rotor dynamics v14 open days feb 2012

© 2011 ANSYS, Inc. February 22, 20121

ANSYS Release 14.0Rotordynamics

Steve Varnam

ANSYS UK


There is a wide range of Dynamics capabilities available within the ANSYS Structural Mechanics product portfolio:

ANSYS Dynamics

Nonlinear Transient

DynamicsModal Harmonic Response

Modal Superposition

Linear Transient

DynamicSpectrum Harmonic Response

Response Spectrum Random Vibration

Rigid Body Dynamics Flexible Dynamics

Dynamics capabilities - review


Modal and Harmonic many releases ago

Full Transient 11.0

Random Vibration 11.0

Response Spectrum 12.0

Harmonic mode-sup linked to modal 13.0

Perturbation Method 13.0

Mode-sup Transient 14.0

Rotordynamics 14.0

Recent Analysis Type Migration to WB Mechanical


Dynamics in WB Mechanical

11.0

Full transient 11.0

14.0

12.013.0


Different licence levels support different capabilities

ANSYS Dynamics

Nonlinear Transient

Dynamics

(ST+)

Modal

(DS+)

Harmonic Response

(ST+)

Modal Superposition

Linear Transient

Dynamic (PR+)Spectrum

Harmonic Response

(PR+)

Response Spectrum

(PR+)

Random Vibration

(ST+)

Rigid Body Dynamics

(Standalone)

Flexible Dynamics

(ST+)

Dynamics capabilities – Licence levels


• Rotordynamics analysis requires a licence level of Structural or above.

Rotor Dynamics – Licence Level


Rotordynamics - Motivation

ANSYS Mechanical users need to be able to quickly create shaft geometriesas well as analyze dynamic characteristics of rotating systems

Industrial fan (Venti Oelde)


Background

tFuKuCuM

•The general equation of motion in matrix form is:

•Different analysis types solve different forms of this equation:

– Modal analysis: F(t) is set to zero, and [C] is usually ignored.

– Harmonic Response analysis: F(t) and u(t) are both assumed to be harmonic in nature, i.e, X sin(wt), where X is the amplitude and w is the frequency in radians/sec.

– Flexible Dynamic analysis: The complete, general form of the equation is solved.


Background

tFuKBuCGuM

• For Rotor Dynamics, this equation becomes:

•Where the additional terms are:

– G : The gyroscopic matrix, which depends on the rotational velocity (or velocities) of the analysis model.

– B : The rotating damping matrix, also depends upon the rotational velocities. It modifies the apparant stiffness of the model and can produce unstable motion.


Background

Typical applications include:

• High speed machinery such as turbine engine rotors, computer disk drives, etc.

• Seals - very small rotor-stator clearances

• Flexible bearing supports

• Rotor Instability

Rotordynamics analysis aims at:

• Finding Critical Speeds (Campbell diagrams)

• Calculating unbalance response

• Calculating response to base excitation

• Predicting Rotor Whirl and system stability

• Simulating transient start-up and shutdown


Structural Elements for Rotordynamics

Element Type Detail

Structural Mass MASS21

3D Beam BEAM188BEAM189

3D Pipe PIPE288PIPE289

Structural Shell SHELL181SHELL281

3D Structural SolidSOLID185SOLID186SOLID187

General Axisymmetric Solid SOLID272SOLID273Elements supporting Coriolis


Bearing Modeling

Specific Bearing Element

Bearing element choice depends on:• Shape (1D, 2D, 3D)• Cross terms• Nonlinearities


Modal Analysis

Orbit Plot

Complex Frequency Printout

Specify the rotational velocity and activate

the Coriolis effect

Deformed Shape

Animation


Modal Analysis – Campbell

Set up a Multiple Load Step Modal Analysis

Frequencies - Whirls - Stability

Critical Speeds

Logarithmic Decrement


Harmonic Analysis – Unbalance Response

Specify the Unbalance Force on Inner Spool

Orbit PlotUnbalance Response


Transient Analysis 1

Start-up and Stop Simulation

Transient Response

Specify the RotationalVelocity/Time History


Transient Analysis 2

Stability Verification

Transient Orbits

Specify a Short Duration Force


Documentation - Verification Manual

Verification Tests

VM247


Rotordynamics Analysis Guide

Analysis Guide specific to Rotordynamics


Technology Demonstration Guide


Workbench Implementation – new at v14

• Geometry creation in Design Modeler

• Analyze dynamic characteristics of rotating systems with the effects of damping, Coriolis and different rotational velocities

