Air Foil Bearings Research Articles

Designing Fuzzy Logic Control for the BLDC Motor Based on Airfoil Bearing

Due to removing the mechanical brushes in BLDC motors, BLDC motors are widely used in many industrial applications. Therefore, they are maintenance-free and their control is easy to design, especially for high-speed applications. For example, eco-friendly vacuum cleaners prevent atopic dermatitis, allergic rhinitis, and asthma. Other applications are Micro Gas turbines or compressors with small impellers due to miniaturization, BLDC motors must rotate at very high speeds to maintain the compressor's compression ratio. Generally, airfoil bearings should be used instead of ball bearings because of the friction in high-speed motors. Unfortunately, the characteristics of airfoil bearings depend on rotational speed. In this work, a BLDC motor with an airfoil bearing is controlled by a PID controller, this work analyzed the BLDC SYSTEM to determine the PID coefficient using the feedback method. The proposed controller Fuzzy Logic is used for adaptive control. In addition, the controller of BLDC motors combines auto-tuning and self-tuning technology. The results demonstrate that the proposed method gives efficient control by reducing the settling time and maximum peek overshot. The designed controller for the airfoil-bearing BLDC motor has a good performance.

Air Foil Thrust and Journal Bearing Coatings: A Review

Abstract Surfaces of air foil thrust and journal bearings in high-speed turbomachinery are coated to improve their operational integrity, particularly when the aerodynamic load-carrying capacity is reduced during instances of startup and shutdown. Surface coatings, as protective barriers in air foil bearings, can mitigate the adverse effects of direct surface interactions on such occasions. This article provides an in-depth review of the body of important research conducted for the study of coated air foil thrust and journal bearings, highlighting the state of the art in coating technology. The review features the role of composite coatings, designed to provide favorable thermal, mechanical, and frictional characteristics. This article also highlights the trends in the selection of coatings for air foil bearings, pertinent to desired thermo-mechanical performance.

Suppression of nonsynchronous vibration in a foil air bearing rotor system through piezoelectric actuation of the top foil—A theoretical investigation

It is well documented that the static and dynamic performance of foil air bearings (FABs) can be improved through the alteration of the radial clearance profile. One way of achieving such controllability is through piezoelectric actuation of the top foil. Such a piezoelectric foil air bearing (PFAB) avoids the dynamics complications introduced by alternative actuating mechanisms. So far, theoretical analysis of a PFAB pad in isolation has shown that top foil actuation can raise the static load capacity. This paper theoretically investigates the potential for improving the dynamic performance. A computational approach that uses Galerkin Reduction (GR) to model the air film and considers the detachment of the top foil from the bump foil is upgraded for multi-pad PFABs, thus facilitating parameter optimization. The investigation considers two conventional FAB rotor systems from the literature that exhibit strong sub-synchronous vibrations under high unbalance. It is found that the optimal voltage and placement of piezoelectric patches can result in total suppression of the strong sub-synchronous frequencies, as well as a rise in the onset of instability speed. The polarity of the voltage required for suppression of the sub-synchronous frequencies is found to be opposite to that required to raise the load capacity.

Study on the rotordynamics of a high-speed motor supported by air foil bearings

Study on the rotordynamics of a high-speed motor supported by air foil bearings

The application of the bilinear foil model to three-pad foil air bearings in rotordynamic analysis including reduced order modelling

Foil air bearings (FABs) are the mainstay of oil-free turbomachinery technology which is undergoing rapid expansion. A rotor system using such bearings is a nonlinear multi-domain dynamical system comprising the rotor, the air films and the foil structures. Multi-pad (segmented) FABs offer opportunity for enhanced stability performance but are naturally more computationally challenging than single (360°) pad FABs. Their analysis has been limited to a simple model that ignores the detachment of the top foil from the underlying foil. Although a correction can be applied for the rotor vibration, the actual top foil deflection cannot be predicted. Additionally, reduced order modelling techniques have so far not been applied to such bearings. This paper presents the nonlinear and linearised dynamic analyses of three-pad FAB rotor systems considering foil detachment and using both Galerkin Reduction (GR) and Finite Difference (FD) to model the air film. Various models for the force distribution on the top foil are considered for use within a bilinear foil model, focusing on the ability to achieve numerical convergence. GR halved the computation time for a waterfall graph, without compromising the accuracy of the prediction of the nonlinear response. The results are validated against results from the literature.

