Oil Film Damping Research Articles

Simulation method for dynamic characteristics of rotor-support system subjected to environmental loads

An improved finite element method was proposed to investigate the dynamic characteristics of rotor system with environmental loads (temperature and aerodynamic forces) in aeroengines. According to the axial temperature distribution within shaft elements, the polynomials were established for physical properties of material. The derivation for coefficient matrices under thermal loads, and the tensile stiffness matrix considering axial aerodynamic forces were completed, based on the Timoshenko beam theory. A high-pressure rotor was simulated with operating temperature 200∼600∘C, and the magnitude of aerodynamic force is 105N. Furthermore, a squeezed film damper (SFD) was adopted to this rotor-support system, its steady responses were solved by the equivalent coefficient method, and the Newmark-HHT method was utilized to solve the transient responses. The results indicate that the first two critical speeds are reduced by 1.85 % and 2.07 %, which is mainly caused by thermal loads. The rising temperature leads to lower elastic modulus, higher Poisson's ratio and expansion ratio. With the amount of a mass unbalance being 500 g·mm located at the 1st-stage compressor disk (CD1): the 1st resonance peaks at CD1 and turbine disk (TD) increase by 4.56 % and 4.98 %, respectively, and the 2nd resonance peaks at CD1 and TD rise 5.88 % and 5.00 %, separately. Owing to SFD damping, the first two resonance peaks at CD1 and TD decrease by 69 % and 51 %, respectively. Compared to 40 °C, the first two resonance peaks at CD1 increase by 88 % and 55 % at the oil temperature 100 °C. The oil-film damping deteriorates significantly due to the lower oil viscosity in higher temperature. When operating near the first-order critical speed, the transient responses of rotor perform as simple harmonics, circular precession trajectory, dominant rotational frequency, and periodic motions. Overall, the dynamic characteristics of rotor-SFD-support systems exposed to environmental loads can be predicted by the proposed simulation method.

Nonlinear dynamic characteristics analysis method of planetary gear train torsional vibration considering meshing oil film force

Planetary gear train is an important part of automatic transmission. The oil film between teeth is one of the key factors affecting the torsional vibration of planetary gear train. Selecting the appropriate oil film stiffness is of great significance for analyzing the nonlinear dynamic characteristics of planetary gear train. A method for analyzing the nonlinear dynamic characteristics of planetary gear system torsional vibration considering the oil film force between teeth is proposed in this paper. A 3-DOF torsional vibration model of planetary gear train considering oil film is established. In this model, the oil film between teeth is equivalent to a time-varying nonlinear spring-damper element, and nonlinear factors such as backlash and meshing error are also considered. The effects of meshing oil film thickness on oil film stiffness and damping are analyzed, and the torsional vibration characteristics of planetary gear train under different meshing stiffness, meshing damping ratio, and rotational speed are analyzed based on bifurcation diagrams. The results show that in one meshing cycle, the meshing oil film thickness first becomes larger and then becomes smaller. When the meshing oil film thickness increases, the meshing oil film stiffness and the equivalent meshing oil film damping become smaller. The torsional vibration of planetary gear train can be effectively reduced by increasing meshing stiffness, damping ratio, rotational speed within a certain range. This method provides technical support for reducing torsional vibration of planetary gear train and realizing stable transmission of planetary gear train.

Navigating the Dynamics of Squeeze Film Dampers: Unraveling Stiffness and Damping Using a Dual Lens of Reynolds Equation and Neural Network Models for Sensitivity Analysis and Predictive Insights

The squeeze film damper (SFD) is proven to be highly effective in mitigating rotor vibration as it traverses the critical speed, thus making it extensively utilized in the aeroengine domain. In this paper, we investigate the stiffness and damping of SFD using the Reynolds equation and neural network models. Our specific focus includes examining the structural and operating parameters of SFDs, such as clearance, feed pressure of oil, rotor whirl, and rotational speed. Firstly, the pressure distribution analytical model of the oil film inside the SFD based on the hydrodynamic lubrication theory is established, as described by the Reynolds equation. It obtained oil film forces, pressure, stiffness, and damping values under various sets of structural, lubrication, and operating parameters, including length, clearance, boundary pressure at both sides, rotational speed, and whirling motion, by applying difference computations to the Reynolds equation. Secondly, according to the significant analyses of the obtained oil film stiffness and damping, the following three parameters of the most significance are found: clearance, rotational speed, and rotor whirl. Furthermore, neural network models, including GA-BP and decision tree models, are established based on the obtained results of difference computation. The numerical simulation and calculation of these models are then applied to show their validity with all given parameters and the three significant parameters separately as two sets of model input. Regardless of either set of model inputs, these established neural network models are capable of predicting the nonlinear stiffness and damping of the oil film inside an SFD. These sensitive parameters merely require measurement, followed by the utilization of a neural network to predict stiffness and damping instead of the Reynolds equation. This process serves structural enhancement, facilitates parameter optimization in SFDs, and provides crucial support for refining the design parameters of SFDs.

