cbeam solidmodelling intro(1)

8/11/2019 CBeam SolidModelling Intro(1)

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ANSYS OverviewofSolidModelingOperations

SeeAnsys MechanicalAPDLHelp:

ThefollowingpagescontainextractsfromtheANSYSmanualpages


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Solidmodelentities:Keypoints,Lines,Areas&Volumes

Thepurposeofusingasolidmodelis

torelieveyouofthetimeconsuming

task of building a complicated finite

elementmodelbydirectgeneration.

Some solid modeling and meshing

operationscan

help

you

to

speed

up

the creation of your final analysis

model

Thepointsthatdefinetheverticesof

yourmodelarecalledkeypointsand

arethe"lowestorder"solidmodel

entities.

If,inbuildingyoursolidmodel,youfirstcreateyourkeypoints,andthenusethosekeypointstodefine

the"higherorder"solidmodelentities(thatis,lines,areas,andvolumes),youaresaidtobebuilding

yourmodel"fromthebottomup."Modelsbuiltfromthebottomuparedefinedwithinthecurrently

activecoordinatesystem.

Alternativelyyoucanbuildyourmodelfromthetopdown:TheANSYSprogramalsogivesyouthe

abilitytoassembleyourmodelusinggeometricprimitives,whicharefullydefinedlines,areas,and

volumes. ThisfeatureisnotpresentedherebutyoucanrefertotheANSYSHelpmanualforfurther

information.

CreatingYourSolidModelfromtheBottomUp

Anysolidmodel,whetherassembledfromthebottomuporfromthetopdown,isdefinedintermsof

keypoints,lines,areas,andvolumes

Keypoints

Keypoints are the vertices, lines are

the

edges,

areas

are

the

faces,

and

volumes are the interior of the

object. Notice that there is a

hierarchy in these entities: volumes,

the highestorder entities, are

bounded by areas, which are

bounded by lines, which in turn are

boundedbykeypoints.

When buildingyour model from the

bottomup,youbeginbydefiningthe

lowestorder solid model entities,

keypoints. Keypoints are defined

within

the

currently

activecoordinatesystem.Youcanthendefinelines,areas,andvolumesconnectingthesekeypoints.Youdo

notalwayshavetoexplicitlydefineallentitiesinascendingordertocreatehigherorderentities:you

can define areas and volumes directly in terms of thekeypointsat theirvertices. The intermediate

entitieswillthenbegeneratedautomaticallyasneeded.Forexample,ifyoudefineabricklikevolume

intermsoftheeightkeypointsat itscorners,theprogramwillautomaticallygeneratethebounding

areasandlines.


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Lines

Linesaremainlyusedtorepresenttheedgesofanobject.Aswithkeypoints,linesaredefinedwithin

thecurrentlyactivecoordinatesystem.Youdonotalwaysneedtodefinealllinesexplicitly,because

theprogramwillgeneratethenecessarylinesinmanyinstanceswhenanareaorvolumeisdefined.

Linesarerequiredifyouwanttogeneratelineelements(suchasbeams)ortocreateareasfromlines.

Areas

Flatareasareusedtorepresent2Dsolidobjects(suchasflatplatesoraxisymmetricsolids).Curved

as well as flat areas are used to represent 3D surfaces, such as shells, and the faces of 3D solid

objects.Areasarerequired ifyouwishtouseareaelementsor ifyouwishtocreatevolumesfrom

areas. Most commands that create areas will also automatically generate the necessary lines and

keypoints;similarly,manyareascanbeconveniently generatedbydefiningvolumes.

Volumes

Volumesareusedtorepresent3Dobjects,andarerequiredonlyifyouwishtousevolumeelements.

Mostcommandsthatcreatevolumeswillalsoautomatically generatethenecessarylowerorder

entities.

Meshing:

Your ultimate objective in building a solid model is to mesh that model with nodes and elements.

Onceyouhavecompletedthesolidmodel,setelementattributes,andestablishedmeshingcontrols,

you can then let the ANSYS program generate the finite element mesh including nodes, elements,

loads and support conditions. By taking care to meet certain requirements, you can request a

"mapped"meshcontainingallquadrilateral,alltriangular,orallbrickelements. Amappedmesh, if

designedwell,canleadtobetterelementshapesundultimatelymoreaccurateresults.

Solidmodelloads:

IntheANSYSprogram,loadsarenormallyassociatedwithnodesandelements.However,usingsolid

modeling,youwilloftenfinditinconvenient todefineloadsatnodesandelements.Fortunately,you

mayassign

loads

directly

to

the

solid

model;

when

you

initiate

the

solution

calculations

(with

aSOLVE

command), the program will automatically transfer these solid model loads to the finite element

model.

FreeMeshing MappedMeshing


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Revisingyourmodel(clearinganddeleting):

Beforeyoucanreviseyourmodel,youneed tobeawareofthehierarchyofsolidmodelandfinite

element model entities. A lower order entity cannot be deleted if it is attached to a higherorder

entity. Thus, a volume cannot be deleted if it has been meshed, a line cannot be deleted if it is

attached to an area, and so forth. If an entity is attached to any loads, deleting or redefining that

entitywilldeletetheattachedloadsfromthedatabase.Thehierarchyofmodelingentitiesisaslisted

below:

Highest Elements(andElementLoads)

Nodes(andNodalLoads)

Volumes(andSolidModelBodyLoads)

Areas(andSolidModelSurfaceLoads)

Lines(andSolidModelLineLoads)

Lowest Keypoints(andSolidModelPointLoads)

Ifyouneedtoreviseasolidmodelafterithasbeenmeshed,youmustusuallyfirstdeleteallthe

nodesandelementsintheportionofthemodeltoberevised,usingthexCLEARcommands(Main

Menu>Preprocessor>Meshing>Clear). Oncethesolidmodeliscleared,youcandelete(fromthetop

down)and

redefine

solid

model

entities

to

revise

your

model.

