-2/3of import one. Therefore, it is of great significant for research on synchronous operation stability of rotating machinery with multi-unit shaft.Taking a large compressor for example, this paper focuses on the synchronous operation stability of its low pressure side including big gear, turbine, medium-pressure cylinders rotor and Low pressure cylinder. Although all elements of multi-unit shaft are all through the debug before installation, there is still the occurrence of exceeded vibration after that. So it is necessary to study the stability of its operation. In this paper, the dynamic model of Multi-unit shaft is set up firstly, which is followed by the analysis of modal harmony response in the environment of ANSYS software including the study of operation stability, and then, the critical speed and the amplitude of vibration are designed optimally by means of ANSYS. At last, the elevation of multi-unit shaft system is calculated by using MATLAB, the investigation process in detail is following as:(1)The finite element method is employed to divide the unit mesh of multi-unit shaft system, which dynamic mode is set up by using APDL language in ANSYS software.(2)After the setting up of model, we analyze the dynamic characteristics of multi-unit shaft system by ANSYS, including the analysis of modal and that of harmony response, among which bending vibration and torsional vibration are taken into consideration, respectively. and the former20-order natural frequencies, critical speed and vibration models are derived, as well as the operational stability in the steady. state. The effect of unbalanced forces on the whole system is discussed by analyzing the harmony response under the working speed, among which in interesting conclusion is reached that the effect of the unbalanced forces at the end of shaft of turbine is the greatest.(3)Based on the aforementioned work, the whole multi-unit shaft system is designed optimally through programming in ANSYS, in which the zero order method and one order method are used to optimize the natural frequency and the total amplitude of vibration, respectively. Furthermore, the better results are obtained by the comparison of two optimal methods.(4)Considering the bend of each rotor under the gravity and the effect of the load distribution versus the elevation of system, in order to ensure the stable operation of system, the spin axis of the rotor must be possessed a smooth curve (deflection curve), as well as the rationality of design for the loads of each bearing. The deflection curve of the multi-unit shaft system and its practical support reaction force are derived by programming in MATLAB, which is the stronger foundation of the future work.