rotor dynamics with ansys mechanical solutions

8/9/2019 Rotor Dynamics With ANSYS Mechanical Solutions

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2008 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary


Rotordynamics with ANSYS

Mechanical Solutions

Pierre THIEFFRY

Product Manager

ANSYS, Inc.


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Agenda

General features

Generalized axisymmetric element

Rotordynamics with ANSYS Workbench

An ANSYS V12.0 example

Future plans


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General features


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Rotordynamics features

Pre-processing:

Appropriate element formulation for all geometries

Gyroscopic moments generated by rotating parts

Bearings

Rotor imbalance and other excitation forces (synchronous andasynchronous)

Rotational velocities

Structural damping

Solution: Complex eigensolver for modal analysis

Harmonic analysis

Transient analysis


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Rotordynamics features

Post-processing

Campbell diagrams

Orbit plots

Mode animation Transient plots and animations

Users guide

Advanced features:

Component Mode Synthesis for static parts


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Appropriate element formulation

The following elements are supported for rotordynamicsanalysis (stationary reference frame):

Mass MASS21

Beam BEAM4, PIPE16BEAM188, B

EAM189PIPE 288/289

Solid SOLID45, S

OLID95SOLID185, S

OLID186,

SOLID187Shell SHELL63SHELL181, SHE

LL281General

axisymmetric

elements

SOLID272, SOLID273

N e w i nA N S Y S12 .0

New inANSYS12.0


7/35 2008 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary


The new 272/273 elements:

Are computationallyefficient whencompared to 3D solid

Support 3D non-axisymmetric loading

Allow a very fast setup ofaxisymmetric 3D parts:

Slice an axisymmetric 3DCAD geometry to get

planar model Mesh with 272/273

elements

No need to calculateequivalent beamsections

Can be combined with

full 3D models,including contact

2D axisymmetric mesh

3D representation

3D results (not necessarily axisymmetric)



Bearings

2D spring/damper with cross-coupling terms: Real constants are stiffness and damping

coefficients and can vary with spinvelocity

Bearing element choice depends on:

Shape (1D, 2D, 3D)

Cross terms

Nonlinearities

Description Stiffness and Damping crossterms

Nonlinear stiffness anddamping characteristics

COMBIN14 Uniaxial spring/damper No NoCOMBI214 2-D spring/damper Unsymmetric Function of the rotationalvelocity

MATRIX27 General stiffness ordamping matrix

Unsymmetric No

MPC184 Multipoint constraintelement

Symmetric for linearcharacteristics - None fornonlinear characteristics

Function of the displacement



Imbalance and other excitation

forces

Possible excitations caused byrotation velocity are:

Unbalance ( )

Coupling misalignment (2*)

Blade, vane, nozzle,diffusers (s* )

Aerodynamic excitations asin centrifugalcompressors (0.5* )

Input made as a force on themodel

yF

zF

2

0

2

b

FmrF ==z

y

m

tr



Rotating damping

Considered if the rotatingstructure has:

structural damping (MP,DAMP orBETAD)

or a localized rotatingviscous damper(bearing)

The damping forces can induce

unstable vibrations.

The rotating damping effect isactivated along with theCoriolis effect (CORIOLIS

command).

Damper COMBI214

Beam BEAM4, PIPE16BEAM188, BEAM189

Solid SOLID45, SOLID95

SOLID185, SOLID186,

SOLID187General

axisymmetric

SOLID272, SOLID273

(new in V 12.0 )

Elements supporting rotating damping



Campbell diagrams & whirl

Variation of the rotor naturalfrequencies with respectto rotor speed

In modal analysis performmultiple load steps atdifferent angular

velocities

As frequencies split withincreasing spin velocity,ANSYS identifies:

forward (FW) andbackward (BW)

whirl stable / unstable

operation

critical speeds

Also available for multispoolmodels



Orbit plots

In a plane perpendicular to thespin axis, the orbit of a nodeis an ellipse

It is defined by threecharacteristics: semi axesA , B and phase in a localcoordinate system (x, y, z)where x is the rotation axis

Angle is the initial positionof the node with respect tothe major semi-axis A.

