Mech Intro2 14.0 L09 Cont+MeshCon
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Transcript of Mech Intro2 14.0 L09 Cont+MeshCon
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2011ANSYS,Inc. February13,20121 Release14.0
14.0Release
IntroductiontoANSYS
MechanicalPart2
Lecture9
ContactandMeshConnections
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ChapterOverviewInthischapterextendthediscussionofcontactcontrolbeguninthepart1introductorycourse. Wealsointroducethemeshconnectioncapabilityforuse
withsurfacemodels:
A. ContactReview
B. ContactUtilities
C. AutomaticContactDetection
D.ContactSymmetry
E. ContactControl
F. TheContactPinball
G.SpotWelds
H.ContactResults
I. MeshConnectionsJ. Workshop9,ContactOffsetControl
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A.ContactReview
Part1ofIntroductiontoMechanicaltouchedonthebasicsofcontactelements.
Inpart2wewillexpandonsomeoftheconceptsandbroadenthecoverage.
Keepinmind,however,contactisahighlynonlinearfeatureandiscoveredinits
entiretyintheMechanicalNonlineartrainingcourse.
Contactelementscanbethoughtofasaskincoveringthesurfacesthatareexpected
tointeractwithoneanother.
Onesideofacontactpairisreferredtoasthecontactanditsmateasthetarget.
Mechanicalusesacolorcodingsystemtodifferentiatethecontactandtargetsurfaces.
Target
Contact
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B.ContactUtilitiesWhenimportingassembliescontactregionsareautomaticallycreatedbased
ontheproximityofsurfacestoone
another.
Tolerancecontrols
for
each
contacts
branchallowstheusertospecifythe
rangeofautocontactdetectionviaslider
barorlengthvalue.
WithintheConnectionsbranchindividual
contactgroupscanbeorganizedformore
efficientcontactmanagement.
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...ContactUtilities
Althoughautomaticcontactdetectionisthedefault
(connectionsdetails),itcanbedeactivatedforimporting
andgeneratedlaterbyRMBfromacontactgroup.
Transparencycanbeonoroffbasedonconnectionsbranchdetailssetting:
Withtransparencyonpartsnotassociatedwiththe
highlightedcontactregionaredisplayedas
wireframe.
ON OFF
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C.AutomaticContactDetection
Asmentioned,autodetectioncanbemodifiedusinga
slidercontrol. Theactualtolerancevaluewillbe
reportedbelowtheslider.
AlternativelythetolerancetypecanbesettoValue
andalength
unit
entered
directly.
specify
the
range
of
autocontactdetectionviasliderbarorlengthvalue.
Thecursortargetwillgraphicallyindicatethe
tolerancevaluecurrentlyactive.
AnoptiontoUseRangeallowsautomaticcontactsearchingtobelimitedtoaminimumsearchvalue.
Theminimumisenteredasapercentageofthe
tolerancevalueanditsresultingvalueisreportedas
well.
Tolerance
Display
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D.ContactSymmetry
InMechanicalonesideofacontactpairisreferredtoas
thecontactwhiletheotherisreferredtoasthetarget.
Contactsurfacesarerestrictedfrompenetratingthroughthe
targetsurface.
Whenone
side
is
designated
the
contact
and
the
other
side
the
target,thisiscalledasymmetriccontact.
Ifbothsidesaremadetobecontact&targetthisiscalled
symmetriccontact.
By
default,
Mechanical
uses
auto
asymmetric
contact: Contactbeginsassymmetricbutthesolverretainsthefirstpair
wherecontactisdetectedanddeactivatestheother.
Symmetric
ContactAsymmetric
Contact
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...ContactSymmetry
AsymmetricContactSelection:
Contactdetectionpointsareassociatedwiththetargetface. Untilacontactfaceis
detectedtobepenetratingthetarget,contacthasnotoccurred.
Noticeintheexamplebelow,thechoiceofcontact/targethasamajorimpacton
penetrationwhen
asymmetric
contact
is
used.