Study of the Effect of Static Eccentricity on Vibration Damping Properties of Squeeze Film Dampers Considering the Two-Phase Flow Case

To analyze the effect of static eccentricity on the air ingestion distribution and vibration damping properties of the SFD, a numerical simulation study of SFDs considering two-phase flow was carried out based on CFD using a transient solution method and dynamic mesh technique. The results show that the angle between the static eccentricity direction and the circumferential direction of the oil supply hole increases and the air ingestion area in the oil film expands. In contrast, the oil film damping decreases, and the larger the static eccentricity distance, the greater its effect on the air ingestion area in the oil film. When the circumferential angle is small, the oil film damping increases with the increase of static eccentricity distance, and when the circumferential angle is large, the oil film damping decreases with the increase of static eccentricity distance and then increases. With the increase of static eccentricity distance, the air ingestion area at both ends of the oil film increases. At the same time, studying the effect of dynamic eccentricity shows that as the dynamic eccentricity increases, the oil film damping first decreases and then increases, and the air ingestion area increases. Comparing the 1 hole, the 2 hole, and the 3 hole oil supplies, the air ingestion area is significantly larger in the 1 hole oil supply than in the 2 hole or the 3 hole oil supplies, and the oil film damping of the 1 hole oil supply is smaller than the oil film damping of the 2 hole or the 3 hole oil supplies. It can be seen from the present study that in the actual installation of the SFD, when the circumferential angle is less than 60°, the static eccentricity can be increased appropriately. When the circumferential angle is greater than 60°, the static eccentricity can be appropriately reduced.

Dynamic characteristics of open-ends squeeze film dampers with air ingestion

Abstract In order to explore the air ingestion characteristics of the open-ends squeeze film dampers (SFD), a 3D computational fluid dynamics solution model of the SFD was proposed based. The setting of opening boundary conditions was considered, which was verified experimentally by the bidirectional excitation. The results revealed that with the same precession frequency, the smaller radial clearance leads to the greater oil film damping. An increasing oil supply and oil holes led to the smaller air ingestion range at the end. The design guideline for the open-ends SFD was investigated in the present work.

A Study on the Thermal Properties of Oil-Film Viscosity in Squeeze Film Dampers

Considering the variation in temperature of the oil film in squeeze film dampers (SFDs) caused by squeezing, a more comprehensive analysis of SFD can be obtained. Aiming to investigate the viscosity thermal effect of the oil film in SFDs, this study established a 3D CFD solution model. Based on the total energy model, the viscosity thermal effect was performed. With the mixture multi–phase flow model, the Zwart–Gerber–Belamri (Z–G–B) cavitation model, and the use of the additional mass coefficient, the two–phase flow phenomenon in SFDs was discussed. The oil film at various temperatures and the temperature distribution of different oil types under different working conditions were analyzed. Furthermore, the influence of the SFD thermal effect on the two–phase flow phenomenon were particularly carried out. Meanwhile, the simulation results of the SFD thermal effect were experimentally verified. The results revealed that the maximum temperature of the SFD oil film was enhanced with the increase in the eccentricity ratio and precession frequency. The temperature of the oil film was closely related to the oil dynamic viscosity. The dynamic viscosity of the oil was reduced, which was caused by the SFD thermal effect, thus leading to decreased oil–film damping, enlarging the vaporization level and the range of vapor cavitation, as well as the ingested air amount. CFD simulation results of the thermal effect were in good agreement with the experimental data, which verified the accuracy of the proposed model.

