Active axial vibration control of a shaft-bearing system excited by the dynamic thrust force

The axial vibration of a shaft-bearing system induced by the thrust excitation is usually composed of multiple tones. To suppress the axial vibration of the shaft-bearing system, two inertial electro-magnetic actuators are mounted symmetrically at the thrust bearing and work in parallel to exert control forces. The control signal is generated by an adaptive algorithm with subband filtering, which aims to attenuate over a broadband the vibration of the thrust bearing and its foundation induced by the dynamic thrust force. To reduce computational complexity, the recursive computation is partly realized with the auto-regressive moving average (ARMA) model. The proposed active control approach is evaluated numerically at first with the dynamic model of the shaft-bearing system and then verified with an experimental system. It is demonstrated by the numerical and experimental results that the active control approach is able to suppress the multi-tone vibration of the thrust bearing and the foundation. Moreover, in comparison to the single-band adaptive feedback algorithm, the adaptive algorithm with subband filtering is more effective when the disturbance contains multiple tones.

Rotordynamics of an Improved Face-grinding Spindle: Rotational Stiffness of Thrust Bearing Increases Radial Stiffness of Spindle

The support is a key factor affecting performance of face-grinding spindle. However, advantage of traditional rolling element bearing is not highlighted when it is for large-size face grinding. This technical brief aims to develop a combined support for the face-grinding spindle consisting of a water-lubricated hydrostatic thrust bearing and two types of radial rolling bearings, and the flexible rotor dynamics of the spindle with the combined support is analyzed using the modified transfer matrix method. The results show that the rotational stiffness of water-lubricated hydrostatic thrust bearing can increase the radial stiffness of the face-grinding spindle, so the small-size rolling bearings can be utilized as the radial support for the spindle by aid of such rotational stiffness. A comparative study of comprehensive performance between the spindle supported by rolling bearings and the replacement spindle designed with our proposed combined support shows that the proposed one has technical advantage of large axial load-carrying capacity, low frictional power loss, low temperature rise and etc.

Structure design and performance analysis of aerostatic thrust bearing with compound restrictors

Aerostatic thrust bearing compensated by multi-orifices and porous material restrictor simultaneously is proposed to improve the static performance of the bearing. Load Carrying Capacity (LCC), stiffness and the flow field characteristics of the bearing are obtained by Computational Fluid Dynamic (CFD) simulation. The influences of supply pressure, orifice number, orifice diameter, orifice distribution, porous material thickness and permeability coefficient on the bearing performance are analysed. It is indicated that LCC and stiffness of the bearing with compound restrictors are much higher than those of the bearing with porous material restrictor or multi-orifice restrictor if gas film thickness is in rational range. The bearing with compound restrictors has better stability than that of the bearing with multi-orifice restrictor. Moreover, the optimum bearing parameters with compound restrictors are given to improving the performance of aerostatic thrust bearing.

Theoretical and Experimental Investigation on Air Film Pressure Field Characteristics of Aerostatic Thrust Bearing

This paper studied the air film pressure field (AFPF) characteristics of aerostatic thrust bearing, in which we proposed the measurement equipment for the 2D AFPF and successfully verified the theoretical simulation results. The experimental results agreed well with the theoretical results. However, in the area between the distribution circle of orifice to the air film outlet boundary, the experimental air film pressure (AFP) was slightly higher than the theoretical one. While for the area between the distribution circle of orifice and the center of the bearing, it showed the opposite law. Besides, the increase ratio of the AFP was close to that of the external load with its increase.

