In this paper, based on the theory of rotor dynamics, the nonlinear dynamics of a rotor system with an eccentric rotor is analyzed. Taking the double-support rotor system with a single turntable as the object, the mathematical modeling method of the rotor system with an eccentric rotor and the rotation analysis of the turntable are analyzed in detail. According to ANSYS software, the influence of eccentricity on the rotor system and the relationship between eccentricity and nonlinearity are analyzed.

Purpose As a core rotating component of power machinery and working machinery, the rotor system is widely used in the fields of machinery, electric power and aviation. When the system operates at high speed, the system stability is of great importance. To enhance the system stability, squeeze film damper (SFD) is being installed in the rotor system to alleviate vibration. The purpose of this paper is to first classify the rotor system into two types, the dual rotor system and the single rotor system, and to comprehensively and specifically mention the method of generating the dynamic model. Next, based on the establishment of a dynamic model with and without SFD in the rotor system, the optimization design of the rotor system with SFD was carried out using a genetic algorithm. Through sensitivity analysis, SFD clearance, shaft stiffness and oil viscosity were determined as design variables of the rotor system, and the objective function was the minimization of the maximum amplitude of the rotor system with SFD within the operation speed range. Design/methodology/approach In this paper, first, the rotor system was classified into two types, namely, the dual rotor system and the single rotor system, and the method of creating a dynamic model was comprehensively and specifically mentioned. Here, the dynamic model of the rotor system was derived in detail for the single rotor system and the dual rotor system with and without SFD. Next, based on the establishment of a dynamic model with and without SFD in the rotor system, the optimization design of the rotor system with SFD was carried out using a genetic algorithm. The sensitivity analysis of the unbalanced response was carried out to determine the design variables of the optimization design. Through sensitivity analysis, SFD clearance, shaft stiffness and oil viscosity were determined as design variables of the rotor system, and the objective function was the minimization of the maximum amplitude of the rotor system with SFD within the operation speed range. Findings SFD clearance, shaft stiffness and oil viscosity were determined as design variables of the rotor system through sensitivity analysis of the unbalanced response. These three variables are basic factors affecting the amplitude of the rotor system with SFD. Originality/value In the existing studies, only a dynamic model of a single rotor system with SFD was created, and the characteristic values of pure SFD were selected as optimization variables and optimization design was carried out. But in this study, the rotor system was classified into two types, namely, the dual rotor system and the single rotor system, and the method of creating a dynamic model was comprehensively and specifically mentioned. In addition, optimization design variables were selected and optimized design was performed through sensitivity analysis on the unbalanced response of factors affecting the vibration characteristics of the rotor system.

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Background Squeeze Film Damper plays an important role in enhancing the dynamic stability of the rotor and damping rotor vibrations and transmitted forces when traversing critical speeds. Depending on how SFD is designed, SFD can reduce the vibration and transmission forces of the rotating system and it can have the opposite effect. In particular, depending on how the single eccentric rotor system with SFD is mathematically accurately modeled and optimize, the stability of the single eccentric rotor system with SFD is further increased. Purpose The purpose of this study is to improve the stability of the single eccentric rotor system by optimizing the variables affecting the vibration characteristics of the single eccentric rotor system with SFD. Methods By using Lagrange function, the dynamic model for the single eccentric rotor system with SFD was comprehensively and specifically mentioned, and the motion equation of centroid path of the single rotor system with SFD was formulated. Next, the optimization design of the single eccentric rotor system with SFD was carried out using a genetic algorithm and MATLAB program. Results After optimizing the design of the single eccentric rotor system with SFD, the amplitude of the single eccentric rotor system with SFD was reduced by 15.2% compared to before the optimization, and the stability of the single eccentric rotor system was further improved. ConclusionIn this paper, we investigated the dynamic modeling method, the motion equation of centroid path and optimization design method of the single eccentric rotor system with SFD. This results will contribute the nonlinear dynamic behaviors of the single eccentric rotor system, and provide a theoretical basis for the analysis of the dynamic modeling, the optimization design, and the nonlinear dynamic characteristic analysis of the dual rotor system.

It is of great importance to reveal the refrigeration mechanism at low-temperature around 4 K in pulse tube for improvement of the cooling performance in 4 K pulse tube crycoolers (PTCs). In this paper, the thermo-physical process in 4 K pulse tube was studied analytically from microscopic viewpoint using CFD simulation. The thermodynamic cycles of different gas parcels throughout the pulse tube were investigated. It was found that the real gas characteristics of the helium at the pulse tube cold end manifest more apparently from the central part nearer to the wall outside the boundary layer. Furthermore, it was revealed that boundary layer has the weakened heat loss or helpful effect on refrigeration in phase-shifting 4 K pulse tube operating at low frequency. This research newly provides intensified understanding of the inherent characteristics of 4 K GM-type pulse tube.