Influences of Randomly Uncertain Factors on Dynamic Coefficients of an Interlocking Labyrinth Seal-Rotor System

Many randomly uncertain factors inevitably arise when gas flows through a labyrinth seal, and the orbit of the rotor center will not rotate along a steady trajectory, as previously studied. Here, random uncertainty is considered in an interlocking labyrinth seal-rotor system to investigate the fluctuations of dynamic coefficients. The bounded noise excitation is introduced into the momentum equation of the gas flow, and as a result, the orbit of the rotor center is expressed as the combination of an elliptic trajectory with the bounded noise perturbation. Simulation results of the coefficients under randomly uncertain perturbations with various strengths are comparatively investigated with the traditional predictions under ideal conditions, from which the influences of random uncertain factors on dynamic coefficients are analyzed in terms of the rotor speed, pressure difference, and inlet whirl velocity. It is shown that the deviation levels of the dynamic coefficients are directly related to the random perturbations and routinely increase with such perturbation strengths, and the coefficients themselves may exhibit distinct variation patterns against the rotor speed, pressure difference, and inlet whirl velocity.

Modelling and Analysis of a Virtual Prototype of a Rotary Machine in MSC.ADAMS

The article presents an analysis of the virtual model of Laval (Jeffcott) rotor in the software environment MSC.ADAMS. The parameters describing the stability of the rotor operation were monitored and evaluated, i. j. critical angular velocity and trajectory of the rotor center of gravity (orbit). The results were compared with the values measured on the experimental equipment, as well as with the values obtained by analytical calculation. The paper further presents a simulation in which the second critical velocity was reached. The paper further presents a simulation in which the second critical velocity was reached.

Dynamics of mass variable rotor and its application in modeling tuning operation

The vibration of a rotor with variable mass as a one-mass system with two degrees of freedom is investigated. An analytical procedure for solving of the system of two coupled second-order differential equations with slow time variable parameters is developed. The trajectory of the rotor center for various initial conditions is obtained. The method developed in the paper is applied for determining the vibration of the work piece during turning operation. The analytically obtained results show the influence of mass variation, cutting parameters and cutting force on the dynamic properties of the work piece. A decrease in mass of the work piece increases the amplitude of vibration. The amplitude increase is faster if the cutting velocity is higher. The obtained results are compared with experimentally obtained ones. The correlation between vibration and surface roughness is determined.

Optimization of the interference parameters of an Orbit motor using genetic algorithm

In the present study, the leakage of fluid due to gap generation at the contact points is eliminated by introducing interference between the rotor and the stator of an Orbit motor. Interference is incorporated in the system by modifying the roller radius, the chordal thickness, and the pitch circle radius. In an Orbit motor of interference-fit type, the contact points and the rotor center deviate from their original positions as found in an Orbit motor of perfect-fit type. A corrective technique based on minimization of the potential energy of the system is used to obtain the rotor center of an interference-fit motor. The rotor profile is initially generated around the geometrically obtained center of a perfect-fit motor. It is then shifted in the direction of decreasing potential energy, until the rotor center corresponding to minimum energy is attained. The main drawback of introducing interference is the generation of an unbalanced torque which affects the output torque of the motor. Thus, optimization of interference parameters using genetic algorithm is carried out to determine a system for which no gap is generated at the contacts and simultaneously it is ensured that the unbalanced torque ripple amplitude is minimum.

Research on the nonlinear dynamic characteristics of opposed high-speed gas bearing systems

In recent years, the opposed high-speed gas bearing system has been gradually valued and used in the field of precision machinery, especially for precision instruments and mechanisms requiring high speed, high precision, and high rigidity. Although the bearing capacity is not as good as the oil film bearings, it can provide a working environment where the rotor can generate high speed and low heat without deformation of the shaft, and the gas pressure distribution of clearance in bearing also has better stability. Due to the strong nonlinearity of the gas film pressure function of gas bearings and the fact that the actual shaft system possesses dynamic problems including critical speed, spindle imbalance or improper bearing design, it will cause the rotation process of the shaft to produce a nonperiodic motion and instability, and even chaotic motion under certain parameters. And these irregular movements can even cause machine damage or process delays when serious, so in order to understand the process of working under the conditions where the system will have a nonperiodic phenomenon and to avoid the occurrence of irregular vibration especially chaos. In this paper, the opposed high-speed gas bearing system feature will be discussed in detail with three different numerical analysis methods, i.e. the finite difference method, perturbation method, and mixing method. The relevant theories include dynamic trajectories, spectrum analysis, bifurcation diagram, Poincare map, and the maximum Lyapunov exponents. From the results of nonlinear dynamic behavior of the rotor center, periodic and nonperiodic motions occur at different rotor masses and bearing parameters, respectively. Especially, for the chaos of shaft exists at specific intervals and can be distinguished efficiently. Meanwhile, it is found to ensure that the bearing system can suppress the phenomena of chaos actively by adjusting the bearing parameters, and reduce the system loss caused by irregular vibration. It is expected to be an important basis for designing a precision shaft or mechanism and to enhance the stability and performance of bearing system.