Target Surface Contact Surface
Target SurfaceContact Surface
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Thefollowingguidelinescanbebeneficialforpropermanualselectionofcontact
surfacesforAsymmetricbehavior:
Ifaconvexsurfacecomesintocontactwithaflatorconcavesurface,theflatorconcave
surfaceshouldbetheTargetsurface.
Ifonesurfacehasacoarsemeshandtheotherafinemesh, thesurfacewiththecoarse
meshshouldbetheTargetsurface.
Ifonesurfaceisstifferthantheother,thestiffersurfaceshouldbetheTargetsurface.
If
one
surface
is
higher
order
and
the
other
is
lower
order,
the
lower
order
surface
shouldbetheTargetsurface.
Ifonesurfaceislargerthantheother,thelargersurfaceshouldbetheTargetsurface.
Asnotedearlier,ANSYSMechanicaldefaultcontactisautoasymmetric.
...ContactSymmetry
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E.ContactControlFivecontacttypesareavailable:
BondedandNoSeparationcontactarelinearandrequireonly1
iteration.
Frictionless, Rough
and
Frictionalcontact
are
nonlinear
and
requiremultipleiterations.
Nonlinearcontacttypesallowaninterfacetreatmentoption:
AddOffset:
input
zero
or
non
zero
value
for
initial
adjustment.
AdjustedtoTouch:ANSYSclosesanygaptoajusttouching
position.
Contact Type Iterations Normal Behavior (Separation) Tangential Behavior (Sliding)
Bonded 1 No Gaps No Sliding
No Separation 1 No Gaps Sliding Allowed
Frictionless Multiple Gaps Allowed Sliding Allowed
Rough Multiple Gaps Allowed No SlidingFrictional Multiple Gaps Allowed Sliding Allowed
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...ContactControlInterfacetreatmentoptions:
Add offset: contact surface is
numerically offset a given amount
in positive or negative direction
(offset can be ramped on).
Adjusted to touch: offsets contact
surface to provide initial contact
with target regardless of actual
gap/penetration.
TCC T
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...ContactControlInterfacetreatmentexamplemodelingapressfit:
Thegeometrymodelcontainsapininaholewhichareofthesamediameter.
Contactoffsetisusedtosimulateapressfitofanoversizedpin. Theresulting
stressplotisshown.
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F.TheContactPinball
ThePinballRegionisacontactsettingthatdifferentiatesbetweenfarfieldopen
andnearfieldopenstatus.Itcanbethoughtofasasphericalboundary
surroundingeachcontactdetectionpoint.
ContactStatus:
Insidepinball= nearfieldcontact
Outsidepinball=farfieldcontact
Allowsthesolverto moreefficientlyprocesscontactcalculations.
Pinball radius
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...TheContactPinball
PinballSize:
ProgramControlled(default)calculatedbasedonunderlyingelementtypeandsize.
AutoDetectionValueequaltotheToleranceValue
asset
on
the
Global
Contact
Settings.
Radiusmanuallyspecifiedinthedetails.
Auto Detection Value or a
user defined PinballRadius will appear as a
sphere on the ContactRegion for easy verification.
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...TheContactPinball
ThereareseveralusesforthePinballRegion:
Providescomputationalefficiencyincontactcalculations,bydifferentiatingnear
andfaropencontactwhensearchingforwhichpossibleelementscancontacteach
other. Allowsbondedandnoseparationcontacttobeactivewhengapsarepresent
(withinthepinballradius).
AffectshowmanynodeswillbeincludedintheMPCequations.
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G.SpotWeldsSpot
welds
provide
ameans
of
connecting
shell
assemblies
at
discrete
points:
SpotwelddefinitionisdoneintheCADsoftware. Currently,onlyDesignModelerand
Unigraphicsdefinesupportedspotwelddefinitions.
