Dynamics Of Geared Rotor System In Five-Shaft Integrally Centrifugal Compressor And Its Nonlinear Characteristics

Multi-shaft integral gear assembly centrifugal compressor is an important and modernly advanced equipment in energy and petrochemical field. As the key component of the integral gear assembly centrifugal compressor, the geared rotor-bearing system is composed of many rotors by gear meshing, and the rotors always working above their critical speed under high load all the time, which makes the dynamic performance of the rotor system more complicated, and the effect of the nonlinear factors of bearings and gears on the centrifugal compressor will be more obvious. According to some statistics, the rotor accidents is the dominate accidents of the large centrifugal compressor units in energy and petrochemical industry of China, and generally recognized as large vibrations and frequent vibration damage. However, in most compressor manufacturing companies, conventional design method is still used in rotor system designing. That is, the rotor system of the whole machine which multi-shaft coupled by gears is always divided into different rotor systems or sub-systems composed of single shaft, while the nonlinear parameters of the bearing and meshed gear are also neglected. The analysis and designing strategy based on the separated single-shaft rotor system and the simplified methods may induce dangerous operation of the machine, cause abnormal vibration, or even impact to the production. It is necessary to study the coupling dynamic characteristic of the geared rotor system in the integral gear assembly centrifugal compressor, and learn its nonlinear characteristic and the vibration regularity.Under the support of National Key Basic Research Program of China (973 program, Fundamental research of the high-efficiency and reliability of the geared centrifugal compressor,2012CB026000, Subject Five-The vibration fault mechanism and the principle and method of the intelligent interlock protection of the compressor unit), the geared rotor-bearing system of a centrifugal compressor with five shafts is taken as research object in this paper, and dynamics and nonlinear effects of which is studied, where the numerical simulation and experimental studies are included. The main contents of this dissertation are as follows:Firstly, the finite element modelling method of the geared rotor-bearing system is proposed, where the linear mesh stiffness of engaged helical gears is involved. Then, the scaled model test rig of a five shafts integral gear assembly centrifugal compressor is designed according to the similarity theory with geometry distortion, which is verified by comparing with the simulation results of the original rotor system. And the critical speeds and the coupling responses of the rotor system with mesh stiffness are calculated based on the FE model by means of analytic method, including lateral vibration, axial vibration and the fluctuation of the meshing force. The simulation results are verified by the test results.Secondly, the kinetic parameters of the journal bearings and the film thrust bearing are calculated under different loading based on Reynolds equation and the static equilibrium hypothesis. Then, the bearing stiffness and damper database of the test rig is established. Base on the database, the response calculation method of the rotor system considered the nonlinear oil film force is proposed and the influence of the changing loads on the dynamic characteristic of geared rotor-bearing system is studied, which explains the causes of 'critical load' to a certain extend and presents a calculation method of the'critical load'.Finally, the finite element model of geared rotor-bearing system with nonlinear gear mesh force is established based on the nonlinear time-varying model, which realizes the high precision nonlinear dynamic simulation of the geared rotor-bearing system with multipoint engagement in integral gear assembly centrifugal compressor. Then, the influence of time-varying stiffness, gear clearance, transmission error and the system load on the meshing force and dynamic response of geared rotor-bearing system are studied, which is verified by the test results.The contents and conclusions in this paper would provide theoretical support for the dynamic optimization design, fault monitoring and diagnosis on the multi-shaft integral gear assembly centrifugal compressor.