DISTRIBUTION OF THE NORMAL REACTIONS ON THE QUANTOMOBILE WHEELS

Introduction: The progress of science has made it possible to create new quantum engines (QEs) powered by physical vacuum energy. A QE will generate a vector-based propulsive force, or thrust, applicable to the vehicle body directly, with no transmission required. Traditional cars will be upgraded with QEs and thus converted into quantomobiles. QE thrust application at the point of the vehicle body, hovering above the bearing surface, introduces changes in the traditional diagram of forces acting on the vehicle. Therefore, it is necessary to assess the influence of thrust on the longitudinal stability of the quantomobile. Methods: In the course of the study, we upgraded the diagram of forces acting on the traditional vehicle, by introducing QE thrust (bearing in mind vehicle hovering above the bearing surface). We also developed a corresponding mathematical model for the distribution of the normal reactions on the wheels, taking into account QE placement. Results: Among the developed calculation complexes to perform a qualitative analysis of the influence of force factors on the quantomobile chassis load, a complex representing the longitudinal thrust and the thrust height was distinguished. Discussion: These complexes may serve as the basis of calculation units for more detailed programming, analysis, and synthesis of the design of vehicles with QEs, assessment of the longitudinal stability of the vehicle, optimization of QE placement in the quantomobile body. Example: The method developed is presented using a quantomobile similar to a KamAZ-4326 automobile. Conclusion: The considered diagram of forces acting on a quantomobile, including QE thrust above the bearing surface, shall become generic for force diagrams of quantomobiles with additional thrusters intended to increase the longitudinal stability of the vehicle.

Inertial contributions to friction measurements in thrust bearings

Surface textures decrease friction in lubricated sliding contact. Traditionally, the friction reduction for a given textured surface is determined by using the Reynolds equation, which neglects fluid inertia. However, as the separation and relative motion between the surfaces increase, inertia can affect the measured tangential and normal forces for flow over a textured surface, and thus cause the coefficient of friction to differ from the purely viscous, Stokes flow prediction. Here, the increase in torque and normal force between a moving plate and stationary textured surface, which simulates a textured thrust bearing, are calculated as a function of the Reynolds number in the thin film limit. The predictions for a non-textured thrust bearing are compared to fully 3-D numerical simulations of the incompressible Navier-Stokes equation, and the predictions for textured thrust bearings are compared to experimental data given in the literature. Good agreement is seen between the predictions and the data, validating the predicted scaling laws. This work also suggests that inertia can be used as a secondary effect to reduce friction in lubricated sliding, and textures that take advantage of the inertial effects will have lower friction than textures that only use purely viscous effects.

An improved dynamic modeling approach of aerostatic thrust bearing considering frequency-varying stiffness and damping of air film

The damped mass-spring model is often employed for the dynamic modeling and vibration analysis of aerostatic bearing systems by taking the air film as equivalent springs. However, the stiffness and damping of the air film are frequency-dependent, making the commonly used approach of taking static stiffness or fixed value as the spring coefficient no longer applicable for a bearing subject to a complex external force containing different frequencies. To address this issue, this paper develops the damped mass-spring model for the aerostatic thrust bearing considering the frequency-varying stiffness and damping by means of the linear superposition method. It indicates that the air bearing is still a linear system despite the frequency-dependent character of dynamic coefficients because the bearing vibration satisfies the superposition principle. The improved dynamic modeling approach is able to accurately and efficiently predict the overall dynamic response of the thrust plate when the it is subjected to a multi-frequency vibration. In solving the overall dynamic response, the stiffness and damping associated with the responses of the transient part and steady part correspond to the natural vibration frequency and external disturbance frequencies, respectively. The feasibility and accuracy of the improved modeling approach are partly or completely verified by the direct trajectory calculation method, the CFD dynamic mesh simulation and a modal test. The proposed modeling method provides an effective way for the vibration analysis of air bearings, and in the meantime avoids the possible numerical errors caused by the traditional modeling approach.

Texture optimization and verification for the thrust bearing used in rotary compressors based on a transient tribo-dynamics model

Rotary compressors are designed more and more compact and the compressor cylinder's ambient pressure is designed very high to facilitate oil separation and improve efficiency. However, these designs cause the working condition of the thrust bearing becoming harsher, and severe wear may occur. The present study is aimed at mitigating its wear condition through surface texturing. Based on a transient tribo-dynamics model considering the coupling effect of the journal and thrust bearings, a texture optimization study for the thrust bearing is conducted, in which three different stochastic optimization algorithms are utilized. The results show that thrust bearings with optimized textures have significantly reduced contact forces and wear under a high working frequency due to an extra hydrodynamic support around the texture dimples. The optimized texture designs are fabricated on the thrust bearing surfaces by a high-accurate picosecond laser machine and their performance is assessed through experiments using a compressor performance test platform. The experiment results confirm that the textured thrust bearing has a lower wear depth. Moreover, the coefficient of performance (COP) of the testing compressor with textured thrust bearing is increased while its input power decreases, which implies a reduced friction force and a higher energy efficiency.