The COMBI214 element allows stiffness and/or damping characteristics in 2 perpendicular directions as well as cross-terms. To define a bearing in the YZ plane:

et,1,combi214
keyopt,1,2,1		                        ! YZ plane
r,1,KYY,KZZ,KYZ,KZY,CYY,CZZ
rmore,CYZ,CZY

In the case of a hydrodynamic bearing for example, the characteristics may vary with the rotational velocity. In this case, you need to specify OMEGS as the table parameter primary variable (*DIM command). It is supported when activating the CORIOLIS command in a modal analysis (ANTYPE,MODAL), full harmonic analysis (ANTYPE,HARMIC), or full transient analysis (ANTYPE,TRANS).

An example of varying characteristics KYY and KZZ is given below:

et,1,combi214 
keyopt,1,2,1		                          ! YZ plane

! define table KYY
*DIM,KYY,table,3,1,1,omegs	              ! table of dimension 3 depending upon omegs 
KYY(1,0) = 0 , 1000 , 2000	              ! 3 rotational velocities (rd/s)
KYY(1,1) = 1.e+6 , 2.7e+6 , 3.2e+6       ! stiffness characteristic at each rotational velocity

! define table KZZ
*DIM,KZZ,table,3,1,1,omegs	              ! table of dimension 3 depending upon omegs
KZZ(1,0) = 0 , 1000 , 2000	              ! 3 rotational velocities (rd/s)
KZZ(1,1) = 1.4e+6 , 4.e+6 , 4.2e+6       ! stiffness characteristic at each rotational velocity

r,1,%KYY%,%KZZ%

In the case of a squeeze film damper, the characteristics may vary with the rotor eccentricity and/or the phase shift between the rotor displacements in the two nodal directions. In this case, you need to specify ECCENT and/or THETA as the table parameter primary variables (*DIM command). A basic example of varying characteristics KXX is given below:

*dim, KXX,table,2,2,, eccent, theta
KXX(1,0) = 0, 1.e-2		! 2 eccentricity values
KXX(0,1) = -180			! 2 theta values (in degree)
KXX(0,2) =  180
KXX(1,1) = 1.e+5, 1.e+4		! stiffness values for each
KXX(1,2) = 1.e+6, 1.e+5		!  value of eccentricity and theta (2x2)

The characteristics can be imported directly from an ASCII text file using the APDL macro importbearing1.mac. The format of this text file is described in Appendix A: Bearing Characteristics File Format. An example of the macro usage is shown below:

! Import the bearing characteristics read in file bearingAP.txt
!  and create the table parameters K11_3, K12_3...
importbearing1, ‘bearingAP’, 3
! Define the bearing element real constants
r,1, %K11_3%, %K22_3%,%K12_3%,%K21_3%,%C11_3%,%C22_3%,
rmore, %C12_3%, %C21_3%

In a static analysis, the stiffness and damping characteristics of a plain cylindrical journal bearing or squeeze film damper can be calculated using a small perturbation near a user-defined equilibrium position.

Example inputs are shown in Example: Calculation of a Plain Cylindrical Journal Bearing Characteristics and Example: Calculation of a Squeeze Film Damper Characteristics.

These characteristics can then be used as COMBI214 real constants (KEYOPT(1) = 0) in a subsequent modal or harmonic analysis.

In a nonlinear large-deflection transient analysis, the bearing forces are calculated based on the bearing definition (real constants and material viscosity) and the instantaneous displacements and velocities.

A simple example input is shown in Example: Transient Analysis of a Plain Cylindrical Journal Bearing.