• Identify Critical Speeds with Campbell Plots

• Supported for solid and line bodies


Geometry Creation

Geometries can be imported from a CAD system or imported from a simple text file definition as used in preliminary design


Modal Analysis Enhancement

Turn on damping

DampedUndamped

No damping

Added solvers

DampingControls


Damped Modal Analysis (cont)

Note the output table is in engineering terms(damped frequency, stability, etc.), not mathematical ones(real/imaginary eigenvalue)


Animation with Decay

Toggle to turn on/off time decay during animation for damped modal analysis

Control the number of cycles to visualize the effects of decay


Rotational velocity with Coriolis effect

Rotational velocity enabled in Modal analysis

Option to turn on Coriolis Effect


Campbell Diagram

Basic setup for Campbell Diagram- Tabular Rotational velocity- Damped solve- Turn on Coriolis Effect- Turn on Campbell Diagram- Minimum 2 solve points

Specify rotational velocity for the number of points


Campbell Diagram (cont)


Fast Critical Speed Map

The new APDL Math feature extends the APDL scripting environment of Mechanical APDL:

• extraction of data from ANSYS files (FULL, EMAT, MODE, and SUB)

• powerful matrix/vectors manipulation routines

• direct access to solvers

• Speed up dependant upon number of rotational velocity steps required to identify critical speeds.

In a Rotordynamics analysis, APDL Math can be used to obtain the critical speed map directly


Fast Critical Speed Map

APDL Math script – see CRITICALSPEEDMM.MAC

0][ 2 MK w 0GjMM with

*SMAT, K, D, IMPORT, FULL, file.full, STIFF*SMAT, M, D, IMPORT, FULL, file.full, MASS*SMAT, G0, D, IMPORT, FULL, file.full, DAMP

*SMAT, zMG0, Z, COPY, M*AXPY,, alpha, G0, 1,, zMG0*SMAT, zK, Z, COPY, K

/SOLUANTYPE, MODALMODOPT, UNSYM, 6*EIGEN, zK, zMG0,, EiV, EiMFINI

loo

p o

n b

ear

ing

stif

fne

ss

Solve


Import/Export of Bearing Characteristics

ANSYS provides an interface that allows to import bearing characteristics from an external file – see IMPORTBEARING.MAC


Industrial Applications

ANSYS Rotordynamics


Industrial Application #1:Centrifugal Compressor

Two Tilting Pad Bearings with dynamic coefficients

Eight Stage Centrifugal Compressorused for natural gas re-injection at an

offshore drilling site



Tilting Pad Bearing: 5 identical pads Analyzed with THPAD (ROMAC)

Macro ImportBearing.mac

ET, 1, COMBI214R, 1, %KYY%, %KZZ%, %KYZ%, %KZY%, %CYY%, %CZZ% RMORE, %CYZ%, %CZY%



Campbell Diagram: Bearings with Variable Characteristics

(undamped)



Unbalance Response – Bearings with Variable Characteristics (damped)

Configuration 1

Configuration 2

unbalance 3.4 oz.in @ 0 deg




Industrial Application #2:Chiller

Free-Free Testing Apparatus used for initial model calibration

Courtesy of Trane, a business of

American Standard, Inc.

Centrifugal Compressor Shaft for a Chiller



Courtesy of Trane, a business of American Standard, Inc.

Solid Model of Compressor Shaft plus Chiller Assembly in ANSYS

Workbench



Housing and entire

chiller assembly

represented by a CMS

superelement

Finite element model of

rotor and impellers


CMS SuperelementRepresentation



Impeller

Bearing

locations

Outline of CMS

superelement


Chiller Assembly Details




Chiller Shaft Assembly Modes

Deformed ShapeShaft + CMS Supporting Structure


Industrial Application #3:Hard Disk Drive

ANSYS 4 disk modelDisk thickness = 0.8mm

Total mass = 87.5gSpin = 755 rd/s7855 elements

3 disks HDD sketch


Industrial Application #3:Hard Disk Drive

Campbell Diagram for 1 disk


Summary

The previous slides have described the elements of completerotordynamics analysis, with ANSYS

Key enabling features:– CAD import and automatic meshing– Library of elements– All analysis types (including prestress)– Dedicated post-processing– Multi-spool dynamics simulation– Direct connection to bearing codes– Account for the flexibility of the

supporting structure and/or the disks– Connect directly to other ANSYS tools via

Workbench (Design Explorer)


Questions?

rotor dynamics v14 open days feb 2012

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