Calculation of Dynamic Coefficients of Air Foil Journal Bearings Using Time-Domain Identification

Dynamic coefficients of a bearing are basic elements of rotor dynamics analysis. At present, there are still some issues in the calculation of the dynamic coefficient of air foil bearing. In this paper, the dynamic coefficients of the air foil bearing are calculated by time-domain identification. This method does not need to linearize the system equations, so it is generally applicable to different models for air foil bearings. Using the established method, this paper verified the calculation results using the foil model with axial uniform deformation for the first time, and the influence of the foil model on the dynamic coefficients was studied. The calculation results of the foil models with axial uniform deformation and axial independent deformation have significant differences. Furthermore, the accuracy of the dynamic coefficient method for different disturbance amplitudes was compared. The results indicate that the dynamic coefficient method has good accuracy over a large disturbance range.

An Investigation to Find the Effects on Air Foil Bearing by the Variation of Foil’s Structural Parameters

The newest advancement in the realm of bearing technology, Air Foil Bearings (AFB) is a marvel that allows for operation at both incredibly low and high temperatures without fail. Their minimalistic design eliminates the requirement for lubrication and sealing systems, making them not only more efficient but also more eco-friendly. When it comes to speed, these bearings give no quarter - they can handle even the most extreme of conditions with ease. Air foil bearings rely on the structural design of top and bump foils to support and distribute pressure in the air film. To increase bearing capacity, these foils must be thick enough to withstand greater force. It is crucial to explore how varying foil thickness and bump height-pitch ratios may affect the performance of an air foil bearing. The researchers at the ANSYS Fluent lab set out to understand the dynamics of air foil bearings. By adjusting the thickness of the top and bump foils, they were able to observe how stress, stiffness, and air film clearance changed in relation to each other. Their results showed that even minor changes in foil thickness, bump height, and bump pitch had a significant impact on bearing performance. With their discoveries, these engineers have unlocked a new understanding of this complex technology - one that will help guide its continued development into the future. The thickness of the foil may not confer much strength, but it certainly does wonders for reducing stress and maintaining load-bearing capabilities. Its suppleness, however, cannot be denied – a boon for air foil bearings.

Vibration characteristics control of hybrid radial gas foil bearing-rotor system: Simulation and experiment

Currently, tiny, high-speed rotating machines frequently employ air foil bearings. Air is employed as the working medium, however, when the rotor speed is high, the rigidity of the air film is insufficient, which restricts the usage of air foil bearings. This study utilizes the external gas supply method of hydrostatic gas bearings to strengthen the air film stiffness of air foil bearings. The original air foil bearings are combined with external gas supply piping to create the hybrid gas foil bearing(HGFB), which may be utilized to increase the air film support stiffness of the bearings through the external gas supply. Additionally, by altering the gas supply pressure, this bearing may be used to actively manage the vibration characteristics of the shaft system, allowing the bearing performance to be adjusted to changing operating conditions. The static and dynamic properties of the HGFB with a 24 mm diameter are solved in this study using Newton's iterative approach and the finite difference method. The bearing-rotor system is modeled using this information. An Analysis is done on the impact of various air supply pressures and throttle hole widths on bearing performance and vibration characteristics of the shaft system. In this article, the vibration parameters of the bearing-rotor system are tested using an open-loop control test. The open-loop control experiment on the vibration response of the bearing-rotor system is performed using HGFBs with orifice sizes of 0 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, and 1.0 mm. The experimental results confirm the accuracy of the simulation results. Correspondingly, this paper conducted closed-loop control comparison experiments on the vibration properties of the bearing-rotor system using the PID control method and the fuzzy PID control method in succession. It then evaluated the control effect of the two control strategies on the vibration of the bearing-rotor system and managed to improve the conventional PID control method used for gas bearings.