ExampleofRevisingaMeshedSolidModel


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ModellingExample:Tiploadedcantilever

UsesolidmodellingtoprepareaFEmeshofthe

tip loaded cantilever beam shown and then

analyseit.

All

cantilever

dimensions

are

given

using

consistentunits.

ModellingSteps:

StartANSYSAPDLandenterthePreProcessor

Preparation:

Beforecreatingtheelementsyoushoulddefinethetypeofelement,RealConstants(e.g.thickness)

andmaterialpropertiesasfollows:

PreprocessorElementTypeADDADDthenselect SolidQuad4Node182.

ClickOptionsandsettheKeyOptionforElementBehaviourK3toPlanestrsw/thk

Preprocessor

Real

Constants

ADD

OK

then

enter

TK(I)

=1.

PreprocessorMaterialPropsMaterialModelsStructuralLinearElasticIsotropic leavethe

defaultmaterialas1thenclick OK. InthematerialsdialogboxenterEX=1e4andNUXY=0.

InordertobeabletoplotKeypoint,lineandAreanumbers,theymustfirstbeswitchedon.Thiscan

bedonefromthemainmenu.

1) Select: PlotCtrlsNumbering

2) ChecktheboxesforKeypoints,LinesandAreas

P=202

L=10

XY

E=104

=0.3 Thicknesst=1.0


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1)Create4KEYPOINTSwithcoordinatesasfollows:

KP X Y Z

1 0.0 1.0 0.0

2 0.0 1.0 0.0

3 10.0 1.0 0.0

4

10.0

1.0

0.0

PreprocessorModellingCreateKeypointsInActiveCS

(ToentermorethanoneKeypointusetheApplybutton)


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2)Create4LINESconnectingthekeypointsasfollows:

Line KP Start KP End

1 1 2

2 2 3

3 3 4

4 4 1

PreprocessorModellingCreateLinesStraightLine

(ToentermorethanoneLineusetheApplybutton. Youcanenterthekeypointnumberinthe

selectionboxoralternativelypickthekeypointusingthemouse)


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3)Create1AREAboundedbythe4LINES:

PreprocessorModellingCreateAreasArbitraryByLines

SelectLines1,2,3,4usingthemouseorenterthelinenumbersdirectlyintheselectionbox. Make

suretoenterthelinesinthegivensequence.


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4)MeshtheAreausingdefaultsettings:

PreprocessorMeshingMeshToolAreasFree

SelectArea1usingthemouseorentertheAreanumberdirectlyintheselectionbox.


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FromthePlotCtrlsMenuselectNumberingandthen:

a)SwitchonNodenumbers

FromthePlotmenuselectPlotNodes


b)SwitchonElementnumbersandswitchoffNodenumbers

FromthePlotmenuselectPlotElements

FromthePlotCtrlsMenuselectNumberingandswitchoffNodeandElementnumbersasrequired.


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5)SpecifySupportconditionsontheLinesandKeypoints:


SwitchonKeyPointandLinenumbers

FromthePlotMenuPlotLINES

Now

define

the

support

conditions

using

the

following

menu

sequence:

PreprocessorLoadsDefineLoadsApplyStructuralDisplacementOnKeypoints

Inthedialogueboxthatappearsapplythefollowingconstraints:

Keypoint1:UY

NowdefinethesupportconditionsonLine1inUXdirection:

PreprocessorLoadsDefineLoadsApplyStructuralDisplacementOnLines


Line1:UXonly


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6)SpecifyForcesontheKeypoints:

Nowdefinethesupportconditionsusingthefollowingmenusequence:

PreprocessorLoadsDefineLoadsApplyStructuralForce/MomentOnKeypoints


Keypoint2: FY=10

Keypoints3,4:FY=10

7)SaveandSolve:


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8)Enterthepostprocessorandcheckresults

ListReactionsandcheckvalueswithahandsolution.

Plotstresscontoursforstressinxdirection(SX)andcompareresultswithyourtheoreticalsolution

basedonbeamtheory.

ThetheoreticalsolutionleadstoastressvalueatthefixedendofSX=300intheextremefibres. The

expectedverticaldisplacement is1.031atthefreeend.

Tocheckstressvaluesatdifferentnodes,usethemenuoption:

GeneralPostprocQueryResults SubgridSlou.

ThenselectStressSX fromthedialogboxandpick thenodewhere

thestressisrequired.

Discuss the difference in results between theoretical and FE

solutions. Cantheresultsbeimproved?


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Revisingthemesh

9)Clearthecurrentmesh(deleteallelementsandNodes):

PreprocessorMeshingMeshTool

InthedialogboxthatappearsclickClearandselecttheAreathatcontainstheelements.Inthiscase

thereis

only

1area

to

clear.

Allelementsandnodeswillbedeleted


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9)MeshtheAreaaftersettingnewlinedivisions:

FromthePlotMenuPlotLINES

PreprocessorMeshingMeshTool

IntheMeshtoolboxclickonSetlines

SelectLines1&4andtheninthedialogueboxthatappears

setthenumberofelementdivisionsalongthoselines=4

(NDIV=4)

Repeattheprocedureforlines2&4andsetthenumberofdivisions=16

FinallyusetheMeshtoolboxagainandselect

MeshbutmakesurethebuttonMappedis

selected.

cbeam solidmodelling intro(1)

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