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CADFEM ANSYS Extension for the calculation of hydrodynamic plain bearings

Mastering Complexity

The behavior of plain bearings depends to a large extent on the static and dynamic properties of the lubricating film in the plain bearings. Elastohydrodynamics (EHD) has become established for the simulation of lubricating film formation.

With Tribo-X inside ANSYS, the calculation of hydrodynamic radial plain bearings can be carried out comfortably and efficiently in ANSYS Mechanical. The goal is the correct dimensioning of the bearings as well as the realistic mapping of the speed-dependent stiffness and damping in dynamic FEM analyzes.

The main advantages

  • Complete integration of plain bearing calculation with Tribo-X in ANSYS Workbench
  • Short calculation times despite high level of detail
  • Consideration of elastic deformations of the bearing and their repercussion on the gap geometry
  • Complete illustration of the Stribeck curve by considering mixed friction
  • Identification of speed and load dependent bearing coefficients
  • Fully parametric workflow
Workflow for a parametric warehouse analysis

Coupling of hydrodynamics and FEM

The "Hydrodynamic Bearing" analysis system combines the two domains of hydrodynamics in the lubrication gap and deformation of the lubrication gap environment using the finite element method. The lubrication film formation in plain bearings is determined on the basis of the generalized Renolds differential equation with Tribo-X. The deformation is calculated with ANSYS Mechanical. The bearing analysis is based on the CAD bearing model, in which the bearing play is automatically recognized as a gap area. All information relevant to operation, such as the load and the speeds, are specified directly as boundary conditions in ANSYS Mechanical.

The results of bearing analysis with Tribo-X enable static and transient analysis of the bearing capacity and friction of plain bearings. Fast variation analyzes help to adapt and optimize the bearing design to the respective application.

Hydrodynamic pressure distribution in ANSYS

Bearing Coefficients

The vibration behavior of a slide-bearing rotor is essentially influenced by the stiffness and damping properties of the bearings. Both properties can be described by sliding bearing coefficients. Depending on the load situation and speed, the bearing coefficients may change significantly, so that a different system behavior is present. For this purpose, Tribo-X determines the stiffness and damping coefficients representative of the bearing for each operating condition. These can be transferred directly to the rotor dynamics analysis in ANSYS and thus enable the consideration of speed- and load-dependent stiffness and damping coefficients for further rotordynamic investigations.

The results of the Tribo-X analysis enable an assessment of the load capacity of the journal bearing. Fast variation analyses help to adjust the bearing design according to the loading scenario. For the identified bearing design the  coefficients can be directly transferred to ANSYS Mechanical considering rotational speed dependent stiffness and damping coefficients for further rotordynamic analyses. The consideration of elastic deformation of the bearing allows a more precise computation of the lubricant gap which in turn leads to a more reliable bearing design.


Bearing deformation (EHD)

Since bearing deformation can affect the formation of lubricating film due to lightweight or high stress, Tribo-X inside ANSYS allows consideration of elastic deformation of the bearing and thus performing an EHD bearing calculation. Elastic deformations can map the resulting gap size with greater accuracy, especially at low speeds, high loads or low stiffnesses, thus helping to optimize the bearing design and prevent bearing damage.

Mixed Friction

During start-up and shut-down processes, high loads and low viscosities, hydrodynamic radial plain bearings pass through the mixed friction area.
For the mixed friction transition as well as in the mixed friction region itself, the surface roughness of bearing and shaft play a major role. Tribo-X inside ANSYS takes into account the roughness of bearing and shaft and thus allows the complete calculation of a Stribeck curve.

Cavitation & load capacity

Cavitation can occur in the divergent lubrication gap of a radial plain bearing. This must be described using suitable algorithms if the bearing coefficients or the heat balance of the bearing are to be calculated correctly. Tribo-X includes a cavitation model that adequately depicts occurring cavitation and combines a high quality of statement with high computational speed.

Parameter Studies

Complete integration of the friction bearing calculation with Tribo-X in ANSYS makes parameter studies easy. The continuous working process allows the simultaneous variation of the material parameters, design parameters and operating parameters of the plain bearing. The high performance of the solver results in very short computation times, which enables a holistic optimization of the shaft-bearing housing system.

Partner presentation Tribo Technologies GmbH

Through the cooperation of CADFEM and Tribo Technologies you benefit from the pooling of know how and knowledge on all sides. We have combined this knowledge for you in the joint product Tribo-X inside ANSYS.

Tribo Technologies is a spin-off of the Chair of Machine Elements and Tribology at Otto von Guericke University Magdeburg and offers simulation software as well as innovative simulation, testing and development services in the field of tribology. Tribo Technologies aims to bring the latest findings and developments from tribology research into practice. To ensure this, there is a close link to the University of Magdeburg, to other national and international research institutions and many industrial partners.

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