piston thermal stress analysis via ansys traditional and ansys workbench
TRANSCRIPT
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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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2008 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary
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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2008 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary
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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Thermal analysis: T, HTC by
component
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8/10/2019 Piston Thermal Stress Analysis via Ansys Traditional and Ansys Workbench
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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
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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)
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LS 2: Apply boost pressure to crown
Vertical constraintson piston crownremoved andreplaced with boostpressure
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LS 3: Remove vertical pin constraint,
rotational
constraint on rod
Vertical constraintson pin removed (pinis now held in placeby boost pressureon piston)
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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)
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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
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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
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LS 11: Release pin and rod constraints
Removedisplacementconstraints on pin
Remove rotational
constraint on rod (letit rotate freely)
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LS 12: Remove thermal results
For stability,
constrain pin invertical and thrustdirections at LoadStep 4 position(approximately itsfinal position)
Removetemperature map
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LS 13: Release artif icial pin and rod
constraints
Remove vertical andhorizontaldisplacementconstraints on pin
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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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