Design process and simulations for the rotor system of a high-efficiency 22 kW micro-gas-turbine range extender for electric vehicles

This paper proposes a design process for a high-efficiency micro-gas-turbine (MGT)-based range extender(RE). The study includes a conceptual system design and a detailed design of an MGT RE. This design adopts a two-spool intercooled and recuperated high-speed MGT. The study focuses on the design of a low-pressure (LP) rotor system integrated with an electric generator, where a permanent magnet synchronous generator (PMSG) with a round transversally polarized bar permanent magnet (PM) is selected as a generator type. The turbine and compressor sides of the rotor are supported by dual back-to-back angular contact ball bearings modeled using a detailed five degrees of freedom contact model. The bearing cartridge is supported by squeeze film dampers (SFDs). The SFD that supports the bearings is modeled with a linear spring and an oil-film damper. Simulation results dictate that stresses in the magnet and sleeve vary due to several design parameters, thus time-efficient simulation is strongly required for effective design optimization. Also, the results indicate that the SFD design optimization range leading to acceptable rotordynamics requirements is narrow.

Armature Structure Optimization of Annular Multipole Solenoid Valves Based on Electromagnetic Force Distribution

To improve the dynamic response speed of high-speed solenoid valves in electric fuel injection systems of marine diesel engines, a numerical simulation model of the solenoid valve is described in this paper. The accuracy of the simulation model was verified on the test bed of the solenoid valve. The effect of the punch position and the size of the dynamic response of the solenoid valve were investigated by using the distribution law of the electromagnetic force in the armature. The results of the test showed that armature drilling in the inter-yoke zone can optimize the solenoid closing response time, but it has little impact on the solenoid opening response time. From this rule, two groove schemes were further designed. Through comparison and calculation, it can be concluded that the fan groove scheme is better than the trapezoidal groove scheme, and that the opening and closing response times of the solenoid valve should be targeted in order to multi-target optimize the fan groove geometric parameters and the armature thickness. The results show that after optimization, the weight of the motion part is reduced by 21.6%, the opening response time of the solenoid valve is reduced by 11.1%, and the closing response time is reduced by 30.0%. While reducing the oil film damping of the armature motion, the overall dynamic response characteristics of the solenoid valve are improved.

Damping analysis of micro-gyroscope with ball-disk rotor

According to the structure of the micro-gyroscope with a ball-disk rotor, the corresponding Reynolds equation is solved by using the motion equation, continuity equation, and state equation. The damping coefficients of axial vibration, radial vibration, and rotation around the Z axis are derived theoretically. The damping theoretical model of the micro-gyroscope is constructed to analyze the gas film damping and oil film damping of the ball-disk rotor in three degrees of freedom motion.

Investigation of stiffness and damping coefficients in fluid film bearing with bio-oils and mineral-based oil

Rotating machinery utilizes fluid film bearings because of their good load carrying capacity and inherent damping properties. Fluid film bearings offer stiffness and damping parameters to ensure dynamic stability. The damping and stiffness characteristics of oil film significantly change the critical speed and unbalance response of the rotor. The damping and stiffness coefficients (direct, cross-coupled) may lead to system instability, also known as self-excited vibrations. Bio-oils have good tribological and physiochemical properties. They are also environment-friendly and bio-degradable. In this work, bio-oils (rapeseed, palm olein, and soybean) are evaluated in terms of their dynamic characteristics to that of mineral-based SAE40 lubricant for journal-bearing applications. The analytical extraction of damping and stiffness coefficients is performed based on the experimental dynamic viscosity data at different temperatures. In comparison to SAE40, the bio-oils have shown improved responsiveness. Bio-oils showed lower cross-coupled stiffness coefficients than SAE40, the primary source of rotor instability. The main contribution of this study is that it provides damping and stiffness coefficients for various bio-oils at different eccentricity ratios and viscosities for different types of oils. This may be used to characterize the dynamic properties of the fluid film bearing under various operating circumstances. It is concluded that the difference in cross-coupled stiffness favors bio-oils. Whereas, the difference in cross-coupled damping favors SAE40 by around 6%. This discrepancy is decreased to less than 2% for all oil’s final eccentricity ratio values (bio-oils and SAE40).

An Improved Dynamic Transmission Error Model Applied on Coupling Analysis of Gear Dynamics and Elastohydrodynamic Lubrication

Abstract In order to study the coupling effect of cylindrical gear dynamics and elastohydrodynamic lubrication (EHL), based on dynamic theory, a dynamic model of a six degrees-of-freedom (6DOF) coupled system is established. Based on the numerical solution of EHL, an improved dynamic transmission error (DTE) model was established. The oil film stiffness, oil film damping, and center oil film thickness obtained by the numerical solution were used in the gear dynamics analysis. The dynamics and EHL characteristics of the gear system are analyzed and compared with the general model. The results show that by using the improved DTE model, the comprehensive stiffness and comprehensive damping of the gear increase and fluctuate slightly. The amplitude of the tooth surface meshing force and dynamic response decreases. Under the action of tooth surface meshing force, the oil film pressure and thickness show oscillation characteristics.

