Rotordynamics Module Updates

For users of the Rotordynamics Module, COMSOL Multiphysics® version 5.6 includes active magnetic bearing modeling, attachments for a rotor–stator connection, and the ability to model turbulence effects in hydrodynamic journal bearings. Learn about these and other rotordynamics features below.

Active Magnetic Bearing

An active magnetic bearing (AMB) is an electromagnetic bearing supported by a feedback control mechanism. You can now model such a bearing with a PID controller in both the Solid Rotor and Beam Rotor interfaces. Like any other bearing, they provide support to a rotating component on a stationary component. Active magnetic bearings can also be used to control large-amplitude vibrations when needed. These bearings are commonly used in an environment where the use of lubricants is prohibited. Due to contactless support, this type of bearing has minimal losses. You can see this feature used in the new Vibration Control in a Motor Drive Using an Active Magnetic Bearing tutorial model.

The vibration response of the motor drive without AMB.

The vibration response of the motor drive with AMB.

Attachments for Rotor–Stator Connection

Attachments can now be used as the foundation of a bearing to connect rotor and stator components. To support this, attachments are now available with a Rotordynamics Module license; they are added in structural mechanics interfaces such as Solid Mechanics, Shell, Beam, etc. With this functionality, it is a lot easier to set up a connection between stationary and rotating parts through bearings. You can view this new functionality in the Modeling of Vibration and Noise in a Gearbox: Bearing Version and Vibration Control in a Motor Drive Using an Active Magnetic Bearing tutorial models.

A gearbox model with the top of the housing cut out to show the internal gears and shafts; the velocity is shown in teal and purple; the stress is shown in red, yellow, and green; and the SPL is shown in rainbow. A gearbox model that uses attachments The housing is connected to the shafts through attachments. Results show the velocity of gears and shafts, von Mises stress in the housing, and sound pressure level.
A motor drive assembly model with the stress visualized in a rainbow color table. A motor drive assembly model that uses attachments Stress in a motor drive assembly; the motor housing and platform are connected to the rotor using attachments.

Turbulence Effects in Hydrodynamic Journal Bearings

Turbulence effects in hydrodynamic journal bearings can now be modeled in an averaged sense using a set of flow factors and shear stress factors. This effect can be modeled in the following two cases:

  • Turbulence induced due to high speed of the rotor with sufficiently smooth surfaces of the journal and bearings
  • Turbulence induced due to roughness of the journal and bushing surfaces

In the second case, two lubrication regimes can be modeled: full-film lubrication and mixed lubrication. For full-film lubrication, the contact load is supported by the pressure in the lubricant film only. For mixed lubrication, the contact load is supported by both the lubricant film pressure and the asperity contact pressure. Mixed lubrication modeling is important in heavily loaded contact surfaces.

A closeup view of the COMSOL Multiphysics version 5.6 UI showing the Model Builder, Hydrodynamic Journal Bearing settings, and the Graphics window containing two pressure plots for a journal bearing. Journal bearing example Film pressure and asperity contact pressure in a journal bearing.

Preload in Roller Bearings

Preload in roller bearings is used to make the contact between rollers and races more uniform. This helps in reducing bearing vibration, noise, and wear. You can apply an axial or radial preload in a roller bearing depending on its type. For preloaded bearings, a prestressed analysis can also be performed to determine the eigenfrequency and frequency response of a rotor-bearing system.

A closeup view of the COMSOL Multiphysics version 5.6 UI showing the Model Builder, Radial Roller Bearing settings with the Geometric Properties and Clearance and Preload sections expanded, and the Graphics window containing a Campbell plot. Demonstrating preload in roller bearings Snapshot of a model showing the settings for the preload in the roller bearing.

Improvement in Dynamic Coefficients for a Gas Bearing

Previously, dynamic coefficients in bearings were calculated by ignoring the compressibility effects of the lubricants. For liquid lubricants, this is a good approximation, but for gas bearings, the effects of compressibility of the gas and journal acceleration during whirl are very important for accurately computing the dynamic coefficients. Both of these effects are now accounted for in the dynamic coefficient computation of gas bearings.

A 1D plot of the effect of compressibility for a bearing. Effect of compressibility Effect of lubricant's compressibility on the stiffness of the bearing.

Evaluation Group for Dynamic Coefficients

An evaluation group is automatically added by default in Results if you choose to compute the dynamic coefficients of a bearing. After the computation is completed, you can evaluate the Dynamic Coefficients in a table, using this group. If you have performed a parametric study, the coefficients for each parameter value are available in a table. You can quickly create a table plot to study the variation of each coefficient with respect to the studied parameter. You can see this new functionality used in these updated models: Evaluation of Dynamic Coefficients of a Plain Journal Bearing and Damping Coefficients of a Squeeze Film Damper.

A closeup view of the COMSOL Multiphysics version 5.6 UI showing the Model Builder, Evaluation Group settings, and the Graphics window containing a plot of dimensionless stiffness and the Dynamic Coefficients tab open. Demonstrating an evaluation group Computation of dynamic coefficients in the bearing. The evaluation group is highlighted.

New Tutorial Models

COMSOL Multiphysics® version 5.6 brings several new tutorial models to the Rotordynamics Module.

Vibration Control in a Motor Drive Using an Active Magnetic Bearing

A 1D plot of vertical displacement at coupling with and without AMB and two 3D simulations overlaid on the plot. Vibration control with active magnetic bearing model Comparison of the vibration response with and without AMB at a particular location on the rotor. The stress profile at a particular instance with and without AMB is shown in the inset.

Application Library Title:

vibration_control_with_amb

Download from the Application Gallery

Thermal Stress in a Rotor Due to Bearing Heat Loss

Two 3D models of a rotor, where one shows temperature in white-to-red color gradient and the other shows stress in a rainbow color table. Thermal stress in a rotor Temperature (left) and stress (right) profile in the rotor.

Application Library Title:

rotor_thermal_stress

Download from the Application Gallery

Modeling of Vibration and Noise in a Gearbox: Bearing Version

A gearbox model with the top of the housing cut out to show the internal gears and shafts; the stress is shown in rainbow and the bearing forces are shown with black arrows. Gearbox model with bearing forces Stress in the housing and velocity in the gears and shafts. Bearing forces are shown using black arrows.

Application Library Title:

gearbox_vibration_noise_bearing

Download from the Application Gallery