1. Modeling tools for Rotordynamics and Bearings Tribodays 2017, Älvkarleby
Niklas Rom, PhD
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5. Purpose of Rotordynamics Modeling
Vibration and stability
Critical speeds
Design such that stresses and deformations are within the permissible limit.
Analyze assemblies of rigid and flexible bodies connected through joints, gears, springs, dampers.
Static and dynamic balancing of the rotors
Vibration transmission to the connected components
Vibration and stability in rotating components induced by external or self excitation.
Find the critical speeds and the regions of stability in a system and optimize the design.
Design such that stresses and deformations are within the permissible limit.
Analyze assemblies of rigid and flexible bodies connected through joints, gears, springs, dampers.
Static and dynamic balancing of the rotors
Vibration transmission to the connected components
A turboset rotor

6. Design Questions
Changes in properties of the supports and mounted components?
Operating speed OK?
Rotor vibration is transferred to the connected components?
Forces and torque experienced by the supports?
Stresses and deformations in the rotor components?
Risk of failure of a component due to large deformations or fatigue?
Eigenmodes of the overall system?
Dynamics affected by changes in properties of the supports and mounted components?
Is the operating speed of the rotor in the safe operating range?
How much of the rotor vibration is transferred to the connected components?
What are the forces and torque experienced by the supports?
Stresses and deformations in the rotor components?
Is there a risk of failure of a component due to large deformations or fatigue?
What are the eigenmodes of the overall system?
Vibrations in the flexible shafts of a gear train

7. Beam Rotor Interface
Abstract model of the rotor represented by a series of line segments
Timoshenko theory based 3D beam element
Analysis types:
Stationary, Parametric
Time dependent
Eigenfrequency
Frequency domain
Transient with FFT
Material models:
Linear Elastic Material (Initial stress and strain, Thermal Expansion, Damping)

8. Solid Rotor Interface Rotor is represented using 3D solid geometry
Analysis types:
Stationary, Parametric
Time dependent
Eigenfrequency
Frequency domain
Transient with FFT
Material models:
Linear Elastic Material (Initial stress and strain, Thermal Expansion, Damping)
Rigid
Plasticity, Viscoelasticity, Creep
Geared connections

9. Solid Rotors vs Beam Rotors
Geometrically linear and non-linear formulation
Geometrically linear formulation only
Spin softening can be accounted for
Spin softening not present
Deformable journal and mounting
Journal and mountings assumed rigid
Computationally expensive, especially when performing a sweep over rpm
Computationally very fast
Splitting of bending, axial, and torsional vibrations not possible
Option to suppress axial and torsional vibration
Centrifugal softenining
Stress stiffening

10. Hydrodynamic Bearing
Film between the journal and bushing is modeled as a surface
Reynolds equation used to model the pressure and velocity distribution in the film
Space dimension: 3D
Bearing types
Plain, Elliptic, Split halves, Multilobe, Tilted pad, User defined
Cavitation
Pressure field within a hydrodynamic bearing

11. Geared Rotors (Tutorial)
Multiple rotors connected through helical gears
Lateral and torsional vibrations in the rotors
Eigenfrequency, Frequency Domain, Time Dependnent
Von-Mises stresses in a gear pair.
In this tutorial model, learn how to model multiple rotors connected through helical gears using the Rotordynamics Module, an add-on product to the Structural Mechanics Module and COMSOL Multiphysics®. When modeling geared rotors, the presence of gears in the system induces the lateral and torsional vibrations in the rotors. The gear mesh is assumed to be elastic, having a constant stiffness value.
We demonstrate an eigenfrequency analysis to compute the eigenfrequencies of the system for different speeds of the driving rotor. A transient analysis is also performed for the given speed of the driving rotor and the load torque on the driven rotor. With these analyses, we can compute the orbits of gear centers and forces on the bearings. The transient analysis is performed for both rigid and elastic gear mesh in order to analyze the effect of gear mesh stiffness on the rotor vibrations.
The simulation results for this tutorial model include a Campbell diagram showing the variation of eigenfrequencies with the rotational speed, critical speeds of the rotor, frequency response curves for the gear displacement and rotation, the von Mises stress distribution in the shafts, orbits of the gear centers in the rotating and fixed frames of reference, and the dynamic transmission error when transferring rotation from one shaft to another.

12. Multiphysics: Washing Machine Walk (Machinery and Robotics)
A simplified MBD model of a horizontal-axis portable washing machine is simulated.
Predicts the onset of walking instability during the spinning cycle.
Active balancing method is also implemented to eliminate the instability and vibrations.
Unbalanced force components.
Total slip margin.

13. More multiphysics Rattle from gearbox coupled to acoustics
Rotordyamics
Air acoustics
Vibration and noise from 5-speed synchro in near-field and far-field

14. More multiphysics: Rotor and beams
Disk
Rig
Shaft

15. Results

16. Orbit

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22. Concluding: Simulation to the masses
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