Prediction of nonlinear dynamic coefficients of tilting-pad journal bearings with pad perturbation

In this paper, a modified partial derivative method is developed to predict the linear and nonlinear dynamic coefficients of tilting-pad journal bearings with journal and pad perturbation. To this end, Reynolds equation and its boundary conditions along with equilibrium equations of the pad are used. Finite difference, partial derivative method, and perturbation technique have been employed simultaneously for solving these equations. The accuracy of the results is investigated by comparing the linear dynamic coefficients of three types of tilting-pad journal bearings with those published the literature. It is shown that the nonlinear dynamic coefficients depend on Sommerfeld number, eccentricity ratio, and length to diameter ratio. Similar to the case of linear dynamic coefficients of TPJB, it is observed that the eccentricity ratio effects on nonlinear dynamic coefficients are more notable when the eccentricity ratio is higher than 0.8 or less than 0.2.

Numerical Study of Single Pad Externally Adjustable 120° Pad Bearing Using Fluid Structure Interaction

High-speed turbomachinery like turbine generators and marine propulsion systems uses special fluid film bearing called externally adjustable pad bearing due to their great advantages. The principal feature of this bearing is to alter the radial clearance and film thickness along the circumferential direction to improve the bearing performance parameters. In the present study, the effect of radial and tilt adjustment of 120° pad both in upward (or negative) and downward (or positive) direction on the bearing performance is predicted for various eccentricity ratios using the CFD technique. Later the influence of fluid film pressure on the bearing pad is examined using the FSI technique. Furthermore, the effect of eccentricity ratio on the bearing performance and also on pad structure is also analyzed using CFD coupled FSI analysis. The solution technique of the present numerical analysis is validated with the already published literature and the results are in good agreement. The numerical results suggest that for bearing with negative radial and negative tilt adjustment, bearing performance is superior compared to the other adjustments. However, the structural deformation is also significant for the negative radial and negative tilt adjustment. It is also observed that pad deformation increases with the increase in eccentricity ratio as there has been a rise in fluid film pressure.

Investigation of the Dynamic Characteristics of an Eccentric Annular Seal on the Basis of a Transient CFD Method with Three Whirl Models

Many annular seals suffer eccentricity because of rotor–stator misalignment or the deflection of a flexible rotor, which has a strong influence on the vibration characteristics and stability of rotating machines. In this article, a transient CFD method based on three whirl models is employed to research the dynamic characteristics of annular seals at various static eccentricities. The influence of the whirl amplitude on the dynamic characteristics of eccentric annular seals are also explored. The results of the transient CFD method are compared with the bulk flow model results and the experimental results. It is shown that the transient CFD method possesses high prediction precision for direct damping, with a maximum error of 25%. Negative kyx increases by 166% when the static eccentricity ratio is increased from 0 to 0.5. The dynamic characteristics of the annular seal operating at high static eccentric ratio are sensitive to whirl amplitude, and the model with an amplitude of 1% Cr has great advantages for the prediction of direct virtual-mass, while the model with an amplitude of 10% Cr has great advantages for the prediction of cross-coupled damping.

Coupling Effect of Eccentricity and Slenderness Ratios on RCFST Column Instability Modes

The instability damage modes of rectangle concrete-filled steel tube (RCFST) columns that are subjected to eccentric compression can be divided into two types based on the modified Jezek analytical procedure, namely, the eccentricity ratio (γ) and the slenderness ratio (λ) coupling effect. The RCFST columns have unilateral compression yield failure mode when γ is small. However, it has compressive and tensile mode on both sides when the value of γ is large. In this work, parametric analyses were performed to test 32 RCFST long columns by varying γ with different λ combinations. From the analysis, it was found that the results of the theoretical analysis of the load-tension strain (P-ε) responses and the instability modes of the RCFST long columns are similar to the experimental results. Further, the proposed analytical method aids in better understanding the effects of γ and λ coupling on the stability behavior of the RCFST columns.

Study on Lubrication Efficiency and Friction Power Loss of Engine Based on a Hybrid Hydrodynamic Model

Friction loss is one of the main factors affecting engine power. Reducing friction power losses to improve the power of engines is a significant concern for designers. Especially, under the background of energy-saving and emission reduction, it is indispensable to carry out an in-depth investigation on engine bearing lubrication characteristics. Unlike the previous studies of separate modelling, a new modelling method of coupling the dynamic and lubrication model is proposed in this paper. The bearing capacity, friction force, friction coefficient and eccentricity ratio were taken as the evaluation criterion, and the influence of design parameters such as angular speed, bearing radius and width on the lubrication efficiency and friction power loss (LE-FPL) were studied. The results indicate that increasing the angular speed, bearing radius or width can effectively reduce the eccentricity ratio and raise the minimum oil film thickness, which is beneficial to improve the lubrication efficiency. However, the above methods to improve engine lubrication efficiency will lead to more power loss of engine to a certain extent. Therefore, studies on reducing the friction power loss for the engine and on improving the lubrication efficiency for the engine should be considered coordinately in the dynamic design and optimisation of the engine.