Study on Vibration and Bifurcation of an Aeroengine Rotor System with Elastic Ring Squeeze Film Damper

To analyze the problem of vibration and bifurcation in the rotor system of the aeroengine with the elastic ring squeeze film damper (ERSFD) and elastic supports, the theoretical equation of the dynamic rotor system is developed in this paper, based on the rotor system, elastic ring squeeze film damper (ERSFD), and three elastic supports. The estimated analytical solution of the oil film force is solved using the short bearing approximation theory and the semi‐oil film inference theory in the suspension and the inner and outer boss contact. Considering the oil film stiffness and damping of rolling bearings, the rolling bearing force model is established based on the elastohydrodynamic lubrication (EHL) theory. By the average method, the vibration and bifurcation modes are obtained concerning the bearing coefficient and parameters. The range optimization of parameters can be appropriately improved to enhance the dynamic characteristics of the device given different parameters of the hole of oil seepage, the stiffness, the position of elastic supports, and other structural parameters.

Calculation method for comprehensive damping of ball bearings based on multigrid method

PurposeAs an important part of the rotor system, the damping coefficient of ball bearing has a great influence on the dynamic characteristics of the system. This study aims to propose a theoretical calculation method and an experimental test method to obtain the damping coefficient of ball bearing.Design/methodology/approachBased on Hertzian contact theory and elastohydrodynamic lubrication theory, the point contact oil film damping analysis model of ball bearing is established. The comprehensive damping calculation method considering external radial load, centrifugal force, ball spin, rotational speed and lubricating oil film is derived. The multigrid method is used to obtain the oil film pressure and thickness distribution in the contact zone. The variation trend of comprehensive damping with bearing radial load, rotational speed, oil film thickness and viscosity is analyzed. The test platform is designed and the influencing factors of damping are tested.FindingsThe validity of the model and reliability of the test device are verified by comparing the good consistency obtained in the work. The results show that the comprehensive damping of ball bearing increases with the increase of radial load and decreases with the increase of rotational speed.Originality/valueAt present, the existing bearing damping model can achieve approximate calculation of damping, but the factors considered in these models are not comprehensive enough. Besides, few studies exist regarding test platform of bearing damping, and a perfect test plan has not yet been formed. In this paper, the comprehensive damping calculation model of ball bearing is improved, and a complete experimental scheme is proposed to provide reference for the comprehensive damping theory and experimental research of bearing.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0342/

Research on Friction and Impact Load Response of Ship Shafting

Liang, X. and Ji, H., 2020. Research on friction and impact load response of ship shafting. In: Gong, D.; Zhang, M., and Liu, R. (eds.), Advances in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 106, pp. 514–517. Coconut Creek (Florida), ISSN 0749-0208.With the increase of rotating speed, the vibration speed of impact load increases. The slower, the slower and the faster, the vibration maintenance time is also different. This shows that when the rotation speed of the shaft changes, the oil-film lubrication characteristics of the bearing change, and the oil-film stiffness and oil-film damping of the bearing change, thus showing the support of the sliding bearing. Different from the fixed elastic damping bearing, which is not affected by rotating speed, the oil film dynamically changes its support stiffness and variable damping characteristics. Therefore, when the rotating speed is in the self-excited vibration region of the sliding bearing, the impact time is long, and the amplitude attenuation is slow. When the rotating speed is not in the self-excited vibration region of the bearing, it is in good agreement with the theoretical calculation results.

Dynamic Characteristics of Encased Differential Gear Train with Journal Bearing

Taking the marine encased differential gear train as an example, the relationship between the journal bearing parameters and the meshing force of the transmission system is analyzed. In this paper, the dynamic model of the encased differential gear train with journal bearing is established considering the factors of time-varying meshing stiffness and comprehensive transmission error. In this dynamic model, four stiffnesses and four damping coefficients are applied to characterize the asymmetry and interaction of the oil film stiffness and damping of planet bearing. The system responses are calculated by the Fourier series numerical algorithm. The results show that the introduction of journal bearing in encased differential gear train can contribute to gearbox vibration reduction. Moreover, the planet bearing parameters (e.g., clearance-to-radius ratio and eccentricity ratio) of the differential stage affect the meshing forces of both the differential and encased stages. In addition, the influence of the planet bearing parameters of the encased stage on the meshing force of the encased stage is more obvious than that of the differential stage. This work may develop a theoretical analysis framework for the design and manufacture of marine transmission systems in the future.

