© 2011 ANSYS, Inc. June, 2012 1
Rotordynamics in ANSYS
ASME Turbo Expo 2013 Dave Looman Tech. Support Mgr.
© 2011 ANSYS, Inc. June, 2012 2
Rotordynamics in ANSYS - Outline
Introduction ANSYS Rotordynamics capabilities by analysis type Continuing Rotordynamics Enhancements Benchmark Studies & Industrial Applications Summary and Questions
Image Courtesy of Beckman Coulter, Inc.
© 2011 ANSYS, Inc. June, 2012 3
Benefits of Using ANSYS for RotorDynamics
Complete Solution in ANSYS… • CAD import and automatic meshing • Library of elements types • Analysis types - including prestress • Dedicated post-processing
Image Courtesy of Electric Machinery Co.
© 2011 ANSYS, Inc. June, 2012 4
…Benefits of Using ANSYS for RotorDynamics
Complete Solution in ANSYS… • Multi-spool dynamics simulation • 3D model of supporting structure and/or disks • Direct connection to bearing codes – ROMAC • Direct connection to other ANSYS tools
Geometry, Mesh,
Simulation, …
Optimization and Design Exploration
Tools
Parameters: Geometry, Bearing Stiffness, …
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Rotordynamics Analyses: Modal, Harmonic, Transient
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Modal Analysis
Orbit Plot
Mode Information Frequency Stability Damping Ratio Log Decrement
Deformed Shape Animation
Images Courtesy of Electric Machinery Co.
Specify Rotational Velocities
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Modal Analysis – Campbell Diagram
Critical Speed Whirl Direction Stability
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Modal Analysis - Log Decrement Plot
UNSTABLE
STABLE
• The logarithmic decrement plot is used to measure stability
0 Log Dec Line
Mode 3 becomes unstable
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• Critical Speed Map can be used to show the evolution of the critical speeds of the rotor with respect to the bearing stiffness
Modal Analysis - Critical Speed Map
Critical Speed Map generated by the CRITSPEEDMAP macro
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Harmonic Analysis – Unbalance Response
Centrifuge
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Phase Angle
Amplitude
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Harmonic Analysis - Orbit plots
In a plane perpendicular to the spin axis, the orbit of a node is an ellipse
It is defined by three characteristics: semi axes A , B and phase ψ in a local coordinate system (x, y, z) where x is the rotation axis
Angle ϕ is the initial position of the node with respect to the major semi-axis A.
PRINT ORBITS FROM NODAL SOLUTION LOCAL y AXIS OF ORBITS IN GLOBAL COORDINATES 0.0000E+00 0.1000E+01 0.0000E+00 LOAD STEP= 1 SUBSTEP= 4 RFRQ= 0.0000 IFRQ= 2.5606 LOAD CASE= 0 ORBIT NODE A B PSI PHI ymax zmax 1 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 2 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 3 0.38232 0.38232 0.0000 0.0000 0.38232 0.38232 4 0.70711 0.70711 0.0000 0.0000 0.70711 0.70711 5 0.92301 0.92301 0.0000 0.0000 0.92301 0.92301
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Transient Analysis – Stability Verification
Unstable Orbits
Stable Orbits
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Rotordynamic Features Features
Campbell Diagram
Unbalance response to synchronous and asynchronous excitations
Visualize and printout the orbits characteristics
Animation
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Basic Features
Features
Support Line, Mass, Solid, Shell Elements
Support for Axiharmonic Element
Dedicated bearing element COMBI214
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Dedicated Bearing Element
Element Description Characteristics cross terms
Nonlinear characteristics
COMBIN14 Uniaxial spring/damper None None
COMBI214 2D spring/damper Unsymmetric Function of Ω and Eccentricity
MATRIX27 General stiffness and damping matrices
Unsymmetric None
MPC184 Multipoint constraint Symmetric for linear, none for nonlinear
Function of the displacement
Sample COMBI214 Table Input *DIM,KYY,TABLE,3,1,1,OMEGS KYY(1,0) = OMEGA1,OMEGA2,OMEGA3
KYY(1,1) = KYY1 , KYY2 , KYY3
R,1, %KYY%
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Interface to THPAD
IMPORTBEARING.MAC supplied by ANSYS imports bearing data for use with COMBI214
ANSYS Bearing Element COMBI214
ASCII file generated by ROMAC Tilt Pad Bearing program