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...SpotWeldsAs
said,
spot
welds
are
created
as
point
pairs
on
opposing
surfaces
in
the
geometrymodeler:
Noticetheactualconnectionisaccomplishedusingabeamconnectionbetweenthe
points.
A
spider
web
of
beams
is
radiated
from
each
point
to
distribute
the
load.
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...ContactResultsSelect
the
contact
region(s)
for
the
Contact
Tool
(2
methods):
1. Worksheetview(details):selectcontactregionsfromthelist.
Contact,targetorbothsidescanbeselected.
2. Geometry:selectcontactregionsonthegraphicsscreen.
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...ContactResults
Contactresultsareassociatedwiththecontactsideonly. Withautoasymmetric
contact,sincethesolverchooseswhichsideisdesignatedcontactitmaynotbe
obviousattheoutsetwhichsidewillshowresults.
Example:
in
this
case
we
see
the
larger
of
the
2
blocks
below
has
been
designated
contactbytheautomaticcontactdetection. Referringtoslide9showsthe
choice,basedonsize,isreversed(assumingmesh,materials,etc.aresimilar).
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...ContactResults
Aftersolving,thecontacttoolworksheetisusedtorequest resultsforboth
sidesofthecontactpair.
Noticeintheupperfigure(viewingthe
contactface),theresult showsfarfield
whichisnotmeaningfulsincethecontact
isbondedtogether.
Only whenweviewthesmallerblock
frombelowcanweseethetrueresult,
sticking.
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...ContactResults
Againthelowershows theviewofthe
contactside. Since
it
ultimately was
declaredthetargetbythesolverhowever,
noresultsaredisplayed.
Similarly,wecanrequestresultsfromoneortheothersidesofacontactpair.
Whenasymmetryisusedhowever,resultswillonlyappearonthesidethatis
finallydesignatedasthecontact. Recallthetargetsidewasthesmallerblockbut,
duetoautoasymmetry,itbecamethecontactside.
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ContactResults
Hereasymmetriccontactpairshowsresults
onbothsurfaces.
Incasesofsymmetriccontact,resultswillbedisplayedonbothsideshoweverthe
actualresultistheaverageofthecontactandtargetresults.
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I.MeshConnectionsThe
mesh
connection
feature
allows
you
to
join
the
meshes
of
topologically
disconnectedsurfacebodies:
Previouslyconnectionssuchasthisrequiredageometryapplicationtorepair
gaps(e.g. DesignModelerorCAD).
Mesh
connections
are
made
at
the
mesh
level
using
either
edge
to
edge
or
edge
tofaceconfigurations.
Unlikegeometrysolutions,amultibody partisnotrequired.
MeshConnectionExample
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...MeshConnectionsMesh
connections
use
the
concept
of
master
and
slave
geometry
to
control
howtheconnectionismade:
Master:indicatesthegeometry/topologyontowhichothergeometryis
projected.
Slave:
indicates
the
geometry
that
will
be
projected
onto
the
master
geometry.
Mastergeometrycanbefacesoredgeswhereasslavegeometrycanonlybe
edges.
Slave
MasterProjection
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...MeshConnectionsManual
Mesh
Connection:
Scopemaster/slavegeometry.
Entertolerancevalue,sliderorusesheetthickness.
UseSheetThickness:allowssettingascalefactorwhichwillresultina
tolerancevalue
based
on
the
thickest
surface
geometry
involved
in
the
mesh
connection.
Snaptoboundary=No:resultsinstraightprojectionoftheslaveontothemaster.
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...MeshConnectionsManual
Mesh
Connection:
Snaptoboundary=Yes:SearchesforboundaryonthemasterwithintheSnap
ToleranceorElementSizeFactor.
Elementsizefactorisbasedontheelementsizeslocatedonthemaster
geometry. Notethekinkedsurfaceintheexamplebelow.Thesnaptoboundaryfeaturewasused
withexaggeratedtolerancestoillustratepotentialproblems.
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