In the Hydrodynamic Journal Bearing node you specify the geometric dimensions, journal and foundation motion and lubricant properties necessary to model the fluid-film journal bearing.

The journal surface is considered as the reference surface. Select Reference normal orientation — Same direction as geometry normal or Opposite direction to geometry normal to specify the normal of the journal that points toward the lubricant film.

Select Bearing type — Cylindrical, Elliptical, Split halves, Multilobe, Tilting pad, or User defined. Then, go to the relevant section below to continue defining the properties.

Enter the Clearance, C, between the journal and bearing when the centers of the journal and bearing coincide.

Enter the Minimum clearance, Cmin, and Maximum clearance, Cmax, when the centers of the journal and bearing coincide.

Enter a Clearance, C, and select the Preload factor — Specify or Compute from offset.

Enter a Clearance, C, and select the Preload factor — Specify or Compute from offset.

Finally, enter the Number of pads, N.

Enter a Clearance, C, and select the Preload factor — Specify or Compute from pad clearance.

Finally, enter the Number of pads, N; Pad outer radius, Rp; Pad tilt angle, δ; and Pivot offset factor, f.

Enter the Height of the bearing above reference plane as a function of the polar coordinates. The default expression contains variables <phys>.r_e1 and <phys>.Th, which are the axial and azimuthal coordinates of the reference surface. <phys>.r_e1 is the coordinate of a point on the bearing surface along the bearing axis. <phys>.Th is the azimuth angle of a point on the bearing surface with respect to the local y direction of the bearing.

Select Bearing center — From geometry or User defined. In the From geometry case, the centroid of geometry is computed.

Select one of the Moving or Flexible foundation options. In both the cases, respective subnodes Moving Foundation or Flexible Foundation are automatically added.

Select Specify — Displacement, Eccentricity and direction, or Load. Then, go to the relevant section below to continue defining the properties.

If Displacement is selected, select Journal displacement — User defined and enter the displacement values.

If Eccentricity and direction is selected, enter values for the Eccentricity, e, and the Attitude angle relative to local y direction, ϕy.

If Load is selected, select Journal Load — User defined and enter the load values.

Enter the value for Mass of the journal. Also enter the value for the Initial journal displacement. Both are generally needed for a time-dependent study. In a stationary study, Initial journal displacement is used as an initial guess for the journal displacement.

Select Velocity of the journal — Angular speed, Revolutions per time or Velocity field.

This section is only available when Fluid type is Liquid (Reynolds equation) in the Physical Model section.

Select the Film type — Sommerfeld or Gümbel. In the Sommerfeld case, a complete 2π film is considered in the net force calculation in the bearing. In the Gümbel case, only half of the film where the pressure is positive (π film) is used for computing the net force in the bearing.

This section is only available when Reynolds equation is selected in Equation type in the Physical Model section at the physics node.

Select Contact surfaces — Smooth (the default) or Rough. Then, go to the relevant section below to continue defining the surface properties.

Select Flow type — Laminar (the default) or Turbulent. In the Laminar case no further input is needed. In the Turbulent case, select Flow factors — Automatic (the default) or User defined. In the Automatic case, flow factors for smooth surfaces are used by default. In the User defined case, enter values for the Pressure flow factor, axial direction, Φ1; the Pressure flow factor, circumferential direction, Φθ; and the Shear stress factor, circumferential direction, Φfθ. The default values correspond to the flow factors for smooth surfaces.

Enter a value for the Surface roughness, σ. Select the Flow factors — Patir and Cheng (the default) or User defined. If Patir and Cheng is selected, enter values of the constants k1, γ1, kθ, and γθ for the pressure flow factors, and the constants A1, α1,1, α2,1, α3,1, Aθ, α1,θ, α2,θ, and α3,θ for the shear flow factors. Subscripts 1 and θ refer to the axial and circumferential directions, respectively. If User defined is selected, enter values for the flow factors matrices Φl, Φsl, Φfl, Φfsl, and Φfpl. Note that the components of the matrices are in local directions with the first index referring to the axial direction and the second index referring to the circumferential direction.

