Loaded Journal Bearings Research Articles

Computer Aided Design Techniques for Dynamically Loaded Journal Bearings

In this paper a generalized computer aided design methodology is developed to design the dynamically loaded journal (aircraft and engine) bearings with comprehensive study. As part of procedure development a typical dynamic load case of inline engine connecting rod bearing and main bearings are taken for analysis. The determinate method of bearing force evaluation is adopted. The mobility concept is employed to predict the figures of merit (minimum film thickness, maximum film pressure). It is shown that the mobility expressions based on Goenka curve fits predict performance parameters in close agreement with data based on experiences. The entire generalized design strategy is also programmed with graphic interactions. The results are available within a few seconds from an interactive computer terminal, once initial data describing the application have been entered.

A prediction model for suction cavitation erosion in a journal bearing

Suction damage occurred often in dynamically loaded journal bearings. A new theoretical model, including lubrication module, boundary module and prediction module, was proposed to investigate the suction damage in a journal bearing. The results showed that, a stable cavitation area with steady temperature fields formed in the film rupture region, but no suction cavitation erosion occurred in a constant load journal bearing. It was concluded that, suction cavitation erosion occurred within the region of suction cavitation, and higher dimensionless deformation coefficients stood for more muscular suction damage strength within suction cavitation regions. It was beneficial to reduce transient impact force applied to a journal bearing for resisting suction cavitation erosion, leading to an increase of a periodic pressure coefficient.

A Computationally Efficient, Mass Conserving Generalized Short Bearing Formulation for Dynamically Loaded Journal Bearings

Abstract This paper describes a computationally efficient, finite element implementation of a generalized short bearing (GSB) formulation to account for mass conservation in cavitated bearing regions. The method is applied to a set of examples representing partial and full journal bearings under transient loads and kinematics. Bearing performance trends are captured well by the GSB formulation when compared with results obtained from a complete two-dimensional formulation and from experiments. The computational speed of the GSB formulation is approximately 40 to 200 times faster than the complete formulation for the examples provided in the paper.

Friction in Highly Loaded Journal Bearings

Friction in Highly Loaded Journal Bearings

3D Surface Roughness Effects on Transient Non-Newtonian Response of Dynamically Loaded Journal Bearings

The influence of 3D surface roughness on the transient non-Newtonian response of a dynamically loaded journal bearing under mixed lubrication is studied. A study of the transient non-Newtonian response of a dynamically loaded journal bearing under mixed lubrication condition is performed including the effects of 3D surface roughness parameters such as roughness orientation and characteristics of surface roughness of opposing surfaces and the variation of fluid viscosity across and along the fluid-film thickness due to shear thinning and viscoelastic behavior of the lubricant. The Reynolds equation is modified to include the effects of surface roughness, viscosity variation across the fluid-film, and viscoelastic properties of the lubricant. The power law model and Maxwell's model are employed to characterize shear thinning and viscoelastic properties of the lubricant, respectively. The solution of the modified average Reynolds equation is obtained using a finite element method and appropriate iterative schemes. Results are presented for a journal bearing subjected to sinusoidal loading. The bearing transient response was found to be significantly affected by the characteristics of surface roughness of opposing surfaces. The bearing with stationary roughness was observed to have good load-carrying capacity.

A New Model of Thermoelastohydrodynamic Lubrication in Dynamically Loaded Journal Bearings

Abstract A comprehensive method of thermoelastohydrodynamic (TEHD) lubrication analysis for dynamically loaded journal bearings is presented. An algorithm for mass conserving cavitation is included, and the effect of viscosity variation with the temperature is taken into account. The Reynolds equation in the film is solved using the finite element (FE) discretization. Thermal distortions as well as the elastic deformation of the bearing surfaces are computed using the FE method. The temperature of the lubrication film is treated as a time-dependent three-dimensional variable with a parabolic variation with respect to the film thickness. In order to compute the temperature of the film and its surrounding solid surfaces, a new heat flux conservation algorithm is proposed. An important element in this analysis is the consideration of thermal boundary layers for solids. It is known that the thermal transients on the film-solid interfaces and the dynamic loading have the same period (one cycle). However, beyond the thermal boundary layers, the time scale for thermal transient in the journal and bushing are several orders of magnitude greater than those for the oil film. The Fourier series approximates the instantaneous temperature fields in the solid boundary layers. In this way, the mean heat flux that passes into the solid can be computed and a steady-state heat conduction equation can be used to obtain thermal fields inside the solids. Finally, solving the complex problem of big-end connecting-rod bearing TEHD lubrication proves the efficiency of the algorithm. Oil film temperatures are found to vary considerably over the time and space.

