Kumar Vaidyanathan

Calculation of Journal Bearing Dynamic Characteristics Including Journal Misalignment and Bearing Structural Deformation

A detailed journal bearing analysis for accurate evaluation of film dynamic characteristics is presented. The new formulation is based on a local perturbation of the oil film at each computational node that captures the important effects of journal misalignment and bearing structural deformation in rotor dynamics and engine NVH applications. The new algorithm is an extension to the classical approach of evaluating film dynamic characteristics based on journal eccentricity perturbation. The governing equations for the oil film pressure, stiffness, and damping are solved using a finite difference approach and their output is validated with numerical results from the literature.

An Elastohydrodynamic Coupling of a Rotating Crankshaft and a Flexible Engine Block

A comprehensive formulation is presented for the dynamics of a rotating flexible crankshaft coupled with the dynamics of an engine block through a finite difference elastohydrodynamic main bearing lubrication algorithm. The coupling is based on detailed equilibrium conditions at the bearings. The component mode synthesis is employed for modeling the crankshaft and block dynamic behavior. A specialized algorithm for coupling the rigid and flexible body dynamics of the crankshaft within the framework of the component mode synthesis has been developed. A finite difference lubrication algorithm is used for computing the oil film elastohydrodynamic characteristics. A computationally accurate and efficient mapping algorithm has been developed for transferring information between a high-density computational grid for the elastohydrodynamic bearing solver and a low-density structural grid utilized in computing the crankshaft and block structural dynamic response. The new computational capability is used to compute the vibratory response of an automotive V6 engine due to combustion and inertia loading.

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

Non-Newtonian Effects on the Performance of Dynamically Loaded Elliptical Journal Bearings Using a Mass-Conserving Finite Element Cavitation Algorithm

The effects of non-Newtonian lubricant behavior are investigated numerically for elliptically shaped journal bearings subjected to transient loads. The analysis is based on the mass-conserving finite element cavitation model of Kumar and Booker. The results reveal that non-Newtonian effects have an important influence on journal bearing performance. It is found that there is a significant increase in the maximum film pressure and flow rate whereas a significant decrease in the minimum film thickness and power loss. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001

Approaching Mixed Elastohydrodynamic Lubrication of Smooth Journal-Bearing Systems with Low Rotating Speed

When a conformal interface is under low velocity and heavy load conditions, solid contact (or dry contact) may occur even in a system with smooth surfaces. This paper presents two approaches for solving steady-state and transient mixed elastohydrodynamic lubrication problems of journal bearings with smooth surfaces under low rotating speed. The first approach uses the reduced Reynolds equation with a combined finite element–backward finite difference scheme and the second applies a zero film thickness equation to describe the mechanical behavior of mating surfaces at solid contact points. The major advantages of these two approaches are (1) no division of the solution domain into a lubricated area and a solid contact area is necessary and (2) the solid contact pressure, lubricant pressure, and eccentricity ratio can be solved simultaneously. Numerical examples are presented for the application of these approaches. For the steady-state cases under low velocity studied in this work, pressure distributions approach those found in a dry contact state. This comparison confirms that the contact treatments are proper. Moreover, a transient case under sinusoidal loading was analyzed with these two approaches, and the results showed good agreement. This comparison further supports the use of these approaches. Presented at the STLE Annual Meeting in Las Vegas, Nevada May 15-19, 2005 Review led by Alan Lebeck

Probabilistic and sensitivity analyses for the performance characteristics of the main bearings in an operating engine due to variability in bearing properties

Surrogate models (metamodels) are developed and used to evaluate an engine bearing performance and perform probabilistic sensitivity analyses. The metamodels are developed based on results from a simulation solver computed at a limited number of sample points. An integrated system-level engine simulation model, consisting of flexible crankshaft and block dynamic models, connected by a detailed hydrodynamic lubrication model, is employed for constructing the metamodels. An optimal symmetric Latin hypercube sampling algorithm is utilised. The metamodels are employed for performing probabilistic and sensitivity analyses. The initial clearance between the crankshaft and each main bearing and the oil viscosity comprise the random variables. The maximum oil pressure and the percentage of time (time ratio) within each cycle that a bearing operates with oil film thickness less than a user defined threshold value at each main bearing constitute the system performance variables.