Select the Include asperity contact pressure checkbox to include the pressure contribution due to metal-to-metal contact between the asperities in the bearing reaction. This refers to a mixed lubrication condition where the total pressure in the bearing is a summation of the contribution from the fluid-film pressure and the metal-to-metal contact pressure. Enter values for the Surface asperity density, η; the Radius of curvature at peak, r0; and the Effective modulus, Ee.

The default Dynamic viscosity μ is taken From material. For User defined, enter a different value or expression.

With the default options, the Density ρ is taken From material. For User defined enter a different value or expression.

If Gas (modified Reynolds equation) is being solved, the density is determined automatically by the ideal gas law.

If Liquid with cavitation is being solved, the density is assumed to take the form ρ = ρc exp(βpf), where pf is the fluid pressure, ρc is the density at the cavitation pressure, and β is the compressibility. In this case, enter the values for the Density at cavitation pressure, ρc, and the Compressibility, β.

Select a Film flow model — No-slip walls, Slip at walls, User defined-relative flow function, or User defined-general. The film flow model is used to compute the mean fluid velocity as a function of the pressure gradient, the journal velocity, and the bearing velocity. Within the gap, the fluid velocity profile is a linear combination of the Poiseuille and Couette velocity profiles.

Use Slip at walls when slip occurs at the journal or bearing. In this case, the difference between the journal or bearing velocity and the fluid velocity is proportional to the tangential part of the normal stress tensor component. The slip length divided by the fluid viscosity is the constant of proportionality in this relationship. The mean fluid velocity is computed using this assumption, given the pressure gradient and the journal and bearing velocities.

Enter a Slip length, journal, Lsj. Select the Use different slip length for bearing checkbox to enter a Slip length, bearing, Lsb.

For Gas (modified Reynolds equation), it is possible to use the gas mean free path to specify the slip length. Change the Type of slip setting (which defaults to Slip length with the settings described above) to Mean free path and same accommodation coefficients or to Mean free path and different accommodation coefficients.

Select an option to define the Mean free path — Compute from material properties, User defined expression, or User defined with reference pressure.

The Rarefied-total accommodation option provides a rarefied gas model that assumes total accommodation at the journal and the bearing. This model is accurate to within 5% over the range 0 < Kn < 880 (here Kn is the Knudsen number, which is the ratio of the mean free path to the film thickness). An empirical function, fitted to stationary solutions of the Boltzmann equation, is used to define the Poiseuille component of the flow.

Select an option to define the Mean free path — Compute from material properties, User-defined expression, or User defined with reference pressure.

To select a Force model, choose:

The Rarefied-general accommodation option provides a rarefied gas model that assumes the same accommodation coefficient, α, at the journal and bearing. This model is accurate to within 1% over the ranges 0.7 < α < 1 and 0.01 < Kn < 88 (here, Kn is the Knudsen number, which is the ratio of the mean free path to the film thickness). An empirical function, fitted to stationary solutions of the Boltzmann equation, is used to define the Poiseuille component of the flow.

Select an option to define the Mean free path — Compute from material properties, User-defined expression, or User defined with reference pressure.

To select a Force model, choose:

The User defined-relative flow function option enables user-defined models in which an effective fluid viscosity is employed. The fluid viscosity is divided by an additional factor Qch, which can be defined as an arbitrary expression in the user interface. It is also possible to define the expressions for the fluid forces on the journal and on the bearing (these are included as feature inputs in other physics interfaces).

The User defined-general option enables you to define arbitrary flow models. Both the Poiseuille and Couette terms in the mean velocity can be defined arbitrarily. It is also possible to define the expressions for the fluid forces on the journal and on the bearing, (these are included as feature inputs in other physics interfaces).