Piston Thermal Stress Analysis via Ansys Traditional and Ansys Workbench

8/10/2019 Piston Thermal Stress Analysis via Ansys Traditional and Ansys Workbench

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

2008 ANSYS

Automotive Conference

Piston Thermal/Stress Analysis ViaTraditional ANSYS and ANSYS

Workbench

Luke Moughon

Analysis Engineer

Cummins Inc.


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Cummins Inc.

Manufactures and markets

a complete line of diesel

and natural gas-powered

engines for on-highway andoff-highway use

Markets: heavy- and

medium-duty truck, bus,

recreational vehicles, fire

truck and emergency

vehicles, light-duty

automotive and industrial

applications

Cummins is comprised of Engine,

Components, Power Generation &

Distribution business units

Engines range from 31 to

3,500 horsepower and

from 1.4 liters to 91 liters.


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Overview of Process

Start-up ShutdownRun

Piston Fatigue Life Structural Analysis Thermal Analysis

Max. cylinder pressure, hot

Min. cylinder pressure, hot

Min. cylinder pressure, cold1 Engine Cycle

Twin goals

Capture various engine

conditions in structural

analysis

Transition gradually

between them (for

numerical stability)


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7/24 2008 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary

Thermal analysis: T, HTC by

component



LS 1: Position parts

Pin moveddownward by pin-pinbore clearance

Piston moveddownward by twicethe pin-pin boreclearance

Piston and pinmoved laterally to

contact skirtConrod rotated asmall anglecorresponding topeak cylinderpressure

Beam

ANSYS Traditional: beam connects conrod stub to single node at big end

ANSYS Workbench: beam unavailable; use full conrod/crankshaft instead

Traditional Workbench



LS 1: Constrain parts

Piston crownconstrained invertical direction

Piston pipconstrained in bothhorizontal directions

Pin constrained invertical direction

Pin constrained in its

axial directionPin constrained atbottom ID in thrustaxis direction andcoupled to top ID to

prevent rotationNode at end ofconrod constrainedin all 6 DOFs

Liner constrained in

all three directions(top and bottom OD)



LS 2: Apply boost pressure to crown

Vertical constraintson piston crownremoved andreplaced with boostpressure



LS 3: Remove vertical pin constraint,

rotational

constraint on rod

Vertical constraintson pin removed (pinis now held in placeby boost pressureon piston)



LS 4: Remove thrust constraints on pin, pip

Horizontal (thrust-direction) constraintson pin and piston pipremoved (parts held inplace by contact);leave couple in placeto prevent rotation

Remove rotationalconstraint on rod (letit rotate freely)

Couple

ANSYS Traditional: couple used to

prevent pin rotation

ANSYS Workbench: couple unavailable

eliminated (less stable)



LS 5: Increase pressure to PCP

Increase pressurefrom boost pressureto peak cylinderpressure (PCP)


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LS 7: Constrain for peak side load

Reduce pressure tocylinder pressure atpeak side load

Rotate node at big

end to the conrodangle at peak sideload

Reposition node atbase of conrod sothat the small endreturns to its originallocation

For stability,constrain pin invertical and thrustdirections (i.e., holdpin at its previousposition)

For stability, preventrod from rotating



LS 8: Release pin and rod constraints

Removedisplacementconstraints on pin

Remove rotational

constraint on rod (letit rotate freely)


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LS 10: Rotate rod back to PCP position

Rotate node at bigend so pistonreturns to position atpeak pressure

Reposition node atbase of conrod sothat the small endreturns to its originallocation

For stability,constrain pin invertical and thrustdirections (i.e., holdpin at its previousposition)

For stability, preventrod from rotating



LS 11: Release pin and rod constraints

Removedisplacementconstraints on pin

Remove rotational

constraint on rod (letit rotate freely)



LS 12: Remove thermal results

For stability,

constrain pin invertical and thrustdirections at LoadStep 4 position(approximately itsfinal position)

Removetemperature map



LS 13: Release artif icial pin and rod

constraints

Remove vertical andhorizontaldisplacementconstraints on pin



Other Differences (Traditional vs.

Workbench)

Meshing

Traditional: very difficult for piston models due to highly complex

geometry Workbench: excellenteasy and efficient

Number of equilibrium iterations specification (neqit)

Traditional: straightforward code

Workbench: requires the addition ofcode snippet (e.g., neqi t , 100)

Profiling

Traditional: move actual nodes to reflectprofile

Workbench: duplicate contact elements,

profile new elements, rename to same real ID

as originals (implemented via code snippet)


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Relative Advantages of ANSYS

Revisions

ImportanceTraditional

11.0

Workbench

11.0 SP1

Workbench

12

Pre- and post-processing 10

Meshing 10

Surfaceprofiling 10

Thermal BC

gradient6

Couple nodes 6

Beam

elements2

Equilibriumiterations 2


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Piston Thermal Stress Analysis via Ansys Traditional and Ansys Workbench

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