An analysis on the influence of air ingestion on vibration damping properties of squeeze film dampers

Considering the effect of air ingestion, a three-dimensional CFD model of open ends squeeze film damper (SFD) was established based on transient time step solution method and dynamic mesh technique. And the model was experimentally verified by bidirectional excitation experiment. Experiment and CFD simulation shows that air ingestion was caused by the pressure difference between oil film and external environment. With increasing precession frequency and eccentricity ratio, air ingestion area is gradually expanding resulting in increasing air volume, shrinking effective coverage of oil film and performance degradation of damper. Thereby, oil film damping shows the tendency to reduce. Compared with the case without considering air ingestion, the case considering air ingestion has obviously smaller peak pressure in the CFD simulation.

Investigation on Steady State Unbalance Response of Rotor with Elastic Ring Squeeze Film Damper

In this paper, the method for calculating steady state response of a rotor system with elastic ring squeeze film damper(s) is studied. The finite difference method is used to calculate the oil film pressure field which excludes the influence of rotating speed and considers the action of oil orifices starting with the governing equations of oil film. The mechanical characteristic curves of ERSFD are obtained by integrating the film pressure field, based on which the steady state response of the rotor system with ERSFD(s) is calculated by the finite element method and iteration method. The calculating response is compared with the experimental data, and it is found that the calculating response is in good agreement with the actual one, with the relative error of no more than 15%, which verifies the correctness of the above algorithm, and conclusion that the elastic ring extrusion oil film damper can be regarded as a linear element when the eccentricity journal of the journal is relatively small is obtained.

Investigation on stiffness and damping of transient non-Newtonian thermal elastohydrodynamic point contact for crowned herringbone gears

Abstract The stiffness and damping models of elastohydrodynamic point contact for herringbone gears with crown modification both in normal and tangential directions are developed. The lubrication performance of crowned herringbone gears in transient non-Newtonian thermal elastohydrodynamic point contacts are investigated to validate the developed models. The effects of operating and geometric parameters of crowned herringbone gear on stiffness and damping of elastohydrodynamic point contact are analyzed. The results show that in herringbone gear transmission, crown modification significantly affects oil film stiffness and damping. Low rotation speed substantially increases the damping. Helix angle contributes to the tangential stiffness and damping. This indicates that rationally selecting parameters can obtain appropriate oil film stiffness and damping to alleviate impact and vibration of herringbone gears.

Effects of oil film stiffness and damping on spur gear dynamics

An enhanced spur gear dynamic model considering the combined stiffness and damping of both gear tooth and oil film is established. To acquire the combined stiffness and damping involved in the modified dynamics equations, Ishikawa formulas are adopted to calculate the gear mesh stiffness, and given the viscous-elastic oil film in elastohydrodynamic lubrication line contact equivalent to massless spring and damping elements, the models of oil film stiffness and damping in normal and tangential directions are then developed. The combined stiffness is deduced from the stiffness of both the gear tooth and oil film, while the combined damping is derived from the damping of these parts. Effects of oil film stiffness and damping on the gear dynamics are investigated, and the dynamic response of the developed model is in contrast to that of the conventional model. The results show that by utilizing the enhanced dynamic model, the displacement fluctuation in transient stage fast decays and displacement response reaches steady state faster. The speed and acceleration fluctuations in the period converting from transient to steady stages are obviously reduced, and the response curves of speed and acceleration in steady stage are smoother. Moreover, the oil film normal damping plays large role in the gear periodic motion. This indicates that the oil film stiffness is prone to effectively alleviate impact and the oil film damping is inclined to substantially reduce vibration and frictional heat for a gear drive.

Alternative calculation on transient elasto-hydrodynamic lubrication

PurposeThe purpose of this study is to propose a new method to solve transient elasto-hydrodynamic lubrication (EHL) problem.Design/methodology/approachFirst, the steady-state EHL solution is modified so that the elastic deformation theory is combined with oil film stiffness distribution instead of steady-state Reynolds equation. Second, subsequent dynamic EHL procedure develops, recursively using transient distributed oil film stiffness and damping, where each time-marching solution is iteratively searched by ensuring both oil film force growth and elastic deformation update for each load increment.FindingsThis method increases calculation speed and provides both distributed EHL stiffness and damping for transient regimes.Originality/valueThis method is of interest for fast applications such as rolling bearings or gears.