A Study of Dynamically Loaded Journal Bearings Lubricated with Non-Newtonian Couple Stress Fluids

This paper is to theoretically investigate the behavior of dynamically loaded journal bearings lubricated with non-Newtonian couple stress fluids. To take into account the couple stress effects due to the lubricants blended with various additives, the modified Reynolds equation for dynamic loads governing the film pressure is derived. The film pressure is solved numerically with Reynolds boundary conditions and then various bearing characteristics are calculated. The effects of couple stresses on bearing performance characteristics are analyzed. The results conclude that couple stress fluids lubrication improves the bearing performance under dynamic loads.

Comparison of Mobility Method and Mass Conservation Method in a Study of Dynamically Loaded Journal Bearings

The inverse problem of dynamically loaded journal bearings was solved using generalized Reynolds equation coupled with a complete mass conservative cavitation boundary conditions, as outlined by the Jacobsson-Floberg and Olsson (JFO) cavitation theory. In the course of solution, the modi®ed Thomas algorithms was employed, instead of standard Gauss±Jordan reduction method, which fully utilizes the sparse character of the system matrix, and thus greatly reduces computational time. The developed model was tested against the well-known mobility method for the case of journal bearings in a commercial reciprocating air compressor. It was found that the mobility method overestimates minimum ®lm thickness and underestimates such parameters as lubricant ow rate and bearing power loss. In general, the level of error is acceptable for most industrial applications. However, for the journal bearing where the feed pressure is time dependent and starvation e€ects are predominant, the mobility method may produce large not acceptable errors.

Comparison of Mobility Method and Mass Conservation Method in a Study of Dynamically Loaded Journal Bearings

Comparison of Mobility Method and Mass Conservation Method in a Study of Dynamically Loaded Journal Bearings

Combined Surface Roughness Pattern and Non-Newtonian Effects on the Performance of Dynamically Loaded Journal Bearings

The effects of three surface roughness patterns (purely circumferential, axial and isotropic) are investigated for an elliptically shaped journal bearing subjected to dynamic loading. The mass-conserving, finite element, scheme proposed by Kumar and Booker (1991) is used to model the cavitation. Moreover, a non-Newtonian model is included to account for shear thinning effects of the lubricant. The results show that the circumferential (microgrooved) surface pattern produces larger and more beneficial effects on bearing performance than do the other surface roughness patterns. Due to surface pattern effects, the maximum film pressure is found to decrease by as much as 12% and the minimum film thickness can increase by as much as 17%, depending on the bearing geometry, the loading and the asperity heights. Surface roughness patterns were found to have little effect on the flow rate and friction torque. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in San Francisco, CA October 21–24, 2001

TEHD Behavior of Non-Newtonian Dynamically Loaded Journal Bearings in Mixed Lubrication for Direct Problem

A transient non-Newtonian TEHD analysis for dynamically loaded journal bearings in mixed lubrication is developed for direct problem. A mass conserving cavitation is included and viscoelasticity subsuming shear thinning is characterized by the upper converted Maxwell fluid and the power law fluid models. The Reynolds equation, the transient two-dimensional energy equation in the film, the quasi-steady-state two-dimensional heat conduction equation in the bushing and heat balance in the journal are solved using finite difference formulations. The thermal and elastic deformation equations are solved using the finite element method. The relation between the average contact pressure and the average gap is numerically determined in micro scale. Effects of roughness texture, degree of asperity contact, shear index, relaxation time, thermal and elastic deformations on bearing behavior are investigated.

Application of the Spectral Technique to the Analysis of Dynamically Loaded Journal Bearings

Successful use of a realistic bearing model in engineering practice depends heavily on the efficiency of the tool used. The analysis of dynamically loaded bearings requires repeated solutions of the Reynolds equation at each point of the journal orbit, therefore, the method used for this problem should be very fast. A new (spectral) method is presented, which allows the Reynolds equation to be solved sufficiently quickly and accurately. This method can be defined as a modification of the Galerkin method for partial differential equations as suggested by Kantorovich. The solution of the Reynolds equation is sought as a Fourier series with respect to the circumferential coordinate. This allows the original partial differential equation to be reduced to a system of ordinary differential equations which, in turn, is further approximated with a linear algebraic system. Since the matrix of this system is banded, the system can be solved efficiently with simple recursive relations. A novel method is introduced to determine the loaded zone corresponding to the Reynolds boundary conditions. The method uses ideas of functional analysis. Consideration of the loaded zone as a function, along with a condition for the pressure to be non-negative, allows a functional equation to be written and then solved with the Euler or Runge-Kutta methods. A comparison with published FE results for a steady-state case as well as for the dynamic load is shown.