Numerical investigations on high-speed turbo-compressor rotor systems with air ring bearings: Nonlinear vibration behavior and optimization

Regarding aerodynamic bearings, mainly two basic types can be distinguished: air bearings with a rigid housing and air foil bearings with an elastic supporting structure. Here, a modified bearing concept -- called air ring bearing -- is investigated, which may be considered as a further development of rigid air bearings or as a combination of the two basic bearing types. The idea of air ring bearings is to insert a ring-shaped bearing bushing between the shaft and the foil structure. Alternatively, a visco-elastic supporting structure (e.g., an elastomer) can be applied to connect the bushing ring with the housing. In the first case, external dissipation is mainly generated by dry friction. In the latter case, viscous damping is used to provide external dissipation. Due to the external friction/damping generated by the ring mounting structure, rotor systems with air ring bearings can be operated above the linear threshold speed of instability so that stable self-excited vibrations with moderate amplitudes can be achieved in the complete speed range. Here, a detailed transient co-simulation model for rotor systems with air ring bearings is presented. The rotor is represented by a multibody model. The air films of the two bearings are represented by two nonlinear time-dependent finite element systems. The multibody model and the two finite element subsystems are solved simultaneously by means of an explicit sequential co-simulation technique. Due to the strong nonlinearities, the system shows interesting vibration and bifurcation effects, which are investigated in detail with the help of run-up simulations.

Simulation of air foil bearings for use in turbo compressor applications

Simulation of air foil bearings for use in turbo compressor applications

Simulation of air foil bearings for use in turbo compressor applications

Simulation of air foil bearings for use in turbo compressor applications

The Application of the Arbitrary-Order Galerkin Reduction Method to the Dynamic Analysis of a Rotor With a Preloaded Single-Pad Foil-Air Bearing

Abstract The compressible Reynolds equation (RE) is typically integrated within a fully coupled dynamical foil-air bearings (FABs)-rotor system via spatial Discretization transformation, e.g., finite difference (FD), finite element (FE). An alternative way of integrating the RE is through Galerkin reduction (GR). The motivation for using GR is the computational benefit coming from the drastic condensation of the problem due to the elimination of the two-dimensional grid used for the air film in FD or FE. This paper presents a novel application of arbitrary-order GR to both nonlinear and linearized analyses of rotor systems supported by single-pad FABs with variable radial clearance (preload). Simulations using FD gave a close correlation with those using GR for all preloads, with discrepancies increasing as the preload approaches the nominal clearance (c). The simulations show that the preload has to exceed a certain level in order to delay the onset of instability speed (OIS), and significant delay in OIS and suppression of subsynchronous vibration is possible when the preload is comparable to c. Experimental validation is provided.

Stability and bifurcation analysis of a rotor in rigid and foil air bearings utilized for the identification of the air whirl effect

Stability and bifurcation analyses of holistic rotor-air bearing models are performed. Both, fluid and foils are modeled in a non-linear way, while the model of the latter is validated by measurements. A model order reduction is applied to the fluid film equations to increase computational efficiency. Intentionally, a minimal rotor model is considered in order to isolate the effects of the bearing on the overall system’s behavior. Instead of time integration methods, bifurcation analyses are applied. Thus, different solutions are identified, their stability is assessed and corresponding branch points are determined. The method is applied in order to compare a rigid gas journal bearing with a foil air bearing. In particular for the foil air bearing, parameter studies are performed to investigate the effect of design changes on the rotor stability and the resulting vibrations. The impact of different static rotor unbalances is considered, too. Furthermore, the effect of air whirl – occurring in both bearing types – is identified and explained.

Tribocorrosion behavior of bare and nanocoated foils used on high-speed air-foil bearings

Tribocorrosion behavior of bare and nanocoated foils used on high-speed air-foil bearings

Nonlinear and linearised analyses of a generic rotor on single-pad foil-air bearings using Galerkin Reduction with different applied air film conditions

The compressible Reynolds Equation is typically integrated within a fully-coupled dynamical foil-air bearings (FAB)-rotor system via spatial discretisation transformation e.g. Finite Difference (FD), Finite Element (FE). This paper presents a novel application of an arbitrary-order Galerkin Reduction (GR) method, which does not involve spatial discretisation, to both nonlinear and linearised analyses of rotor systems supported by single-pad FABs. The novel aspects are: application to generic flexible rotors; Jacobian-based linearisation of the GR-transformed system for the extraction of the full mode set and linear stability map; the facility to apply a pressure constraint at a circumferential location and/or the Gümbel condition. These developments are comprehensively verified on two previously considered systems by comparing alternative (GR, FD-based) simulations. The overall features of the experimental nonlinear phenomena are predicted satisfactorily. Transient nonlinear dynamic analysis (TNDA) with GR is found to be less prone to numerical divergence than with FD. For static equilibrium, stability and modal analysis (SESMA), GR is found to be over twice as fast, requiring 70-90 times less memory for saving the results.