A locally refined finite element approach for journal-bearing system analysis

The effect of roughness should be taken into consideration in the lubrication and geometric design of heavy-duty machine elements. Deterministic simulation techniques have been developed for the investigation of point-contact mixed-lubrication problems. Such approaches should also been extended to deterministic mixed lubrication solutions for journal-bearing conformal-contact systems. However, journal-bearing mixed lubrication involves a much larger area of surface interaction as compared to point contact problems. It is difficult to use similar micro/nano scale meshes directly to journal bearings under the current computer capability. It is a great challenge to develop a new deterministic numerical technique for the mixed lubrication of journal bearing systems with the consideration of the effect of surface roughness design. This paper presents a special technique for deterministic analyses of journal-bearings in mixed lubrication conditions, in which the coarse mesh is used to determine the elastic deformation of the journal bearing, whilst locally refined meshes are used for the effect of roughness. Journal-bearing systems in heavy machinery are often subject to dynamic loading. Therefore, a transient refinement scheme is also introduced.Copyright

Probabilistic Computations for the Main Bearings of an Operating Engine Due to Variability in Bearing Properties

This paper presents the development of surrogate models (metamodels) for evaluating the bearing performance in an internal combustion engine. The metamodels are employed for performing probabilistic analyses for the engine bearings. The metamodels are developed based on results from a simulation solver computed at a limited number of sample points, which sample the design space. An integrated system-level engine simulation model, consisting of a flexible crankshaft dynamics model and a flexible engine block model connected by a detailed hydrodynamic lubrication model, is employed in this paper for generating information necessary to construct the metamodels. An optimal symmetric latin hypercube algorithm is utilized for identifying the sampling points based on the number and the range of the variables that are considered to vary in the design space. The development of the metamodels is validated by comparing results from the metamodels with results from the actual simulation models over a large number of evaluation points. Once the metamodels are established they are employed for performing probabilistic analyses. The initial clearance between the crankshaft and the bearing at each main bearing and the oil viscosity comprise the random variables in the probabilistic analyses. The maximum oil pressure and the percentage of time (the time ratio) within each cycle that a bearing operates with oil film thickness less than a user defined threshold value at each main bearing constitute the performance variables of the system. The availability of the metamodels allows comparing the performance of several probabilistic methods in terms of accuracy and computational efficiency. A useful insight is gained by the probabilistic analysis on how variability in the bearing characteristics affects the performance of the bearings.

Probabilistic Analyses for the Performance Characteristics of the Main Bearings in an Operating Engine Due to Variability in Bearing Properties

This paper presents the development of surrogate models (metamodels) for evaluating the bearing performance in an internal combustion engine. The metamodels are employed for performing probabilistic analyses for the engine bearings. The metamodels are developed based on results from a simulation solver computed at a limited number of sample points, which sample the design space. An integrated system-level engine simulation model, consisting of a flexible crankshaft dynamics model and a flexible engine block model connected by a detailed hydrodynamic lubrication model, is employed in this paper for generating information necessary to construct the metamodels. An optimal symmetric Latin hypercube algorithm is utilized for identifying the sampling points based on the number and the range of the variables that are considered to vary in the design space. The development of the metamodels is validated by comparing results from the metamodels with results from the actual simulation models over a large number of evaluation points. Once the metamodels are established they are employed for performing probabilistic analyses. The initial clearance between the crankshaft and the bearing at each main bearing and the oil viscosity comprise the random variables in the probabilistic analyses. The maximum oil pressure and the percentage of time (the time ratio) within each cycle that a bearing operates with oil film thickness less than a user defined threshold value at each main bearing constitute the performance variables of the system. The availability of the metamodels allows comparing the performance of several probabilistic methods in terms of accuracy and computational efficiency. A useful insight is gained by the probabilistic analysis on how variability in the bearing characteristics affects its performance.© 2003 ASME