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Recent Enhancements -
Campbell Diagram in WB Mechanical at 14.0
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Recent Enhancements
Rotordynamics Solver Controls in WB Mechanical at 14.0
Import Shaft Geometry from text file in WB DM at 14.0
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Recent Enhancements
Support for Bearings in WB Mechanical at 14.5
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Recent Enhancements – Bearing Stiffness and Damping as a function of Eccentricity at 14.0
Transient Analysis of a 3 disk Rotor • Bearing stiffness and damping defined as a function of eccentricity
• Rotational velocity ramped from zero
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15.0 Enhancement – CMS of Rotor
QA Test of Full Rotor vs Partial CMS Rotor
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Industrial Applications and Benchmark Study
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ROMAC Benchmark – Tilt Pad Bearings
Eight Stage Centrifugal Compressor used for natural gas re-injection
Tilt Pad Bearings with dynamic coefficients
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ROMAC Benchmark Description
Shaft: - Total length: 2.81m - 35 stations (nodes) - 34 beams - 35 point masses
- 15 masses with rotary inertia - 20 masses with no rotary inertia
Bearings: - Tilting pad bearings - Velocity dependent stiffness and
damping
Analyses done: - Critical speed map computation - Unbalanced responses on 1st and 2nd bending modes
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Benchmark Results – Critical Speed Map
Critical speed map: • Critical speed versus bearing stiffness (no damping or cross terms)
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Benchmark Results – Unbalanced Response
Unbalanced response First bending mode - Unbalanced magnitude = 2.44E-03 N.m - Load applied on station 17
Second bending mode - Unbalanced magnitude = 2.44E-03 N.m - Load applied on station 11 and 24 with 180° phase
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ROMAC Benchmark - Squeeze film damping
Shaft: Material standard steel 25 nodes and 24 elements l = 0.0254 m each, axis length L = 0.6096 m d = 0.0508 m Disks: d = 0.0508 m Thickness = 0.0508 m at stations 10, 13 and 16 Bearings: Phase 1: Constant Symmetric Properties Kxx = Kyy = 1.7512E+07 N/m Cxx = Cyy = 1.7512E+02 N/m Cxy = Cyx = Kxy = Kyx = 0 Phase 2: Velocity and eccentricity dependent stiffness and damping Kxy = 3.503E+05 N/m = q (Aerodynamic cross-coupling) Kyx = - Kxy Cxx = Cyy = Cxy1 = Cyx1 = 0
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Benchmark Phase 1 Results
Campbell Diagram (ANSYS) Campbell Diagram (ROMAC)
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Centrifugal Compressor Shaft for a Chiller
Free-Free Testing Apparatus at Trane
Courtesy of Trane, a business of American Standard, Inc.
3D model with Mass of attachments
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Shell Support Structure with Rotor Components
Courtesy of Trane, a business of American Standard, Inc.
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Chiller Structure Modeled with CMS SuperElement
Courtesy of Trane, a business of American Standard, Inc.
CMS Superelement
Finite Element Model of Rotor and Impellers
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Rotordynamics Analysis Guide
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Technology Demonstration Guide
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Verification Manual
Verification Tests
VM247
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Summary
Key Features: – CAD import and automatic meshing – Library of elements types
– BEAM, SHELL, SOLID, COMBI214 – Analysis types - including prestress
– modal, harmonic, transient – Dedicated post-processing – Multi-spool dynamics simulation – Direct connection to bearing codes - ROMAC – Rotordynamics Guide – Account for flexibility of supporting structure and/or the disks – Continuing enhancements – Connect directly to other ANSYS tools via Workbench platform
– DesignXplorer, nCode DesignLife, etc. – Easy to use!
Image Courtesy of Electric Machinery Co.
© 2011 ANSYS, Inc. June, 2012 36
Faster, more complete and accurate machine analysis…
with ANSYS
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