Modeling tools for Rotordynamics and Bearings Tribodays 2017, Älvkarleby Niklas Rom, PhD 08-4129554 niklas.rom@comsol.se © Copyright 2016 COMSOL. Any of the images, text, and equations here may be copied and modified for your own internal use. All trademarks are the property of their respective owners. See www.comsol.com/trademarks.

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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

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

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)

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

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

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

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.

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.

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

More multiphysics: Rotor and beams Disk Rig Shaft

Results

Orbit

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