Finite Element Analysis of Herringbone Groove Journal Bearings: A Parametric Study

1998 ◽  
Vol 120 (2) ◽  
pp. 234-240 ◽  
Author(s):  
Nicole Zirkelback ◽  
Luis San Andre´s
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Parametric Study ◽  
Journal Bearing ◽  
Forced Response ◽  
Information Storage ◽  
Element Analysis ◽  
Force Coefficients ◽  
Rotating Systems ◽  
Reaction Forces

Currently, the herringbone groove journal bearing (HGJB) has important applications in miniature rotating machines such as those found in the computer information storage industry. Grooves scribed on either the rotating or stationary member of the bearing pump the lubricating fluid inward thus generating support stiffness and improving its dynamic stability when operating concentrically. The narrow groove theory (NGT), traditionally adopted to model the concentric operation of these bearings, is limited to bearings with a large number of grooves. A finite element analysis is introduced for prediction of the static and rotordynamic forced response in HGJBs with finite numbers of grooves. Results from this analysis are then compared to available experimental data as well as to estimates from the NGT. A bearing geometry parametric study is then conducted to determine optimum rotordynamic force coefficients. A discussion on the temporal variation of the bearing reaction forces and force coefficients for a rotating journal with a small number of grooves is also presented. These changes can be significant at high operating eccentricities, possibly inducing a parametric excitation in rotating systems employing this type of bearing.

Extended Finite Element Analysis of Journal Bearing Dynamic Forced Performance to Include Fluid Inertia Force Coefficients

2012 ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Small Amplitude ◽  
Forced Response ◽  
Inertia Force ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Force Coefficients ◽  
Reaction Forces ◽  
Bearing Stiffness

Reynolds equation governs the generation of hydrodynamic pressure in oil lubricated fluid film bearings. The static and dynamic forced response of a bearing is obtained from integration of the film pressure on the bearing surface. For small amplitude journal motions, a linear analysis represents the fluid film bearing reaction forces as proportional to the journal center displacements and velocity components through four stiffness and four damping coefficients. These force coefficients are integrated into rotor-bearing system structural analysis for prediction of the system stability and the synchronous response to imbalance. Fluid inertia force coefficients, those relating reaction forces to journal center accelerations, are routinely ignored because most oil lubricated bearings operate at relatively low Reynolds numbers, i.e., under slow flow conditions. Modern rotating machinery operates at ever increasing surface speeds to deliver more power in smaller size units. Under these operating conditions fluid inertia effects need to be accounted for in the forced response of oil lubricated bearings, as recent experimental test data also reveal. The paper presents a finite element formulation to predict added mass coefficients in oil lubricated bearings by extending a basic formulation that already calculates the bearing stiffness and damping force coefficients. That is, a small amplitude perturbation analysis of the lubrication flow equations keeps the temporal fluid inertia effects and develops a set of equations to obtain the bearing stiffness, damping and inertia force coefficients. The method does not impose on the cost of the original formulation which makes it very attractive for ready implementation in existing software. Predictions of the computational model are benchmarked against archival test data for an oil-lubricated pressure dam bearing supporting large compressors. The comparisons show fluid inertia effects cannot be ignored for operation at high rotor speeds and with small static loads.

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