Orbit plots are available forbeam models

PRINT ORBITS

LOCAL y AX

0.0000



Rotordynamics analysis guide

New at release12.0

Provides adetailed

description ofcapabilities

Providesguidelines forrotordynamics

model setup



Sample models available



New Element Technology

General Axi-symmetric Element: 272/2733D elements generated based on 2D meshBoundary conditions applied in 3D spaceNonlinearities, Node to surface contact

BenefitsMultiple Axis can be defined in any directionTake advantage of axi-symmetry but deformationis general in 3D1 element in (hoop) direction

Struc

tura

lMech

an

ics

I

L

J

K

A

B

Y Z

X

3D view ofshaft



Application to rotordynamics

The new 272/273 elements:

Are computationallyefficient whencompared to 3D solid

Support rotordynamicsanalysis

Support 3D non-axisymmetric loading

Allow a very fast setup ofaxisymmetric 3D parts:

Slice an axisymmetric 3DCAD geometry to getplanar model

Mesh with 272/273elements

No need to calculate

equivalent beamsections

2D axisymmetric mesh

3D representation

3D results (not necessarily axisymmetric)


18/35 2008 ANSYS, Inc. All rights reserved. 18 ANSYS, Inc. Proprietary 2008 ANSYS, Inc. All rights reserved. 18 ANSYS, Inc. Proprietary

Rotordynamics with ANSYS

Workbench

An example



Storyboard

The geometry is provided in form of aParasolid file

Part of the shaft must be reparametrized to

allow for diameter variations A disk must be added to the geometry

Simulation will be performed using thegeneralized axisymmetric elements, mixing

WB features and APDL scripting Design analysis will be made with variations

of bearings properties and geometry



Project view

Upper part of the schematicsdefines the simulationprocess (geometry tomesh to simulation)

Lower part of the schematicscontains the designexploration tools

Parameters of the model aregathered in one location(geometry, bearing stiffness)



Geometry setup

Geometry isimported inDesign Modeler

A part of the shaftis redesignedwith parametricdimensions

Model is sliced tobe used withaxisymmetricelements

Bearing locationsare defined

A disc is added tothe geometry

Initial 3D geometry

Final axisymmetric model

Bearings location

Additional disk


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Geometry details

Part of the original shaft isremoved and recreated with

parametric radius

3D Model sliced to createaxisymmetric model

Bearing locations and named selections are created (namedselections will be transferred as node components for the simulation)

Additional disk created withparameters (the outer diameter

will be used for design analysis)


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Mesh

The modelis meshedusing theWBmeshingtools


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Simulation

Simulation isperformed using anAPDL script thatdefines:

Element types

Bearings Boundary

conditions

Solutionssettings(Qrdamp

solver) Post-processing

(Campbellplots andextraction ofcritical

speeds)

Axisymmetric modelwith boundaryconditions

Expanded view


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APDL script

Spring1 componentcomes from namedselection

Mesh transferred asmesh200 elements,converted tosolid272


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Simulation results

The APDL scriptscan createplots andanimations

The results canalso beanalyzed withinthe MechanicalAPDL interface

Results areextracted using*get commandsand exposedas WBparameters(showing theperformance ofthe design)


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Mode animation (expanded view)


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Design exploration

The model has 2 geometryparameters (disc and shaftradius) as well as a stiffnessparameters (bearingsstiffness)

4 output parameters areinvestigated: first and secondcritical speeds at 2xRPM and4xRPM (obtained from

theCampbell diagrams and*get commands)


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Sample results

A response surface ofthe model is createdusing a Design ofExperiments

Curves, surfaces andsensitivity plots arecreated and thedesign can beinvestigated

Optimization tools arealso available

Sensitivity plots:the bearingstiffness has noinfluence on thefirst and secondcritical speeds, thedisc radius is thekey parameter

Evolution of criticalspeed with shaftand disc radius


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Optimization

A multi-objectiveoptimizationis describedand possiblecandidatesare found(usually, thereare multipleacceptableconfigurations)

Trade-off plotsgive anindicationabout theachievableperformance


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Campbell diagrams

Multiple steps (modal)

Rotational velocityscoped onbodies( (multispoolanalysis) available inmodal analysis

OutputQuantities:frequencies or

stability values

X axis is rotationalvelocity


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Additional enhancements

Provide modal solver choice (QRDAMP, LANB)

The connection folder hosting bearings:

Location

Damping and stiffness (as functions ofw)

Coriolis option available from the Analysis settings(like the large deflection or inertia relief)

Orbit plots for beam models

Exposure of generalized axisymmetric elements


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Modal post-processing (already

available at V12)

For complex modes, tabular data display both

imaginary and real parts

Complex eigenshapes

Mode animation similar toANHARM


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Results parameterization

The user will probably want to be able toparameterize frequencies (real and/orimaginary part) but also the criticalfrequencies (from Campbell results)

Doing so, he will be able to perform DXanalyses :

to examine the variations of criticalfrequencies

To examine the evolution of the stability of amode wrt various parameters

rotor dynamics with ansys mechanical solutions

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