Review of Research Status and Development of Foil Air Bearings

Review of Research Status and Development of Foil Air Bearings

Dynamics, stability and bifurcation analysis of rotors in air ring bearings

Classical air foil bearings consist of a top foil, which is usually supported by a bump or beam foil structure. For this bearing type, the air gap is a function of the top foil deformation. Here, an alternative air bearing design – called air ring bearing – is investigated, which may be regarded as a straightforward and very obvious modification of the classical air bearing design. The basic idea is to insert a rigid ring between the shaft and the foil structure. The ring may therefore be considered to be elastically mounted in the housing by means of a bump or beam-type structure. Alternatively, a viscoelastic supporting structure (elastomer) may be used to connect the ring with the housing. Hence, the air film is separated by a rigid ring from the supporting structure. As a consequence, the bearing gap for the fluid film has rigid walls, which simplifies the numerical calculation significantly.In this manuscript, a detailed numerical analysis of rotor systems supported in air ring bearings is presented. The basic nonlinear dynamical effects occurring in such rotor systems are investigated with a particular focus on the stability and bifurcation behavior. Therefore, a detailed co-simulation model of the rotor/bearing system is used. Different possible bifurcation scenarios are described and explained with the help of run-up simulations.Rotor systems with air ring bearings exhibit a completely different vibration and stability behavior than rotors in classical air foil bearings. Diverse interesting nonlinear vibration phenomena, not known in connection with classical air foil bearings, are discussed in detail and physically explained in a clear manner.

An optimal parameter identification approach in foil bearing supported high-speed turbocharger rotor system

High-speed turbocharger rotors are often supported on double film floating ring bearings. In recent times, foil bearings are increasingly used as an alternative to floating ring bearings for supporting such lightweight rotors. Present work aims at the dynamic modeling and stability studies of the automotive turbocharger rotor system supported on the airfoil bearings under varying operating conditions. The effects of different parameters including rotor spin speed, bearing clearance, bump foil thickness, and foil pitch on the dynamic response of the rotor system are illustrated. The nonlinear relationship between the bearing parameters and vibration response data is modeled using supervised neural network scheme. With the use of counter propagation neural network model, inverse identification methodology of the bearing parameters is performed. Further, an optimal design of foil bearing parameters using a surrogate model is proposed with a modified particle swarm optimization scheme. The resultant design parameters are employed, and the percentage reductions in vibration amplitudes of dynamic response are reported.

The dynamic response of a rotor supported by two foil-air bearings with an enhanced model of foil structure

Foil-air bearings have presented their advantageous performance due to their different structures when compared to traditional air bearings. However, it is the nonlinear characteristic of this kind of bearing that has drawn studies on dynamic response of the rotor-bearing system, especially rotor stability. In this paper, an improved foil dynamic model with internal bending moment included has been proposed to determine the nominal stiffness of the foil structure. Based on that, the nominal stiffness of the foil structure has been investigated with different geometry parameters of the foil structure. By such means, the stability of the rotor-bearings system has been theoretically studied through an equation system in a common turbocharger structure. The results can be effectively used for designing and suitably selecting some geometry parameters of foil-air bearings to have a good rotor performance in this case.

On modeling the static shape control of an adaptive air foil bearing

Aerodynamic foil bearings are used in various industrial applications, e.g. in cooling turbines, small gas turbines or exhaust gas turbochargers, to support light, high-speed rotors under extreme operating conditions. Air (or another gas) is used as a lubricant in these bearings. In addition, the possible thermal deformations and production errors can be compensated by a flexible foil structure between the lubricant film and the bearing housing in air foil bearings. Since many static and dynamic properties of the lubricant are strongly dependent on the inner contour of the bearing, the idea of an adaptive air foil bearing (AAFB) is developed to optimize the performance of the bearing at different operating points. This paper focuses on a semi-analytical approach based on plate theory and the Ritz method for approximating the static shape control of a piezoelectrically actuatable AAFB. The main objective of this study is to consider adaptive bearing shells in calculating the behavior of an AAFB, as they provide additional degrees of freedom to a passive air foil bearing without adaptivity. Before the final step is taken, the model presented in this analysis is used for the shape optimization of the adaptive frame of AAFB in order to achieve the most efficient shape adaption with regard to target shapes.