In the Hydrodynamic Thrust Bearing node you specify the geometric dimensions, collar and foundation motion and lubricant properties necessary to model a fluid-film thrust bearing.

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

Select Bearing type — Tilting pad, Tapered, Step, or User defined. Then, go to the relevant section below to continue defining the properties.

Enter the Number of pads, N, Pad arc, γp, Inner diameter, di, and Outer diameter, do to define the pad geometry. Select the Include pad inertia checkbox to model the effect of pad inertia when determining the film thickness. Inertial effects are important only in a time-dependent study. If selected, enter the Pad thickness, tp and Density, ρ to determine the moment of inertia of the pad. Finally enter the Groove depth, hg which is used to determine the film thickness in the groove.

Enter the Number of pads, N; Pad arc, γp; Inner diameter, di; Outer diameter, do; and Groove depth, hg, to define the pad geometry. Finally select Groove type — Constant width or Constant arc.

Enter the Number of pads, N; Pad arc, γp; Inner diameter, di; Outer diameter, do; Step height, hs; and Film thickness on pad surface, hfilm, to define the pad geometry. Finally select Groove type — Constant width or Constant arc.

Enter the Initial clearance as a function of the polar coordinates. The default expression contains variables <phys>.rd and <phys>.Th, which are the radial and azimuthal coordinates of the reference surface. <phys>.rd is the radial coordinate of a point on the bearing surface with respect to bearing center. <phys>.Th is the azimuthal 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. A subnode Moving Foundation or Flexible Foundation is automatically added.

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

Select Collar displacement — User defined and enter the displacement values, uc.

Select Collar load — User defined and enter the load values, Wc.

Enter the values for the Mass of the collar, mc. Also enter the value for the Initial collar displacement, uc0. Both are generally needed for a time-dependent study. In a stationary study, Initial collar displacement is taken as an initial guess for the collar displacement.

Select Velocity of the collar — 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 Equation type is Liquid (Reynolds equation) in the Physical Model section at the physics node.

Select Contact surfaces — Smooth (the default) or Rough. Then, go to 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, radial direction, Φr; 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 kr, γr, kθ, and γθ for the pressure flow factors, and the constants Ar, α1,r, α2,r, α3,r, Aθ, α1,θ, α2,θ, and α3,θ for the shear flow factors. Subscripts r and θ refer to the radial and circumferential directions, respectively. If User defined is selected, enter values of 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 radial 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 collar 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 collar or bearing. In this case, the difference between the collar 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 collar and bearing velocities.

Enter a Slip length, collar, Lsc. 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 collar 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 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 collar 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 collar and on the bearing, (these are included as feature inputs in other physics interfaces).