THD Analysis of High Speed Heavily Loaded Journal Bearings Including Thermal Deformation, Mass Conserving Cavitation, and Turbulent Effects

Theoretical and experimental THD analyses of high speed heavily loaded journal bearings are presented. Numerical solutions include thermal deformation, mass conserving cavitation and turbulent effects. The pressure and temperature distributions, the eccentricity ratio, and the flow rate are measured. Agreement between theoretical results and experimental data is satisfactory. [S0742-4787(00)00803-1]

Transient Non-Newtonian Thermohydrodynamic Mixed Lubrication of Dynamically Loaded Journal Bearings

A transient non-Newtonian THD theory of dynamically loaded journal bearings in mixed lubrication is presented. A mass conserving cavitation is included and shear thinning and viscoelasticity are characterized by the power law and the upper convected Maxwell models, respectively. The 2-D energy equation is solved with ISOADI (isothermal shaft and adiabatic bushing inner surface) boundary conditions. The journal is treated as a quasi-steady and lumped thermal element. [S0742-4787(00)02001-4]

Effects of Surface Texture on Hydrodynamic Lubrication of Dynamically Loaded Journal Bearings

The effects of two-sided purely longitudinal, transverse and isotropic surface roughness on the hydrodynamic lubrication of dynamically loaded finite journal bearings are analyzed using Christensen's stochastic model of hydrodynamic lubrication of rough surfaces and considering running-in effect on roughness height distributions. A detailed study of the above system in terms of the nominal minimum film thickness and the maximum film pressure demonstrates that the effects of roughness are closely tied to the roughness texture and structure, features of nominal geometry, and operating factors.

A Finite Element Analysis of Dynamically Loaded Journal Bearings in Mixed Lubrication

Modern high performance engines require bearings to operate under high temperature and heavy bad with complicated hading cycles. These severe conditions result in mainshaft and connecting rod bearings operating in an ever thin film lubrication regime. The effects of surface waviness, roughness and bearing housing deformation can no longer be neglected. To account for such effects a mixed elastohydrodynamic lubrication model for finite-long journal bearings has been developed. This model couples an average Reynolds equation for a particular longitudinal surface texture with an asperity-to-asperity contact model. The governing equations of the model were discretized by the finite element method. The resulting nonlinear equations were subsequently solved by a modified Newton-Raphson algorithm. Simulations have been performed for various waviness and roughness with both rigid and flexible bearing housings.

A Transient Thermohydrodynamic Analysis Including Mass Conserving Cavitation for Dynamically Loaded Journal Bearings

A comprehensive transient thermohydrodynamic analysis for dynamically loaded journal bearings such as engine crankshaft bearings has been developed. A key element in this analysis is consideration of different time scales for the oil film, journal and bushing. Another important element of this analysis is consideration of moving grids in the oil film. Mass conserving cavitation is included via the Elrod cavitation algorithm. The 3-D energy equation is solved without any simplification in the oil film or the bushing. The journal is treated as a lumped thermal element. We found that the time scales for thermal transients in the oil film are of the same order as the period of the dynamic loading (one engine cycle for a crankshaft bearing); consequently, thermal transients in the oil film were considered. However, the time scales for thermal transients in the journal and bushing are several orders of magnitude greater than those for the oil film. Consequently, these elements were treated as if they were in quasi-steady state over one loading cycle. Results from this analysis are presented for an engine crankshaft main bearing under sinusoidal loading. Oil film temperatures are found to vary considerably over time and space.

Dynamically Loaded Journal Bearings: Position of Maximum Pressure Ratio

The position of the maximum “pressure ratio” in dynamically loaded bearings, using short bearing theory, has previously been published only in graphical (map) form. Simple equations are derived here so that this position (relative to the load line) can be obtained directly in numerical form.

Experimental Temperature and Pressure Profiles for Two Steadily Loaded Journal Bearings

Experimental temperature and pressure profiles for a steel and a bronze bearing are examined. The comparisons show systematic differences between these otherwise identical bearings. These comparisons suggest that there would be merit in including thermal deformation in the analysis if high accuracy were required. The additional accuracy obtained could be especially important in accurately predicting the characteristics of sensitive high performance turbomachinery.

Investigation of the Failure of Heavily Loaded Journal Bearings

This paper gives details of a combined theoretical and experimental investigation of a plain journal bearing under heavily loaded conditions together with a metrological study of the bearing geometry. It was found that under high loading conditions a simplified analytical expression relating the Sommerfeld number to the non-dimensional minimum film thickness, using a hydrodynamic solution of the isoviscous form of the Reynolds equation, could be developed. An alternative theoretical solution based on elastohydrodynamic lubrication was also considered. In addition, experimental work determined a variety of operating conditions that produced metal-to-metal contact. These operating conditions were then compared with the theoretical minimum film thickness calculations and bearing manufacturing data. This process was used to determine combined failure criteria based on operating conditions and machining capability.