Journal Bearing
Journal bearings restrict the translational motion of the journal in the lateral direction. In addition, they also restrict the rotation of the journal about both the lateral axes due to the finite length of the journal. The modeling of journal bearings can be done at different levels of detail, as described below.
No Clearance Bearing
This type of bearing completely restricts the translational and rotational motion of the journal in the lateral direction. You can use this approximation when the bearings are very stiff, so that the motion of the journal in the bearing is small and does not significantly affect the overall response of the rotor.
Cylindrical Hydrodynamic Bearing
This bearing model is a lumped model of a cylindrical hydrodynamic journal bearing. The underlying model is based on the Reynolds equation with a short-bearing approximation. The properties of bearing are therefore dependent on the operational condition such as the bearing loading and rotational speed. This bearing model is applicable if the rotor is supported by a cylindrical hydrodynamic bearing with a small width to diameter ratio.
Bearing Stiffness and Damping Coefficient
This model acts as a lumped spring-damper system, and is useful if the bearing stiffness and damping coefficients are known a priori. For example, if the dynamics coefficients of a fluid-film bearing have been determined using the Hydrodynamic Bearing interface. Both functional and tabular forms of these parameters are supported. For the tabular data, you need to use an interpolation function.
Bearing Forces and Moments
In many cases, it is easier to evaluate the reaction of the bearing on the journal because reaction forces and moments due to bearing can be applied directly on the journal. Usually, forces and moments in the bearing are functions of the journal motion. Force and moment data obtained through experiments or simulation can also be used through interpolation functions in this model.
Multiphysics Coupling
When it is necessary is to capture effects of oil whirl and whip, a multiphysics coupling can be used to model the bearing. These phenomena are connected with the hydrodynamic instability of the bearing. In this case, the Solid Rotor or Beam Rotor interfaces can be coupled with the Hydrodynamic Bearing interface.