Effect of Eccentricity and Surface Roughness On Probabilistic Performance of Two Axial Groove Bearing

This paper presents the effect of eccentricity and surface roughness on the probabilistic performance of two axial groove hydrodynamic journal bearing. In general, it is difficult to quantify experimentally the variabilities involved in dynamic responses of the hydrodynamic bearing due to the randomness involved in surface asperity and eccentricity ratio. The deterministic models available for the analysis of the bearings are not capable to include such uncertainties. These uncertainties arise from the manufacturing imperfections, misalignment of the bearing, frictional wear, uncertain operating condition, model inaccuracy. To simulate such variabilities, Monte Carlo simulation (MCS) is carried out. Stochastic steady-state and dynamic coefficients are obtained by solving the Reynolds equation using the surrogate-based finite difference method. Sensitivity analysis of the performance parameters with respect to stochastic input parameters is portrayed. The moving least square (MLS) model is constructed as the surrogate to increase the computational efficiency. The significant influences of stochastic input parameters such as surface roughness and eccentricity ratio are observed on the random hydrodynamic performance of two axial groove journal bearing.

Numerical analysis on the performance characteristics of a new gas journal bearing by using finite difference method

This paper proposes a novel gas journal bearing in which orifices are different in diameter and distribute unevenly. Finite Difference Method (FDM) combined with Linear Perturbation Method (LPM) is used to solve the unsteady-state Reynolds equation of the flow field in the bearing clearance. Moreover, four types of bearing structures are used to discuss the effects of orifices different in diameter and uneven distribution on the bearing performance. The results demonstrate that the new bearing has better static and dynamic performances compared with those of traditional bearing in which orifices are equal in diameter and distribute evenly. Moreover, thin gas film thickness, high supply pressure, and large eccentricity ratio are hopeful for improving load capacity of the new bearing. Furthermore, the stability of the novel bearing is improved if eccentricity ratio is 0.25–0.3.

An Analysis for Magnesium Alloy Curvature Products Formed by Staggered Extrusion (SE) Based on the Upper Bound Method

Staggered extrusion (SE) is a new method to solve the bottleneck of traditional curvature products, such as long manufacturing cycle, many forming processes and difficult quality control. How to quantitatively control the curvature of extruded products is the key to implement this method. Herein, the upper bound method is used to calculate and analyze the power consumption of each characteristic zone in the SE process. The theoretical model of extrusion load and curvature is established. The results show that the staggered distance h has an important influence on the curvature κ. When the staggered distance h increases from 8 mm to 24 mm and other conditions remain unchanged, the curvature κ increases from 0.0546 to 0.1607. Any combination of the staggered distance h and the extrusion ratio λ corresponds to an eccentricity ratio ξ. The eccentricity ratio ξ decreases with the increase of the staggered distance h or the extrusion ratio λ. By comparison, it can be seen that the variation trend of the theoretical predicted value and the FE modelling in the steady-state extrusion stage is consistent. The experimental results are in good agreement with the curvature theory prediction model. These results provide a scientific basis for the formulation of the SE process and precisely controlling magnesium alloy curvature products.

Influences of eccentricity ratio on the internal flow and cavitation characteristics of progressing cavity pump

A Progressing Cavity Pump (PCP) works by forming a progressive seal cavity through the eccentric rotation of rotor. PCP parameters, such as eccentricity ratio [Formula: see text], can influence its performance and cavitation characteristics. The internal correlation among clearance fluid, cavitation characteristics, and pump performance should be explored to reveal the variation laws of internal flow and cavitation characteristics in PCP under different [Formula: see text]. In this study, a contrast analysis on external characteristics (e.g. volume efficiency) of pump with different eccentricity ratios was carried out by combining an RNG [Formula: see text] turbulence model based on Singhal full-cavitation model and the model pump test method. Moreover, gas volume distribution of PCP was analyzed and the optimal value range of eccentricity ratio was proposed. Results demonstrate that the axial force and axial power of PCP basically remain the same, volume efficiency increases, and cavitation performance decreases with the increase of [Formula: see text], and the optimal value for [Formula: see text] ranges from 0.17 to 0.24. In addition, a revised NPSHQ is proposed to quantify the cavitation characteristics of PCP.