Investigation of the Effect of Gravity Anomalies on the Precession Motion of Single Gyroscope Gravimeter

Obtained a complete mathematical model of motion of unbalanced three-axis gyroscope, based on which was studied the influence of gravity anomalies on the precessional motion of single gyroscope gravimeter. There are research results of mathematical modeling of gravitational perturbations impact on precessional movement of gyroscope. The results have showed a proportional relationship between the value of gravitational perturbations and the precession angle, and have proved that increase in rotor center-of-gravity shift leads to a proportional increase in gravitational perturbations impact. The obtained results may be practically used in designing sensors of gravity anomalies, the knowledge of which (gravity anomaly) is used in mineral exploration and inertial navigation.

Detecting phase singularities and rotor center trajectories based on the Hilbert transform of intraatrial electrograms in an atrial voxel model

This work aimed at the detection of rotor centers within the atrial cavity during atrial fibrillation on the basis of phase singularities. A voxel based method was established which employs the Hilbert transform and the phase of unipolar electrograms. The method provides a 3D overview of phase singularities at the endocardial surface and within the blood volume. Mapping those phase singularities from the inside of the atria at the endocardium yielded rotor center trajectories. We discuss the results for an unstable and a more stable rotor. The side length of the areas covered by the trajectories varied from 1.5 mm to 10 mm. These results are important for cardiologists who target rotors with RF ablation in order to cure atrial fibrillation.

Vibration Suppression Evaluation of Smart Journal Bearing Using Giant Magnetostrictive Actuators

A new kind of smart hydrodynamic journal bearings with giant magnetostrictive actuators (GMA) is introduced. The static and dynamic displacement outputs of the designed GMA are up to tens of microns, about the same order of magnitude as the conventional journal bearing clearance. Vibration suppression of the new smart journal bearing is theoretically evaluated using a simple Jeffcott rotor-bearing system. Kinematic equations are set up including the magneto-mechanical coupling model for GMA. The bearing oil film force under large vibration is calculated using a fast and efficient non-stationary oil film database technique. The unbalance vibration orbit of the rotor center is simulated. A simple synchronous proportional control method for GMA with different control phases and gains is investigated. The suppress effect of unbalance vibration and improvement of oil whip unstable speed is evaluated. The simulation proves that the new journal bearing has better stability, and that rotor vibration can be actively suppressed.

Dynamic Analysis of a Flexible Rotor Supported on Two Turbulent Model Journal Bearings with Micropolar Fluid Lubrication

This paper presents the complex dynamic analysis of a flexible rotor–bearing system supported by two turbulent micropolar fluid film journal bearings under nonlinear suspension. The Modified Reynolds equation based on the assumptions of turbulent flow and the micropolar parameters has been considered. The system considers Short bearing approximation to simplify the numerical computations. The pressure distribution thus obtained is used to find out the resulting forces about the journal center in the radial and tangential directions. The Non-dimensional dynamic equations are derived considering appropriate non dimensional parameters and solved using MATLAB for a wide range of non-dimensional speed ratios. Plots of the journal center trajectories and rotor center trajectories are obtained. The results show that the system undergoes undesirable nonsynchronous vibrations due to bearing center displacement. Micropolar fluid is found to stabilize the system even when the flow of the system becomes turbulent. The study presented enhances the understanding of the nonlinear dynamics of turbulent journal bearings with respect to dimensionless parameters.

Bifurcation and Nonlinear Dynamic Analysis of Externally Pressurized Double Air Films Bearing System

This paper studies the chaotic and nonlinear dynamic behaviors of a rigid rotor supported by externally pressurized double air films (EPDAF) bearing system. A hybrid numerical method combining the differential transformation method and the finite difference method is used to calculate pressure distribution of EPDAF bearing system and bifurcation phenomenon of rotor center orbits. The results obtained for the orbits of the rotor center are in good agreement with those obtained using the traditional finite difference approach. The results presented summarize the changes which take place in the dynamic behavior of the EPDAF bearing system as the rotor mass and bearing number are increased and therefore provide a useful guideline for the bearing system.